ION EXCHANGE THESIS

Zinc Removal by ion exchange using lewatit vp oc 1026 Resin

DECLARATION

I, William C. Miinga do hereby declare that this project is entirely my own, and that

all the sources of information towards this project has been duly acknowledged,

and that it has never been done previously or submitted at this institution or any

other for similar purpose.

Author’s signature: ……………….................. Date: ……………………………

MR MIINGA WILLIAM

Supervisor’s signature: ……………………… Date: …………………………

MISS MWAMBA PRECIOUS

Supervisor’s signature: ………………………. Date: ………………………….

MR KALUNGA KELVIN

WILLIAM C. MIINGA Page i


DEDICATION

I dedicate this final year project report to my late parents Mr. Albert Miinga and Mrs.

Kolida m’hango Miinga and my Aunt Mrs. Susan m’hango mwale for their tireless

efforts in supporting and encouraging me throughout my academic endeavors, my

family members and my special friend Moira Chanza for the inspiration and

encouragement during my stay at the Copperbelt University. May our Lord and

savior Jesus Christ richly bless you all.

WILLIAM C. MIINGA Page ii


ACKNOWLEDGEMENT

May I wish to acknowledge each and every one who gave me both physical and

moral support during my stay at CBU, but first and foremost I want to thank the

almighty GOD for taking care of me throughout my entire life especially at the

Copperbelt University.

I would like to thank my supervisor Miss Mwamba (CBU) for the supervision

rendered to me and big thanks go to the Management of Chambishi Metals Plc. for

giving me the opportunity to carry out my final year project in their company. I

greatly owe my heartfelt appreciation to the following individuals for the support

rendered which enabled me acquire credible appreciation of chambishi metals

research and development as well as analytical departments operations. The

Training coordinator Mr P. mumba, am humbled to see that you are really

committed to the development of students career, this is as it should be. To my

boss Mr K. Kalunga and Mr E. Bwalya, a brother’s keeper and trainers is just the

best way to describe both of you. You received me with open hands during my stay

at chambishi metals and I saw great men in you that knew exactly what students

need and you proactively facilitated.

I am particularly aware that, there are many more people who in one way or the

other, either directly or indirectly made it posible for me to complete my industrial

attachment sucessfully. I do not underestimate anybody and their efforts, I have

recognised everybody duely and with all due respect despite having not listed

everyones name,to you all I say ’’ Well done Team’’ and may God bless you.

WILLIAM C. MIINGA Page iii


ABSTRACT

Chambishi Metals plc has increased production by putting up new infrastructures

like the Copper Solvent Extraction (CuSX) plant as well as increasing the capacity

of the Copper Tank House but the Cobalt circuit has remained the same.

Currently, Chambishi Metals Plc treats concentrates coming from a mine in DRC

Congo known as Tenke-Fungurume Mine. These concentrates contain both Co and

Cu metals, and they are Camec (Boss) and Tenke concentrates. And also Nkana

Mopani concentrates and Nampundwe pyrites are also treated at the roaster plant

as supplement (when Sulphur from the two concentrates is not adequate for SO2

production which is used in H2SO4 acid production). Due to the difference in their

chemical compositions, these concentrates are treated in different ways. Copper

removal in the purification circuit is currently being achieved by electro stripping at

the electro-stripping section of copper solvent extraction and the residue copper is

precipitated in the cleanup train. Zinc rejection is being achieved by solvent

extraction using Di-2-EthylHexyl Phosphoric Acid (D2EHPA) as an extractant and

the residue zinc is precipitated in the cleanup train. Iron is precipitated in the ferric

and clean up trains.

The objective of the project was to establish whether the resin lewatit vp oc 1026

can be used to remove zinc impurities from the cobalt streams of “Chambishi

Metals plc.” purification circuit by the use of Ion Exchange. Laboratory tests were

carried out to verify this. This was done by loading the resins with TM2 overflow

and optimizing the cobalt elution with time by eluting with 5.6 g/l and 9.4 g/l

sulphuric acid and optimizing the zinc elution with time by eluting with 93.9 g/l and

110 g/l sulphuric acid.

Test works were carried out by passing cobalt rich solution through a 120ml bed

volume of lewatit vp oc 1026 at a flow rate of 10BV/hr and 7.5BV/hr during the

optimized cycle at ambient temperature. The pH and temperature of the effluent

were measured until the breakthrough was reached.

During loading, the feed pH dropped from the initial 3.3 at ambient temperature to

a pH value of about 2, after which it rose in the first 600 minutes at the slower rate

WILLIAM C. MIINGA Page iv


until saturation was reached. The loading of zinc on the resin was efficient as

breakthrough took place only after 1500 minutes i.e. after 7.2 litres of feed solution

had been passed through the resins.

The percent split elution shows that eluting with 5.6 g/l sulphuric acid (H2SO4), of the

Iron, Copper, Zinc and Cobalt that was loaded on the resin, an average of 8 % Cu

and 2.5% Zn, 93% Co and 8 % Fe went to the Cobalt eluate, which is a good

recovery for a stream that is recycled back into the plant, and 91.5 % Cu, 97.6 %

Zn, 6.5 % Co and 92.5% Fe went to the Zinc eluate were it is supposed to go when

110g/l eluant (H2SO4) is used. Here the split was very good. With 9.4 g/l (H2SO4) of

the Iron, Copper, Zinc and Cobalt that was loaded on the resin, 94% Zn went to the

Cobalt eluate, a stream that is recycled back in the plant. Hence with 9.4g/l eluant

the split was very poor as compared to the Cobalt eluate at 5.6 g/l H2SO4.

The optimum Cobalt loading was achieved at pH 2.5 and flowrate 7.5BV/hr for

1800 minutes. Optimum Cobalt elution was achieved with 5.6 g/l sulphuric acid.

The optimum cobalt-zinc elution was done for 72 minutes. Based on the results the

current purification circuit flowsheet (Figure 2.1) can be replaced by the proposed

purification circuit flowsheet (Figure 4.9). The testworks thus far shows that the

resin lewatit vp oc 1026 can be used to remove zinc impurities from the cobalt

streams of chambishi metals purification circuit by ion exchange.

WILLIAM C. MIINGA Page v


Table of Contents

DECLARATION.........................................................................................................................iDEDICATION...........................................................................................................................iiACKNOWLEDGEMENT........................................................................................................iiiABSTRACT.............................................................................................................................ivTable of Contents....................................................................................................................viList of Figures.......................................................................................................................viiiList of Tables...........................................................................................................................ixCHAPTER ONE.......................................................................................................................21. INTRODUCTION......................................................................................................31.1. PROJECT BACKGROUND.....................................................................................41.2. PROJECT MAIN OBJECTIVE................................................................................41.3. PROJECT SPECIFIC OBJECTIVES.....................................................................4CHAPTER TWO......................................................................................................................52.1. PLANT OPERATION PROCESS DESCRIPTION...............................................6

2.1.1. ROASTER PLANT................................................................................................62.1.2. COPPER SOLVENT EXTRACTION (Cu- SX) PLANT....................................72.1.3. COPPER TANKHOUSE.......................................................................................92.1.4. LIME PLANT..........................................................................................................9

2.1.4.1. Quick Lime.....................................................................................................102.1.4.2. Rock Lime.....................................................................................................10

2.1.5. COBALT PLANT OPERATION PROCESS DESCRIPTION.........................11a) Cobalt purification circuit....................................................................................12b) Cobalt tank house...............................................................................................29

2.2. CURRENT FLOW SHEET AT COBALT PURIFICATION PLANT...................33CHAPTER THREE................................................................................................................34

3.1. BASIC CONCEPTS OF ION EXCHANGE.............................................................353.2. TYPES OF RESINS..................................................................................................37

3.2.1. CATION AND ANION EXCHANGE RESIN..................................................373.2.2. HEAVY – METAL – SELECTIVE CHELATING RESINS...........................403.2.3. LEWATIT VP OC 1026 RESINS...................................................................41

3.3. TECHNOLOGY / EQUIPMENT DESCRIPTION................................................413.3.1. BATCH AND COLUMN EXCHANGE SYSTEMS.......................................413.3.2. ION EXCHANGE RESINS AND COLUMNS...............................................423.3.3. FIXED – BED COLUMN SYSTEMS.............................................................42

WILLIAM C. MIINGA Page vi


3.3.4. INTEGRATED AGAINST MODULAR DESIGNS........................................433.3.5. SINGLE Vs DUPLEX COLUMN OPERATION...........................................443.3.6. COUNTER FLOW Vs COCURRENT FLOW / REGENERATION...........443.3.7. OTHER EQUIPMENT / DESIGN CONSIDERATION................................453.3.8. REGENERATION PROCEDURE.................................................................463.3.9. THE MASS TRANSFER ZONE (MTZ).........................................................47

CHAPTER FOUR..................................................................................................................48APPARATUS AND METHODOLOGY................................................................................484.0. APPARATUS AND EXPERIMENTAL PROCEDURES.....................................49

4.1. APPARATUS AND REAGENTS USED...............................................................494.2. SAMPLES................................................................................................................494.3. EXPERIMENTAL PROCEDURES.......................................................................49

4.3.1. LOADING..........................................................................................................494.3.2. ELUTION..........................................................................................................50

CHAPTER FIVE.....................................................................................................................51RESULTS AND DISCUSSIONS..........................................................................................515.1. 1st CYCLE.................................................................................................................52

5.1.1. FIRST CYCLE SPLIT EFFICIENCY...................................................................555.2. 2ND CYCLE...............................................................................................................56

5.2.1. SECOND CYCLE SPLIT EFFICIENCY...........................................................595.3. 3RD CYCLE...............................................................................................................60

5.3.1. THIRD CYCLE SPLIT EFFICIENCY................................................................635.4. PROPOSED FLOWSHEET FOR Zn REMOVAL...............................................65CHAPTER SIX.......................................................................................................................66CONCLUSIONS AND RECOMMENDATION...................................................................666.1. CONCLUSIONS......................................................................................................676.2. RECOMMENDATIONS..........................................................................................677. APPENDICES.........................................................................................................68REFERENCES......................................................................................................................71

WILLIAM C. MIINGA Page vii


List of Figures

Figure 1.1a: Flow sheet showing material flow at Quicklime Preparation

Figure 1.1b: Flow sheet showing material flow at rock lime Preparation

Figure 1.2: Flow diagram showing material movement at Ferric Train

Figure 1.3a: Diagram showing the preparation and movement of E24 solution.

Figure 1.3b: Showing the preparation and movement of E24 solution.

Figure 1.3: Showing the flow of material at the Co tank House

Figure 1.4: Flow sheet showing liquor movement at Zn SX plant

Figure 1.5: Flow sheet showing liquor movement at Clean-up Train

Figure 1.6: showing the movement of liquor at hydroxide train

Figure 1.7: Showing the movement of liquor at resolution train

Figure 1.8: Showing the movement of liquor in clarifier/carbon columns

Figure 1.9: Showing the movement of liquor at IONEX.

Figure 2.0: Showing the flow of material at the Cobalt tank House.

Figure 2.1: Current Chambishi Metals Cobalt Plant Flow Sheet

Figure 2.2 Schematic sections through a cation exchange resin

Figure 2.3 Discharge capacity vs pH profile for weak acid and weak base resin

Figure 4.1Loading profile for Co, Cu, Zn and Fe at 10BV/hr.

Figure 4.2Cobalt elution profile using 9.4gpl H2SO4 at 5BV/hr.

Figure 4.3 Zinc elution profile using 93.9 gpl H2SO4 at 5BV/hr.

Figure 4.4 Loading profile for Co, Cu, Zn and Fe at 10BV/hr.

Figure 4.5 Cobalt elution profile using 9.4gpl H2SO4 at 5BV/hr

Figure 4.6 Zinc elution profile using 93.9 gpl H2SO4 at 5BV/hr.

Figure 4.7 loading profile for Co, Cu, Zn and Fe at 7.5BV/hr

Figure 4.7 Cobalt elution profile using 5.6 g/l H2SO4 at 5BV/hr

Figure 4.8 Zinc elution profile using 110 gpl H2SO4 at 5BV/hr.

Figure 4.9Proposed flow sheet for the removal of Zn from TM2 overflow

WILLIAM C. MIINGA Page viii


List of Tables

Table 2.1- selectivity of ion exchange resins in order of decreasing preference

Table 4.1 Percentage split of cobalt eluate using 9.4 gpl H2SO4

Table 4.2 Percentage split of Zinc eluate using 93.9 gpl H2SO4

Table 4.3 Percentage split (2nd cycle) of Cobalt eluate using 9.4 gpl H2SO4

Table 4.4 Percentage split (2nd cycle) of Zinc eluate using 93.9 gpl H2SO4

Table 4.6 percentage split (3rd cycle) of zinc eluate using 110gpl H2SO4

Table 4.5 percentage split (3rd cycle) of cobalt eluate using 5.6 gpl H2SO4

Table 6.1 Loading profile results in the first stage

Table 6.1.2 Cobalt elution results 1st stage

Table 6.1.3 Zinc elution profile results 1st stage

Table 6.2 Loading profile results in the 2ND CYCLE

Table 6.2.2 Cobalt elution results 2nd stage

Table 6.2.3 Zinc elution profile results 2nd stage

Table 6.3 Loading profile results in the third stage

Table 6.3.2 Cobalt elution profile results 3nd stage


WILLIAM C. MIINGA Page ix


CHAPTER ONEINTRODUCTION

1. INTRODUCTION

WILLIAM C. MIINGA Page x


This project was successfully performed at Chambishi Metals plc situated along

Kitwe – Chingola road on the Copperbelt province of Zambia.

The cobalt plant at Chambishi Metals is currently processing two concentrates a

mixture of copper and cobalt from Congo DR. Copper, Zinc, Iron and Nickel are

currently by product elements; only cobalt is the metal being processed for export.

TENKE and CAMEC are the trade names for the two concentrates which are being

processed. The two concentrates are very rich in cobalt and contain about 30-

40%Co, 5-10%Cu, 3-5%Fe and some other impurities like Zn, Ni and Mn.

The company’s main objective is to produce quality cobalt and copper at higher

recoveries and lower costs in the safest working environment. To achieve this

objective the company engages in different projects like carrying out test works to

improve on the removal of Zinc impurities from the Cobalt rich streams of the

purification circuit by Ion Exchange.

Chambishi Metals plc is divided into the following plants:

Roaster plant

Acid plant

Copper Tank House/ Lime plant

Copper Solvent Extraction

Cobalt Purification plant

Cobalt Tank House

Smelter plant(not operational)

The refinery plant consists of copper tank house, cobalt tank house and cobalt

purification. Currently, the company produces 3000 - 3600 tons of cobalt per

annum.

WILLIAM C. MIINGA Page xi


1.1.PROJECT BACKGROUND

Chambishi Metals plc has four trains in the purification circuit namely ferric train,

clean up train, hydroxide train and resolution train. Each train acts as a purifying

aid in attaining exportable cobalt metal with a higher price on the world market.

The purpose of the trains is to remove iron, zinc, nickel and copper from the

process liquor solution coming from the Cu-SX plant and other recycled streams.

The ferric train consists of eight mechanically agitated tanks where material

gravitates through into the thickener (TM1). Iron is precipitated in the ferric and

clean up trains by changing the pH of the process liquor solution from Cu-SX plant

from pH 1 to pH (2-3). The overflow of thickener 1 is pumped to zinc SX plant for

zinc. Zinc Removal from TM1 O/F is achieved by solvent extraction using D 2EHPA

as an extractant and shell sol as a diluent and the residue zinc in the process liquor

solution from Zn-SX plant is precipitated in the clean-up train. The clean-up train is

responsible for the control of zinc in the thickener O/F at < 4ppm concentration. It

consists of five cascading vessels and a thickener (TM2). The overflow of thickener

2 is pumped to the hydroxide train.

1.2.PROJECT MAIN OBJECTIVE

To establish whether lewatit vp oc 1026 resins can be used to remove zinc

impurities from cobalt streams of the purification circuit of chambishi metals plc by

ion exchange.

1.3.PROJECT SPECIFIC OBJECTIVES

Optimization of Cobalt elution by eluting with 9.4 and 5.6 g/l sulphuric acid.

Optimization of zinc elution by eluting with 93.9 g/l and 110 g/l sulphuric

acid.

Propose a flow sheet for the removal of zinc from the cobalt stream.

WILLIAM C. MIINGA Page xii


CHAPTER TWO

PLANT DESCRIPTION

WILLIAM C. MIINGA Page xiii


2.1. PLANT OPERATION PROCESS DESCRIPTIONCurrently, Chambishi Metals Plc treats concentrates coming from a mine in DRC

Congo known as Tenke Fungurume Mine. These concentrates contain both Co and

Cu metals, and they are Camec (Boss) and Tenke concentrates. Due to the

difference in their chemical compositions, these concentrates are treated in

different ways.

Between the two, Camec concentrate has got high tenors of Cu, therefore before it

can be treated for Co; it is first stripped-off Cu. This is done by leaching it at

Roaster Plant, and the pregnant leach liquor is sent to Cu-SX plant for Cu

Extraction i.e. the copper in the process liquor solution is removed by contacting it

with the organic solution. This is done to remove the copper in liquor so that it can

be electro-won at the copper tank house. Cu in Co electrolyte act as an impurity if

allowed to go to Co tank house, therefore, it is removed out of solution before it is

sent to Co Purification Plant. Tenke concentrate, is re-pulped and prepared right at

the purification plant.

Stripped liquor from Cu-SX plant and prepared Tenke cake are both pumped to Co

purification circuit for impurity removal. A pH based method of purification is

employed by using lime and sulphuric acid to remove impurities like Fe, Cu, Ni and

Zn. Zn is removed by solvent extraction (SX) process while Ni is removed by ion

exchange (IX). The purified and clarified solution is then pumped to Co Tank House

for Co electro-winning.

Co electro-winning is carried out using DC current across lead anodes and

stainless cathodes where Co is electroplated. The pulling cycle averages on 4

days. Electro-won Co is stripped and crushed into flakes which are degassed

under vacuum at temperatures of about 750-820oC to reduce hydrogen in the

metal to 5ppm or less. The degassed flakes are then burnished to remove scale

and surface oxidation. The product is then drummed in 250kg for shipment.

2.1.1. ROASTER PLANT

The roaster plant is the heart of chambishi metals. This is the plant whose main

aim is to obtain as much Cu/Co as possible in solution and the rest of the minerals

WILLIAM C. MIINGA Page xiv


which are considered as impurities into solids.the major parameters in the roaster

include

pH

Pressure

Temperature.

O2 Blowing rate

a) BRIEF PROCESS DESCRIPTION

Chambishi Metals Plc treats several concentrates namely frontier mine

concentrate, boss mine concentrate, Nkana Mopani concentrate and nampundwe

pyrites. However, during the familiarization program the plant was only treating

frontier and boss mine concentrates. Due to the difference in their chemical

compositions, these concentrates are treated in different ways. The concentrates

are first stored in the vat ridge upon delivery by the trucks. The material is

thereafter taken to the bin flows at the roaster plant and then in the feeders where

they are blended according to the requirements of the process controllers and

transported by conveyor belts CV1 and CV2 to the slurry tanks and finally into the

roaster. In the roaster the operating pressure should be above 5% SO2, so as to

reduce on the loss of SO2 as fumes through the stack and the operating

temperature should be 6800 C.

b) LEACHING PROCESS AT ROASTER PLANT

During the leaching process the overflow together with the filtrate from the roaster

belt filter goes into TK30 and then to copper solvent extraction (Cu-SX) for

extraction of Copper. The sulphur that is produced from the roaster is compressed

and used in the production of concentrated sulphuric acid at the acid plant .The

underflow goes to the neutralization circuit.

2.1.2. COPPER SOLVENT EXTRACTION (Cu- SX) PLANT

This is the plant that is concerned with the extraction of copper from solution

preferentially by a solvent. The feed is the pregnant leach solution (PLS) from

roaster plant. The PLS is first received in the PLS pond to allow the total

WILLIAM C. MIINGA Page xv


suspended solids to settle. From the pond PLS is pumped to the mixer were it is

mixed with extractant in the diluent shell sol hence extraction commences. This

plant has two sections known as Cu-SX1 and Cu-SX2. There are generally two

major processes during copper processing at Cu-SX1

Extraction happens at area 500

Stripping happens at area 530

The first step is the extraction process in which the PLS (CuSO4) is contacted with

the barren organic (HR) through agitation method of contacting. PLS is pumped to

the dispersion overflow pump (DOP) where it is agitated and pumped to the spiral

tanks for uniform mixing of the organic and the PLS. The method of contact

between organic and PLS is counter-current. The extraction section comprises

three settlers E1, E2 and E3.From the spiral tanks the organic together with PLS

moves into E1 where the loaded organic (copper rich organic) is separated from

the raffinate (solution that remains after the copper has been removed from

PLS).The process continues in E2 up to E3 where the raffinate (H2SO4) exits while

the loaded organic (R2Cu) exits via E1 to the striping section. This process can be

summarized by the following equation;

CuSO4 (aq) + 2HR (org) ↔R2Cu (org) + H2SO4(aq) 1.0a

a) FACTORS AFFECTING THE EFFICIENCY OF EXTRACTION

PLS and organic ratio

pH

Flow rates of organic and PLS

Mixing intensity

b) STRIPPING

Stripping is the opposite of extraction. At the stripping section the loaded organic

(R2Cu) contacts the spent electrolyte (H2SO4) from purification plant counter-

currently. The SE strips copper from the loaded organic through the settlers S1, S2

and S3 leaving it barren. The barren organic (HR) goes back to the extraction

WILLIAM C. MIINGA Page xvi


section via S3 while the advance electrolyte (CuSO4) goes to copper tank house

for electro-winning of the copper via S1.

H2SO4 (aq) + R2Cu (org) ↔ 2HR (org) + CuSO4 (aq) 1.0b

2.1.3. COPPER TANKHOUSE

This is the part of the purification plant where dissolved Cu in liquor is electro won

out of solution.

Liquor from Cu-SX is pumped to area 460,where it is mixed with Gwar and then

into the cells where it is extracted onto the cathodes. The cathodes placed on the

anodes with direct current applied are dipped into the cells containing the advance

electrolyte. The cathodes are left for a week to allow the electro-wining process to

be completed. During the process of electro-winning there is strong fuming that is

suppressed by the use of plastic mist balls. After the cathodes have been removed

from the cells the copper is stripped off using the automated stripping machine.

The striping involves the use of steam for easy removal of copper from the

cathodes. After the cathodes have been washed the wash water is joined to the

pipes for the spent electrolyte which goes back to copper SX for further stripping of

copper from the loaded organic.

a) FUNCTIONS OF GWAR

To make the copper shiny

To make the copper soft

To make it easier to remove the copper from the cathode at the striping

machine.

2.1.4. LIME PLANTThis is the plant where both quicklime and rock lime are prepared from for use at

purification plant. It is divided into two major parts, that is, rock lime and quicklime

preparation areas.

WILLIAM C. MIINGA Page xvii


2.1.4.1. Quick Lime

This is an oxide alkali used for pH control of different streams in operation. It is

purchased from Ndola lime as calcium oxide (CaO). During its preparation, quick

lime is first charged to a jaw crusher where it is crushed and released into a bin

below the crusher. From the bin, lime mixes with water at a ball mill chute, and

enters the mill. In the ball mill, lime is ground to 75% passing 75microns to achieve

a quicklime solution of desired specific gravity and %solids. Discharge from the ball

mill collects into the sump and pumped into TK40, a stock tank. To pump this lime

to purification, specific gravity in terms of %solids is checked for and is supposed

to be >20% solids. When pumped to purification, quicklime reports to TK90, and is

usually at high temperatures of about >75oC.

Quicklime

HopperStoring bin

Vibrator

Crushed lime17-18%solids

Mill Chute

Water

>20% solids

To TK90 at Purification Plant

Figure 1.1a: Flow sheet showing material flow at Quicklime Preparation

2.1.4.2. Rock Lime

This is a calcium carbonate stone used for pH control during processing of different

materials. It is prepared in a similar way as quicklime except that there is no jaw

crusher involved with this one. However, this process involves the charging of rock

lime to a hopper which gravitates into a ball mill via a chute. Water is added to the

WILLIAM C. MIINGA Page xviii

Jaw Crusher

Ball Millsump

TK40Stock Tank

Sampling point for % solids


feed in the chute, where together, the material flows into the mill. This material is

ground to a specific required size, and the mixture let to flow into TK40, which is a

rock lime stock tank. From this tank, the prepared lime is pumped to TK130 at

purification plant with about 17-18% solids. Consider a simple flow sheet below:

Rock lime

Hopper

Vibrator

Water

To TK130 at Purification Plant With 17-18%solids

Figure 1.1b: Flow sheet showing material flow at rock lime Preparation

2.1.5. COBALT PLANT OPERATION PROCESS DESCRIPTION

The strip liquor, which is a bleed stream after copper removal, constitutes feed to

the cobalt recovery circuit. The stripped liquor from the copper SX plant is pumped

to the cobalt purification circuit for impurity removal. Impurity removal is done using

a pH based precipitation method using lime and sulphuric acid to remove impurities

like iron, copper and zinc. A solvent extraction process is employed in case of the

zinc impurity using D2EHPA as an extractant.

The purified solution from the purification circuit is pumped to the cobalt tank house

for cobalt electro-winning. Cobalt metal is won out of the purified and clarified

solutions. The cobalt metal electro-winning process is done by applying a direct

current across lead anodes and stainless Steel cathodes onto which cobalt is

deposited (plated out) from the electrolyte. The pulling cycle averages 4 days but

WILLIAM C. MIINGA Page xix

Ball Mill Sump

TK40Stock Tank


may be adjusted to compensate for low deposition rates as a result of lower

operating current. In order to remove cobalt sulphate crystals, after pulling, the

cobalt is thoroughly washed in warm water before stripping the metal from the

stainless steel cathode blanks. The electro-won cobalt is crushed into +5mm to -

30mm flakes and the oversize material is recycled to the crusher and the undersize

is classified as fines and it is treated separately. The flakes are then degassed

under vacuum at 750 to 820oC in order to reduce hydrogen gas content in the

metal to 5ppm or less. In order to remove surface oxides and scale, the degassed

flakes are burnished and the product is then packed or drummed in 200kg or

250kg drums for shipment.

a) Cobalt purification circuit

The objective of the cobalt purification circuit is to purify and clarify the stripped

liquor from the cobalt SX in order to removal impurities like copper, nickel, iron,

zinc and sulphides. This is achieved by a pH based precipitation method using lime

and sulphuric acid (H2SO4). All absorption removes sulphides and organics where

activated carbons are used in the carbon columns. Nickel is removed by iron

exchange method.

Purified and clarified solution is pumped to the cobalt tank house for cobalt metal

electro-winning. Applying a direct current across lead anodes and stainless steel

cathodes onto which cobalt is plated out from the electrolyte carries out the cobalt

electro-winning. The cobalt is washed in warm water to remove cobalt sulphate

crystals before the metal is stripped from the stainless cathode blanks. The won

cobalt is crushed into flakes. Samples of flakes are chemically analysed for nickel,

manganese, lead, zinc, copper, iron, sulphur, oxygen and carbon for grading

purposes

The purification circuit has the following stages:

Ferric precipitation cascade

Solvent extraction plant for zinc removal

Clean up precipitation cascade

Hydroxide precipitation

Resolution cascade

WILLIAM C. MIINGA Page xx


Cobalt electrolyte clarification

Ion exchange for nickel removal

a. Ferric precipitation cascade

This is one of the trains at Co purification plant for iron and copper removal from

process liquor solution coming from copper solvent extraction plant and other

recycled streams. It consists of eight mechanically agitated tanks through which

the material gravitates into the thickener (TM1). These tanks include: TK10, TK20,

TK30, TK40, TK50, TK60, TK70 and TK80.

NOTE: TK: Tank, TM: Thickener Module.

De-copperized liquor from Cu-SX plant with composition of Co-5gpl, Cu1500ppm,

Fe-3.5gpl maximum and Zn-100ppm maximum, is pumped to TK10. From TK10,

liquor is pumped to TK20 at 50-60m3/h. Thickener (TM2) underflow also reports to

TK20, which is a mixing tank whose product overflows into TK30. Streams

reporting to TK 40 include: H2SO4 floor sump from Carbon columns and Larox

filtrate and thickener 1 underflow recycle line. At the pH value in the tank of

pH=4.0. Material gravitates to TK50 where H2SO4 is added resulting into pH=3.5.

This overflows into TK60, where both H2SO4 and sodium metabisulphite (Na2S2O5)

are added. Sodium metabisulphite(SMBS) is added in order to reduce the

undissolved Co3+ ions to Co2+ reporting to this train via recycled thickener 2

underflow where Tenke concentrate is fed which bears Co metal in two ionic

forms .i.e. Co2+ and Co3+ ions. In acidic media, Co3+ ions are stubborn and do not

dissolve, hence the need to reduce them to Co2+ ions which are acid soluble. From

TK60, solution overflows into TK70 and finally into TK80. This material finally

gravitates into thickener (TM1).

TM1 is a superstructure-supported thickener for ferric precipitation. To this vessel,

N100 flocculants and Polysilcoagulant are added. Usually Fe precipitate out as

Fe(OH)3 within pH= 2-3. Fe (OH)3 and Fe(OH)2 are slimy and gelatinous materials

where N100 and Polysil are used to settle them. Underflow at pH=4.5, sg=1.15-

1.25, Co<0.08%, collects into TK82 and pumped to either belt or Larox filters for

entrained Co recovery.

WILLIAM C. MIINGA Page xxi

TM1


TM1 O/F at a pH=4.0, Fe<2008ppm, suspended solids<100ppm, Cu<2008ppm,

Zn<100ppm and Co>5gpl, it is pumped to Zinc Solvent Extraction Plant for zinc

removal. Consider a simple flow sheet showing material movement at ferric train:

Fe3+ +3OH =Fe (OH)3 ORFe2+ + 2OH=Fe (OH) 2 1.1

Belt/ Larox filtrates Carbon column flow Repulped flowStripped liquor from Cu T/H TM1 recycle line

TM2 underflowH2SO4

SMBS (7-9m3/h) H2SO4

1.25%Polysil N100 (0.889gpl, 0.5-0.6m3/h)

TM1 O/F to Zn SX and Cu T/H

1.25% Polysil

U/F ph=4.5, s.g=1.18-1.2, Co=0.0-0.08% Belt and Larox Filters

Figure 1.2: Flow diagram showing material movement at Ferric Train

i. Sodium Metabisulphite

Sodium metabisulphite(SMBS) or Sodium Pyrosulfic is an inorganic compound of

chemical formula Na2S2O5. It is mostly used as a Disinfector, Antioxidant, and as

Preservative agent. However, at Chambishi Metals Cobalt Plant, SMBS is used for

reducing of Co3+ ions in cobalt concentrates to Co2+. This is because SMBS like

any other sulphite, acts as a reducing agent in aqueous form i.e.

Na2S2O5(aq) = 2Na+(aq) + SO3

-(aq) + SO2 (aq) 1.1c

WILLIAM C. MIINGA Page xxii

TK10

TK40TK50 PH=4

TK60PH 3.8

TK70PH=3-4

TK80PH=3-4

TK82


SMBS solution is prepared both at leach and pyrite plants where bags of 25kg of

white SMBS powder are stock pilled. At leach plant, it is used for Camec

concentrate leaching and at purification; it is used for Tenke leaching.

ii. Preparation of Flocculants

Flocculation is a process where colloids come out of suspension in the form of floc

or flakes. The action differs from precipitation in that, prior to flocculation, colloids

are merely suspended in a liquid and not actually dissolved in a solution.

Flocculation refers to the process by which fine particles are caused to clump

together into floc. The floc may then float to the top of the liquid, settle to the

bottom of the liquid, or can be readily be filtered from the liquid. A substance which

causes flocculation is known as a flocculant.

Two types of flocculants used at Chambishi Metals purification includes: N100

Superfloc and E24 Magnafloc. N100 superfloc is used for TM1, TM2 and TM3

thickeners, while E24 is used for TM4 thickener.

E24 Magnafloc Preparation

This is prepared in a tank at the lower terrace of the purification plant. To this tank

of 3m3 volume, 2kg of E24 crystals is added, where spent electrolyte from cobalt

tank house is used as solvent. This is mixed well resulting into an E24 Magnafloc

solution of concentration in the range of 0.667gpl. This is stored in a storage tank

of 7.5m3 volume. From this storage tank, the flocculant solution is pumped to TM4

at a continuous flow rate of about 1-1.12 m3/h.

E24 crystals S/E from Co T/H

WILLIAM C. MIINGA Page xxiii


1-1.12m3/h to TM4

0.67gpl 0.667gpl

Figure 1.3a: Diagram showing the preparation and movement of E24 solution.

N100 Superfloc Preparation

This is also prepared at the lower terrace of the purification plant in a tank of

volume 4.5m3. To this tank, 4kg of N100 superfloc crystals is added where water is

used as a solvent. This is mixed together resulting into a solution of 0.889gpl

concentration, which flows into an 11m3 storage tank. From this storage tank, N100

flocculant solution is pumped to TM1, TM2 and TM3 at different flow rates of 0.5-

0.6m3/h, 1.6-1.7m3/h and 2.5-2.7m3/h respectively.

N100 crystals water

0.5-0.6m3/h to TM1

0.889gpl

TM2 (1.6-1.7m3/h)

TM3 (2.5-2.7m3/h)

Figure 1.3b: Showing the preparation and movement of E24 solution.

WILLIAM C. MIINGA Page xxiv

Preparation TankV=3m3

Storage Tank

E24 solution

Preparation Tank

V=4.5m3

Storage Tank0.889gplN100 solutionV=11m3


iii. Larox Filters

There are two larox filters at Chambishi Metals i.e. Larox 1 and Larox 2. These are

pressure filters known as Filter Presses. They are widely used for treating of

slurries with high solids content e.g. filtering of TM1 U/F

Currently, both Larox 1 and Larox 2 filters treat same TM1 U/F material, unless

when the roaster is in operation, Larox 2 is used for filtering of leached calcine from

roaster. Larox 1 produces gypsum as filtered cake while Larox 2 does not, because

Larox 2 does not have a conveyor. Therefore, Larox 2 produces filtered cake,

which is repulped and pumped to the dam while Larox 1 produces gypsum used in

cement and fertilizer manufacturing industries.

Stages of Larox Operation

Larox filters are operated in stages, which include the following:

Filtration: This is the first stage of Larox operation where slurry with

s.g=1.18-1.20 is fed to the frame. The filtrate passes through the cloth while

cake is retained. After filtration, what follows is:

Pipe and Hose Washing

Pressing 1; Cake Washing

Pressing 2; Pipe Drain

Air Drying

Pressure Release

Plate Pack Opening

Cake Discharge

Plate Pack Closing

WILLIAM C. MIINGA Page xxv


b. Solvent extraction for zinc removal

The purpose of the zinc solvent extraction plant is to remove zinc from the process

liquor solution and increase cobalt recovery. To achieve effective zinc control, the

ferric thickener overflow pH should be maintained in the range 3.5-4.5. Pregnant

liquor solution from TM1 (ferric thickener) overflow is pumped through the filter to

remove suspended solids. The filtrate is then pumped to the four mixer-settlers in

series. Zinc extraction is achieved by the use of D2EHPA in a diluents shell sol

3525.

Below is an equation for the extraction of zinc.

ZnSO4 (aq) + 2HR(org) ↔R2Zn(org) + H2SO4(aq) 1.2

Two layers are formed with the top layer being the loaded organic due to its low

density and the bottom layer being the aqueous (raffinate), which is continuously

pumped to the clean-up cascade.

Stripped/scrubbed organic is also fed to four mixer-settlers in a counter current

mode. During extraction zinc is extracted to the organic and the acid is liberated

into the aqueous solution. The loaded organic is then stripped using sulphuric acid.

Zinc is stripped from the loaded organic by mixing it with 150-200gpl H2SO4.

H2SO4 (aq) + R2Zn (org) ↔ 2RH (org) + ZnSO4 (aq) 1.3

The stripped organic is later on scrubbed using 150-180gpl hydrochloric acid. The

raffinate solution rich in cobalt is then pumped to the clean-up cascades for further

processing.

Consider a simple flow sheet showing the movement of liquor in the cells i.e.

WILLIAM C. MIINGA Page xxvi


RAFFINATE TO TM2(<10ppm Zn)

32m3/h150-170gpl Zn

H2SO4+water25-30m3/h stripped organic

180gpl

HCl+water

AqueousFeed TM1 O/F

(60-110m3/h)

Figure 1.4: Flow sheet showing liquor movement at Zn SX plant

c. Clean up precipitation cascade

The purpose of the clean-up precipitation cascade is to control zinc in the thickener

O/F at < 4ppm concentration. It consists of five cascading vessels and a thickener.

These include:

TK10: A receiving vessel of almost all feed streams to the clean-up train. These streams include;

Raffinate solution from Zn SX plant

Prepared Tenke cake

Rock lime, to maintain pH within the range of pH= 6.2-6.5

Larox and belt filtrates

Co eluate from Ionex plant

Repulped TM4 U/F from drum filter

TM1 O/F by-passing line via pp64

Recycled TM2 underflow

WILLIAM C. MIINGA Page xxvii

E4PH=2.8

E3PH=2.9

E2PH=3

E1PH=3

POLISHER FILTER

STRIPPING CELL 1

STRIPPING CELL2

SCRUBBING CELL

STRIPPED/SCRUBBED ORGANIC TANK TK90

LOADED ORGANIC TK280

STRIPPED ORGANIC TANK TK340

STRIPPING SOLUTION TANK TK170

SCRUBBING SOLUTION TANKTK160

RAFFINATE TANK TK190


TK20: This is a mixing and reaction tank receiving feed from TK10. TK30: Receives feed from TK20. It is a pH control vessel where quicklime is added

sometimes depending on the performance of added rock lime. This is in order to

maintain a pH= 6.5- 6.6. TK40: Feed comes from TK30. It is for pH control where

quicklime is also added. This vessel feeds TK50. TK50: This is basically a reaction

vessel realizes it’s feed into TM2. TM2: To its material, N100 flocculant is added.

Its overflow reports to TK20 of the Hydroxide Train while underflow reports to TK40

of the Ferric Train. Consider a simple flow sheet drawn below showing liquor

movement and some other important parameters:

TM4 U/F & Raffinate from ZnSX PlantTenke Co eluate Belt & Larox FiltratesFloor Sump Rocklime

Rocklime/ Quicklime

Quicklime

N100 Superfloc (1.6-1.7%m3/h)

TM2 O/F to TK20 at Hydroxide train (Co>5gpl)

TM2 U/F to Ferric train (Co=5-1.7%, sg=1.15-1.18

Figure 1.5: Flow sheet showing liquor movement at Clean-up Train

WILLIAM C. MIINGA Page xxviii

TK10 (mixing & control vessel)PH=6.2-6.5

TK20(reaction vessel)

TK30 (pH=6.5-6.6)

TK40 (pH=6.4-6.8)

TK50 (reaction vessel)

TM 2


d. Cobalt hydroxide precipitation cascade

The purpose of the hydroxide cascade is to precipitate cobalt and concentrate it by

dewatering. The hydroxide circuit consists of 6 cascading vessels and a thickener.

TK10 receives TM2 o/f and filtrate from drum filters. The liquors are pumped to

TK20 then TK30 where quicklime is added to precipitate cobalt as hydroxide.

TK40, 50 and TK60 are reaction vessels. TK60 discharges into the thickener where

solid/liquid separation takes place with the aid of a flocculant. Caustic soda is

added to increase the pH. The reacted slurry is feed to the thickener for solid/liquid

separation.

Co2+ + OH- =Co(OH)2 1.4

The thickener overflow is disposed off to the tailings dam. The underflow is

pumped to the filter for filtration. The cobalt hydroxide cake is repulped with spent

electrolyte from the cobalt tank house and pumped to the resolution train for further

processing. Consider a simple flow sheet drawn below showing liquor movement

and some other important parameters:

WILLIAM C. MIINGA Page xxix


TM2 O/F belt filter filtrates

Quicklime Hydroxide filtrate, floor sump

Quicklime

N100( 2.5-2.7m3/h)

Water to the dams (<100ppm Co)

Co hydroxide (18-20% solids, s.g=1.08-1.15, Co>15%)

Figure 1.6: showing the movement of liquor at hydroxide train

i. HYDROXIDE BELT FILTER

At Chambishi Metals, this is one of the filters used for filtering of TM3 underflow. It

consists of a long horizontal belt where feed is fed and filtered from.

Operations

The belt receives its feed from TM3 U/F via three pumps: pp72, pp89, pp90 at

approximate flow rates of 21-22m3/h, 25-28m3/h and 6-8m3/h respectively. The feed

reports to the belt moving at a speed of 300-357rpm, from which it is filtered from.

Filtered cake at the end of the belt falls into a chute where it is repulped with

recycled hydroxide liquor solution from TK160. This is done in order to easy the

flow of the filtered hydroxide cake in the chute to TK110. From TK110, repulped

WILLIAM C. MIINGA Page xxx

TK10 (receiver)

TK20 (mixing & pH control vessel (7.8-7.9)

TK30 (REACTION VESSEL)

TK40 (Control vessel pH=8.0-8.1)



TM3


cake is pumped to TK160, where spent electrolyte from carbon columns is fed via

TK89 and TK88 at about 30m3/h. TK160 pumps its material to two vessels, one

reports to the Resolution Train while the other reports back to the belt chute where

it is used for repulping of the filtered cake reporting to TK110.

For belt washing, industrial water used comes from TK150. This used water then

collects into TK140. In the past, TK140 used to pump its recovered water to the

Washate feed zone where solids and Co could be recovered with the filtrate getting

back to TK150 for belt washing. But currently, TK140 pumps its water to hydroxide

train since the Washate zone is no longer in operation. Therefore, water for belt

washing comes from Kafue River into TK150 at a flow rate of 15-25m3/h. Spirages

collects into TK140, then to the Hydroxide train.

ii. HYDROXIDE DRUM FILTERSThere are currently three drum filters used for cobalt hydroxide slurry filtration.

These filters receive their feed from TM3 U/F collecting box via two pumps, pp88

and pp89, at approximate flow rate of 60m3/h. The feed is fed on the drum clothes

via feed panels. Air used for filtration comes from nash vacuum pumps.

During filtration, the collected filtrate is taken back to TM3 via TK20 while the

filtered cake is repulped with spent electrolyte from carbon columns in the chute.

This repuled cake is then pumped to either TK63 or TK64 of the resolution train.

e. Cobalt resolution cascade

Its purpose is to re-dissolve the precipitated cobalt and control zinc. The cobalt

hydroxide from TM3 is filtered and repulped with S/E from electro-winning section

before pumping back to resolution cascade. The train receives repulped hydroxide

cake from the cobalt hydroxide filter and any excess cobalt spent electrolyte.

Sulphuric acid is added to achieve the pH set point. The reacted solution goes for

solid/liquid separation in the thickener. The underflow slurry is pumped to the filters

for filtration. The filtered cake is repulped with water or ferric filtrate and pumped to

the clean-up cascades. The overflow thickener pumped to the clarifier thickener for

clarification. Consider a simple flow sheet below to understand material movement

at resolution train.

WILLIAM C. MIINGA Page xxxi


TM3 U/F & Spent Electrolyte H2SO4

H2SO4

E24 (1.0-1.12m3/h, 0.607gpl)

To TM5

Filtrate to TK10

Repulped cake to TM2

Figure 1.7: Showing the movement of liquor at resolution train

f. Cobalt electrolyte clarification

i. CLARIFIER(TM5)

This is the stage of purification where TM4 O/F solution is clarified prior to feeding

the Co tankhouse.

TM4 O/F reports to TM5 at 100-120m3/h Once in TM5, no chemical is added to the

liquor. TM5 reduces total suspended solids (TSS) in solution to <100ppm. This is

achieved through consistent check-up of U/F specific gravity (s.g) which should

always be <1.15. If the sg is >1.15, the thickener is bleed by opening the

underflow. This is done every two hours, 2-3 times per shift. The O/F liquor at a

pH=5-6, reports to two pre-coat feed tanks: A and B or (TK20 and TK50). From

these two tanks, liquor is pumped to Buffalo filter and the three pre-coat filters; A, B

and C. These filters remove total suspended solids to less than 50ppm. Pre-coat

filters consist of plate leaves for solids removing from solution. Plate leaves are

constantly cleaned to maintain their performance efficiency. This is done by

unscrewing them from the filter and washing them with water, or soaking them in

WILLIAM C. MIINGA Page xxxii

TK10 (control vessel) pH=6.2

TK20 (control vessel) pH=6.1



Drum filter

TM4 (solid/liquid separation)


HCl. From the filters, liquor solution is pumped to carbon feed tanks A and B. From

these two tanks, the solution is pumped to carbon columns for sulphides and

organics removal.

ii. CARBON COLUMNS

Cobalt liquor solution from carbon feed tanks is fed to carbon columns with the

help of solution level measuring devices which are there for liquor level balancing

in the tanks. Carbon columns contain activated carbon granules which remove

both sulphides and organics from solution to < 0.5ppm. From the carbon columns,

process solution is pumped to ion exchange feed tanks which feed liquor to the

Nickel ion exchange plant. However, when sulphides levels in liquor going to ISEP

tend to be >0.5ppm, carbon columns are regenerated. However, back washing is

more often done than regeneration.

Carbon Column Back WashingCarbon granules in columns are restored to their performance efficiency by back

washing. This is done when column cone pressure is 4 bars, and when there is

inadequate feed to the column.

During carbon column back washing, the column is first cut from the line by closing

all lines leading liquor to it. Then a slag of carbon granules is drawn from it into the

regeneration column or back-washing vessel. A slag is the amount of carbon

granules allowed to flow from the column into the regeneration vessel in one

minute. Therefore, during back washing, carbon granules occupying the bottom

cone of the column are made to flow into the back-washing vessel, which is about

1-2 slags. This creates space at the top of the column allowing already back

washed carbon granules in the charge tank to flow into the column.

Once in the regeneration vessel, carbon granules are back washed by passing

water through them from the bottom. This process continuous until the discharge

from the top into the sump is clear water, and it lasts depending on how dirty the

granules were. Back wash discharge collects into the sump and is pumped to TK40

at ferric train. This is done on a daily basis depending on the performance of the

carbon granules as depicted by the operator.

WILLIAM C. MIINGA Page xxxiii


Carbon Regeneration.

This is also done based on the performance efficiency of the carbon granules in

removing of sulphides and organics from Co liquor solution .i.e. when sulphide

levels in solution going for nickel removal at Ion exchange plant exceed 0.5ppm.

During this operation, a carbon column being regenerated is first cut from the line

of the system. But before the column is isolated from the system, a sample is cut

from the liquor passing through the column and pH determined. The column is then

drained-off of all solution and flashed with water until the discharge of water

flashing is with pH=7.

1st Stage: While flashing, hydrochloric acid (HCl) solution is prepared in an acid

tank of volume 18m3. This is done by adding 40% by volume of water to the tank

where 400liters of HCl is added .i.e.

H2O=7.2m3=7200litres

HCl=400litres

Concentration=5.3%HCl solution

Therefore, 5.3%HCl solution is then pumped through the carbon column under

regeneration from the top. This process lasts 4-5 hours, and it helps in removing of

gypsum impurities in the carbon granules.

2nd Stage: When HCl acid pumping is stopped, all valves are closed and water

pumped into the column to flash out HCl from the column. This water collects into

the sump, and pumped to ferric train together with residual HCl in the acid tank.

Then a fresh amount of 40% by volume water is added to the acid tank, where

10kg of 99.7% potassium dichromate (K2Cr2O7) is. To this mixture, 500litres of

sulphuric acid (H2SO4) is also added .i.e.

H2O= 7200litres

Concentration of K2Cr2O7=1.3gpl

Concentration=6.5%H2SO4 solution

This solution is then passed through column for about 4hours. Thereafter, water is

used to flash out acid solution from the carbon column through the bottom.

Samples are cut. When there is >100ppm Co with pH< 2.0, the washing water is

pumped toTK206 at Ni plant, from which it is pumped to thickener 5 at roaster. This

continuous until pH=4, where flashing is stopped and the column put back on line.

Co electrolyte begin to pass through the column and is sent back to purification

WILLIAM C. MIINGA Page xxxiv


plant until its pH=4, that is when it is put back on line. Flow rate is increased

depending on the change in the pH of the solution. Consider the diagram below

showing the liquor movementOverflow

From TM4

TO TM4 sg=1.15 TSS<100ppm

TSS<50ppm

FOUR CARBON COLUMNS

Feed to IONEXSulphides<0.5ppmTSS<50ppm

Figure 1.8: Showing the movement of liquor in clarifier/carbon columns

g. Nickel ion exchange

Its objective is to removal the nickel impurity from the cobalt solution in order to produce

cobalt of less than 0.10% nickel.

The plant consists of thirty cells filled with a special resin type, DOW M4195 and

the cells mounted on a large turntable. The cobalt electrolyte stream is passed

WILLIAM C. MIINGA Page xxxv

TM5PRECOAT FEED TANK

PRECOATE FEED TANK

BUFALLO FILTER PRECOATE

FILTERPRECOATE FILTER

PRECOATE FILTER

CARBON COLUMNS FEED TANK A

CARBON COLUMN FEED TANK B

A B C D

IONEX FEED TANK


through a number of cells in the adsorption zone where both cobalt and nickel load

onto the resin. In order not to lose cobalt during elution, a split elution is done.

Sulphuric acid at a 10 gpl is passed through the resin to strip most of the cobalt

and a portion of the nickel. This stream is then recycled to TM1. Nickel is then

removed using a more concentrated acid of 100 to 150gpl.

The resin is then backwashed to displace the acid, and the resin returns to the

adsorption zone. During this process, the suspended solids are removed. The

cobalt electrolyte is preheated before being fed to the cobalt tank house. Consider

the diagram below to understand the flow of liquor at IONEX Plant;

Co electrolyte from C-columns

>120m3/h, 50-350ppm Ni

H2SO4(5-10gpl)20-25m3/h

H2SO4 (100-150gpl)

Bleed back to TK60

Back wash effluent to TK206

Co electrolyteTo TK10 at Co T/H

To TK206To TK10 at Clean-up Train

Figure 1.9: Showing the movement of liquor at IONEX.

WILLIAM C. MIINGA Page xxxvi

TK90IX FEED TANK

TK40 Ni Eluant Tank

TK30 Co Eluant TK70 Water Tank

TK20 Acid Tank

ISEP VALVE & CELLS

TK50Co Eluate Tank

TK60Ni Eluate Tank


b) Cobalt tank house

Cobalt advance electrolyte from Ion-ex reports to TK10, from which it is passed

through heat exchangers.From TK10 via heat exchangers, Co advance electrolyte

at 120m3/h, Co: Ni=150min, Zn<0.5ppm, TSS<50ppm, Co>20gpl and pH=1.0,

reports to four tank house distribution boxes. These distribution boxes feed the

electrolyte to the cells divided into two sections .i.e. East and West sections. A

section has got 37cells. In each cell, there are 31anodes and 30cathodes. Anode

terminals are made of lead antimony, while cathode ones are made of stainless

steel. Therefore, A/E from the distribution box flows into the cells at a flow rate

dependent on factors such as:

Current

pH

Tenor

Temperature

Cell voltage

Co electrolyte enters the cells as A/E and comes out as S/E (spent electrolyte).

Across these cells, a DC current from two rectifiers is applied on each cathode and

anode. The amount of current across each cell is 13.5KA, with each cathode

carrying approximately 450A. Cell voltage vary from 4.5-7.5V depending on the

material being treated. Anode and cathode plates in a cell are electrically

connected in parallel so that the potential difference across the cell is the same as

the voltage drop between the two terminals. DC current from rectifier flows through

the busbars into the anodes. From the anodes, it passes through the electrolyte

onto the cathode. During this movement, Co metal in electrolyte is electroplated

out of solution onto the cathode terminal. After the days of maturity, cathodes are

removed from the cell and electroplated Co stripped from them.

Two things are common with potential drop across a cell. When it is higher than

that of the cell average, it means that the following conditions might be prevailing

i.e.

Loose, dirty contacts between anode/ cathode hanger bars and knife-edges.

WILLIAM C. MIINGA Page xxxvii


Poorly conducting anodes due to heavy passivation cracks, or loose contact

between the anode and hanger bars.

In case of situation where potential drop is lower than that of the cell average, it is

mostly caused by:

Nodules on the cathodes

Shorts in the cell due to peelers

Cell sludge accumulation

a. Degassing

Cobalt metal is degassed in order to lower its hydrogen gas content. This is done

by heating the metal to temperatures of about 780-820oC in a degassing furnace at

a pressures around 720mmHg in batches of 2.5-5 tons. This forces all the gas

contained in the metal to escape raising the grade of the metal.

b. Burnishing

This is the polishing of the degassed cobalt metal to restore its silver shining

surface. It takes about 30-60minutes to burnish cobalt flakes. After which they are

discharged into 5.0tons capacity hopper prior to filling the shipment drums.

c. Drumming

Cobalt from hoppers is filled into drums, where sampling is done as the drums are

being filled. After being drummed, the metal in the drums is sampled and weighed

besides labeled. Usually, it is packed in drums of 250kg and handled over for

dispatch.

d. Peelers

Peelers refer to cobalt metal that peels off the cathode blanks whilst in cells. They

reduce the current efficiency of the process by causing a lot of shorts in cells nd

they are caused by:

The amount of sulphur in the electrolyte

WILLIAM C. MIINGA Page xxxviii


The amount of manganese in the electrolyte: high amounts cause Co to be brittle

and forms cracks easily.

Suspended solids

Gelatinedosage also cause peelers i.e. if you over-dose.

Temperature gradient across a cell i.e. if high.

Electrolyte flow rate when low resulting into adherents.

Peelers in Co tankhouse are controlled by operating at optimum conditions.

e. Nodules

Just like peelers, they reduce current efficiency by causing a lot of shorts. They

form during electro-winning and are constantly removed from the electroplated

cobalt to prevent them causing shorts. When enough, they are degassed and

burnished before drumming.

f. Dispatch

This is the stage where Co metal packed drums are now packed in groups of fours

and shipped

g. Anode Pretreatment

This is done in order to regenerate the anodes. It is done by preparing

10%concentrated H2SO4 acid in a tank and adding 20kg of Potassium Dichromate

to the tank to come up with 0.2%solution of Potassium Dichromate. This is agitated

for 10min, and anode plates dipped in the solution for 24hours. Then the anodes

are removed and hagged on the racks ready for use.

h. Cathode Preparation

To avoid the formation of peelers and adherents on the cathodes, they are cleaned

before taken back for use. After stripping Co metal, cathodes are dipped into nitric

acid. After which, they are again dipped into hot water and left to dry outside. After

drying, they are soaked into 7.9g/m3gelatine solution after which, they are left to

dry and ready for use.

WILLIAM C. MIINGA Page xxxix


Co electrolyte fromIX

Co>20gpl at >120m3/h, pH=1.0minZn<0.5ppm, TSS<50ppm,

Pretreated anodes, demisting balls

Pulled cathodes

Glued cathodes

Cleaned cathodes

Stripped cathodes

Co sheets 55%Nitric acid

O/S particles recycled

Half Co sheets

U/S particles

Co Export

Figure 2.0: Showing the flow of material at the Cobalt tank House.

WILLIAM C. MIINGA Page xl

TK10

Heat Exchngers

East and West Sections with 74 cells

Wash Tank At 40oC

Glue Dip Tank

Cathode stripping section

Nitric acid Dip tank

Breaking machine

Crushing machine

Degassing at 820oC

BurnishingMetal loaded into drums

Drums sealed, weighed & numbered

TM1(Solid/liquid separation)

Zn SX(Solvent Extraction)



Cobalt recovery plant& waste water disposal

O/F

O/F

U/F

O/F

Larox (Gypsum)

Stripped liquor from Copper Solvent extraction plant

Feed (Tenke)


2.2. CURRENT FLOW SHEET AT COBALT PURIFICATION PLANT

TM= thickener number

O/F= thickener overflow

U/F= thickener underflow

Figure 2.1: Current Chambishi Metals Cobalt Plant Flow Sheet

WILLIAM C. MIINGA Page xli

Cu 445 ppm

Zn ≤ 10 ppm

Resolution Stage

U/F


CHAPTER THREE

LITERATURE REVIEW

WILLIAM C. MIINGA Page xlii


3.1. BASIC CONCEPTS OF ION EXCHANGE

Ion exchange is a reversible chemical reaction where an ion (an atom or molecule

that has gained or lost an electron and thus acquired an electric charge) from

solution is exchanged for a similarly charged ion attached to an immobile solid

particle called Ion Exchanger. These solid ion exchange particles are either

naturally occurring inorganic zeolites or synthetically produced organic resins. The

synthetically produced resins are the predominant type used today because their

characteristics can be tailored to specific application. (R.Minango, 1993)

The process occurs with no structure changes in the resin. At some point during

the ion exchange process ion exchange equilibrium is established. The general

reaction for the exchange of ions A and B on a cation exchange resin can be

represented as follows.

nR-A+resin + Bn+

sol n R-nB+

resin + nA+soln………………………………..2.1

Where R is an anionic group attached to the ion exchange resin, and A+ and B+ are

ions in the solution and n is a group valence.

An organic ion exchange resin is composed of high-molecular _ weight

polyelectrolyte that can exchange their mobile ions for ions of similar charge from

the surrounding medium.

Each resin has a distinct number of mobile ions sites that set the maximum

quantity of exchanges per unit of resin. For exchanger, in the case of Copper ions

(Cu2+) in solution, a resin with Hydrogen ions available for exchange will exchange

those for Copper ions in the solution. The reaction can be as follows. (Dowex,

2011)

2(RSO3H) +CuSO4 (RSO3)2Cu + H2SO4………………………………….2.2

RSO3 indicates the organic portion of the resin and H is the immobile portion of the

ion active group.

Two resin sites are needed for the Copper ions with a plus two valence (Cu2+).

Trivalent ferric ions would require three sites. As shown above, the ion exchange

WILLIAM C. MIINGA Page xliii


reaction is reversible. The degree of the reaction to proceed to the right will depend

on the resins preference or selectivity of a resin for a given ion is measured by the

selectivity coefficient. K which in its simplest form for the reaction

RA+ + B+ RB+ + A ……………………………………………...2.3

Is expressed as K = (concentration of B+ in resin/ concentration of A+ in resin) x

(concentration of A+ in solution/ concentration B+ in solution)

The selectivity coefficient expresses the relative distribution of ion when resin in the

A+ form is replaced in a solution containing B+ ions. Table 2.1 gives the selectivity

of strong acid and strong base ion exchange resins for various ionic compounds.

It should be pointed out that the selectivity coefficient is not constant but varies with

change in solution conditions. It does provide a means of determining what to

expect when various ions are involved. As indicated in Table 2.1, strong acid resins

have a preference for nickel than sodium. Despite this preference, the resin can be

converted back to the hydrogen form by contact with a solution of sulphuric acid

(Eqn 2.4).

(R-SO4)2Cu + H2SO4 2(R-SO3H) + CuSO4 ………………………………2.4

This step is known as regeneration. In general terms, the higher the preference a

resin exhibits for a particular ion, the greater the exchange efficiency in terms of

resin capacity for removal of that ion from the solution. Greater preference for a

particular ion, however, will result in increased consumption of chemicals for the

regeneration. (Dowex, 2011)

WILLIAM C. MIINGA Page xliv


Table 2.1- selectivity of ion exchange resins in order of decreasing preference. (L. Rosato, 1984)

3.2. TYPES OF RESINS

Many different types of resin have been developed namely cation exchangers, anion

exchangers and chelating exchangers.

3.2.1. CATION AND ANION EXCHANGE RESIN

Cation and anion exchange resins have fixed ions known as Co-Ions and mobile

ions of opposite charge called Counter- Ions. The co-ions are bound to an insoluble

microporous matrix, while the counter-ions reversibly interchange with ions in

surrounding solution. Anion exchangers are resins that have fixed positive ion

(cations) on the framework and so can exchange negative ions (anions) from a

solution. Cation exchangers are resins that have fixed negative ions (anions) on the

framework and can exchange positive ions (cations) from a solution, as depicted in

Figure 2.1. It should be noted that in any ion exchange reaction each separate phase

(solution and resin) within the system would maintain its overall electro neutrality.

Figure 2.2 Schematic sections through a cation exchange resin. (R.Minango, 1993)

WILLIAM C. MIINGA Page xlv

Strong Acid Cation

Exchange

Strong Base Anion Exchange

Barium IodideLead Nitrate

Calcium BisulfateNickel Chloride

Cadmium CyanideCopper Bicarbonate

Zinc HydroxideMagnesium FluoridePotassium Sulfate


From Figure 2.1 it can easily be understood that the SO3⁻ions, which are usually

the fixed ions in cation resins, are fixed to the resin framework, while the H+ ions

are free to move throughout the structure. As a result, sodium ions can enter the

resin freely, causing the rejection of hydrogen ions, whereas chloride ions (Cl⁻)

approaching the surface of the resin are repelled by the fixed negative charges

(SO3⁻) and cannot enterbecause it is a cation resin. Note that when a resin has H +

as its free ions, it is said to be in H+ form. If Na+ are the free ions, then it is in the

Na+ form etc.

The anion and cation are produced from the same organic polymers. They differ

from the ionizable group attached to the hydrocarbon network. It is this functional

group that determines the chemical behavior of the resin. Resins can be broadly

classified as strong or weak exchangers.

Most ion exchanger resins in use today are synthetic materials made up of a

polymer matrix (generally chains held together by divinyl Benzene crosslink) with

soluble ionic functional groups attached to the polymer chains. The total number

and kind of functional groups in a resin determine the exchange capacity and the

ion selectivity while the polymer matrix provides insolubility and toughness to the

resin. (benefied, 1982)

Ion exchange resins are usually classified in the following manner:

1. Cation exchange resin (contains exchangeable cations):

a) Strong-acid exchange resins (SAC)

b) Weak-acid exchange resins (WAC)

2. Anion exchange resins (contain exchangeable anion):

a) Strong – base exchange resins (SBA)

b) Weak – base exchange resin (WBA)

WILLIAM C. MIINGA Page xlvi


A. STRONG ACID EXCHANGE RESINS

Strong acid cation exchangers are so named because their chemical behavior is

similar to that of a strong acid. These resins contain function groups derived from

a strong acid (normally sulphuric acid). The resins are highly ionizable in both the

acid (R-SO3H) and salt (R-SO4Na) form. They convert a metal salt to the

corresponding acid by the reaction:

2(R-SO3H) + Na(R-SO4) Na(R-SO3) + H2SO4……………………….2.5

The hydrogen and sodium form of the strong acid resins are highly dissociated

and the exchangeable Na+ and H+ are readily available for exchange over the

entire pH range.

B. WEAK ACID EXCHANGE RESIN

In a weak acid resin, the ionizable acid group is a carboxylic group (COOH) as

opposed to sulfonic acid group (SO3H) used in strong acid resin. Such resins are

useful only within a fairly narrow pH range. Weak acid resins exhibits a much

higher affinity for hydrogen ions than do strong acid resins.

This characteristic allow for regeneration to hydrogen with significantly less acid

than is required for strong acid resins. The degree of dissociated of a weak acid

resin is strongly influenced by the solution pH. A typical weak acid resin has limited

capacity below a pH of 6.0. (Dowex, 2011)

C. STRONG BASE ANION EXCHANGE RESINS

Strong base anions are highly ionized and can be used over the entire pH range.

These resins are used in the hydroxide (OH) for water deionization. They will react

with anions in a solution and can convert an acid solution to pure water.

R-NH3OH + HCL R-NH3CL + HOH…………………….2.6

WILLIAM C. MIINGA Page xlvii


Regeneration with concentrated sodium hydroxide (NaOH) converts the exhausted

resin to the hydroxide form and the regeneration efficiency of these resins is 30 to

50%.

D. WEAK BASE EXCHANGE RESINS

Weak base resins are like weak acid resins, in that the degree of deionization is

strongly influenced by pH. Consequently, weak base resin exhibit minimum

exchange capacity above a pH of 7.0. These resins merely sorb acids: they cannot

split neutral salts but they can remove strong acids by adsorption. (Dowex, 2011)

Figure 2.3 Discharge capacity vs pH profile for weak acid and weak base resin types. (R.Minango, 1993)

3.2.2. HEAVY – METAL – SELECTIVE CHELATING RESINS

Heavy – Metal – Selective chelating resin behave similarly to weak acid cation

resins but exhibits a high degree of selectivity for heavy metal cations. A chelating

resins exhibits greater selectivity for heavy metals in its sodium form than its

hydrogen form. Regeneration properties are similar to those of weak acid resin; the

chelating resin can be converted to the hydrogen form with slightly than

stoichiometric doses of acid because of the fortunate tendency of the heavy metal

complex to become less stable under low pH conditions. (L. Rosato, 1984)

WILLIAM C. MIINGA Page xlviii


3.2.3. LEWATIT VP OC 1026 RESINS

LEWATIT VP OC 1026 is a cross-linked polystyrene based macro porous resin

which contains Di-2-ethylhexyl-phosphate (D2EHPA). This active ingredient is

directly incorporated during the formation of the copolymer and is fixed by

adsorption. This gives a resin of very good matrix and compared with impregnated

resins a relatively high concentration of active ingredient; in addition, loss of

extraction during operation is minimized (as long as the pH of the process solution

as well as rinse water is kept below pH 4). (lanxess, 2011)

A. AFFINITY ORDER FOR TYPICAL CATIONS

Cations are adsorbed by LEWATIT VP OC 1026 in the following order of affinity

which varies as a function of solution pH:

Ti4+ > Fe3+ > In3+ >Sn2+ > Bi3+ > Vo2+ > Be2+ > Al3+ > Zn2+ > Pb2+ > Ca2+ >

Mn2+ > Cu2+ > Fe2+ > Co2+ > Ni2+ > Mg2+ > Cr3+ >>>>>Alkali

(lanxess, 2011)

3.3. TECHNOLOGY / EQUIPMENT DESCRIPTION

The initial part of this section describes some of the more important design

elements of ion exchange systems and the letter part presents a description of

commercially available equipment.

3.3.1. BATCH AND COLUMN EXCHANGE SYSTEMS

Ion exchange processing can be accomplished by either a batch method or a

column method. In the first method, the resin and solution are mixed in a batch

tank the exchange is allowed to come to equilibrium, and the resin is separated

from the solution. The degree to which the exchange takes place is limited by the

preference the resin exhibits for the ion in solution. Consequently, the use of the

resin exchange capacity will be limited unless the selectivity for the ion in solution

is greater than for the exchangeable ion attached to the resin. (Dowex, 2011)

WILLIAM C. MIINGA Page xlix


Because batch regeneration of the solution is inefficient, batch processing by ion

exchange has limited potential for application. Passing a solution through a column

containing a bed of exchange resin is analogous to treating the solution in an

infinite series of batch tanks.

3.3.2. ION EXCHANGE RESINS AND COLUMNS

A wide range of ion exchange resins are manufactured, the choice of which

depends mainly on the type of metal being recovered and the chemical

composition and characteristics of the solution being treated. Properly matching

the ion exchange resin and the process chemistry should result in efficient

operation, quality byproducts and lower operating costs. Inappropriate selection of

the resin can result in total system failure.

Many specialty resins, such as chelacting resins, are also in commercial use.

Chelating resins that exhibits a high selectivity for heavy metal actions over other

cations in solution have been commonly used in metal finishing, especially in the

past ten years. Because of their selectivity, they are especially useful for end of-

pipe polishing following hydroxide precipitation. Chelating resins are also used in

recovery with electroless copper and electroless nickel plating solution. Generally,

chelating resins cannot be used at low pH (<4) and pH adjustment step is typically

needed before the ion exchange process. (Dowex, 2011)

3.3.3. FIXED – BED COLUMN SYSTEMS

Most industrial application of ion exchange used fixed – bed column systems, the

basic component of which is the ion exchange column. The column must;

Contain and support the ion exchange resin.

Uniformly distribute the service and regeneration flow through the resin bed.

Provide space to fluidize the resin during backwash.

Include the piping, valves, and instruments needed to regulate flow of feed,

reentrant, and backwash solutions.

WILLIAM C. MIINGA Page l


After the solution is processed to the extent that the resin becomes exhausted and

cannot accomplish any further ion exchange, the resin must be regenerated. Resin

capacity is usually expressed in terms of equivalents per liter of resin. An

equivalent is the molecular weight in grams of the compound divided by its

electrical charge or valence.

The hydraulic loading of resins will vary considerably form application, depending

on: Column design; type of resin employed; concentration of metal in solution;

other characteristics of the feed solution (e.g., pH) and the allowable concentration

of metal in the column effluent. Typical hydraulic loadings range from 2 to 3 gpl of

rinse water per cubic foot of resin. (R.Minango, 1993)

3.3.4. INTEGRATED AGAINST MODULAR DESIGNS

An integrated ion exchange system design is one in which the various components

needed to perform the ion exchange recovery and regeneration functions are

connected within the one unity. Such systems may also have attached electro

wining units and /or chemical treatment system processing the re-generant.

The modular or point source design separates the ion exchange column from the

regeneration and re-generant processing equipment. With the modular design, the

columns are transported to a central station for regeneration (in some cases the

modules are hard piped) the regeneration station can be either in the plating shop

or at an off-site location (i.e. centralized waste treatment facility).

The modular ion exchange strategy can reduce capital costs for small to medium-

sized application where low to moderation frequency is required. Also the modular

units are considerably smaller and therefore do not occupy as much production

area floor space as integrated units (i.e, if the regeneration station is remotely

located to a non-production area. However, operating costs are usually higher for

modular system due to station (or changing operating modes and valve positions

for had piped modular systems) and initiating regeneration.

Some commercial ion exchange modules have the appearance of large cans and

are referred to as ion exchange canisters. With this type of unit, the canisters can

be stacked upon one another to combine anion ant cation types or to increase the

resin bed volume. Standard column designs are also available. (R.Minango, 1993)

WILLIAM C. MIINGA Page li


3.3.5. SINGLE Vs DUPLEX COLUMN OPERATION

Duplex column ion exchange systems are used in many chemical recovery

operations especially where a continuous feed flow is expected. Dual column

configuration avoids downtime during regeneration. Two different duplex column

arrangements are commonly used. In one arrangement, which is referred to as

parallel / standby, the feed stream flows through either one column or the other, but

never both.

The off-line column is regeneration and then is held in reverse until the other

column is ready for regeneration. This is a somewhat inefficient use of the two

columns since column switching must take place before breakdown occurs, which

happens before the resin is completely loaded with ions of interest. In the second

case, which is referred to as lead / lag, the two columns are placed in series flow.

During operation, the majority of metal removal is accomplished in the first column

(lead column) until it approaches capacity.

The process can continue until the first column is essentially loaded to full

capacity with ions of interest, since the second column (lag column) will remove

the breakthrough of the first column. After breakthrough is reached, the first

column is taken off-line for regeneration. The switching of the two columns,

initiating of regeneration and other functions of modern ion exchange equipment

is usually controlled by a microprocessor. (Levenspiel, 1972)

3.3.6. COUNTER FLOW Vs COCURRENT FLOW / REGENERATION

One method of categorizing the operation of different ion exchange system is by

the direction of the service flow (i.e. rinse water) Vs the direction of the

regeneration flow, with concurrent operation, the service flow and the regeneration

cycle flow in the same direction and with counter flow, they flow in opposite

direction (service flow can be either downward or upward). Counter current flow is

considered by most sources to be the more efficient method. (Levenspiel, 1972)

With concurrent flow the hydrogen ions metal ions from the top to the lower portion

of the bed. Complex removal of these ions can only be accomplished by the use of

excessive levels of acid regerant. With normal regenerant usage, there is a “heel”

WILLIAM C. MIINGA Page lii


left at the exit end of the column (i.e. undisplaced metal ions). On the following

service cycle, the desired exchange reaction occurs in the upper position of the

bed. However, as the hydrogen ion concentration increases

towards the lower section of the bed, some exchange with .previously undisplaced

metal ions to metal ion “leakage”.

After regeneration of the counter flow system, the residual ions are in the top of the

bed, with the bottom being fully converted to hydrogen. Thus, there are no residual

metal ions present at the bottom of the bed to permit the leakage reaction to occur

on the subsequent service cycle.

In addition to reduced ion leakage, counter flow regeneration can increase

operating capacities, decrease the need for waste stream pH adjustment and

reduced waster rinsing requirement.

3.3.7. OTHER EQUIPMENT / DESIGN CONSIDERATION

In addition to the basic ion exchange column, auxiliary equipment is employed for

various purposes, among which include: resin bed channeling and fouling

prevention; pH adjustment of the feed stream; solution pump and flow control;

need for regeneration identification; and regeneration cycle co

Pretreatment of the feed stream is usually performed. Filtration is the basic

requirement for nearly all ion exchange applications. If solids are permitted to enter

the ion exchange bed, they will often create an uneven film on the top of the bed

that acts as a plug. The solids will impede flow and cause channeling through the

bed. Channeling of the feed stream solution will result in incomplete usage of the

bed and inefficient processing. Most commonly, cartridge filtration is used for this

purpose. (Levenspiel, 1972)

Multimedia filters are sometimes used in high flow applications, where changing of

the cartridge filters would be too time consuming. Other types of pretreatment

include pH adjustment and carbon filtration. The adjustment of pH is used for

certain applications where resin capacity can be enhanced by increasing or

lowering the pH. Carbon filtration is used to remove certain organics such as oils

WILLIAM C. MIINGA Page liii


that become irreversible sorbed by the ion exchange resins and oxidants such as

peroxide that can oxidize and ruin the resin.

The means for identifying the point at which regeneration should be initiated varies

among commercially available equipment. The method employed depend on the

overall design of the system (e.g. a lead / lag unit may be able to tolerate some ion

leakage from the first column. (Levenspiel, 1972)

3.3.8. REGENERATION PROCEDURE

After the feed solution is processed to the extent that the resin becomes exhausted

and cannot accomplish any further ion exchange, the resin must be regenerated.

Regeneration displaces ions during the service run and returns the resin to its

initial exchange capacity or to any desired level, depending on the amount of

regenerant used. In general, mineral acids are used to regenerate anions resins. In

normal column operation, regeneration employs the following basic steps:

1. The column is backwashed to remove suspended solids collected by the bed

during service cycle and to eliminate channels that have formed during this

cycle. The backwash flow fluidizes the bed, releases trapped particles and

reorients the resin particles according to size.

During backwash the larger, denser particles will accumulate at the base and

the particle size will decrease moving up the column. This distribution yields a

good hydraulic flow pattern and resistance to fouling by suspended solids.

2. The resin bed is brought into contact with the regenerant solution. In the case of the cation resin, acid elutes the collected ions and converts the bed to the hydrogen form. A slow water rinse then removes any residual acid.

3. The bed is brought into contact with a copper/cobalt solution and other traces of metal ions to convert the resin to the sodium form. Again, a slow rinse is used to remove residual acid. The slow rinse pushes the last of the regenerant through the column.

4. The resin bed is subjected the fast rinse that removes the last traces of the

regenerant solution and ensures good flow characteristics.

WILLIAM C. MIINGA Page liv


5. The column is returned to service. (Dowex, 2011)

3.3.9. THE MASS TRANSFER ZONE (MTZ)

The mass transfer zone is defined as the section of the bed over which there exists

a concentration gradient, based on a percentage breakthrough (i.e. Zn in / Znout).

The selectivity of the resin for Zinc over Cobalt is also used to effect the split

elution, whereby an eluant of low acid strength is first used to strip the Cobalt,

which is recycled to the purification circuit as the value species, while the Zinc

remains loaded on the resin.

A higher acid strength eluant is subsequently passed through the bed to strip the

Zinc as the waste stream. The effectiveness of the split elution technique is

measured primarily by the amount of Cobalt lost to Zinc eluant waste stream and

the amount of Zinc recycled into the process.

The principle design issues are:

To maximize Zinc loading on the resin, while minimizing Cobalt loading: and

To optimize the split elution, so as to minimize the amount of Zinc in Cobalt

recycle stream and the amount of Cobalt in the Zinc waste stream. (Jeffers,

1985)

WILLIAM C. MIINGA Page lv


CHAPTER FOUR

APPARATUS AND METHODOLOGY

4.0. APPARATUS AND EXPERIMENTAL PROCEDURES

WILLIAM C. MIINGA Page lvi


4.1. APPARATUS AND REAGENTS USED

The following are the apparatus and reagents that were used in the laboratory

for carrying out the experiment;

Vacuum pump pH meter clamp stand 130ml laboratory column 200 liters x 2 empty containers Stop watch Beakers (2x4000ml, 2000ml, 450ml, 50ml) Sample bottles 50ml Stirring mechanism Demineralized water and Concentrated sulphuric acid Tubes Different types of graduated measuring cylinders, 10ml, 100ml, Inert resins Sand

4.2. SAMPLES

TM 2 Overflow

Zinc raffinate

Lewatit vp oc 1026 resins

4.3. EXPERIMENTAL PROCEDURES

4.3.1. LOADING

Column test works were done to determine the breakthrough profile of the metal of

interest. Considering the laboratory column (130ml) which was used for test works,

120ml (bed volume) of resins were carefully added to a dry 130ml laboratory column

using a spatula. To avoid the resin from floating to the surface of the solution the

column was equipped with adequate distribution screen at the column’s head.

Lewatit VP OC 1026 has a relatively high percentage of fine beads. Therefore, inert

resins were used to protect the head screen distributors against plugging. To the

bottom screen distributor a layer of sand was added.

WILLIAM C. MIINGA Page lvii


TM2 overflow solution had a pH of 4.5. Lewatit VP OC 1026 operating pH range is 1-

4. Therefore, TM2 overflow solution’s pH was adjusted to pH 3.5 and 2.5 respectively

by adding ZnSX raffinate in the 200L container and then mixing the two solutions

using a stirring mechanism. The apparatus were set-up and water was passed

through the resins with the help of the of tubes and vacuum pump from the beakers

so as to set the flow rate of the pump to 10BV/h i.e. (120ml/BV x 10BV/h) x

1hr/60min=20ml/min.

The column was charged at this flow rate with TM2 overflow solution from a 200L

container cutting timed samples with the help of a stop watch every 1hour but only

taking the 5th sample for analysis of Co, Cu, Zn, Fe, Mn, and Mg. and The barren

solution (Zinc free) was collected from the bottom of the column into another 200L

container. After 4 days the resins were exhausted and a breakthrough curve was

generated.

4.3.2. ELUTION

Loaded cobalt was selectively eluted with a weaker sulphuric acidic solution,

followed by more concentrated acid solution to strip zinc i.e. a two stage Elution

process was considered

1. 0.5% H2SO4----5BV@5BV/h

2. 5%H2SO4----1BV@5BV/h

Elution was done by passing weak-acid concentrations: 9.4g/l H2SO4. At this

stage only cobalt was expected to come out as cobalt eluate.

After cobalt elution, then 93.9g/l H2SO4 was passed through the resin, so that at

this stage, copper, zinc, manganese, magnesium and iron could come out

WILLIAM C. MIINGA Page lviii


CHAPTER FIVE

RESULTS AND DISCUSSIONS

5.1. 1st CYCLE

A. LOADING

WILLIAM C. MIINGA Page lix


During loading, the feed pH dropped from the initial 3.3 at ambient temperature to

a pH value of about 2, after which it started rising at the slower rate until saturation

was reached1. The loading of zinc on the resin was efficient as breakthrough took

place only after 1500 minutes i.e. after 7.2 liters of feed solution has been passed

through the resins.

0 200 400 600 800 1000 1200 1400 1600 1800 20000

50

100

150

200

250

300

350

400

450

0

1

2

3

4

5

6

7

8

9LOADING

Cu ppm Co gpl Zn ppm Fe ppm

TIME(min)

Cu p

pm

Zn ppmCo gpl

Fe ppm

Figure 4.1: Loading profile for Co, Cu, Zn and Fe at 10BV/hr. at ambient temperature

Figure 4.1 shows the breakthrough curves of zinc and cobalt. The zinc

breakthrough was achieved in1500 minutes. The Zinc and Cobalt in the feed were

3.57ppm and 8.563g/l respectively. Lewatit vp oc 1026 was loading very fast in the

first 600 minutes2. And for the first 1300minutes the resins did not stop loading

zinc.

The Zinc in the resultant solution;

1 The drop in PH was because of the ion exchange between zn2+ from solution and H+ in the resins i.e. the process increased the concentration of H+ in solution, hence increasing the concentration of acid in the cobalt leach solution.2 The loading of zinc (or ions) was fast in the first 600minutes because the resins had well-defined number of exchangeable sites (mobile ion sites). Hence, the zinc was adsorbed on the resins reducing the concentration on Zn2+ thus the drop in the Zn graph. As the process continued these sites were depleted i.e. the ion exchange equilibrium was established. Explanation for rise in the graph.

WILLIAM C. MIINGA Page lx


The advance coming out from the column had Zinc in the range <0.1ppm –

2.43ppm; this was against 3.57ppm Zinc in the feed solution passing

through the resin.

The advance coming out from the column had Cobalt in the range 7.573gpl –

8.162gpl; this was against 8.563 gpl Cobalt in the feed solution passing

through the resin. The resin was saturated with Cobalt in just 1500 minutes.

B. 1st ELUTION USING 9.4 gpl

0 10 20 30 40 50 60 700

20406080

100120140160

0

0.5

1

1.5

2

2.5

COBALT ELUTION

Zn ppm Co gpl Fe ppm Cu gplTIME (MIN)

Zn p

pm

Co gpl,Cu gpl,Fe PPM

Figure 4.2: Cobalt elution profile using 9.4gpl H2SO4 at 5BV/hr. at ambient temperature

Figure 4.2: Shows that the resin lewatit vp oc 1026 was rejecting Cobalt

significantly. Cobalt was being rejected very fast in the first 25 minutes and then

after the rate of rejection became constant. The elution was done for 60 minutes to

recover all the cobalt that had been loaded on the resin.


Cobalt eluate coming out during the 1st stage elution process had Zinc in

the range <0.1ppm-146ppm. At this stage, the ideal situation was to have

minor amounts of Zinc in the Cobalt eluate because this is a recovery

stream for cobalt.

WILLIAM C. MIINGA Page lxi


C. 2nd ELUTION USING 93.9 gpl H2SO4

0 2 4 6 8 10 12 140

20

40

60

80

100

120

140

160

180

0

5

10

15

20

25

30

35

40

45ZINC ELUTION

Co ppm Fe ppm Cu ppm Zn ppmTIME(MIN)

Co ppmFe ppm Zn ppm

Cu ppm

Figure 4.3 Zinc elution profile using 93.9 gpl H2SO4 at 5BV/hr. at ambient temperature

Figure 4.3Shows how the loaded Cu, Fe, Co, and Zn on resin were coming out.


The Zinc eluate coming out from the column had Copper zinc and iron in the

range of 9ppm to 6ppm, 0.8ppm to 40ppm and 0.5ppm to 171ppm

respectively. The drop in the graphs shows the elution of these impurities

which were loaded on the resin. At this stage, the ideal situation was to elute

more Zinc in the zinc eluate because this stream is not recycled in the plant.

The Zinc eluate coming out from the column had cobalt in the range of

2ppm to 60ppm this is against 2ppm to 1.508 gpl in the cobalt elution. This

is a good recovery.

WILLIAM C. MIINGA Page lxii


5.1.1. FIRST CYCLE SPLIT EFFICIENCY

1st ELUTION

Table 4.1 Percentage split of Co, Cu, Zn and Fe in cobalt eluate using 9.4 gpl H2SO4 at 5BV/hr.

Time(min

)

Cumulative ,grams % in Co eluate

Co Cu Zn Fe Co Cu Zn Fe

10 0.15080.2131

00.0146

00.000117

099.2

99.9

94.8 3.3

20 0.15500.2168

00.0151

00.000178

098.8

99.8

93.9 2.7

30 0.15690.2180

00.0153

00.000238

098.7

99.8

93.0 2.7

40 0.15760.2185

00.0153

10.000297

098.6

99.7

92.8 2.8

50 0.15790.2188

00.0153

20.000350

098.6

99.6

92.6 2.8

60 0.15810.2190

00.0153

30.000391

098.6

99.6

92.6 3.1

2ND ELUTION

Table 4.2 Percentage split of Co, Cu, Zn and Fe in Zinc eluate using 93.9 gpl H2SO4 at 5BV/hr.

Time(min

)

Cumulative ,grams % in Zn eluate


2 0.0012 0.0002 0.000800.0034

2 0.8 0.1 5.2 96.7

4 0.0019 0.0004 0.000980.0064

2 1.2 0.2 6.1 97.3

6 0.0021 0.0005 0.001150.0087

0 1.3 0.2 7.0 97.3

8 0.0022 0.0007 0.001190.0104

0 1.4 0.3 7.2 97.2

10 0.0022 0.0008 0.001220.0120

6 1.4 0.4 7.4 97.2

12 0.00230.0009

60.00123

20.0120

7 1.4 0.4 7.4 96.9

WILLIAM C. MIINGA Page lxiii


For the Copper, Zinc, iron and Cobalt that was loaded on the resin, an average of

99.7 % Cu and 93.3 % Zn, 98.8 % Co and 2.9% Fe went to the Cobalt eluate.This is

not suitable for a stream that is recycled back into the plant and 0.3 % Cu, 6.7 %

Zn, 1.2% Co and 97.1% Fe went to the zinc eluate. Here the efficiency was very

poor.

5.2. 2ND CYCLE

A. LOADING

0 200 400 600 800 1000 1200 1400 1600 1800 20000

50

100

150

200

250

300

350

400

450

0

1

2

3

4

5

6

7

8

9

LOADING

Cu ppm Co gpl Zn ppm Fe ppm

TIME (MIN)

Cu ppm

Co gplZn ppm,Fe ppm

Figure 4.4 Loading profile for Co, Cu, Zn and Fe at 10BV/hr. at ambient temperature

Figure 4.4 shows the breakthrough curves of cobalt and zinc. The Zn

breakthrough was achieved in just 1800 minutes. The Zinc and Cobalt in the feed

were 3.57ppm and 8.563g/l respectively. Lewatit vp oc 1026 was loading very fast

in the first 900 minutes. And for the first 1500 minutes the resin did not stop

loading zinc.3


3 Because of the availability of the mobile ion sites in the resins

WILLIAM C. MIINGA Page lxiv


The advance coming out from the column had Zinc in the range 1.76ppm –

3.16ppm; this was against 3.57 ppm Zinc in the feed solution passing

through the resin.

The advance coming out from the column had Cobalt in the range 7.491gpl –

8.162gpl; this was against 8.563gpl Cobalt in the feed solution passing

through the resin. The resin was saturated with Cobalt in just 1800 minutes.


0 10 20 30 40 50 60 700

20

40

60

80

100

120

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Cobalt Elution

Cu ppm Zn ppm Co gpl Fe ppm

TIME (Min)

CU PPMZN PPM

Co gplFe PPM

Figure 4.5 Cobalt elution profile using 9.4gpl H2SO4 at 5BV/hr. at ambient temperature

Figure 4.5: shows that the resin lewatit vpoc 1026 was rejecting Cobalt

significantly. Cobalt was being rejected very fast in the first 40 minutes and then

after the rate of rejection became constant. The elution was done for 60 minutes to

recover all the cobalt that had been loaded on the resin.


The Cobalt eluate coming out during 1st stage elution had a higher

concentration of Zinc making the good cobalt eluate poor. At this stage, the

WILLIAM C. MIINGA Page lxv


ideal situation was to have less Zinc in the Cobalt eluate because this

stream is recycled in the plant.

C. 2nd ELUTION USING 93.9 gpl H2SO4

0 2 4 6 8 10 12 140

10

20

30

40

50

60

70

80

0

2

4

6

8

10

12

14

ZINC ELUTION WITH 93.9 gpl

Co gpl Fe ppm Cu ppm Zn ppm

TIME(MIN)

Co ppmFe ppm

Cu ppmZn ppm

Figure 4.6 Zinc elution profile using 93.9 gpl H2SO4 at 5BV/hr. at ambient temperature

Figure 4.6 shows how the loaded Cu, Fe, Co, and Zn on the resin were coming

out.

Zinc in the resultant solution;

The Zinc eluate coming out from the column had Copper, zinc and iron in

the range of 01ppm to 13ppm, 1.35ppm to 12ppm and <0.1ppm to 35ppm


WILLIAM C. MIINGA Page lxvi





07ppm to 70ppm this is against 56ppm to 1.305 gpl in the cobalt elution.

This is a good recovery.

5.2.1. SECOND CYCLE SPLIT EFFICIENCY

1st ELUTION

Table 4.3 Percentage split (2nd cycle) of Co, Cu, Zn and Fe in Cobalt eluate using 9.4 gpl H2SO4at 5BV/hr?

Time(min)

Cumulative ,grams % Co eluate


10 0.13050.01060

0.00260

0.00001

98.9

97.6

91.5 1.4

20 0.19040.01340

0.00500

0.00002

98.6

96.8

93.3 1.4

30 0.22120.01590

0.00720

0.00003

98.3

96.5

94.0 1.5

40 0.23570.01820

0.00920

0.00004

98.2

96.6

94.6 1.5

50 0.24340.01970

0.01080

0.00005

98.1

96.8

95.0 1.9

60 0.24900.02070 0.01170

0.00006

98.1

96.8

95.2 2.2

2nd ELUTION

Table 4.4 Percentage split (2nd cycle) of Co, Cu, Zn and Fe in Zinc eluate using 93.9 gpl H2SO4 at

5BV/hr.

Time(min)

Cumulative ,grams % Zneluate

WILLIAM C. MIINGA Page lxvii



20.0014 0.0003 0.00024

0.00070 1.1 2.4 8.5

98.6

40.0027 0.0004 0.00036

0.00138 1.4 3.2 6.7

98.6

60.0039 0.0006 0.00046

0.00202 1.7 3.5 6.0

98.5

80.0044 0.0006 0.00053

0.00262 1.8 3.4 5.4

98.5

100.0047 0.0007 0.00056

0.00262 1.9 3.2 5.0

98.1

120.0048

0.00068

0.000591

0.00262 1.9 3.2 4.8

97.8

For the Copper, Zinc, iron and Cobalt that was loaded on the resin, an average of

96.8 % Cu and 93.9 % Zn, 98.4 % Co and 1.6% Fe went to the Cobalt eluate, which

is not suitable for a stream that is recycled back in the plant, and 3.2 % Cu, 6.1 %

Zn, 1.6% Co and 98.4% Fe went to the Zinc eluate. Here the efficiency was also

very poor.

WILLIAM C. MIINGA Page lxviii


5.3. 3RD CYCLE

A. LOADING

This is an optimized cycle. The pH of the feed solution was reduced from 3.3 to 2.5

and flow rate was reduced to 7.5BV/hr.

Thus from the results obtained it seems that a decrease in flow rate from 10BV/hr.

to 7.5BV/hr. and pH marginally enhances zinc loading. During loading, the feed pH

dropped from the initial pH=2.5 at ambient temperature to a pH value of about

pH=1.6. this is because of the addition of the H+ ions in the process solution at the

loading stage, below is the equation summarizing this statement;

CoSO4.Zn2++ (RO)2PO2H = (RO)2PO2.Zn2+ + CoSO4.H+

(RO)2PO2H represents D2EHPA (Di-2-ethyl-hexyl phosphoric acid)

The loading of zinc on the resins was efficient while cobalt loading on the resins

under these conditions was reduced from 1.316 gpl from the first two cycles to

0.588 gpl.

0 200 400 600 800 1000 1200 1400 1600 1800 20000

1

2

3

4

5

6

7

8

9

10

0

50

100

150

200

250

300

350

400

450

loading

Co gpl Zn ppm Fe ppm Cu ppm

TIME(MIN)

Co gplZn ppmFe ppm

Cu ppm

Figure 4.7 Loading profile for Co, Cu, Zn and Fe at 7.5BV/hr. at ambient temperature

WILLIAM C. MIINGA Page lxix


Figure 4.7 shows the breakthrough curves of cobalt, copper, zinc and iron. The Zn

breakthrough was achieved in just 1500 minutes. The Copper, Zinc, Iron and

Cobalt in the feed were 381 ppm, 3.57ppm, 2ppm and 8.563g/l respectively.

Lewatit vpoc 1026 was loading very fast in the first 600 minutes. And for the first

1500 minute the resin did not stop loading copper and zinc.

The Zinc/Cobalt in the resultant solution;

The advance coming out from the column had Zinc in the range 0.85ppm –

2.3ppm; this was against 3.57ppm Zinc in the feed solution passing

through the resin.

The advance coming out from the column had Cobalt in the range 8.013gpl – 8.51gpl; this was against 8.563gpl Cobalt in the feed solution passing through the resin. The resin was saturated with Cobalt in just 1800 minutes.


0 10 20 30 40 50 60 700

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0

1

2

3

4

5

6

7

8

9

3rd cycle Elution-1

Co gpl Zn ppm Fe ppm Cu ppm

TIME(MIN)

Fe ppmZn ppmCo gpl

Cu ppm

Figure 4.7 Cobalt elution profile using 5.6 gpl H2SO4 at 5BV/hr. at ambient temperature

Figure 4.7 show that the resin lewatit VP OC 1026 was rejecting Cobalt

significantly. Cobalt was being rejected very fast in the first 40 minutes. The elution

WILLIAM C. MIINGA Page lxx


was done for 60 minutes to recover all the cobalt that had been loaded on the

resin.

The Copper and Zinc in the resultant solution;

The Cobalt eluate coming out during 1st stage elution had a higher

concentration of cobalt as it should be. At this stage, the ideal situation was

to have less Zinc in the Cobalt eluate because this stream is recycled in the

plant.

Furthermore, Cobalt eluate coming out during the 1st stage elution process

had Zinc in the range 0.2ppm-1.44ppm. At this stage, the ideal situation

was to have low concentration of Zinc in the Cobalt eluate because this

stream is recycled in the plant.

C. 2nd ELUTION USING 110 gpl H2SO4

0 2 4 6 8 10 12 140

0.2

0.4

0.6

0.8

1

1.2

1.4

0

50

100

150

200

250

3rd cycle Elution-2

Fe ppm Co ppm Cu ppm Zn ppm

TIME(MIN)

Fe ppmCo ppmCu ppmZn ppm

Figure 4.8 Zinc elution profile using 110 gpl H2SO4 at 5BV/hr. at ambient temperature

Figure 4.8 shows how the loaded Cu, Fe, Co, and Zn on resin were coming out.


WILLIAM C. MIINGA Page lxxi


The Zinc eluate coming out from the column had Copper, zinc and iron in

the range of 02ppm to 146ppm, 01ppm to 60ppm and <0.1ppm to 2ppm





04ppm to 230ppm this is against 58ppm to 1.64 gpl in the cobalt elution.

This is a good recovery.

5.3.1. THIRD CYCLE SPLIT EFFICIENCY

1st ELUTION

Table 4.5 percentage split (3rd cycle) of Co, Cu, Zn and Fe in cobalt eluate using 5.6gpl H2SO4

Time(MIN)

Cumulative ,grams % in Co eluate


10 0.16440.0008

00.0001

40.000010

093.3

3.9

2.3 5.3

20 0.25220.0015

00.0002

40.000020

093.8

6.3

1.7 7.8

30 0.30820.0020

00.0003

00.000030

093.4

7.8

2.0 9.2

40 0.34640.0023

00.0003

60.000040

093.8

8.5

2.2

10.3

50 0.36250.0025

00.0004

00.000050

094.0

8.9

2.5

11.3

60 0.36830.0027

00.0004

40.000060

094.1

9.6

2.8

13.3

2nd ELUTIONTable 4.6 percentage split (3rd cycle) of Co, Cu, Zn and Fe in zinc eluate using 110gpl H2SO4

Time(MIN)

Cumulative ,grams % in Zn eluate


2 0.0060 0.0146 0.006000.0001

23.5

94.8

97.7

92.1

4 0.0118 0.0198 0.011300.0001

86.7

93.0

97.9

94.7

WILLIAM C. MIINGA Page lxxii


6 0.0168 0.0222 0.014100.0002

46.2

91.7

98.3

92.2

8 0.0217 0.0237 0.015100.0003

06.6

92.2

98.0

90.8

10 0.0227 0.0249 0.015600.0003

56.2

91.5

97.8

89.7

12 0.02310.0255

00.01565

50.0003

96.0

91.1

97.5

88.7

For the Copper, Zinc, iron and Cobalt that was loaded on the resin, an average of 8

% Cu and 2% Zn, 93% Co and 8 % Fe went to the Cobalt eluate, which is suitable

for recycle back into the plant, and 91.5 % Cu, 97.6 % Zn, 6.5 % Co and 92.5% Fe

went to the Zinc eluate. Here the efficiency was also very good. Compared to the

other two cycles the third cycle’s split was very good. This was as a result of

changes made to optimize the cobalt eluate. The changes made were as follows;

Reducing the concentration of the 1st stage eluant from 9.4gpl to 5.6gpl H2SO4

Increasing the concentration of the 2nd stage eluant from 93.9gpl to 110gpl

H2SO4

WILLIAM C. MIINGA Page lxxiii


Zn-SX plant

TM 2(Solid/liquid separation)

TM 3(Solid/liquid separation)

Cobalt recovery plant

O/F

U/FLarox (Gypsum)

Stripped liquor from Cu-SX plant

Feed (Tenke)


5.4. PROPOSED FLOWSHEET FOR Zn REMOVAL

TM= thickener number

O/F= thickener overflow

U/F= thickener underflow

TK= Tank

O/F

Zn≤ 10ppm

Resolution Stage

WILLIAM C. MIINGA Page lxxiv

Zn ≥100ppm

Zn ≤ 2ppm

Resolution Stage

Co eluate to TK10 clean up train

Zn eluate to Storage tank

Wash effluent to TK10clean up train

ISEP PLAN

Zn≤ 4ppm


Figure 4.9: Proposed flow sheet for the removal of Zn from TM2 overflow

CHAPTER SIX

CONCLUSIONS AND RECOMMENDATION

WILLIAM C. MIINGA Page lxxv


6.1. CONCLUSIONS

From the investigation conducted through laboratory test works conclusively show

that;

The optimum Cobalt loading was achieved at pH=2.5 and flowrate

7.5BV/hr. for 1800 minutes.

The optimum cobalt elution was achieved with 5.6 gpl sulphuric acid. Of the

total cobalt that was loaded in the resins from the process solution, 93% Co

was split from zinc, copper and iron in cobalt eluate and of the zinc, copper

and iron that were in the resins an average of 8% Cu, 2.4% Zn and 8% Fe

went in Cobalt eluate. For The zinc impurities that were loaded in resins

from the process solution an average of 97.6% zinc was split from cobalt in

the Zinc eluate using 110g/l sulphuric acid.

Based on the results obtained the resin lewatit VP OC 1026 can be used to

remove zinc impurities from the cobalt streams of chambishi metals

purification circuit by ion exchange efficiently and

The current purification circuit flow sheet (figure 2.1) can be replaced by the

proposed purification circuit flow sheet (figure 4.9).

6.2. RECOMMENDATIONS

After looking at the split efficiency of elution for the ALL cycle process it is

recommended

That the procedure should be tried on a plant scale since this project was

based on the lab scale.

That acidic water be used during rinsing of the resins instead of tap water.

This is because the Resin lewatit VP OC 1026 resins are pH sensitivity. The

pH of rinse water should not exceed pH=4 because the resins becomes

unstable when pH=4 is exceeded.

WILLIAM C. MIINGA Page lxxvi


7. APPENDICES

Table 6.1 Loading profile results in the first stage

Temperature: AmbientFeed pH: 3.3Flowrate: 10BV/hr=20 ml/minResin volume: 120 ml

TIME (MIN)

Co gpl Cu ppm

Zn ppm Mn ppm

Mg gpl Fe ppm

0 8.579 381 3.57 471 1.919 2300 8.162 283 3.36 332 1.935 ˂0.1600 7.81 185 < 0.1 29 1.973 ˂1900 7.573 146 0.65

221.914 ˂1

1200 7.584 129 2.43 321 2.057 ˂11500 8.383 157 3.49 472 1.837 ˂11800 8.554 171 3.5 4

91.862 ˂1

Table 6.1.2 Cobalt elution results 1st stage

Flow rate: 5BV/hr= 10 ml/minResin volume: 120 ml

TIME(MIN)

Co gpl Cu gpl Zn ppm

Mnppm

Mg ppm e p

m10 1.50 2.131 146 247 50 1.1720 0.042 0.037 5 13 34 0.6130 0.019 0.012 2 3 23 0.640 0.007 0.005 ˂ 0.1 ˂ 0.1 20 0.5950 0.003 0.003 ˂ 0.1 ˂ 0.1 16 0.5360 0.002 0.002 ˂ 0. ˂

0.1 40.41

WILLIAM C. MIINGA Page lxxvii


Table 6.1.3 Zinc elution profile results 1st stage

Flow rate: 5BV/hr. = 10 ml/minResin volume: 120 ml

TIME (MIN)

Co ppm

Cu ppm

Zn ppm

Fe ppm

Mn ppm

Mg ppm

2 60 9 40 171 16 424 33.5 9 22.8 150 16 306 7 8.5 5.6 114 3

08 4 8 2.4 85 1 810 3 7 1.1 83 1 812 2 6 0.8 0.5 1 8

Table 6.2.2 Cobalt elution results 2nd stage

Flow rate: 5BV/hr= 10 ml/minResin volume: 120 ml

TIME (MIN)

Co gpl

Cu ppm

Zn ppm

Mn ppm

Mg gpl Fe ppm

10 1.305 106 26 502 498 ˂0.120 0.599 28 24 60 172 ˂0.130 0.308 25 22 23 112 ˂0.140 0.145 23 20 10 115 ˂0.150 0.077 15 16 5 93 ˂0.160 0.056 10 9 3 88 ˂0.1



TIME (MIN)

Co gpl

Cu ppm

Zn ppm

Mn ppm

Mg gpl Fe ppm

2 70 13 12 7 40 35

WILLIAM C. MIINGA Page lxxviii


4 67 9 6 6 45 346 58 6 4.2 6 57 328 27 3 3.2 3 30 3010 12 1 1.88 1 18 ˂0.112 7 1 1.35 1 14 ˂0.1

Table 6.3 Loading profile results in the third stage

Temperature: AmbientFeed pH: 2.5Flow rate: 7.5BV/hr.=15 ml/minResin volume: 120 ml

TIME (MIN)

Co gpl

Cu ppm

Zn ppm

Mn ppm

Mg gpl

Fe ppm

0 8.563 381 3.57 471 1.919 2300 8.013 162 1.19 390 2.004 2600 8.202 164 0.85 393 2.044 1900 8.242 168 1.96 383 2.03 1

1200 8.378 172 2.81 372 1.981 11500 8.447 173 3.41 390 2.005 11800 8.588 182 3.48 377 2.007 1

Table 6.3.2 Cobalt elution profile results 3nd stage


TIME(MIN)

Co gpl Cu ppm

Zn ppm

Mn ppm

Mg ppm

Fe ppm

10 1.644 8 1.44 12 53 < 0.120 0.878 7 0.98 11 50 < 0.130 0.56 5 0.6 10 47 < 0.140 0.382 3 0.55 3 27 < 0.150 0.161 2 0.47 2 15 < 0.160 0.058 2 0.4 1 10 < 0.1



WILLIAM C. MIINGA Page lxxix


TIME(MIN)

Co ppm

Cu ppm

Zn ppm

Mn ppm

Mg ppm

Fe ppm

2 238 146 60 338 993 1.174 228 52 53 97 541 0.616 209 24 28 46 327 0.68 49 15 10 25 247 0.59

10 10 12 5 20 120 0.5312 4 6 0.55 10 83 0.41

REFERENCES

Benefied, L. B. (1982). Chemistry for water and wastewater treatment.

Dowex, R. (2011). Dowex resin for separation of nickel from liquid media.

Retrieved 03 04, 2011, from www.adobe.com/acroba.

Jeffers, T. J. (1985). In separation and recovery of cobalt from copper leach

solutions (pp. 47-50).

L. Rosato, B. H. (1984). separation of nickel from cobalt in sulphate medium by ion

exchange. In Hydrometallurgy (pp. 33-44).

Lanxess. (2011, 10 13). lewatit vp oc 1026/pdf. Retrieved 02 11, 2013, from

www.lennectech.com.

Levenspiel, O. (1972). In chemical reaction Engineering (p. 1365). new york: john

wiley and son, Inc.

R.Minango, A. J. (1993). process development in the cobalt purification circuit at

chambishi RLE cobalt plant of ZCCM, Zambia. In Extractive metallurgy of

copper, cobalt and nickel vol.1 (pp. 853-879).

resins, D. (n.d.). Dowex resin for separation of nickel from liquid media. Retrieved

03 04, 2011, from www.adobe.com/acroba.

WILLIAM C. MIINGA Page lxxx

ION EXCHANGE THESIS

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