Hydrometallurgy MINE 292 Introduction to Mineral Processing Lecture 21 John A Meech.

Hydrometallurgy

MINE 292 Introduction to Mineral Processing

Lecture 21

John A Meech

Hydrometallurgical Processing

1. Comminution (Grinding)2. Leaching Metal (Quantity - %Recovery)3. Removal of Metal from Pulp a. Solid/Liquid Separation - CCD thickeners - Staged-washing filtration b. Adsorption (Carbon-in-Pulp and/or Resin-in-Pulp)

(CIP/RIP or CIL/RIL) - granular carbon or coarse resin beads

Hydrometallurgical Processing

4. Purification (Quality - g/L and removing other ions) - Clarification and Deaeration (vacuum) - Precipitation

(Gold: Zn or Al dust) (Copper: H2S or scrap Fe or lime)

(Uranium: yellow cake) (Zinc: lime)

- Solvent Extraction (adsorption into organic liquid) - Ion Exchange (resin elution columns) - Elution (contact carbon or resin with an electrolyte)

Hydrometallurgical Processing

5. Electrowinning or Precipitation followed by Smelting

Hydrometallurgical Processing

Hydrometallurgical Processing

Classifier

Hydrometallurgical ProcessingFeed Grade = 5 g Au/t Ore%Recovery during Grinding = 60% >>> solids content = 2.00 g/t%Recovery during Leaching = 35% >>> solids content = 0.25 g/t%Recovery during CCD = 0%%Recovery Total = 95%Underflow Densities = 50%solidsLeach Density = 40% solidsClassifier O/F Density = 40%solidsPregnant Solution Flowrate = 300%Barren Bleed Flowrate = 25%Gold in Barren Solution = 0.05 g/tCalculate the gold content of the Pregnant Solution and the U/F water from each thickener. What is the actual mill recovery? What difference would occur if fresh solution was added to Thickener E rather than Thickener B?

Metal Recovery by Dissolution

• Primary extraction from ores• Used with ores that can't be treated physically

• Secondary extraction from concentrates• Used with ores that can be beneficiated to a

low-grade level

• Applied to– Copper (both acid and alkali)

CuO + H2SO4 → CuSO4 + H2O

Cu+2 + 4NH4OH → Cu(NH3)4+2 + 4H2O

– Zinc (acid)ZnO + H2SO4 → ZnSO4 + H2O

– Nickel (acid and alkali) – Nickel Laterite OresNiO + H2SO4 → NiSO4 + H2O

NiO + 6NH4OH → Ni(NH3)62+ + H2O

Metal Recovery by Dissolution

Ammonia Leaching of Malachite

NH4Cl → NH4+ + Cl– (1)

NH4+ + H2O → H3O+ + NH3 (2)

CuCO3·Cu(OH)2 + 2H3O+ → Cu2+ + CO2 + 3H2O + Cu(OH)2 (3)

Cu(OH)2 + 2H3O+ → Cu2+ + 2H2O (4)

Overall Leaching ReactionCuCO3·Cu(OH)2 + 4 NH4Cl → 2Cu2+ + 4Cl– + CO2 +3H2O +4NH3 (5)

Formation of complex amine ions Cu2+ + 2NH3 → Cu(NH3)2

2+ (6)

Cu(NH3)22+ + 2NH3 → Cu(NH3)4

2+ (7)

Zinc Roasting/Leaching/Electowinning

Nickel Lateritic Ores

• acid heap leaching method similar to copper• H2SO4 much higher than for copper (1,000 kg/t)• patented by BHP Billiton• being commercialized by

– Cerro Matoso S.A. in Columbia – Vale in Brazil– European Nickel Plc in Turkey, Balkans, Philippines

Metal Recovery by Dissolution

• Applied to– Aluminum (alkali)

Al2O3 + 3H2O + 2NaOH → 2NaAl(OH)4

– Gold and Silver (cyanidation / alkali)

– Uranium (acid and alkali)

Alumina Leaching

Aluminum Smelting

• Fused Salt Electrolysis – Hall-Herault Process

Aluminum Smelting

• Fused Salt Electrolysis – Hall-Herault Process

Uranium Acid Leaching

• Oxidize tetravalent uranium ion (U4+) to hexa-valent uranyl ion (UO2

2+) using MnO2 or NaClO4

• About 5 kg/t of MnO2 or 1.5 kg/t of NaClO4

• UO22+ reacts with H2SO4 to form a uranyl sulfate

complex anion, [UO2(SO4)3]4-.

Leaching Processes

• Tank Leaching (Agitation)• Vat Leaching• Pressure Leaching (high temperature/pressure)• Biological Leaching (Bacteria)• Heap Leaching• In-situ Leaching (solution mining)

Lixiviants

• Lixiviant is a liquid medium used to selectively extract a desired metal from a bulk material. It must achieve rapid and complete leaching.

• The metal is recovered from the pregnant (or loaded) solution after leaching. The lixiviant in a solution may be acidic or basic in nature.

- H2SO4 - NH4OH

- HCl - NH4Cl or NH4CO3

- HNO3 - NaOH/KOH

- HCN >> NaCN/KCN

Tank versus Vat Leaching

• Tank leaching is differentiated from vat leaching as follows:

Tank Leaching– Fine grind (almost full liberation)– Pulp flows from one tank to the next

Vat Leaching– Coarse material placed in a stationary vessel– No agitation except for fluid movement

Tank versus Vat Leaching

• Tanks are generally equipped with– agitators, – baffles, – gas nozzles,

• Pachuca tanks do not use agitators• Tank equipment maintains solids in suspension

and speeds-up leaching• Tank leaching continuous / Vat leaching batch

Tank versus Vat Leaching

• Some novel vat leach processes are semi-continuous with the lixiviant being pumped through beds of solids in different stages

• Retention (or residence) time for vat leaching is much longer than tank leaching to achieve the same recovery level

Important Efficiency Factors

Retention time = total volume of tanks / slurry volumetric flow

- normally measured in hours- gold: 24 to 72 hours- copper: 12 to 36 hours- sequence of tanks called a leach "train"- mineralization & feed grade changes may need higher retention times

Important Efficiency Factors

Particle Size

- material ground to size to expose desired mineral to the leaching agent (“liberation”),

tank leach >>> size must be suspendable by an agitationvat leach >>> size must be most economically viable

- high recovery achieved as liberation increases or kinetics faster is balanced against increased cost of processing the material. Pulp density - percent solids determines retention time - determines settling rate and viscosity - viscosity controls gas mass transfer and leaching rate

Important Efficiency Factors

Pulp density

- percent solids determines retention time

- determines settling rate and viscosity

- viscosity controls gas mass transfer and leaching rate

Important Efficiency Factors

Numbers of tanks

- Tank leach circuits typically designed with 4 tanks

Dissolved gases

- Gas is injected below the agitator or into the vat bottom to achieve the desired dissolved gas levels

- Typically, oxygen or air, or, in some base metal plants, SO2 is used.

Important Efficiency Factors

Reagents

- Adding/maintaining appropriate lixiviant level is critical- Insufficient reagents reduces metal recovery- Excess reagents increases operating costs and may lead

to lower recovery due to dissolution of other metals

- recycling spent (barren) solution reduces need for fresh reagents, but deleterious compounds may build-up leading to reduced kinetics

Pressure Leaching

• Sulfide Leaching more complex than Oxide Leaching • Refractory nature of sulfide ores • Presence of competing metal reactions • Pressurized vessels (autoclaves) are used• For example, metallurgical recovery of zinc:

2ZnS + O2 + 2H2SO4 → 2ZnSO4 + 2H2O + 2S

• Reaction proceeds at temperatures above B.P. of water (100 °C) • This creates water vapor under pressure inside the vessel. • Oxygen is injected under pressure• Total pressure in the autoclave over 0.6 MPa.

Sulfide Heap Leaching

• Ni recovery much more complex than Cu• Requires stages to remove Fe and Mg• Process produces residue and precipitates from

recovery plant (iron oxides/Mg-Ca sulfates)• Final product – Ni(OH)2 precipitates (NHP) or

mixed metal hydroxide precipitates (MHP) that are smelted conventionally

Bio-Leaching

• Thiobacillus ferrooxidans used to control ratio of ferric to ferrous ions in solution (Tf acts as a catalyst)

4Fe2+(aq) + O2(g) + 4H3O+ → 4Fe3+(aq) + 4H2O

• Ferric sulfate used to leach sulfide copper ores

• Basic process is acceleration of ARD

• Typical plant leach times for refractory gold ore is about 24 hours

Bio-Leaching

Bio-Leaching at Snow Lake, Manitoba

• BacTech to use bio-leaching to deal with As and recover gold from an arsenic-bearing waste dump

• Two products– Chemically-stable ferric arsenate precipitate– Gold-rich Residue Concentrate

• 110 tpd of concentrate for 10 years• Annual production = 10,400 oz plus some Ag• CAPEX = $21,400,000 OPEX = $973/oz• Gold Recovery after toll-smelting = 88.6%

SX - Solvent Extraction

• Pregnant (or loaded) leach solution is emulsified with a stripped organic liquid and then separated

• Metal is exchanged from pregnant solution to organic• Resulting streams are loaded organic and raffinate

(spent solution)• Loaded organic is emulsified with a spent electrolyte

and then separated• Metal is exchanged from the organic to the

electrolyte• Resulting streams are stripped organic and rich

electrolyte

Solvent Extraction Mixer/Settler

Reason for 4 Stages of SX

Solvent Extraction and Heap Leaching

Ion Exchange Resins• AMn = synthetic ion-exchange resin

(class A - 0.6–1.6 mm)

• Phenyl tri-methyl ammonium functional groups

• Macro-porous void structure

• Similar to strong base anion exchange resins – Zeolite MPF (GB)– Amberlite IRA (USA) – Levatite MP-500 (FRG)– Deion PA (JPN)

Resin-In-Pulp Pachuca Tank

Resin-In-Pulp Pachuca Tanks

Resin-In-Pulp Pachuca Tanks

Kinetics of RIP for Uranium

Effect of pH on RIP for Uranium

RIP Recovery in each stage

In-situ Leaching•  In 2011, 45% of world uranium production was by ISL • Over 80% of uranium mining in the US and Kazakhstan

• In US, ISL is seen to be most cost effective and environmentally acceptable method of mining

• Some ISLs add H2O2 as oxidant with H2SO4 as lixiviant

• US ISL mines use an alkali leach due to presence of significant quantities of gypsum and limestone

• Even a few percent of carbonate minerals means that alkali leach must be used although recovery does suffer

In-situ Leaching

Average grades of sandstone-hosted deposits range between 0.05% to 0.40% U3O8.

In-situ Leaching

In-situ Leaching

In-situ Leaching• Acid consumption varies depending on operating philosophy

and geological conditions

• In Australia, it is only a fraction of that used in Kazakhstan

• In Kazakh , about 40 kg acid per kg U (ranging from 20-80)

• Beverley mine in Australia in 2007 was 7.7 kg/kg U.

• Power consumption is about 19 kWh/kg U (16 kWh/kg U3O8) in Australia and around 33 kWh/kg U in Kazakhstan

www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Mining-of-Uranium/In-Situ-Leach-Mining-of-Uranium/#.UUihT1fQhLo

In-situ Leaching – well patterns

EMF Chart