HEAP LEACHING TECHNOLOGY Moving the frontier for · PDF fileTitre présentation – Intervenant/réf. - 28 juin 2014 - p.1 HEAP LEACHING TECHNOLOGY Moving the frontier for...

Titre présentation – Intervenant/réf. - 28 juin 2014 - p.1

HEAP LEACHING TECHNOLOGYMoving the frontier for treatment

Applications in Niger and Namibia

Jacques THIRYSergio BUSTOSTechnical DirectionAREVA MINES FRANCE

IAEA, Vienna, June 2014


HEAP LEACHING OF URANIUM ORES

• Interest on heap leaching of uranium ores motivated by expected increased participation of low grade ore treatment in future uranium production• Significant reduction in CAPEX and energy costs by avoiding grinding, agitation tank reactors and filters• Large experience and best practices transfer from conventional copper heap leaching operations• Recent advances in bio-leaching by using archea and other thermophile bacterial strains open opportunities for the treatment of black shale deposits• Actual operation at Somair and the Imouraren Project in Niger, together with Trekkopje Project in Namibia show AREVA’s confidence on this technology• Present extremely low uranium price situation (< 30 US$/lb U) has temporarily slowed and delayed further development and application of this technology• Learnings and experience from operational practice and from R&D activities should help in facing challenges associated to future market demands for safe, efficient and clean uranium production


CONTENTS

The heap leaching unit operation The heap reactor Agglomeration quality Solution flow through the ore bed The reaction system Leaching performance

Integration of the heap in the uranium recovery process The acid heap leaching process The alkaline heap leaching process

Final remarks


THE HEAP LEACHING UNIT OPERATION


THE HEAP REACTOR • Non confined auto-supported packed bed reactor• Non flodded bed solution flow pattern • Bed packing : agglomerated ore particles• Agglomeration is key to ensure:

• heap stability• ore bed permeability under non flooded bed liquid flow condition• enhanced initial reagent distribution all over heap height

Areva / M Ascani


THE AGGLOMERATION QUALITY • The amount of water and possible reagents required to produce a good agglomerate depends on particle size distribution (PSD), particularly on the amount of fines (<150µm)• The PSD is a characteristic response of the ore to blasting and crushing operations• The PSD of spheres can be characterized by the mean diameter Dmean and by the “Uniformity Coefficient” CU describing the spread or standard deviation • The PSD defines the apparent density (App) and therefore, the porosity ()

0

20

40

60

80

100

120

10 100 1000 10000 100000 1000000

Pass

ing,

w %

Particle size, µm

Particle Size DistributionSOMAIR

MA Tamgak

M3 Tamou

M4 Arlette

M1 Ariège F

Typical

Model 1 Typical refers to PSD encountered at copper heap leach operations

Dmean = (D16 + D50 + D84) / 3

CU = D60 / D10

= 1 – App / S

BUT, …..• 0re particles are not spheres !!• And they are randomly packed


SOLUTION FLOW THROUGH ORE BED• Non flooded bed gravity flow leading to the so called “Thin Layer (TL)Leaching” concept (Rauld et al, SME-AIME, Louisiana, March 1986)• Specific discharge flow v° and hydraulic conductivity K related by:

v° [cm/sec] = K [( - *)/(s- *)]3 = g /µ [( - *)/(s - *)]3

• The difference ( – *) is the excess of liquid retained by the oreagglomerates referred to *, which is the liquid retained once the flow hasbeen stopped (at the end of drainage). s is the liquid retention under floodedbed condition.

= ’ DP2 [3 / (1- )2]

• The intrinsic permeability depends on ore PSD and on orepacking characteristics within theore bed:

• Somair typical values are:H = 6 mK = 0.0125 cm/secv° = 3 L/hm2

1,201,301,401,501,601,701,801,902,002,102,20

0,00000,02000,04000,06000,08000,10000,12000,14000,16000,1800

0,00 0,10 0,20 0,30 0,40 0,50 0,60

P= 3

/ (1-)

2

Porosity

M2 Tamgak / Permeability Factor P

e^3/(1-e)^2

Ro App

6m

2m

APP


THE REACTION SYSTEM • Ore mineralogy and solution chemistry

UO3 + 2 HCO3- + CO3

2- = UO2(CO3)34- + H2O

UO3 + 2 H+ + 3 SO42- = UO2(SO4)3

4- + H2

UO2 + 2 Fe+3 + 3 SO42- = UO2(SO4)3

4- + 2 Fe+2

• Impurity dissolutionV2O5 + 2 OH- = 2 VO3

- + H20 CaSO4 + CO3

2- = CaCO3 + SO42-

2 FeO.OH + 6 H+ = 2 Fe3+ + 4 H2OAl2O3 + 6 H+ = 2 Al 3+ + 3 H2O

CaCO3 + 2 H+ = CaSO4 + CO2 + H2O

• Dissolution kinetics controlled by mass transport phenomena, but mainly by reagent supply to the ore solution reaction inter-phase

• Volume application rate is 3 orders of magnitude lower at heap leaching as compared to agitation leaching• Reagents concentration profiles along heap height

Operating condition Unit Heap AgitationSpecific flow rate L/hm2 5 9730Volume application rate m3/td 0,011 12,7Solid-liquid contact time h 900 0,79Solution residence time h 389 4,8Total leaching time h 2160 4


LEACHING PERFORMANCE • Need to distinguish between extraction and recovery• Multiple leach cycles lead to large and slow solution inventory changes• Increased heap height helps in improving [U]PLS, but compromises leaching time• Increased specific flow rate reduces time but also reduces [U]PLS

-20

0

20

40

60

80

100

0,00 0,40 0,80 1,20 1,60 2,00

U D

issol

utio

n &

U E

xtra

ctio

n, %

L/S, m3/t

Trekoppje / U Leaching Performance3 leach cycles, 9 m heap height

U Dissolution %

U Extraction %

0

20

40

60

80

100

0,00 0,40 0,80 1,20 1,60 2,00

U D

isso

lutio

n, %

L/S, m3/t

Trekoppje / U Leaching Performance9 m heap height

U Dissolution 4,5 L/hm2

U Dissolution 6 L/hm2


TESTWORK PROGRAM DEMANDS

Heap Leaching processes set up require many lab scale tests in columns and pilot tests Dedicated Equipments Large number of columns Time for tests CAPEX and OPEX for these

tests

Namibia equipments


TESTWORK PROGRAM DEMANDS

Niger equipments for Somaïr and Imouraren Projects


INTEGRATION OF THE HEAP IN THE URANIUM RECOVERY PROCESS


ACID HEAP LEACHING PROCESSSimilar to Copper heap leaching operationsAnionic amine as SX organic extractant reagentTypical impurity release with final residue. Solution bleeding depending on acid consumption and gangue mineralogyPossible regeneration of oxidant Fe+3 by bacterial activity

1st Cycle

EV1

Agglomerated Ore

OFF1

DS

PLS

PLS Pond

Drain LR

BS

Final Residue

H2SO4

Na2CO3 + H2ONaOH UO4

H2SO4 + H2OH2O2

SDU pp bleedingACE

BS Pond

UO4 pp R

SX-

SX-S

SDU pp UO4

pp

RLS Pond

RLS

Heap Leaching / U Extraction

Back-End / U Recovery

H2O

Solution Bleeding

H2SO4

CO2

SDU pp R


ALKALINE HEAP LEACHING PROCESSNeed of ore washing to minimize [Cl-]PLS and [SO4

2-]PLS

Three leach cycles to increase [U]PLS and to reduce PLS flow to IXNeed of residue rinsing to minimize reagent lossesWater balance very much affected by elution efficiency

1st Cycle

ILS

EV1

Agglomerated Ore 1R

OFF1

DS

PLS

PLS Pond

Drain LR DR2nd & 3rd

EV3EV2

BS

Rinse Final

Residue

ILS Ponds

RS

Na2CO3 / NaHCO3

H2O

ILS

BC + H2ONaOH

UO4H2SO4 + H2O

H2O2

SDU pp RACE

BS Pond

UO4 pp R

IX-A

IX-ESDU pp UO4

pp

RLS Pond

OFF2 / OFF3

RLS

Heap Leaching / U Extraction

Back-End / U Recovery

Wash

H2O

Wash solution ef f luent

WR

RO

H2O recycle


FINAL REMARKS


FINAL REMARKS

• Uranium is being successfully extracted from low grade ores by heap leaching operations• The response of the reaction system both at acid or alkaline leaching conditions is well know• Proper characterization of ore feed is required to anticipate agglomeration quality, heap permeability and stability, and uranium dissolution kinetics and final recovery• Many laboratory, bench scale tests and pilot plant demonstration at proper scale are necessary to provide suitable design parameters and to fit modeling efforts to actual results• Large space for optimization opportunities to reduce ore throughput, water and reagents consumption

• Proper effluent solution management and control as well as proper residue disposal are required for safe and clean operation

HEAP LEACHING TECHNOLOGY Moving the frontier for · PDF fileTitre présentation – Intervenant/réf. - 28 juin 2014 - p.1 HEAP LEACHING TECHNOLOGY Moving the frontier for...

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