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
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.2
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
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.3
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
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.4
THE HEAP LEACHING UNIT OPERATION
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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
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.6
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
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.7
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
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.8
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
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.9
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
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.10
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
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TESTWORK PROGRAM DEMANDS
Niger equipments for Somaïr and Imouraren Projects
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.12
INTEGRATION OF THE HEAP IN THE URANIUM RECOVERY PROCESS
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.13
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
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.14
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
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.15
FINAL REMARKS
Titre présentation – Intervenant/réf. - 28 juin 2014 - p.16
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