HEAP LEACHING TECHNOLOGY Moving the frontier for treatment Applications in Niger and Namibia Jacques THIRY Sergio BUSTOS Technical Direction AREVA MINES FRANCE IAEA, Vienna, June 2014 Titre présentation – Intervenant/réf. - 28 juin 2014 - p.1 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.2 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.3 THE HEAP LEACHING UNIT OPERATION Titre présentation – Intervenant/réf. - 28 juin 2014 - p.4 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.5 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 () D = (D + D + D ) / 3 Particle Size Distribution mean 16 50 84 C = D / D SOMAIR U 60 10 = 1 – App / S 120 100 MA Tamgak BUT, ….. 80 M3 Tamou 60 • 0re particles are not spheres !! M4 Arlette 40 Passing, w % w Passing, M1 Ariège F • And they are randomly packed 20 Typical 0 Model 1 10 100 1000 10000 1000001000000 Typical refers to PSD Particle size, µm encountered at copper heap leach operations Titre présentation – Intervenant/réf. - 28 juin 2014 - p.6 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: 3 3 v° [cm/sec] = K [( - *)/(s- *)] = g /µ [( - *)/(s - *)] • The difference ( – *) is the excess of liquid retained by the ore agglomerates referred to *, which is the liquid retained once the flow has been stopped (at the end of drainage). s is the liquid retention under flooded bed condition. • The intrinsic permeability M2 Tamgak / Permeability Factor P depends on ore PSD and on ore packing characteristics within the 0,1800 2,20 APP 0,1600 2,10 ore bed: 0,1400 2,00 2 ) 0,1200 6m 1,90 2 3 2 1,80 = ’ D [ / (1- ) ] 0,1000 P / (1- 1,70 3 0,0800 1,60 e^3/(1-e)^2 = • Somair typical values are: 0,0600 2m P 1,50 Ro App 0,0400 1,40 H=6m 0,0200 1,30 0,0000 1,20 K = 0.0125 cm/sec 0,00 0,10 0,20 0,30 0,40 0,50 0,60 v° = 3 L/hm2 Porosity Titre présentation – Intervenant/réf. - 28 juin 2014 - p.7 THE REACTION SYSTEM • Ore mineralogy and solution chemistry - 2- 4- UO3 + 2 HCO3 + CO3 = UO2(CO3)3 + H2O + 2- 4- UO3 + 2 H + 3 SO4 = UO2(SO4)3 + H2 +3 2- 4- +2 UO2 + 2 Fe + 3 SO4 = UO2(SO4)3 + 2 Fe • Impurity dissolution - - V2O5 + 2 OH = 2 VO3 + H20 2- 2- CaSO4 + CO3 = CaCO3 + SO4 + 3+ 2 FeO.OH + 6 H = 2 Fe + 4 H2O + 3+ Al2O3 + 6 H = 2 Al + 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 Agitation Specific flow rate L/hm2 5 9730 Volume application rate m3/td 0,011 12,7 Solid-liquid contact time h 900 0,79 Solution residence time h 389 4,8 Total leaching time h 2160 4 Titre présentation – Intervenant/réf. - 28 juin 2014 - p.8 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 Trekoppje / U Leaching Performance Trekoppje / U Leaching Performance 3 leach cycles, 9 m heap height 9 m heap height 100 100 80 80 60 60 U Dissolution % U Dissolution 4,5 L/hm2 40 U Dissolution 6 L/hm2 U Extraction % 40 20 % Dissolution, U 20 U Dissolution & U Extraction, % U Extraction, & Dissolution U 0 0,00 0,40 0,80 1,20 1,60 2,00 0 0,00 0,40 0,80 1,20 1,60 2,00 -20 L/S, m3/t L/S, m3/t Titre présentation – Intervenant/réf. - 28 juin 2014 - p.9 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 Titre présentation – Intervenant/réf. - 28 juin 2014 - p.10 TESTWORK PROGRAM DEMANDS Niger equipments for Somaïr and Imouraren Projects Titre présentation – Intervenant/réf. - 28 juin 2014 - p.11 INTEGRATION OF THE HEAP IN THE URANIUM RECOVERY PROCESS Titre présentation – Intervenant/réf. - 28 juin 2014 - p.12 ACID HEAP LEACHING PROCESS Similar to Copper heap leaching operations Anionic amine as SX organic extractant reagent Typical impurity release with final residue. Solution bleeding depending on acid consumption and gangue mineralogy Possible regeneration of oxidant Fe+3 by bacterial activity EV1 RLS Agglomerated Final LR Ore 1st Cycle Drain Residue H2SO4 OFF1 H2O H2SO4 DS RLS Pond PLS Pond Heap Leaching / U Extraction PLS BS Back-End / U Recovery SX- SDU pp bleeding CO2 SX- SDU ACE S pp UO4 UO4 pp R pp Solution Bleeding SDU pp R BS Pond H2O2 H2SO4 + H2O Na2CO3 + H2O NaOH UO4 Titre présentation – Intervenant/réf. - 28 juin 2014 - p.13 ALKALINE HEAP LEACHING PROCESS - 2- Need of ore washing to minimize [Cl ]PLS and [SO4 ]PLS Three leach cycles to increase [U]PLS and to reduce PLS flow to IX Need of residue rinsing to minimize reagent losses Water balance very much affected by elution efficiency H2O H2O EV1 EV2 EV3 ILS ILS RLS Agglomerated Final Ore WR 1R LR DR Wash 1st Cycle 2nd & 3rd Drain Rinse Residue OFF2 / OFF3 RS H2O recycle OFF1 ILS Ponds RO DS PLS Pond Heap Leaching / U Extraction RLS Pond Wash solution effluent PLS BS Na2CO3 / NaHCO3 Back-End / U Recovery IX-A SDU pp R SDU ACE IX-E pp UO4 UO4 pp R pp BS Pond NaOH H2O2 BC + H2O H2SO4 + H2O UO4 Titre présentation – Intervenant/réf. - 28 juin 2014 - p.14 FINAL REMARKS Titre présentation – Intervenant/réf. - 28 juin 2014 - p.15 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 Titre présentation – Intervenant/réf. - 28 juin 2014 - p.16.