Elution behaviour of metals from carbon SAIMM 2009 M Jeffrey R Pleysier K Bunney

CSIRO. Elution behaviour of metals from carbon Background National Pollution Inventory reporting (NPI) 93 reportable substances Objectives Help industry and government with environmental planning and management Provide communities with information on emissions Promote waste minimisation, cleaner production and efficiency Gold mines Identified as major emitter of Hg Not amalgamations but as ppm levels in cyanide leach liquors. 2

CSIRO. Elution behaviour of metals from carbon Project Objectives - general ID toxic trace elements in CIP streams Deportment Understand of the dissolution of toxic trace elements. (cyanide) Potential to avoid or sequester in benign form. Adsorption/elution characteristic Hg, Ni, Cu, Sr, Cd, As, Pb, Si, Se, Sb, Te, Cr, ……..(19) 3

CSIRO. Elution behaviour of metals from carbon Project Objectives - specific Hg speciation (  carbon) Mine site - Hg only partly elutes  EW and smelt  regen gases Manage Hg in one concentrated stream Elution Column – construct, description (better stripping of Hg) 4

CSIRO. Elution behaviour of metals from carbon Laboratory Elution Column 5

CSIRO. Elution behaviour of metals from carbon Laboratory Elution Column Pump Altex model 110A (PD piston type) 0.1 – 10 mL/min 0 – 25,000 kPa (4000 psi) 6

CSIRO. Elution behaviour of metals from carbon Laboratory Elution Column Pump Gauges (2) 0 – 1500 kPa (0-230 psi) 7

CSIRO. Elution behaviour of metals from carbon Laboratory Elution Column Pump Gauges PRV (2) 70 – 1500 kPa adjustable (10 – 225 psi) 8

CSIRO. Elution behaviour of metals from carbon Laboratory Elution Column Pump Gauges PRV Column ØID 25 x 600 mm SS swagelok fittings 100 g carbon capacity 150 mL void volume. Screens top and bottom (300μm) 9

CSIRO. Elution behaviour of metals from carbon Laboratory Elution Column Pump Gauges PRV Column Heating Electrical heating tape/insulated T/C (type k) PID controller (Eurotherm CE 375) Pre heater coil for eluant. 10

CSIRO. Elution behaviour of metals from carbon Laboratory Elution Column Pump Gauges PRV Column Heating Cooling SS coil in water bucket 11

CSIRO. Elution behaviour of metals from carbon Laboratory Elution Column Pump Gauges PRV Column Heating Outlet 3 way - to gauge - prv - needle control valve 12

CSIRO. Elution behaviour of metals from carbon Commissioning Samples Local mine site C1 (Au 909 g/tHg 187 g/t) C1 aw (Au 1140 g/tHg 229 g/t) C2 aw (Au 355 g/tHg 92 g/t ) Commissioning AARL (2% NaCN + 2% NaOH) 130 O C Pressure 200 kpa 30 min bake 20 BV DI 13

CSIRO. Elution behaviour of metals from carbon Commissioning -profiles Pressure 200 kpa gave poor flow control 700 kpa gave better flow and temp control Profile similar-not effected by pressure 14

CSIRO. Elution behaviour of metals from carbon Commissioning -profiles Pressure Profiles similar Hg eluted sl faster Recovery sl lower Earlier than gold Typical plant recovery 50-60% 15

CSIRO. Elution behaviour of metals from carbon Plant sample –Au profiles Samples 3 loaded carbon samples from local minesite Good profiles and good recoveries for gold Results similar to plant data. 16

CSIRO. Elution behaviour of metals from carbon Plant sample – Hg profiles Samples As previous Hg recovery only 57% Lower if not acid washed 41%. Mechanism of improvement yet to be determined. 17

CSIRO. Elution behaviour of metals from carbon Vary temp – Au profiles Effect of temp 130 o C = 93% Au 160 o C = 97% Au Higher temp Faster elution Higher [Au]s Higher recovery. 18

CSIRO. Elution behaviour of metals from carbon Vary temp – Hg profiles Effect of temp 130 o C = 57% Hg 160 o C = 40% Hg Higher temp = LESS mercury. Higher temp decomposes NaCN ? 19

CSIRO. Elution behaviour of metals from carbon Vary cyanide – Au profiles Effect of cyanide Increasing [NaCN] Increases rate Au Increases recovery 20

CSIRO. Elution behaviour of metals from carbon Vary cyanide – Hg profiles Effect of cyanide Increasing [NaCN] Increases rate Hg Increases recovery But still only 61% Potential to leave Hg on carbon 21

CSIRO. Elution behaviour of metals from carbon Zadra – Au profiles Zadra Maintains [CN] Slower rate Au * soak period added to determine impact on Hg elution * 22

CSIRO. Elution behaviour of metals from carbon Zadra – Hg profiles Zadra Maintains [CN] Similar rate Hg Improved recovery 76% Hg recovery 23

CSIRO. Elution behaviour of metals from carbon Zadra – Au at 110 o C Zadra Maintains [CN] Much slower rate Very poor recovery Temp important for Au 24

CSIRO. Elution behaviour of metals from carbon Zadra – Hg at 110 o C Zadra Maintains [CN] Rapid elution Recovery 87% 25

CSIRO. Elution behaviour of metals from carbon Data  Split elution GoldMercury high templow temp low [CN] high [CN] Mutually exclusive conditions  split elution? Zadra at 90 o C o C AARL 26

CSIRO. Elution behaviour of metals from carbon Split Conditions Zadra at 90 o C 2% NaOH 2% NaCN 1500 mL AARL at 130 o C 30 min soak DI elution 1000 mL 27

CSIRO. Elution behaviour of metals from carbon Split elution results Mercury 98% recovery in 10BV at 90 o C Eluate… high Hg, low Au Hg recovery via S ppt etc Gold 10-15% Au into Hg eluate Further refinements possible (lower temp further???) Gold recycle recovery? 28

CSIRO. Elution behaviour of metals from carbon Summary Recovery of Hg into one stream possible. (ie removal from carbon/regen circuit desirable  solution) Elute/separate Hg/Au with one set of elution conditions not possible, But split or sequential elutions works well Further optimisation/recovery possible 29

CSIRO. Elution behaviour of metals from carbon Further work / objectives ID other toxic trace elements in CIP streams Hg started, As, Se, Cd, Sb, Te, Pb, Cr, Ni, organics ??? Deportment What accumulate where? Potential to avoid or sequester in benign form. Adsorption/elution characteristic Effect of acid washing? Impact on silver In progress. 30

Contact Us Phone: or Web: Thank you Minerals Ron Pleysier Project Scientist Phone: Web:

CSIRO. Elution behaviour of metals from carbon Split elution - Ag Silver Elutes with Hg at low temp in CN Residual with gold

CSIRO. Elution behaviour of metals from carbon Split elution – reverse method Silver Partially elutes with Au at high temp low CN But needs CN to elute bulk Best conditions for silver elution 130 o C with 2%NaCN and NaOH

CSIRO. Elution behaviour of metals from carbon Hg Elutions - updates 10M HNO 3 will strip Hg from carbon on the bench overnight. NaCN strips (atmospheric) at 40, 60, 75, 90 o C 34