17.10 - nigel grigg - silver concentrate leaching presentation 2012 final

7/27/2019 17.10 - NIGEL GRIGG - Silver Concentrate Leaching Presentation 2012 Final

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Use of Intensive Cyanidation to treatSilver Flotation Concentrates

Presenter: Nigel Grigg, General Manager, Gekko Systems SA

Nick Katsikaros, Product Improvement Manager, Gekko SystemsVictor Delgado, Manager, Metallurgical Processes, Hochschild Mining PLC

Tim Hughes, R & D Manager, Gekko Systems


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Intensive Cyanidation leaching is carried out at elevatedlevels of sodium cyanide levels ranging between 5,000 50,000 ppm, in rich oxygen environment >15 ppm dO

High Metal Volume Leaching Rates ConcentratedRecovery

Compare CIL and IC producing ~500oz/day

Medium grade CIL producing ~500 oz/day @ 150 t/h at 4 ppm Au; 45% solids; 24h leach; 5800m 3Volumetric leaching rate = 0.1 gAu/m 3 /hr IC treating BCC concentrate ~500 oz/day @ 2 t/day conc at 7500 ppm Au; 1.5m 3 active volume; 15 hleachVolumetric leaching rate = 700 gAu/m 3 /hr

IC is 7,000 times more space efficient than CIP.

What is Intensive Cyanidation


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What is the ILR?

ILR (Inline Leach Reactor) is Gekko Systems IC concentratetreatment system for gold and silver

Batch and continuous designs Suitable for high and low grade concentrates Based on a rolling drum system Fully automated


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2. The Continuous Flowsheet


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Partially Leached Gold Particle Showing Diffusion Layer Continuous removal of this layer significantly improves

leach kinetics The rolling action attritions this layer providing high shear

required for IC conditions

Mixing Drives IC Kinetics


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1)The high shear mixing zoneremoves the attrition layer fromthe gold speeding up cyanideaccess to the gold surface

2) Solution mixing zone Solutionis drawn out and oxygen is drawn

in.

3) Pure oxygen Zone ensuring highdissolved oxygen levels aresustained.

4) High surface area forsolution/oxygen interface

5) Solution solid mixing zone forfast kinetics and an efficientchemical reaction

ILR Cross Section

ILR Cross Section


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CASE STUDY - MINE BACKGROUND

HOCHSCHILD SELENE MINE Underground silver mine in Peru ~1,000 tonne/day plant (2006)

~13.5 tonne/day high grade Au concentrate Sold the flotation concentrate to smelters Started an Investigation into cheaper way to treat the

concentrates Contacted Gekko to look at a leach facility at the Ares plant


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ILR10000 Module Ares Site


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Site Specific - Modifications

Modifications - Fine Feed (


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ARES - ILR COMMISSIONING

CommissioningTake 1

Only peroxideavailable

Buildingincomplete

Temp slightlylower thanpreviouslyconsidered asambient!


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ARES - ILR COMMISSIONING

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Batch 1 Peroxide and Lead Nitrate

Au Recovery Ag Recovery d O2

Batch 1 Summary Lead Nitrate added twice

(6h and 24h) Effectively leaching was

completed in 18h DO at target after 10h Poor leaching

performance ? 60% recovery Panic? No not yet...


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ILR COMMISSIONING

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Au by solid Ag by solid sO2

Batch 2 Summary 82% Au Recovery 80% Ag Recovery Total leach time 57.5h Low DO until 16 hours Lower peroxide addition Suspected some form of

silver coating orcompound was forming


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ILR COMMISSIONING

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Batch 3 - Summary 15kg/t lead nitrate;

peroxide before cyanide A Pre-oxidation process? Solution assays gave erratic

results 71% Au Recovery 91% Ag Recovery Some promise!


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ILR COMMISSIONING

CommissioningTake 2

Installation 99%complete

Oxygen andperoxide available


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ILR Commissioning

Reground conc. in processwater

Constant peroxide add

Leach time +50 hours96% Au Recovery87.8% Ag Recovery

Fast initial leaching but

then slowed. Recoveries measured by

solids assay

Batch 4 - Summary

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Batch 4 - Process Water Regrind and Peroxide



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ILR Commissioning

Batch 5 - Summary 65 hours

97.1% Au Recovery92.6% Ag Recovery

Slow rates initially

limited by oxygen flow Final leach rate faster

than Batch 4 DO increases as oxygen

demand drops Leach time is +60 h Leaching incomplete

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Batch 5 - Process Water Regrind and Oxygen



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ILR Commissioning

Peroxide additionreduced to keep dObelow 10ppm.

Fast initial rates andimproved final rates. 48 hours


Getting closer.. .

Batch 6 - Summary

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Batch 6 - Barren Solution Regrind and ControlledPeroxide Addition



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ILR Commissioning

Peroxide until dO < 6ppm;with oxygen

48 hours


End of Gekko

commissioning on site Optimization...

Batch 7 - Summary

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Batch 7 - Barren Solution Regrind and CombinedOxidant



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ILR Commissioning

Hypothesis was that high peroxide concentration was creating aslow leaching silver phase or causing a passivation coating.

Reducing peroxide to keep dO below 6ppm improved recovery.

Oxygen generator eventually returned as at high altitude itwas inefficient and expensive. Oxygen was not required.

Operational optimisation of other steps, including clarificationreduced total cycle times.

Batch 8 onwards ...


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Conclusion

Hochschild now produce Silver dore from high grade flotationconcentrates at the Ares site.

Recoveries of + 98% for gold and silver using dO controlled

peroxide addition, achieved within the 48hrs Recoveries matched the testwork predictions. Able to produce dore or sell to the smelter dependant on

requirements.

5 more ILR5000 units purchased to increase production capacity


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Leach Kinetics Grind Sensitive

P80 = 212 um 12hrs - 96% recovery Combined gravity and

flotation concentrates


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PFD - Proposed

ILR18hrs Filtration Direct EWC Bleed to MC Detoxification Silver Dore


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Electrowinning Modelling?

Electrowinning modelling Very high current effeciencies are achieved at high silver

grades Direct electrowinning a cost effective recovery option


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Other Elements?

Other elements inleach into solution?

Need to consider a

zero discharge circuit

But locked cycle testshowed a drop in leachrecovery

Require Detoxification

of a bleed stream

Ag Silver 2677 Cu Copper 223

Al Aluminium


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Detoxification -Cyanide Oxidation

Natural Degredation Alkaline Chlorination Ozone CAROs Acid

H2O2 SO2/AIR

The last 2 options peroxide and INCO process arethe most common.


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Terminology Total, WAD, Free

Fe CNAu CN

Ni CN

Cu CNZn CNAg CN

CN-, HCN= CN F

CN WAD

CNTOT

stronglycomplexed

CNF = Free Cyanide CN WAD = Weak Acid DissociableCNTOT = Total Cyanide OCN - = Cyanate


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After H 2O2 Test work ?

Detox able to get WAD cyanide levels down well under

international discharge to a TSF standards (50ppmWAD) Detox also precipitated out other metals and so we were able

to maintain leach recoveries.

Feed CNwad Peroxide:CNwad Ratio Final Solution CNwad\

16.2 gpl 10:1 2.93 ppm

16.2 gpl 5:1 7.16 ppm

1.62 gpl 10:1 1.16 ppm

1.62 gpl 5:1 2.81 ppm


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ILR Models ILR45K for Silver Concentrates

ILR Models - increasing in size

6 x ILR5000 = 1 x Super ILR45K Design for High Volumes 56tpbatch Flotation concentrates 5tph @ 10hrs residence time


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ILR Models ILR45K for Silver Concentrates

Super ILR45K

Design for High Volumes

i.e. Flotation concentrates

56tpbatch @ 24hrsresidence time

5tph @ 10hrs residencetime


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Conclusion

Intensive Cyanidation of Silver Flotation concentratesis feasible

It offers many financial benefits to the company The ILR is a suitable IC unit Ensure locked cycle test work is performed and

modelling is performed with locked cycle testsolutions

Gekko are continuing to develop a range of technology and services to provide clients withsuitable options


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Questions

17.10 - nigel grigg - silver concentrate leaching presentation 2012 final

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