advances in gold process recovery from complex ores - mining magazine congress 2010

8/3/2019 Advances in Gold Process Recovery From Complex Ores - MINING MAGAZINE CONGRESS 2010

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> RESOURCE PROJECTS > TECHNOLOGY > INTEGRATED SERVICES

> Mineral Processing > Engineering Design > Specialist Services > Simulation & Optimisation > Project Management > Risk Management > Training

Presented by Dean Mitchell, Senior Metallurgist

Mineral Engineering Technical Services Pty Ltd © 2010

MINING MAGAZINE CONGRESS 2010

Advances in Gold Process Recovery From Complex Ores





Who We Are

Mineral Engineering Technical Services

> 22 years in Mineral Processing

> Global & Local Experience

> Consulting

> Studies

> Detailed Design

> Due Diligence, Ni, U, Pb-Zn, Au, Cu, Fe, Al

> Laboratory Testwork





Gold Can Be Free Milling & Refractory

Gold & Silver Ores





Complex & Refractory Gold Ores

> Ores which give poor recoveries when treated with conventionalmethods

> Complex sulphide ores

> Causes of refractory ores

– Fine gold in sulphides

– Insoluble gold compounds

– Coating on the gold

– Preg-robbing gangue minerals

– Cyanide and oxygen consumers

– Deleterious elements Cu, Sb, As etc








Mineralogy


http://slidepdf.com/reader/full/advances-in-gold-process-recovery-from-complex-ores-mining-magazine-congress 7/71> RESOURCE PROJECTS > TECHNOLOGY > INTEGRATED SERVICES> Mineral Processing > Engineering Design > Specialist Services > Simulation & Optimisation > Project Management > Risk Management > Training

Gold Can Be Difficult & Complex

> These are at ppm levels

> Free milling oxide ores straight forward

> MLA (Qemscan) may tell you if the gold is associated with saypyrite or arsenopyrite

> MLA will describe the minerals and liberation has a problem withlow levels of gold

> Concentration of the sample assists optical assessment. SEM.would be necessary to describe the gold in the mineral



QEMSCAN Or MLA & SEM



Samples

> Geometallurgy

> Drill core not RC chips

> Sample all ore >10%

> Include mine waste 10%?

> Geology- recognise ore domains

> Mineralogy

> Processing

> Economics

> Risk management

> Metallurgical mapping






> RESOURCE PROJECTS > TECHNOLOGY > INTEGRATED SERVICES> Mineral Processing > Engineering Design > Specialist Services > Simulation & Optimisation > Project Management > Risk Management > Training

Flowsheet Selection



Flowsheet Selection

> Free milling gold ores- oxide & sulphide- gravity recovery

> Transition ores

> Complex ores- cyanide, oxygen consuming or preg robbing

> Refractory- slightly or highly- roast, bacterial, POX, UFG

> Ore variability, nature of the gangue

> Comminution circuits

> Gravity

> Flotation

> Leaching

> Adsorption

> Stripping







Gravity Gold Recovery



Advantages Of Gravity

> Faster cash flow

> Higher overall recovery

> Lower unit cost

> Reduced CIP feed grade

> Improved leach kinetics

> Reduced carbon loading

> Reduced locked-up gold incircuit

> Reduced cyanideconsumption

> Environmentally-friendly

> The late Andre Laplante used the term-”recovery effort”



Shaking Table Mechanics

> Minerals are subjected to two forces

> Table motion:

– Moves the particles across the table

> Fluid flow :

– Moves the particles down the table

– Effect depends upon the size and density of the particles

> The net result is particles move diagonally across the deck

> But also fan out along the table

F E E D

W a s h W a t e r

Riffles

VIBRATION

Middlings

Dense

Material

Light

Material



Gravity Gold Equipment

> Knelson Concentrator-CD,MD,XD models

― First concentrator 50 “g” to 200 “g”

― Spinning bowl, VG package

― Requires fluidising water

― Batch or semi batch

― Riffled cone, motor, perforated bowl

> BCC-Batch centrifugal concentrators-yields 0.05%

> CGR-Continuous gravity concentrators-10% -20% yield

> Falcon Concentrator-C,SB,UF models

― C-300 “g”, UF 650 “g”

― Spinning bowl

― SB most common

― Cyclone feed application

> Revolutionised fine gold recovery




Piloting Gravity Circuits

> Rare for Greenfields projects

> Very costly and difficult to justify

> More common for Brownfieldsprojects




CAPEX

> Gravity concentrator circuit

― Approximately AU$1 million based on a 1.2 Mtpa gold project

― For larger plants the cost is higher

> Intensive leaching

― Between approximately AU$600,000 to AU$900,000

> The economic justification current cut point for most projects is20% gravity gold recovery




OPEX

> Centifugal concentrators have operating costs between $0.08to $0.12 per tonne of new feed

> Costs include:

― Power

― Water

― Spares

― Maintenance




Process Risks & Problems

> Testwork not based on representative samples

― Mt McClure

― Resolute, Southern Cross ― Bronzewing, Granites

> Presence of galena and tramp iron for tabling

> Poor planning and/or execution of the testwork

> Poor interpretation of the results

> Insufficient bleed of re-circulating load

> Incompatible feed

― Too coarse

― Too dense

― Too many flakes




Trends With Gravity Gold

> Transition from batch to continuous operation

> Gradual replacement of inefficient equipment

> Increased capacities all machines

> Increased mass recovery from <1% to >10%

> Recovering gold as a by-product

> Use of intensive leaching to process concentrates




Examples Of Installations

> IPJ’s at Ballarat Goldfields ― >300 installed worldwide

> IPJs at Pirquitas mineArgentina

> Kelsey Jigs, Barrick Granny

Smith, WA ― 2 by J1800 jigs

IPJs at Ballarat Goldfields

KnelsonXD70 at Paracuta, Brazil

Gekko IPJ Pirquitas mine, Argentina




Examples Of Installations (cont)

> Falcons-Sadiola, Mali ― 2 by SB 5200-6.9 &14.8 increase

recovery on oxide and sulphideore

> Falcons-Telfer, WA ― 8 by SB5200

> Falcons-Kansanshi Copper,Zambia ― 4 by SB5200

> Falcons-Sekisovskoye,

Kazakhstan ― 1 by C2000

― Overall increase 5% recovery




Example Installations

> Knelson XD70 at Paracutamine Brazil

> Knelson- Kinross, Alaska ― 1 by XD 70

― 1 by CS6000 Acacia reactor

> Knelson-Vasgok, Kazakhstan ― 2 by XD70







Intensive Leaching




Flowsheet Acacia Reactor




In Line Leach Reactor




Developments

> Automation

> Continuous ILR

> Modular Supply







Cyanide Leaching




Cyanide Leaching

Sodium cyanide: - used for leaching gold and silver from their ores:

222222)(2242 O H NaOH CN Au NaO H O NaCN Au

Preg Robbing- kerosene passivation

Lead Nitrate, Oxygen Sparging to maximise kinetics

O S i




Oxygen Sparging

I Mill f Fi G i di Fi G ld




IsaMill for Fine Grinding Fine Gold

C id S l bl C & Ni k l




Cyanide Soluble Copper & Nickel

pH-Potential Diagram for the copper-cyanide-water system

-2.0

-1.0

0.0

1.0

2.0

0.0 4.0 8.0 12.0 16.0

pH

E h

[Cu] = 10-4 M

[CN] = 10

-3

M

Cu

CuO

Cu2+

Cu2O

Cu(CN)32-

Cu2O

Cu(CN)2-

CuO22-

Oth Ad




Other Advances

> CIL not CIP

> Silver ores

> Complex sulphides

> Kemix screens

> Pump cells

> Cyanide DETOX

B t i L hi




Bacteria Leaching

> Common bacteria Thiooxidans Ferrooxidans

> Bioleaching performed on:-

― Gold/Copper

― Zinc

― Uranium

― Nickel

― Cobalt

> Bioleaching oxidises the metal and dissolves it into the solution

B T h / Mi t k




BacTech / Mintek

> This involves bio-leaching ofsecondary sulphides with

mesophiles at 36-40ºC, andmoderate and extremethermophiles for chalcopyrite at45-40ºC and 70ºC respectively

> Ultra-fine grinding assists greatlywith the process

> The process usually occurs in aslightly acidic environment

> The BacTech process has beenapplied to a 500 kg/day plant inMexico

POX Gold Sulphide Concentrates




POX Gold Sulphide Concentrates

> Chemistry ok, fast kinetics,recovery 96%+

> Stable waste products-arsenates

> Materials of construction

problematic

> Operability- difficult

> History- poor

>

Future- very promising

Albion




Albion

> Developed byMIM (nowXSTRATA)

> Requires ISAMILLfine grinding

> Atmospheric

leachconditions- nopressure- 70C

> High recoveries+95%

> Pilot plantBrisbane

Intec Gold Process




Intec Gold Process

> Leach withoutCyanide?







Resin Adsorption

Ion Exchange




Ion Exchange



Penjom Gold Project







Stripping Or Elution

Elution – AARL Zadra




Elution – AARL, Zadra

> Elution is a reverse process to

adsorption

> Gold can be stripped off bydisruption of thermodynamicequilibrium between gold insolution and gold on the carbon

> Equilibrium Disruptive features:- – High temperatures

– Lack of cations (Ca2+ , Mg2+, etc)

– High anion concentration (CN-, OH-)



IPS




IPS

> Advantages

― Water quality is not a limitation

― Higher temperatures• Faster

• More efficient than pressure Zadra

― The same capital cost but lower operating cost over time

― A reduced need for reactivation

― A safer operation as no cyanide is used







Electrowinning

Electrochemical Series




Electrochemical Series



EMEW Cell




EMEW Cell

> Cell efficiency drops with solution tenor

> Pre concentration would make these applicable

> Could be used for ILR pregnant solution

> Resin EMEW combination would have

significant advantages

EMEW Results - Ag Solutions




EMEW Results Ag Solutions







New Uses of Old Technology

Cost/Revenue




/

> Silver price US$16.61/ounce

> Gold price US$1093/ounce (26th March 2010)

> The refining charge is US$ 0.64/oz for both gold and silver.

> Once Ag:Au ratio >10:1 Merrill Crowe preferable

> Silver ores >50 g/t Ag, Merrill Crowe preferable

> Elution of silver not cost effective - $800-$1000/tonne to stripcarbon

Leaching Characteristics




g

> Mineralogy dependent (Ag, Ag2S, etc)

> High cyanide

> High DO

> Long leach times

> Chemical reaction:

( ) ( ) ( ) ( ) ( ) ( )aqaq22g2aqsNaOH4+CNNaAu4→OH2+O+NaCN8+Au4

( ) ( ) ( ) ( ) ( ) ( )aqaq22g2aqs NaOH4+CNNaAg4→OH2+O+NaCN8+Ag4

Leach Kinetics




Relative Kinetics Difference Silver Minerals




Lead Nitrate Potential Benefits




> Lead nitrate addition is a function of the mineralogical compositionof the ore:

― Removal of sulphide ions from solution by precipitation as lead sulphide,thus:

• Minimising the possibility of sulphide film formation on gold and silver surface

• The formation of thiocyanates in the subsequent of cyanidation stage

― Improved passivation of reactive mineral surfaces due to the depositionof insoluble lead hydroxide precipitate

― Disruption of films or coatings on the gold or silver surface prior tocyanidation

OH CNS O H OCN S 222 22

2

2

2)(2 OH PbOH Pb

Adsorption Character




> Fleming k lower

> More stages

> Higher carbon inventory

> Load capacity Au +Ag

1

0.0030

10

100

1000

10000

100000

1030.30.03

Gold in Solution mg/l

Equilibrium Actual CIP

G o l d

o n C a r b o n

g / t

EQUILIBRIUM RELATIONSHIPGold on Carbon Vs. Gold in Solution

Stripping Character




> Lower temperature for optimum silver

> Silver complex less stable formmetallic silver

> Silver comes off first

> Longer stripping times

Electrowon Silver Profile




Process Plants




> Waihi NZ-high silver CIP plant

> Mt Muro-mixed CIP and Merrill Crowe

> Toka Tindung-CIP plant

> Kelian-CIP plant

> Misima-CIP plant

> Medusa-CIP plant

> Casposo-Merrill Crowe plant

Merril Crowe-Unit Operations




> Cyanide leaching

> CCD solid liquid separation

> Clarification of pregnant solution

> De aeration of clarified solution

> Precipitation using zinc and Pb(NO3)2

> Filtration of precipitate, aciding

> Smelting of precious metals

Merrill Crowe Limitations




> Water balance

> Effective settling rates and clear overflows.

> Clarified liquor required - <1 ppm solids

> De aeration of solutions - <1 ppm O2

> pH, CN concentration, DO, scale formation

> Solution bleed (build up of zinc)

> Reactive sulphides

> Cementation - 0.33 g Zn/g Au

Water Quality & Mass Balances




> Gravity circuits use large volumes of water and usually theyrequire good quality water

> Reverse Osmosis

> Vacuum Distillation

Conclusions




> Mineralogy is critical - variable

> Low ratio Ag/Au ores best treated using CIP/CIL

> When ratio >10:1 Merrill Crowe is superior

> Merrill Crowe is more capital intensive and water balance issues

are a constraint

> Gravity processes not as efficient for silver ores

> Leaching silver ores requires higher cyanide, higher oxygen and

longer leach times, resulting in lower silver recoveries

> Silver increases the carbon inventory, reducing k values

Gravity Circuit Conclusions




> Mineralogy drives theprocess

> Sample selection,representivity

> GRG prediction

> Qemscan-Nugget effect

> Centrifugal concentratorsare revolution

> Water balance issues

> Cyclone feed rather thanunderflow

> Gold price record

> Advantages of gravityrecovery

> Equipment selection

> Sizing equipment

> CAPEX, OPEX

> Process risks, problems

> Examples

Conclusions




> Silver strips first at a lower temperature during elution

> Electrowinning times are lengthened because of silver

> RIP may offer advantages in the future

> EMEW cell or in combination with a smaller Merrill Crowe is likelyin the future



THANK YOUDownload this presentation at

www.mets.net.au

advances in gold process recovery from complex ores - mining magazine congress 2010

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