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Soluble Metal Recovery Improvement Using High Density Thickeners in a

CCD Circuit

Ruashi II a Case Study

February 2009M. Mulligan (Presenter)

L. Bradford

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Agenda

Introduction Thickener technologies Lab Simulations CCD Simulations High Density vs High Rate Thickeners

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Introduction

Ruashi is a Copper/Cobalt mine in the DRC Circuit overview: Leach-CCD-SX-EW Copper recovery is critical in the CCD circuit Lab & CCD simulations to optimise recovery Selection and design of the best thickener

technology

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Thickener Development

Conventional

High Rate – flocc + dilution

High density – flocc + dilution + compression

Paste – flocc + dilution + compression + residence time

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Different Thickener Technologies

Wt % Solids

Yie

ld S

tres

s, P

a

Filter Cake

Paste Thickener

High DensityThickener

Conventional

High RateThickener

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Counter Current Decantation (CCD)

Ruashi II CCD CircuitFLSmidth Minerals

High Density ThickenersFlocculant

Leach Residue

High Grade PLS

Low Grade PLS

Wash Liquor

Leach Residue

CCD1

CCD5

CCD4

CCD3

CCD2

Interstage Mix

Interstage Mix

Interstage Mix

Interstage Mix

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Lab Simulation

s

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Lab Simulations

Sedimentation testwork done within hours of the leach done at Mintek

Settling & flocculant flux curves 4 litre batch tests 4 litre continuous tests Rheology

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Optimal % Solids for Settling

Optimum = 7% – 8%

Ruashi Post Leach Slurry

Optimum Solids Flux

0

500

1000

1500

2000

2500

3000

3500

0.0% 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% 14.0%

% Solids (m/m)

Se

ttlin

g F

lux

(k

g/h

/m2 )

10.0 g/t MF 1011 15.0 g/t MF 1011 20.0 g/t MF 101125.0 g/t MF 1011 30.0 g/t MF 1011 40.0 g/t MF 101150.0 g/t MF 1011 60.0 g/t MF 1011 70.0 g/t MF 1011

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Optimal Flocculant Dosage

Optimum = 50g/t

Ruashi Post Leach Slurry

Optimum Flocculant Dosage

0.0

10.0

20.0

30.0

40.0

50.0

60.0

5.0 15.0 25.0 35.0 45.0 55.0 65.0 75.0

Flocculant Dosage (g/t)

Se

ttlin

g R

ate

(m

/h)

4.0% 5.5% 7.0% 8.5% 10.0% 11.5% 13.0%

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Underflow % Solids vs Time

Batch: 55% Continuous: 59%

Ruashi Post Leach Sample Deep Tube Test Retention Time vs Solids Concentration

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0

Elapsed Time, hr

Slu

rry S

olid

s C

on

cen

trati

on

, w

t%

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Rheology

Haake Viscometer Measure yield stress

of thickener u/flow Info used to size rake

drive

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Rheology

Ruashi Rheology

0

50

100

150

200

250

300

50.00 52.00 54.00 56.00 58.00 60.00 62.00 64.00

% Solids (m/m)

Yie

ld S

tres

s (P

a)

60 Pa at 59% Solids

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CCD Simulation

s

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CCD Simulations

Variables used in base case simulation

Wash Ratio

U/F Suspended Solids

Concentration (wt%)

Feed Suspended Solids

Concentration (wt%)

Soluble Cu Recovery

(%)

1.6 55 30 +99

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CCD Wash Recovery

C.C.D. THICKENERS CALCULATIONS

96.0

97.0

98.0

99.0

100.0

2 Stages 3 Stages 4 Stages 5 Stages 6 Stages 7 Stages

No. of Stages

Eff

icie

ncy

98% 99% 100%

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Sensitivity to Wash Ratio

SENSITIVITY TO WASH RATIO

80.0

82.0

84.0

86.0

88.0

90.0

92.0

94.0

96.0

98.0

100.0

No. of Stages

Eff

icie

ncy

@ 2.1 WR

@ 1.6 WR

@ 1.1 WR

@ 2.1 WR 93.52 97.48 98.95 99.55 99.80 99.91

@ 1.6 WR 91.21 95.74 97.76 98.78 99.31 99.59

@ 1.1 WR 87.37 92.15 94.61 96.08 97.02 97.65

2 Stages 3 Stages 4 Stages 5 Stages 6 Stages 7 Stages

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Sensitivity to Underflow % Solids

SENSITIVITY TO U/FLOW SOLIDS

96.00

97.00

98.00

99.00

100.00

No. of Stages

Eff

icie

ncy

@ u/f. Sol. (59%)

@ u/f. Sol (55%).

@ u/f. Sol. (51%)

@ u/f. Sol. (59%) 93.40 97.20 98.72 99.39 99.70 99.85

@ u/f. Sol (55%). 91.21 95.74 97.76 98.78 99.31 99.59

@ u/f. Sol. (51%) 88.40 93.65 96.21 97.63 98.46 98.96

2 Stages 3 Stages 4 Stages 5 Stages 6 Stages 7 Stages

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Counter Current Decantation (CCD)

Ruashi II CCD CircuitFLSmidth Minerals

High Density ThickenersFlocculant

Leach Residue

High Grade PLS

Low Grade PLS

Wash Liquor

Leach Residue

CCD1

CCD5

CCD4

CCD3

CCD2

Interstage Mix

Interstage Mix

Interstage Mix

Interstage Mix

U/f % Solids: 59%

Wash Ratio: 1.6

RECOVERY: > 99%

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High Density

vs High Rate

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High Density vs High Rate Thickeners

CCD wash recovery HD always has higher wash recovery per

stage for a given wash ratio

Capital cost implications Per thickener cost is similar – HD diameter

smaller Overall CCD plant costs less with HD – less

stages required

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Increase in Income

Copper Produced (tons/day)Thickener Type High Rate High DensityRecovery (%) 98.78% 99.39%Copper Produced (tons/day) 128.41 129.21Production Days (Days)Copper Produced (tons/year) 44,945 45,222Copper Price ($/ton)Income per Annum ($/year) 242,901,639 244,401,639

Increase per Annum ($/year)

350

5,404

Copper Recovery for 45,000tpa Plant

1,500,000

130.00

Based on 5 stages. Wash ratio = 1.6

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Thickener Design Differences

Higher tank sidewall depth Steeper tank floor slope Higher rake mechanism torque Rake mechanism – Pickets Thickener discharge cylinder

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Conclusions

Lab simulations & CCD simulations are important for decision making and design of a CCD plant

5 High Density thickeners give a better recovery than 6 High Rate thickeners for Ruashi

Capex and Opex costs both lower with High Density thickeners at Ruashi

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Questions ???