leachability characteristics of agglomeration on … characteristics of agglomeration on...

Leachability characteristics of agglomeration on copper-cobalt ore

exposed to acid leaching environments

Kimberly Finke Morrison, PE, RGMorrison Geotechnical Solutions, Inc.

Tailings & Mine Waste ‘16

Keystone, Colorado

October 2-5, 2016

Summary

Background

Agglomeration

Hydraulic Testing:

Column Leach Testing

Compression-Percolation Testing

Consolidation-Permeability Testing

Conclusions

Background

Katangan Copper Belt

Rich copper (~4%TCu) mineralization with cobalt (~0.5%TCo)

• Oxide and sulphidemineralization

• Open pit and underground mining

• Milling of high grade ore

Considering heap leaching of low grade ore (1-2.5%TCu / 0.5-1%TCo)

Heap Leaching - General

Practiced since the mid-sixteenth century in Hungary

Low capital and operating costs make it an attractive option

Site Heap Leaching Experience

Test pad performance:• Evaluate potential for

development of a permanent leach pad

• Ore generally >4.75mm delivered to pad

• Estimated Cu recovery 70%, with lesser Co recovery

Crusher Fines (<4.75mm) contain economic mineralization

Crush + Screen + Deliver

Could Crusher Fines be heap leached?

Coarse Crushed Ore

Crusher Fines

0 0 5

19

13

10

75 5

8

30

25 19 9.5 4.76 2 0.85 0.43 0.25 0.15 0.075 -0.075

Frac

tio

n R

eta

ine

d (%

)

Particle Size (mm)

Gravel Fines Sand

Materials tested:

• Crushed Leached Ore (from test pads)

• Coarse Ore (non-leached)

• Crusher Fines

Tests performed:

• Index testing

• Agglomeration amenability

• Column leach testing

• Ore geotechnical testing

Ore Testing Program

Geotechnical testing of Crushed Leached Ore performed prior to evaluating use of Crusher Fines for heap leaching

Agglomeration

Agglomeration

Non-agglomerated ore Agglomerated ore

“Agglomerates” crushed ore fines into either uniform larger particles, or onto coarse-grained particles within the crushed ore matrix

May improve efficiency of leach by increasing ore permeability

Allows pre-mixing of solution with ore fines

Agglomeration - History

Mid-1970s US Bureau of Mines research:

• Evaluate agglomeration procedures for cyanide leach pads

• Crushed ore (<1”) agglomerated with Portland cement and water or cyanide solution

• Cured for 8 hrs (min.)

• Technology adopted with first commercial agglomeration heap operation in 1980

Agglomerating Agents

Common agglomerating agents: • Portland cement, lime, fly ash, polymers,

leach (i.e., raffinate) solution

Works by:• Acting as a cement (i.e., add strength)

- OR -

• Exchange Na+ cations in the clay particles of the ore with Ca2+ cations from the binder (improve workability and permeability)

Most agglomerating agents require neutral or alkaline pH

Agglomerating Agents Used

Sulfuric acid leach process used to recovery Cu

Agglomerating agents tested:

• Sulfuric acid solution (i.e., raffinate)

• Anionic (-) polymer (HAF-52)

Laboratory-Scale Agglomeration

Agglomerates produced in a cement mixer (baffles removed)

Mixer rotates at 24 rpm with D=45.7 cm

Critical speed of 38%

Typical agglomerating drums operate at 20 to 50% of critical speed

Test No.

Ratio(Coarse:Fines)

Coarse Fraction

(wt. %)

Fines Fraction

(wt. %)

Agglomerating Agent

AT-1 -- 0 100

Sulfuric acid only

AT-2 -- 30 70

AT-3 -- 50 50

AT-4 -- 70 30

AT-5 -- 85 15

AT-6 5:1 83 17

Mix of sulfuric acid and polymer

AT-7 4:1 80 20

AT-8 3:1 75 25

AT-9 2:1 67 33

AT-10 1:1 50 50

AT-11 1:2 33 67

Tested Ore Blends

Generating Agglomerates

Generating Agglomerates

Agglomerate Summary

Sulfuric Acid Addition:• 17% (by wt) concentration

• Target 15 to 20 kg/t

Polymer Addition:• Polymer emulsion to target

0.6kg/t

Preliminary Results:• 19-38mm agglomerates

• >%Fines = >Agglomerating agent to produce agglomerates

• Agglomerate moisture contents 13-15% (by wt)

Agglomerates evaluated using dry and wet test methods

Agglomerate Evaluation- Dry Test Method -

Drop Test:

• Samples air dried

• Drop agglomerates on steel plate from 1.8m height

Visual inspection of agglomerate breakdown

Agglomerates with less fines appeared to be slightly stronger

Agglomerate Evaluation- Wet Test Method #1 -

Submerge agglomerates in water for 30 min on No. 10 screen

Measure wt% retained on screen

Soak Test:

Agglomerate Evaluation- Wet Test Method #2 -

Place agglomerates on a No. 10 screen

Dip into tub of water 10x

Measure wt% retained on screen

Wash Test:

Test No.

Ratio(Coarse:Fines)

Soak Test(wt. % Lost)

Wash Test(wt. % Lost)

Agglomerating Agent

AT-1 0:1 33.0 12.1

Sulfuric acid only

AT-2 3:7 24.7 3.1

AT-3 1:1 26.6 11.3

AT-4 7:3 24.1 3.8

AT-5 17:3 33.8 5.1

AT-6 5:1 22.0 5.2

Mix of sulfuric acid and polymer

AT-7 4:1 26.7 4.1

AT-8 3:1 21.2 3.6

AT-9 2:1 21.2 3.4

AT-10 1:1 26.0 4.2

AT-11 1:2 25.7 3.5

Agglomerate Evaluation- Wet Evaluation Results -

Ore blends with 25 to 33% Crusher Fines could produce stable agglomerates (3:1 and 2:1 Ratios, Coarse:Fines)

Agglomeration Results

Hydraulic Testing

Hydraulic Testing

To simulate varying hydraulic conditions within the heap:

Column Leach Test

Compression-Percolation

Consolidation-Permeability

Column Leach TestingTest Set-Up

Four (4) column tests:

• Standard Plexiglas columns (D=20cm; H=2m)

• 3:1 and 2:1 (Coarse:Fines) blends

• Agglomerated w/ and w/o polymer binder

• Cured 3 days prior to testing

• Application rate=11.6 L/hr/m2

• Leach cycle = 100 days

Significant previous data (test pads and column leach tests) with non-agglomerated coarse ore

Column Leach TestingResults

Cu Recovery: 67 to 73%Co Recovery: 37 to 46%

Column Leach TestingResults

Coarser feed material (Columns #1 & #2) produced slightly improved Cu and Co extractions

Addition of polymer binder did not have an adverse effect on metal recoveries

Columns not run to exhaustion

Recoveries compared well to reported recoveries from non-agglomerated ore placed on test pads

Ore Geotechnical TestingSamples Tested

Geotechnical testing of agglomerated vs. non-agglomerated post-leach ore material:• Leached Coarse Ore (Non-plastic)• Column #1 and #2 samples (LL=26-27; PI=6-7)

Ore Geotechnical TestingCompression-Percolation Test

Unsaturated ore hydraulic conductivity:

• Tested at proposed solution application rate

• Pass/Fail Test

• Sensitive to ore size

• Incremental increase to applied load

• Failing tests exhibit ponding at surface

• Monitor settlement and percolation (e.g., collapsible ores)

Ore Geotechnical TestingCompression-Percolation Test

Solution application rate of 10 L/hr/m2 (Design)

Applied loads equivalent to 10, 20 and 30m ore heights

Leached Coarse Ore ponded solution at 550 kPa(achieved 18% of design)

Percolation rate exceeded design for Agglomerated Ore (“pulsing” noted)

10m20m

30m

Reaction Frame

Steel Vessel

Hydraulic Ram

Perforated Loading Plate

Introduce leach solution

Effluent

Perforated Bearing Plate

Porous Plates

Ore

Ore Geotechnical TestingConsolidation-Permeability Test

Saturated ore hydraulic conductivity:

• Represents the maximum solution application rate for the ore

• Allows the designer to assess whether the ore heap is likely to become saturated under future loading conditions

Ore Geotechnical TestingConsolidation-Permeability Test

Applied loads equivalent to 10, 20 and 30m ore heights

Minor decrease in saturated permeability under load:

• Leached Coarse Ore:

o k= 3.0E-2 to 2.1E-2 cm/s

o n=0.35 to 0.33

• Agglomerated Ore:

o k=7.8E-2 to 7.3E-2 cm/s

o n=0.32 to 0.30

10m20m 30m

Conclusions

Heap leaching is an attractive option for processing of low grade ores, but may be impacted by poor ore permeability

Agglomeration, commonly employed to increase permeability and percolation characteristics, may pose challenging in acid leaching environments

Agglomeration using an anionic polymer + sulfuric acid proved beneficial for the Cu/Co ore tested:• Allowed mixing of Crusher Fines at ratio of 3:1 (Coarse:Fines)

• Improved the permeability and percolation characteristics of the ore over non-agglomerated ore (coarse only)

• Able to achieve similar Cu/Co recoveries to non-agglomerated ore

Conclusions

Questions

Kimberly MorrisonMorrison Geotechnical Solutions, Inc.Lakewood, CO 80228www.morrisongeo.comkimberly@morrisongeo.com