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