1. HEAP LEACH RECOVERY STUDY
BASED ON CRUSHED ORE
PARTICLE SIZE DISTRIBUTION
AND COMPACTION DEGREE
Sangho Lee, Ph.D., PE
Franz Campero, Ph.D., PE

2. 2
 d
Heap Leaching Process

3. 3
 Kinetics of Leaching Process – convective
mass transfer (rapid preferential flows) vs.
diffusive mass transfer (slow uniform flows)
 Effective wetting surface – increased in finer
ores vs. limited in coarse ores
 Permeability – larger in coarse ores and
smaller in finer ores
 Chemical degradation of agglomerated ores
at the lower level due to significant pressure
and acidic or caustic environment
Basic Principles and Findings

4. 4
 Design key points for heap leaching success
‐Fine migration control of heap piles to
prevent generation of bench seepage or
pooling above base drainage layer
‐Enhance efficiency of leaching recovery in
view of contact area and retention time
between lixiviant and crushed ores
‐Find cost effective solution replacing
agglomeration to prevent fine migration
within heap material
Introduction

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 Problems of current heap leaching process
‐No analytical method available for risk of
crushed ore segregation/internal erosion
‐No quality control program on compaction
degree monitoring while heap pile stacking
‐No prescreening process or feasibility
study with particle size analysis of crushed
ores prior to costly agglomeration
Introduction (continued)

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Particle Segregation/Internal Erosion

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Pore Space and Constriction Area

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• Actual contact
probability between
different particle sizes
• Volume based GSD
‐exaggerated for
coarse particle
contact (=0)
• Number based GSD
‐exaggerated for fine
particle contact (=3)
Grain Size Distribution (GSD)
vs. Constriction Size (CSD)
Relationship btw. GSD and CSD

9. 9
 Effective GSD (y*)
converted from
weight base GSD (y)
  range (0 <  << 3)
  evaluated from
experimental work
(Aberg,1992) (=1)
Actual CSD of particle medium
dy
yx
dy
yx
yy
y

1
00 )(
1
)(
1
)(* 

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Compaction influence on CSD

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Max. particle size susceptible to piping
depending upon compaction degree

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 Synthesis of SWCC from CSD of Heap Ores
Soil‐Water Characteristic Curve

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Exemplary Heap Material

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Segregation Susceptibility

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Compatibility Check with Drain Rock

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 Hydrodynamic Parameter Evaluation
Unsaturated Flow Simulation within
Heap Material

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Hydrus 1‐D Simulation
of Unsaturated Flow within Heap

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Head Distribution within Heap
(Eulerian Scheme)

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Head Distribution within Heap
(Lagrangian Scheme)

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Flux Distribution within Heap

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Smin.=66% Smin.= 83%
Saturation Degree within Heap

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 Poorly graded or well graded ores (classified
with conventional uniformity and curvature
indices) do not fully represent the
piping/segregation susceptibility of heap pile
 Fine migration susceptibility (piping potential)
within heap pile can be successfully evaluated
with GSD and compaction degree of crushed
ores
Conclusion (I)

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 Hydraulic conductivity of heap material is
governed by initial moisture content, fine
content, compaction/consolidation degree
and grain size distribution of crushed ore
 Preferential flow pattern not preventable
due to nature of non‐uniform ore properties
but generation of low conductivity zone can
be reduced with fine migration control and
installation of PVD
Conclusion (II)

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 Hydrodynamic parameters for unsaturated
flow analysis can be reasonably estimated
not from series of column tests but from
synthesis of SWCC based on GSD and
compaction degree measurements of the
crushed ore.
 To support the practicality of using
synthesized SWCC, a follow‐up study is
required to compare the synthesis results
with the actual field/lab monitoring data.
Conclusion (III)