sme presentation
TRANSCRIPT
HEAP LEACH RECOVERY STUDY BASED ON CRUSHED ORE PARTICLE SIZE DISTRIBUTION AND COMPACTION DEGREESangho Lee, Ph.D., PE Franz Campero, Ph.D., PE
2
d
Heap Leaching Process
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
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
5
Problems of current heap leaching process‐No analytical method available for risk ofcrushed 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)
6
Particle Segregation/Internal Erosion
7
Pore Space and Constriction Area
8
• 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
Effective GSD (y*) converted from weight base GSD (y)
range (0 < << 3) evaluated from
experimental work (Aberg,1992) (=1)
Actual CSD of particle medium
dyyx
dyyx
yyy
1
00 )(1
)(1)(*
10
Compaction influence on CSD
11
Max. particle size susceptible to piping depending upon compaction degree
12
Synthesis of SWCC from CSD of Heap Ores
Soil‐Water Characteristic Curve
13
Exemplary Heap Material
14
Segregation Susceptibility
15
Compatibility Check with Drain Rock
16
Hydrodynamic Parameter Evaluation
Unsaturated Flow Simulation within Heap Material
17
Hydrus 1‐D Simulation of Unsaturated Flow within Heap
18
Head Distribution within Heap (Eulerian Scheme)
19
Head Distribution within Heap (Lagrangian Scheme)
20
Flux Distribution within Heap
21
Smin.=66% Smin.= 83%
Saturation Degree within Heap
22
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)
23
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)
24
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)