From Soilvision Systems
Jack A Caldwell
August 2007
Pad Description
The basic components of Heap Leach Pads are described by Hutchinson and Ellison (1992)[1]. A recent review of the state of practice of Heap Leach Pad layouts is that by Thiel and Smith (2003)[2]. An excellent powerpoint presentation is that by J.F. Lupo of Golder Associates. Wikipedia has a brief overview. See also the many papers in the InfoMine library.
Consultants
I suspect that any reasonable consulting group
servicing the mining industry will tell you they have and can design a heap
leach pad. All that is needed is the
ability to prepare a grading plan, select a liner, specify drains, and
establish the slope stability of a heap, write a plausible closure plan, and
leave it to the metallurgists and chemist to work out the right solutions to
apply when. Maybe, but as always past
success is the best indicator of future performance. So here are a few consultants whose heap leach
experience is documented in their websites.
If I omit your company, be assured this is my oversight, not conscious
decision—for I have sought to include all companies I am aware of.
Arcadis is a big company; it is hard to establish their heap leach credentials,
but this link provides an interesting case history.
Golder
Associates provides a comprehensive suite of services related to heap leach pad
design, construction, operation, and closure.
Kappes, Cassiday & Associates in
Knight Piesold has undertaken extensive
research, testing and analysis on the deformation and collapse capacities of
drain pipes, liner systems and their compatibilities with foundation and
overliner materials as well as with hydraulic and geo
Leach, Inc. will design and supervise laboratory and field test programs to evaluate the heap leaching of copper and gold ores. They have an extensive library of publications that are available on request.
LinRae Consulting Services,
Inc offers to undertake design and construction support of heap leach
facilities from their
O’Kane Consultants have done the work and have written about it. I much admire their innovative
approaches.
W. Joseph Schlitt is a consulting
metallurgist-hydrometallurgist. He
writes the best papers I have read—see the list of publications on his website
and the proceedings of the 2006 SME Conference.
Here is a quote from his website: W. Joseph Schlitt has 40
years of worldwide hydrometallurgical experience. His experience includes
engineering, process assessments, research and development, and plant-oriented
studies in the nonferrous industry. Primary emphasis is in hydrometallurgy
and chemical processing, particularly copper heap, dump, bio-, and in situ
leaching, plus metal value recovery. Additional experience covers other
leaching and recovery systems including molybdenum, zinc, vanadium, uranium,
nickel and precious metals.
SRK has the specialists, including for example William Gibson in
Sinclair Knight Merz is a leading water and environmental consulting company that has
applied their skills to heap leach pad water management.
Smith Williams Consultants has over 42 years of domestic and
international heap leach pad experience, including permitting, geotechnical
site investigation, surface water diversion design, water balance, pad and pond
design, and pad closure. They have been involved in design and construction of
over 60 heap leach pads, totaling over 300 million square feet (approximately
27.8 million square meters) of leach pad area.
Water Management Consultants describes their proprietary Heap
Leach Dynamic Technology as being able to “improve leaching efficiency, increase recovery and lower costs.”
Vector Engineering and Mark Smith is the original heap leach pad
consultant in my mind. They dominate the
South American market for the design, construction oversight, operation, and
closure of big heap leach pads. Mark
Smith et al have written most of the definitive
Construction & Operation
General
Operation of the HLP is done in accordance with industry-, company-, and site-specific procedures. Generally this involves compliance with formal and/or informal Standard Operating Procedures, Health and Safety Plans, Emergency Response Plans, permits, and relevant and applicable laws and regulations.
Ore
Suppliers of systems to apply solution to the HLP are listed in the Infomine supplier’s catalogue.
Solution Application Systems
Suppliers of systems to apply solution to the HLP are listed in the Infomine supplier’s catalogue. For example, see Ore Max and Black-Line International.
Contract Mining
Your heap leach pad can be managed by contract. Contact the Washington Group International for example. AMES lists four projects where they have been involved in heap leach pad construction.
Envirocon have closed out heap leach pads in Nevada.
Performance Evaluation
Software
Computer codes to simulate and model the performance of leach pads abound—any code that calculates a factor of safety against instability will work on a heap leach pad problem, and the same is true for most aspects of heap leach pad performance.
Jensen and Taylor compare some codes. Here are others:
SOILVISION SYSTEMS sells SVFlux to analyze unsaturated flow in a pad—when coupled with ChemFlux you can study the effect of the input chemistry on the output chemistry.
METSIM has a heap leach model that is part of their comprehensive suite of computer codes to address complex chemical, metallurgical, and environmental processes. The heap leach module performs mass balances around the heap leach process including chemical reactions, precipitation and evaporation, solids and water inventories, heap drainage and control logic. The model is non-steady state and generates time dependent plots.
Leach, Inc. has a software package to scale up and simulate a heap leaching operation based on engineering and kinetic fundamentals of the leaching process. Using results from a column leach test or a commercial heap operation LEACH will allow you to quickly predict heap performance under different operating conditions such as particle size distributions, heap heights, solution flow rates and solution chemistry.
Stability – Static
Industry standard methods and/or computer programs may be used to evaluate the factor of safety of the slopes of Heap Leach Pads. Key to the use of any of these programs is the geometry of the Heap Leach Pad, the strength of the ore as placed in the pad, and the angle of friction between the liner beneath the pad and the materials placed directly above the liner.
Stability – Seismic
The response of a Heap Leach Pad to an earthquake depends on the magnitude of the event, the properties of the materials in the pad, and the liner interface strength. Potential responses include:
· Sliding of the ore over the liners.
· Mass deformation of the slopes of the pad.
Methods used in the landfill industry to evaluate the seismic response of landfills may be used to quantify the potential for liner sliding and mass deformation – see Kavazanjian and Matasovic.
Erosion
Control of erosion during operation of the HLP is generally best effected by appropriate surface contouring as part of the placement of the ore on the HLP, by limiting runon, and by directing runoff to sediment control dams and basins. See the TechnoMine review on this topic.
Performance Monitoring
HeritageGeophysics.com describe installation of an electronic leak detection system under a heap leach pad to monitor the liner performance. See a similar program by Terraplus.