Remediation options to reduce acid drainage from historical mining operations at Mount Lyell, western Tasmania
Supervising Scientist Report 108
Supervising Scientist, 1996
ISBN 0 642 24307 7
- SSR108 - Remediation options to reduce acid drainage from historical mining operations at Mount Lyell, western Tasmania (PDF 5.5 MB)
- Title and publishing information (PDF - 469 KB)
- Chapters 1-4 (PDF - 1.3 MB)
- Chapters 5-6 and References (PDF - 3.8 MB)
The former Mount Lyell Mining and Railway Company Limited (MLMRCL) lease is large and the problems associated with the mine drainage, waste rock dumps and river tailings are typical of a number of old mine sites in Australia and internationally. The magnitude of the acid drainage (AD) loads from the lease are comparable with the major acid drainage producing mines in the United States, Canada and Great Britain. By far the greatest loads are from the Haulage Creek catchment which receives the surface discharge of the mine dewatering, adit drainage from old workings and drainage from major waste rock dumps. This catchment contributes 99.3% of the total copper loads to the Queen River and 98.7% of the lease. Approximately 2.5 tonnes of copper per day is released into the Queen River from the Queen River catchment.
The remediation of the Mount Lyell lease to totally eliminate on-going acid drainage and release of copper from the site is an unrealistic objective, but it is feasible to put in place strategies that will result in a progressive reduction in the contaminant load from the site.
Previous works by the Mount Lyell Mining and Railway Company Limited (MLMRCL) and the Hydro Electric Commission (HEC) have had some effect on loads in the Linda and Comstock catchments draining to Lake Burbury and the recently recommenced mining operations by Copper Mines of Tasmania (CMT) will result in a progressive reduction in copper loads to the Queen River system due to partial treatment of waters draining from the lease. However, it is regarded as unacceptable by the Sustainable Development Advisory Council (SDAC) that the balance of the waters are left untreated and SDAC acknowledges that this is a government and community responsibility (SDAC 1995).
A review of acid drainage remediation technology has revealed that to meet water quality objectives for downstream rivers and Macquarie Harbour, the only feasible means of reducing the acid mine drainage loads is by a conventional neutralisation water treatment plant. This will require substantial capital investment and ongoing operating costs.
A pilot test of a Solvent Extraction/Electrowinning (SX/EW) plant design carried out in 1993 by the former Mount Lyell Mining and Railway Company Limited as a condition of its Licence to Operate, has shown that high grade copper can be won from the drainage from the Haulage Creek catchment. Further feasibility studies by CMT have indicated that a modern SX/EW plant could be constructed to recover copper from the high concentration streams in the Haulage Creek catchment. Financial analyses indicate that the plant with traditional neutralisation treatment of the effluent (raffinate) to remove acidity and other metals would be viable and is commercially attractive and financially robust. It therefore appears feasible to construct and operate the plant to recover copper from the major concentrated copper sources and treat the raffinate effluent as a commercial venture.
It is estimated that with the SX/EW plant and raffinate treatment of the major Haulage Creek loads, the acidity and copper loads to the Queen River could be reduced by up to approximately 95%, depending on the effectiveness of collection of ad loads and water management. Aluminium, zinc and iron loads would be reduced by similar amounts, with manganese and sulphate less affected.
The SX/EW plant could operate as long as the effluent streams coming from the dumps and the underground workings have significant metal loads and could be independent of mining operations. It could therefore represent a long-term solution to the remediation of the site.
The use of SX/EW technology in this application would be a world first and of worldwide interest and application.
The balance of the lease site has acid drainages with much lower loads and flows and other options have been identified which could remediate these sources. These include the reduction in loads by flooding and covering AD sources, the passive treatment of adit drainages by successive alkalinity producing systems, and alkalinity addition to receiving waters by anoxic limestone drains and limestone addition.
Trials are recommended for these technologies which will have worldwide application if proven successful.
It is estimated that with the remediation measures identified, the AD loads from the lease site to both the Lake Burbury and Queen River catchments can be reduced by approximately 95%, such that water quality objectives can be met downstream.
The ongoing operations of CMT have resulted in a marked improvement in the environment of the lease site and provided the impetus for ongoing remediation works. It is important that any ongoing site remediation works and future mining activities should consider the long-term planning for mine closure and site rehabilitation, otherwise at some time in the future the Tasmanian Government may again be facing an expensive solution to an ongoing long-term environmental problem.