In-Situ Leach (ISL) Uranium Mining Method Far From ‘Benign’
By Dr. Gavin Mudd
Hydrogeologist / Environmental Engineer, Monash University
The mining technique of in situ leaching (ISL), often referred to as solution mining, is becoming an increasingly favoured method for the extraction of uranium across the world. This is primarily due to its low capital and operating costs compared to conventional mining. Little is known about the environmental impact of this method, and mining companies have been able to exploit this to promote the method as “environmentally benign”.
The ISL process involves drilling groundwater bores or wells into a uranium deposit, injecting corrosive chemicals to dissolve the uranium within the ore zone, then pumping back the uranium-laden solution.
The method should only be applied to uranium deposits located within a groundwater system or confined aquifer, commonly in palaeochannel deposits (old buried river beds).
Although ISL is presented in simplified diagrams by the nuclear industry, the reality is that geological systems are inherently complex and not easily predictable.
There are a range of options for the chemistry of the mining solutions. Either acidic or alkaline chemical agents can be used in conjunction with an oxidising agent to dissolve the uranium.
Typical oxidising agents include oxygen or hydrogen peroxide, while alkaline agents include ammonia or sodium-bicarbonate or carbon dioxide. The most common acidic chemical used is sulphuric acid, although nitric acid has been tried at select sites and in laboratory tests.
The chemicals can have serious environmental impacts and cause long-term and potentially irreversible changes to groundwater quality.
The use of acidic solutions mobilises high levels of heavy metals, such as cadmium, strontium, lead and chromium. Alkaline solutions tend to mobilise only a few heavy metals such as selenium and molybdenum. The ability to restore the groundwater to its pre-mining quality is, arguably, easier at sites that have used alkaline solution chemistry.
A review of the available literature on ISL mines across the world can easily counter the myths promulgated about ISL uranium mining. Whether one examines the USA, Germany, Russia and former annexed states, Bulgaria, the Czech Republic, Australia or new ISL projects across Asia, the truth remains the same – the ISL technique merely treats groundwater as a sacrifice zone and the problem remains “out of sight, out of mind”.
ISL uranium mining is not controllable, is inherently unsafe and is unlikely to meet “strict environmental controls”. It is not an environmentally benign method of uranium mining.
The use of sulphuric acid solutions at ISL mines across Eastern Europe, as well as a callous disregard for sensible environmental management, has led to many seriously contaminated sites.
Perhaps the most severe example is Straz pod Ralskem in the Czech Republic, where up to 200 billion litres of groundwater is contaminated. Restoration of the site is expected to take several decades or even centuries. For the USA, solution escapes outside of the ‘controlled mining zone’ and difficult restorations have been documented at ISL sites in Texas and Wyoming – including both acid and alkaline leach sites. Australia has encountered these same difficulties, especially at the controversial Honeymoon deposit in South Australia during pilot studies in the early 1980s and at Manyingee in Western Australia until 1985.
The Honeymoon pilot project used sulphuric acid in conjunction with ferric sulphate as the oxidising agent. The wells and aquifer experienced significant blockages due to the minerals jarosite and gypsum precipitating, lowering the efficiency of the leaching process and leading to increased excursions. The aquifers in the vicinity of Honeymoon are known to be connected to aquifers used by local pastoralists to water stock.
For Australia, water of any quality is precious – and particularly so when the only secure supply of water in a region is from groundwater. With the rise of water treatment technologies such as desalination, water of any quality is a valuable resource – environmentally as well as for possible community and industry use. An acid leach-type ISL project, especially as approved for Beverley and Honeymoon without remediation of polluted groundwater, therefore imposes a major environmental risk and pollution burden on future users of groundwater in these regions. ISL mining is therefore far from sustainable.
Journal articles, conferences papers etc. by Dr. Mudd: http://users.monash.edu.au/~gmudd/
ENVIRONMENTAL POLLUTION – ROUTINE CONTAMINATION OF GROUNDWATER
This summary is drawn from the Friends of the Earth, Australia submission to the Beverley Four Mile uranium mine application, March 2009.
In-situ leach (ISL) uranium mining involves pumping an acid solution (or an alkaline solution in some cases) into an aquifer. This dissolves the uranium ore and other heavy metals and the solution is then pumped back to the surface. The small amount of uranium is separated at the surface. The liquid radioactive waste – containing radioactive particles, heavy metals and acid – is simply dumped in groundwater.
The 2004 CSIRO report states: “As stated in the Beverley Assessment Report, the bleed solutions, waste solutions from uranium recovery, plant washdown waters and bleed streams from the reverse osmosis plants are collected prior to disposal into the Namba aquifer via disposal wells. These liquid wastes are combined and concentrated in holding/evaporation ponds, with excess injected into selected locations within the mined aquifer. The injected liquid is acidic (pH 1.8 to 2.8) and contains heavy metals and radionuclides originating from the orebody.”
(Taylor, G.; Farrington, V.; Woods, P.; Ring, R.; Molloy, R. (2004): Review of Environmental Impacts of the Acid In-Situ Leach Uranium Mining Process.- CSIRO Land and Water Client Report.)
From being inert and immobile in the ore body, the radionuclides and heavy metals are now bioavailable and mobile in the aquifer.
The volume of liquid waste is discussed in the 7/1/09 Beverley Four Mile Project Public Environment – Report and Mining Lease Proposal document:
“With the inclusion of maximised recycling of water, approximately 2.5 L/s (averaged over a year) of liquid waste will be generated once the Beverley extraction circuits are decommissioned. This will be disposed of at Beverley ML 6321 in the hydraulically isolated formerly mined Beverley Sands aquifers in the North, Central and South wellfields.
“It is noted that initially the Beverley Four Mile resin elution circuit and Beverley ML 6321 capture and elution circuits will operate in parallel. During this time the combined volume of liquid waste will remain within an annualised average rate of 5 L/s.
“At the indicated rate there is enough disposal volume in those three wellfields to accommodate up to 16 years of liquid waste. Additional volume exists in Beverley North East, East and Deep South wellfields. Any extension of liquid waste disposal in these areas would be subject to a successful application to the regulatory authorities using the Beverley Mine Procedure for Management of Liquid Waste Disposal (Appendix C of the MARP, Heathgate 2008c) or its approved successor.”
The Beverley Four Mile proponents have no plans to remediate the polluted aquifer as they say the pollution will ‘attenuate’ – that the aquifer will return to its pre-mining state over time. This claim has been queried by the scientific community as being highly speculative with no firm science behind it.
The 2004 CSIRO report endorsed the dumping of liquid waste in ground-water yet the information and arguments it used in support of that conclusion were tenuous. In short, the CSIRO report exaggerates the problems of pursuing waste management methods other than dumping it in groundwater, and the report trivialises the impacts of dumping liquid waste in groundwater.
The CSIRO report notes that attenuation is “not yet proven” and the timeframe of “several years to decades” could hardly be more vague. The 2004 CSIRO report states in its Executive Summary:
“The use of acid rather than alkaline leaching and disposal of liquid wastes by re-injection into the aquifer is contentious. Available data indicate that both the leach solution and liquid waste have greater concentrations of soluble ions than does the pre-mining groundwater. However as this groundwater has no apparent beneficial use other than by the mining industry, this method of disposal is preferable to surface disposal. Although not yet proven, it is widely believed and accepted that natural attenuation will result in the contaminated water chemistry returning to pre-mining conditions within a timeframe of over several years to decades.”
Elsewhere the 2004 CSIRO report notes uncertainties associated with attenuation:
“The EIA for Beverley and Honeymoon suggest that natural attenuation will occur, however, exact timeframes are not given. The issue of predicting attenuation is made more complex by not fully understanding the microbiological or the mineralogy of the surrounding ore bodies, before and after mining, and how these natural conditions will react with the altered water quality introduced by the injection of leachate, and re-injection of wastewaters. Following general practice, geochemical modelling was undertaken with a series of assumptions where data were not available. Although these assumptions are considered reasonable by the review team, some technical experts have a differing opinion. In any case the results must be considered approximate.
“The monitoring results from Beverley are limited by the short duration of mining and operation, and there are currently no completely mined-out areas for which the water chemistry can be followed after mining to verify the extent of the expected natural attenuation. However, pH results for an area that was trial-mined in 1998 and then left until full-scale mining of the same area was due are shown in Figure 13.
“Note that whilst other data are available for these wells there are not consistent trends in other analytes. There has been little recovery of groundwater chemistry towards background in the test-production wells other than a favourable change for pH. There are presently no equivalent monitoring data for the northern area, which is presently being mined.”
Even if full attenuation does occur over time, it is unlikely to occur in the timeframe of post-mine-closure monitoring proposed by the mining proponent. The 7/1/09 Beverley Four Mile Project Public Environment – Report and Mining Lease Proposal document states:
“Heathgate proposes an initial period of five years from the conclusion of commercial operations to complete the decommissioning of facilities. A monitoring and maintenance program is proposed to run for a further two years, for a total of seven years from the final conclusion of mining activities. The total monitoring period will be reviewed with the regulatory authorities and may be extended.
“Facilities will therefore be fully decommissioned within seven years from the conclusion of the commercial operation. This period includes a post-completion monitoring period for vegetation maintenance, groundwater sampling, drainage repairs and other activities to ensure the long-term permanent rehabilitation of the site.”
The 2004 CSIRO report states: “Natural attenuation is preferred to adjusting the chemistry of the wastewater prior to re-injection as the latter would result in the need for additional chemicals on-site, generation of contaminated neutralisation sludges which would have to be disposed of, risk of potential clogging of pore spaces in the aquifer and associated higher costs.”
Those are not insurmountable problems. Moreover there are alternatives to adjusting the chemistry of waste-water then reinjecting it into the aquifer, such as evaporation followed by management of solid wastes. As the CSIRO report notes:
“10.6 Alternatives to Liquid Waste Re-Injection
“Suggestions made during the community consultation process included not re-injecting the liquid wastes into the aquifer, and neutralisation of waste before re-injection.
“Not re-injecting the waste into the aquifer would require either sophisticated water treatment and/or the installation of much larger evaporation ponds. Both would generate solid wastes to be disposed of in a solid waste repository. When the wastes dried out they would become a possible dust source, which could increase the potential radiation exposure of workers, in particular in relation to dust inhalation, but also from radon inhalation and gamma exposure. Environmental radiation levels at the surface would also increase. These are presently negligible issues associated with the existing ISL practices.
“Neutralisation of the waste liquid prior to re-injection would precipitate out some metal salts, which would need to be filtered before re-injection, and be disposed of in a solid waste repository.
“Also following re-injection it is likely that the re-injection bores would rapidly clog owing to precipitation around the bores, as the injected water and existing acidic water in the aquifer interact. Clogging of re-injection wellfields and associated problems with pipelines and pumps may increase the risk of spills due to operational problems with equipment and increased maintenance.”
None of the issues raised by the CSIRO amount to compelling reasons to support dumping liquid waste in groundwater. Some of the reasons cited are absurd and cast serious doubt over the credibility of the CSIRO review – for example dust suppression is simple and inexpensive.
The SA government should:
* conduct or commission a thorough comparative assessment of the options for managing liquid waste.
* insist that the proponents rehabilite the aquifer to pre-mining conditions and insist on monitoring/remediation until pre-mining conditions are achieved.
The 2004 CSIRO report states:
“For the Beverley operation, groundwater monitoring is required to be conducted for seven years after mining to demonstrate that their expectations in regard to natural attenuation are being borne out.
“Research into the use of and ability of chemical amendments to assist with or speed up the processes of natural attenuation processes may be beneficial, especially where the latter may be slow and/or incomplete. This approach may also be of benefit in the case of plant or equipment failure with resultant contamination of soil or shallow aquifers.”
Has any follow-up work been done to investigate the potential to assist or hasten attenuation?
The 2003 Senate References and Legislation Committee report into the regulation of uranium mining in Australia reported “a pattern of under-performance and non-compliance”, it identified “many gaps in knowledge and found an absence of reliable data on which to measure the extent of contamination or its impact on the environment”, and it concluded that changes were necessary “in order to protect the environment and its inhabitants from serious or irreversible damage”. On ISL mining, the 2003 Senate report stated:
“The Committee is concerned that the ISL process, which is still in its experimental state and introduced in the face of considerable public opposition, was permitted prior to conclusive evidence being available on its safety and environmental impacts.”
“The Committee recommends that, owing to the experimental nature and the level of public opposition, the ISL mining technique should not be permitted until more conclusive evidence can be presented on its safety and environmental impacts.”
“Failing that, the Committee recommends that at the very least, mines utilising the ISL technique should be subject to strict regulation, including prohibition of discharge of radioactive liquid mine waste to groundwater, and ongoing, regular independent monitoring to ensure environmental impacts are minimised.”
In relation to the Beverley mine, Dr. Gavin Mudd, a hydrogeologist based at Monash University, notes: “The critical data which could answer scientific questions concerning contaminant mobility in groundwater has never been released by General Atomics. This is especially important since GA no longer maintain the mine is ‘isolated’ from surrounding groundwater, with desires to expand the mine raising legitimate concerns over the groundwater contamination legacy left at Beverley.”
The 2004 CSIRO report states in its Executive Summary:
“While ISL technology has environmental and safety advantages when projects are well planned and operated (Underhill 1998), there are several acid ISL operations that have been developed and operated with little or no consideration for the environment. The conditions at these sites are a direct consequence of the Soviet-era operation of uranium mines without effective management of environmental aspects of production, without restoration of contaminated areas, much less planning and design for reclamation and long-term containment of wastes. Similar operating conditions without effective pollution control and closure concepts were apparent at uranium sites in other centrally planned economies such as East Germany, Czechoslovakia and Hungary prior to 1990.”
“… The environmental consequences from acid ISL operations under the Soviet-era are significant and a component of the many environmental problems from this era, the majority of which were from mine water/groundwater/tailings/waste rock arising from underground and open cut mines. It is noted that as many of the environmental problems were related to the governance and institutional arrangements of the era, direct comparison with practices in Australia cannot be made.”
However a number of the criticisms made of Soviet-era management apply to uranium mining in SA:
* Captured bureaucracies (e..g PIRSA)
* Slack regulation.
* Political interference (e.g. Rann pre-empting assessment by describing Beverley Four Mile as a “world class” project).
* Orwellian doublespeak (e.g. Peter Garrett describing ISL as “world’s best practice”).