Environmental Aspects of Uranium Mining
- In most respects the environmental aspects of a uranium mine are the same as those of other metalliferous mining.
- Most uranium mines in Australia and Canada have ISO 14001 certification.
- Radioactivity associated with the uranium ore requires some special management in addition to the general environmental controls of any mine.
- The uranium itself has a very low level of radioactivity, comparable with granite. Virtually all the radioactive material from the associated minerals in the ore processed ends up in the tailings dam.
In many respects uranium mining is much the same as any other mining. Projects must have environmental approvals prior to commencing, and must comply with all environmental, safety and occupational health conditions applicable. Increasingly, these are governed by international standards, with external audits.
Once approved, open pits or shafts and drives are dug, waste rock and overburden is placed in engineered dumps. Tailings from the ore processing must be placed in engineered dams or underground. Finally the whole site must be rehabilitated at the end of the project. Meanwhile air and water pollution must be avoided.
These processes are common to all metalliferous mining, and are well recognised and understood.
In the case of in situ leach (ISL) mining, there is much less disturbance – simply multiple boreholes, and rehabilitation is simpler. An important international conference in 2009 presented a best practice guide to ISL mining published by the International Atomic Energy Agency (IAEA).
In 2014 the OECD Nuclear Energy Agency published a 140-page report: Managing Environmental and Health Impacts of Uranium Mining. “Uranium mining and milling has evolved significantly over the years. By comparing currently leading approaches with outdated practices, this report demonstrates how uranium mining can be conducted in a way that protects workers, the public and the environment. Innovative, modern mining practices combined with strictly-enforced regulatory standards are geared towards avoiding past mistakes committed primarily during the early history of the industry when maximising uranium production was the principal operating consideration.”
In 2017 the World Nuclear Association published an internationally standardized reporting tool to understand the sustainable development performance of uranium mining and processing sites. This checklist had been developed by its members over several years with the goal of achieving widespread agreement on a list of topics and indicators for common use in demonstrating producers’ adherence to sustainable development performance. Accompanying guidelines have also been prepared to help utilities and producers use the checklist. The voluntary checklist was developed to align with the Association’s policy document on best practice in mining.
Uranium
Uranium itself is radioactive, though with the major isotope U-238 having a half-life equal to the age of the earth, it is certainly not strongly radioactive. U-235 has a half-life one-sixth of this and emits gamma rays as well as alpha particles. Hence a lump of pure uranium would give off some gamma rays, but less than those from a lump of granite. Its alpha radioactivity in practical terms depends on whether it is as a lump (or in rock as ore), or as a dry powder. In the latter case the alpha radioactivity is a potential, though not major, hazard. It is also toxic chemically, being comparable with lead. Uranium metal is commonly handled with gloves as a sufficient precaution. Uranium concentrate is handled and contained so as to ensure that people do not inhale or ingest it.
The gamma radiation detected by exploration geologists looking for uranium actually comes from associated elements such as radium and bismuth, which over geological time have resulted from the radioactive decay of uranium.
Environmental approvals
At an early stage of the feasibility study, environmental studies of the site begin. These escalate in detail and progressively focus on issues of concern in relation to the proposal, in consultation with state authorities (who in Australia generally operate under an agreement with the Commonwealth to ensure that its concerns are addressed).
Depending on the government jurisdiction, an environmental effects or impact statement is published and made available for public comment. After consideration of comments and in the light of judgements by a wide range of state authorities, approval may then be given by the state government for the project to proceed.
International standards and certification
The International Atomic Energy Agency (IAEA) has published a guide for both technical and non-technical aspects of environmental matters in uranium mining (and other mining involving radioactive materials): Lessons Learned from Environmental Remediation Programmes, IAEA Nuclear Energy Series, 2014.
The International Organisation for Standardisation (ISO), based in Geneva, has developed a number of world standards for quality management (9000 series) and for environmental management (14000 series). The latter relate to minimising harmful effects and achieving continual improvement through a formal environmental management system (EMS) which is subject to external audit.
ISO 14001 is the world's most recognised EMS framework, enabling organisations to demonstrate sound environmental management. Many mining companies have been certified as conforming to its requirements. In Australia and Canada, major uranium mining companies either have or are close to having ISO 14001 certification. This is also the basis of other ISO certification, such as for audits, reporting and life cycle assessment.
ERA's Ranger mine for instance is audited every six months by an accredited external body and undergoes full re-certification every three years.
The basic EMS under ISO 14001 is under four linked headings: Plan-Do-Check-Act. It must take into account both routine hazards and abnormal situations.
Wastes from mining & milling
In most respects, conventional mining of uranium is the same as mining any other metalliferous ore, and well-established environmental constraints apply in order to avoid any off-site pollution.
From open cut mining, there are substantial volumes of barren rock and overburden waste. These are placed near the pit and either used in rehabilitation or shaped and revegetated where they are. At Ranger mine, the development of the first orebody involved a waste to ore ratio of slightly over 2:1.
However, uranium minerals are always associated with more radioactive elements such as radium and radon in the ore which arise from the radioactive decay of uranium over hundreds of millions of years. Therefore, although uranium itself is not very radioactive, the ore which is mined, especially if it is very high-grade such as in some Canadian mines, is handled with some care, for occupational health and safety reasons.
Mining methods, tailings and run-off management and land rehabilitation are subject to Government regulation and inspection. For instance in Australia the Code of Practice and Safety Guide: Radiation Protection and Radioactive Waste Management in Mining and Mineral Processing was published in 2005. It is simpler than its two predecessors (on health & wastes) and moves away from undue prescription to performance-based and audited regulatory approach.
Mining operations are undertaken under relevant national health and radiation protection codes of practice. These set strict health standards for exposure to gamma radiation and radon gas. Standards apply to both workers and members of the public. See associated paper: Occupational Safety in Uranium Mining.
Tailings & radon
Solid waste products from the milling operation are tailings. They comprise most of the original ore and they contain most of the radioactivity in it. In particular they contain all the radium present in the original ore. At an underground mine they may be first cycloned to separate the coarse fraction which is used for underground fill. The balance is pumped as a slurry to a tailings dam, which may be a worked-out pit as at Ranger and McClean Lake.
When radium undergoes natural radioactive decay one of the products is radon gas. Because radon and its decay products (daughters) are radioactive and because the tailings are now on the surface, measures are taken to minimise the emission of radon gas. During the operational life of a mine the material in the tailings dam is often kept covered by water to reduce surface radioactivity and radon emission (though with lower-grade ores neither pose a hazard at these levels).
On completion of the mining operation, it is normal for the tailings dam to be covered with some two metres of clay and topsoil to reduce radiation levels to near those normally experienced in the region of the orebody, and for a vegetation cover to be established. At Ranger and Jabiluka in North Australia, tailings will be returned underground, as was done at the now-rehabilitated Nabarlek mine. In Canada, ore treatment is often remote from the mine that the new ore comes from, and tailings are emplaced in mined out pits wherever possible, and engineered dams otherwise.
The radon gas emanates from the rock and tailings as the radium or thorium decays. It then decays itself to (solid) radon daughters, which are significantly alpha radioactive.*
* The uranium orebody contains both U-235 and (mostly) U-238. About 95% of the radioactivity in the ore is from the U-238 decay series. This has 14 radioactive isotopes in secular equilibrium, thus each represents 7% of the total. (In the case of Ranger ore – with 0.3% U308 – it has about 450 kBq/kg, so irrespective of the mass proportion, 32 kBq/kg per nuclide in that decay series.) When the ore is processed, the U-238 and the very much smaller masses of U-234 (and the U-235) are removed. The balance becomes tailings, and at this point has about 86% of its original intrinsic radioactivity. However, with the removal of most U-238, the following two short-lived decay products (Th-234 & Pa-234) soon disappear, leaving the tailings with a little over 70% of the radio-activity of the original ore after several months. The controlling long-lived isotope then becomes Th-230 which decays with a half life of 77,000 years to radium-226 followed by radon-222.
Radon occurs in most rocks and traces of it are in the air we all breathe. However, at high concentrations it is a health hazard.
A 1998 paper looks at the long-term population dose due to radon from uranium mining and shows that it is insignificant.
Water
Run-off from the mine stockpiles and waste liquors from the milling operation are collected in secure retention ponds for isolation and recovery of any heavy metals or other contaminants. The liquid portion is disposed of either by natural evaporation or recirculation to the milling operation. Most Australian and many other mines adopt a "zero discharge" policy for any pollutants.
Process water discharged from the mill contains traces of radium and some other metals which would be undesirable in biological systems downstream. This water is evaporated and the contained metals are retained in secure storage. During the operational phase, such water may be used to cover the tailings while they are accumulating.
With in situ leach (ISL) operations, the orebody stays in the ground, in a contained aquifer, and uranium is recovered by circulating oxygenated and acidified groundwater through it, using injection and recovery wells. The saline quality of this groundwater in Australian ISL mines makes it far from potable in the first place, and after the uranium is recovered, oxygen input and circulation are discontinued, leaving the groundwater much as it was.
The main environmental consideration with ISL is avoiding pollution of any groundwater away from the orebody, and leaving the immediate groundwater no less useful than it was initially.
Descriptions of how environmental management is undertaken at Australia's three uranium mines, Ranger, Olympic Dam, and Beverley are under the Environmental Management headings of Australia's Uranium Mines, in the sections on the respective mines.
In relation to Ranger, the Office of the Supervising Scientist was established by the Commonwealth Government in 1979 to oversee environmental protection at uranium mines in the Alligator Rivers region of the Northern Territory.
Rehabilitation
Apart from tailings, other solid wastes at a mine include equipment which is not able to be sold at the end of the operation. This is usually buried with the tailings.
At the conclusion of mining, tailings are covered permanently with enough clay and soil to reduce both gamma radiation levels and radon emanation rates to levels near those naturally occurring in the region, and enough rock to resist erosion. A vegetation cover is then established.
Mary Kathleen in Queensland was the site of Australia's first major rehabilitation project of a uranium mine. It involved the plant site, a 28 hectare tailings dam, and a 60 ha evaporation pond area. All this has now returned to being a cattle station, with unrestricted access. The rehabilitation project was completed at the end of 1985 at a cost of some $19 million, and won an award for engineering excellence.
The Nabarlek uranium mine in the Northern Territory, c 270 km east of Darwin, was the first of the "new generation" of uranium mines to commence operations and the first to be rehabilitated. Environmental protection was stressed at Nabarlek since before mining commenced, and everything proceeded with eventual rehabilitation very much in mind. During the life of the operation the company worked together with government agencies, the Northern Land Council (NLC) and Aboriginal land owners to ensure a high standard of environmental management, culminating in its decommissioning and successful rehabilitation.
At Ranger the planning of final restoration is well-established, and each year the company prepares a full-costed plan which assumes that mining could cease that year. All rehabilitation objectives must be achieved, including ecosystem viability, radiological safety, and landform stability (re erosion). This plan has been used as the basis for calculating the financial provision required for eventual closure at the end of mine life. In 2013 the net present value of the closure model for the Ranger project area and surrounds was estimated at A$640 million, fully provided for in the balance sheet. After substantial work had been commenced, at the end of 2016 the company had a rehabilitation provision of A$511 million plus provision for another A$100 million if required.
A simpler model which can be applied is for the basic estimated cost of rehabilitation upon closure to be a bond held by the government, and such bonds are a routine requirement for any mines today. In the case of Ranger, ERA is obliged to secure funds for certain costs of rehabilitation in case of any need for premature closure. An annually amended plan is submitted to government outlining this provision, which is reviewed by an independent auditor. Money for this purpose is partly in a trust fund administered by the Commonwealth government and partly covered by bank guarantee.
Apart from groundwater considerations discussed above, rehabilitation of ISL mines is very straightforward, making this a technique with remarkably low environmental impact. Upon decommissioning, wells are sealed or capped, pipes and process facilities removed, any evaporation pond revegetated, and the land can readily be returned to its previous uses.
Experience at many mine sites is networked throughout the industry and available to present and future operators.
Health of workers
In Australia all uranium mining and milling operations are undertaken under the Code of Practice and Safety Guide: Radiation Protection and Radioactive Waste Management in Mining and Mineral Processing, which sets strict health standards for radiation and radon gas exposure, for both workers and members of the public.
In Canada the Canadian Nuclear Safety Commission is responsible for regulating uranium mining as well as other aspects of the nuclear fuel cycle. In Saskatchewan, provincial regulations also apply concurrently, and set strict health standards for both miners and local people. Similar standards are set in other countries.
While uranium itself is only slightly radioactive, radon, a radioactive inert gas, is released to the atmosphere in very small quantities when the ore is mined and crushed. Radon is one of the decay products of uranium and radium, and occurs naturally in most rocks – minute traces of it are present in the air which we all breathe.
Australian uranium mines have mostly been open cut and therefore naturally well ventilated. The Olympic Dam and Canadian underground mines are ventilated with powerful fans. Radon levels are kept at a very low and certainly safe level in uranium mines. (Radon in non-uranium mines also may need control by ventilation.)
Gamma radiation may also be a hazard to those working close to high-grade ores. It comes principally from radium in the ore, so exposure to this is regulated as required. In particular, dust is suppressed, since this represents the main potential exposure to alpha radiation as well as a gamma radiation hazard.
At the concentrations associated with uranium (and some mineral sands) mining, radon is a potential health hazard (actually due to its short-lived decay products), as is dust. Precautions taken during the mining and milling of uranium ores to protect the health of the workers include:
- Good forced ventilation systems in underground mines to ensure that exposure to radon gas and its radioactive daughter products is as low as possible and does not exceed established safety levels.
- Efficient dust control, because the dust may contain radioactive constituents and emit radon gas.
- Limiting the radiation exposure of workers in mine, mill and tailings areas so that it is as low as possible, and in any event does not exceed the allowable dose limits set by the authorities. In Canada this means that mining in very high-grade ore is undertaken solely by remote control techniques and by fully containing the high-grade ore where practicable.
- The use of radiation detection equipment in all mines and plants.
- Imposition of strict personal hygiene standards for workers handling uranium oxide concentrate.
At any mine, designated employees (those likely to be exposed to radiation or radioactive materials) are monitored for alpha radiation contamination and personal dosimeters are worn to measure exposure to gamma radiation. Routine monitoring of air, dust and surface contamination is undertaken.
Canadian mine and mill facilities are designed to handle safely ore grades of up to 26% U.
If uranium oxide is ingested it has a chemical toxicity similar to that of lead oxide. Similar hygiene precautions to those in a lead smelter are therefore taken when handling it in the drying and packing areas of the mill.
The usual radiation safeguards are applied at an ISL mining operation, despite the fact that most of the orebody? radioactivity remains well underground and there is hence minimal increase in radon release and no ore dust.
See also WNA information paper on Occupational Safety in Uranium Mining.
Appendix
Environmental Management at Australian Uranium Mines
Ranger Mine (ERA)
ERA has been recognised for its world-class environmental management, achieving ISO 14001 certification in 2003.
Until 1996 tailings from the treatment plant were emplaced in an engineered dam on the lease, but they are now being deposited into the worked out pits. No process or other contaminated water is released from the site.
The Ranger mine is on a 7860 hectare lease which is surrounded by the World Heritage listed Kakadu National Park of 1.98 million hectares. About 500 hectares is actually disturbed by the mining and milling activities (0.025% of the total area). Rainfall is monsoonal, with 700-2200 mm (average 1540 mm) falling in the wet season. The vegetation at Ranger is tropical open eucalypt forest, similar to much of the National Park.
The project area is leased from the Aboriginal traditional owners, title to the land being held by the Kakadu Land Trust. The Company contributes 4.25% of its gross sales revenue (the major part of its royalties of 5.5%) to NT aboriginal groups plus an annual rental of $200 000 for the use of the land. Ranger has paid a total of $226 million in nominal terms in royalties since the project began in 1980. The money is paid to the Commonwealth Government and then distributed to Northern Territory-based Aboriginal groups, including 30% to the Gundjeihmi Aboriginal Corporation (representing Traditional Owners), under the 1979 terms of the Commonwealth's Aboriginal Land Rights (NT) Act of 1976. Additional payments of over $7 million are on account of Jabiluka. The balance of royalty (1.25% of revenue) is paid to the NT government by the Commonwealth Government.
The Company has a substantial environmental division, employing about 30 people and with an annual budget of nearly $3 million. Part of this environmental effort is directed to land management issues of relevance not simply to Ranger, but to the surrounding National Park and World Heritage area. These include maintenance of biodiversity, fire management including control burning (which is very important and contentious in the region), terrestrial and aquatic weed control, feral animal control, mycorrhizal establishment, and rehabilitation of disturbed areas (including rock waste dumps, etc). Ranger is possibly the first mining operation deliberately to burn its own revegetated areas to assist the development of an appropriate vegetation community (Eucalypts and Grevilleas instead of Acacia dominance). Related issues being studied include artificial wetland filters, soil formation from waste rock, and hydrology. Among Ranger's long term research priorities are projects which are relevant to eventual use of the land by its aboriginal owners.
Olympic Dam Mine (BHP Billiton)
The mine lease of 18,000 hectares is managed by BHP Billiton Olympic Dam. The mine, smelter and infrastructure occupy about 7.5% of the lease area. Environmental management activities account for approximately one third of expenditure from the overall environmental budget, which is in excess of A$ 2 million. In February 2005, Olympic Dam was successful in obtaining ISO14001 certification for the site Environmental Management System.
The mine lease and the adjacent 11,000 hectare municipal lease have been destocked (of sheep and cattle) since 1986. Following the release of rabbit haemorrhagic disease (RHD), rabbit numbers in the region dropped significantly, and are currently at approximately 40 per square kilometre, compared with plague numbers of up to 600 /km 2 in the late 1980s. Red Kangaroo numbers on the mine lease are about 20 per square kilometre, which is slightly higher than surrounding areas because of the access to water. In order to discourage wildlife from entering the tailings storage facility, alternative waterholes have been provided and deterrents installed on the dams and ponds. The evaporation ponds have been fenced with fine mesh to exclude small mammals and reptiles. Foxes and cats are controlled on the lease by shooting and trapping.
BHP Billiton Olympic Dam manages four pastoral stations in the area surrounding the mine and municipal leases with a total area of 1,136,000 hectares. These properties are conservatively stocked to maximise protection of sites of environmental or cultural significance.
The Arid Recovery project, which covers an area of 8,600 hectares, is situated largely on the mine lease and BHP Billiton-operated pastoral stations, with the remaining area (6 hectares) donated by local pastoralists. Arid Recovery is an ecosystem restoration initiative working to restore Australia's arid lands. The program is a partnership between BHP Billiton, the South Australian Department for Environment and Heritage, the University of Adelaide and the community group Friends of Arid Recovery. The reserve is surrounded by a unique cat, rabbit and fox-proof fence. Five locally extinct species have been reintroduced into the reserve.
Before clearing is undertaken for any development work or exploration on the mine and municipal leases, an Environmental/Indigenous Heritage Clearance Permit is required. During this process, all significant slow-growing trees and shrubs and areas of cultural significance are identified. Efforts are made to minimise disturbance caused by operational activity on the leases, and rehabilitation is undertaken afterwards where practical. Considerable attention has been given to rehabilitation of the hundreds of drill pads, some dating from initial exploration, so that many are now scarcely visible even on aerial photos.
Rock waste and the coarse fraction of tailings are used as mine backfill. Fine tailings material, still containing potentially valuable minerals (rare earths etc.) is emplaced in tailings dams on the lease covering about 400 hectares.
During 1994 seepage of contaminated water from the tailings dams was identified. This was of concern to the company, the regulators and the public because of the perceived threat to the quality of groundwater immediately below the tailings dams. Studies undertaken demonstrated that the pollutants in the seepage were quickly adsorbed on to clays and limestone in the soil and rock under the tailings dams, and, due to the low permeability and transmissivity of the rock, that there was no potential harm to the groundwater resource. The level of the groundwater under the tailings dams is monitored and modelled on a quarterly basis.
BHP Billiton Olympic Dam submits an Environmental Management and Monitoring report annually to the Department of Primary Industries and Resources South Australia (PIRSA) and the Environment Protection Authority (EPA). This comprehensive report covers all areas of potential environmental impact, including air emissions, site groundwater management, water supply and management of the Great Artesian Basin, flora and fauna monitoring and annual radiation dose to members of the public. Reporting on progress with action items identified in the Environmental Management Program is provided, as well as involvement with community activities.
The annual Sustainability Report is on the Internet:
http://bhpbilliton.com/bb/sustainableDevelopment/reports.jsp
Olympic Dam has a Rehabilitation and Closure Plan covering cost estimate basis, summary of closure requirements (for the metallurgical facilities, pilot plant, mine, tailings dams, wellfields, exploration areas, town facilities, power line corridor and miscellaneous facilities), community consultation requirements, closure strategy (including post operational land use objective and completion criteria) and closure plan review requirements. The plan provides a breakdown for each area to be decommissioned, including engineering works required (ie demolition and cleaning), environmental works (removal of contaminated material and rehabilitation), specific closure obligations for each area of plant, final land use objectives, closure assumptions, closure material sources, waste disposal sites, cost saving opportunities and liabilities/risks/hazards.
Demolition costs are budgeted based on quotations from a specialist demolition contractor and rehabilitation costs are estimated based on a quotation from a mining contractor with extensive rehabilitation experience. Progressive closure costs have been estimated for each year until actual closure of the site. The financial provision – A$ 244 million at mid 2006 – is calculated in line with BHP Billiton Accounting Standards.
Beverley Mine (Heathgate Resources)
An Environmental Management and Monitoring Plan (EMMP) has been developed with the regulating authorities, who determined the requirements of it, including those for radiation protection. The Plan provides for ongoing management of every aspect of the operation. Monitoring to detect possible horizontal excursions from the mining zone or any vertical leakage into other aquifers is a fundamental facet of mine operations.
In contrast to the main ISL operations in USA extracting uranium from aquifers with potable water, the groundwater quality at Beverley is very low, being fairly saline and orders of magnitude too high in radionuclides for any permitted use. Fluids from mined areas are progressively moved to new mining areas, thus reducing the overall effect on the aquifer. After completion of mining, when oxygen input and leaching are discontinued, the groundwater reverts to about pH 4.5, and eventually to its original condition at about pH 7.
Heathgate bought the 2350 sq km Wooltana pastoral lease, from which the 13.5 sq km project area is fenced off and destocked. This area, mainly Mitchell grass plain, will be allowed to rehabilitate naturally to guide later revegetation of mined areas.
Upon decommissioning a wellfield, wells are sealed and capped, pipes are removed and the surface revegetated progressively. At the end of the mine's life, process facilities will be removed and after discussion with the stakeholders the land can revert to its previous uses. Heathgate has provided financial guarantees to the state government in respect to ongoing mine site rehabilitation up to the final completion of mining.
Sources:
Environmental Management and Rehabilitation of the Nabarlek Uranium Mine, UIC mines paper # 5
Mary Kathleen Uranium Ltd, Review Report: Rehabilitation of the Mary Kathleen Mine, 1986.
Code of Practice and Safety Guide: Radiation Protection and Radioactive Waste Management in Mining and Mineral Processing (2005)
IAEA 2014, Lessons Learned from Environmental Remediation Programmes, IAEA Nuclear Energy Series NW-T-3.6.
NEA 2014, Managing Environmental and Health Impacts of Uranium Mining, OECD/NEA 7062.