The Queensland State Government recently announced it would take up uranium mining again. The topic of uranium mining often raises concern about environmental risk. While past uranium mining in Queensland led to environmental damage, changes to regulation in the intervening years should ensure Queensland won’t face similar problems this time.
Thirty years ago, the Australian Government’s three-mine policy banished uranium mining to two sites in the Northern Territory and one site in South Australia.
Before this, uranium mining existed throughout Queensland, notably at Mary Kathleen and Rum Jungle in the Northern Territory. The practices applied during this time, extending from the 1950s to the late 1970s, left a legacy of dispersed tailings, reactive waste rock and affected downstream aquatic ecosystems from heavy metals and acidity associated with the mining. There were no sustained health effects to the population from these operations.
By the 1980s, far more rigorous mining practices were adopted. The change was propelled by enquires such as the Fox Report, which resulted in tighter regulation by the Northern Territory government. It meant better managed processes at sites such as Ranger, Nabarlek and Jabiluka under the watchful eye of the Supervising Scientist watchdog.
Subsequently the mining of uranium at Ranger and Nabarlek proceeded without any serious incidents or long term effects to the environment. This can be credited to the advances made in expertise and an increased understanding of the mining process, but primarily to the increased regulation. The tailings and evaporated residues from storage dams have been returned to the mined out pits that are essentially geologically-stable structures. Some waste rock has been stabilised above ground.
The mining process
In terms of rehabilitation practices, uranium mining uses similar methods to other kinds of metal mining.
Waste rock has to be removed before the uranium can be mined. The properties and composition of the waste rock can result in acid formation (as happened at Rum Jungle) if it isn’t neutralised. This acid can then find its way into aquatic ecosystems.At Ranger and Nabarlek there was no acid-producing waste rock.
Most of the mined material is crushed and ground before being extracted with sulfuric acid. It is then processed to concentrate the uranium, which is concentrated and shipped overseas, leaving behind processed tailings.
Tailings are neutralised to increase their pH and transferred to a repository for storage. The repository is usually an above–ground dam or mined-out pit. This storage pit is generally considered geologically stable as the original uranium deposit was about the same age as the earth.
Dealing with radiation
Tailings contain the decay products of natural uranium, particularly radium 226 which has a half life of 1600 years and emits radon gas, which can build up in confined spaces if not vented. Uranium mining waste is generally classified as low level radioactive waste (while the activation products from reactors are classified as high-level waste).
Uranium is primarily an alpha radiation emitter and is only a health hazard when dust is inhaled or ingested. Therefore prevention of dust dispersion by covering prevents this pathway of exposure to uranium. Drinking water supplies are carefully monitored and have not exceeded drinking water guidelines, apart from some naturally occurrences associated with natural mineralisation.
The radiation effects from uranium itself are minimal. They are essentially only a hazard to workers, and only if they are exposed to uncontrolled inhalation of dust. As a heavy metal, uranium has some toxicity. It’s about the same as other metals and is usually at environmentally low levels compared with other heavy metals such as cadmium, copper, lead and zinc.
In tailings, uranium may get into groundwater if seepage is alkaline. These are long term processes that require good design features to minimise seepage and also to control the spread of dust which may contain radium. Proper tailings dam construction and storage will minimise the dispersal of uranium and other heavy metals.
Modern mining practices minimise the events that led to the environmental effects observed at Rum Jungle and Mary Kathleen in the past. Modern mining is well described in the Australian Government series on Leading Practices in Mining. Radiation must be specifically monitored, and miners must adhere to stringent guidelines typically set by the International Commission on Radiological Protection and the World Health Organization.
The best examples of responsible uranium mining with minimal environmental effects are the operations in the Northern Territory at Ranger and Nabarlek. These have demonstrated track records of success based on good design and sound regulatory practices. This is in contrast to the public perception that uranium can’t be beneficial or mined safely.
Australia’s decision to not mine uranium from more than a selected few deposits has delayed further uranium mining in Queensland. It did not stop uranium mining and generation of profits elsewhere in the world, such as Canada. It did prevent Australia and Queensland in particular from receiving the mining income. This situation now looks likely to be rectified. The best prospects for development are deposits with higher grades and an absence of sulfide mineralisation with polymetallic features.