Written by: Ada Collins
[I] Introduction
Uranium is a naturally occurring chemical element within the metallic actinide series. In recent years, it has become an integral input for generating electricity and with an average concentration of 2.8 parts per million in Earth’s crust, it is mined extensively (World Nuclear Association, 2023). Australia is one of the world’s major extractors of uranium, alongside Canada, Kazakhstan, and Namibia, and has multiple uranium mines throughout its landscape. Ranger uranium mine, surrounded by Kakadu National Park in the Northern Territory, is an open cut mine operated by Energy Resources of Australia Ltd (ERA) which actively mined uranium from 1981 to 2012.
In May of 2018, ERA submitted a closure plan to the Supervising Scientist Branch (SSB) for assessment, which was updated in June of that year and received an assessment report in September. Processing of stockpiled ore continued until 2021 and rehabilitation of the site is underway with projected completion in 2026 (Supervising Scientist, 2018). This paper aims to consider the processes of uranium mining with specific note of energy, matter, and throughput, in addition to the rehabilitation measures taken by ERA.
[II] Uranium Mining and Milling Processes
Mining operations at Ranger commenced in 1980 with full production starting in October 1981, producing uranium oxide concentrate (U3O8) at a rate of around 3,300 tons per year (World Nuclear Association, 2022). Because the Ranger uranium ore body lies close to the surface, open pit, or open cut, mining is used for access. Open pit mining involves a large pit which is formed by removing much of the overlying rock and producing significant amounts of waste rock (WNA, 2023). Mining energy input of open pit mining depends on several variables: overburden, or stripping ratio, hauling distance, specific consumption of explosives, thermal conversion ratio of diesel extraction engines, and the hardness of the rock. The direct energy input is mechanical and is converted into thermal energy units, while indirect energy input to produce that capital required for mining, is split into electric and thermal energy (Van Leeuwen, 2019). After the orebody is mined, it undergoes a process known as milling, which refines the ore to be used in other markets, notably in energy utilities. Ore is ground and crushed then is leached with sulfuric acid, prompting the following chemical reactions:
[UO3 + 2H+ ⇒ UO22+ + H2O]
[UO22+ + 3SO42- ⇒ UO2(SO4)34-]
Resulting UO2 is oxidized to UO3 which is later treated again depending on the final uranium products usage. Milling energy input strongly depends on the ore grade, hardness of the rock, and the mineralogy of the ore. Ranger mine has operated on the lower end of the energy consumption spectrum in comparison to the world average due to its several optimal conditions; it has a soft and acidic orebody, which requires less energy to process than harder or alkaline ores, and has a relatively high ore grade (G = 0.23% U), meaning the uranium is easier to extract as it is more prevalent. In addition, it is estimated that the energy consumption stemming from the mining process at Ranger is lower than the global average based on its low overburden ratio and assumed low hauling distance, although ERA has not disclosed the mine’s specific hauling distance (Van Leeuwen, 2019).
Figure 3 demonstrates the Ranger uranium mine mass balance in 2005, including figures derived from ERA data in the green shaded boxes, and Figure 4 outlines the processing flowsheet of producing usable uranium based on ERA data. When processing of stockpiled ore ceased in January 2021, Ranger had produced over 132,000 tons of U3O8 over the course of its active years and concluded its final sale in October 2022 (ERA, 2022). ERA U3O8 is sold to energy utilities across Japan, South Korea, China, the United Kingdom, France, Germany, Spain, Sweden and the United States (WNA, 2022). The company only sells uranium to countries complying with stringent safeguards that ensure the uranium produced is used solely for clean electricity generation (Davies, 1997).
[III] Generation of Waste and Pollution
Unsurprisingly, mining has an impact on its direct and surrounding environment, generating waste and pollution in the process. Open cut mining generates barren rock and overburden waste, or the material laying above the mining site, which are typically dealt with during rehabilitation processes (Government of India, 2021). In addition, electric and thermal energy generated in diesel engines yield both work and pollution in the form of greenhouse gas emissions. Figure 5 presents CO2 equivalent emissions from mining and ore processing at Ranger, with method 1 estimating mining and milling emissions based on direct and indirect energy inputs and method 2 basing estimations on direct electricity consumption generated by diesel generators (Van Leeuwen, 2019).
As mined ore is refined during milling processes, solid waste products are generated, varying from slimes to coarse sands. These waste products, known as tailings, contain the entirety of the radioactivity from the original ore and are stored in tailing storage facilities (TSF) before being consolidated after mining is completed. Uranium tailings contain radium which releases radon gas as it undergoes radioactive decay (WNA, 2023). Exposure to radon gas and radioactivity is dangerous and the Commonwealth of Australia has determined that all tailings must be placed in the mined out pits prior to the completion of mining operations and must covered and rehabilitated to ensure that the tailings and any related contaminants are “physically isolated from the environment for at least 10,000 years” (The Commonwealth of Australia, 1999). ERA’s activities at Ranger are closely monitored and evaluated by the SSB which oversees the Alligator Rivers Region, which is inclusive of Kakadu National Park. In addition to evaluating ERA’s annual reports regarding their active operations and rehabilitation progress, the SSB conducts its own environmental research consisting of early detection monitoring and assessment of long-term ecosystem-level response (Australian Government, 2021). The former classification includes annual monitoring reports of the Magela Creek and Gulungul Creek, located to the east and west of the mine site, respectively. For both creeks, researchers monitor electrical conductivity, magnesium, uranium, manganese, total ammonia nitrogen, turbidity and radium-226 levels. The monitoring studies establish various trigger values that, when breached, indicate a potential issue requiring action or investigation to determine whether mining activities are responsible. The most recent reports for the 2023-2024 wet season for both creeks were relatively normal and did not require major investigations (Office of the Supervising Scientist, 2024).
[IV] Rehabilitation
As stated in the introduction, rehabilitation at Ranger must be completed by 2026 based on current agreements. The SSB’s assessment of the Ranger Closure Plan in 2018, however, did not believe that tailings consolidation could be completed by 2026 given the ERA’s outlined models (Supervising Scientist, 2018). Whether this deadline will remain stagnant is not determined at the present time. ERA’s most recent annual Mine Closure Plan was released in December of 2023 and included an indicative timeline of the company’s planned rehabilitation activities which will result in final landform formation between 2034 and 2035, demonstrated in Figure 6 (ERA, 2023). It is critical that the final landform over the mine site is similar to its original surface and geomorphically stable. In addition, revegetation of local native plant species will take place to ensure the rehabilitated site will blend into the surrounding landscape (Paulka, 2022).
[V] Conclusion
Uranium mining is a process that can last decades and whose impacts may be felt for centuries. Operations at Ranger have demonstrated the depths and dimensions of Australian mining regulations and requirements. ERA’s operations at Ranger Mine in compliance with the Government of Australia and under the supervision of the SSB have aimed to produce uranium efficiently while accounting for environmental damage, generated waste, and pollution. As the ERA undergoes its rehabilitation efforts at Ranger, it will continue to mitigate its direct impact on the physical mine site and the SSB will continue to oversee, assess, and monitor the mine’s conditions.
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References:
Araujo, F. S. M., Taborda-Llano, I., Nunes, E. B., & Santos, R. M. (2022). Recycling and Reuse of Mine Tailings: A Review of Advancements and Their Implications. Geosciences, 12(9). https://doi.org/10.3390/geosciences12090319
Australia’s Uranium Mines. (2022, June). World Nuclear Association. https://world-nuclear.org/information-library/country-profiles/countries-a-f/appendices/australia-s-uranium-mines.aspx
Environmental Requirements of the Commonwealth of Australia for the Operation of Ranger Uranium Mine. (1999). The Commonwealth of Australia. https://www.dcceew.gov.au/sites/default/files/documents/ranger-ers.pdf
Gulungul Creek monitoring data: 2023 to 2024 wet season. (2024). Office of the Supervising Scientist, Commonwealth of Australia. https://www.dcceew.gov.au/sites/default/files/documents/gulungul-creek-monitoring-data-2023-24.pdf
Jan Willem Storm van Leeuwen. (2019). Process analysis of the Ranger mine (Nuclear Legacy and the Second Law, p. 18). Nuclear Consulting Group. https://www.stormsmith.nl/Resources/m44Rangerv2-20191010F.pdf
Johnston, A., & Needham, S. (2002). Environmental impact of the Ranger uranium mine, Alligator Rivers Region, Northern Territory, Australia (1011–4289; pp. 158–168). http://inis.iaea.org/search/search.aspx?orig_q=RN:33032909
Magela Creek monitoring data: 2023 to 2024 wet season. (2024). Office of the Supervising Scientist, Commonwealth of Australia. https://www.dcceew.gov.au/sites/default/files/documents/magela-creek-monitoring-data-2023-24.pdf
Monitoring. (2021, October 10). Australian Government Department of Climate Change, Energy, the Environment and Water. https://www.dcceew.gov.au/science-research/supervising-scientist/ranger-mine/monitoring
OBR (Overburden removal). (2021, July 22). Government of India. https://coal.gov.in/index.php/en/major-statistics/obr#:~:text=In%20mining%2C%20overburden%20
Paulka, S. (2022). Ranger Mine: Closing a uranium mine surrounded by a World Heritage listed national park (M. Tibbett, A. Fourie, G. Boggs, M. Tibbett, A. Fourie, & G. Boggs, Eds.; pp. 665–668). Australian Centre for Geomechanics. https://papers.acg.uwa.edu.au/p/2215_47_Paulka/
Ranger Mine Closure Plan 2023 (p. 29). (2023). Energy Resources of Australia Ltd. https://www.energyres.com.au/uploads/Ranger-MCP-2023-Main-Document.pdf
Ranger uranium mine. (2021, October 3). Australian Government Department of Climate Change, Energy, the Environment and Water. https://www.dcceew.gov.au/science-research/supervising-scientist/ranger-mine
Riley, S. (1995). Aspects of the differences in the erodibility of the waste rock dump and natural surfaces, Ranger Uranium Mine, Northern Territory, Australia. Applied Geography, 15(4), 309–323. https://doi.org/10.1016/0143-6228(95)00014-U
Sale of the last drum of uranium oxide produced at Ranger. (2022, October 13). Energy Resources of Australia. https://www.energyres.com.au/ranger-rehabilitation/stories/sale-of-the-last-drum-of-uranium-oxide-produced-at-ranger/
Supervising Scientist. (2018). Assessment Report: Ranger Mine Closure (658; p. 1). Australian Government Department of the Environment and Energy. https://www.dcceew.gov.au/sites/default/files/documents/assessment-report-ranger-closure-plan-2018.pdf
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Figures:
Fig. 1: Ranger uranium mine. (2021, October 3). Australian Government Department of Climate Change, Energy, the Environment and Water. https://www.dcceew.gov.au/science-research/supervising-scientist/ranger-mine
Fig. 2: Australia’s Uranium Mines. (2022, June). World Nuclear Association. https://world-nuclear.org/information-library/country-profiles/countries-a-f/appendices/australia-s-uranium-mines.aspx
Fig. 3: Jan Willem Storm van Leeuwen. (2019). Process analysis of the Ranger mine (Nuclear Legacy and the Second Law, p. 8). Nuclear Consulting Group. https://www.stormsmith.nl/Resources/m44Rangerv2-20191010F.pdf
Fig. 4: Jan Willem Storm van Leeuwen. (2019). Process analysis of the Ranger mine (Nuclear Legacy and the Second Law, p. 9). Nuclear Consulting Group. https://www.stormsmith.nl/Resources/m44Rangerv2-20191010F.pdf
Fig. 5: Jan Willem Storm van Leeuwen. (2019). Process analysis of the Ranger mine (Nuclear Legacy and the Second Law, p. 41). Nuclear Consulting Group. https://www.stormsmith.nl/Resources/m44Rangerv2-20191010F.pdf
Fig. 6: Ranger Mine Closure Plan 2023 (p. 29). (2023). Energy Resources of Australia Ltd. https://www.energyres.com.au/uploads/Ranger-MCP-2023-Main-Document.pdf
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