Geochemistry of arsenic in uranium mine mill tailings,Saskatchewan, Canada |
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| Institution: | 1. Department of Civil and Environmental Engineering, University of Alberta, 303 Civil/Electrical Bldg., Edmonton, AB, T6G 2G7 Canada;2. Department of Geological Sciences, University of Saskatchewan, Canada;1. Geoscience Australia, GPO Box 378, Canberra, ACT, 2601, Australia;2. The Australia National University, Canberra, ACT, 0200, Australia;4. CSIRO Marine and Atmospheric Research, PMB 1, Aspendale, VIC, 3195, Australia;1. College of Petroleum Engineering Institute, Northeast Petroleum University, Daqing 163318, China;2. Energy Research Institute of the Lower Saxon, Clausthal University of Technology, 38640 Goslar, Germany;3. Institute of Oil and Gas, Peking University, 100871 Beijing, China;1. School of Marine Sciences, China University of Geosciences (Beijing), Beijing 100083, China;2. Ministry of Education Key Laboratory of Oil & Gas Resources and Exploration Technologies, Yangtze University, Wuhan 430100, China;3. School of Geosciences, Yangtze University, Wuhan 430100, China;4. Research Institute of Exploration and Development, PetroChina Daqing Oilfield Company, Daqing 163458, China;1. Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Bhopal, Bhopal Bypass Road, Bhauri, Bhopal, 462066, MP, India;2. Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK, S7N 5E2, Canada;3. SRK Consulting (Canada) Inc., 22nd Floor, 1066 West Hastings Street, Vancouver, BC, V6E 3X2, Canada;4. Department of Civil, Geological and Environmental Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK, S7N 5A9, Canada;1. Department of Conservation Ecology and Entomology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa;2. Department of Environmental Sciences, Bindura University of Science Education, Private, Bag 1020, Bindura, Zimbabwe;3. Zimbabwe Mine Environment Research Network (ZIMERN), Agriculture House, No. 1, Adylin Road, Marlborough, Harare, Zimbabwe;4. Biosystems and Environmental Engineering Research Group, Department of Soil Science and Agricultural Engineering, University of Zimbabwe, Box MP 167, Mt Pleasant, Harare, Zimbabwe;5. Department of Natural Resources, Bindura University of Science Education, Private Bag 1020, Bindura, Zimbabwe;6. Restoration and Conservation Biology Research Group, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg, South Africa |
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| Abstract: | The Rabbit Lake U mine in-pit tailings management facility (TMF) (425 m long×300 m wide×91 m deep) is located in northern Saskatchewan, Canada. The objectives of this study were to quantify the distribution of As phases in the tailings and evaluate the present-day geochemical controls on dissolved As. These objectives were met by analyzing pore fluid samples collected from the tailings body for dissolved constituents, measuring Eh, pH, and temperature of tailings core and pore fluid samples, conducting sequential extractions on solid samples, conducting geochemical modeling of pore fluid chemistry using available thermodynamic data, and by reviewing historical chemical mill process records. Dissolved As concentrations in 5 monitoring wells installed within the tailings body ranged from 9.6 to 71 mg/l. Pore fluid in the wells had a pH between 9.3 and 10.3 and Eh between +58 and +213 mV. Sequential extraction analyses of tailings samples showed that the composition of the solid phase As changed at a depth of 34 m. The As above 34 m was primarily associated with amorphous Fe and metal hydroxides while the As below 34 m was associated with Ca, likely as amorphous poorly ordered calcium arsenate precipitates. The change in the dominant As solid phases at this depth was attributed to the differences in the molar ratio of Fe to As in the mill tailings. Below 34 m it was <2 whereas above 34 m it was >4. The high Ca/As ratio during tailings neutralization would likely precipitate Ca4(OH)2(AsO4)2:4H2O type Ca arsenate minerals. Geochemical modeling suggested that if the pore fluids were brought to equilibrium with this Ca-arsenate, the long-term dissolved As concentrations would range between 13 and 126 mg/l. |
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