Authors: Wiramanaden, C; Barnhart, B; Nash, T; Heffner, H

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Wiramanaden, C, Barnhart, B, Nash, T & Heffner, H 2023, 'Radium-226 treatment 20 years post uranium mine closure', in B Abbasi, J Parshley, A Fourie & M Tibbett (eds), Mine Closure 2023: Proceedings of the 16th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth,

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In Elliot Lake, Ontario, uranium mining occurred from the 1950’s until the 1990’s when decommissioning took place. Within the Elliot Lake area, Rio Algom Limited owns eight tailings management areas (TMAs) which are currently (since the mid-1990’s to present day) in active care and maintenance with management focused on water management, treatment, and environmental monitoring. Of the eight TMAs, four are flooded. Radium-226 is a parameter of concern associated with mine impacted water and monitored within the receiving environment. Raw water from the TMAs also contains sulphate due to the historical use of sulphuric acid to extract uranium as well as sub-aerial pyrite oxidation of tailings prior to flooding. The decommissioning environmental impact statement (EIS) predicted that within the flooded TMA basins, radium-226 and sulphate concentrations would decrease over time. As part of the closure and decommissioning process for the Elliot Lake mines, a focused and integrated performance monitoring framework was developed to monitor contaminants of concern at the source (within the TMAs), within the pathways (treated effluents and seepage), and within receiving environments. Since decommissioning, the TMAs have exhibited a trend towards decreased radium-226 and sulphate concentrations as was predicted in the decommissioning EIS. However, effective (conventional) treatment for radium-226 has relied upon elevated sulphate concentrations that were present in the raw TMA water. Conventional radium-226 treatment involves barium chloride addition to raw TMA water to induce barite (barium sulphate) precipitation, which co-precipitates and/or adsorbs radium-226. These treatment solids settle out prior to discharge of the clarified water to the receiving environment. Thermodynamically, barite will precipitate at the decreased sulphate concentrations currently (2022) observed within the basins. However, barite precipitation and settling prior to discharge has become increasingly challenging. Radium-226 monitoring has shown that treatment efficacy decreases during periods of high precipitation in the spring and fall. In this study, a combination of bench tests with field surveys were used to test the hypothesis that treatment challenges are caused by seasonal influx of organic acids, combined with the dilution of sulphate due to run-off. These tests were completed in two flooded TMAs at Elliot Lake, where each TMA responded differently with respect to the characteristics of organic acids and how they interfered with barite precipitation and particle settling. This phenomenon has the potential to affect other decommissioned TMAs where radium-226 is being treated using barite precipitation.

Keywords: radium-226, sulphate, post-closure, water treatment, barite

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