Reactive Transport Modeling forthe Proposed Dewey Burdock Uranium In-Situ Recovery Mine, Edgemont, South Dakota, USA

摘要

In-situ recovery (ISR) mining extracts uranium by enhanced dissolution and mobilization of solid-phase uranium in sandstone aquifers. Geochemical changes that occur due to the ISR mining process are important for local groundwater users, regulatory agencies, and other stakeholders to understand in order to evaluate the potential effects on surrounding groundwater quality during and after mining. Reactive transport modeling is being used at the proposed Dewey Burdock ISR mine to simulate the geochemistry of: 1) uranium roll-front deposition; 2) current groundwater conditions; 3) mining processes; 4) post-mining restoration; and, 5) long-term groundwater quality after restoration. This modeling uses groundwater flow coupled with rock/water interations to understand geochemical changes during each stage. Conceptually, uranium roll-fronts are formed as oxygenated, uranium-rich groundwaters enter reducing zones where uranium minerals precipitate to form uranium ore. Through geologic time, the groundwater flow direction and incoming groundwater geochemistry can change, which may or may not alter the uranium roll-front deposit. During the mining process, oxygen and a complexing agent (such as carbon dioxide) are added to oxidize, solubilize, and remove the uranium. Post-mining, the mining solution is removed, and reducing agents may be added to re-precipitate uranium. Longer term geochemistry depends upon the remaining solid-phase minerals, their reactivity, and the composition of the incoming groundwater. All of these processes are highlighted through the use of a simple three-dimensional reactive transport model (groundwater flow and geochemistry). While this research focuses specifically on the proposed Dewey Burdock uranium ISR site near Edgemont, South Dakota, the procedures described are generally applicable to any proposed uranium ISR mine.