Alternatives for Management and Treatment of Wastewater Derived from 'In Situ Recovery' Uranium Mining

摘要

In situ recovery (ISR) of uranium, or "solution mining," when applicable, can be an economically and environmentally preferable for uranium recovery when compared to open pit or underground mining methods. Advantages of ISR mining include: minimal surface disturbance, minimal risk of worker or public exposure to radiation, and groundwater restoration which can be accomplished by gradually returning the ore body aquifer to applicable pre-mining water quality standards. This paper presents an evaluation of wastewater management alternatives for ISR uranium mining and associated U_3O_8 production facilities. All wastewater streams associated with uranium extraction by wellfield operations, uranium recovery from wellfield solution by ion exchange, conversion to the U_3O_8 product, and groundwater restoration are considered in this evaluation. Typical wastewater quality characterizations and the most stringent of state and federal regulations for effluent discharge were used as the basis for conceptual process design. Characterization of secondary wastes as "11e.(2) byproduct material" requiring special handling and disposal due to presence of radionuclides, and additional treatment for removal of uranium and radium from the waste streams are also evaluated. Wastewater treatment and management alternatives were developed, including deep well disposal, mechanical evaporation, chemical precipitation and reverse osmosis, and spray-enhanced solar evaporation. Evaluation criteria included: environmental impacts (carbon footprint) and safety, equipment complexity, labor intensity, ancillary systems required (treatment chemical reagents and residuals handling), process footprint, estimated capital costs, estimated operating costs, and calculation of 20-year net present values. Deep well disposal was ranked as the preferred wastewater management alternative, followed by spray-enhanced solar evaporation. It is important to note that the preferred deep well disposal alternative assumes that an onsite deep well can be developed and permitted, and will have the capacity to receive the full flow of all wastewater streams. If deep well capacity is not available or is limited, then other treatment alternatives must also be re-evaluated.