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In situ alkaline leaching has environmental benefits compared with in situ acid leaching or conventional mining and milling, but the control and treatment of liquid effluents have become increasingly important as a result of more stringent regulatory requirements. Details are given of an operation in north China which employs CO2 + O2 leaching of U in an aquifer, ion exchange recovery of U, elution with NaCl and NaHCO3 and precipitation with NaOH. During production operations about 99.5% of the water produced is enriched with O2 and CO2 and re-injected into the wellfield. Process water that can be recycled includes barren liquid, the solution used to wash the loaded resin, the solution employed to regenerate the resin, the mother liquid obtained during precipitation and the yellowcake filtration liquor. Resin regeneration waste solutions have high contents of chloride and other chemicals and are subjected to reverse osmosis. The solution obtained from reverse osmosis, waste solutions obtained from washing the barren resin and 10% of the precipitation mother liquor are pumped to a pond for natural evaporation. Most of the chemical constituents in the groundwater meet the relevant quality standards and the U and 226Ra concentrations of the fresh water obtained by reverse osmosis also match radiation and environmental standards., In situ alkaline leaching has environmental benefits compared with in situ acid leaching or conventional mining and milling, but the control and treatment of liquid effluents have become increasingly important as a result of more stringent regulatory requirements. Details are given of an operation in north China which employs CO2 + O2 leaching of U in an aquifer, ion exchange recovery of U, elution with NaCl and NaHCO3 and precipitation with NaOH. During production operations about 99.5% of the water produced is enriched with O2 and CO2 and re-injected into the wellfield. Process water that can be recycled includes barren liquid, the solution used to wash the loaded resin, the solution employed to regenerate the resin, the mother liquid obtained during precipitation and the yellowcake filtration liquor. Resin regeneration waste solutions have high contents of chloride and other chemicals and are subjected to reverse osmosis. The solution obtained from reverse osmosis, waste solutions obtained from washing the barren resin and 10% of the precipitation mother liquor are pumped to a pond for natural evaporation. Most of the chemical constituents in the groundwater meet the relevant quality standards and the U and 226Ra concentrations of the fresh water obtained by reverse osmosis also match radiation and environmental standards.