A Novel Solvent Extraction Technology to Recover Uranium from Strong Sulfuric Acid Strip Liquor

摘要

Alamine 336, a tertiary amine, is used for uranium solvent extraction(SX) by most uranium operations such as BHP Billiton’s Olympic Damand ERA’s Range in Australia. After extraction, ammonium sulfate orammonia is commonly used for stripping. This results in environmentalconcerns due to the generation of wastewater containing ammonium. Inaddition, the volatility of ammonia brings risks associated with operationand transportation. Therefore, stripping with sulfuric acid is desired in theindustry. Unfortunately, a high H_2SO_4 concentration of 4–6 M is requiredfor uranium stripping, resulting in difficulty in uranium recovery in thesubsequent step since large amounts of neutralisation reagent are consumedand large amounts of solid wastes are generated. At present, only RabbitLake in Canada uses strong sulfuric acid stripping for uranium recoveryTo overcome the problems associated with uranium stripping usingstrong acid, a novel SX technology has been developed to separate andrecover uranium from the strong acid-loaded strip liquor. In the method,the uranium in the loaded strip liquor containing 4–6 M H_2SO_4 is extractedand then stripped using a strip solution with a low concentration of H_2SO_4. Itwas found that uranium was efficiently extracted from the synthetic loadedstrip liquor containing 4–6 M H_2SO_4 by the newly developed organic system.The uranium extraction from the 4–6 M H_2SO_4 solution reached more than 80 per cent at an aqueous to organic ratio (A/O) of 1:1 in a single contact(Figure 1). More than 80 per cent of uranium was stripped in a single contactusing 0.5 M H_2SO_4 as shown in Figure 2. As a result, the uranium can betransferred from the high acidity-loaded strip liquor to a low acidity solutionfor recovery. The uranium extraction distribution isotherms showed thatthe uranium loading in the novel SX system could reach 40 g/L in two tothree stages, indicating that the SX system has very high uranium-loadingcapacity. Subsequently, uranium recovery can be readily performed in thelow acidity-loaded strip liquor by precipitation using H_2O_2. After uraniumrecovery, the uranium depleted raffinate is recycled for stripping afterdestroying the remaining H_2O_2 at high temperature. Therefore, using thedeveloped novel SX technology, neutralisation of strong acid is unnecessaryand the waste discharge is also avoided. This new SX technology willsignificantly lower the operating costs for uranium production and largelyreduce environmental pollution.During the test work, it was found that the uranium extraction andstripping was fast and no phase separation problems were observed. Thenovel SX technology has the following advantages with a conceptual flowsheet shown in Figure 3: -- it is ready to be coupled with a uranium stripping step using 4–6 M H_2SO_4acid-- it transfers uranium from a strong H_2SO_4 solution to a weak H_2SO_4solution for recovery-- the strong H_2SO_4 solution could be recycled to the uranium extractionstep after making up-- uranium in the low concentration H_2SO_4 solution can be readily recoveredwith much less neutralisation and waste disposal-- the reagent cost in the novel SX process is low and it is commerciallyavailable-- no large amounts of solid and liquid wastes are generated for disposal.