THE SELECTIVE EXTRACTION OF MOLYBDENUM FROM A URANIUM STREAM IN A SULPHATE MEDIUM

摘要

Molybdenum can be found in significant amounts in certain uranium ores, such as the Karoo Sands in South Africa. During sulphuric acid leaching, molybdenum is leached together with uranium. If untreated the molybdenum is co-extracted during the uranium recovery process, using either anion exchange resins or amine-type solvent extractants. The molybdenum could poison these extractants and also cause contamination of the uranium yellow cake product. A further problem is possible crud formation due to limited solubility in the organic phase of certain molybdenum complexes. Carbon columns could be used for molybdenum adsorption; however carbon columns are preferred for molybdenum removal from pregnant strip solutions as opposed to pregnant leach liquors to reduce the carbon inventories that are required. Another drawback of carbon columns is the slow molybdenum adsorption rate.This paper focuses on a solvent extraction process for the selective extraction of molybdenum in the presence of uranium in sulphuric acid leach liquors. The efficiency of the molybdenum removal from the uranium leach stream was evaluated using 2-hydroxy-5-nonylacetophenone oxime. Metal-distribution equilibria, extraction equilibrium isotherm and batch counter-current tests were done for molybdenum extraction using 15 (v/v) % 2-hydroxy-5-nonylacetophenone oxime with the addition of 7.5 (v/v) % Isodecanol in Shellsol D70 using uranium pregnant leach liquor. It was found that, at a pH value of 1.5, selective extraction of molybdenum was possible. Batch counter-current extraction tests produced a loaded organic phase which contained 1.26 g/L molybdenum at steady state leaving 4 mg/L molybdenum in the raffinate, which related to >96% extraction. Degradation tests were carried out using 15 (v/v) % 2-hydroxy-5-nonylacetophenone oxime, and 7.5 (v/v) % Isodecanol in Shellsol D70, simulating extraction conditions, at 20°C and 40°C over a period of 91 days. Results obtained indicated that there were negligible variations in molybdenum maximum loadings over the 91 day period. The process described will result in a higher purity uranium yellow cake product and a saleable molybdenum product. This will increase the revenue potential of a deposit which contains both uranium and molybdenum in significant quantities.