Minerals Beneficiation - Solvent-in-Pulp Extraction of Uranium from Acid Leach Slurries

Solvent-in-pulp extraction of uranium from acid leach slurries of flotation concentrates is described. Solvent extraction was carried out in a 10 in. diam pulsed-plate column. The extractant was a 0.1 M tertiary amine (General Mills Alamine 336) in a kerosene diluent containing isodecanol as an emulsion suppressor and third phase inhibitor. In pilot plant operation at the Beaverlodge mill of Eldorado Mining and Refining, Ltd., slurry feeds containing up to 35% solids were processed at a throughput rate of 13.5 tpd of dry feed. Uranium extraction obtained was as high as 98%. Amine losses to the raffinate were approximately 0.07 lb amine per ton of original dry feed. The Beaverlodge Mill of Eldorado Mining and Refining employs a carbonate leach for the extraction of uranium from the ore.',' Prior to carbonate leaching sulphides are removed by flotation to reduce reagent consumption. This flotation concentrate containing some uranium is then leached with sulfuric acid, filtered, and the uranium precipitated with magnesium hydroxide. The precipitate is then returned to the carbonate leach circuit. Although the tonnage of flotation concentrate treated by acid leaching is low, reagent costs are relatively high. Also maintenance costs on the acid leach filtration circuit were beginning to show significant increases. The choice of solvent extraction-in-pulp as an alternative to the present circuit was influenced by the following factors: 1) elimination of acid pulp filtration, 2) increase in overall recovery because of soluble loss elimination, 3) reduction of reagent cost (mill sodium carbonate solutions are used as strip), and 4) production of higher purity precipitate at the mill site. Because a solvent-in-pulp process would be difficult to test on a bench-scale, the Eldorado experience in the use of pulse columns,3-5 mixer-settlers,6 and solvent-in-pulp operations in particular7 was applied directly to the initial pilot plant carried out during the summer of 1965 and followed by the second pilot plant in 1966. The latter work, which is presented in this paper, determined the following factors for anticipated scale-up to plant production: 1) overall uranium recovery by this process, 2) tonnage throughput expected, and 3) solvent losses anticipated for the full-scale plant. The equipment used consisted of a 10 in. diam extraction pulse column and three mixer-settlers for scrubbing, stripping, and acid equilibration. All equipment was designed by Eldorado and much of the pilot plant was built at the mill site. PROCESS CHEMISTRY Feed to the acid leach plant consists of a sulphide flotation1,2 concentrate containing mainly pyrite, uranium and graphite, with a particle size of 90%