Development of a phosphate precipitation method for the recovery of uranium from lean tenor alkaline leach liquor

This paper describes results on precipitation studies carried out on liquors containing low to medium concentration of uranium in alkaline (carbonate-bicarbonate-sulphate) media using phosphate based reagents. Studies with various phosphate reagents showed comparable performance with two variants namely, disodium/potassium hydrogen phosphate or sodium/potassium dihydrogen phosphate. Influence of various process variables on the yield and product quality indicated that pH of the liquor is a critical factor besides the NaHCO3 and Na2SO4 content in the leach liquor. The conditions found optimal for near complete precipitation, about 99%, are: pH 6.3, NaHCO3 20 g/L (max.) and Na2SO4 100 g/L (max). Physical characterization of the precipitated uranyl phosphate by XRD, SEM and particle size analyzer indicated presence of two major uranium phases, namely, H2(UO2)2(PO4)2·8H2O and UO2(HPO4)·4H2O called as chernikovite. The experimental studies indicated the possibility of phosphate reagents in precipitating uranium values from alkaline process liquors over a fairly wide range of uranium concentration such as, about 50 mg/L to 2 g/L with good precipitation efficiency.