Recovery of uranium(VI) from acidic wastes using tri-n-octylphosphine oxide and sodium carbonate based liquid membranes

Acidic wastes containing low concentrations of uranium are generated during uranium purification and processing. This study has been initiated to develop a suitable emulsion liquid membrane (ELM) technique for selective separation and recovery of uranium from such wastes using tri-n-octylphosphine oxide (TOPO) in paraffin as a carrier and sodium carbonate as a stripping agent. The waste, having a composition of nearly 600 ppm U(VI), 360 ppm Fe(III), 325 ppm Ca(II), 390 ppm Mg(II) at an acidity of 1.2 M HNO3, was used as the feed phase. A comparison of ELM extraction was done between synthetically prepared uranyl feed solution and acidic wastes. Various factors that affect the emulsion stability as well as percentage extraction of uranium have been optimized in order to obtain maximum concentration of uranium from acidic wastes. An attempt was made to recover uranium without making any substantial changes to the wastes composition. In presence of various metal ions, selective permeation of uranyl ions through liquid membrane was observed to be more than 70%. Batch type extractions of U(VI) by the ELM method were performed to simulate a two-stage counter extraction and the experimental findings suggest that the U(VI) concentration in the final raffinate can be lowered to below 50 ppm. Potential of the method for the selective separation of U(VI) from acidic wastes is, thus, established. (C) 2002 Elsevier Science B.V. All rights reserved.