Intensification of emulsion liquid membrane extraction of uranium(VI) by replacing nitric acid with sodium nitrate solution

Abstract

Use of emulsion liquid membrane (ELM) extraction of uranium(VI) from lean streams containing nitric acid using tri-n-butyl phosphate (TBP) suffers from major drawback that TBP transports nitric acid to the strip phase, thereby reducing the driving force for extraction. This problem is completely eliminated by using near neutral sodium nitrate solution as the feed. The membrane phase is light liquid paraffin, containing TBP and the strip phase is aqueous sodium carbonate. Emulsion is stabilized using polymeric surfactant system, which exhibits low rate of leakage of the strip phase and no noticeable swelling of the emulsion. The key step is pH control of the continuous phase between 4.0 and 4.5 in order to neutralize sodium carbonate leaking from the emulsion phase. Effect of concentration of NaNO3 in the feed phase, Na2CO3 in the strip phase and volume ratio of the feed to the strip phase, on the rate of extraction of uranium(VI) and its enrichment, is studied. Using this process, it is possible to achieve nearly quantitative extraction of uranium(VI) with enrichment factor greater than 60. The superiority of the present process is established by comparing its performance with ELM extraction of uranium(VI) from nitric acid.