Evaluation of the solvent extraction organic phase in a uranium extraction plant

Abstract

Using kerosene as an aromatic organic diluent in the liquid–liquid separation process for the extraction of uranium in the solvent extraction section of the AngloGold Ashanti South Uranium Plant near the town of Orkney in South Africa, incurs a multitude of safety, health and environmental problems. A possible solution may be to replace the currently used aromatic–based organic diluent with an aliphatic–based organic diluent. A range of aliphatic organic diluents were tested to determine the extraction efficiency of these alternative diluents, if they were to be applied to the process currently implemented by the AngloGold Ashanti South Uranium Plant. The aliphatic organic diluents under investigation were: Biodiesel-B–100 Shellsol D70 Sasol Wax SSX 150 Sasol Wax SSX 210 The aliphatic diluent yielding the highest uranium extraction efficiency, and having the most desirable physical characteristics, was Sasol Wax SSX 210. Sasol Wax SSX 210 was selected to replace kerosene as the diluent in the solvent composition to conduct the next phase of the study. The solvent’s composition was then optimised to obtain a desirable solvent make–up containing the newly chosen aliphatic diluent, third–phase inhibitor and tertiary alkyl amine. The most favourable solvent composition was found to be; 5 vol.% Alamine 336 with 2 vol.% isodecanol and 93 vol.% SSX 210. A third parameter, pH, was identified as an influencing factor on the overall efficiency of the process. A theoretical explanation for the influence that pH has on the process, confirmed by an experimental analysis, was examined to determine which pH characteristics contributed to the efficiency of the extraction process. A final indication of the success of the newly implemented aliphatic solvent was determined via a precipitation simulation. The structure of crystals precipitated from the loaded strip liquor (OK liquor) was evaluated to ensure that the required product would adhere to product specifications.