COMPARATIVE STUDY OF SOLVENT EXTRACTION PROCESSES FOR URANIUM RECOVERY FROM SALINE LIQUORS

摘要

Conventional urariium recovery by tertiary amine based solvent extraction (SX) is known to be adversely affected by the presence of chloride in feed solutions. There are a number of alternative processes proposed to overcome this problem which are based on the following reagents: i. Mixed reagent di-2-ethylhexylphosphoric acid (DEHPA) and Alamine 336; ii. Mixed reagent DEHPA and tetradecyl(trihexyl)phosphonium chloride (Cyphos IL-101); iii. Single reagent based on bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272); and iv. Single reagent based on tri-hexyl and tri-octyl phosphine oxides (TOPO or Cyanex 923). The DEHPA/Alamine 336 system relies predominantly on a cation exchange mechanism for uranium extraction which is not sensitive to chloride concentration [1]. The mixed reagent is antagonistic with respect to ferric ion extraction. Stripping is carried out with sodium carbonate. This solvent mixture has been applied on an industrial scale at Honeymoon, in South Australia [2]. A DEHPA/ Cyphos IL-101 mixed reagent has been proposed in a study by CSIRO [3]. The solvent extracts uranium from acidic liquors containing chloride and is selective with respect to ferric ion. Stripping with sulfuric acid has been suggested. A process based on Cyanex 272 has been proposed by ANSTO [4]. The reagent extracts uranium via a cation exchange mechanism, is selective with respect to ferric and strips with sulfuric acid. Finally a patent has recently been filed referencing the use of phosphine oxides, which extract uranium from chloride solutions via a solvating mechanism. Stripping with ammonium sulfate is proposed [5]. In this paper we present results of a comparative study undertaken on these four reagents systems, discussing the various process related advantages and disadvantages with particular emphasis on loading capacity and sulfuric acid stripping efficiencies.