A Brief Review on Solvent Extraction of Uranium from Acidic Solutions

Uranium solvent extraction (SX) from aqueous acidic solutions is reviewed. First the uranium availability in earth as well as resources, mining and production reports is presented and followed by SX basic flowsheet and various important stages. Extraction, scrubbing, stripping and finally solvent equilibrium are presented in a flow-sheet form. The second half of the review discusses the various extractants used for uranium extraction and separation from acidic solutions. The extractants are divided in four types: 1) nitrogen-based extractants, 2) phosphorous-based extractants, 3) sulfur-based extractants, and 4) other extractants. Nitrogen-based extractants cover predominantly the amides and amines functional group containing extractants. The phosphorous-based extractants: tri-butyl-phosphate (TBP), di(2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexyl phosphonic acid mono-2-ethylhexyl (PC88A), tri-n-octyl-phosphine oxide (TOPO or Cyanex 923) and bis(2,4,4-trimethyl pentyl) phosphinic acid (Cyanex 272) are the most important members of this category. Sulfur-based extractants mainly sulfoxides and other sulfur-containing extractants are discussed. Heterocyclic compounds encompass isoxazolones, pyrazolones, crown ethers and other available extractants. A compact summary of the literature on uranium SX processes as well as extraction efficiencies is given in table form.