Selective and Efficient Ligandless Water-in-Oil Emulsion Liquid Membrane Transport of Thorium (IV) Ions

The present paper concerns on the selective and very efficient transport of thorium(IV) ions from aqueous solutions through an emulsion liquid membranes composed by paraffin and a surfactant, without carrier requirement. The influence of pH of the external aqueous phase, the surfactant concentration in the membrane phase, the type and concentration of the acid used in the receiving phase, the emulsification and mixing speed on the process efficiency were examined and discussed. The optimized conditions were: liquid paraffin as diluent, 5% surfactant (non-ionic polyamine surfactant span-80), emulsification rate 5250 rpm, 15 min of stirring at 750 rpm in the extraction step, pH 5, oil/aqueous ratio of 3 in emulsions and using 0.3 M solution of sulfuric acid as stripping phase. Under optimized experimental conditions, thorium ions were selectively and quantitatively transported from its mixture solution with lanthanides La(III), Sm(III), Eu(III) and Er(III). The concentration of thorium ions, in single component transport experiment, was measured spectrophotometrically using ArsenazoIII as indicator at 655 nm, and the analysis of metal ions in competitive experiments was performed by an ICP-OES instrument under recommended conditions provided by the instrument’s manufacturer.