Improvement of the stripping characteristics of Fe(III) utilizing a mixture of di (2-ethylhexyl) phosphoric acid and tri-n-butyl phosphate

It has long been known that the stripping of Fe(III) extracted with D2EHPA is difficult since a high concentration of HCl is required. To overcome this difficulty, the usage of a mixture of D2EHPA-TBP-kerosene in the stripping of Fe(III) was investigated. It was found that this mixture is effective in the stripping of Fe(III), and that less concentrated acid solution is required as a stripping agent. Batch-type extraction or stripping experiments were conducted to simulate multi-stage counter-current extraction or stripping. It was found that use of the mixture in a three-stage operation can easily yield above 98% extraction or stripping. To examine the role of TBP in the improvement of Fe(III) stripping from the mixed solvent, the extraction of HCl with TBP and the spectrum of Fe(III) loaded organic phases were investigated. The experimental results indicated that Fe(III) exchange reaction between Fe(III)-loaded D2EHPA and HCl-loaded TBP proceeds in the mixed solvent. A possible mechanism for Fe(III) stripping from the mixed solvent, involving the reaction between the Fe(III)-D2EHPA complex and TBP in the organic phase, has been proposed.