Extraction of Chromium(VI) from Acid Solutions by Tri-Iso-Octylamine

Abstract

Triisooctylamine (TIOA) was used to extract Cr(VI) from several acid solutions of HCl, HBr, HNO₃ and HClO₄. The results were divided into two groups according to the acid solutions used: HCl and HBr, or HNO₃ and HClO₄. Chromium(VI) is extracted according to an ion-exchange reaction which has been found for amine-Cr(VI) extraction systems. However, the ion-exchange mechanism holds only at low acidities. At high acidities, Cr(VI) is coextracted with HCl or HBr by TIOA.
It was found that TIOA extracts Cr(Vl) as Cr₂O₇^2– from HClO₄ solution and as HCrO₄^– from HCl, HBr, and NHO₃ solutions. An extraction model which could explain the distribution equilibria was proposed, and the extraction constants were then determined.