Extraction of chromium(vi) from acid solutions by tri-iso-octylamine

Triisooctylamine (TIOA) was used to extract Cr(VI) from several acid solutions of HC1, HBr, HN0₃ and HCI0₄. The results were divided into two groups according to the acid solutions used: HC1 and HBr, or HN0₃ and HC10₄. 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 HC1 or HBr by TIOA. It was found that TIOA extracts Cr(VI) as Cr₂OU from HC10₄ solution and as HCr0₄ from HC1, HBr, and NH0₃ solutions. An extraction model which could explain the distribution equilibria was proposed, and the extraction constants were then determined.