EXTRACTION OF CHROMIUM(VI) FROM ACID-SOLUTIONS BY TRI-ISO-OCTYLAMINE

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(VI) as Cr2O72- 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.