Chromic acid recovery from waste acid solution by an ion exchange process: equilibrium and column ion exchange modeling

A four-step ion exchange process for chromic acid recovery from waste acid solution was proposed in the present work. Strong acid anionic (OH-type) ion exchange resin was used in the first step to capture chromic acid (H2CrO4) which was converted to sodium chromate (Na2CrO4) by sodium hydroxide (NaOH) solution in the second step. Sodium chromate was converted back to chromic acid using strong base cationic (H-type) ion exchange resin in the third step and in the fourth step, the exhausted ion exchange resin was regenerated by hydrochloric acid (HCl) solutions. Batch and column experimental tests were conducted to provide data for theoretical modeling and to verify the system performance of the recovery process. Results of batch equilibrium tests indicated that Freundlich isotherm describes well both chromic acid and sodium chromate adsorption equilibrium. A theoretical column model adopted in this work was found to describe well the ion exchange breakthrough characteristics. The four-step process was proved to be efficient and was capable of providing continuous chromic acid recovery operation. (C) 2002 Elsevier Science B.V. All rights reserved.