Diffusion dialysis using a series of anion exchange membranes was employed to recover HCI acid from the waste acid solution. Effects of flow rate, flow rate ratio of water to feed, and Fe ion concentration on the recovery of HCI were investigated. It was found that the now rate ratio was an important factor in the diffusion dialysis operation, and the recovered HCI concentration and Fe ion concentration in diffusate decreased significantly with the change of flow rate ratio from 0.4 to 1.7. In addition, the higher the Fe ion concentration in the feed, the higher the Fe leakage in the recovered acid solution. The HCI recovery efficiency was influenced not only by the recovered acid concentration, but also the outlet now rate. While using the actual pot galvanizing waste HCI solution with the co-existence of 2.70 mol/L of Fe and 0.07 mol/L of Zn ions, over 88% HCI recovery efficiency could be achieved and Fe leakage was within the range of 11-23%. However. over 56% of Zn leakage was found due to the formation of negative Zn complexes in solution, which was unfavorable for the recovered acid reuse. (C) 2008 Elsevier B.V. All rights reserved.