Recovery of sulfuric acid and iron from titanium dioxide waste acid by membrane electrolysis combined with selective electrodialysis

Abstract

The waste acid generated during the production of titanium dioxide contained a high proportion of ferrous ions. Comprehensive utilization of these waste acid involves the recovery of sulfuric acid and iron. However, traditional methods faced difficulty in attaining the desired outcome. Therefore, this study proposed a treatment process primarily based on membrane electrolysis. Initially, selective electrodialysis was employed to recover sulfuric acid from the waste acid. The effects of initial acid concentration, potential, and operating time on the performance of selective electrodialysis were investigated. Subsequently, a three-chamber membrane electrolysis method was utilized to oxidize Fe2+ to Fe3+ in the anode chamber and generate OH– in the cathode chamber. Both compounds were directed to the precipitation chamber through ion exchange membranes, resulting in the formation of iron hydroxide and the successful recovery of iron. The findings revealed that when the waste acid had a high initial concentration, it was recommended to operate at a higher potential. When treating 18 % of the waste acid, 77.5 % of the sulfuric acid can be recovered while 78 % of the ferrous ions were retained. As the acidity decreased, the potential could be reduced, resulting in a higher recovery rate of sulfuric acid and retention rate of Fe2+. By using a current of 150 mA during membrane electrolysis and maintaining a pH of 2.4 in the precipitation chamber, a purity of 94 % iron hydroxide was achieved. The ion flux of the anion exchange membrane decreased by 19 % after 8 h of electrolysis. This reduction could be mitigated by cleaning the membrane with titanium dioxide waste acid with a pH of 0.4 for 30 min. This study is expected to introduce innovative ideas and methods for the efficient and high-purity recovery of resources from titanium dioxide waste acid.