Influence of flocculant polyacrylamide on concentration of titanium white waste acid by direct contact membrane distillation

Abstract

Effort has been made to investigate the concentration of titanium white waste acid (TWWA) by direct contact membrane distillation (DCMD) and the focus is the influence of polyacrylamide (PAM) on membrane wetting and fouling. It was found that the presence of PAM in feed reduced membrane flux and retarded wetting development, even though its level in feed of H 2 SO 4 solution was only 0.0002 wt%. The difference between the tests using pure water and neat PAM aqueous solution, respectively, as feed also indicated the above effect registered with PAM. AFM results showed that the addition of PAM in feed solution changed the membrane shell surface morphology. However, conclusive proof of the PAM existence in membrane cross-section and inner surface was not obtained, probably due to its low concentration in feed solution. Two approaches were tried to recover membrane flux. In comparison with operation w/o any treatment, HCl solution rinsing did not lead to obvious improvement in membrane flux recovery, while rinsing combined with gas purge has clearly delayed the degradation in acid concentration factor. Nevertheless, even the latter could not ensure long term stability. High tortuosity and low hydrophobicity of the membranes used were suggested as underlying causes and should be addressed in the future. Comparison of hollow fiber membrane performance in treating pure water (left) and 0.0002% PAM aqueous solution (right) by DCMD showed that PAM reduced membrane flux and retarded wetting development.