Mass transfer during membrane distillation treatment of wastewater from hot-dip galvanization

Hot-dip galvanized products are widely applied in many fields in China. The treatment of the wastewater containing acid and many metal ions from the hot-dip galvanizing industry is an important environmental issue. In this paper, we experimentally investigated the membrane distillation technique to treat the wastewater from the hot-dip galvanizing industry, and determined the factors that affect the membrane distillation performance. The transport behavior of multi-components (i.e. HCl and H2O) through the porous membranes was studied in detail. The results indicate that it is promising to use the air gap membrane distillation configuration to treat the wastewater and recover hydrochloric acid. The increase of the feed temperature leads to the increase of the permeate flux in general. The presence of FeCl2 and the acidity of the feed affects the acidity of the permeate. FeCl2 in the feed can enhance the acidity of the permeate significantly, especially when the acidity of the feed is low. The adding of 9.5 wt% FeCl2 in the feed can increase the acidity of the permeate by about 10 times when the acidity of the feed is 6 wt%. The overall metal ion (Fe2+) rejection ratio is higher than 99.99% by membrane distillation technique.