Cyanide removal from industrial wastewaters using gas membranes

Results are presented for the removal of cyanide from four industrial wastewaters using hollow fiber gas membranes in a pilot plant. The plant was operated in batch mode using 1000 L of feed solution. The plant contained 10 hollow fiber modules with total membrane surface area of 180 m2. The strip stream consisted of 10% NaOH. The overall mass transfer coefficient for cyanide has been determined experimentally and found to agree well with predictions using empirical correlations. Both the feed and membrane mass transfer coefficients contribute to the overall mass transfer coefficient. The strip side mass transfer coefficient may be ignored. Real wastewaters often contain other volatile species. These volatile species will also transfer to the strip solution. If the volatile species does not react with the strip stream, all three individual mass transfer coefficients contribute to the overall mass transfer coefficient. Good agreement between the experientially determined overall mass transfer coefficient and the predicted values is obtained for other volatile species. The osmolarity of a wastewater may be different to that of the strip solution. Consequently, water vapor transport due to osmotic distillation will occur from the lower to higher osmolarity solution. The effects of osmotic distillation should be considered when sizing the feed and strip tanks.