Toxic Metal Removal from Electroplating Wastewater Using Silylated Silica Gel

摘要

A preliminary study was undertaken to evaluate the usefulness of silylated silica gel in removing toxic metals from electroplating wastewater. A number of complexing and chelating systems immobilized on silica gel are available. Most involve relatively complicated syntheses, produce materials that are not stable at room temperature for long periods of time, or have very low metal removal capacities. Samples of material prepared in the laboratory could remove 22-24 milligrams of copper per gram of silica gel. Small-scale column studies using samples of electroplating wastewater showed that levels of cadmium, chromium, copper, nickel and zinc could be reduced significantly. Cost estimates based on the coating system used in this study show that 12.4 cents worth of silane are required to remove one gram of copper. Theoretically, the costs could be reduced to 5.2 cents per gram of copper removed. Metals removed on immobilized diamine can be recovered by stripping the silica gel column with strong oxidizing acid. The diamine coating can be replaced by treating the silica gel with additional silane. The stability, ease of preparation, and ability to recover metals make immobilized diamine a useful system for electroplating wastewater treatment.