Study On Treatment For High Concentration Cyanide-contained Wastewater

The cyanide-containing wastewater mainly derives from different process industries, such as those waters from the processing of precious metals resource, coal conversion or coking effluents, electroplating waste, chemical engineering and meter industries. It is very important to treat this kind of wastewater because of the redundant toxic contaminants it contains. The recent advance in the treatment methods for cyanide-contained wastewater was reviewed in the paper. The cyanide-containing wastewater has varied characteristics, therefore, different processing and treatment strategies should depend on the source and character of the waters. Complexing precipitation method for cyanide-containing wastewater has many advantages, however, the contents of cyanide of treated water is higher than the highest permission discharging contents of cyanide. We analyzed the ferrous ferrocyanide's and ferric ferrocyanide's balance concentration in different pH. It showed that it is difficult to make the concentration of total cyanide under permission discharging contents. But, it is possible to make the treated water by complexing precipitation have little ferrous ferrocyanide and ferric ferrocyanide. Then we easily use oxidation method making the water under permission discharging. The results of the experiments showed that the optimal conditions of complexing precipitation were: FeSO4 dosage 1.05 times of the theoretical value, aeration ror 20min and pH=6. Chlorine dioxide is a very activated oxidant. The results of the experiments showed that the optimal conditions of ClO₂ oxidation process for complexing precipitation treated water were: stable chlorine dioxide is activated 10min, 1.313% activated stable chlorine dioxide dosage is 15mL/L wastewater, mix for 30min and pH=6. The concentration of total cyanide was under permission discharging contents after ClO₂ extensive oxidation. We used stable chlorine dioxide stabled by different stable reagent for treatment. It showed the reagent for stable had little effect for the cyanide-containing wastewater treatment. Complexing precipitation and chlorine dioxide are reacted by two steps. It is expensive in treatment process. We can make the process by one step. Two steps are reacted in the same pH. The ferrous ferrocyanide and ferric ferrocyanide are very stabled in water on pH equal to 6. The results of the experiments showed the concentration of total cyanide could be under permission discharging contents by affiliate ClO2 to wastewater followed Complexing precipitation. The optimal conditions of Complexing precipitation -ClO2 oxidation process was: FeSO4 dosage 1.05 times of the theoretical value, aeration for 20min and pH=6; followed, affiliate ClO2 to wastewater, chlorine dioxide dosage is 18mL/L wastewater, mix for 30min. The concentration of total cyanide was under permission discharging contents after treatment. This process is cheaper because it omitted the step of filtration before the treatment by ClO2.