Concurrent Removal of Cyanide and Hexavalent Chromium from Aqueous Solution by Coagulation and Flocculation Processes

Cyanide and chromium present in the wastewater of various industries such as iron and steel، coal mining، and metal plating. High toxicity and their adverse effects on health of living organisms are the reasons for necessity of controlling the levels of these pollutants in the nature. The objective of this study was concurrent removal of cyanide and chromium from aqueous solution through coagulation and flocculation processes. This pilot-scale experimental study was carried out using a conventional Jar-test apparatus. During the precipitation process، the effect of pH، concentration of ferric chloride and settling time on the removal of pollutants from aqueous solutions were studied. Cyanide and chromium concentrations were determined respectively by colorimetry and flame atomic absorption spectroscopy methods. The results showed that respective removal efficiencies for cyanide and chromiumare 38 and 93% at the optimum conditions of pH=7، FeCl3 concentration of 10 mg/l، and settling time of >60 minutes. Moreover، no significant changes were observed in removal efficiencies when settling time increased to more than 60 minutes. Although، chemical precipitation method was an appropriate option for chromium removal، however، it did not work well in removing cyanide. Thus، considering limitations on effluent discharge for these pollutants، it is recommended to apply this method in conjunction with other processes such as Fenton in order to enhance the process efficiency.