APPLICATION OF STARCH XANTHATES FOR CADMIUM REMOVAL - A COMPARATIVE-EVALUATION

Attempts to solve the problems of heavy metals removal and recovery from wastewaters have led to the development and application of several techniques. One of the techniques involves application of starch and cellulose-based products, especically xanthates. Both water-soluble and insoluble starch xanthate processes have been claimed to be successful based on the studies conducted with relatively simple wastewater. The major objectives of this study have been to evaluate the effectiveness of insoluble starch xanthate (ISX) for the removal of cadmium, study the effect of complexing agents/ligands on the interaction of cadmium with ISX and soluble starch xanthate (SSX), and to make overall comparison of ISX and SSX processes for cadmium removal. Both SSX and ISX can bring down the aqueous phase cadmium concentration to less that 1mg/liter (Indian effluent discharge standard) irrespective of the pH (in the range of 3 to 7), ionic strength, and initial cadmium concentration. The metal binding capacity of ISX is maximum in the pH range of 4 to 5 and is constant irrespective of equilibrium metal concentrations as well as different doses of ISX used at lower pH values (3 to 5). The metal uptake by ISX/SSX in the presence of EDTA is affected considerable. ISX shows higher uptake of cadmium in the presence of EDTA as compared to SSX. The insoluble xanthate process appears to have an edge over soluble xanthate process in terms of metal removal capacity, reliability, and ease of operation, particularly for cadmium.