REMOVAL OF CADMIUM FROM WATERS

Abstract

Cadmium in waste streams is present as cadmium ion (cd++) and/or complexed cadmium salt. High concen-tration of cadmium is reported in plating wastes and mine drainage. The cadmium level in various waste streams ranges from 15-25,000 mg/1. Such waste waters, if not managed properly are likely to contaminate sur-face water as well as ground water. Water used for domestic and 'irrigation purposes should not have cadmium more than .01 and .05 mg/l respectively. The removal of cadmium from water and waste water is essential. The soluble cadmium salts from waste water i,re either precipitated as hydroxides (pH 8-10) or sulfides (pH 6-6.5) . The precipl,tation techniques are generally of low efficiencies when cadmium salts are present in low concentration. Also, the processes reported in literature require an addi- tional unit to adjust the pH. Therefore, it necessitated to develop an alternate method to remove cadmium ions from water. Keeping this in view, the present project was undertaken to explore the possibility of using materials like saw dust, charcoal etc. as complexing and adsorbing agents to remove cadmium ions from water. Synthetic wastes containing cadmium chloride (concentration range0.5 mg/1-10 mg/1) were prepared. Bench Scale experiments were conducted with saw dust, sulfonated saw dust, charcoal and activated carbon. The activated carbon was used to compare the results with other absorbents. The kinetics and thermodynamics of all the absorbents have been studied. Equilibrium is attained in 15 min with saw dust and sulfonated saw dust, in 30 min with a--tivated Carbon, and in 60 min with Charcoal (untreated) respectively.