Treatment of trace thallium in contaminated source waters by ferrate pre-oxidation and poly aluminium chloride coagulation

Abstract

Thallium (Tl) was released into the environment through growing human activities, and removing trace Tl from polluted source water is a severe challenge. This work demonstrated that by combining K2FeO4 pre-oxidation with poly aluminum chloride (PAC) coagulation, removal efficiency of trace Tl [including Tl(I) and Tl (III)] in source waters could be substantially elevated. Compared with KMnO4 pre-oxidation, K2FeO4 pre-oxidation is more effective on Tl removal. Over 87% of total-Tl (initial concentration: 0.76 μg/L) was removed by 3 mg/L K2FeO4, and the residual Tl was below 0.1 μg/L. Compared with Tl(I), Tl(III) was easier to be removed by K2FeO4. Efficiency of K2FeO4 pre-oxidation combined with activated carbon adsorption on Tl removal is limited, while PAC coagulation could enhance the removal of Tl with K2FeO4 pre-oxidation. K2FeO4 + PAC treatment could effectively attenuate the leakage of Tl from settled floc as well. Effects of background constituents and operation procedures on Tl removal were investigated, and optimized operation procedures were explored. Our findings suggest that K2FeO4 pre-oxidation combined with PAC coagulation could be an effective method for the control of trace Tl in contaminated source water.