Significantly improving trace thallium removal from surface waters during coagulation enhanced by nanosized manganese dioxide.

Thallium (Tl) is an element of high toxicity and significant accumulation in human body. There is an urgent need for the development of appropriate strategies for trace Tl removal in drinking water treatment plants. In this study, the efficiency and mechanism of trace Tl (0.5 μg/L) removal by conventional coagulation enhanced by nanosized manganese dioxide (nMnO) were explored in simulated water and two representative surface waters (a river water and a reservoir water obtained from Northeast China). Experimental results showed that nMnO significantly improve Tl(I) removal from selected waters. The removal efficiency was dramatically higher in the simulated water, demonstrating by less than 0.1 μg/L Tl residual. The enhancement of trace Tl removal in the surface waters decreased to a certain extent. Both adjusting water pH to alkaline condition and preoxidation of Tl(I) to Tl(III) benefit trace Tl removal from surface waters. Data also indicated that competitive cation of Ca decreased the efficiency of trace Tl removal, resulting from the reduction of Tl adsorption on nMnO. Humic acid could largely low Tl removal efficiency during nMnO enhanced coagulation processes. Trace elemental Tl firstly adsorbed on nMnO and then removed accompanying with nMnO settling. The information obtained in the present study may provide a potential strategy for drinking water treatment plants threatened by trace Tl.