Recyclable polymer-based nano-hydrous manganese dioxide for highly efficient Tl(I) removal from water

Tl(I) in water even at a trace level is fatal to human beings and the ecosystem. Here we fabricated a new polymer-supported nanocomposite (HMO-001) for efficient Tl(I) removal by encapsulating nanosized hydrous manganese dioxide (HMO) within a polystyrene cation exchanger (D-001). The resultant HMO-001 exhibited more preferable removal of Tl(I) than D-001 and IRC-748, an iminodiacetic chelating polymer, particularly in the presence of competing Ca(II) ions at greater levels in solution. Such preference was ascribed to the Donnan membrane effect caused by D-001 as well as the specific interaction between Tl(I) and HMO. The adsorbed Tl(I) was partially oxidized into insoluble Tl(III) by HMO at acidic pH, while negligible oxidation was observed at circumneutral pH. The exhausted HMO-001 was amenable to efficient regeneration by binary NaOH-NaClO solution for at least 10-cycle batch runs without any significant capacity loss. Fixed-bed column test of Tl(I)-contained industrial effluent and natural water further validated that Tl(I) retention on HMO-001 resulted in a conspicuous concentration drop from 1.3 mg/L to a value lower than 0.14 mg/L (maximum concentration level for industrial effluent regulated by US EPA) and from 1-4 mu g/L to a value lower than 0.1 mu g/L (drinking water standard regulated by China Health Ministry), respectively.