Manganese dioxide has been widely studied for heavy metals removal nowadays. This study investigated the impact of thiosulfate/permanganate (S2O32-/ Mn(VII)) molar ratio (0.1, 0.25, 0.375, 0.5, 2, 3) on the removal of Cd(II) by in situ formed manganese dioxide at different pH conditions (pH 5∼9). At pH 5, the removal of Cd(II) increased from7.8% to 95.6% as the S2O32-/ Mn(VII) ratio increased, which may be related to the amount of MnO2 formed and the bridging effect of Mn2+ between MnO2 and [Cd-(S2O32-)x] complex. At pH 6∼8, the removal of Cd(II) at around molar ratio of 0.375 (equivalent dose) was found to be the highest compared to the condition of insufficient or excessive S2O32-. As the oxidative ability of MnO2 gets weaker at higher pH, inadequate Mn2+ was produced from the reduction of MnO2 by S2O32- to perform the bridging effect. More than 91% of Cd(II) was removed at pH 9 with all S2O32-/ Mn(VII) molar ratio conditions, which could be ascribed to the combined effect of adsorption and formation of insoluble species of cadmium at alkaline condition. This work reveals the underlying mechanisms for the different influences of S2O32-/ Mn(VII) molar ratio on Cd(II) removal at the pH 5∼9, which has significant implications for engineering application.

Cd(II) removal by manganese dioxide formed in situ from permanganate by thiosulfate: Influence of permanganate: Thiosulfate molar ratio

253rd National Meeting (2017)

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