Amechanistic Investigation on the Removal of Cr(Ⅵ) Anion by Its Adsorptive-reductive Coupling Immobilization onto Siderite

A synthetic siderite mineral material was employed to explore the sorption isotherms and kinetics of Cr(Ⅵ), aiming to reveal the removal characteristics of siderite for aqueous chromate anion Cr(Ⅵ) from waters by its adsorptive-reductive coupling immobilization. Here, an emphasis was placed to investigate the effect of solution pH on the efficiency for Cr(Ⅵ) removal, then all the siderite samples before and after reacting with Cr(Ⅵ) were characterized and analyzed in-depth. The results showed that the reaction process for Cr(Ⅵ) removal by synthetic siderite were quite well fitted to the Langmuir adsorption isotherm model, and the removal kinetics just well followed the pseudo-second-order kinetic model. Cr(Ⅵ) can be rapidly reduced to Cr(Ⅲ) by Fe(Ⅱ) on siderite surface, but Cr(Ⅵ) oxidative ability is somewhat decreased as solution pH increases, thus leading to chromium removal rate to be decreased obviously at the higher pH. Fe(Ⅲ)-Cr(Ⅲ) hydroxide co-precipitation had formed on siderite surface, so that Cr(Ⅵ) anion could be effectively removed by siderite.