Effects of PH and Metal Cations on the Oxidation of as(III) by Pyrolusite

Abstract

In this study, the effects of pH and metal cations such as Mn(II) and Ca(II) on the oxidation of As(III) by pyrolusite were investigated. Our results showed that the oxidation of As(III) was significantly dependent on pH values. The oxidation rate increased with a decrease of pH from 4.0 to 6.0 or an increase of pH from 8.0 to 9.0, while be the lowest at pH 7.0. The removal of aqueous As(III) and the release of produced As(V) were inhibited when Mn(II) was simultaneously added into the system, which could be explained that added Mn(II) bounded to pyrolusite and consequently blocked the adsorption and oxidation of As(III). Higher concentration of Mn(II) lowered the oxidation of As(III) at both pH 5.83 and 7.82. The addition of Mn(II) caused a greater decrease in the oxidation rate of As(III) than did the addition of Ca(II). The lower oxidation rate of As(III) was observed with the higher concentration of Ca(II) at pH 5.83, while the trend was opposite at pH 8.72.