Effects of pH on Cr-Fe interaction during Cr(VI) removal by metallic iron

In the present investigation, the effect of pH on Cr-Fe interactions has been studied by carrying out Cr(VI) removal utilising metallic iron from the dichromate solutions of pH 2 to 7 by batch shaking process. Since the presence of ferrous iron in the solution is mainly responsible for Cr(VI) reduction, solubility of iron from the metallic iron was also measured. The maximum Cr(VI) removal efficiency was found at pH 2 but pH 3 was considered to be a suitable solution condition for Cr(VI) removal due to the occurrence of a minimum level of iron in the treated solution. Chemical analysis of Cr(VI) reacted iron and treated dichromate solutions has indicated the reduction of Cr(VI) to Cr(III) at the metal surface itself at pH 2 and 3 and in the solution at pH 4 and above. A considerable decrease in chromium concentration on the iron surface in the pH range 4 - 7 as compared to pH 2 and 3 was also observed by EDXA analysis. These studies confirmed that after reduction, involvement of Cr(III) with Fe takes place at the metallic iron surface itself at pH 2 and 3 while it reduces with the rise of pH.