Influences of humic acid, bicarbonate and hardness on Cr(VI) removal by zero-valent iron in batch experiments

The hexavalent chromium (Cr(VI)) removal by zero-valent iron (Fe⁰) was investigated under various groundwater geochemistry conditions though batch experiments. The results showed that the collective influences of humic acid, HCO₃^-, and Ca²⁺ on the reactivity of zero-valent iron for Cr(VI) removal were different from their individual impacts. The sole presence of humic acid did not show a significant impact to Cr(VI) reduction, while HCO₃^- exerted a great buffering effect on the reaction. When humic acid and Ca²⁺ co-present in the solution, the pH increased slowly but Cr(VI) removed rapidly. In contrast, pH remained at below 8.0 and 7.8 and Cr(VI) removal rate were 97.77% and 98.82% at the 60 mins in solutions containing 2 mM and 6 mM of HCO₃^-, respectively. These experimental results were also demonstrated by a pseudo-first-order model followed.