Understanding chromate reaction kinetics with corroding iron media using Tafel analysis and electrochemical impedance spectroscopy.

The kinetics of chromate removal from contaminated water by zerovalent iron media are not well understood. This study investigated the reactions occurring on iron surfaces in chromate solutions in order to understand the removal kinetics and to assess the long-term ability of zerovalent iron for removing Cr(VI) from contaminated water. Tafel polarization analysis and electrochemical impedance spectroscopy were used to determine the corrosion rates and charge-transfer resistances associated with Cr(VI) removal by iron wires suspended in electrolyte solutions with initial Cr(VI) concentrations of 10 000 μg/L. The condition of the iron surfaces at the time of their exposure to chromate determined the effectiveness of the iron for chromate removal. Both iron coated with a water-formed oxide and initially oxide-free iron were effective for chromate removal. However, iron coated with an air-formed oxide was an order of magnitude less effective for removing soluble chromium. Although iron with the air-formed oxi...