Electrochemical reduction of nitrates and nitrites in alkaline media in the presence of hexavalent chromium

Abstract

Electrochemical reduction of nitrates and nitrites in alkaline media at constant current is rendered inoperable in the presence of hexavalent chromate. Even at chromate concentrations as low as 9mgdm−3, the chromium hydroxide film, formed by the reduction of chromate, interferes with the reduction of nitrate and nitrite. We show that reversing the polarity of the electrodes at constant time intervals minimizes the adverse effects of the chromium hydroxide film, enabling the electrochemical reduction of nitrates and nitrites to proceed efficiently. The optimum current and reversal time are coupled through an optimum charge density of 625Ccm−2 per cycle. We also demonstrate through long-term studies that the reversal technique can be operated on a continuous basis.