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

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, the chromium hydroxide ®lm, 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 e€ects of the chromium hydroxide ®lm, enabling the electrochemical reduction of nitrates and nitrites to proceed eciently. The optimum current and reversal time are coupled through an optimum charge density of 625C cm per cycle. We also demonstrate through long-term studies that the reversal technique can be operated on a continuous basis.