Electrochemical regeneration of Fe2+ in Fenton oxidation processes

This study is to establish optimal conditions for the minimization of iron sludge produced in Fenton oxidation processes by electro-regenerating Fe2+ with constant potential (CPM) or constant current mode (CCM). Results indicate that the optimal cathodic potential for Fe2+ regeneration is -0.1 V vs. the saturated calomel electrode (SCE) in terms of current efficiency. Keeping the initial Fe3+ concentration ([Fe3+](0)) constant, the average current density produced at -0.1 V vs. SCE (CPM) is approximately equal to the optimal current density applied in the CCM. The suitable pH range is below the pH value determined by Fe3+ hydrolysis. As expected, increasing cathode surface area and solution temperature notably increases Fe2+ regeneration rate. At the optimal potential, the average current density increases linearly with [Fe3+](0), exhibiting a slope of 8.48 x 10(-3) (A/m(2))(mg/L)(-1). The average current efficiency varies with [Fe3+](0), e.g., 75% and 96-98% at 100 and greater than or equal to 500mg/L [Fe3+](0), respectively. Once reaching 75% of Fe2+ regeneration capacity, further regeneration becomes difficult due to Fe3+ mass transfer limitation. Fe2+ can also be effectively regenerated by dissolving iron sludge at low pH (usually less than or equal to 1). The unit energy consumption is 2.0-3.0 kW h per kg Fe2+ regenerated. (C) 2003 Elsevier Science Ltd. All rights reserved.