Electrochemical regeneration of Fe^2+ 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 Fe^2+ with constant potential (CPM) or constant current mode (CCM). Results indicate that the optimal cathodic potential for Fe^2+ regeneration is -0.1V vs. the saturated calomel electrode (SCE) in terms of current efficiency. Keeping the initial Fe^3+ concentration ([Fe^3+]0) constant, the average current density produced at -0.1V 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 Fe^3+ hydrolysis. As expected, increasing cathode surface area and solution temperature notably increases Fe^ 2+ regeneration rate. At the optimal potential, the average current density increases linearly with [Fe^3+]0, exhibiting a slope of 8.48×10^-3(A/m^2)(mg/L)-1. The average current efficiency varies with [Fe^3+]0, e.g., 75% and 96–98% at 100 and >= 500mg/L [Fe^3+]0, respectively. Once reaching 75% of Fe^2+ regeneration capacity, further regeneration becomes difficult due to Fe^3+ mass transfer limitation. Fe^2+ can also be effectively regenerated by dissolving iron sludge at low pH (usually <=1). The unit energy consumption is 2.0–3.0 kW h per kg Fe^2+ regenerated.