A new approach to increasing the efficiency of low-pH Fe-electrocoagulation applications

摘要

Incomplete oxidation of Fe(Ⅱ) species released from the anode to Fe(Ⅲ) may impede iron electrocoag-ulation processes conducted under low dissolved oxygen and/or pH < 7 conditions, accompanied by the typically high buffering capacity of wastewater. This paper introduces a new approach to overcome this drawback by applying a second electrochemical cell (Ti/RuCb anode and Ti cathode) to be operated in parallel to the electrocoagulation cell. The second unit oxidizes Ch ions invariably present in the water to HOCI, which is capable of oxidizing Fe(II) species at a high rate, irrespective of pH or C_(2(eq)) concentration. An electrolytic cell with a Ti/RuO_2 anode and Ti cathode was shown to successively oaqperate in parallel to a sacrificial electrocoagulation cell (Fe anode and Ti cathode) to attain complete Fe(Ⅱ) conversion to Fe(III) under low-pH conditions, in which, in the absence of the 2nd cell, unwanted Fe(Ⅱ) species would have dominated the dissolved iron species. Current efficiency for Cl2 production was 12.4% and 45.7% at 200 and 1000mg Cl/l, respectively. Under three practical conditions (pH 6,[Cl~-]-200mg/l; pH 6, @@[Cl~-]-400mg/l; pH 5, [Cl~-]-600mg/l) the power demand of the combined system was 25.29, 12.7 and 8.1 kWh/kg Fe(Ⅲ)~(produced), respectively, suggesting that the presented approach is competitive at [Cl~-]>~600mg/l.