Scrap iron packed in a Ti mesh cage as a sacrificial anode for electrochemical Cr(VI) reduction to treat electroplating wastewater

A novel sacrificial anode comprised of scrap iron packed inside a cage made of titanium mesh was developed for Cr(VI) reduction. With electric currents applied, the surface passivation of scrap iron electrode could be avoided. Due to the large surface area with open structures provided, the applied current densities (1.18–3.54 mA/cm²) were low, resulting in low operating voltage and energy consumption. Complete Cr(VI) removal was achieved with electric currents applied, whereas only 20% of the Cr(VI) was removed without electricity. Direct Cr(VI) reduction on the iron surface was a dominant mechanism for the system operated at low (0.25 A) or no current. Acidic pH levels were more effective in Cr(VI) removal, due to more adsorption of Cr(VI) onto the precipitated Fe hydroxide. The trend in total Cr removal was almost the same as that of Cr(VI) removal, but time required to complete total Cr removal was extended. With intermittent electricity supply at a high electric current intensity, the energy consumption of the system was more efficient. Using scrap iron as a sacrificial anode under the intermittent current condition can save 72–77% of the total operational costs required by the conventional plate electrode.