Electrocoagulation using stainless steel anodes: Simultaneous removal of phosphates, Orange II and zinc ions

Two stainless steel anodes, AISI 420 and AISI 310, and pure iron were compared in an electrocoagulation study for the simultaneous removal of phosphates, Orange II and Zinc ions from a synthetic wastewater at a current density of 11.7 mA cm^-2 and a surface area to volume ratio of 19.4 m^-1. High removal efficiencies were observed with AISI 420 and pure iron, reaching values between 88% and 99%, while significantly lower values, approximately 30%, were obtained with AISI 310. The AISI 310 performed well in the removal of Zn²⁺ due to its removal as Zn(OH)₂. The variations in the performance of the steel anodes were attributed to the lower chromium content of the AISI 420, which gives less passive behaviour. This was supported using polarisation data, where a 10-fold increase in the corrosion current was obtained for AISI 420 compared to AISI 310. Furthermore, Cr(VI) was observed in the solution phase when AISI 310 was employed as the anode, illustrating the importance of the alloying concentrations. While rust particles were seen during the non-continuous use of the iron anode, they were not observed with the AISI 420 anode.