Electrochemical preparation and characterization of a new configuration SnO2 anode and its application for treating petroleum refinery wastewater

Abstract

In the present work, the feasibility of removing chemical oxygen demand (COD) from petroleum refiner wastewater (PRW) was examined through an anodic oxidation process using a SnO2-copper substrate anode in a prototype tubular batch electrochemical reactor. The SnO2 anode was prepared by cathodic deposition from a nitrate solution and characterized by techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). Effects of current density, [Sn2+]/[HNO3] molar ratio, and time on the properties of the prepared anode were investigated. The XRD results showed that main peaks corresponded to deposition of tetragonal SnO2. Besides, broad peeks were observed indicating that the deposits have a lower degree of crystallinity. The results confirmed that increasing current density higher than 10 mA/cm2 results in formation of a mixture of SnO2 and Sn deposits. Additionally, the results proved that [Sn2+]/[HNO3] molar ratio has the main effect on the electrodeposition process, where keeping this ratio lower than 0.33 is recommended to ensure pure SnO2 film deposition. The best conditions for electrodeposition of SnO2 as a compact film on a copper substrate were a current density of 10 mA/cm2, [Sn2+] of 25 mM, [HNO3] of 125 mM to make a molar ratio of 0.2, and 30 min to confirm the formation of deposits without cracks and having an atomic percent (Sn/O) of 20.6/65. The application of the prepared anode for removing of COD from PRW confirmed a good performance with a removal efficiency of 79 % at current density of 12 mA/cm2, pH of 7.8, and operating time of 150 min in which an energy consumption of 9.93 kWh/kg COD was required. The degradation of COD using the SnO2 electrode was found to obey a pseudo first-order kinetic. The application of anodic oxidation using the new configuration of the SnO2 anode can be considered an eco-friendly process for treating wastewater, featuring easy scale-up to an industrial scale at high removal efficiency and lower cost.