Investigation of electrode passivation during electrocoagulation treatment with aluminum electrodes for high silica content produced water

Abstract

One of the main challenges for the implementation of electrocoagulation (EC) in water treatment are fouling and passivation of the electrodes, especially for applications with high contaminant concentrations. For the first time, we investigated in this study the process of fouling mitigation by polarity reversal during the EC treatment of boiler blowdown water from oil-sands produced water, characterized by high silica concentrations (0.5–4 g L−1). This effluent is typically obtained from an evaporative desalination process in oil production industries. Potentiodynamic characterisation was used to study the impact of passivation on the anode dissolution. Although a charge loading of 4,800 C L−1 was found to remove about 98% of silica from a 1 L batch of 4 g L−1 Si solution, fouling reduced the performance significantly to about 40% in consecutive cycles of direct current EC (DC-EC) treatment. Periodic polarity reversal (PR) was found to reduce the amount of electrode fouling. Decreasing the polarity period from 60 to 10 s led to the formation of a soft powdery fouling layer that was easily removed from the electrodes. In contrast, with DC operation, a hard scale deposit was observed. The presence of organics in the field samples did not significantly affect the Si removal, and organics with high levels of oxygen and sulfate groups were preferentially removed. Detailed electrochemical and economic investigations suggest that the process operating at 85 °C achieve 95% silica removal (from an initial concentration of 481 mg L−1) with an electrical energy requirement of 0.52 kWh m−3, based on a charge loading of 1,200 C L−1, an inter-electrode gap of 1.8 cm and a current density of 16 mA cm−2.

Mechanistic Insight into Electrode Processes by Operando Visualization of Interfacial pH Using Fluorescent Nanosensors

“…Super-Faradaic efficiencies for electrocoagulation using Al electrodes are known to occur due to non-Faradaic (chemical) Al dissolution at the cathode. 37 The dissolution of Al occurs at highly alkaline and acidic pH while its passivation window occurs between pH of 4 and 8.5. At the cathode surface, the average interfacial pH was >11 and approximately around pH 9 in SPW and FPW, respectively, favoring more rapid non-Faradaic Al dissolution in SPW that is consistent with the observed Faradaic efficiencies.…”

“…The difference in the Faradaic efficiency between the two systems could also be explained by the amphoteric nature of aluminum and the pronounced fouling in FPW. Super-Faradaic efficiencies for electrocoagulation using Al electrodes are known to occur due to non-Faradaic (chemical) Al dissolution at the cathode . The dissolution of Al occurs at highly alkaline and acidic pH while its passivation window occurs between pH of 4 and 8.5.…”

A sustainable system for decontamination of cephalexin antibiotic using electrocoagulation technology and response surface methodology

“…An oxidation reaction takes place at the anode surface (red surface), resulting in the dissolution of Al and the formation of metal cations such as Al 3+ and oxygen ions in solution, which bind to the hydroxide ions released by the reduction reaction from the cathode surface (black surface). The formed metal hydroxides form bridges between the particles leading to instability and displacement of suspended solids, and then the coagulation process occurs (Yasri et al, 2022).…”

Comparison Study on Sonodirect and Sonoalternate Current Electrocoagulation Process for Domestic Wastewater Treatment

“…Electrocoagulation offers great potential for removing soluble ionic species, a very important metal, from wastewater [ 22 ]. Electrocoagulation is one of the electrochemical processes in which soluble iron (Fe) and/or aluminum (Al) is used as the anode and/or cathode, and metal ions (Fe 2+ or Fe 3+ , Al 3+ ) are released due to anodic oxidation [ 23 , 24 ].…”