Iron electrocoagulation for kinetic hydrate inhibitor removal

Electrocoagulation, through the oxidation of a sacrificial Fe anode to release coagulants in situ, is an emerging electrochemical technology for wastewater treatment with the effective trapping and ease of separation of pollutants. In this work, the effects of some parameters (i.e., initial pH, supporting electrolyte, and current density) on the electrochemical dissolution of iron electrodes have been studied. The effects of electrolyte composition, pH, and current density on iron dissolution were systematically correlated with coagulation performance, providing mechanistic insight into iron-driven removal of kinetic hydrate inhibitors.The results indicated that iron dissolution was purely electrochemical oxidation of Fe into Fe 2+ fitting with Faraday’s law. In aerated conditions, Fe 2+ is oxidized into Fe 3+ , which forms hydroxo-iron complexes. Under neutral and alkaline conditions, hydroxide ions produced at the cathode react with dissolved iron ions to form insoluble hydroxo-iron species. In addition, potentiodynamic polarization results indicated that the formation of a passive layer on the iron anode gradually reduces the rate of iron dissolution, limiting the continuous release of iron into the solution. The nature of the supporting electrolyte had a significant influence on the corrosion and pitting potentials. Iron dissolution was shown to be higher in presence of sodium chloride (NaCl) when pitting corrosion takes place, whilst the dissolution of iron was inhibited in the presence of sulfate ions (Na 2 SO 4 ) and phosphate ions (NaH 2 PO 4 ). Furthermore, electrocoagulation using iron electrodes (Fe-electrocoagulation) was used to remove kinetic hydrate inhibitor (KHI, poly(N-vinylcaprolactam) from water. Unlike previous studies that primarily evaluated electrocoagulation through overall pollutant removal, this study linked the electrochemical dissolution and passivation behavior of the iron anode with the generation of hydroxo-iron species responsible for KHI removal. The effects of current density, initial concentration of KHI, and initial pH on KHI removal by Fe-electrocoagulation have been investigated. The results showed that Fe-electrocoagulation was successful in removing up to 95% KHI in 0.1 M NaCl aqueous solutions. The total organic carbon (TOC) analysis confirmed that KHI removal by Fe-electrocoagulation depends largely on the current density and pH conditions. The highest TOC removal was obtained at a low current density (< 5 mA cm − 2 ) in acidic conditions.