Electrochemical response of mild steel in ferrous ion enriched and CO2 saturated solutions

•The influence of ferrous ion on CO2 corrosion was investigated.•Ferrous ion suppresses the cathodic reaction at the initial corrosion stage.•The adsorbed ferrous ions promote the formation of FeCO3 layer.•A ferrous ion adsorption triggered re-deposition mechanism was proposed.•The detailed mechanistic process during CO2 corrosion was clarified.

To elucidate the role of ferrous ion in CO2 corrosion, the electrochemical behavior of mild steel samples in CO2-saturated brine solutions with various concentrations of ferrous ion were systematically investigated. An apparent inhibition effect was observed with increasing the concentration of ferrous ion and the immersion times. Ferrous ion would initially suppress the cathodic reaction activity by surface adsorption, and then promote the formation of corrosion product layers. A ferrous ion adsorption triggered re-deposition mechanism was proposed to explain the nucleation of FeCO3 layer during CO2 corrosion. Finally, a mechanistic process of CO2 corrosion was clearly presented.