Effect of ferrous ion on sulfate-reducing bacteria influenced corrosion of mild steel

In this investigation, we analyse the corrosion behavior of mild steel immersed in two inoculated cultures with different ferrous concentration-0 mg/L and 30 mg/L. The optical microscope and electrochemical impedance spectroscopy (EIS) were used to obtain the photos and EIS data of mild steel with different immersing time. The Focus Ion Beam (FIB) was used to observe and cut the corrosion products of mild steel. The EDS was used to analysze the composition of corrosion products. The EIS data was analyzed with equivalent circuit. According to The result of the analysis, the resistance of the biofilm formed on the surface of mild steel immersed in the culture without ferrous ion (sample I) was higher than that immersed in the culture with ferrous ion (sample II). On the contrary, the capacitivity of the biofilm formed on the surface of sample I was lower than that of sample II. From the FIB photos we can learn that compared with sample I, the amount of sticking SRB on the surface of sample II was greater, the biofilm formed on sample II was thicker and was more loose, the corrosion of sample II was more serious. With respect to the EDS result, there is S in the biofilm formed on sample II. To sum up the above, the result of EIS dovetailed with the results of optical microscope, FIB and EDS. Ferrous can speed up the SRB influenced corrosion of mild steel.