Effect of various dissolved species on anaerobic iron corrosion
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Iron corrosion is an extremely complicated process because numerous factors such as pH, DO, temperature, inhibitor, and other various constituents in water can exert a controlling influence. The economic importance of problems that are caused by corrosion has been recognized. Therefore, the necessity of better understanding corrosion phenomenon is apparent. The effect of phosphorus, especially in oxidation states different than phosphate (+V) (e.g., PO3-3, PO2-3 and PH3 gas), on anaerobic iron corrosion was examined. Tests were conducted at pH 3, 7, and 10- 11 in a solution of 10-3 M NaCl. There was not a significant catalytic effect of phosphorus species on anaerobic iron corrosion. Higher levels of PH3 did markedly increase H2 evolution, consistent with observations of other researchers, but it is possibly due to oxidation of PH3 by iron surfaces with production of H2. Various constituents were also tested for iron corrosion in anaerobic solution [Al3+ (soluble), Al(OH)3, Cu2+, Si(OH)4, Boron, NOM, and sulfide] at pH pH 3, 7, and 10-11. None of these appeared to inhibit corrosion compared to a control. At pH 7, soluble Al3+ and Cu2+ in solution led to much higher production of H2 relative to a control. Phosphorus species had little impact on iron corrosion rates in the presence of sulfides (198 mg/L as S2-). In much of the research, recovery of H2 in the headspace was much lower than was predicated based on classic equations. This implies that some other, and as yet unappreciated, reactions are occurring in this system. However, in other instances the recovery of hydrogen was consistent with classical theory. Future work should examine the circumstances in which agreements and disagreements with classic theory occur.
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