Electrochemical identification of higher oxides of manganese in corrosion relevant deposits formed by microorganisms

Certain cases of microbiologically influenced corrosion (MIC) in natural waters are attributed to the activity of manganese oxidizing microorganisms (MOMOs). These cases are typically related to stainless steel and are characterized by an anodic potential shift of the steel. This so-called ennoblement is attributed to microbiologically formed deposits containing manganese dioxide and related Mn(III,IV)-compounds. A method for the identification of such oxidizing compounds in the complex matrices of natural samples, often mixed with corrosion products, by directly assessing their electrochemical properties seems of interest. Cyclic voltammetry with carbon paste electrodes with electrolytic binder in an alkaline medium was evaluated for this purpose. The results obtained with samples from 5 different locations and of laboratory cultures are presented. Samples of typically less than 1 mg are required and semiquantitative information is received from the cathodic current peak during the reduction cycle. A subsequent anodic cycle provides redundant information due to reoxidation and aids in the interpretation of the voltammograms. The method may be considered as an additional electrochemical tool for the characterization of deposits in cases of MIC by MOMOs.