Experimental study of corrosion of two stainless steels during the oxidative bacterial dissolution of pyrite using mass loss and electrochemical techniques

Corrosion problems have been encountered in reactors used in pilot plants f or the development of different bacterial leaching (bioleaching) processes, A large part of this corrosion is attributable to bacterial activity, i.e. biocorrosion, and basic information is needed for a better understanding a nd control of this phenomenon, The bioleaching solution associated with the presence of bacteria is highly acidic and requires the use of highly corro sive-resistant steel. The selection of materials for the manufacture of ind ustrial bioleaching reactors is difficult and random. Consequently, it is n ow essential to study the behavior of selected stainless steels during biol eaching in order to determine their potential suitability for industrial us e. The main objective of the present study is to compare the respective res istance of two such steels to various types of corrosion and determine whic h of the steels is most appropriate for manufacturing reactors at an indust rial scale. The corrosive medium was a solution generated during the biolea ching of a cobaltiferous pyrite, where a bacterial population comprised of three species was used. Metal coupons and electrodes were made out of two g rades of stainless steel and their corrosion during bioleaching was monitor ed by methods based on the weight loss of the coupons and on the electroche mical behavior of the stainless steel electrodes. By combining the weight l oss and electrochemical results, it has been possible to show that (i) the two steels have a similar and satisfactory behavior, with a corrosion-erosi on rate of less than 25 mum/year, and (ii) samples left for more than 1 mon th in the medium are not affected by localized corrosion, thus confirming t he accelerated corrosion tests indicating the high resistance of the two st ainless steels to localized corrosion. (C) 2001 Elsevier Science B.V. All r ights reserved.