Attachment of Leptospirillum ferrooxidans on pyrite monitored by electrochemical impedance spectroscopy

IGNACIO GONZALEZ; EDUARDO CORTON; ALBERT SAAVEDRA

Freiberg

Workshop; International Biohydrometallurgy Symposium (IBS 2017); 2017

Dechema

The aim of this work was to evaluate the use of electrochemical impedance spectroscopy (EIS) technique as a method to follow the adhesion of L. ferrooxidans to an electrode in real time. The bacterial adhesion study was made on pyrite previously chemically (oxidation) treated. The chemical treatment allowed us to have pyrite with different surface characteristics, where mainly Fe or S compounds were present on the mineral. Pyrite without oxidation process was used as control. The tests were performed in a 3 electrode electrochemical cell in 0K culture medium (pH 1.8), where pyrite was the working electrode. Five bacterial cell concentrations were assayed (bact.mL-1): 2.2x108, 1.1x108, 2.2x107, 1.1x107 and 2.2x106. Bacterial adherence was monitored by bacterial count and EIS at a single frequency; moreover, all the surfaces were analyzed by Raman spectroscopy. Bacterial counts showed that the bacterial adhesion was maximum in the oxidized pyrite with predominance of Fe (38±3.2%) and minimal in the oxidized pyrite with predominance of S (18±3.2%). On the other hand, by using the EIS data, it was possible to identify the electrochemical changes generated by the adhesion of bacteria to the mineral, which occurs at frequencies between 0.05 and 0.1Hz. The data obtained by bacterial counts and EIS were fitted to Freundlich type isotherms, presenting the same behavior. With this study, we demonstrated that the EIS data may be a new method for monitoring the microorganism adherence process in real time. The knowledge obtained in this study will be used to develop a device for screening of biomining microorganisms.