Effect of mesophilic microorganisms on the electrochemical behavior of galena

In recent years, the bioleaching of sulfidic raw materials has been of great interest. However, the application of this biotechnology is now very limited for many different complex reasons. The mechanism of the chemical and electrochemical reactions taking part in the process is not well understood. The application of electrochemical techniques is useful in its elucidation. Among the common sulfides, galena has been studied very little with respect to its behavior during bioleaching. Therefore, the electrochemical evolution of massive electrodes of lead sulfide in the presence and absence of a mixed culture of mesophilic microorganisms was investigated by the application of potentiometry, anodic and ca-thodic polarization and cyclic voltammetry. The agitation rate, the use ofpH control and the composition of the nutrient mediums did not have any significant affects on the oxidation of galena. However, the temperature (25° to 45 °C), the scan rate (4 to 100 mV/s) and the acid used to adjust the pH were significant variables that influenced sulfide oxidation. Therefore, the peak (600 to 1,000 mV) corresponding to the oxidation of sulfide ions from the mineral was only detected in the presence of a complexing anion of lead. In the presence of bacteria, the peaks corresponding to galena oxidation decreased and, at the same time, new peaks appeared both during the oxidation at −300 mV and during the reduction of the mineral surface at 150 and −300 mV. These signals were more important when the attack time increased. The rest potential ofbioleached mineral increased with an increase in leaching time, which was related to the electrochemical transformation of the galena surface.