Response Surface Methodology Analysis of the Effect of the Addition of Silicone Oil on the kLa Coefficient in the Bioleaching of Mine Tailings

Bioleaching is suggested as a methodology with benefits in ex situ/in situ bioremediation for reducing metal contamination in dredged sediments. The process of bioleaching assisted by microorganisms in a stirred tank is widely used, among other biohydrometallurgical techniques, for the efficient extraction of metals of interest if the recovery costs of valuable metals allow it. Measurement of the mass transfer capacity of oxygen in an aerobic bioreactor is of vital importance; this factor determines the productivity of the system, since it promotes microbial growth and hence enables a bioconversion process at the mineral surface takes place. The main objective of the present research was to determine the volumetric oxygen transfer coefficient (kLa) during the manganese bioleaching process in a stirred tank reactor using silicone oil as a vector to improve the transfer of gaseous substrates. Experiments were carried out in triplicate with a 22 factorial design analyzing temperature (30 and 40 °C) and stirring speed (300 and 500 rpm). The effect of viscosity on the system was also determined by modifying the concentrations of mining waste (30, 40, and 50%), ferrous sulfate (FeSO4 · 7H2O) (2, 4, 8, and 14%), and silicone oil (0, 5, and 10%) at 0 and 24 h of mixing. The results showed an increase in the value of kLawith respect to time, from kLa(0 h, 30 °C, 500 rpm) = 8.75 s−1 to kLa(24 h, 40 °C, 500 rpm) = 18.18 s−1; ANOVA statistical analysis was performed with the Fisher and Tukey tests and showed that there were statistically significant differences.