Abstract Microbial biomass is considered a renewable and environmentally friendly resource. Thus, the research conducted a kinetic study and thermodynamic equilibrium modeling of the cobalt (Co) and manganese (Mn) bioadsorption process using the Rhodococcus opacus (RO) strain as a biosorbent. The inactive biomass subjected to 0.1 M NaOH pretreatment was brought into contact with synthetic solutions of Co and Mn. The experimental data for the Co(II) and Mn(II) bioadsorption process were fit to the Langmuir model with kads of 0.65 and 0.11 L.mg-1, respectively. A better statistical fit was also obtained for the pseudo-second order kinetic model (R2Co(II) = 0.994 and R2Mn(II) = 0.995), with 72.3% Co(II) and 80% Mn(II) removals during the first 10 min. In addition, a higher affinity of RO for the Co(II) ion was observed, with maximum uptake values of 13.42 mg.g-1; however, a higher adsorption rate was observed for Mn(II) ion (k = 0.21 g.mg-1.min-1 at 318 K). The bioadsorption process was spontaneous and dependent on temperature, being endothermic and irreversible for the Co(II) ion (∆H = 2951.91 J.mol-1) and exothermic and reversible for the Mn(II) ion (∆H = -2974.8 J.mol-1). The kinetic and thermodynamic equilibrium modeling allowed to identify the main mechanisms involved in the biosorption process of both metals.

Abstract The use of biosurfactants as reagents represents a promising alternative to the conventional surfactants used in the mineral industry because they may present low toxicity and high biodegradability. Therefore, this research studied the hematite and quartz flotation kinetics using surfactant produced by Rhodococcus erythropolis as bioreagent. The flotation kinetics of both minerals were evaluated under established conditions: biosurfactant concentration of 10 mg/L and solution pH of 3. The maximum floatability values were of 99.98% and 17.53% for hematite and quartz, respectively, after 2 minutes of flotation. Finally, the kinetics study indicated that the experimental data of hematite floatability was better fitted to both the first and non-integral order kinetics, while the experimental data of quartz floatability was better fitted to the non-integral order kinetic.

Abstract It is well known that the culture conditions of microorganisms may affect their surface properties, zeta potential and hydrophobicity via the modification of the cell wall functional groups or metabolic products. The R. opacus bacteria strain was separately adapted to the presence of apatite and quartz, after which a cellular adaptation procedure was developed by repeated sub-culturing with a successive increase in the mineral content. Zeta potential, surface tension, FTIR and microflotation studies were used to evaluate the behavior of the cells that were developed under defined culture conditions. The cellular adaptation induced a modification of the bacterial surface charge. The FTIR results showed a modification of its functional groups. The surface tension results suggested that longer growing time promoted a higher production of metabolites. The use of mineral-adapted cells promoted an improvement in the flotability of both minerals, but it was more significant for apatite flotation. Additionally, the mineral flotability remained unchanged when the cells developed under a longer culture time. Nevertheless, there was a reduction in the surface tension.