Abstract The aim of this study is to assess the floatability of hematite using a crude biosurfactant (BS) extracted from Rhodococcus opacus. Throughout high-pressure ethanol extraction, unrefined surfactant was extracted from the bacteria with a yield of 0.3 g/L. An FTIR analysis on this extract, shows the presence of alcohol (–OH) and ketone (C=O) groups, as well as saturated and unsaturated carbon chains, which might originate from mycolates and trehalolipids moieties reported in literature. In addition, FTIR analysis on the modified mineral surface with the unrefined surfactant, confirms a strong interaction between hematite and the crude biosurfactant, showing similar vibrational peaks regarding the hydroxyl and carboxylate groups at 1631 and 3436 cm-1, respectively. Biosurfactant interaction with the mineral particles shifted the isoelectric point from 7.5 to 3.2, turning the hematite more hydrophobic in acidic environments. Surface tension measurements indicate that the unrefined surfactant is slightly more effective, decreasing the surface tension of water compared to the bacteria itself, with a variation of 4 mM/m. Finally, throughout microflotation tests in a Hallimond tube, it is shown that the surfactant doubles bacteria recovery efficiency, reaching a maximum recovery of around 95 % in acidic conditions, which is consistent with electrophoretic studies. The statistical models adjust well the experimental data, achieving R2 values of 93.6 and 91.1% for the hematite flotation using the biomass and the biosurfactant, respectively.

Abstract Adsorption of microorganisms and/or their different components onto a mineral surface would modify the surface characteristics of the mineral. Thus, this investigation evaluated the adsorption capacity of the Rhodococcus opacus strain onto an apatite surface. Zeta potential and contact angle measurements of the mineral showed dislocations of the values after interaction with the microorganism. The maximum adsorption density reached was 24.10 mg of bacterial cells per gram of mineral using a biomass concentration of 400 mg/L. The experimental data were linearly fitted by the Freundlich model and the adsorption density as a function of time was linearly fitted by the pseudo-second order kinetic equation. The results showed that the bacterial strain has affinity for the apatite surface and ability to make it hydrophobic.

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.