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.
Highlights
Mineral resources are steadily diminishing and the search for new technology able to recover low grade deposits is becoming evident
Previous studies showed the potential of developing a new technology by the harnessing of microorganisms as bioreagents (Yang et al, 2013; Mesquita et al, 2003)
The present study evaluates the effectiveness of the crude biosurfactant extracted from the grampositive bacteria Rhodococcus Opacus, recovering hematite mineral at neutral and acid conditions
Summary
Mineral resources are steadily diminishing and the search for new technology able to recover low grade deposits is becoming evident. Nowadays there is an increasing awareness of the environmental impact of the mining industry. Mineral flotation processes use surfactants that significantly contribute to water pollution when released in effluents (Zoller et al, 2000). The use of microorganisms and their by-products to selectively recover minerals with a lower environmental impact could be a relevant alternative. Previous studies showed the potential of developing a new technology by the harnessing of microorganisms as bioreagents (Yang et al, 2013; Mesquita et al, 2003). The potential uses of microbes in the flotation process was properly discussed by Kinnunen et al (2020). The authors suggested that certain categories of bacteria could be used as potential flotation collectors
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