Bacterial cell adhesion onto mineral surfaces is important in a broad spectrum of processes, including bioweathering, bioleaching, and bacterial cell transport in the soil. Despite many research efforts, a detailed explanation is still lacking. This work investigates the role of surface-active compounds, cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and pure rhamnolipid (RH), in the process of bacteria attachment on the schwertmannite surface. The surface energy was calculated based on the wettability of the tested systems, and for bacteria it was 54.8 mJ/m², schwertmannite-SDS 54.4 mJ/m², schwertmannite-CTAB 55.4 mJ/m², and schwertmannite-RH 39.7 mJ/m². The total energy of adhesion estimated based on thermodynamic data was found to be negative, suggesting favorable conditions for adhesion for all examined suspensions. However, including electrostatic interactions allowed for a more precise description of bacterial adhesion under the tested conditions. The theoretical analysis using the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) approach showed a negative value of total adsorption energy only in bacteria-mineral suspensions, where SDS and rhamnolipid were added. The calculated data were in good agreement with experimental results indicating the significance of electrostatic forces in adsorption.

E3S Web of Conferences, open access proceedings in environment, energy and earth sciences

Increasing environmental concern forces the reduction in the share of synthetic surfactants in the production of various industries, including mineral processing, by replacing them with more environmentally friendly compounds of biological origin. Several studies on the use of biosurfactants in mineral processing are currently available in the literature, but they contain limited information related to the physicochemistry of these processes. Therefore, this review aims to summarise publications from the last decade related to the role of microorganisms and their metabolic products in mineral surface modification applied in mineral processing. Theoretical principles of bacteria–mineral interactions are presented. Salt-type, sulphide, and oxide minerals were discussed with greater attention to the physicochemistry of biosurfactant–mineral interactions, such as the wettability and surface charge. The advantages and disadvantages of using bacterial cells and surface-active microbial compounds were proposed. The trends and challenges of biomodification in flotation and flocculation were discussed.

The adsorption of biosurfactants and polysaccharides changes the surface properties of solid particles, which is important for controlling the release of arsenic compounds from the solid phase and preventing undesirable bioleaching. Microbial leaching and scorodite adhesion experiments, including pure and modified mineral material, were conducted in a glass column with a mineral bed (0.8–1.2 mm particle size) to test how rhamnolipids (Rh) and lipopolysaccharides (LPS) affect surface properties of mineral waste from Złoty Stok (Poland) and secondary bio-extraction products (scorodite). Adsorption tests were conducted for both solid materials. The adsorption of Rh and LPS on the solids was shown to modify its surface charge, affecting bioleaching. The highest bio-extraction efficiency was achieved for arsenic waste with adsorbed rhamnolipids, while the lowest, for the LPS-modified mineral. Under acidic circumstances (pH~2.5), the strongly negative zeta potential of arsenic-bearing waste in the presence of Rh creates conditions for bacteria adhesion, leading to the intensification of metal extraction. The presence of a biopolymer on the As waste surface decreases leaching efficiency and favours the scorodite’s adhesion.

Reductive dissolution is like “biomining in reverse gear”. Selected sulfur reducing bacteria (SRB) can be used under anaerobic conditions – as in bioleaching – for metal recovery from oxide minerals and laterite. General assumptions of the BioSulphide^® and Ferredox processes for nickel recovery from laterite ores and copper from acid mine drainage or waste water were presented.