Effect of Surface Modification on Mineral Waste Dissolution Using Microorganisms: Physicochemical Aspects

Abstract

The bioleaching efficiency of various solids, including mining waste, is influenced by the physicochemical changes occurring on the particle surface in the presence of microorganisms. Mineral modification is widely used in mineral processing and can also be applied in bioextraction and bioremediation. Surfactant adsorption can serve as a tool to control bacterial attachment, a critical factor in such processes. Bacterial adhesion promotes the intensification of leaching, while increased mobility reduces the metal removal. Therefore, the impact of such modification and its further effect on the release of toxic metals from mining waste was investigated, focusing on physicochemical aspects. Bioleaching experiments were conducted in shaken flasks for four weeks, with solid to liquid ratio of 1:10. Two types of surfactants were used: cationic (cetyltrimethylammonium bromide) and anionic (sodium dodecyl sulfate). Zeta potential was measured using the classic streaming potential and streaming current method. The surface morphology of the leaching residue was analysed using scanning electron microscopy. Secondary precipitates formed were identified by X-ray diffraction, revealing jarosite formation. The presence of surfactants caused a change in the surface charge of particles, which could affect the behaviour of bacteria during leaching and, thus, its efficiency. Arsenic was identified as the primary toxic element. When no modifications were applied, its recovery from the solid reached 1631 g/L after four weeks of leaching. Conditioning of the mineral waste with surfactants before the process resulted in lower metal content: 1264 mg/L for a cationic surfactant and 937 mg/L for an anionic surfactant. Moreover, a correlation was observed between the efficiency and the measured surface area — higher recovery rates were associated with larger specific surface area values. The adsorption of surface-active agents altered the surface properties of the waste material. Treatment with the anionic surfactant increased the negative zeta potential, whereas exposure to the cationic surfactant resulted in a positive surface charge. At the end of the bioleaching, all leaching residues exhibited a positive zeta potential. This effect was primarily caused by the formation of positively charged iron(III) precipitates under acidic conditions. It has been demonstrated that in the presence of microorganisms, arsenic can be released from mining waste and that surface modification with surfactants inhibits this process, which may have potential applications in preventing unwanted effects of bioweathering.