Microbially induced selective flocculation of hematite from kaolinite

• Bioinduced selective flocculation of hematite from kaolinite demonstrated.
• Growth of B.subtilis in kaolinite promoted secretion of mineral-specific proteins.
• Bacterial interaction rendered hematite hydrophilic and kaolinite hydrophobic.
• Bacterial cells and exopolysaccharides exhibited higher adsorption on hematite.
• Extracellular proteins exhibited higher adsorption on kaolinite.

Microbially induced selective flocculation of hematite from kaolinite has been demonstrated using Bacillus subtilis. Growth of bacterial cells in the presence of kaolinite resulted in enhanced production of extracellular proteins while that of hematite promoted significant secretion of exopolysaccharides. Bacterial cells were adapted to grow in the presence of the minerals and use of hematite-grown and kaolinite-grown cells and their metabolic products in the selective flocculation of hematite and dispersion of kaolinite illustrated. Bacterial cells and extracellular polysaccharides exhibited higher surface affinity towards hematite, rendering it hydrophilic; while significant protein adsorption enhanced surface hydrophobicity of kaolinite. Bacterial interaction with hematite and kaolinite resulted in significant surface chemical changes on the minerals. Due to higher surface affinity towards extracellular proteins, zeta potentials of kaolinite shifted in the positive direction, while those of hematite shifted in the negative direction due to higher adsorption of extracellular polysaccharides. Bacterial interaction promoted selective flocculation of only hematite, while kaolinite was efficiently dispersed. Mineral-specific stress proteins were generated on growing B. subtilis in the presence of kaolinite. Interfacial aspects of microbe–mineral interactions are illustrated to explain microbially-induced selective flocculation of hematite from kaolinite with relevance to clay and iron ore beneficiation.

Scanning electron micrographs of Bacillus subtilis attached onto (a) hematite and (b) kaolinite.Figure optionsDownload as PowerPoint slide