A comparative study of biopolymer adsorption on model anisotropic clay surfaces using quartz crystal microbalance with dissipation (QCM-D).

Mitigation of colloid clay particles is critical during flotation and flocculation processes in mineral processing. Most organic and inorganic mitigation reagents have negative impacts on the environment and human health; therefore, biologically derived substances have been attracting attention as alternative reagents. Given the anisotropic nature of clay surfaces, it is imperative to understand reagent adsorption on the individual edge and basal plane surfaces of clays. Quartz crystal microbalance with dissipation (QCM-D) was used in this study to determine the adsorption characteristics of three biopolymers (the protein-based biopolymer, lysozyme, and protein and polysaccharide-based oligomers; protamine and pectin) on model surfaces of the anisotropic edge and basal planes of the clays (e.g., kaolinite and serpentine). SiO sensor representing the tetrahedral basal plane, AlO and Mg(OH) representing the octahedral basal planes, AlSiO and MgSiO representing the edge faces of clays were used as model surfaces of clay minerals. For kaolinite, protamine adsorbed preferentially on the silica (SiO) tetrahedral surface at pH 7 and on the alumina (AlO) surface at pH 10. Protamine adsorbed primarily on magnesium hydroxide (Mg(OH)), representative of serpentine, at pH 7 and 10. Lysozyme adsorbed preferentially and irreversibly on the edge basal plane surfaces of both clays at pH 10, while it showed a higher affinity for octahedral surfaces (alumina and magnesium hydroxide) at pH 7. In contrast, pectin adsorbed strongly on the magnesium hydroxide, representative of the basal plane surface of serpentine. An adsorption study revealed that electrostatic attraction and/or hydrogen bonding mechanisms contributed to the adsorption of biopolymers on clay surfaces. This investigation provides a fundamental and practical understanding of biopolymer interactions with clay surfaces during selective flotation and flocculation.