Multi-Scale Interfacial Interaction Mechanism Between Unsaturated Fatty Acids And Alumina-Silica Minerals In Bauxite

The interaction between collectors and aluminosilicate minerals has a crucial influence on the flotation efficiency of bauxite.Although new collectors for bauxite flotation are commonly reported,fatty acid series reagents are still the main industrial application collectors.Industrial oleic acid is mainly composed of unsaturated fatty acids such as oleic acid and linoleic acid.Because of the different linoleic acid content,industrial oleic acid with different iodine value and freezing point is produced,which leads to different flotation behaviors.At present,the adsorption behavior of unsaturated fatty acid collectors on the surface of typical aluminosilicate minerals has been widely studied,but the micro-adsorption mechanism,micro-nano mechanical mechanism and wetting and spreading mechanism of such collectors on the surface of aluminosilicate minerals in different media environments have not been fully understood.In view of this,this thesis chooses oleic acid and linoleic acid as collectors,and studies the interaction between oleic acid,linoleic acid and aluminosilicate minerals in air and water,revealing the microscopic adsorption mechanism of unsaturated fatty acids on the surface of aluminosilicate minerals,the mechanical mechanism of the interaction between unsaturated fatty acid droplets and aluminosilicate minerals,and the wetting and spreading mechanism of unsaturated fatty acid droplets on the surface of aluminosilicate minerals,with a view to providing theoretical guidance for efficient flotation separation of aluminosilicate minerals and practical application related to wetting and spreading phenomenon.In this thesis,diaspore and kaolinite are taken as the research objects.The crystal chemistry characteristics and surface properties of diaspore and kaolinite are studied,and the microscopic adsorption behavior of unsaturated fatty acids on the main cleavage surfaces of two alumina-silica minerals is studied at atomic/molecular scale based on quantum chemical calculation.The mechanical behavior of interaction between unsaturated fatty acid droplets and alumina-silica mineral substrates was studied by using a self-made observation system for oil droplet-mineral interaction behavior,and the effects of impact velocity,impact distance and surface wettability on the interaction force were discussed.The macroscopic wetting behavior of unsaturated fatty acid droplets on the surface of alumina-silica minerals was studied by using a self-made oil droplet spreading behavior observation system.Based on the consideration of droplet phase viscosity dissipation,solid-liquid friction dissipation near the three-phase contact line and energy dissipation caused by surrounding fluid,a dynamic wetting theoretical model was established to describe the oil droplet spreading behavior in different media environments,and the dynamics behavior of oil droplet spreading was analyzed.The conclusion of single mineral flotation is verified by artificial mixed ore flotation test.The crystal chemical characteristics and surface properties of diaspore and kaolinite were studied.The cleaved surface of diaspore is composed of broken A1―O or A1―OH bonds.Because of the layered structure and the weak hydrogen bond between adjacent units,kaolinite is easily cleaved along the basal plane under the action of external force.Based on the broken bond density and surface energy,the degree of difficulty in exposing the main cleavage planes of the two aluminosilicates is as follows:diaspore（010）plane<（001）plane<（100）plane,kaolinite（001）plane<（110）plane<（010）plane.Al³⁺exists in the major cleavage planes of diaspore and kaolinite,which can be used as adsorption sites of collectors.However,the distribution density of Al³⁺on the major cleavage planes of diaspore and the proportion of broken Al―O bonds are significantly higher than those of kaolinite.The microscopic adsorption mechanism of unsaturated fatty acids on the surface of alumina-silica minerals was studied.Oleic acid and linoleic acid mainly characteristically adsorb on diaspore surface by hydrogen bonding between their polar groups and the（010）and（001）planes of diaspore in molecular form.And at the same time,they can chemically adsorb on diaspore surface by forming fatty acid salts with Al³⁺exposed on the（010）and（001）planes in the form of anions.They mainly form strong hydrogen bonds with（001）and（001）basal planes of kaolinite through their polar groups in the form of molecules,so that characteristic adsorption occurs.Compared with kaolinite,the adsorption of oleic acid and linoleic acid on diaspore surface has stronger chemical adsorption besides characteristic adsorption,so the adsorption strength of the two collectors on diaspore surface is higher than that of kaolinite.The mechanical mechanism of interaction between unsaturated fatty acid droplets and alumina-silica mineral substrates in different media environments was studied.According to the evolution characteristics of oil droplet-mineral interaction force with relative distance during the interaction between oil droplets and mineral substrates and the shape of oil droplets at a specific moment,the effects of impact velocity,impact distance and surface wettability on the interaction force are analyzed from the perspectives of wetting force,maximum adhesion force and detachment force.Wetting force depends on liquid properties,droplet size and mineral surface wettability,while the maximum adhesion force and detachment force are mainly determined by droplet properties,surface wettability and the length of three-phase contact line.Under the same impact distance,with the increase of impact velocity,the wetting force,maximum adhesion force and detachment force have not changed obviously,indicating that the impact velocity has little influence on the interaction force.Under the same impact velocity,the wetting force remains constant with increasing the impact distance,while the maximum adhesion force and detachment force increase significantly,indicating that the impact distance has a great influence on the interaction force.In addition,the interaction force of oleic acid/linoleic acid droplets-diaspore in air is greater than that of oleic acid/linoleic acid droplet-kaolinite,which indicates that the surface wettability of minerals is the dominant factor to determine the interaction force.In contrast,the interaction force of oleic acid/linoleic acid droplet-diaspore in water phase is smaller than that of oleic acid/linoleic acid droplet-kaolinite,which indicates that the existence of hydration layer on mineral surface has an important influence on the interaction force of oil droplet-mineral.The spreading dynamics behavior of unsaturated fatty acid droplets on the surface of alumina-silica mineral substrates in different media environments were studied.The whole spreading process of oil droplets on the mineral surface in the air can be divided into three stages:the early linear rapid spreading stage dominated by inertia force,the middle exponential slow spreading stage dominated by viscous force and the final equilibrium spreading stage under the joint action of various forces,while the spreading of oil droplets on the mineral surface in the water phase only includes the early rapid spreading stage dominated by inertial force and the late slow spreading stage under the joint action of various forces.According to the dynamic wetting theory model,which is based on considering the viscous dissipation of droplet phase,the solid-liquid friction dissipation near the three-phase contact line and the energy dissipation caused by the surrounding fluid,the difference of oil droplet spreading dynamics in the two media mainly lies in the different energy dissipation modes of the system.The energy dissipation of the oil-water-solid system includes not only the viscous dissipation of droplet phase and the solid-oil friction dissipation near the contact line,but also the energy dissipation caused by the surrounding fluid（water）,while the energy dissipation of the oil-gas-solid system only includes the former.In addition,whether in air or water medium,the quasi-equilibrium contact angle of oleic acid/linoleic acid droplet-diaspore system is smaller than that of oleic acid/linoleic acid droplet-kaolinite system,which means that the wetting degree of oleic acid/linoleic acid on diaspore is higher than that on kaolinite.Experimental study on flotation of alumina-silica minerals with unsaturated fatty acids was carried out.Under the action of a single collector（oleic acid and linoleic acid）,the flotation recovery of diaspore is significantly higher than that of kaolinite.Moreover,compared with linoleic acid,oleic acid has stronger collecting ability for alumina-silica minerals.Under the action of mixed collectors,with the increase of the ratio of linoleic acid to oleic acid,the difference of flotation recovery between diaspore and kaolinite gradually increases,and at the same time,with the increase of linoleic acid content,the flotation performance of artificial mixed ore becomes better,which proves that the existence of linoleic acid can enhance the selectivity of industrial oleic acid.The thesis contains 98 figures,37 tables and 207 pieces of references.