Research On The Formation Characteristics And Stability Mechanism Of Nanobubbles In Complex Solution Chemistry

With the improvement of mechanization of mineral mining,the size of minerals to be separated by traditional foam flotation technology is decreasing,which leads to the problem of fine particle separation.It is generally believed that the nanoscale of bubbles is of great significance in improving flotation efficiency.Considering the complexity of the flotation slurry environment in practical flotation applications,this thesis first studied the generation characteristics of nanobubbles in pure water systems,including the determination of optimal imaging parameters for nanobubbles,nanobubble identification,factors affecting nanobubble nucleation,and the mechanical stability of nanobubbles.Then,common surfactant solutions(CTAB,SDS,Trition X-100),single salt solutions(Na Cl),and mixed solutions(SDS、Na Cl)in flotation systems were selected,and nanobubbles were exposed to these solutions to study their generation characteristics,including geometric and mechanical properties.Finally,the stability mechanism of nanobubbles under solution chemical conditions was elucidated,providing technical support for further enriching the theory of nanobubble stability and promoting the application of nanobubbles in practical flotation.Under the AFM intelligent mode,the height of nanobubbles on the surface of Highly Oriented Pyrolytic Graphite(HOPG)decreased with increasing peak force,and combined with the analysis of nanobubble surface force curves,the optimal peak force for imaging nanobubbles was determined to be 300 p N.Nanobubbles were effectively identified from three aspects: response to gas solubility characteristics,response to nanomechanical properties,and response to surface wetting properties,and the experimental data support the gas-phase nature of the internal structure of nanobubbles.Nanobubbles can only be generated at hydrophobic interfaces and nanobubbles preferentially nucleate in rough areas of the substrate.Under vertical impact forces,the height of nanobubbles changes but the number does not;under horizontal scrubbing forces,the number of nanobubbles changes but the geometric properties remain stable.In the surfactant system,the properties of the surfactant solution remained stable before and after solution replacement,and there were no other pollutants affecting the properties of the bubbles.The height of the nanobubbles increased with the addition of the surfactant solution.When the surfactant concentration exceeded the critical micelle concentration,the height change of the bubbles was not obvious,and even a decrease in height was observed in the nonionic surfactant solution.The contact angle of the nanobubbles did not change significantly with size and had a small size dependence.The apparent hardness of nanobubbles in different concentrations of cationic surfactants varied between 0.0571-0.0248 n N/nm,that of anionic surfactants varied between 0.0444-0.0386 n N/nm,and that of nonionic surfactants varied between 0.0240-0.0196 n N/nm with changing surfactant solution concentration.In different surfactants,the apparent hardness values of nanobubbles at different concentration gradients were consistent with the changes in their geometric characteristics at that concentration gradient.In a single salt solution system,the geometric properties of nanobubbles did not change before and after solution replacement.In a mixed solution system,the geometric properties of nanobubbles varied with the concentration of SDS in the mixed solution system.The results of surface tension analysis show that the surface tension of nanobubbles in surfactant solution varies between 16.24-56.18 m N/m.From the perspective of thermodynamics and energy,and based on the quantitative relationship described by the adsorption equilibrium of surfactant at air-water interface,it is concluded that low surface tension contributes to the short-term stability of nanobubbles,but it cannot be used as a mechanism explanation for its long-term stability.The results of molecular dynamics simulation analysis show that the addition of surfactant will not completely replace the gas monolayer at the solid-liquid interface.Nanobubbles are stable in surfactant solution under the gas compensation of gas monolayer and the hindrance of surfactant to gas diffusion.This dissertation contains 94 pictures,6 tables,and 102 references.