| Foamflotation is one of the most cost-effective methods for treating fine particles,and the formation and stability of foam is an important factor affecting the flotation effect.Studies have shown that the addition of inorganic salt ions can improve the stability of foam and thus improve the flotation effect,but the microscopic foam stabilization mechanism of inorganic salt ions is not clear.Based on this,six alkali halides composed of metal cations Na+,K+and halogen anions Cl-,Br-and I-with a simple structure of 1:1 were selected as research objects,and the effects of alkali halides on macroscopic two-phase foam properties,microscopic bubble coalescence behavior,solution environment and interface properties at the molecular scale were studied,and the bubble stabilization mechanism of alkali halide on gas-liquid two-phase foam was revealed.The effect of alkali halide on the stability and foam properties of macroscopic two-phase foam was studied by using a small flotation column.The results showed that with the increase of alkali halide content in the solution,the maximum foam layer height and the rupture time of the foam layer in Na Cl,KCl,Na Br and KBr solutions showed an increasing trend,the gas holdup and residence time also showed an increasing trend,the foam layer height and gas holdup in Na I and KI solution increased first and then stabilized,and the rupture time and residence time of the foam layer were not obvious compared with the pure underwater effect,which indicated that the addition of alkali halide could enhance the stability of the two-phase foam to a certain extent.The enhancement effects of six alkali halides on the stability of macroscopic two-phase foam were as follows:Na Cl>KCl>Na Br>KBr>Na I≈KI;The results show that the addition of alkali halide can increase the total number of bubbles in the solution,increase the percentage of spherical small bubbles,and reduce the speed of single bubbles when they reach the liquid level for the first time,which indicates that alkali halide has the ability to inhibit bubble coalescence,thereby stabilizing the foam.The surface tension of alkali halide solution was tested by interfacial tensiometer,and the results showed that the surface tension of the six alkali halide solutions increased with the increase of concentration.The microfluidic chip system was used to study the effect of alkali halide on microscopic bubble merger.The results showed that there was a transition concentration of alkali halide in the process of inhibiting bubble coalescence,and the transition concentration of the six alkali halides showed Na Cl<KCl<Na Br<KBr<Na I<KI.When the concentration of alkali halide is lower than the transition concentration,a stable liquid film cannot be formed between the bubbles,and the bubbles will coalescence rapidly;When the concentration of alkali halide is higher than the transition concentration,Na Cl,KCl,Na Br and KBr can inhibit bubble coalescence,and the bubble coalescence time increases with the increase of their concentration,but the inhibitory effect of Na I and KI on bubble coalescence is not obvious,only slightly greater than the bubble coalescence time in pure water,which is consistent with the test results of macro foam stability.In addition,the test results also show that when the coexistence anion remains unchanged,the effect of alkali halide containing Na~+in inhibiting bubble coalescence is significantly stronger than that of alkali halide containing K~+.When the coexistence cation is unchanged,the ability of the anion to inhibit bubble coalescence shows the law of Cl~->Br~->I~-.Then,the effects of different alkali halides on the molecular structure and surface interface properties of water in solution were studied with the help of molecular dynamics simulation(MDS),and the radial distribution function,diffusion coefficient and enrichment degree of ions at the gas-liquid interface in molecular dynamics simulation were mainly analyzed.The results show that the addition of alkali halide can destroy the original pure water structure.Under the condition that the coexistence of anion is unchanged,the first peak position of the radial distribution function of Na~+-O in the solution is on the right side of K~+-O,and the first peak of Na~+-O is significantly higher,that is,Na~+is more closely related to the water molecules in the first layer of hydration shell,and the diffusion coefficient of Na~+in solution is also significantly smaller than the diffusion coefficient of K~+,that is,Na~+can more constrain the migration of surrounding water molecules,which indicates that the hydration capacity of Na~+is stronger than that of K~+.Similarly,when the coexistence cation is unchanged,the first peak position of Cl~--H,Br~--H,and I~--H shifts to the right and the first peak in turn shows a downward trend,and the diffusion coefficient is Cl~-<Br~-<I~-,which indicates that the degree of influence of three anions on the molecular structure of water,that is,the strength of hydration,is:Cl~->Br~->I~-.According to the enrichment degree of anions and cations in alkali halide at the gas-liquid interface,it is found that cations can attract more water molecules in the liquid phase in the form of hydrated ions,which is difficult to migrate to the interface,and the enrichment degree of cations at the interface is as follows:K~+>Na~+;However,the small number of water molecules around anions tends to be enriched at the gas-liquid interface,and the enrichment degree of the three anions at the gas-liquid interface is as follows:I~->Br~->Cl~-.In addition,the degree of enrichment of the same anion at the gas-liquid interface is also related to the hydration ability of its coexisting cation.Under the condition that the number of water molecules remains unchanged,there is a competitive relationship between the attraction of anions and cations to water molecules.The stronger the hydration ability of coexisting cations,the higher the enrichment degree of anions at the gas-liquid interface.Conversely,the lower the degree of enrichment.There are 61pictures,9 tables and 111 references in this paper. |
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