Study On The Mechanism And Molecular Simulation Of Compound Reagents For Gasification Ash Flotation

As a relatively large amount of solid waste resources in China,resource recovery and utilization of coal gasification ash is the key to realize a circular economy.The gasification ash is the product of high-temperature gasification of coal,and the surface properties of the residual carbon change greatly.It is difficult to achieve efficient separation of carbon and ash from gasification ash using conventional flotation reagents for coal,so it is crucial to explore flotation chemicals for gasification ash.The paper took Yinchuan coal-to-oil gasification ash slag as the main research object,selected diesel as the main flotation agent,and compound surfactant DTAB,TX-100,and SDS with diesel at the mass ratio of 1%,5%,and 10%,respectively,to explore the influence on flotation of gasification ash.Meanwhile,the interfacial interaction between the residual carbon surface and the compounding agent was analyzed in a targeted manner.The interaction energy and adsorption effect of the reagent with oxygen-containing functional groups and residual carbon were studied by molecular dynamics simulation.The surface/interfacial tension between the reagent and water,the potential change before and after adsorption,and the change of adsorption capacity were measured by surface/interfacial tension meter,zeta potential meter,and UV spectrophotometer.The LOI of the gasification ash sample is 22.06%,the fixed carbon content is only17.16%,and the combustible component content is less.The dominant particle size of the sample is-0.045 mm,and the yield is as high as 66.58%.The residual carbon of this particle size accounts for 59.24%,which is the main particle size for carbon removal in flotation.The ash sample mainly contains crystalline minerals such as quartz,mullite,and anhydrite,among which Si O₂ and Al₂O₃ exist in the glass phase.The fine slag has glass beads,sintered minerals,and porous materials with pore and cracks structures,while the carbon surface contains hydrophilic functional groups,all of which add to the difficulty of carbon ash separation in the flotation of gasification ash fine slag.The adsorption morphology and interaction energy between surfactants and different oxygen-containing functional groups were investigated by molecular dynamics simulations.DTAB molecules are in free state,few molecules are adsorbed on oxygen-containing functional groups,while TX-100 and SDS molecules are adsorbed on oxygen-containing functional groups in an inclined or lying manner.The three surfactants are more likely to adsorb carboxyl and hydroxyl groups,and mainly in the form of van der Waals forces,and SDS also in the form of electrostatic forces.In addition,the adsorption behavior of the agent in the aqueous phase with residual carbon was investigated by constructing water/agent/residual carbon systems.The dodecane molecules in the DTAB compounding agent system are free in the aqueous phase.The dodecane molecules in the TX-100 compounding system are free in the aqueous phase at low concentrations and tend to adsorb on the surface of residual carbon at high concentrations.In the SDS compounding agent system,the dodecane molecules are adsorbed on the surface of residual carbon at one end and stretched to the aqueous phase at the other end,and the alkane chains are stretched in the aqueous phase in the following order:5%SDS>10%SDS>1%SDS.The changes of surface/interfacial tension of the solution system after the addition of surfactants were analyzed by a surface/interfacial tension meter.The order of magnitude of the effect on water surface tension with increasing agent concentration was:SDS>TX-100>DTAB;the order of magnitude of the effect on diesel surface tension was:SDS>DTAB>TX-100;the magnitude of the effect on oil-water interfacial tension was:SDS>TX-100>DTAB.The effect of compounding agent on the surface zeta potential of gasification ash was investigated by the Zeta potential meter.The results show that the mixture of TX-100 and diesel has little effect on the surface potential of gasification ash;DTAB ionizes bromine ions in the solution,which makes the diesel positively charged,and the surface potential of the gasification ash slag is shifted to the positive direction;SDS ionizes sodium ions in solution to make diesel negatively charged,and its compounding agent promotes the negative shift of potential on the surface of gasified ash fines.The adsorption capacity of the compounding agent on the surface of gasification ash was measured by a UV spectrophotometer.The adsorption effect of the trapping agent on the surface of gasification ash fines is enhanced by compounding TX-100 and SDS with diesel respectively,and DTAB has little effect on the adsorption of the agent on the gasification ash fines after compounding with diesel.The adsorption effect of TX-100 compounding agent was better at lower surfactant compounding mass concentration;the adsorption effect of SDS compounding agent was better at higher agent compounding mass concentration.In the gasified ash flotation test,the raw sample was directly unit flotation,using diesel as collector,and the resulting concentrate tailing had similar burn loss at low chemical dosage,and only when the collector dosage reached 10 kg/t did the carbon ash show significant separation.After proper grinding and dissociation of gasification gray fines,carbon gray separation at low diesel dosage can be achieved,but the separation effect is limited.After DTAB is compounded with diesel,the concentrate rate is low and the tailing burn-off is high at low dosage,and the concentrate rate increases when the dosage is increased,and the change of tailing burn-off is not obvious.The residual carbon recovery of ash is generally lower than that of diesel as collector.After TX-100 was compounded with diesel,the flotation residual carbon recovery of ash gradually increased as the mass concentration of TX-100 compounded increased.At TX-100 compound mass concentration of 10%,with the increase of collector dosage,the carbon content of concentrate increases and the carbon removal effect of tailing improves significantly.The compounding of SDS with diesel oil has significantly improved the carbon ash separation effect of coal-to-oil gasification ash.At SDS compounding mass concentration of 5%,the most significant effect on carbon ash separation was achieved,with residual carbon recovery rate of 92.87%and tailing LOI of 2.20%.This paper contains 48 figures,13 tables and 100 references.