The Extraction Of SiO₂ From Fly Ash By CO₂ Microbubbles

In recent years,the fly ash emissions from power plants have continuously increased,making fly ash the largest single source of solid pollution in China.Carbon dioxide is a major source of greenhouse gases and also a rich source of carbon.The effective use of carbon dioxide is particularly important.Therefore,the nano-silica material can be prepared by carbonization of the fly ash leachate,which can realize high value-added use of waste treatment and waste.It is known that the sodium silicate can undergo carbonation with carbon dioxide to produce SiO₂.However,in the conventional reaction system,CO₂ is introduced by bubbling,and the size of the bubbles is larger,so that the bubble will be relatively larger buoyancy in the water and the residence time in the system will be shorter.In addition,the escape situation in the system is very serious,and the reaction time is prolonged,leading to a low CO₂ absorption and utilization efficiency.As to this problem,We intend to use microbubble to replace the traditional bubble method to improve the efficiency of CO₂ utilization.Firstly,we used interfacially active SiO₂ to stabilize the bubbles,i.e.,Pickering bubbles.By adjusting the amount of silane,the amount of the interfacially active SiO₂,and the temperature to investigate the bubbles properties.The microbubbles were then introduced into the carbonation reaction of the water glass and compared with the conventional bubbling system.The effects of temperature,reactant concentration,the CO₂ flow rate on yield,BET and CO₂ utilization were explored.And the properties of the materials were characterized by infrared spectroscopy,XRD,SEM,TEM,and nitrogen adsorption.The results found that under the same conditions,CO₂ utilization effective in the microbubble system increased obviously,and the SiO₂ got by microbubble method have uniform structure,high specific surface area,and good dispersibility may be due to the effect of interfacial effect.Secondly,microbubbles are obtained through a micro-bubble generator and applied to the carbon-dioxide reaction to prepare nano-SiO₂.The effects of reactant concentration,temperature,surfactant type,and surfactant dosage on the yield and structure of the product were investigated.The results show that nano-SiO₂ with a specific surface area of up to 654 m²/g can be obtained by the micro-bubble generator.At the same time,due to the influence of the interface effect of the micro-bubble,a rod-like structure of silicon oxide can be obtained.