Study On Preparation Of Mesoporous Materials And Water Purifying Agent From Coal Gasification Fine Slag

China is rich in coal and poor in petroleum and natural gas.Due to this special energy structure,in recent years,coal chemical industry has obtained very fast development,thus the coal gasification slag has become a new solid waste with huge emissions.In order to reduce the occupancy of land resources and the harm to the environment resulted by the coal gasification slag,it is urgent to research and recycle the coal gasification slag.On the other hand,mesoporous materials have widespread applications in adsorption,catalytic chemistry,electrochemistry,biosciences and other fields due to their large specific surface area,ordered pore structures and controllable surface groups.However,the majority of the methods for preparing mesoporous materials are template method.Its high preparation cost greatly limits the industrial production of mesoporous materials and their application in general fields,such as purification of industrial wastewater.This article studied a low cost method-acid leaching method to prepare mesoporous materials based on the natural properties of coal gasification fine slag.Coal gasification mainly consists of two parts:Residual carbon after coal gasification process and glass silica-alumina microspheres.The main body of silica-alumina microspheres is SiO₂,with various metal oxides,such as Al₂O₃,CaO and Fe₂O₃resided in it.Our research found that a mesoporous structure was resulted after leaching out the metal oxides in the glass microspheres,and the mesoporous silica microsphere?named MGS?can be formed by burning the carbon at 600?.In addition,in the process of coal gasification,the residual carbon in coal gasification slag would be activated into porous carbon by steam,CO₂ and other gases at high temperature,and the pore size of it is also attributed to mesoporous range.Therefore,for certain coal gasification slags,a carbon-silica composite mesoporous material?named CSM?can be formed by only acid leaching out of the metal oxides in the glass microspheres,with very low preparation cost and enormous application value.The effects of various conditions on the pore structure of mesoporous silica microspheres and carbon-silicon composite mesoporous material were fully discussed in this article.The results showed that the pore structure of the prepared mesoporous materials is mainly affected by two factors:the concentration of hydrochloric acid and the particle size of coal gasification fine slag.The optimal acid concentration is 16wt%,and the specific surface area and pore volume of mesoporous materials increase along with the decrease of the particle size.At the best react conditions,mesoporous silica microspheres MGS1 with specific surface area of 364 m²/g,pore volume of0.34cm³/g and carbon-silica composite mesoporous material CSM1 with specific surface area of 500 m²/g,pore volume of 0.54 cm³/g were prepared,and the pore sizes of the two mesoporous materials are mainly distributed between 2 and 6 nm.In addition,the pore structure in carbon and silica can be clearly seen by TEM,and the XRD showed that the main phase of two mesoporous materials were amorphous state.In the process of acid reaction,H⁺will combine with the"Si-O"defect on the surface of silica to form silanol groups?Si-OH?,which has an important effect on the adsorption properties of mesoporous materials.In this article,the types and quantities of silanol groups on the surface of MGS1 were characterized by Fourier transform infrared spectroscopy and acid-base titration method.The results showed that the types of silanol groups are mainly isolated silanol groups and silanol groups,and the number of silanol groups is 1.21/nm².The mesoporous materials prepared in this article's experiment can be applied in many different fields,such as purification of industrial wastewater,adsorption of harmful gases and serving as inorganic fillers for polymer materials,etc.This research explored MGS1 and CSM1's adsorption effect for methylene blue,to verify their adsorption ability.The results showed that the adsorption process of methylene blue onto the two mesoporous materials conformed to pseudo-second-order kinetic model,and the adsorption equilibrium conformed to Langmuir isotherm equation,that is,the adsorption of methylene blue onto the two mesoporous materials belonged to chemical adsorption,and eventually monolayer covered on their surface.The adsorption mechanisms of methylene blue on MGS1's surface are electrostatic mechanism and hydrogen bonding mechanism.What's more,Langmuir isothermal equation showed that the maximum adsorption capacity of MGS1 for methylene blue was 140.57 mg/g,and that of MGS1 for methylene blue was 182.48 mg/g.This value exceeds most methylene blue adsorbents and can even reach the adsorption level of some mesoporous materials prepared by template method.However,its preparation cost is much lower than that of template method,which proves its broad application prospects in adsorption field.The filtrate after acid leaching reaction contains a large number of metal ions.If discharged directly in actual production,it will cause serious water pollution,which is not in line with the aim of solid waste recycling.For the solution rich in Fe³⁺and Al³⁺,with the increase of the pH value,Fe?OH?₃ and Al?OH?₃ molecules are continuously polymerized,forming Fe?OH?₃ and Al?OH?₃ colloids eventually,which have strong adsorption ability.The research indicated that adding a small amount of polyvinylamide to the filtrate as a polymerizer and using NaOH to adjust the pH value near 3 can polymerize Fe⁺and Al⁺into Fe?OH?₃ and Al?OH?₃ colloids,thus forming Fe-Al polymerized water purifying agent.In this experiment,the prepared water purifying agent has a good purification effect on the suspension,and the turbidity removal rate for the kaolin suspension can reach up 97 percent.In conclusion,this article reported a new method to prepare mesoporous materials,which greatly reduced the cost of preparing mesoporous materials and solved the problem that mesoporous materials are difficult to be large-scale industrialized production,making the wide application of mesoporous materials possible.Meanwhile,the recycling of coal gasification slag reduced the land environmental pollution resulted by the coal gasification industry.In addition,the waste liquid was prepared into water purifying agent by a simple method,which realizes zero pollution of the whole production process and increases the added value of the industry again.It has a high economic benefits and environmental significance.