Formation Of Al-MCM-41 Synthesized From Fly Ash And Its Adsorption And Regeneration Of Methylene Blue

The contradiction between contemporary human beings and the environment has become increasingly prominent,in which the problem of water pollution is a difficult problem facing mankind in the twenty-first century.There are many reasons for water pollution,and the discharge of industrial wastewater is the main reason,so people have never stopped exploring the treatment methods of industrial wastewater.Dyestuff wastewater is a representative kind of industrial wastewater.In this study,macromolecular cationic dye methylene blue was used to simulate dyestuff wastewater.The method of synthesizing zeolite adsorbent from fly ash to treat dyestuff wastewater was explored.In this paper,mesoporous material Al-MCM-41 was synthesized by alkali melting hydrothermal synthesis using fly ash from power plant as silica-aluminium source.The optimum forming conditions were determined by adsorption capacity and mechanical strength experiments under the conditions of forming pressure of 20 MPa and particle size of 0.6～1 mm.Static adsorption experiments were conducted to investigate the effects of different conditions on adsorption efficiency.It was found that increasing the amount of adsorbent could increase the adsorption rate and decrease the adsorption capacity of adsorbent per unit;AlMCM-41 had strong adsorption capacity at pH≥5 and was not easy to adsorb methylene blue under acidic conditions;higher temperature was not conducive to the adsorption reaction of AlMCM-41;and the adsorption equilibrium time of Al-MCM-41 particles for methylene blue solution was about 2 hours.Langmuir,Temkin and Freundlich adsorption isotherm models were used to fit the adsorption process.Langmuir model had a good fitting effect.Monolayer adsorption was the main mode of adsorption,and the adsorption process was physical adsorption and exothermic reaction.The maximum adsorption capacity of Al-MCM-41 qmax,fitted at 30,40,50℃ were 115.49,111.78,109.61 mg/g,respectively.qexp was 117.05,114.01,111.50 mg/g,respectively.They are basically the same.The fitting results of quasi-first,quasi-second and Elovich absorption kinetics models show that the fitting effect of quasi-first and quasi-second order kinetics models is better than that of quasi-first order kinetics model,and quasi-second order kinetics model is slightly better than that of quasi-first order kinetics model.The results showed that the main factor affecting the adsorption rate of methylene blue on Al-MCM-41 was the concentration of adsorbent.The regeneration experiments of Al-MCM-41 particles which lost the adsorption capacity after reaching the adsorption equilibrium showed that the regeneration of Al-MCM-41 particles by hydrogen peroxide had good adsorption performance.With the increase of regeneration time,the regeneration rate of Al-MCM-41 particles increased and reached regeneration equilibrium after 240 minutes.Excessive high and low concentration of H2O2 solution are not conducive to the regeneration of adsorbents.The optimal concentration of H2O2 is 0.990 mol/L.The more methylene blue loaded,the worse the regeneration ability of the polymer sieves.The increase of regeneration temperature can accelerate the time of reaching regeneration equilibrium,but can not improve the regeneration rate.After 10 recycling cycles,the regeneration rate of AlMCM-41 particles is over 70%,and the reusability of Al-MCM-41 particles is good.After repeated regeneration cycles,the average pore size of Al-MCM-41 particles changed little,and the specific surface area and pore volume decreased significantly.The main reason for the decrease of equilibrium adsorption capacity is that residual methylene blue components are blocked and accumulated in the pore channels.The most widely distributed pore size of the regenerated material is 2.73 nm,which is less than 3.09 nm at the initial synthesis stage.The pore structure has not changed significantly.Al-MCM-41 particles can be reused.After many times of regeneration,the basic morphology of the material remained unchanged,and the size of the material was about 0.2～0.3 micron.The material still had obvious pore structure.