Synthesis Of Layered Sodium Silicates From Rice Husk Ash For Use As Absorbent To Removal Of Pb(Ⅱ) From Aqueous Solution

In recent years,for the use of phosphorus builders detergents,resulting in serious river nutrition,bring the serious pressure to environment protection.Layered sodium silicates,which have the excellent ion exchange capacities,strong adsorption properties and pH buffering ability,are regarded as a new phosphorus-free detergent builder and have received wide attention.However,the high cost and relatively complex process limit the application of layered sodium silicates.The use of a wide range of renewable rice husk ash as silicon source to prepare layered sodium silicate,not only achieve the re-use of agricultural waste,but also can reduce the exploitation of siliceous mines,which is also of great significance to environmental protection and environmental pollution control.Moreover,layered sodium silicates are used in heavy ion adsorption,which not only broaden the application of this material,but also provide the effective theoretical basis for layered sodium silicates to remove of heavy ion from aqueous solution.In this thesis,rice husk ash as silicon source,and sodium hydroxide as the sodium source are used to prepare layered sodium silicates by solid phase method.By XRD,SEM,FTIR,the composition,structure and microstructure of layered sodium silicates were characterized,and the preparation conditions were optimized.The calcium and magnesium ion exchange capacity and water immersion stability of layered sodium silicates were analyzed.The adsorption properties of layered sodium silicates on Pb²⁺ were studied,and the adsorption mechanism was discussed.This thesis has obtained the following results:（1）Rice husk ash and sodium hydroxide in a molar ratio of 1: 1,the influence of crystal stabilizer dosage,crystal stabilizer types,reaction temperature and reaction time on the products had been studied.The results showed that the optimum conditions for the preparation of layered sodium silicates by solid phase method were at 720°C for 90 min in conjunction with Alcl3 with the amount of Al/Si molar ratio of 0.02.（2）In the optimum conditions,the prepared layered sodium silicates showed a high δ-Na2Si2O5 phase content,which reached 90%.The prepared layered sodium silicates were composed of irregular crystal particles,and the intergranular bonding was more loose and there were more pores.The prepared layered sodium silicates had a greater specific surface area and pore capacity than the commercial layered sodium silicates.（3）The prepared layered sodium silicates exhibited excellent Ca2（10）and Mg2（10）binding capacities(Ca²⁺: 406 mg/g,Mg²⁺: 453 mg/g),which reached the industry standard for use as detergents.（4）The water immersion stability of layered sodium silicates was analyzed.The results showed that the addition of AlCl3 with Al/Si molar ratio of 0.02 can improve the immersion stability of the prepared layered sodium silicates.（5）The process conditions for adsorption of Pb²⁺ by layered sodium silicates were optimized.The optimum parameters were found to be adsorbent dose 2g/L,pH=6,contact time 10 min,contact temperature 25°C for 100mg/L Pb²⁺ ion concentration,which exhibited a Pb²⁺ removal rate 99% and saturated adsorption capacities 53.70 mg/g.（6）The adsorption kinetics,adsorption isotherm,thermodynamics of adsorption and adsorption mechanism were studied.The adsorption process for layered sodium silicates adsorption on Pb²⁺ followed the Langmuir model and the pseudo second order kinetics model.The adsorption enthalpy change ΔH=27.79KJ/mol for the adsorption on Pb²⁺,indicating that the adsorption reaction was the endothermic physical adsorption process,the adsorption free energy ΔG<0,indicating that the adsorption reaction was spontaneous.（7）The adsorption mechanism revealed surface complexation and physical adsorption play a major role in the adsorption of layered sodium silicates on Pb²⁺.