Preparation And Adsorption Properties Of Porous Magnesium Silicate

Synthetic magnesium silicate has good selectivity and highly efficient adsorption characteristics.It can be widely used in the treatment of industrial waste water,decolorization and acid-reduction treatment of frying oils,and purification of polyether polyols.In the process of material preparation,the pH value,concentration,and the mode of addition of the reactants are closely related to the structure and adsorption properties of the synthesized magnesium silicate.In this dissertation,the magnesium silicate sample was prepared by precipitation method using magnesium sulphate solution and sodium silicate solution as the raw materials.The acid-modulated and alkali-adjusted pH value of sodium silicate solution and calcination temperature was studied respectively,and its effect on the structure and adsorption properties of magnesium silicate sample was also studied.The specific experimental results are as follows:(1)Amorphous magnesium silicate was prepared with sodium silicate and magnesium sulfate.The magnesium silicate samples calcined at different temperatures were all porous materials,and their specific surface area,pore volume and external surface area decreased with increasing calcination temperature,but there was no change in the chemical composition and valence state of the samples.Among them,the specific surface area of the uncalcined sample was 362 m2·g-1.TPD analysis showed that the high temperature calcination was conductive to the formation of stronger acid-base adsorption center.Then with the increasing of the calcination temperature,the number of total alkaline sites and total acid sites on the samples surface decreased,meanwhile,the methylene blue adsorption amount and the oleic acid adsorption rate in vegetable oil all decreased.(2)The pH value of the sodium silicate solution was adjusted from 11.80 to 11.26 with 1 mol·L-1 H2SO4 solution,and the synthetic magnesium silicate samples were amorphous and had porous texture.Among them,the specific surface area of the sample synthesized by sodium silicate solution with pH value of 11.39 reached 482 m2·g-1.With the decreasing of the pH value of the sodium silicate solution,the strength of the acid-base active center of the samples remained basically unchanged,while the number of total alkaline sites decreased and total acid sites increased.The adsorption of methylene blue on all samples accorded with the pseudo-second-order kinetic model.The adsorption of methylene blue on the sample synthesized by sodium silicate solution with pH value of 11.39 reached 145.74 mg·g-1,while the adsorption rate of oleic acid on the sample synthesized by sodium silicate solution with pH value of 11.76 reached 13.12%.(3)The pH value of sodium silicate solution was adjusted from 11.80 to 13.47 with NaOH,and the synthesized magnesium silicate samples were amorphous and the porous materials.Among them,the specific surface area of the sample synthesized by sodium silicate solution with pH value of 12.00 reached 433 m2·g-1.With the increasing of the pH value of the sodium silicate solution,the strength of the acid-base active center of the sample remained basically unchanged,while the number of total alkaline sites increased and total acid sites decreased.The adsorption of methylene blue on all samples accorded with the pseudo-second-order kinetics model.The adsorption of methylene blue and oleic acid on sample synthesized by sodium silicate solution with pH value of 12.00 were relatively large,which were 116.83 mg·g-1 and 14.01%,respectively.