Preparation, Characterization And Adsorption Properties Of Magnesium Silicate Gels

Magnesium chloride is very rich in the ocean. Magnesium salt has not been applied effectively, which wastes magnesium resources and pollutes the environment. Therefore, the development and utilization of the marine magnesium resources would resolve the question of the comprehensive utilization of chemical resource and develop the new field of magnesium usage. This thesis involved the preparation of magnesium silicate gels by the ways of sol-gel and hydrothermal methods based on the reaction of magnesium chloride, magnesium sulfate and sodium silicate. The physicochemistry properties (special surface area, pore-size distribution, surface activated group, structure morphology, surface acid-base property and stability) of the obtained samples were characterized through N2adsorption/desorption isotherms analysis, X-ray diffractometer, FT-IR spectrometers, Scanning electron microscope and other chemical analysis methods. Moreover, the adsorption properties of the as-prepared magnesium silicates gel were determined through the remove the dyes, heavy metal ions and PO43-from aqueous solution, and the principle of thermodynamic and kinetics in the adsorption process was also studied, then the adsorption mechanism was discussed. The main research contents and results are as follows:1. The different Mg/Si molar ratio magnesium silicate gels were prepared through sol-gel and hydrothermal methods. The adsorption capacity of magnesium silicate gels was evaluated through MB as target object. The effect of reactant concentration, time and hydrothermal temperature on the synthesis of magnesium silicate gels was investigated. The results showed the material adding order, reactant concentration, sodium silicate solution pH value, Mg/Si molar ratio, magnesium source and silicate source and hydrothermal temperature would influence the synthesis of magnesium silicate gels. The optimal synthesis condition could be obtained with reactant concentration as1mol·L-1, Mg/Si molar ratio as1:1, pH value as10-12and hydrothermal temperature as120℃。2. The structure morphology of magnesium silicate gels was determined by modern analytical instruments and chemical analysis methods. The results presented the N2 adsorption/desorption isotherms were belonged to the classical type IV with the obvious hysteresis loop. The special surface area of magnesium silicate gels obtained from sol-gel varies from202.49-494.19m2·g-1with the average pore size as2-5nm, and the high special surface area as576.4m2·g-1was obtained through hydrothermal method. The calcinations influenced the special surface area and pore structure seriously. FT-IR showed the abundant silicon hydroxyl group and magnesil group on the magnesium silicate gels surface. XRD diffraction patterns have three amorphous diffraction peaks, which proved magnesium silicate gels were non-critical phase structures. SEM analysis demonstrated that magnesium silicate gels were amorphous structure and the particals showed preferably dispersibility and inter-particles aggregation. The studies of surface acid-based properties and chemical stability showed magnesium silicate gels had good buffer function and chemical stability.3. MB chosen as adsorption target object indicated the difference in the adsorption properties of the different Mg/Si molar ratio magnesium silicate gels and R-MS-Cl-1showed the best adsorption efficiency. The samples obtained with hydrothermal method displayed better adsorption properties and the hydrothermal temperature greatly affected the adsorption of the different Mg/Si molar ratio magnesium silicate gels. Based on the difference in the adsorption of the different contaminants onto magnesium silicate gels, the effect of the pollutant concentration, adsorbent dose, solution pH value, contact time and temperature on the adsorption properties was investigated.4. MB, WAR2R, basic brow and chrysophenine were chosen as adsorption objects to study the adsorption properties of magnesium silicate gels. The results proved the rate of removal increased with increasing dyes concentration, and it was not affected by solution pH value. The studies of the adsorption thermodynamics showed Langmuir adsorption model could describe the adsorption process of four dyes and the adsorption was preferential adsorption. Adsorption free energy ΔG<0showed the adsorption process were spontaneous, irreversible process. Enthalpy change ΔH>0presented the adsorption action was endothermic, and the little AH value explained the adsorption was physical adsorption in nature, and high temperature was favorable for the adsorption. The studies of kinetics proved Pseudo second-dynamics equation could describe the adsorption behavior and the adsorption equilibriums could be attained in a short time. Intra-particles diffusion was not the unique control step and the whole adsorption process contained three stages:rapid adsorption process, adsorption equilibrium process gradually and adsorption equilibrium process.5. The optimal adsorption condition of PO43-onto H-MS-Cl-2was the adsorbent dose as2g·L-1and PO43-initial concentration as50mg·L-1. The solution pH values did not influence the adsorption efficiency and the equilibrium adsorption capacity was41mg·g-1. Freundlich adsorption model and Pseudo second-dynamics equation could describe the adsorption behavior, and the rate constant k2decreased with increasing the adsorption temperature. The thermodynamics parameters with ΔG<0,ΔH>0,ΔS>0presented the adsorption was spontaneous, endothermic and physical adsorption process. The value of adsorption enthalpy change AH showed the weak force between H-MS-Cl-2and PO43-.6. The adsorption of nickel and cobalt ions onto R-MS-Cl-1showed good adsorption efficiency and the adsorption equilibrium time was reached in1.5-2h. The maximum removal was attained with solution pH equal to5, Pseudo-second order adsorption kinetics could describe the adsorption behavior very well and reflect the adsorption mechanism of ions adsorbed onto magnesium silicate gel. Adsorption was spontaneous, rapid and physically endothermic process at the different temperature, and the high temperature was favorable for the adsorption of two metal ions.The study focused on the natural rich magnesium silicate minerals with the high adsorption properties and the rich magnesium resources in the brine. A series of the different Mg/Si molar ratio magnesium silicate gels were synthesized by sol-gel and hydrothermal methods, and successfully applied in the removal of dyes (MB, WAR2R, Basic brown and Chrysophenine), heavy metal ions (nickel and cobalt ions) and PO43-from aqueous solution. The aims of the research involve in preparing a kinds of new adsorbent materials which could have a certain practical value and high-efficiency environmental benefits in environmental governance and providing the new fields for the utilization of magnesium salt. Therefore, the research would have important theory innovation significance, potential practical value and obvious environmental benefits.