Preparation And Adsorption Behavior Of Magnesium Contained Porous Materials

Magnesium chloride is abundant in salt lakes in China. In some extent, it is bad for life and production. In order to make use of magnesium chloride, magnesium contained porous materials were prepared by mixture of magnesium chloride, silica and silica solution. The optimum preparation conditions were assured by uniform designs. The magnesium contained porous materials prepared under the optimum conditions were characterized by N2 adsorption/desorption isotherms, X-ray diffractometer, FT-IR spectrometers and thermogravimetry. The adsorption capacities of magnesium contained porous materials were evaluated by adsorbing dyes, metal ions and fluoride from aqueous solution, SO2 from gas and water vapor from air.The preparation of magnesium chloride modified silica need two steps of dehydration. The optimum preparation conditions were: first dehydration temperature of 60℃, second dehydration at 140℃for one and a half day. The BET surface areas of the sample prepared is 232.35 m2·g-1, which is intervenient of silicon dioxide (303.61 m2·g-1)and magnesium chloride(24.05 m2·g-1). The average pore radius is 10.95 nm, while the pore radius for silicon dioxide and magnesium chloride are 11.41 nm and 7.37 nm, respectively. These data indicate that the combined desiccant is not mechanical mix, but magnesium chloride penetrate into the pore of silica. The combined method can conquer the disadvantage of low uptake capacity of silicon dioxide and the deliquescence of magnesium chloride. And the water vapor uptake capacity of magnesium chloride modified silica is about 5 to 30 times larger than silica gel.Magnesia modified silica was prepared by three ways, namely superfluous solution soakage, equal solution soakage and equal solution soakage- precipitation methods. Compare the three methods, it can be find that the equal solution soakage way is easy to operate, economic and the best property for adsorption. By changing the concentration of magnesium chloride and repetitious soakage, the content of magnesia can be much more. The optimum preparation conditions were: Dipping at 25℃for 24 h, and then calcining at 500℃for 4 h. Sol-gel is the way for preparation of porous magnesium silicate use magnesium chloride and silicon solution. In uninterrupted mix round, the magnesium chloride and silica solution are mixed. The optimum pH value is about 10. Then, 0.2 % polyacry lamide act as flocculant was added in mixture. After aging for 24 h, the mixture were calcined at 7500℃for 1 h. The content of magnesia in porous magnesium silicate was controlled by the concentration of magnesium chloride solution. The BET surface area changed from14.18 m2·g-1 to 177.37 m2·g-1.The magnesium contained materials prepared were examined for the adsorption of dyes (Methylene blue and Weak acid red), metal ions ( Cu2+ and Ni2+) and fluoride from aqueous solutions by varying the parameters of adsorption time, temperature, initial pH, initial concentration and salinity of solution. Studies showed the adsorption of all the pollutants are followed the pseudo-second order model and could be described by Langmuir isotherm, Freundlich isotherm and D-R isotherm. Also, the adsorption mechanisms are not the same.The study of adsorption SO2 onto magnesia modified silica prepared showed that the adsorption capacities increase with the increasing of sorbent amount and decrease with the flow velocity and SO2 inlet concentration. Water vapor is beneficial for desulfurization. The adsorption amount of SO2 is much better than commercial silicon dioxide when water vapor presented. The adsorption mechanism of SO2 study showed that the mechanism of SO2 adsorption in SO2-H2O system is of physical adsorption and it could be changed to chemical adsorption when water vapor presented. The chemical adsorption played a more important role than physical adsorption.The study of preparation and adsorption behavior of magnesium contained porous materials show that all the materials have good characteristics. This is the first study of preparation of magnesium contained materials by magnesium salts from brine and salt lakes, the study can serve two purposes. First, it can provide a new way for magnesium salts from brine utilization; second, a useful, cheap and value-added sorbent for pollution treatment can be made. So this study is such an exploring research that has the certain prospect, innovation and important applied foreground.