Synthesis And Sorption Properties Of The Porous Magnesian/Silics Materials

In this paper, magnesium chloride modified silica and magnesia modified silica were prepared by plus-impregnation used magnesium salt and silica gel as raw materials. The magnesian contained porous materials were analyzed and characterized by XRD, DTA-TGA, infrared spectroscopy, BET, scanning electron microscopy. The adsorption properties of those materials were evaluated by absorption experiments for moisture, dyes (Methylene blue and basic violet) and heavy metal ions (Ni²⁺) from wastewater.The synthesis of MgCl2·xH2O/silica by plus- impregnation needs two steps of drying. The optimum synthesis conditions were: firstly dehydrat at 60℃then the second dehydration temperature is 130℃for 5 h. The BET surface area of the desiccant is 124.41 m2·g-1 and the average pore size is 14.64 nm. At the experiments contions, the final moisture uptake of MgCl2·xH2O/silica is about 10 to 15 times larger than final moisture uptake of silica gel.Two kinds of magnesia modified silica (CKGS and ZCGS) were prepared by two types of silica gel. The optimum preparation conditions of CKGS were: using 2mol/L magnesium chloride aqueous solution, at pH=5.84, dipping at 25℃for 5 h, then calcining at 500℃for 5 h. The optimum preparation conditions of ZCGS were: using 2mol/L magnesium chloride aqueous solution, at pH=5.23, dipping at 25℃for 2 h, then calcining at 400℃for 5 h. Two magnesia modified silica analyzed and characterized using modern instruments. The results show that the pore size and the surface areas of two absorbents were decreased. IR spectrogram showed that the peaks of silica gel were also contained; the characteristic peaks of MgO presented at XRD spectrogram. TG-DSC spectrograms shown two compounds have good stabilization.Two kinds of magnesia modified silica (CKGS and ZCGS),used as the adsorbents to remove dyes (Methylene blue and basic violet) and metal ions (Ni²⁺) from wastewater, were studied by changing adsorption time, temperature, initial pH and initial concentration. As the result shown, the adsorbents have good performance to adsorpt pollutants; the adsorption of all the pollutants can be described by Langmuir isotherm and the adsorption follow the pseudo-second order model. The chemical adsorption is the main process.As the results shown, all the adsorbents which prepared by magnesium salts modified silica gel can be well employed to air dehumidification, and adsorbent organic matters, heavy metal ions from wastewater. The preparation of magnesium chloride/magnesia modified silica composites can serve two purposes. Firstly, a new way for preparation of inorganic-organic porous material for environmental protection is given; secondly, it's also given a new way to enlarge utilization of magnesium salts from salt lakes in western China.