Preparation Of Magnesia-based Activated Carbon And Research Of Its Adsorption Capacity

In this paper, a series of compounds were prepared with magnesium salts and activated carbon as raw materials by plus-impregnation, incipient-impregnation, mechanical mixing and chemical precipitation & compounding in situ, such as magnesium chloride/activated carbon composites, magnesium hydroxide/ activated carbon composites and magnesia/ activated carbon composites. These compounds were analyzed and characterized by DTA-TGA, BET surface area and pore structure analyzer, X-ray diffraction, infrared spectroscopy and scanning electron microscopy and other modern instruments. The adsorption properties of magnesia-based activated carbon compounds were evaluated by moisture absorption, removal of organic matter and heavy metal ions in wastewater, sulfur compound from FCC gasoline.The compounds such as magnesium chloride/activated carbon composites, magnesium hydroxide/ activated carbon composites and magnesia/ activated carbon composites were prepared by plus-impregnation, incipient-impregnation, mechanical mixing and chemical precipitation & compounding in situ. It showed that the specific surface area of these mesoporous compounds changed with changing the calcination temperature and time, the average pore size of whom larger than 2nm. After the magnesium salt load in the activated carbon, the peak intensity weaken, which indicated that the crystal structure of magnesium salt was destroyed. It was found that magnesium were inside and outside the pores in activated carbon, respectively, in the form of magnesium chloride, magnesium hydroxide and magnesium oxide. Mg and C have a certain fusion.It was showed that the water adsorption capacity increased with the content of magnesium chloride and the relative humidity increasing. The moisture adsorption onto the magnesium chloride/activated carbon composite was followed the pseudo-second order model. The adsobnet could be recycled and reused.The static and dynamic adsorption performance of dyes from aqueous solution on the magnesium oxide-based activated carbon composites(magnesium chloride/activated carbon composites, magnesium hydroxide/activated carbon composites and magnesia/activated carbon composite materials) were studyed. Static adsorption experiment results showed that the adsorption courses were all fast processes;the adsorption of all kinds of dyes onto the composites were followed the pseudo-second order model and could be described respectively by Langmuir or Freundlich isotherm; the adsorption capacities of Weak Acid Red 2R on magnesium chloride/activated carbon were 35.84～714.57mg·g-1 at the temperature of 20～40℃; the adsorption capacityes of Weak Acid Red 2R, Weak Acid Red B,Weak Acid Brilliant Blue RAWL, Methylene and Disperse Navy Blue S-3BG on magnesium hydroxide/activated carbon composites were 178.57～125mg·g-1,32.57～31.55mg·g-1, 37.88～34.82mg·g-1,166.67～212.72mg·g-1 and 120.48～192.31mg·g-1 under the temperature of 20～40℃, while those were 63.69～59.17mg·g-1 and 105.26～70.42mg·g-1 to Weak Acid Red B and Weak Acid Brilliant Blue RAWL on magnesia/activated carbon composites at the same temperature; thermodynamic studies have shown that the adsorption processes of dyes on the magnesium-based activated carbon composites were spontaneous.Dynamic adsorption experiments showed that the mass transfer driving force increased with increasing the initial concentration of dyes, which leaded to the adsorption amount of the Weak Acid Red 2R and the Weak Acid Red B;with the increase of column height and the saturation adsorption time increasing, the percentage of adsorption increased; with the flow rate increasing, through time and the adsorption capacity decreased; the composites prepared were well for a wide range of pH values, but best for acidic conditions; adsorption column could be recycled and reused, with important practical application.The magnesia-based activated carbon composites prepared were examined for the adsorption of heavy metal ions from aqueous solutions by varying the parameters of adsorption time, temperature, initial pH, adsorbent dosage and initial concentration. Studies showed that the adsorption courses were all fast processes; the adsorption of all kinds of heavy metal ions onto the composites were followed the pseudo-second order model;the adsorption of Cu2+ on the magnesia/activated carbon composite and Ni2+ on the magnesium hydroxide/activated carbon composite could be described by Langmuir isotherm, but the adsorption of Cr(VI) on the magnesia/activated carbon composite could be described by Freundlich isotherm; under the temperature of 20～50℃,the adsorption capacities of Cu2+ and Cr(Ⅵ) on CAC1 (CAC1 was prepared using magnesium chloride and straw pulp black liquor as main raw materials) were 22.12～91.74mg·g-1 and 27.03～384.62mg·g-1,but the adsorption capacities of Cu2+ and Cr(VI) on DMC (DMC was prepared using magnesium chloride and activated carbon as main raw materials) were 63.58～85.26mg·g-1 and 32.14～53.26mg·g-1 under the temperature of 25～45℃; the adsorption capacities of Ni2+ on magnesium hydroxide/activated carbon composite were 27.86～34.36mg·g-1 under the temperature of 20～50℃;the adsorption of all kinds of heavy metal ions was found to be endothermic.The removal performance of sulfur compounds from FCC gasoline by magnesium oxide/activated carbon composites with magnesium sulfate and straw pulp black liquor as raw materials (CAS) or with magnesium chloride and activated carbon as raw materials (DMC) was evaluated using dynamic adsorption method. It was found that when sorbent granularity at the range of 40～60 meshes, the best technological parameters of adsorption temperature, volume ratio of gasoline and space velocity to CAS and DMC were 80℃,1.0,5h-1 and 90℃,1.0,5h-1 respectively, sulfur removal efficiencies were higher. In the same conditions, the sulfur hold and desulfurization performance of magnesium oxide/activated carbon composites were higher than activated carbon and magnesium oxide, respectively; when the initial desulfurization capacity of CAS was higher than DMC, DMC had a greater sulfur hold significantly than CAS.GC-FPD chromatograms of gasoline desulfurized clearly showed that sulfur compounds, such as thiophene and 3-methyl-thiophene, in FCC gasoline were adsorbed by magnesia/activated carbon composites, and benzothiophene was removed completely. Magnesia/activated carbon composites after regeneration at 300℃for 2h with nitrogen purge still had a higher desulfurization capacity:desulfurization rate of 88.56%, and the penetration time was 110min.The studies showed that the composites prepared by magnesium salts modified activated carbon could be well applied to air dry, removal of organic matter, heavy metal ions in wastewater and sulfur compounds in FCC gasoline. The preparation of magnesia-based activated carbon composites by magnesium salts and activated carbon can serve two purposes. One hand, it can provide a new way for preparation of inorganic-organic porous material for environmental protection; but on the other hand, it's very important for utilization of magnesium salts from salt lake's of China's western.