Study On Preparation And Adsorption Characteristics Of Magnesia/Activated Carbon Composites

Magnesia/activated carbon composites are prepared by CO₂ activation from magnesium salt and straw pulp black liquor, magnesium salt and commercial activated carbon respectively. The optimum preparation conditions are assured by uniform design. The magnesia/activated carbon composites prepared under the optimum conditions are characterized by N₂ adsorption/desorption isotherms, scanning electron microscope(SEM), energy dispersive spectrometry(EDX) and X-ray diffraction(XRD). The adsorption capacities of magnesia/activated carbon composites are evaluated by adsorbing anion dyes Weak acid red 2R, reactive yellow, and heavy metal ions Cu²⁺, Cr(VI) from aqueous solution.The optimum preparation conditions for preparing magnesia/activated carbon composites from magnesium salt and straw pulp black liquor are: MgCl₂·6H₂O dosages of 0.3 mol·L^-1, activation temperature of 550℃, activation time of 3.5 h and CO₂ flow velocity of 300 ml·min^-1. Iodine adsorption value under the best conditions are 508.34⁵25.86 mg·g^-1. The BET surface area of the samples is 388.96 m²Â·g^-1, and the average pore radius and micropore volume are 4.14nm, 0.08 mL·g^-1. The results show that the samples have mesoporous nature.The optimum preparation conditions for preparing magnesia/activated carbon composites from magnesium salt and commercial activated carbon are: MgCl₂·6H₂O dosages of 3.7mol·L^-1, activation temperature of 800℃, activation time of 2.8 h, and CO₂ flow velocity of 200 mL·min^-1. Iodine adsorption value under the best conditions are 905.35⁹23.17mg·g^-1. The BET surface area is 687.21m²Â·g^-1. The average pore radius and micropore volume are 2.09nm, 0.31 mL·g^-1, which show that the samples have mesoporous nature.BET results indicate that magnesium and carbon are uniformly dispersed in the Samples. The magnesia/activated carbon composites prepared containe main elements: C, O and Mg, while the latter product containes certain amount of impurities Si.The adsorption capacities of magnesia/activated carbon composites are evaluated by adsorbing anion dyes Weak acid red 2R, reactive yellow, heavy metal ions Cu²⁺ and Cr(VI) from aqueous solutions by varying the parameters of adsorption time, initial pH, adsorbent dosage and initial concentrations. Studies show that the adsorption of anion dyes Weak acid red 2R, reactive yellow, Cu²⁺ onto magnesia/activated carbon composites prepared can be described by Langmuir isotherm, and the saturated adsorption mount are 166.67,178.74,212.36mg·g^-1; 83.67,92.36,96.54mg·g^-1and 63.58,76.37,85.26 mg·g^-1 at 25,35 and 45℃. While the adsorption of Cr(VI) followes Freundlich adsorption isotherm model. Studies show that the adsorption of Cu²⁺ and Cr(VI) onto magnesia/activated carbon composites prepared follows the pseudo-second order model. The composites regenerated by calcinying at 550℃still perform well.Magnesia/activated carbon composites are prepared from magnesium salt and straw pulp black liquor, magnesium salt and commercial activated carbon respectively. Magnesia/activated carbon composite showes good adsorption properties and it may provide a new way for magnesium salts from brine utilization.