Preparation Of Composite Adsorbents Of Activated Carbon Supported Manganese/magnesium And Adsorption Of Rhodamine B

Granular activated carbon（GAC）is widely used in the field of water treatment because of its abundant pore structure,large specific surface area and stable physical and chemical properties.However,with the increasing difficulty of environmental improvement,the activated carbon of higher adsorption capacity is needed to deal with the different pollutants in the environment.Modification of activated carbon is one of the most effective methods to expand its scope of application and improve its function.Method of “impregnation-coprecipitation-calcination” was used to prepare MnO₂-AC modified material for Rhodamine B removal.Optimal preparation conditions were obtained through the orthogonal experiment and discussion of main influence factors such as: Mn（NO₃）₂ concentration of 0.1mol/L,Na₂CO₃ concentration of 0.5mol/L,impregnation time of 1.0h,calcination temperature of 360℃,calcination time 3.5h.The modified materials were characterized by X-ray diffraction,scanning electron microscopy and thermal analysis.It was found that the surface roughness increased after modification;manganese content was 4.41mg/g,its specific surface area was 1.08 times of AC,the total pore volume was 2.69 times of AC.Microporous and mesoporous content was increased.MnCO₃ was decomposed into MnO₂ under the calcination temperature of 360℃.This same preparation method of MgO-MnO₂-AC modified material was carried out and optimal conditions were: Mn（NO₃）₂ concentration of 0.1mol/L,Na₂CO₃ concentration of 0.5mol/L,MgCl₂ concentration of 0.5mol/L,NaOH concentration of 0.3mol/L,impregnation time of 1.0h,calcination temperature of360℃,calcination time 2.5h.It was found that the surface of MgO-MnO₂-AC morphology and pore structure has changed,microporous and mesoporous content was increased,manganese content was 5.51mg/g,magnesium content was 34.24mg/g,its specific surface area was 1.46 times of GAC,the total pore volume was 3.69 times of GAC.Under the calcination temperature of 360℃,Mg（OH）₂,MnCO₃ and Mn（OH）₂were decomposed into MgO and MnO₂,respectively.Rhodamine B was choosen as the static adsorption substance of composite adsorbents,and compared the adsorption performance with the original activated carbon.The results showed that under the Rhodamine B concentration of 50mg/L,reaction temperature of 25℃,AC,MnO₂-AC and MgO-MnO₂-AC adsorbent dosageof 0.3g,avoid light reaction of 11 h,the adsorption capacity reached 9.65mg/g,15.76mg/g and 16.19mg/g,respectively,and the adsorption capacity of modified adsorbents were stronger than that of the original activated carbon.Two kinds of modified materials were fitted with the pseudo second-order kinetics equation;and the adsorption behavior was appropriated Langmuir isotherm model;the adsorption process was spontaneous and exothermic,the higher temperature was favorable to the reaction.