Modification Of Expanded Graphite And Its Adsorption Properties For Heavy Metal Ions

Expanded graphite is a porous material,often used as an adsorbent,has attracted attention in the treatment of metal ion wastewater,but the effect of a single expanded graphite as an adsorbent is not ideal.Therefore,the adsorption process of modified graphite with Al（NO₃）₃ and chitosan was studied in this paper.The adsorption properties of Cr⁶⁺,Cu²⁺ and Cd²⁺ were studied.The main research contents are as follows:（1）The effects of the concentration of Al（NO₃）₃ impregnation solution,the temperature of water bath and the activation temperature on the properties of the preparedγ-Al₂O₃/expanded graphite adsorbent were investigated.The optimum conditions were as follows: the concentration of impregnation solution was 0.025g/mL,The bath temperature was 60℃ and the activation temperature was 145℃.The properties of γ-Al₂O₃/expanded graphite adsorbents were characterized by SEM,XRD,FT-IR and TG-DTG.The results show that the modified γ-Al₂O₃/expanded graphite adsorbents are loose and well-Specific surface area,and the overall performance is relatively stable.（2）The effects of single factor such as pH value,stirring time,initial concentration of solution,amount of adsorbent and temperature on the adsorption rate of Cr⁶⁺,Cu²⁺ and Cd²⁺ were investigated by using γ-Al₂O₃/expanded graphite as adsorbent.The optimum conditions were obtained as follows: pH(Cr⁶⁺)=3、t(Cr⁶⁺)=60 min、C(Cr⁶⁺)=200 ug/mL;pH(Cu²⁺)=4、t(Cu²⁺)=30 min、C(Cu²⁺)=200 ug/mL;pH(Cd²⁺)=7、t(Cd²⁺)=80 min、C(Cd²⁺)=150 ug/mL,and the adsorption of Cr⁶⁺ is stronger.The whole adsorption process is in accordance with the quasisecond-order kinetic equation model and the Langmuir isotherm model,and the adsorption follows the monolayer adsorption.（3）The chitosan/expanded graphite composite adsorbent was prepared by impregnating the expanded graphite with chitosan solution.The effect of chitosan and expanded graphite on the adsorption rate was investigated.The optimum conditions were obtained: the mass ratio of chitosan to expanded graphite was 0.5,and the mixture was stirred for 3 hours.The properties were characterized by SEM,XRD,FT-IR and TG-DTG,the results show that the chitosan/expanded graphite composite adsorbent contains the functional groups such as-COOH,-OH and-NH2.Chitosan adhered to the surface of expanded graphite,the surface structure of expanded graphite has a promoting effect on the attachment of chitosan.The chitosan/expanded graphite adsorbent prepared after modification has large dispersibility,and in high temperature conditions,heat stability,less weight loss.（4）The effects of single factor such as solution pH value,stirring time,initial concentration,amount of adsorbent and temperature on the adsorption rate of Cr⁶⁺,Cu²⁺ and Cd²⁺ in solution were investigated by using chitosan/expanded graphite as adsorbent.The best experimental conditions are: pH(Cr⁶⁺)=3、t(Cr⁶⁺)=60 min、C(Cr⁶⁺)=200 ug/mL;pH(Cu²⁺)=4、t(Cu²⁺)=30 min、C(Cu²⁺)=200 ug/mL;pH(Cd²⁺)=7、t(Cd²⁺)=80 min、C(Cd²⁺)=150 ug/mL,and the adsorption of Cu²⁺ is stronger.The whole adsorption process is in accordance with the quasisecond-order kinetic equation model and the Langmuir isotherm model,and the adsorption follows the monolayer adsorption.