Experimental Study On Preparation And Metal Ions Removal Capability Of Expanded Graphite

Expanded graphite is a kind of poriferous material. It has a wide range of pore diameter and a great pore volum. So it has a great potential in practical use for a adsorption. The main objective of this research is to study the adsorption capability of expanded graphite against three kinds of metal ions and optimize the reaction condition. Based on the data aquired in experiments, some mathematical analysis is conducted and some theories are given to explain the experiment results. Furthemore, in order to improve the metal ion adsorption capability of expanded graphite, the expanded graphite is modified by applying relevant modifier.Commercial expandable graphite (purchased from Qingdao Nanshu Hongda Graphite Co. Ltd, China) was directly placed into MicroWave oven.Then, the expanded graphite was prepared. For provide the material characterization, the BET equation and BJH method were used to calculate the specific surface area, pore volume and pore size distribution. The scan electric microscope (SEM) and FT-IR were used to investigate the morphology and chemistry structural characteristics.The experimental results of Pb,Cr and Sn adsorption onto the expanded graphite showed that the pH value of solutions is the most important factor to the effect on the three kinds of metal ions adsorption capacity of expanded graphite.Under the conditions of the initial pH:4-6,concentration of Pb(â…¡):300mg/L and the adsorption time:300min, the adsorption capacity could reach at 63mg/g. Under the condition of the initial pH of Cr(â…¥)=3, the expanded graphite reveals the highest adsorption capability for Cr solution. Under the conditions of the initial pH:2-3, concentration of Sn(â…¡):300mg/L and the adsorption time:120min, the adsorption capacity could reach at 343mg/g. Furthermore, the adsorption equilibrium data were fitted according to Langmuir, Freundlich and Temkin adsorption isotherms, respectively. The results show that the Langmuir isotherm can agree with the adsorption behavior of the three kinds of metal ions on expanded graphite. The calculated Langmuir limit adsorption capacities were 70.42mg/g,2.77mg/g and 378.78mg/g. The adsorption was analyzed using pseudo-first-order, pseudo-second-order, Elovich and Ritchie's kinetics models and the adsorption kinetics were found to follow pseudo-second-order kinetics model.The experimental results of Pb adsorption onto the modified expanded graphite by loading Mg(OH)2 showed that the adsorption capacity increased greatly comparing the expanded graphite. The adsorption quantity could reach at 105mg/g from the original 70mg/g. Under the conditions of the initial pH:4-6,concentration of Pb(â…¡):300mg/L, dosage of the modified expanded graphite:0.035g and the adsorption time:120min, the removal rate could reach at 98%. The adsorption equilibrium data were fitted according to Langmuir, Freundlich and Temkin adsorption isotherms, respectively. The results show that the Langmuir isotherm can agree with the adsorption behavior of Pb on modified expanded graphite. The adsorption was analyzed using pseudo-first-order, pseudo-second-order, Elovich and Ritchie's kinetics models and the adsorption kinetics were found to follow pseudo-second-order kinetics model.