Study On The Preparation Technologies And Properties Of Activated Carbon Separated From Fly Ash

Activated carbons were prepared from the carbon powder separated from the fly ashwith various methods, physical activation, chemical-physical activation and KOHchemical activation. The activation processing of the ACs from the fly ash wasinvestigated. The influences of the ACs activation process on their pore structure andadsorption capacity of the AC were systematically studied. The results showed thatACs could be obtained from the fly ash by the physical activation method. Thespecific surface area and the yield rate of the ACs were enhanced by a pretreatment inammonium-salt solution, and the volume ratio of ammonium-salt solution to carbonpowder (ml:g) effects the specific surface area of ACs obviously. The ACs with highspecific surface area were obtained from the fly ash by the chemical activation withKOH solution. The optimal preparation process was decided by an orthogonal designobtaining the ACs with the specific surface area up to 2322.3m2/g, resulting in largerpore volume and better adsorption capacity. The property of AC was improved due toKOH reacting with the inorganic matters such as SiO2 and Al2O3 of the raw materials.KOH could be used not only as the reagent for activating the carbon powder but forremoving the ash of ACs because some soluble compounds generated and removed bysequent water washing.The analysis of the pore structure on the ACs showed that the pore size distribution ofthe ACs obeys some regular. The pore volume and the size distribution of the ACinfluence its specific surface area. The higher specific surface area of the ACsdepends on their narrow pore diameter and large pore volume. The specific surfacearea of the AC results in the adsorption capacity to the organic vapor from gas andCr(VI) from liquid phase.The results of X-ray diffraction (XRD) revealed that the ACs made by variousactivation methods had different micro-crystal structures. The micro-crystal size andthe layer distance of AC were calculated according to the equation of Bragg and theformula of Sherry. The results showed that the degree of graphitization decreased andthe content of the amorphous carbon increased with enhancing the specific surfacearea of the ACs. The irregular degree of micro-crystal structure increased.An oxidization processing in the oxidizing liquid reagents subsequent to heattreatment on the commercial AC changed the content of oxygen functional groups onthe surface of ACs and enhanced the ion exchange capacity of ACs. The analysis ofX-ray photoelectron spectroscopy (XPS) showed that the content of oxygen andcarbon changed greatly due to the oxidization. The adsorption capacity of ACs onCr(VI) from the waste water was increased resulting from the oxidizationmodification on the surface of ACs.