Recycling of Residual Oil Fly Ash: Synthesis and Characterization of Activated Carbon by Physical Activation Methods for Heavy Metals Adsorption

In this study, the recycling possibility of residual oil fly ash (ROFA) towards preparing activated carbon and its application in environmental remediation through adsorbing Cu (II) and Pb (II) ions from aqueous solutions were investigated. Activated carbons were prepared using two different physical activation methods such as under steam flow at 950 0C, and combined steam and CO2 flow at 850 0C for 2 hours. Characterization of activated carbons was done by BET surface area method, scanning electron microscopy (SEM), Fourier transform infra-red spectroscopy (FTIR), and X-ray diffraction technique (XRD). Combined gasification increased the surface area of ROFA particles quite higher (110.89 to 423.09 m2/g) than only steam activation (275.07 m2/g). Development of microporosity was also achieved during the treatments and it increased from 0.043 cc/g (raw ash) to 0.325 in steam activated samples, and 0.078 in combined gas activated samples. FTIR analysis showed the presence of aromatic, ester, and hydroxyl functional groups on the ROFA surface after the treatment while XRD examination confirmed its carbonaceous and amorphous nature. pH 5 was found optimum for the adsorption studies at which the removal efficiencies were > 71% for Cu (II) and > 80% for Pb (II), while the concentration was 25 ppm for both metals. The Langmuir isotherm model was found statistically significant for both Cu (II) (R2 > 0.95) and Pb (II) (R2 > 0.99). ROFA has been successfully recycled in this work and the activated carbons might be considered for industrial applications.