REMOVAL OF HEAVY METALS FROM AQUEOUS SOLUTION USING ACTIVATED CARBON PREPARED FROM AGRICULTURAL WASTES

SOURCE:

Faculty: Physical Sciences
Department: Pure And Industrial Chemistry

CONTRIBUTORS:

Abugu, H. O.
Okoye, P.A.C.
Ajiwe, V.I.E.

ABSTRACT:

The adsorption of Mn, Ni, Cd and Pb by four agro-waste based activated carbons prepared from pear nut seed, oil bean shell, palm kernel shell and snail shell was investigated in order to analyse the equilibrium and kinetic effects of the process, as well as assess its viability as an adsorbent. The activated carbon was prepared by carbonization at 600oC and 800oC for 30minutes and activated with H3PO4, HCl and H2SO4. The agro-wastes were characterized for the elemental and proximate content. Some physical properties of the carbon such as surface area, pH, pore volume, carbonization temperature were determined. Both the activated and non-activated carbons were characterized using Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscope (SEM) to determine the functional groups present and the surface morphology of the carbon respectively. Batch adsorption studies were carried out to study the adsorption process. Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models were used to describe the adsorption type. Pseudo first-order and pseudo second-order kinetics models as well as intraparticle diffusion model were also used to fit the experimental data. The pH values of the adsorbents ranged from 6.31 to 6.82, while the adsorbents surface area ranged from 267 to 1010 m2/g. The elemental content analysis showed the presence of some heteroatoms such as N2, O2, H, S8 and the FTIR showed the presence of several functional groups such as CO, COOH, OH, NH, CH. The SEM results also showed that there was higher number of pores on the activated carbons than the non-activated carbons which was as a result of the activation process. The experimental data was found to fit very well to the Freundlich Isotherm model which suggests heterogeneous adsorption. Pseudo second-order model best described the kinetics of the adsorption process which suggests chemisorptions. The Hybrid fractional error function (HYBRID) and Marquardt’s percentage standard deviation (MPSD) non-linear regression error functions, as well as the closer values of the calculated adsorption capacities of the activated carbons to the experimental adsorption capacities, also suggests pseudo second-order to be the best kinetic model to describe the adsorption process. The intraparticle diffusion model showed that the rate limiting step in the adsorption process was controlled by one or more steps such as external diffusion, pore diffusion, surface diffusion, adsorption on the pore surface or a combination of more than one step rather than intraparticle diffusion. Pear nut seed activated carbon carbonized at 8000C and activated with H2SO4 gave the highest percentage adsorption of Pb from the wastewater examined, while the least was shown by Snail shell activated carbon carbonized at 8000C and activated with H3PO4. Finally, the best adsorbent for Ni and Pb adsorption was Oil Bean activated carbon carbonized at 600oC and 800oC and activated with HCl respectively. But for Cd, it was Palm kernel activated carbon carbonized at 800oC and activated with HCl, while for Mn, it was Snail shell activated carbon carbonized at 600oC and activated with H3PO4. In all generally, carbonization at a higher temperature gave a lower percentage yield but better adsorption capacity. H3PO4 was observed to be the best activating agent followed by H2SO4 while HCl was the least.