Abstract:
Low cost oxidized and un-oxidized activated carbon samples were prepared from
saw dust and seed shells of Ziziphus jujube by chemical activation with phosphoric
acid (H3PO4), followed by carbonization at 450 oC. The prepared carbon samples
were characterized and utilized for the adsorptive removal of toxic heavy metals from
aqueous solutions such as chromium (VI), cadmium (II) and lead (II) ions. All
samples were found to be microporous in nature with low ash content, sufficient BET
surface area and pore volumes. The effect of various parameters like solution pH,
contact time, initial concentration, temperature, carbon dosage and shaking speed, on
adsorption of metal ions was investigated. The adsorption of Cr (VI) decreased while
that of Cd (II) and Pb (II) increased by increasing pH. Maximum adsorption of Cr
(VI) was observed in the pH range of 2–4 at equilibrium time of 300-420 min.
Equilibrium time for Cd (II) and Pb (II) adsorption was found to be 420-480 min at
all temperatures. Batch experiments revealed that the adsorption of all the metal ions
increased with increase in contact time, initial concentration, temperature and carbon
dosage, etc. Thermodynamic studies indicated the feasibility, spontaneity and
endothermic nature of the adsorption process. Among different isotherm and kinetic
equations, Langmuir’s model and pseudo - second order equation were found to
better describe the experimental data. The adsorption capacity of oxidized samples
was found to be higher than that of un-oxidized samples for Cr (VI) but lower for Cd
(II) and Pb (II). In comparison to Cd (II) ions, the removal of Pb (II) ions was higher.
The results suggested that the prepared activated carbon samples could be used
effectively as eco-environment friendly adsorbents for removal of Cr (VI), Cd (II)
and Pb (II) ions from aqueous solutions.
Keywords: Activated carbon; Ziziphus jujube; Adsorption; Heavy metals;
Chromium; Cadmium; Lead; Thermodynamic; Kinetic
