Abstract:
Silica was extracted from corn cob (Zea rugosa) ash by sol gel method and magnetite was
prepared by conventional co-precipitation method. The obtained magnetite was doped with
silica under some reaction conditions to obtained magnetite-doped silica composite. Both
adsorbents; derived silica and magnetite-doped silica were subjected to batch mode
experiments for various parameters such as pH, temperature, contact time and initial metal
concentration in aqueous solutions. Adsorption kinetics, isothermsand thermodynamic data
were also evaluated. Equilibrium was attained within 90 min with maximum removal of
80.2% at pH 2 for derived silicaand within 60 min with maximum removal of 93.2% at pH
1for magnetite-doped silica. The adsorption of Cr(VI) followed pseudo-second-order kinetic
model with R2 value of 0.999. This was further supported by Intra-particle diffusion model
which was not the sole rate-controlling step. The experimental data were modeled with
various isothermsand results indicated that the equilibrium data of magnetite-doped silica and
derived silica fitted well with the Langmuir and Freundlich isotherms respectively. Based on
the data obtained, it was deduced that the sorption of Cr(VI) ion was feasible, spontaneous
and exothermic while the nature of adsorption was physisorption. Desorption experiments
with 0.5 M HCl amongst other eluting solvents inferred the reusability of the
adsorbent.Statistically, the data obtained for the adsorption studies were subjected to students’
t-test at 95% significant level. The P values of all the parameters studied were less than 0.05
(P ˂ 0.05) indicating that, there was a significant difference between the adsorption
performances of the two adsorbents. The results indicate that magnetite-doped silica had
better adsorption performance than thecorn cob derived silicain the removal ofCr(VI) ions
from aqueous solutions.
