ADSORBENTS FOR CD REMOVAL FROM WATER WASTE: A SHORT REVIEW OF THE RECENT DEVELOPMENT - Management of Hazardous Residues Containing Cd - page 22

observed that the maximum metal removal was at pH 5.6. The highest value of
Langmuir maximum uptake was 1 mg g -1 . Samples treated with nitric acid
solutions showed Cd 2+ desorbability of approximately 100%.
A comparison of various low-cost adsorbents derived from different
agricultural and industrial wastes for the removal of Cd 2+ is summarized in
Table 1.
1.2. A GRICULTURAL W ASTES - BASED
A CTIVATED C ARBON
Agricultural waste is an excellent material for the activated carbon
production due to its low ash content and reasonable hardness. Therefore, the
conversion of agricultural waste in low-cost adsorbents is a promising
alternative method related to environmental problems, such as: large amounts
of biomass disposal, the reduction of the preparation costs and added value to
the agricultural waste [101].
The adsorption of Cd 2+ on bean husk-based activated carbon (AC),
prepared by a heat-treatment process followed by chemical activation using
HNO 3 , was evaluated by Chávez-Gerrero et al. [102]. The adsorption capacity
of husk-based carbon (OC) increased from 60 mg g -1 to 180 mg g -1 after the
activation with HNO 3 . Infrared (IR) and energy X-ray spectroscopy (EDX)
results suggested that surface reactivity of the AC is greater than OC due to a
higher concentration of oxygen in the first one.
Rao et al [103] studied the Cd 2+ adsorption from aqueous solutions using
activated carbon prepared from Phaseolus aureus hulls (ACPAH). The
removal of the metallic ions by ACPAH was dependent on pH values and the
optimum pH value was 8. They observed that the removed amount increased
when the agitation time also increased.
The thermodynamic equilibrium was reached in 60 min when an aqueous
solution with Cd 2+ concentration of 80 mg L -1 was used in the experiments.
The maximum adsorption capacity was 15.7 mg g -1 . Desorption studies were
carried out using different concentrations of HCl solution. These results
showed that the desorption capacity increased when the concentration of HCl
also increased. However, the desorption capacity remained constant (72.3%) at
0.2 M HCl.
The sorption of cadmium and copper ions from aqueous solutions by
carbon derived from Ceiba pentandra hulls was investigated by Rao et al .
[104]. The adsorbent exhibited good sorption potential for copper and