ADSORBENTS FOR CD REMOVAL FROM WATER WASTE: A SHORT REVIEW OF THE RECENT DEVELOPMENT - Management of Hazardous Residues Containing Cd - page 25

experiments showed that the equilibrium time, optimum pH and adsorbent
dosage were 90 min, pH > 6 and 1.0 g/50 ml, respectively. The adsorption
process is an exothermic one, since the adsorption capacity decreased from
1.85 to 1.56 mg g -1 when the solution temperature increased from 20 to 40 ºC.
Their results showed that the activated carbons, obtained from the olive stones,
were an excellent alternative adsorbent for removing Cd 2+ from the aqueous
solution.
The adsorption of Cd 2+ by activated carbon derived from bagasse was
studied by Mohan and Singh [114]. The thermodynamic equilibrium was
attained after 12 h. They observed that either Freundlich or Langmuir models
could be used to fit the experimental data, but the overall data were slightly
better fitted by the Freundlich isotherm. Thermodynamic parameters indicated
the feasibility of the activated carbon derived from bagasse of being used as a
remover agent of Cd 2+ from an aqueous solution.
The properties of various low-cost activated carbons, which derive from
different agricultural wastes related to the removal of Cd 2+ from aqueous
solutions, are summarized in Table 2.
1.3. B IOSORBENTS
Biosorbent materials are alternative materials used to replace conventional
processes of Cd 2+ removal from wastewaters. The surfaces of microorganisms
are vitally important for the interaction between cells and their environment. In
their physiological state, the surfaces of microorganisms are negatively
charged. Due to the presence of various functional groups, such as: carboxyl,
hydroxyl, amine and phosphate, these charges exist. The physical chemistry
phenomenon of the metallic ion biosorption is based on the ion exchange
and/or complexation processes, which are relatively rapid and reversible [115].
Ozdemir et al. [116] studied the cadmium ion adsorption from aqueous
solution onto extracellular polysaccharide (EPS) produced by Chryseomonas
luteola TEM05 in the alginate beads. The maximum adsorption capacities for
calcium alginate, calcium alginate + EPS, calcium alginate + C. luteola
TEM05 and calcium alginate + EPS + C. luteola TEM05 were 52.91, 64.10,
62.5 and 61.73 mg g -1 , respectively.