ADSORBENTS FOR CD REMOVAL FROM WATER WASTE: A SHORT REVIEW OF THE RECENT DEVELOPMENT - Management of Hazardous Residues Containing Cd - page 12

husk, a surplus agricultural byproduct, was investigated by Kumar and
Bandyopadhyay [71]. They observed the increasing in the sorption capacity
from 8.58 mg g -1 to 11.12, 20.24, 16.18 mg g -1 when raw rice husk (RRH) was
treated by epichlorohydrin (ERH), NaOH (NRH) sodium bicarbonate
(NCRH), respectively. They also observed a reduction in the equilibrium time
from 10, 2, 4 and 1 h, when RRH was treated by ERH, NRH and NCRH,
respectively. The results showed that the NCRH indicated could be an
excellent alternative for the heavy metal removal, due to: its low cost, the short
Cd 2+ uptake time and elevated sorption capacity.
Rice husk ash is found to be an effective adsorbent for Cd 2+ and Ni(II)
removal [72]. High percentage of the metallic ions removal was observed,
provided that the initial adsorbate concentration in the solution is low. In the
binary metallic mixtures, the affinity of the adsorbent for Ni(II) was greater
than that for Cd 2+ .
The adsorption potential of mung bean husk was tested for Cd 2+ removal
[73]. The maximum adsorption capacity at equilibrium (1h) was 34.9 mg g -1 .
The sorption capacity was found to be pH dependent and the maximum
adsorption occurred at a pH 5 solution. Mung bean husk showed no significant
loss in the Cd 2+ sorption capacity after five cycles of sorption-desorption
processes.
Husk of black gram, a waste of no commercial value, was investigated as
a new biosorbent of cadmium from aqueous solution [74]. Biosorption was
rapid and the thermodynamic equilibrium was achieved in 30 min. Among the
various desorbing agents, 99.89% cadmium recovery was achieved with 0.1 M
HCl. The highest value of Langmuir maximum uptake was found to be 38.8
mg g -1 at pH 5 and 25 ºC.
Garg et al. [75] reported the adsorption of Cd 2+ onto three kinds of
agricultural residues: sugarcane bagasse (SCB), maize corncob (MCC) and
jatropha oil cake (JOC). The maximum Cd 2+ removal was observed at pH 6.0,
with a contact time of 60 min, at a stirring speed of 250 rpm, using an
adsorbent dose of 20 g L -1 . The adsorptive capacities of JOC, MCC and SCB
were 87, 106 and 69 mg g -1 , respectively. The effects of the pH, agitation
speed, particle size and concentration of corncob particles on the adsorption of
cadmium ions were investigated by Shen and Duvnjak [76]. The uptake
capacity of cadmium ions on corncob particles increased with the increase of
the initial pH and agitation speed, but it decreased with the increase of the
particle size. The amount of the adsorbed ions also increased with the increase
of the corncob particle concentration, but the ratio adsorbed ions/adsorbent
mass decreased. The Cd 2+ adsorption capacity for corncob at pH 7.6 was found