ADSORBENTS FOR CD REMOVAL FROM WATER WASTE: A SHORT REVIEW OF THE RECENT DEVELOPMENT - Management of Hazardous Residues Containing Cd - page 9

adsorption capacity increased from 14.53 to 16.47 mg g -1 when the
temperature was raised from 20 to 50 ºC. The thermodynamic parameters
show that the adsorption of Cd 2+ onto eucalyptus bark was spontaneous.
The capacity of sorbents prepared from juniper wood (JW) and bark (JB)
to adsorb Cd 2+ from aqueous solution was also compared [53]. The Cd 2+
adsorption capacity of JB is about two to three times higher than that of JW.
This difference is related to a higher concentration of carboxylate groups in JB
than JW. Juniper was also examined by Shin and Rowell [54] as a
lignocellulosic biosorbent for removing heavy metals from water. Cadmium
ion adsorption capacity of the sulfonated juniper wood (17 mg g -1 ) was much
higher than the untreated juniper wood (3 mg g -1 ). Therefore, the enhancement
of cadmium sorption capacity of juniper wood is due to the presence of the
sulfonic acid groups, which work as binding sites for heavy metals.
The bio-char, byproduct from the fast wood/bark pyrolysis during the bio-
oil production, was investigated as adsorbents for the Cd 2+ removal from water
by Mohan et al. [55]. Four kinds of bio-char residues were tested: oak bark,
pine bark, oak wood, and pine wood chars. The amount of the adsorption of
Cd 2+ on the chars followed the order: oak bark char > pine bark char ≈ oak
wood char .
Papaya wood was evaluated as a new biosorbent of heavy metals by Saeed
et al . [56]. Sorption was most efficient at pH 5. Metallic ions biosorption
increased as the ratio between the quantities of the ionic solution and biomass
decreased. Conversely, the ratio biosorption by the biosorbent mass decreased
as the quantity of biomass increased. The adsorption capacity was found to be
17.2 mg g -1 . The metal-loaded papaya wood was completely desorbed with
0.1N HCl. During repeated biosorption-desorption processes no loss in the
efficiency of cadmium (II) removal was noted for five cycles.
Naiya et al. [57] used sawdust and neem bark as low-cost natural
adsorbent for the Cd 2+ removal from aqueous solution. FTIR studies indicated
that the functional groups C-O, C=O and C-N are responsible for metal
binding. The monolayer capacities of sawdust and neem bark were found to be
26.7 and 25.6 mg g -1 , respectively.
Sharma and Bhattacharyya [58] evaluated the removal of cadmium onto
neem leaf powder, prepared from the mature leaves of the Azadirachta indica
(neem) tree. Cadmium ion adsorption capacity of neem leaf powder (NPL)
was found to be 158 mg g -1 . The adsorption process is exothermic and
spontaneous at temperature slightly higher than ambient temperatures. The
desorption experiments showed that the NPL-Cd 2+ linkages were reversible
and strong, acid or alkali was used for breaking the adsorbate-adsorbent bonds.