ADSORBENTS FOR CD REMOVAL FROM WATER WASTE: A SHORT REVIEW OF THE RECENT DEVELOPMENT - Management of Hazardous Residues Containing Cd - page 24

The authors observed that the sample group activated by steam presented a
higher adsorption capacity than the sample group activated by carbon dioxide.
Cd 2+ adsorption on carbon produced from nutshells of walnut, hazelnut,
pistachio, almond and apricot stone was investigated by Kazemipour et al.
[109]. The amount of Cd 2+ adsorbed on the carbon sources followed the order:
hazelnut>apricot>almond>walnut>pistachio. All carbon samples removed
more than 50% of the metallic ion from wastewater, except for carbon samples
prepared from pistachio.
Apricot stones were carbonized and activated after the treatment with
sulphuric acid (1:1) at 200 ºC for 24 h [110]. The adsorption capacities values
for the adsorption process of the metallic ions on activated apricot stones were
the following: Cr(VI) > Cd(II)>Co(II) > Cr(III) > Ni(II) > Cu(II) > Pb(II).
Tajar et al. [111] studied the adsorption of cadmium onto the nut shell-
based activated carbon (PAC), the commercial activated carbon (CAC), the
sulfurized nut shell-based activated carbon (SPAC) and sulfurized commercial
activated carbon (SCAC). The removal of the cadmium ions depended on the
ion concentration. They noticed that the removal efficiency decreased when
the ion concentration increased. Adsorption of cadmium on these adsorbents
was also pH-dependant and the maximum adsorption percentage occurred in
the pH range 8-12. The maximum adsorption capacities were 90.09, 104.17,
126.58 and 142.86 mg g -1 for CAC, PAC, SCAC and SPAC, respectively.
Desorption results showed that the spent SPAC was effectively regenerated for
further use by a simple chemical process.
The potential of the date pits to be used as an inexpensive precursor to
prepare activated carbons was investigated [112]. Steam as well as zinc
chloride activated carbons were prepared from date pits. FT-IR assigned the
presence of different functional groups, including phenolic and lactonic, -OH,
quinonic and carboxylate, aromatic -C-H and -C-O. The adsorption of Cu 2+ ,
Pb 2+ and Cd 2+ was studied in the equilibrium method. The physical activation
(steam) leaded to the formation of the basic surfaces, while the chemical
activation (zinc chloride) leaded to the acid surfaces. Zinc chloride activated
carbons had a higher adsorption power (66.5-120 mg g -1 ) in comparison with
steam activated carbons (61.9-105 mg g -1 ). The adsorption behavior was
affected by the textural and chemical properties of the surface.
Kula et al. [113] investigated the Cd 2+ removal using olive stone after the
activation by ZnCl 2 . They studied the influence of the different amounts of the
activation agent and the adsorbent particle size on the adsorbent surface area.
The activated carbons obtained by a treatment with an aqueous solution of
ZnCl 2 (20%) had a specific surface area equal to 790.25 m 2 g -1 . Their