Environmental Engineering Reference
In-Depth Information
The metal sludge is a waste product of the electroplating industry.
Bhatnagar and Minocha [23] studied its adsorption potential in Cd 2+ removal
from water. Results showed that the maximum adsorption capacity increases
from 58.48 to 68.96 mg g -1 when temperature increases from 25 to 45 ºC.
Thus, they showed that the metal sludge is a good adsorbent of Cd 2+ and the
adsorption is an endothermic process.
The Cd 2+ adsorption onto manganese nodule residue was investigated by
Agrawal and Sahu [24]. The presence of the manganese and iron metals in the
manganese nodule residue played a significant role in Cd 2+ ions removal. The
adsorption of Cd 2+ in this adsorbent was found to be a spontaneous and
exothermic process. The adsorption capacity for Cd 2+ was found to be 19.8 mg
g -1 .
Kandah [25] studied the Cd 2+ removal by low grade phosphate (LGP).
They observed that the equilibrium time was achieved after 30 min, the
maximum adsorption capacity was 7.54 mg g -1 and desorption with 0.1 N
H 2 SO 4 was done in three cycles.
The sugar beet pulp (SBP), an industrial byproduct and solid waste of
sugar industry, was used for Cd 2+ adsorption by Pehlivan et al. [26]. The
sorption of Cd 2+ by SBP seemed to involve an adsorption phenomenon
together with ion exchange and electrostatic interactions. The maximum Cd 2+
sorption capacity of this biosorbent was 46.1 mg g -1 for Cd 2+ at pH 5.3 and 25
ºC. Sugar beet pulp was also used as adsorbent for removing heavy metals
from aqueous solutions by Reddad et al. [27]. They observed that the metal
removal was strongly dependent on pH and, to a lesser extent, on the ionic
strength. The interaction of the carboxyl groups with the polysaccharide group
is the predominant mechanism of Cd 2+ sorption on SBP samples. Reddad et al.
showed that the adsorptive capacity of sugar beet pulp was 24.4 mg g -1 at pH
5.5. Pectins were successfully extracted from the sugar-beet pulp, but after
pectins demethylation, they gelled in the presence of CaCl 2 . Mata et al.
investigated the Cd 2+ removal from aqueous solution by sugar-beet pectin gels
[28]. The monolayer adsorption capacities of pectin hydrogel and pectin
xerogel were 30.87 and 56.91 mg g -1 , respectively and the Cd 2+ ions were
completely recovered from xerogels using 0.1M HNO 3 . The main mechanism
associated with adsorption process is the chelation or complexation by the
carboxyl groups and ion exchange. In the later mechanism the calcium ions are
replaced by cadmium ions on the gel structure. Mota et al. [29] studied the
Cd 2+ removal by pectin xerogels prepared with sugar beet. They noticed that
the xerogel of sugar-beet pectin is a stable sorbent and it is able to resist the
multiple sorption-desorption-regeneration cycles. In this study they used
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