Environmental Engineering Reference
In-Depth Information
[42]. The tobacco dust exhibited strong capacity for the adsorption of several
heavy metals, such as Pb(II), Cu(II), Cd(II), Zn(II) and Ni(II), with the
respective equilibrium loadings of 39.6, 36.0, 29.6, 25.1 and 24.5 mg of metal
per g of sorbent. Moreover, the heavy metals loaded onto the biosorbent could
be easily released with a dilute HCl solution. FTIR showed no substantial
change in the chemical structure of the tobacco dust subjected to biosorption.
The heavy metal uptake by the tobacco dust may be interpreted as metal-H ion
exchange or metal ion surface complexation adsorption or both.
The use of orange wastes, generated in the orange juice industry, for
removing Cd 2+ from aqueous solutions was investigated by Pérez-Marín et al.
[6]. Orange waste contains cellulose, pectins, hemicellulose, chlorophyll
pigments and other low molecular weight compounds, including limonene.
The percentage of Cd 2+ uptake for a solution of 100 mg L -1 increased from 8 to
98% when pH increased from 2 to 6. The kinetic studies at optimum pH
(pH~6) indicated that the equilibrium time for Cd 2+ adsorption in orange waste
was 1h and the adsorptive capacity of orange waste was 48 mg g -1 at pH 6.
Marín et al. studied how the chemical modification affects the capacity of
orange waste of removing Cd 2+ from aqueous medium [43]. Batch sorption
tests carried out with both, raw and modified biomass, were used to compare
the biosorption efficiency and hence the contribution of active compounds
existing in the biomass. Esterification treatments reduced the biosorption of
cadmium, zinc and chromium drastically. These treatments included pectins
removal from raw materials and carboxyl group esterification. Therefore,
pectins and carboxyl groups played an important role in the biosorption
process of heavy metals onto orange waste. The esterification treatment
reduced the percentage of the metal removal. This reduction, in comparison
with raw material, was higher than 79%, 65% and 82% for Cd, Zn and Cr
metallic ions, respectively. The acetylated or methylated biomass did not
provided significant differences in the sorption uptake in relation to raw
biomass, which indicates that amine and hydroxyl groups have negligible
effect on metal sorption onto orange waste. The maximum adsorption capacity
of the raw material was found to be 41.6 mg g -1 .
Tamarind fruit shell (TFS), a byproduct of the tamarind pulp industry, was
used in Cd 2+ adsorption by Anirudhan and Radhakrishnan [44]. They studied
the effect of the chemical modification of TFS on Cd 2+ adsorption process.
The modified tamarind fruit shell (FPTFS) is 2.0 times more effective than
TFS for Cd 2+ removal from aqueous solutions. The high percentage of Cd 2+
removal obtained by the use of FPTFS may be due to the high stability
provided by formaldehyde polymerization and also due to the introduction of -
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