Sawdust, obtained from wood industry is an abundant
by-product which is easily available in the countryside at
negligible price. It contains various organic compounds
(lignin, cellulose and hemicellulose) with polyphenolic
groups that could bind heavy metal ions through different
mechanisms. An experiment on the efficiency of sawdust in
the removal of Cu2+ and Zn2+ ions was conducted by Sˇ c´iban
et al. (2006a). Two kinds of sawdust, poplar and fir
wood were treated with NaOH (fibre-swelling agent) and
Na2CO3 solutions and the adsorption capacities were compared
with the untreated sawdusts. For unmodified sawdust,
both types of woods showed higher uptakes of
Cu2+ ions than Zn2+ ions, and adsorption followed Langmuir
isotherm model. Equivalent amounts of adsorption
capacities were recorded by both types of sawdust for
Zn2+ and Cu2+ ions, although these two adsorbents have
different anatomical structure and chemical composition.
After treating with NaOH, a marked increase in adsorption
capacity was observed for both heavy metal ions, especially
for Zn2+ ions (2.5 times for Cu2+ and 15 times for Zn2+).
The adsorption capacities shown by Langmuir model were
6.92 mg g1 (poplar sawdust) and 12.70 mg g1 (fir sawdust)
for Cu2+, and 15.83 mg g1 (poplar sawdust) and
13.41 mg g1 for Zn2+ (fir sawdust), respectively. In
another experiment, Sˇ c´iban et al. (2006b) found that the
leaching of coloured organic matters during the adsorption
can be eliminated by pretreatments with formaldehyde in
acidic medium, with sodium hydroxide solution after formaldehyde
treatment, or with sodium hydroxide only.
According to Sˇ c´iban et al. (2006a), NaOH improved the
adsorption process by causing the liberation of new
adsorption sites on the sawdust surface. An increase in
the concentration of NaOH for modification purpose however
did not cause a significant increase of the adsorption
capacity. The authors suggest that no greater than 1% of
concentration of NaOH solution should be used for modification.
The temperature of modification was also not a
significant factor for the main increase of adsorption
capacities of modified sawdusts. It was observed that only
a slight increase in Cu2+ and Zn2+ adsorption occurred
when the fir sawdu