biosafe, and much more environmentally friendly than traditional
activated carbon, and ion exchange resins.5,10
In recent years, the research of waste biomass from our daily
life and production has aroused much attention. As a sorbent
of heavy metal ions, the waste biomass is not only inexpensive
and harmless but also able to powerfully adsorb the heavy metal
ions from aqueous solution. Most of the natural biomacromolecular
sorbents include cellulose and lignin or chitin and
chitosan, which can strongly adsorb the heavy metal ions. At
present, egg shell, millet shell, wastepaper, sawdust, straw, and
nonliving algal biomass are all used for the removal of the heavy
metal ions. It is reported that the highest adsorptivity of mercury
ions at initial concentration of 200 mg L-1 on natural chitosan
is 55%.11 A condensation product between glutaraldehydechitosan
and sulfhydryl alanine exhibits the maximal sorption
capacity of mercury ions of up to 1600 mg g-1 at an initial
Hg-ion concentration of 290 mg L-1.12 It appears that the
chemically modified chitosan would be one of the best seminatural
sorbents of mercury ions, but with an accompanying
loss of an advantage of low cost as compared with the purely
natural sorbents. Similarly, a time-consuming process of pretreatment
also largely increases the utilization cost of the
nonliving algal biomass Oedogonium sp. and Nostoc sp. as
sorbents.
because they tend to accumulate in organisms and exhibit a high
toxicity when adsorbed into the body. Therefore, serious water
pollution from hazardous heavy metals is becoming one of the
toughest problems which have attracted rather considerable
attention. The removal of heavy metal ions from aqueous
solution has traditionally been carried out by several techniques,
such as reverse osmosis, neutralization-precipitation, and ion
exchange,6 among which sorption7-9 has shown to be an
effective and economically feasible alternative method. Natural
sorbents may have a potential marketing advantage in the
wastewater treatment over other sorbents including synthetic
sorbents, because natural biomass is much cheaper, more