Another popular method for the removal of heavy metals from
aqueous solutions is adsorption. Parameters taken into consideration
when choosing an appropriate adsorbent are mainly the sorption
capability, regeneration ability, kinetic parameters, price and market
availability. Maximum sorption capability is the most important
parameter that characterizes each sorbent. It is the maximum amount
of the adsorbed substance available for the uptake per sorbent unit
mass or unit volume (usually in mg/g or meq/g). The sorption
capability is determined experimentally at constant temperature, and
the results are presented as isotherms. Sorption capability is a very
important parameter that allows for estimation of process costs, since
the determined isotherms allow to predict the amount of sorbent
required for effective sorption. Ability to regenerate the sorbent is
very important in cyclic processes, especially when expensive and
selective sorbents are used. Kinetic parameters allow to determine the
rate of the sorption process. The choice of the sorbent is determined
by its price and market availability. Prices of sorbents fall within a
wide range. Waste materials from various industrial processes and
biological materials—biosorbents—are also used. Biosorption is the
natural capability of the biomass to immobilize dissolved components,
e.g. heavy metal ions, on its surface. Biomass is composed
mostly of polysaccharides, proteins and fats, and has many functional
groups able to bind heavy metal ions.