A culture of Arthrobacter sp. was tested for its ability to
sorb copper, cadmium, and iron ions, and chemical modeling
of experimental data was used to interpret the mechanism
of biosorption. The purpose of the initial phase was to
clarify the nature and concentration of active acidic sites
on cell wall with the aid of potentiometric titration of an
aqueous cellular suspension and IR analysis of the lyophilized
biomass in solid phase. The experimental results showed
that the cell wall probably has at least two weakly
acidic sites. In the second part of the experimental work
Arthrobacter sp. was suspended in the presence of copper,
cadmium, and iron ion solutions at different equilibrium
pH values. Adsorption isotherms were obtained by using
an original procedure defined as the “subsequent additions
method” (SAM). The results showed a strong influence
of pH, especially over pH 5. A chemical model based on
a possible set of reactions between ions in solution and the
biomass has been developed. Mechanistic modeling
revealed the complexity of the metal biosorption phenomenon
and the need to consider different biosorption mechanisms.
Up to pH 5 experimental data at different equilibrium
pH values can be described using a model which takes
into account only two mechanisms (ion exchange and
complexation). Over pH 5 other mechanisms (probably
precipitation or coprecipitation on cell wall surface) should
be considered.
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