Biosorption of metal ions on Arthrobacter sp.: Biomass characterization and biosorption modeling

A culture of Arthrobacter sp, was tested for its ability to sorb copper,cad mium, and iron ions, and chemical modeling of experimental data was used to interpret the mechanism of biosorption. The purpose of the initial phase w as to clarify the nature and concentration of active acidic sites on cell w all with the aid of potentiometric titration of an aqueous cellular suspens ion and IR analysis of the lyophilized biomass in solid phase. The experime ntal results showed that the cell wall probably has at least two weakly aci dic sites. In the second part of the experimental work Arthrobacter sp, was suspended in the presence of copper, cadmium, and iron ion solutions at di fferent equilibrium pH values. Adsorption isotherms were obtained by using an original procedure defined as the "subsequent additions method" (SAM). T he results showed a strong influence of pH, especially over pH 5. A chemica l model based on a possible set of reactions between ions in solution and t he biomass has been developed. Mechanistic modeling revealed the complexity of the metal biosorption phenomenon and the need to consider different bio sorption 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 (pro bably precipitation or coprecipitation an cell wall surface) should be cons idered.