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, 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.