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Adsorption of Cu(II) to Bacillus subtilis: A pH-dependent EXAFS and thermodynamic modelling study

journal contribution
posted on 2011-11-01, 00:00 authored by Ellen MoonEllen Moon, C L Peacock
Bacteria are very efficient sorbents of trace metals, and their abundance in a wide variety of natural aqueous systems means biosorption plays an important role in the biogeochemical cycling of many elements. We measured the adsorption of Cu(II) to Bacillus subtilis as a function of pH and surface loading. Adsorption edge and XAS experiments were performed at high bacteria-to-metal ratio, analogous to Cu uptake in natural geologic and aqueous environments. We report significant Cu adsorption to B. subtilis across the entire pH range studied (pH ∼2-7), with adsorption increasing with pH to a maximum at pH ∼6. We determine directly for the first time that Cu adsorbs to B. subtilis as a (CuO5Hn)n-8monodentate, inner-sphere surface complex involving carboxyl surface functional groups. This Cu-carboxyl complex is able to account for the observed Cu adsorption across the entire pH range studied. Having determined the molecular adsorption mechanism of Cu to B. subtilis, we have developed a new thermodynamic surface complexation model for Cu adsorption that is informed by and consistent with EXAFS results. We model the surface electrostatics using the 1pK basic Stern approximation. We fit our adsorption data to the formation of a monodentate, inner-sphere RCOOCu+surface complex. In agreement with previous studies, this work indicates that in order to accurately predict the fate and mobility of Cu in complex biogeochemical systems, we must incorporate the formation of Cu-bacteria surface complexes in reactive transport models. To this end, this work recommends logKRCOOCu+=7.13 for geologic and aqueous systems with generally high B. subtilis-to-metal ratio. © 2011 Elsevier Ltd.

History

Journal

Geochimica et Cosmochimica Acta

Volume

75

Issue

21

Pagination

6705 - 6719

Publisher

Elsevier

Location

Amsterdam, The Netherlands

ISSN

0016-7037

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2011, Elsevier