Jump to main content
Jump to site search

Issue 8, 2016
Previous Article Next Article

Sorption selectivity of birnessite particle edges: a d-PDF analysis of Cd(II) and Pb(II) sorption by δ-MnO2 and ferrihydrite

Author affiliations

Abstract

Birnessite minerals (layer-type MnO2), which bear both internal (cation vacancies) and external (particle edges) metal sorption sites, are important sinks of contaminants in soils and sediments. Although the particle edges of birnessite minerals often dominate the total reactive surface area, especially in the case of nanoscale crystallites, the metal sorption reactivity of birnessite particle edges remains elusive. In this study, we investigated the sorption selectivity of birnessite particle edges by combining Cd(II) and Pb(II) adsorption isotherms at pH 5.5 with surface structural characterization by differential pair distribution function (d-PDF) analysis. We compared the sorption reactivity of δ-MnO2 to that of the nanomineral, 2-line ferrihydrite, which exhibits only external surface sites. Our results show that, whereas Cd(II) and Pb(II) both bind to birnessite layer vacancies, only Pb(II) binds extensively to birnessite particle edges. For ferrihydrite, significant Pb(II) adsorption to external sites was observed (roughly 20 mol%), whereas Cd(II) sorption was negligible. These results are supported by bond valence calculations that show comparable degrees of saturation of oxygen atoms on birnessite and ferrihydrite particle edges. Therefore, we propose that the sorption selectivity of birnessite edges follows the same order of that reported previously for ferrihydrite: Ca(II) < Cd(II) < Ni(II) < Zn(II) < Cu(II) < Pb(II).

Graphical abstract: Sorption selectivity of birnessite particle edges: a d-PDF analysis of Cd(ii) and Pb(ii) sorption by δ-MnO2 and ferrihydrite

Back to tab navigation
Please wait while Download options loads

Supplementary files

Publication details

The article was received on 04 Mar 2016, accepted on 28 Apr 2016, published on 02 May 2016 and first published online on 02 May 2016


Article type: Paper
DOI: 10.1039/C6EM00136J
Citation: Environ. Sci.: Processes Impacts, 2016,18, 1030-1041
  •   Request permissions

    Sorption selectivity of birnessite particle edges: a d-PDF analysis of Cd(II) and Pb(II) sorption by δ-MnO2 and ferrihydrite

    C. M. van Genuchten and J. Peña, Environ. Sci.: Processes Impacts, 2016, 18, 1030
    DOI: 10.1039/C6EM00136J

Search articles by author