CD-MUSIC-EDL modeling of Pb2+ adsorption on birnessites: Role of vacant and edge sites

Wei Zhao, Wenfeng Tan*, Mingxia Wang, Juan Xiong, Fan Liu, Liping Weng, Luuk K. Koopal

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

8 Citations (Scopus)

Abstract

The surface complexation modeling of metal adsorption to birnessites is in its infancy compared to the charge-distribution multi-site ion complexation (CD-MUSIC) models for iron/aluminum (hydr)oxides. Therefore, using X-ray diffraction with Rietveld refinement to obtain the reactive sites and their densities, a CD-MUSIC model combined with a Stern-Gouy-Chapman electrical double layer (EDL) model for the external surface and a Donnan model for the interlayer surface is developed for birnessites with different Mn average oxidation state (MnAOS). Proton affinity constants and the charge distributions of Pb surface complexes were calculated a priory. By fitting Pb adsorption data to the model the obtained equilibrium constants (logKPb) of Pb complexes were 6.9-10.9 for the double-corner-sharing and double-edge-sharing Pb2+ complexes on the edge sites and 2.2-6.5 for the triple-corner-sharing Pb2+ complex on the vacancies. The larger logKPb value was obtained for higher MnAOS. Speciation calculations showed that with increasing MnAOS from 3.67 to 3.92 the interlayer surface contribution to the total Pb2+ adsorption increased from 43.2% to 48.6%, and the vacancy contribution increased from 43.9% to 54.7%. The vacancy contribution from interlayer surface was predominant. The present CD-MUSIC-EDL model contributes to understand better the difference in metal adsorption mechanism between birnessite and iron/aluminum (hydr)oxides.

Original languageEnglish
Pages (from-to)10522–10531
JournalEnvironmental Science and Technology
Volume52
Issue number18
Early online date6 Aug 2018
DOIs
Publication statusPublished - 2018

Keywords

  • adsorption
  • Birnessite
  • CD-MUSIC Modeling
  • Electrical double layer model
  • External surface
  • Interlayer space
  • Manganese oxide
  • Mn average oxidation state
  • Pb
  • Rietveld refinement

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