Chromium (III) and bismuth (III) complexation to organic matter: EXAFS Spectroscopy and equilibrium modeling
2013 (English)In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 77, no 5, 1235- p.Article in journal, Meeting abstract (Refereed) Published
The complexation of chromium(III) and bismuth(III) to organic matter was investigated by batch equilibrations with Suwannee River Fulvic Acid (SRFA) and with mor layer material (Risbergshöjden Oe). In the SRFA systems, 3 mM chromium(III) solutions were equilibrated with 9 g L-1 SRFA and equilibrated at different pH values ranging from 2 to 6. Characterization of the reaction products was made at MAX-Lab, Lund, Sweden, using Cr K-edge EXAFS spectroscopy at 5 989 eV. The spectra were interpreted using both conventional data treatment using EXAFSPAK and with wavelet transform (WT) analysis. The results show that chromium(III) formed monomeric organic complexes with SRFA. There was no evidence of polymerization with the exception of the particulate phase at pH 6, which was attributed to a limited extent of Cr(OH)3 formation.
The mor layer material was equilibrated with chromium(III) and bismuth(III) solutions as a function of pH, time and competing ions (iron(III), aluminium(III), copper(II)). Again Cr
K-edge and Bi L3-edge EXAFS spectroscopy was used, at 5 989 and 13 419 eV. The experiments showed a predominance of monomeric organic complexes for chromium(III). The sorption of chromium(III) was pH-dependent and to some extent found to be influenced by competition from aluminium(III) and copper(II). Chromium(III) complexation was found to be very slow at pH < 4, and equilibration times of three months or longer were required to reach equilibrium under these conditions. Concerning bismuth(III), complexation was quicker and found to be very strong, with more than 94 % bound at pH 1.2 at a high bismuth(III) loading. EXAFS spectroscopy showed that two complexes were involved, one monomeric and one di- or trimeric, with the latter being predominant at higher pH values, although it was present already at pH 1.2. In the organic bismuth(III) complexes, the bismuth(III) octahedron was found to be strongly distorted, which implies strong binding to organic acid functional groups. The complexation of bismuth(III) remained essentially unchanged even in the presence of a potent competitor such as iron(III).
The results from the spectroscopic investigation and from the quantitative solution data were used to calibrate new and improved complexation models for the Stockholm Humic (SHM) and the NICA-Donnan models. In the case of the Stockholm Humic Model, both complexes as found by EXAFS spectroscopy were considered explicitly; this ensured the model to predict minimum competition effects in agreement with the laboratory results.
Place, publisher, year, edition, pages
2013. Vol. 77, no 5, 1235- p.
IdentifiersURN: urn:nbn:se:kth:diva-124503OAI: oai:DiVA.org:kth-124503DiVA: diva2:635895
12th International Conference on the Biogeochemistry of Trace Elements (ICOBTE), June 16-20, Athens, USA
FunderSwedish Research Council
QC 201401242013-07-072013-07-072014-01-24Bibliographically approved