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Combining selective sequential extractions, X-ray absorption spectroscopy, and principal component analysis for
Andreas C Scheinost1, Ruben Kretzschmar, Sabina Pfister
1Institute of Terrestrial Ecology, ETH Zurich, CH-8952 Schlieren, Switzerland. scheinost@ito.umnw.ethz.ch
Environmental Science & Technology
|January 14, 2003
Summary
Combining selective sequential extractions with X-ray absorption fine-structure spectroscopy accurately identified zinc speciation in contaminated soil. This novel approach precisely quantified both mobile and mineral-bound zinc, overcoming limitations of individual methods.
Area of Science:
- Environmental Chemistry
- Soil Science
- Spectroscopy
Background:
- Selective sequential extraction (SSE) and X-ray absorption fine-structure (XAFS) spectroscopy are used for metal speciation.
- Both methods have limitations when multiple metal species coexist in soils and sediments.
Purpose of the Study:
- To test a combined SSE and XAFS approach for determining zinc speciation in a smelter-contaminated, acidic soil.
- To improve the identification and quantification of zinc species by combining chemical extraction and spectroscopic analysis.
Main Methods:
- Collected XAFS spectra after each of 6 SSE steps.
- Analyzed spectra using multishell fitting, principal component analysis (PCA), and linear combination fits (LCF).
Main Results:
- In topsoil, Zn was predominantly found in franklinite (60%), sphalerite (30%), and aqueous Zn2+ (10%).
- In subsoil, aqueous Zn2+ (55%) prevailed, with 45% incorporated into hydroxy-Al interlayers of phyllosilicates.
- The combined method precisely quantified mobile and recalcitrant zinc species.
Conclusions:
- The combined SSE-XAFS approach overcomes individual method limitations for analyzing complex metal speciation.
- Formation of Zn-bearing hydroxy-interlayers is a newly observed mechanism reducing zinc solubility in acidic soils.
- This systematic combination of techniques offers high reliability and precision for identifying and quantifying metal species.