Speciation and distribution of copper in a mining soil using multiple synchrotron-based bulk and microscopic...

Area of Science:

• Environmental Science
• Geochemistry
• Materials Science

Background:

• Copper contamination in mining sites poses environmental risks.
• Understanding copper speciation is crucial for effective remediation strategies.

Purpose of the Study:

• To elucidate the molecular-level speciation and distribution of copper in a historically contaminated mining soil.
• To identify the primary binding phases and complexation mechanisms of copper.
• To assess the utility of combined synchrotron-based techniques for soil analysis.

Main Methods:

• Characterization using multiple synchrotron-based techniques: bulk and spatially resolved X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy.
• Microscopic X-ray fluorescence (U-XRF) and scanning transmission X-ray microscopy (STXM) nanoanalysis.
• Quick Cu L3,2-edge XANES spectroscopy (Q-XANES) to assess Cu(II) photoreduction.

Main Results:

• Soil copper is predominantly associated with iron oxides, not soil organic matter.
• Copper exhibits inner-sphere complexation with Fe(III) oxides.
• The presence of copper sulfide (Cu2S) was identified in specific microsites.
• Combined synchrotron techniques provided a comprehensive understanding of copper speciation in a heterogeneous soil matrix.

Conclusions:

• Synchrotron-based techniques are highly effective for detailed soil contaminant speciation.
• Copper's association with iron oxides influences its environmental reactivity and fate.
• This research aids in predicting and managing copper contamination in mining environments.