Solving mercury (Hg) speciation in soil samples by synchrotron X-ray microspectroscopic techniques

Area of Science:

• Environmental Science
• Geochemistry
• Analytical Chemistry

Background:

• Mercury (Hg) contamination in soils poses significant environmental and health risks.
• Understanding Hg speciation is crucial for assessing pollution sources and mobility.
• Previous studies often lacked the resolution to fully characterize Hg species in complex matrices.

Purpose of the Study:

• To directly determine the chemical forms of mercury (Hg) in contaminated soil samples.
• To investigate the influence of particle size on Hg speciation.
• To identify the origin of Hg contamination and its evolving pollution potential.

Main Methods:

• Direct mercury speciation analysis using sequential extractions.
• Bulk and micro-analytical techniques employing synchrotron X-rays.
• Microspectroscopic methods including micro-XRF, micro-XRD, and micro-XANES for detailed analysis.

Main Results:

• Identified metacinnabar (beta-HgS), cinnabar (alpha-HgS), corderoite (Hg(3)S(2)Cl(2)), and an amorphous Hg-Cl-S phase.
• Metacinnabar and amorphous phases were more abundant in the <2 micrometer soil fraction.
• No interactions were observed between Hg species and soil components.
• All Hg species originated from the weathering of a specific mercury-containing waste material (K106).

Conclusions:

• The weathering of mercury-containing waste is transforming into a more hazardous pollution source.
• Hg speciation is size-dependent, with finer particles accumulating specific Hg phases.
• Advanced synchrotron-based techniques are essential for accurate mercury speciation in soils.