Local Structure Analysis of Strontium Sorption to Hydrous Manganese Oxide

Area of Science:

• Environmental Science
• Geochemistry
• Materials Science

Background:

• Understanding contaminant distribution is crucial for environmental remediation.
• Hydrous manganese oxides (HMO) are important sorbents in natural systems.
• Mechanistic models require detailed knowledge of sorption processes.

Purpose of the Study:

• To investigate the sorption mechanism of strontium (Sr) onto hydrous manganese oxide (HMO).
• To elucidate the local coordination environment of Sr upon sorption.
• To assess the impact of Sr sorption on the structure of HMO.

Main Methods:

• X-ray absorption fine structure (XAFS) analysis, specifically Sr K-edge and Mn K-edge measurements.
• Variable temperature (298, 220, 77 K) and variable loading (10⁻⁴ to 10⁻² mol Sr/g HMO) experiments.
• Analysis of extended X-ray absorption fine structure (EXAFS) data to determine coordination environments and bond distances.

Main Results:

• Sr sorption resulted in a coordination environment with 10-12 oxygen atoms at ~2.58 Å, indicating retained hydration.
• Temperature dependence of the Sr-O bond suggests physical adsorption.
• Mn K-edge data confirmed the local coordination of manganese remained intact, with a highly ordered amorphous structure.

Conclusions:

• Strontium likely adsorbs physically to HMO while retaining its hydration shell.
• The structure of hydrous manganese oxide is robust and not significantly altered by strontium sorption.
• These findings contribute to developing mechanistic models for contaminant transport.