Agar-stabilized sulfidated microscale zero-valent iron: Its stability and performance in chromate reduction

Area of Science:

• Environmental Science
• Materials Science
• Chemistry

Background:

• Microscale zero-valent iron (mZVI) is widely used for groundwater remediation.
• Sulfidation enhances mZVI reactivity, creating sulfidated microscale zero-valent iron (SmZVI).
• The effect of polymer coatings on SmZVI performance is not well understood.

Purpose of the Study:

• To investigate the impact of polymer coating on SmZVI stability and reactivity.
• To evaluate the capacity and kinetics of chromate reduction by polymer-coated SmZVI.
• To elucidate the reaction mechanisms involved.

Main Methods:

• SmZVI was prepared by milling mZVI with elemental sulfur.
• SmZVI stability was assessed in agar solution.
• Chromate reduction experiments were conducted with uncoated and agar-coated SmZVI (A-SmZVI).
• X-ray photoelectron spectroscopy (XPS) was used to analyze surface species.

Main Results:

• Optimal SmZVI was achieved with a 0.05 S/Fe molar ratio and 10h milling.
• Agar dispersion (2.0 g/L) improved SmZVI stability.
• Agar coating (A-SmZVI) reduced chromate reduction capacity by 56% and kinetics by 70.4%.
• XPS analysis revealed participation of Fe0, Fe(II), FeS, and S(-II) in the reaction.

Conclusions:

• Polymer coating negatively impacts SmZVI performance for chromate reduction.
• Agar films hinder electron transfer and reduce reaction rates.
• Multiple reductive species on A-SmZVI contribute to redox reactions, with S(-II) oxidation being a key process.