High-level arsenite removal from groundwater by zero-valent iron

Area of Science:

• Environmental Science
• Geochemistry
• Water Treatment

Background:

• Arsenic contamination in groundwater poses significant risks to human health and ecosystems.
• Superfund sites often exhibit high concentrations of arsenic, necessitating effective remediation strategies.
• Permeable reactive barrier (PRB) technology using zero-valent iron is a promising in-situ remediation approach.

Purpose of the Study:

• To evaluate the efficacy of zero-valent iron (ZVI) for arsenic remediation in contaminated groundwater.
• To elucidate the arsenic removal mechanisms mediated by ZVI.
• To assess the long-term stability of removed arsenic and the performance of PRB technology.

Main Methods:

• Batch and flow-through column studies were conducted using synthetic groundwater spiked with arsenic (III).
• High arsenic concentration solutions (50 mg/L) simulated contaminated Superfund site conditions.
• Surface precipitate analysis (identifying green rust) and sequential extraction techniques were employed.

Main Results:

• Arsenic removal by ZVI followed a two-step reaction: rapid initial removal and a subsequent slow phase.
• Arsenic removal kinetics approximated zero-order at high concentrations, with observed breakthrough over time.
• ZVI demonstrated an arsenic removal capacity of approximately 7.5 mg As/g Fe.
• Carbonate green rust was identified as a significant factor in arsenite uptake.
• Approximately 28% of removed arsenic was found as arsenate, indicating surface oxidation.

Conclusions:

• Zero-valent iron is effective for arsenic remediation, with green rust playing a crucial role.
• The two-step removal process and observed breakthrough highlight the need for monitoring long-term PRB performance.
• Surface oxidation contributes to arsenic removal, influencing the stability of the remediated arsenic.