What is Zaro-Valent Iron (ZVI)?

Pure iron powder—most commonly known as zero-valent iron (ZVI)—is a workhorse material in in-situ ground and groundwater remediation, especially for sites contaminated with chlorinated solvents and certain metals. By specifying the term zero-valent we distinguish pure iron powder from iron compounds and many iron alloys.

What is iron powder doing in remediation?

Iron powder is used as a chemical reducing agent. When metallic iron (Fe⁰) is placed in soil or groundwater, it corrodes:

Fe0 → Fe2+ + 2e−

Those released electrons break down contaminants into less toxic or non-toxic compounds.

Key contaminants treated with iron powder

1. Chlorinated solvents (biggest use)

Examples:

  • Trichloroethylene (TCE)
  • Tetrachloroethylene (PCE)
  • Vinyl chloride
  • Carbon tetrachloride

Mechanism:
Reductive dechlorination — chlorine atoms are stripped off and replaced by hydrogen.

End products:
Ethene, ethane, chloride ions (harmless at environmental levels)

2. Heavy metals & metalloids

Iron powder helps by chemical reduction + immobilization.

ContaminantEffect
Chromium (Cr⁶⁺)Reduced to Cr³⁺ (far less toxic, insoluble)
ArsenicAdsorbed onto iron oxides
LeadImmobilized as insoluble compounds
UraniumReduced to immobile U(IV)

3. Nitrates & some pesticides

  • Nitrates → ammonium or nitrogen gas (site-dependent)
  • Certain explosives (TNT, RDX) can also be degraded

How iron powder is deployed in the field?

1. Permeable Reactive Barriers (PRBs)

  • Trench filled with iron filings
  • Groundwater flows through the iron
  • Passive, long-term (10–30 years)

Typical iron form:
Coarse iron filings (0.25–2 mm)

2. Direct soil or groundwater injection

  • Iron powder slurried with water (sometimes polymers)
  • Injected via wells or direct-push rigs

Typical iron form:

  • Fine iron powder (10–100 µm)
  • Stabilized nano-iron (nZVI)

3. Excavation + blending

  • Contaminated soil removed
  • Iron powder mixed mechanically
  • Soil replaced or stabilized onsite