Zero valent iron (ZVI) is widely employed as a medium in permeable reactive barriers for groundwater remediation. ZVI has strong reducibility in reacting with a wide range of pollutants including halogen organics and heavy metals to detoxify contaminated soil. Both micro- and nanoscale ZVI particles have been investigated in the past decades. Due to the large specific surface area, laboratory-made nano scale ZVI particles show superior reactivity and remediate efficiency over micro scale ZVI particles. Unfortunately, the reactivity and mobility of nano scale ZVI particles have been reported poor in real field applications due to severe aggregation and passivation, which can be weakened by increasing the particle size. However, as the particle size is increased, the reactivity m...[ Read more ]

Zero valent iron (ZVI) is widely employed as a medium in permeable reactive barriers for groundwater remediation. ZVI has strong reducibility in reacting with a wide range of pollutants including halogen organics and heavy metals to detoxify contaminated soil. Both micro- and nanoscale ZVI particles have been investigated in the past decades. Due to the large specific surface area, laboratory-made nano scale ZVI particles show superior reactivity and remediate efficiency over micro scale ZVI particles. Unfortunately, the reactivity and mobility of nano scale ZVI particles have been reported poor in real field applications due to severe aggregation and passivation, which can be weakened by increasing the particle size. However, as the particle size is increased, the reactivity may deteriorate. Therefore, the remediate efficiency is greatly dependent on the particle size of ZVI. Actually, the fabrication method of ZVI particles also greatly affects the particle performance. In this study, the difference between ZVI nanoparticles and microparticles fabricated through Physical Vapor Condensation is compared in various properties and investigated in decoloration reactions of methylene blue under different conditions. It is found that medium sized particles (1~10 μm) have the poorest remediation performance under mild acid conditions because these particles contain high Mn level caused by the fabrication method. In strong acid environment, Mn enhances the decoloration performance of ZVI particles. In addition, co-precipitation is found to be the main decoloration mechanism for ZVI particles and show no significant dependence on particle dimension under continuous mixing experimental conditions.