Ferragels: A new family of materials for remediation of aqueous metal ion solutions

A nanoscale form of zero-valent iron, dispersed on high surface area supports, is found to reduce soluble metal ions [Cr(VI), Hg(II), Pb(II), Tc(VII)], and ReO4^- (as a surrogate for TcO4^-) to insoluble forms much faster than does unsupported zero-valent iron. The supported iron materials (`Ferragels') were mixed with aqueous solutions of metal salts. In the case of technetium, alkaline salts were added to the solution to simulate Hanford tank waste. The redox reaction of Fe⁰ and the aqueous ions continues until the metal contaminant is removed from solution as an insoluble oxide. The rate of reduction is approximately linear with the E₀ of the metal ion. The initial rates increase proportionately with increasing initial concentrations, suggesting Nernstian behavior. The material used to support the nanoscale iron, while ostensibly inert to the redox reaction, has a strong effect on the rates of reaction. This effect arises from the evenness of dispersion of the iron nanoparticles on the support surface, as well as the surface roughness, which affects the specific loading of iron. The best general support tested was a commercial resin, but this resin was unstable in the (pH 14) Hanford simulants. The best support support tested for TcO₄^- removal was a poorly crystalline ZrO₂ powder.