title: Mimetite Formation from Goethite-Adsorbed Ions.
abstract: Bioavailability of arsenic in contaminated soils and wastes can be reduced to insignificant levels by precipitation of mimetite Pb5(AsO4)3Cl. The objective of this study is to elucidate mechanisms of the reaction between solution containing lead ions and arsenates adsorbed on synthetic goethite (AsO4-goethite), or arsenate ions in the solution and goethite saturated with adsorbed Pb (Pb-goethite). These reactions, in the presence of Cl, result in rapid crystallization of mimetite. Formation of mimetite is faster than desorption of AsO4 but slower than desorption of Pb from the goethite surface. Slow desorption of arsenates from AsO4-goethite results in heterogeneous precipitation and formation of mimetite incrustation on goethite crystals. Desorption of lead from Pb-goethite is at least as fast as diffusion and advection of AsO4 and Cl in suspension allowing for homogeneous crystallization of mimetite in intergranular solution. Therefore, the mechanism of nucleation is primarily driven by the kinetics of constituent supply to the saturation front, rather than by the thermodynamics of nucleation. The products of the reactions are well documented using microscopy methods such as scanning electron microscopy, electron backscattered diffraction, X-ray diffraction, and Fourier transform infrared spectroscopy.
authors.affiliation: 1Faculty of Geology, Geophysics and Environmental Protection,AGH University of Science and Technology,al. Mickiewicza 30, 30-059 Krakow,Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Kleszczewska-Zębala
authors.affiliation: 1Faculty of Geology, Geophysics and Environmental Protection,AGH University of Science and Technology,al. Mickiewicza 30, 30-059 Krakow,Poland.
authors.forename: Maciej
authors.initials: M
authors.lastname: Manecki
authors.affiliation: 1Faculty of Geology, Geophysics and Environmental Protection,AGH University of Science and Technology,al. Mickiewicza 30, 30-059 Krakow,Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Bajda
authors.affiliation: 2Department of Geology,Miami University,501 E. High St.,Oxford,OH 45056,USA.
authors.forename: John
authors.initials: J
authors.lastname: Rakovan
authors.affiliation: 3X-ray Science Division,Advanced Photon Source,Argonne National Laboratory,9700 South Cass Avenue,Argonne,IL 60439,USA.
authors.forename: Olaf J
authors.initials: OJ
authors.lastname: Borkiewicz
keywords: EBSD; apatite; arsenate; desorption; nucleation