title: Arsenate sorption on monohydrocalcite by coprecipitation during transformation to aragonite.
abstract: The metastability of monohydrocalcite (CaCO3·H2O: MHC) suggests high reactivity to dissolved trace elements. Using kinetic and isotherm sorption experiments with different reaction times (24h, 48h), As(V) sorption on MHC was examined to elucidate As(V) uptake by MHC. Although the MHC was transformed to aragonite with time, the MHC in higher As(V) loading conditions was able to persist longer than in lower loading conditions. Actually, As(V) uptake was negligible for samples in which the MHC remained. However, remarkable uptake of As(V) was observed for samples in which a complete transformation of MHC to aragonite occurred. Results of kinetic study confirmed that the timing of the MHC transformation coincided perfectly with that of As(V) removal from the solution. XAFS measurements showed that the local structure of As after the MHC transformation was almost identical to that of As in the As(V) coprecipitated aragonite. Sorption behavior of As(V) during the transformation is explainable theoretically by the substitution of As(V) into the aragonite structure. The distribution coefficient and (apparent) maximum sorption capacity of As(V) sorption on MHC after 48h at low-to-moderate As(V) concentrations are 500L/kg and 25μmol/g, respectively, which are much higher than those of simple adsorption of As(V) on calcite.
authors.affiliation: Institute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan. Electronic address: fukushi@staff.kanazawa-u.ac.jp.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Fukushi
authors.affiliation: Department of Earth Sciences, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Sakai
authors.affiliation: Japan Atomic Energy Agency, Mizunami, Gifu 509-6132, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Munemoto
authors.affiliation: Department of Earth and Planetary System Sciences, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Yokoyama
authors.affiliation: Department of Earth and Planetary Sciences, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan.
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Takahashi
keywords: Aragonite; Arsenate; Coprecipitation; Monohydrocalcite; Transformation