title: Nature and reactivity of layered double hydroxides formed by coprecipitating Mg, Al and As(V): Effect of arsenic concentration, pH, and aging.
abstract: Arsenic (As) co-precipitation is one of the major processes controlling As solubility in soils and waters. When As is co-precipitated with Al and Mg, the possible formation of layered double hydroxides (LDHs) and other nanocomposites can stabilize As in their structures thus making this toxic element less available. We investigated the nature and reactivity of Mg-Al-arsenate [As(V)] co-precipitated LDHs formed in solution affected by As concentration, pH, and aging. At the beginning of the co-precipitation process, poorly crystalline LDH and non-crystalline Al(Mg)-oxides form. Prolonged aging of the samples promotes crystallization of LDHs, evidenced by an increase in As K XANES intensities and XRD peak intensities. During aging Al- and/or Mg-oxides are likely transformed by dissolution/re-precipitation processes into more crystalline but still defective LDHs. Surface area, chemical composition, reactivity of the precipitates, and anion exchange properties of As(V) in the co-precipitates are influenced by pH, aging, and As concentration. This study demonstrates that (i) As(V) retards or inhibits the formation and transformation of LDHs and (ii) more As(V) is removed from solution if co-precipitated with Mg and Al than by sorption onto well crystallized LDHs.
authors.affiliation: Dipartimento di Agraria, Università di Napoli Federico II, Via Università 100, 80055 Portici (Napoli), Italy.
authors.forename: Alessia
authors.initials: A
authors.lastname: Sommella
authors.affiliation: Dipartimento di Agraria, Università di Napoli Federico II, Via Università 100, 80055 Portici (Napoli), Italy.
authors.forename: Antonio G
authors.initials: AG
authors.lastname: Caporale
authors.affiliation: Dalton Nuclear Institute, The University of Manchester, Manchester M13 9PL, United Kingdom.
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Denecke
authors.affiliation: Karlsruhe Institute of Technology, ANKA Synchrotron Facility, Hermann-von-Helmholtz-Platz 1, Karlsruhe, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mangold
authors.affiliation: Dipartimento di Agraria, Università di Napoli Federico II, Via Università 100, 80055 Portici (Napoli), Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Pigna
authors.affiliation: Bangor University, School of Chemistry, Bangor LL 57 2UW, United Kingdom.
authors.forename: Anna
authors.initials: A
authors.lastname: Santoro
authors.affiliation: Department of Soil, Plant and Food Sciences, University of Bari "Aldo Moro", Via G. Amendola 165/A, 70126 Bari, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Terzano
authors.affiliation: Dipartimento di Agraria, Università di Napoli Federico II, Via Università 100, 80055 Portici (Napoli), Italy. Electronic address: violante@unina.it.
authors.forename: Antonio
authors.initials: A
authors.lastname: Violante
keywords: Aging; As(V)MgAl co-precipitates; Layered double hydroxides (LDHs); Sorption/desorption; Transformation