Study of the precipitation equilibria of arsenate anion with calcium and magnesium in sodium perchlorate at 25 degrees C

摘要

The stabilities of solid Ca and Mg arsenates were established by solubility experiments from the PH and total aqueous Ca, Mg and As concentrations. The experimental data were consistent with the following solid phases defined as a function of the PH range: Ca-3(AsO4)(2). 10H(2)O (7 < pH < 10), CaNaAsO4. 7.5H2O (10 < pH < 12), MgHAsO4. 4H(2)O (6.5 < PH < 7.1) and Mg-3(AsO4)(2). 8H(2)O (7.2 < pH < 9). All the experimentation was performed at constant ionic strength in aqueous NaClO4 solutions and at 25 degreesC, where the stoichiometric solubility products of the different solids were calculated. The corresponding thermodynamic solubility products of all the precipitates were computed by means of the Modified Bromley's Methodology (MBM) that considers the variation of the activity coefficients of the ions involved in the precipitation equilibria with the medium and ionic strength. Moreover, all the solid arsenates obtained were characterised by FT-IR and FT-Raman spectroscopies and the hydration of each precipitate was confirmed by X-Ray Diffraction data. (C) 2003 Elsevier Ltd. All rights reserved.