Titre du document / Document title

Interaction of gypsum with As(V)-bearing aqueous solutions : Surface precipitation of guerinite, sainfeldite, and Ca₂NaH(ASO₄)₂·6H₂O, a synthetic arsenate

Auteur(s) / Author(s)

RODRIGUEZ Juan D. ; JIMENEZ Amalia ; PRIETO Manuel ; TORRE Laura ; GARCIA-GRANDA Santiago ;

Résumé / Abstract

The interaction of arsenate-bearing aqueous solutions with gypsum at a starting pH of 9 and 25 °C results in surface precipitation of guerinite, Ca5(HAs04)2(As04)₂·9H₂O, sainfeldite, Ca5(HAsO₄)2(As04)2'4H20, and occasionally Ca2Na(HAsO₄)(AsO₄)·6H₂O, a new arsenate. These three solid phases are characterized by the simultaneous presence of HAsO^2-₄ and AsO^3-₄ groups in their structure, which is explainable since crystallization occurs within a pH range in which both HAsO^2-₄ and AsO^3-₄ are available in the aqueous solution. The interaction leads to a decrease in the As(V) concentration in the aqueous phase to reach values controlled by the solubility of these solid phases. The study combines several macroscopic experiments, in which changes in the solution chemistry are monitored as a function of time, with the characterization of solid phases by SEM-EDS and XRD. The crystal morphologies of the precipitating phases are interpreted on the basis of their respective structures. The thermodynamic solubility products of both guerinite and the new arsenate have been determined, being 10^-31.17±0.05 and 10^-13.83±0.03, respectively. The reaction paths followed by the system and the equilibrium endpoints have been modeled using the geochemical code PHREEQC.

Revue / Journal Title

The American mineralogist   ISSN 0003-004X   CODEN AMMIAY 

Source / Source

2008, vol. 93, n^o5-6, pp. 928-939 [12 page(s) (article)]

Langue / Language

Anglais

Editeur / Publisher

Mineralogical Society of America, Washington, DC, ETATS-UNIS  (1916) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 503, 35400019779108.0240