Arsenite sorption and co-precipitation with calcite

Gabriela Roman-Ross (1) , Gabriel Cuello (2) , Xavier Turrillas (3) , Alejandro Fernandez-Martinez (1, 2) , Laurent Charlet (1)

1 LGIT - Laboratoire de Géophysique Interne et Tectonophysique
2 ILL - Institut Laue-Langevin
3 ICC - Instituto Ciencias COnstruccion Eduardo Torroja

Sorption of As(III) by calcite was investigated as a function of As(III) concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log [As(OH)3°/ Assat] plot is S-shaped and has been modelled on an extended version of the surface precipitation model. At low concentrations, As(OH)3° is adsorbed by complexation to surface Ca surface sites, as previously described by the X-ray standing wave technique. The inflexion point of the isotherm, where As(OH)3° is limited by the amount of surface sites (ST), yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this value, the amount of sorbed arsenic increases linearly with solution concentration, up to the saturation of arsenic with respect to the precipitation of CaHAsO3(s). The solid solutions formed in this concentration range were examined by X-ray and neutron diffraction. The doped calcite lattice parameters increase with arsenic content while c/a ratio remains constant. Our results made on bulk calcite on the atomic displacement of As atoms along [0001] direction extend those published by Cheng et al., (1999) on calcite surface. This study provides a molecular-level explanation for why As(III) is trapped by calcite in industrial treatments.

Mots clés: calcite; arsenite; adsorption; coprecipitation

Domaines: Chimie-Physique [physics.chem-ph]; Géochimie; Géophysique [physics.geo-ph]; Interfaces continentales, environnement

Gabriela Roman-Ross, Gabriel Cuello, Xavier Turrillas, Alejandro Fernandez-Martinez, Laurent Charlet. Arsenite sorption and co-precipitation with calcite. Chemical Geology, 2006, 233 (3-4), pp.328-336. ⟨10.1016/j.chemgeo.2006.04.007⟩. ⟨hal-00203399⟩