Boletín de la Sociedad Geológica Mexicana
Volumen 67, núm. 3, 2015, p. 457-465
Modeling the additive effects of Pb(II) and Cu(II) on the competitive attenuation of As(V) through solid precipitation versus adsorption to goethite
Katherine Vaca-Escobar1, Mario Villalobos2,*
1 Posgrado en Ciencias de la Tierra, Instituto de Geología, UNAM, Ciudad Universitaria, Coyoacán, México DF 04510, México.
2 Departamento de Geoquímica, Instituto de Geología, UNAM, Ciudad Universitaria, Coyoacán, México DF 04510, México.
Mine-related activities cause widespread contamination of aqueous environments with high concentrations of arsenic and accompanying heavy metals. The natural attenuation of As(V) in soils and groundwater under oxic conditions occurs mainly through sorption processes to iron and aluminum (hydr)oxides; as well as through the formation of highly insoluble heavy metal(II) arsenates.
In the present investigation we used thermodynamic modeling to predict the environmental geochemical behavior of As(V) in the presence of Pb(II), Cu(II) and goethite, in an effort to approach the complexity of multi-component real contaminated scenarios. The key to this modeling was the coupling of a highly robust Surface Complexation Model of As(V) adsorption to goethite, which uses combined tenets of the Triple-Layer and CD-MUSIC models, together with appropriate metal(II) arsenate solid formation constants as well as those of all chemical equilibria taking place in the aqueous phase. Mixed-metal arsenates were predicted to form and increase the predominance region of the precipitation reactions for a highly surface-reactive goethite, at the expense of the adsorption mechanism, but the model yielded no aqueous As(V) released at any condition investigated.
Keywords: Adsorption, precipitation, arsenate, goethite, lead, copper, Surface Complexation Model, Triple-Layer Model, CD-MUSIC Model.