title: Effect of the presence of pyrite traces on silver behavior in natural porous media.
abstract: In order to better understand the fate of the toxic element Ag(I), sorption of Ag(I) was studied from batch experiments, at different pHs (2-8) and at 298 K. A pure quartz sand (99.999% SiO2) and "natural" quartz sand (99% SiO2, and traces of Fe, Al, Mn (hydr)oxides, of clays and of pyrite) were used as sorbents. The Ag(I) sorption behavior depends strongly on pH with isotherm shapes characteristic of Langmuir-type relationship for initial Ag concentration [Ag(I)], range between 5.0×10(-7) and 1.0×10(-3) M. Even if the Ag (I) sorption capacity on pure quartz sand is very low compared to the natural quartz sands, its affinity is rather high. From speciation calculations, several sites were proposed: at pHi 4, 6 and 8, the first surface site is assumed to be due to iron (hydr)oxides while the second surface site is attributed to silanols. At pHi 2, sorption of Ag(I) was assumed to be on two surface sites of iron (hydr)oxides and a third surface site on silanol groups. Even if the sand is mainly composed of silica, the trace minerals play an important role in sorption capacity compared to silica. The conditional surface complexation constants of Ag(I) depend on pH. On the other hand, it is shown that the Ag speciation depends strongly on the history of "natural" quartz sand due to initial applied treatment, little rinsing or longer washing. In the presence of low amount of pyrite, strong complexes between Ag(I) and sulfur compounds such as thiosulfates due to oxidative dissolution of pyrite are formed what decreases Ag sorption capability. SEM-EDS analyses highlighted the surface complexation-precipitation of Ag2S and Ag(0) colloids which confirmed the important role of pyrite on Ag(I) speciation.
authors.affiliation: Université de Toulouse; INPT, LCA (Laboratoire de Chimie AgroIndustrielle), UMR 1010, ENSIACET, 4, Allée Emile Monso, CS 44362, F-31030 Toulouse Cedex, France; INRA, LCA (Laboratoire de Chimie AgroIndustrielle), F-31030 Toulouse, France.
authors.forename: Delphine
authors.initials: D
authors.lastname: Charrière
authors.affiliation: CMP+L (Centro Mexicano para la Producción más Limpia Instituto Politecnico Nacional), Av. Acueducto S/N, col. Barrio la Laguna. Ticoman, 07340 México, D. F., Mexico.
authors.forename: Manuel de A
authors.initials: Mde A
authors.lastname: Hernández Cortázar
authors.affiliation: Université de Toulouse; INPT, LCA (Laboratoire de Chimie AgroIndustrielle), UMR 1010, ENSIACET, 4, Allée Emile Monso, CS 44362, F-31030 Toulouse Cedex, France; INRA, LCA (Laboratoire de Chimie AgroIndustrielle), F-31030 Toulouse, France. Electronic address: philippe.behra@ensiacet.fr.
authors.forename: Philippe
authors.initials: P
authors.lastname: Behra
mesh_terms: D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D008956:Models, Chemical; D010087:Oxides / Q000737:chemistry*; D016062:Porosity; D011791:Quartz / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D018030:Silver Compounds / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*
chemical_list: D010087:Oxides; D018030:Silver Compounds; D012989:Soil Pollutants; D013440:Sulfides; C011342:pyrite; D011791:Quartz; D012822:Silicon Dioxide; D007501:Iron
keywords: Colloids; Langmuir-type model; Pyrite; Quartz sand; Reduction; Silver; Sorption; Speciation