Enhanced metal adsorption on solid suspensions by organic molecules

This laboratory study mimicked the pollution of a suspension of silica beads, used as a crude model of sand, by naphthalene in mixture with carbofuran at first, and then by this mixture in association with a metal salt, Pb(NO(3))(2). The silica properties and the working conditions were such that they allowed us to only observe physisorption, which is the first and essential step of any adsorption mechanism. Naphthalene and carbofuran were, respectively, chosen as hydrocarbon and pesticide. Naphthalene adsorption from simple solutions is rather large compared to other organic adsorptions, and carbofuran seems to adsorb on a layer of naphthalene when the latter is mixed in solution with carbofuran. Like other organics, naphthalene favours the adsorption of lead ions, but ionic adsorption is considerably increased by the combination of naphthalene and carbofuran. The Wagner-Onsager-Samaras theory shows that the result implies a special organization of organic molecules at the interface. Conclusions about some environmental mechanisms of fixation, or release, of ions on sands in the case of simple physisorption are drawn from the study.