Chemical Mechanisms Responsible for the Immobilization of Selenite Species from an Aqueous Medium in the Presence of Copper(I) Oxide Particles

Abstract : The ability of cuprite (Cu2O) to reduce the mobility of selenite species (SeO32- or HSeO3-), by means of chemical immobilization from an aqueous medium, was evaluated from batch experiments. The effect of pH was critically discussed as it was found to have a major influence on the nature of the mechanism involved in the uptake process of selenite by cuprite. Three pH-dependent mechanisms were evidenced by combining quantitative analysis of selenite solutions after equilibration with cuprite, solid-phase characterization, and surface analyses. In the presence of protons, the immobilization of selenite occurs via the formation of a copper selenite solid (i.e., chalcomenite, CuSeO3·2H2O). The driving force is the acid-catalyzed dissolution of cuprite into CuI species, followed by their fast disproportionation into Cu0 and CuII, this latter reacting with selenite to give the precipitation product. In an alkaline medium (pH > 7.5), selenite was mainly accumulated on the cuprite surface according to two distinct mechanisms depending on the time scale of the experiment. A fast adsorption process was predominant at short equilibration times (typically a few minutes), involving the substitution of the surface hydroxyl groups of Cu2O by the selenium oxyanion. Longer times (several days) led to the progressive coverage of the cuprite surface by transient Cu(OH)2, which was found to react with HSeO3- species to form an insoluble layer on the cuprite particles. Furthermore, in relation to the possible use of cuprite as a scavenger for radioactive selenium species in polluted environments, the competitive influence of chloride anions on the immobilization processes was investigated and discussed with respect to the kind of uptake mechanisms.
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Jérôme Devoy, Alain Walcarius, Jacques Bessière. Chemical Mechanisms Responsible for the Immobilization of Selenite Species from an Aqueous Medium in the Presence of Copper(I) Oxide Particles. Langmuir, American Chemical Society, 2002, 18 (22), pp.8472-8480. ⟨10.1021/la025780z⟩. ⟨hal-01942011⟩

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