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Article Dans Une Revue ACS Sustainable Chemistry & Engineering Année : 2018

Adsorption of Cerium Salts and Cerium Oxide Nanoparticles on Microbubbles Can Be Induced by a Fluorocarbon Gas

Résumé

Retrieving heavy metals from wastewaters has become an important environmental challenge. We report that exposing dilute aqueous solutions or dispersions of cerium compounds (CeO 2 , Ce(SO 4) 2 , CeF 4) to perfluorohexane-saturated air results in substantial adsorption of these salts at the air/water interface, as consistently reflected by a marked decrease in interfacial tension, as assessed by bubble-shape profile analysis tensiometry. No detectable adsorption is observed in the absence of the fluorocarbon. Adsorption to the interface is also achieved when, and only when, CeO 2 nanoparticle dispersions are exposed to the fluorocarbon vapor. We also found that microbubbles could be generated in cerium salt solutions and CeO 2 nanoparticle dispersions when they are formed in the presence of perfluorohexane-saturated air, without need for any surfactant or chelating agent. Optical microscopy, static light scattering, and ζ potential measurements were used to establish the ability for the fluorocarbon to induce the formation and stabilize these microbubbles. These findings could provide the basis for a new approach to heavy metal (including radioactive element) recovery and recycling from industrial and other effluents that would combine ionic flotation and fluorocarbon gas-driven adsorption on microbubbles. Extraction of critical raw materials from dilute solutions could also be considered. ■ INTRODUCTION Averting the release of heavy-metal-containing industrial effluents to the environment has become mandatory. This is the case, in particular, for wastewaters released from mining, recycling, or nuclear energy production sites, not to mention nuclear power site decommissioning. Unrelenting efforts are being devoted to assessing the ecological impact and health risks and setting authorized limits for heavy metal and radioactive element discharges, reducing the environmental impact of such effluents, and remediation. 1 On the other hand, there is concern that supplies will not meet demand for many strategic metals in the future, 2,3 thereby founding another powerful incentive for developing new procedures for metal recovery from dilute aqueous media and for recycling critical metallic materials. Such procedures could therefore have substantial economic and environmental value and be part of effective sustainability strategies. 4 The recycling rates of metals are presently far below their potential and need boosting, which calls for innovative retrieval technologies. 5−7 Recycling also contributes to climate change mitigation by saving energy and reducing greenhouse gas emissions. 8 Cost-and energy-effective technologies could moreover open access to numerous heavy metals from seawater, a virtually inexhaustible potential source for strategic raw materials, including over four billion tons of uranium. 9,10 Several techniques and combinations of techniques, including chemical precipitation, ion-exchange, ultrafiltration, coagulation−flocculation, liquid−liquid or liquid−solid extraction , flotation, gravitational, electrochemical, electromagnetic, and bioremediation methods, are currently being used to separate and collect heavy metals, including radioactive metals, from wastewater. 11,12 Commonly used liquid−liquid processes for decontamination require use of (not so environmentally friendly) solvents and surfactants. 13 Another effective process for heavy metal ion recovery, particularly from dilute solutions, is ionic flotation. 14−18 Separation by ionic flotation involves the generation and stabilization by a surfactant or chelating agent of air bubbles on which metal ions adsorb. The bubbles will thus collect the metal ions, and the metal-ion-loaded bubbles will then float toward the surface and form foams that are easily retrieved. However, subsequent separation of the surfactant adds an extra step that is not always simple to achieve on a large scale.
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hal-02408147 , version 1 (12-12-2019)

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Camille Justeau, Andrea V Vela-Gonzalez, Alex Jourdan, Jean Riess, Marie Pierre Krafft. Adsorption of Cerium Salts and Cerium Oxide Nanoparticles on Microbubbles Can Be Induced by a Fluorocarbon Gas. ACS Sustainable Chemistry & Engineering, 2018, 6 (9), pp.11450-11456. ⟨10.1021/acssuschemeng.8b01471⟩. ⟨hal-02408147⟩
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