Jean-Marie Lecuire

Hydrometallurgical extraction of zinc from zinc ferrites

The production of steel in electric arc furnaces (EAF) generates a by-product called EAF dusts. Due to the presence of significant amounts of leachable compounds of zinc, lead, cadmium, chromium and nickel, EAF dusts are classified as hazardous wastes. The quantity of EAF dust generated per year around the world represents a possible recovery of about 900 t of zinc. The major obstacle in the hydrometallurgical extraction and beneficial reuse of zinc is the presence of highly stable zinc ferrite ZnFe2O4. The amount of zinc in this form is about 50% of the total zinc. The objective of the process studied is to extract zinc from zinc ferrites contained in EAF dusts without destroying the iron oxide matrix, which can be recycled in the steel industry. The process is a hydrometallurgical treatment of waste based on the destruction of the ferrite structure. For this, ZnFe2O4 is treated by FeCl3·6H2O. The reaction consists of O2−/Cl− exchange allowing the recovery of zinc as ZnCl2 and iron as hematite αFe2O3. The separation of these products is obtained by aqueous leaching. In a first step, the process was studied on zinc ferrites synthesised in the laboratory, then extended to real samples. All the zinc is extracted after a 8 h treatment at 150 °C with a molar ratio FeCl3·6H2O/ZnFe2O4 of 10. The ultimate solid residues, which have been concentrated in iron, should be oriented towards the steel industry. The process has been also applied to roasted zinc concentrates containing zinc ferrite.

Synthesis, properties and performances of electrodeposited bismuth telluride films

Bismuth telluride alloy films of uniform thickness have been successfully prepared by electrodeposition from a solution containing Bi3+ and HTeO2+ ions in 1 mol dm–3 nitric acid (pH = 0) on stainless steel. The electrodeposited films are monophasic and exhibit a polycrystalline structure (Rm). The film composition is dependent on the electrolyte composition and the current density. The electrical properties of the electrodeposited samples have been determined. The obtained films are n-type semiconductors with high carrier concentration.

Hydrometallurgical recovery of zinc and lead from electric arc furnace dust using mononitrilotriacetate anion and hexahydrated ferric chloride

The purpose of this work was to study the feasibility at laboratory-scale of a new hydrometallurgical process for treating electric arc furnace dusts (EAFD). The proposed process is intended to extract zinc and lead from EAFD without destroying the iron oxides matrix. So, this material can be recycled by the steel industry. Independently of the origin of the samples, major mineralogical forms present in these wastes are Fe3O4, ZnO, ZnFe2O4 and PbOHCl. The proposed process consists of a hydrometallurgical treatment of wastes based on selective leaching of zinc and lead. Initially, a leaching is carried out utilizing a chelating agent, nitrilotriacetate anion (NTA3-), as the protonated form HNTA2-. Treatment of five EAFD samples for an hour at room temperature with a molar solution of reagent results in total leaching of the ZnO. In all cases the solubilized iron does not exceed 3 wt.%. The recovery of zinc and lead is performed by precipitation of metallic sulfides with a solution of Na2S4 sodium tetrasulfide 2M. These metallic sulfides can be used as metallurgical raw materials and the chelating reagent can be reused in the process after pH adjustment. The results of the normalized leaching test AFNOR X31-210 conducted on the leaching residues, shows that all the samples meet acceptance thresholds for hazardous wastes landfill. However, the residues contain a considerable amount of zinc as ZnFe2O4. The extraction of the zinc element requires the destruction of the ferrite structure. In this process, ZnFe2O4 is treated by FeCl3.6H2O. The reaction consists in a particle O2-/Cl- exchange allowing the recovery of zinc as ZnCl2 and iron as hematite Fe2O3. The separation of these products is accomplished by simple aqueous leaching. All of the zinc is extracted in a 8h treatment at 150 degrees C with a molar ratio FeCl3.6H2O/ZnFe2O4 equal to 10. Ultimate solid residues, which have been concentrated in iron, can be oriented towards the steel industry.

In situ spectroscopic ellipsometric study of porous alumina film dissolution

Porous alumina films have been synthesised by anodisation of high purity aluminium in 0.4 M phosphoric acid at constant current density. The dissolution process of those coatings in 2 M phosphoric acid has been investigated by in situ spectroscopic ellipsometry (SE) combined with electrochemical measurements. A sharp drop of the open current potential is observed due to film removal. The dissolution time depends on total barrier layer thickness. Those results are confirmed by SE measurements. A three layer optical model has been used to interpret SE spectra. During the dissolution process, the porous top layer has a quasi-constant thickness, whereas porosity increases significantly. The dissolution proceeds within the pores. Only the thickness of pure alumina barrier layer (upper part) decreases during the dissolution process whereas the interface barrier layer (lower part) does not change.

In-situ ellipsometric study of copper passivation by copper heptanoate through electrochemical oxidation

Inhibition of copper in a desearated sodium heptanoate solution (0.08 M, pH 8.0) by electro-oxidation has been investigated. Rp measurements were carried out to compare inhibition efficiency using this original method with that based on other usual chemical oxidation methods. In-situ spectroscopic and kinetic ellipsometric measurements have been performed to study the passivation mechanism of copper. The inhibition of copper is attributed to the formation of a protective layer composed of a mixture of copper II heptanoate and copper hydroxide. Two growth rates are observed during the passivation process. A model of a duplex layer is proposed. The thickness of the passive film is evaluated at 14±1.5 nm.

Molybdenum cluster chalcogenide electrochemistry—I. Potentiodynamic study of topotactic insertion reactions

Abstract The insertion/de-insertion topotactic reactions in the Chevrel-type molybdenum cluster chalco-genides Mo6X8 (X = S, Se) are studied in the potentiodynamic mode on crystallite bed electrodes. We define the best conditions for the identification of the successive steps of the insertion (MxMo6X8). The phenomenon of the cation diffusion in the host lattice is responsible for the voltamperogram features.

Molybdenum cluster chalcogenide electrochemistry—III. Study of cadmium insertion into the host-lattices MoyXz

Abstract The insertion of the Cd2+ cation is studied by the potentiodynamic way in the case of the Chevrel Mo6X8phases (X = S, Se, Te) and the condensed cluster phases MoyXz. The voltamperogram analysis allows different redox systems to be classified. Comparison of the results does not give evidence for a simple relationship with the parameters governing the insertion phenomena.

Electrodeposition of Bi2Te3 films

The Bi2Te3 and its derivative compounds are very interesting materials in the field of thermoelectric refrigeration at room temperature. An electrochemical deposition that is an alternative process of the standard synthesis is developed in our laboratory. The study of the reduction of TeIV+ and BiIII+ and their mixtures, in aqueous solvent, evidences the direct formation of near stoichiometric Bi2Te3 compounds. The electrodeposition is performed according to the reaction: 2BiO++3HTeO+2+13H++18e−→Bi2Te3↓+8H2OThe synthesis is realized in an acid electrolyte (HNO31M), allowing the stability of TeIV+ and BiIII+ salts. The Bi/Te ratio in the electroformatted films is varying with the solution composition and the applied current density. The X‐ray controls of all the compounds obtained by this method show only one product, with a good crystallinity. The patterns are consistent with the space group R‐3m of Bi2Te3. However, it should be noted orientation effects. The films exhibit qualitative thermoelectric prope...

Molybdenum cluster chalcogenide electrochemistry—II. Determination of the insertion system normal potentials from the analysis of the i = f(E) curves in the potentiodynamic way

Abstract In the electrochemical study of the topotactic insertion/de-insertion reactions, the behaviour of the crystallite-bed electrodes have been considered from a theoretical point of view. The diffusional models give evidence that the normal potential of the M n + , Mo y X z /M x Mo y X z system can be determined by using a potentiodynamic method.