Elimination par électrodialyse des ions Fe(II) d’une solution d’acide sulfurique

Ce travail a pour objectif d’appliquer la technique d’électrodialyse à l’épuration d’une solution synthétique d’acide sulfurique chargée en cations Fe (II), dont la composition est proche à celle d’un bain acide usé. L’étude a été menée sur une solution synthétique d’acide sulfurique contenant du Fe(II) comme impureté métallique. L’influence de quelques paramètres tels que la densité de courant, le débit, la nature de la membrane, la concentration de l’acide (H2SO4) et la température sur l’efficacité d’élimination de Fe(II) a été étudiée. Les résultats obtenus montrent que le taux d’épuration de l’acide sulfurique augmente avec la densité de courant, le débit de circulation de la solution et la température et diminue avec l’augmentation de la concentration de l’acide de la solution à traiter. Cette étude a permis de montrer qu’il est possible, sous les conditions opératoires suivantes: CMX ; 20 mA.cm-2; 25°C ; 7 h, d’épurer à 66,32% par électrodialyse une solution acide sulfurique contaminée par les ions Fe (II).Mots clés: décapage chimique- électrodialyse –membrane – épuration - acide sulfurique. Elimination by electrodialysis of Fe (II) ions with a sulfuric acid solutionThis work was aimed at applying the electrodialysis technique for the purification of a synthetic solution of sulfuric acid charged by cations of Fe(II), where the composition content is close to that of reel industrial acid bath. The study was conducted on a synthetic solution of sulfuric acid containing Fe(II) as a metal impurity. The influence of some parameters such as current density, flow, nature of the membrane, the concentration of acid (H2SO4) and the temperature on the removal efficiency of Fe (II) was studied. The results obtained showed that the treatment rate of the sulfuric acid increases with the current density of the solution circulating flow rate and temperature and decreases with increasing acid concentration of the solution to be treated. In conclusion this study has shown the possibility, under the following operating conditions: CMX; 20 mA.cm-2; 25°C; 7 h, to purify the sulfuric acid solution contaminated by Fe (II) with a rate of around 66.32% by electrodialysisKeywords: pickling- electrodialysis- membrane – purification - sulfuric acid

Cadmium extraction from phosphate ore. Effect of microwave

AbstractThis study discusses the operating variables for removal of cadmium from phosphate ore using Na2EDTA. These variables include the reaction time, Na2EDTA concentration, liquid/phosphate ore ratio, number of extractions and microwave extraction. Na2EDTA induced a two-step extraction process including a rapid extraction within the first hour, and a subsequent gradual release that occurred over the following hours. The cadmium extraction efficiency increased progressively with the increasing of Na2EDTA concentration. The extraction efficiency of cadmium increased with increasing liquid/phosphate ratio in the 5–200 range. Consecutive extractions using low concentrations were more effective than a single soil extraction with concentrated Na2EDTA. Microwave was beneficial to improve the removal in soil washing, and using microwave could partly substitute for agitation

Electroextraction of heavy metals from diluted solutions by a process combining ion-exchange resins and membranes

International audienceThe electroextraction of heavy metals (Pb2+, Cu2+, Zn2+ and Cd2+) from diluted solutions was achieved by continuous electropermutation combining ion-exchange resins and membranes. Under an applied current, the metallic cations fixed onto the resin are substituted by protons coming from the anodic compartment, and are transferred into a receiver compartment, at the cathodic side, where they are concentrated. Electroextraction operations were performed under various experimental conditions of current density (27 A m2), flow rate (0.090.9 dm3 h1), cation concentration (40400 mg dm3) and nature of regenerating acid solutions (HNO3, HCl, H2SO4). Despite the resins were loaded with the metallic cations before introducing in the feed compartment of the cell, high levels of removal (up to 99%) were achieved. High mass transfer was obtained leading to a concentration factor of about five in the receiver

Removal of heavy metals from diluted mixtures by a hybrid ion-exchange/electrodialysis process

International audienceThe electroextraction of heavy metals (Pb2+, Cu2+, Zn2+ and Cd2+) from diluted solutions was achieved by continuous electropermutation combining ion-exchange resins and membranes. Various mixtures of these cations were used, in which either the molar cation concentrations were identical, or only one cation concentration was higher than the others. Ion-exchange measurements were performed in order to compare the resin affinity to cations. It followed the sequence Pb2+ >> Cd2+ > Cu2+ ≥ Zn2+. Results of electropermutation experiments were analysed in terms of concentration ratios in the resin and feed and receiver solutions. The fluxes of competitive ionic species depended on their concentration and diffusivity in the ion-exchange material and consequently, on the relative affinity of the exchanger for these ionic species. Among the four studied cations, the behaviour of Pb2+ was significantly affected by its high interaction with ion-exchanging sites of the resin and membranes

Cobalt electrochemistry in aqueous chloride solutions: study of the cobalt oxidation

International audienceThe electrochemical oxidation of cobalt and the cobalt electrode open circuit potential have been studied in the complexing aqueous cobalt chloride solutions, when the pH of the solution, the CoCl2 concentration and the temperature were changed on a large scale. The open circuit potential of an immobile cobalt disk electrode did not obey NERNST`s law. It was 0.17 to 0.2 V more positive than the Co/Co(II) equilibrium potential and close to the hydrogen electrode equilibrium potential; it increased linearly with log[CoCl2]/M and decreased with pH. The hydrogen evolution kinetics was rather slow and controlled by convective diffusion when the potential was set at a more negative potential than –1 V/SCE. CoCl2 additions did not affect this kinetics significantly for pH = 3, whereas they slowed it down for pH 3. The kinetics of the cobalt dissolution was controlled by the slow transfer of the Co(II) sp. to the solution. It was accelerated by CoCl2 or NaCl additions to the electrolyte, which increased the free Cl- sp. concentration. The dissolution of cobalt in complex aqueous chloride solutions was assumed to result either in the formation of Co(H2O)62+ or of CoCl+ sp. at the electrode surface, according to either of the two mechanisms: Co + 6 H2O => Co(H2O)62+ + 2 e, Co + Cl- => CoCl+ + 2 e. The effects of either high CoCl2 and NaCl concentrations or of the most anodic overpotentials were linked to the evolution of conductivity and viscosity of the electrolyte

Cobalt electrochemistry in aqueous chloride solutions: study of the cobalt oxidation

International audienceThe electrochemical oxidation of cobalt and the cobalt electrode open circuit potential have been studied in the complexing aqueous cobalt chloride solutions, when the pH of the solution, the CoCl2 concentration and the temperature were changed on a large scale. The open circuit potential of an immobile cobalt disk electrode did not obey NERNST`s law. It was 0.17 to 0.2 V more positive than the Co/Co(II) equilibrium potential and close to the hydrogen electrode equilibrium potential; it increased linearly with log[CoCl2]/M and decreased with pH. The hydrogen evolution kinetics was rather slow and controlled by convective diffusion when the potential was set at a more negative potential than –1 V/SCE. CoCl2 additions did not affect this kinetics significantly for pH = 3, whereas they slowed it down for pH 3. The kinetics of the cobalt dissolution was controlled by the slow transfer of the Co(II) sp. to the solution. It was accelerated by CoCl2 or NaCl additions to the electrolyte, which increased the free Cl- sp. concentration. The dissolution of cobalt in complex aqueous chloride solutions was assumed to result either in the formation of Co(H2O)62+ or of CoCl+ sp. at the electrode surface, according to either of the two mechanisms: Co + 6 H2O => Co(H2O)62+ + 2 e, Co + Cl- => CoCl+ + 2 e. The effects of either high CoCl2 and NaCl concentrations or of the most anodic overpotentials were linked to the evolution of conductivity and viscosity of the electrolyte

Improving the efficiency and selectivity of Cd 2+ removal using a modified resin in the continuous electropermutation process

International audienc

Switching on thermal and light-induced spin crossover by desolvation of [Fe(3-bpp)2](XO4)2·solvent (X = Cl, Re) compounds

Thermal desolvation is a very attractive method for the post-synthetic modification of the physicochemical properties of switchable materials. In this field of research, special attention has been paid to the possibility of modifying the thermo- and photo-induced spin crossover (SCO) properties of metal complexes as they can act as solvent sensors. Two new [Fe(3-bpp)2](ClO4)2·2.5H2O·MeOH (1·sol) and [Fe(3-bpp)2](ReO4)2·3H2O (2·sol) compounds, where 3-bpp is 2,6-di-(1H-pyrazol-3-yl)pyridine, were prepared and structurally characterized, and their solvated and desolvated phases were additionally investigated spectroscopically, magnetically and photomagnetically. Single-crystal X-ray structures of 1·sol and 2·sol consist of similar [Fe(3-bpp)2]2+ units arranged in π–π stacked layers separated by H-bond-stabilised layers consisting of solvent molecules and anions. Moreover, both materials show desolvation-assisted SCO from a low (LS, S = 0) to high-spin state (HS, S = 2) at around 340 K, followed by a reversible gradual spin conversion with T1/2 ≈ 210 K and 304 K for 1 and 2, respectively. Photomagnetic studies of 1·sol and 1 confirmed the efficiency of the light-induced excited spin-state trapping (LIESST) phenomenon with relaxation temperatures T(LIESST) = 82 K and 66 K for the solvated and desolvated phases, respectively. In the case of 2·sol, no LIESST effect was observed while the desolvated phase 2 exhibits a LIESST behaviour at T(LIESST) ≈ 50 K.Bistabilité magnétique dans de nouveaux systèmes moléculaires à base de ligands anioniques pontantsEtude femtoseconde rayons X et optique de la dynamique ultrarapide de photocommutation de matériaux moléculaires magnétique