Electrochemical behavior of lanthanum and yttrium ions in two molten chlorides with different oxoacidic properties: The eutectic LiCl-KCl and the equimolar mixture CaCl2-NaCl

The electrochemical behavior of LaCl3 and YCl3 was studied in two molten chloride mixtures with different oxoacidic properties, the eutectic LiCl-KCl and the equimolar CaCl2-NaCl melt at different temperatures. The stable oxidation states of both elements have been found to be (III) and (0) in both melts, and it was found that both La(III) and Y(III) cations were less solvated by the chloride ions in the calcium-based melt, which was explained by the stability of CaCl4 2- ions in that melt. Transient electrochemical techniques, such as cyclic voltammetry, chronopotentiometry and chronoamperometry were used in order to study the reaction mechanism and the transport parameters of electro active species at a tungsten electrode. The results showed that in the eutectic LiCl-KCl, the electro crystallization of lanthanum and yttrium seems to be the controlling electrochemical step while in CaCl2-NaCl this phenomenon has not been observed. That was explained in terms of the differences in the physicochemical properties of the systems, especially interfacial tensions. In the eutectic LiCl-KCl chronoamperometric studies indicated instantaneous and three dimensional nucleation and crystal growth of lanthanum and yttrium whatever the applied over potential of the rare earth metal is, whereas in the equimolar mixture CaCl2-NaCl, the corresponding electrochemical exchanges were found to be quasi-reversible, and the values of the kinetic parameters, K0 and α,were obtained for both reactions. Mass transport towards the electrode is a simple diffusion process, and the diffusion coefficients have been calculated. The validity of the Arrhenius law was also verified by plotting the variation of the logarithm of the diffusion coefficient versus 1/T

Introduction to the French GEOTRACES North Atlantic Transect (GA01): GEOVIDE cruise

The GEOVIDE cruise, a collaborative project within the framework of the international GEOTRACES programme, was conducted along the French-led section in the North Atlantic Ocean (Section GA01), between 15 May and 30 June 2014. In this special issue (https://www.biogeosciences.net/special_issue900.html), results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among 18 articles. Here, the scientific context, project objectives, and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue

Recovery of Platinum Group Metals From Secondary Sources by Selective Chlorination from Molten Salt Media

The use of molten salts as “solvents” offers interesting possibilities for the treatment of ores, industrial by-products as well as scraps, allowing the development of processes that are mid-way between pyro- and hydrometallurgy, with the advantage of salts offering a wide choice of chemical and electrochemical properties. The molten mixtures can be fed to industrial electrolytic cells (electrometallurgy) where the reactions can take place. One example of this type of reactions is the selective chlorination using gaseous mixtures in a molten chloride salt mixture. Within the frame of the EU-financed project PLATIRUS (GA 730224), the possibility of selective chlorination of platinum group metals (PGM) contained in spent automobile catalyst samples, using a molten salt as reaction media was investigated. To predict the selective separating conditions of the PGMs from the sample matrix, the Pourbaix-type E-pO2− diagrams of the most relevant components in the spent catalyst were compared with those of relevant chlorinating gaseous mixtures, i.e., Cl2/O2. This allowed to predict the optimal chlorinating conditions, which were tested and confirmed experimentally using Cl2 gas.acceptedVersio

Distributions of total and size-fractionated particulate ²¹⁰Po and ²¹⁰Pb activities along the North Atlantic GEOTRACES GA01 transect: GEOVIDE cruise

Vertical distributions of total and particulate polonium-210 (210Po) and lead-210 (210Pb) activities in the water column were measured at 11 stations in the North Atlantic during the GEOTRACES GA01 transect: GEOVIDE cruise in May–June 2014. Total 210Po activity was on average 24&thinsp;% lower than 210Pb activity in the upper 100&thinsp;m, and it was closer to unity in the mesopelagic (100–1000&thinsp;m). The partitioning coefficients (Kd) along the transect suggest the preferential association of 210Po relative to 210Pb onto particles. The prominent role of small particles in sorption was confirmed by the observation that over 80&thinsp;% of the particulate radionuclide activity was on small particles. To account for the observed surface water 210Po&thinsp;∕&thinsp;210Pb disequilibria, particulate radionuclide activities and export of both small (1–53&thinsp;µm) and large ( &gt; 53&thinsp;µm) particles must be considered. A comparison between the GEOVIDE total particulate 210Po&thinsp;∕&thinsp;210Pb activity ratios (ARs) and the ratios in previous studies revealed a distinct geographic distribution, with lower particulate ARs in the high-latitude North Atlantic (including this study) and Arctic in relation to all other samples. For the samples where apparent oxygen utilization (AOU) was calculated at the same depth and time as the 210Po&thinsp;∕&thinsp;210Pb AR (40 stations including this study), there was a two-phase correlation between the total particulate AR and AOU, likely reflecting the nature of the particles and demonstrating the forces of remineralization and radionuclide decay from particles as they age.</p