Copper recovery from dilute solutions in the Falling-Film cell

The removal of copper from dilute solutions is examined in electrochemical reactors where the electrolyte flows as a thin film in an inclined channel between a plane plate and a sheet of expanded metal (Falling-Film cell). Copper is recovered as a thin sheet from the plane plate. The results are compared with a known simplified model and the variations of the faradaic yield with the operating conditions are discussed.Nomenclature A _e electrode surface area - b width of inclined channel - C(t) copper concentration at timet - C ₀ initial copper concentration - d interelectrode distance - overall current density - overall limiting current density - overall mass transfer coefficient - L length of the channel - Q _v volumetric flow rate - Q _vl volumetric flow rate per unit of channel width (=Q _v/b) - t time - t _s residence time in the reactor, defined by Equation 1 - mean flow velocity of the liquid film, defined by Equation 2 - V volume of electrolyte in the circuit - V _R reactor volume - v _sn normalized space velocity, defined by Equation 9 - inclination angle with respect to the horizontal - instantaneous faradaic yield - time-averaged faradaic yield - v _e number of electrons exchanged in the electrochemical reaction     

Influence de la pâte interstitielle sur l’aptitude à l’écoulement du béton frais

Résumé L’étude de l’écoulement du béton frais est abordée en considérant ce matériau hétérogène comme un milieu diphasique, constituté par la pate interstitielle, d’une part, et par les granulats, d’autre part. La pate interstitielle est définie par sa teneur en eau. Pour cela, un appareillage simple dont le principle de fonctionnement consiste à filtrer de l’eau sous pression à travers un échantillon de granulats permet de déterminer la quantité d’eau retenue par ceux-ci. Cette dernière correspond à la quantité d’eau mobilisée par les granulats dans le béton et dont se trouve alors privée la pate. La pate interstielle ainsi définie, peut ensuite être caractérisée par un paramètre rhéologique. En outre, l’étude de l’écoulement du béton frais effectuée au maniabilimètre L.C.L. met en évidence la concentration en granulats dans le béton à partir de laquelle interviennent les phónomènes de frottements intergranulaires dont l’influence sur l’écoulement devient rapidement très importante.

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Summary The study of fresh concrete flow is approached by taking this heteregeneous materials as a diphasic medium, constituted by the interstitial paste on one hand and the aggregates on the other hand. The interstitial paste is defined by its water content. A simple apparatus, the working principle of which consists in filtering water under pressure through a sample of aggregate, makes it possible to determine the quantity of water retained by them. This latter corresponds to the quantity of water retained by the aggregate in concrete and which therefore, is removed from the paste. The interstitial paste defined in the way can be characterized by a rheological parameter. Moreover, the study of fresh concrete flow carried out with the “maniabilimètre L.C.L.” sets up the aggregate concentration in concrete beyond which friction phenomena between agregates take place in the flow. Their influence on the flow quickly becomes very important.

     

Dynamic mechanical properties of polymers

A technique, employing samples in the form of tuning forks, to measure the mechanical properties of polymers is presented. Results for low density polyethylene, polypropylene, and polycarbonates are shown. A large transition is observed for polypropylene at approximately +10°C and a small transition at ?100°C for the polycarbonates. Polycarbonate data has also been obtained from 20 to 150°C, at approximately 70 cps. Effects of time, temperature, and history are presented.     

A trilogy on surfaces. I. The temperature-surface tension coexistence curve

Experimental data and theoretical considerations on the shape of the temperature-surface tension coexistence curve are presented for binary mixtures. It is found that the interfacial tension is proportional to the difference between the surface tensions raised to the nth power where n is of the order of 4.0.     

Rheo-optical properties of polymers: Relaxation and recovery during absorption and desorption of organic liquids

As part of a study in elucidating the mechanisms by which crazing is initiated in polymers, we have measured the force and birefringence decay which occurs in several polymers when placed in contact with methanol. In all cases, the force decay can be used to determine the rate of bulk diffusion of the liquid into the polymer. In contrast, the birefringence decay appears to be related to shear relaxation mechanisms which are highly dependent on the type of material. For example, in the case of simple rubbers such as polyisoprene, the rates of decay of force and birefringence are identical within experimental error. In contrast, in amorphous thermoplastics the force decay is typically an order of magnitude faster than the birefringence decay. These results are discussed in terms of distortional and orientational birefringence and with respect to the morphology of the glassy state.     

Relative stabilities of Ce(IV) and Ce(III) limiting carbonate complexes at 5-50 °C in Na aqueous solutions, an electrochemical study

The normal potential of the Ce(IV)/Ce(III) redox couple was determined by square wave voltammetry (SWV) at different temperatures in solutions with a constant ratio [CO₃²⁻]/[HCO₃⁻] ≈10 for high ionic strengths (3.29 mol dm⁻³ at 4.39 mol dm⁻³): varies from 259.5 to 198.0 mV/S.H.E. in the 15-50 °C range. Linear variations were found for versus (RT/F)ln(mCO₃²⁻), leading to the stoichiometry, Ce(CO₃)₆⁸⁻ for the Ce(IV) limiting complex. But the slopes of these linear variations were actually found in the range 1.8-1.9, not exactly 2. This was interpreted as dissociation of the Ce(IV) limiting complex following the reaction: Ce(CO₃)₅⁶⁻ + CO₃²⁻ → Ce(CO₃)₆⁸⁻ and as dissociation of the Ce(III) limiting complex following the reaction: Ce(CO₃)₃³⁻ + CO₃²⁻ → Ce(CO₃)₄⁵⁻; for which maximum possible values of log₁₀ K_IV,6 and log₁₀ K_III,4 were estimated via fitting in the 15-50 °C temperature range (log₁₀ K_IV,6 = 0.42 (0.97) and log₁₀ K_III,4 = 0.88 (7.00) at 15 °C (50 °C). The normal potential was found to decrease linearly with T, these variations correspond to , with T⁰ = 298.15 K and . The apparent diffusion coefficient of Ce(IV) was determined by direct current polarography (DCP), cyclic voltammetry (CV) and square wave voltammetry. It was found to depend on the ionic strength and to be proportional to T.     

Effect of impeller type on the mixing in torus reactors

Torus reactors are characterized by a homogeneous fluid circulation without dead zones. Torus reactors were used for applications in biotechnology, food processing, polymerization and liquid waste treatments. The relatively simple extrapolation of performances, due to the absence of dead volume, is one of the main advantages of this reactor, with low shear stresses and an effective radial mixing allowing efficient heat dissipation. This study is based on the mixing in order to analyse the fluid circulation, mainly in turbulent flow regime, and to characterize the torus reactor with the axial dispersion plug flow model. The objective of this study is to characterize the flow and the mixing in the torus reactors in batch and continuous modes. The mixing analysis was made according to the flow parameters and to the geometrical characteristics of the reactor and impeller. The mixing in the torus reactor can be characterized by the Péclet number, Pe_D, defined with torus diameter. A representative model based on plug flow with axial dispersion and partial recirculation was proposed.     

Lagrangian trajectory model for turbulent swirling flow in an annular cell: comparison with residence time distribution measurements

Knowledge of the flow field can be very useful for reactor design and optimization. Data concerning the displacement and trajectories of reactive elements are of primary interest for a better understanding of process running. Results can be deduced from computational fluid dynamics or experimental measurements. However, numerical simulation is difficult to achieve for complex flow such as swirling decaying flow, and trajectories need to be calculated on the basis of velocity field measurements. This problem can be simplified by using a Lagrangian formulation, in which case the only major difficulty is to express the influence of turbulence on calculated trajectories. Velocity fluctuations can be considered as pure random functions or related to turbulence correlations. These two methods were used to calculate trajectories of elementary fluid particles in a swirling decaying flow on the basis of hydrodynamic characteristics obtained by particle image velocimetry (PIV) studies. Trajectory dispersion was then compared with experimental results obtained by PIV measurements of the instantaneous flow field. This comparison shows the great dependence of velocity fluctuation (and thus of trajectories) on spatial correlations. Finally, the correct mathematical formulation of velocity fluctuation was checked by using the trajectory calculation algorithm to determine residence time distribution (RTD). A comparison with experimental RTD confirmed the efficiency of the method for determining trajectories in swirling decaying flow.     

Kinases of the Focal Adhesion Complex Contribute to Cardiomyocyte Specification

Differentiation of pluripotent stem cells to cardiomyocytes is influenced by culture conditions including the extracellular matrices or similar synthetic scaffolds on which they are grown. However, the molecular mechanisms that link the scaffold with differentiation outcomes are not fully known. Here, we determined by immunofluorescence staining and mass spectrometry approaches that extracellular matrix (ECM) engagement by mouse pluripotent stem cells activates critical components of canonical wingless/integrated (Wnt) signaling pathways via kinases of the focal adhesion to drive cardiomyogenesis. These kinases were found to be differentially activated depending on type of ECM engaged. These outcomes begin to explain how varied ECM composition of in vivo tissues with development and in vitro model systems gives rise to different mature cell types, having broad practical applicability for the design of engineered tissues.