Alkali Chloride Melts Research Articles

Kinetics of aluminium deposition from aluminium chloride—alkali chloride melts

The kinetics of aluminium deposition from NaClAlCl 3 and NaClKClAlCl 3 melts ( c AlCl 3 < 0.4 mol%) was studied by linear sweep voltammetry and potential step amperometry. The reduction of AlCl 3 on tungsten and aluminium electrodes was found to be diffusion controlled. The diffusion coefficients of AlCl 3 were: 3.5 × 10 −5 cm 2 s −1 at 820°C in NaClAlCl 3, 2.7 × 10 −5cm 2s −1 at 825°C, and 2.1 × 10 −5cm 2s −1 at 705°C in KClNaClAlCl 3. The rate constant for AlCl 3 reduction at these conditions was found to be in the order of 0.2 cm s −1, in good agreement with extrapolated literature data.

Effect of the addition of fluoride on the conditional solubility of alumina in LiCl-KCl eutectic melt

Owing to its well-known high complexing power toward Al 3+ ion, fluoride ion is able to increase the solubility of alumina in alkali chloride melts. To determine the extent of this effect, the formation of aluminium(III) fluoro-complexes was studied potentiometrically in LiCl-KCl eutectic at 470°. But the sodium fluoride addition appeared to produce not only the complexation effect but also a mineralization effect on alumina. So, the thermodynamical stability of alumina formed in this melt by precipitation from aluminium chloride with carbonate ion (oxide anion donor) depends on the fluoride ion concentration. These two effects explain the solubility variation of alumina in the LiCl-KCl eutectic + NaF mixtures. A pF − - pO 2− diagram, which represents the stability area of the various aluminium (III) species is established, and leads to some conclusions concerning the electrowinning of aluminium from molten chloride melts. The cumulative formation constants of the aluminium(lII) fluoro-complexes (AlF 3−i i) have been obtained, whose values are the following: 2.5 ± 0.4, 4.7 ± 0.6, 5.7 ± 0.5, 7.5 ± 0.4, 8.0 ± 0.5, 9.0 ± 0.6, respectively for i = 1, 2, 3, 4, 5 and 6. It has been shown that oxyfluoride species such as AlOF 1− j i does not exist. The solubility products of gamma and alpha-alumina have been determined and are equal to 10 −42.9 and 10 −44.0 respectively (all the constants are given in the molality scale). They differ widely from the solubility product of the alumina obtained in the absence of fluoride ion, ie 10 −27.4.

Nepheline--Alkali Feldspar Equilibria: I. Experimental Data and Thermodynamic Calculations

Nepheline-alkali feldspar equilibria with alkali chloride aqueous solutions have been determined for the temperature range 400 to 700 °C at 1000 bars pressure. Nepheline-alkali feldspar equilibria with alkali chloride melts have been determined for the temperature range 800 to 1100 °C at approximately 6 bars pressure. (1) NaAlSiO4 + KCl(aq) = NaCl(aq) + KAlSiO4 (2) NaAlSiO4 + KCl(melt) = NaCl(melt) + KAlSiO4 (3) NaAlSi3O8(high) + KCl(aq) = NaCl(aq) + KAlSi3O8(San) (4) NaAlSi3O8(low) + KCl(aq) = NaCl(aq) + KAlSi3O8(Mic) (5) NaAlSi3O8(high) + KCl(melt) = NaCl(melt) + KAlSi3O4(San) (6) NaAlSi3O8(low) + KCl(melt) = NaCl(melt) + KAlSi3O8(Mic) From these, two diagrams of phase relationships were derived for the following exchange equilibria: (7) NaAlSiO4 + KAlSi3O8(San) = NaAlSi3O8(high) + KAlSiO4; (8) NaAlSiO4 + KAlSi3O8(Mic) = NaAlSi3O8(low) + KAlSiO4. The effect of pressure on these equilibria has been determined by comparing the experimental data for 1000 and 5000 bars (t = 500 °C) and thermodynamic calculations. It has also been shown that the effect of excess silica in nepheline solid solution on the K—Na distribution between nepheline and alkali feldspar is substantial and opposite to that of temperature. In the high temperature region an increase in silica content in nepheline of 2 wt. per cent eliminates the effect on the redistribution of a temperature increase of 100 °C. These cation exchange data and unit cell data for the crystal phases are used to calculate thermodynamic mixing properties of nepheline solid solution and alkali feldspar solid solution for a wide range of temperature and pressure.

Chemical behaviour of radiosulphur obtained by 35Cl( n, p) 35S during in-core irradiation of alkali-chloride melts

Chemical behaviour of radiosulphur obtained by 35Cl( n, p) 35S during in-core irradiation of alkali-chloride melts

Crystal Structures of K2MgCl4 and Cs2MgCl4

Supporting evidence for complex ion formation in MgCl2 alkali chloride melts was sought from a single crystal X-ray analysis of the title compounds. Crystals of K2MgCl4 are tetragonal, a = 4.94, c = 15.58 Å, Z = 2, space group I 4/mmm. The compound is isostructural with K2NiF4, and was determined with MoK α diffractometer data and refined by full-matrix least-squares to R = 0.046 for 180 reflections.Crystals of Cs2MgCl4 are orthorhombic, a = 9.777, b = 7.514, c = 13.234 Å,Z = 4, space group Pnma. The compound is isostructural with β-K2SO4, and was determined with MoKα diffractometer data and refined by full-matrix least-squares to R = 0.074 for 1084 reflections. The K2MgCl4 structure contains an infinite two-dimensional array of MgCl6 octahedra sharing edges. The Cs2MgCl4 structure contains discrete MgCl42− anions which likely continue to exist in the melt close to the melting point.

Thermodynamic Properties of Zinc Chloride in Alkali Chloride Melts by Electromotive Force Measurements

Electromotive force measurements on the ZnCl2–ACl systems where A = K, Rb, and Cs were made using cells of the type[Formula: see text]in the temperature range 450° to 800 °C. The partial molar free energies, enthalpies, and excess entropies have been determined from the temperature dependence of the emf results. These thermodynamic properties exhibit increasing negative departure from ideality as the basicity of the alkali metal salt increases. The results are interpreted in terms of an acid–base reaction and are discussed in relation to current models.

Thermodynamic Properties of Manganous Chloride in Alkali Chloride Melts by Electromotive Force Measurements

Electromotive force measurements on the systems where were made using cells of the type largely in the temperature range 0°–900°C. The partial molar free energies, enthalpies, and entropies of mixing have been calculated from the emf results. The systems indicate negative deviations from ideality which are increasing from Li throughout to Cs. The concentration dependence of the partial molar enthalpies and entropies of mixing has been interpreted on the basis of the “complex ion” model previously developed which is applicable to reactive change asymmetrical fused salt mixtures. The entropy of mixing has been treated by postulating vibrational as well as a configurational contributions. The vibrational contributions have the largest negative values in the system. The effect of the vibrational contribution on the partial molar properties is also discussed.

Properties of the solutions of the alkali-chlorozirconate compounds in alkali-chloride melts

The activities of Li2ZrCl6, Na2ZrCl6, and K2ZrCl6 in the systems LiCl–Li2ZrCl6, NaCl–Na2ZrCl6, and KCl–K2ZrCl6, respectively, were calculated from available pressure data using a modified form of the Gibbs–Duhem relationship. The calculations indicate positive deviations from ideality that decrease with increasing size of the alkali metal cation.

A New Method for Preparing Hydroxide‐Free Alkali Chloride Melts

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