Chloride melt anode process

In an individual molten carbamide, the electrode processes are feebly marked at melt decomposition potentials because of its low electrical conductivity. Both electrode processes are accompanied by gas evolution (NH3, CO, C02, N2) and NH2CN (approximately) is formed in melt. In eutectic carbamide-chloride melts electrode processes take place mainly independently of each other. The chlorine must evolve at the anode during the electrolysis of carbamide - alkali metal and ammonium chloride melts, which were revealed in the electrolysis of the carbamide-KCl melt. But in the case of simultaneous oxidation of carbamide and NH4CI, however, a new compound containing N-Cl bond has been found in anode gases instead of chlorine. It is difficult to fully identify this compound by the experimental methods employed in the present work, but it can be definitely stated that... 

Other Metals. AH the sodium metal produced comes from electrolysis of sodium chloride melts in Downs ceUs. The ceU consists of a cylindrical steel cathode separated from the graphite anode by a perforated steel diaphragm. Lithium is also produced by electrolysis of the chloride in a process similar to that used for sodium. The other alkaH and alkaHne-earth metals can be electrowon from molten chlorides, but thermochemical reduction is preferred commercially. The rare earths can also be electrowon but only the mixture known as mischmetal is prepared in tonnage quantity by electrochemical means. In addition, beryIHum and boron are produced by electrolysis on a commercial scale in the order of a few hundred t/yr. Processes have been developed for electrowinning titanium, tantalum, and niobium from molten salts. These metals, however, are obtained as a powdery deposit which is not easily separated from the electrolyte so that further purification is required. 

Anode processes yield gaseous chlorine, fluorine, carbon chloride or fluoride. In the case of melts containing dissolved tantalum oxide, carbon oxides (mostly carbon dioxide) are formed on the graphite anode [28,37]. 

Aluminum anodization in basic A1C13-MEIC melts was studied by Carlin and Osteryoung [462], and two different anodization processes were observed. The first step occurred in the catholic region, at a potential of -1.1 V, versus the aluminum electrode, and it was controlled by diffusion of chloride to the electrode surface. The authors found that the number of chlorides required to produce one A1C14 anion for each Al being anodized was 4. The second anodization which occurs on the anodic side of 0 V was not diffusion limited. It has not been possible to reduce the A1C14 anion in basic melts. 

Kuznetsova, S.V, Glagolevskaya,A.L., and Kuznetsov, S.A. (1993) Anodic processes occurring during hafnium dissolution in chloride-fluoride melts, Soviet Electrochemistry 28, 558-563. 

Sm VSm Transformation in Chloride Melts Stability of samarium ions (Sm % Sm " ) in the alkaline chloride melts changes as functions of the solvent salt cations and temperature [4]. Sm " exhibits a higher stability for a larger solvent salt cation and lower temperature. Electrochemical reduction of Sm " into Sm in KQ-NaCl-CsCl melt at an inert cathode has been found to occur in two steps as shown in Eqs. 12 and 13. And the reduction of Sm " to Sm° takes place at near the decomposition potential of the supporting electrolyte. In addition, Sm " losing one electron to form Sm " takes place at the anode in terms of reaction Eq. 14, making Sm " Sm /transformation at the electrodes therefore, this process can circulate in the cathode and anode, and therefore nearly no Sm metal can be obtained at the cathode, resulting an extremely low current efficiency. This is the rea-sOTi why samarium caimot be produced from the chloride melts by molten salt electrolysis. It is reported that when the concentration of Sm " ions reach 0.1 wt% in the chloride melts, the current efficiency will be substantially decreased. Eu " behaves in nearly the same manner as Sm " in the chloride melts. 

Figure 1.1.1 The polarisation curve and logarithm of the CO and CO2 mole fractions in the off-gas for the NaCI-Na20 system with 0.15 mol% Na20 at 825 C [1]. Espen Sandnes, The anode process on carbon in chloride-oxide melts, Ph.D. thesis. The Norwegian University of Technology and Science, 2008, ISBN 978-82-471-8415-8 (printed version) ISBN 978-82-471-8429-5 (electronic version) ISSN 1503-8181...

Anode Processes on Carbon in Chloride Melts with Dissolved Oxides 19... 

Sandnes, E. (2008) The anode process on carbon in chloride-oxide melts. Doctoral thesis, NTNU, Trondheim, p. 120. 

Mohamedi, M., Bprresen, B., Haarberg, G.M. and Tunold, R. (1996) Study of the Anode Process on Carbon Electrodes in the Pure Magnesium Chloride Melt with Dissolved Magnesium Oxide at 1023K, Electrochem. Soc. Proc., 12th Int. Symp. on Molten Salts, 96-41, 417-427. 

The kinetics of the electrode processes in vanadium-containing chloride melts was investigated in the middle of the last century [1-5]. Most of the studies were conducted using polarization measurements. Data obtained by different authors are rather fragmentary and often contradictory. For example, there is no information on anodic dissolution of vanadium metal in chloride electrolytes. 

In the present work in situ high-temperature electronic absorption spectroscopy was employed to identify the corrosion products of metals and alloys in fused salts. Corrosion of metals in molten salts under an inert atmosphere has an electrochemical origin and anodic dissolution was used here to facilitate the process studied. Spectroscopic investigation of stainless steel anodic dissolution in alkali chloride melts allows determining the sequence in which the steel components are dissolved. To interpret the observed phenomena, the spectra recorded after steel dissolution were compared with the absorption spectra of the melts containing the products of anodic dissolution of pure metals constituting the stainless steels studied. 

FIGURE 12.15 In the Downs process, molten sodium chloride is electrolyzed with a graphite anode (at which the Cl ions are oxidized to chlorine) and a steel cathode (at which the Na4 ions are reduced to sodium). The sodium and chlorine are kept apart by the hoods surrounding the electrodes. Calcium chloride is present to lower the melting point of sodium chloride to an economical temperature. 

The quality of the refined metal, and the current efficiency strongly depend on the soluble vanadium in the bath and the quality of the anode feed. As the amount of vanadium in the anode decreases, the current efficiency and the purity of the refined product also decrease. A laboratory preparation of the metal with a purity of better than 99.5%, containing low levels of nitrogen (30-50 ppm) and of oxygen (400-1000 ppm) has been possible. The purity obtainable with potassium chloride-lithium chloride-vanadium dichloride and with sodium chloride-calcium chloride-vanadium dichloride mixtures is better than that obtainable with other molten salt mixtures. The major impurities are iron and chromium. Aluminum also gets dissolved in the melt due to chemical and electrochemical reactions but its concentrations in the electrolyte and in the final product have been found to be quite low. The average current efficiency of the process is about 70%, with a metal recovery of 80 to 85%. 

INCO [International Nickel Company] An electrolytic process for extracting nickel from nickel sulfide matte. The matte is melted and cast into anodes. Electrolysis with an aqueous electrolyte containing sulfate, chloride and boric acid dissolves the nickel and leaves the sulfur, together with precious metals, as an anode slime. Operated in Manitoba by International Nickel Company of Canada. 

Sodium is produced by an electrolytic process, similar to the other alkali earth metals. (See figure 4.1). The difference is the electrolyte, which is molten sodium chloride (NaCl, common table salt). A high temperature is required to melt the salt, allowing the sodium cations to collect at the cathode as liquid metallic sodium, while the chlorine anions are liberated as chlorine gas at the anode 2NaCl (salt) + electrolysis —> Cl T (gas) + 2Na (sodium metal). The commercial electrolytic process is referred to as a Downs cell, and at temperatures over 800°C, the liquid sodium metal is drained off as it is produced at the cathode. After chlorine, sodium is the most abundant element found in solution in seawater. 

Strontium metal is not found in its elemental state in nature. Its salts and oxide compounds constitute only 0.025% of the Earths crust. Strontium is found in Mexico and Spain in the mineral ores of strontianite (SrCO ) and celestite (SrSO ). As these ores are treated with hydrochloric acid (HCl), they produce strontium chloride (SrCy that is then used, along with potassium chloride (KCl), to form a eutectic mixture to reduce the melting point of the SrCl, as a molten electrolyte in a graphite dish-shaped electrolysis apparatus. This process produces Sr cations collected at the cathode, where they acquire electrons to form strontium metal. At the same time, Cl anions give up electrons at the anode and are released as chlorine gas Cl T. 

Lithium metal is produced commercially by electrolysis of a fused eutectic mixture of hthium chloride-potassium chloride (45% LiCl) at 400 to 450°C. The eutectic mixture melts at 352°C in comparison to the pure LiCl melting at 606°C. Also, the eutectic melt is a superior electrolyte to LiCl melt. (Landolt, P.E. and C. A. Hampel. 1968. Lithium. In Encyclopedia of Chemical Elements.C. A. Hampel, Ed. Reinhold Book Corp. New York.) Electrolysis is carried out using graphite anodes and steel cathodes. Any sodium impurity in hthium chloride may be removed by vaporizing sodium under vacuum at elevated temperatures. All commercial processes nowadays are based on electrolytic recovery of the metal. Chemical reduction processes do not yield high purity-grade metal. Lithium can be stored indefinitely under airtight conditions. It usually is stored under mineral oil in metal drums. 

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