Molten salt electrolysis apparatus and process

Abstract

The invention provides a process and an apparatus for the production of a metal selected from metallic alkali metals, M, and alkaline earth metals, M ac from the molten salts thereof, the apparatus including at least an electrochemical cell with planar anodes and cathodes installed in the following sequence: {a-c-a) n to produce alkali metal or alkaline earth metals electrolytically!y from the respective chloride salts thereof, wherein n represents the number of times the sequence of anode-cathode-anode is repeated.

1 .- 20 . (canceled) 
     
     
         21 . An apparatus for the production of a metal selected from metallic alkali metals, M, and alkaline earth metals, M ae  from the molten salts thereof, the apparatus including at least an electrochemical cell with planar anodes and cathodes installed in the following sequence: (a-c-a) n  to produce alkali metal or alkaline earth metals electrolytically from the respective chloride salts thereof, wherein n represents the number of times the sequence of anode-cathode-anode is repeated, and wherein a metal collector assembly is installed above each cathode to collect molten alkali metal or alkaline earth metal that floats to the top of the electrolyte from where it is withdrawn from the cell. 
     
     
         22 . An apparatus as claimed in  claim 21 , wherein the alkali metal, M is selected from lithium and sodium. 
     
     
         23 . An apparatus as claimed in  claim 21 , wherein the alkaline earth metal M ae  is magnesium. 
     
     
         24 . An apparatus as claimed in  claim 21 , wherein diaphragms which are made of steel mesh, perforated plate, or slotted plates are installed between each pair of opposed anodes and cathodes. 
     
     
         25 . An apparatus as claimed in  claim 24 , wherein the metal collector assembly is electrically isolated from both the anodes and cathode of an anode-cathode-anode set while the metal collector assembly and the diaphragms are electrically connected to each other. 
     
     
         26 . An apparatus as claimed in  claim 24 , wherein both the metal collector assembly and the diaphragms are cathodically protected by molten alkali metal or alkaline earth metal collected in the assembly. 
     
     
         27 . An apparatus as claimed in  claim 21 , wherein the cathodes are installed through the bottom of the cell and the anodes through the side or opposing sides of the cell. 
     
     
         28 . An apparatus as claimed in  claim 21 , wherein the electrochemical cell is lined with chlorine resistant refractory material or is made of metal, provided that the metal exposed to chlorine gas in the head space of the cell is sufficiently resistant to attack by chlorine. 
     
     
         29 . An apparatus as claimed in  claim 21 , wherein a direct current power source is supplied to provide the electrical potential and current required for the reaction. 
     
     
         30 . A method for the production of metal selected from alkali metals and alkaline earth metals from a mixture of molten chloride salts including the chloride salt of the alkali metals and alkaline earth metals by electrolysis, said method including
 arranging three or more electrodes in an (a-c-a) n  arrangement in an electrolysis cell, wherein n represents the number of repetitions of the anode-cathode-anode electrode arrangement;   maintaining an electrical potential between the electrodes sufficient for the electrolytic decomposition of the alkali or alkaline earth metal salt in the electrolysis cell;   feeding the molten alkali metal or alkaline earth metal salt into the electrolysis cell;   permitting the gas produced at the anode to cause circulation of the molten electrolyte used in the cell upwards along the face of the anode surface in the spaces between each anode and opposing cathode, over the active anode body, then downwards behind the anode body before turning around to flow upwards again over the face of the anode (or anodes); and   permitting the metallic alkali metal or alkaline earth metal to become separated by density from the molten electrolyte and thus recovered.   
     
     
         31 . A method as claimed in  claim 30 , which includes maintaining the metallic alkali metal or alkaline earth metal under an inert atmosphere during extraction thereof. 
     
     
         32 . A method as claimed in  claim 30 , wherein the molten alkali metal or alkaline earth metal salt is selected from sodium, lithium, or a magnesium salt. 
     
     
         33 . A method as claimed in  claim 32 , wherein the sodium salt is NaCl in which case the electrolyte contains NaCl, CaCl 2 , and BaCl 2  allowing the cell to be operated at temperatures from about 550 to 700° C. 
     
     
         34 . A method as claimed in  claim 32 , wherein the lithium salt is LiCl in which case the electrolyte consists predominantly of a mixture of KCl and LiCl allowing the cell to be operated at temperatures from about 400 to 500° C. 
     
     
         35 . A method as claimed in  claim 32 , wherein the magnesium salt is MgCl 2  in which case the electrolyte consists predominantly of a mixture of KCl, NaCl, CaCl 2 , BaCl 2 , and MgCl 2  allowing the cell to be operated at temperatures from about 660 to 800° C. 
     
     
         36 . A method as claimed in  claim 30 , wherein the alkali metal or alkaline earth metal is recovered at a temperature above its melting point, in liquid form. 
     
     
         37 . A method as claimed in  claim 30 , wherein the alkali metal or alkaline earth metal is recovered at a temperature below the melting point of the pure alkali metal or alkaline earth metal salt from which the alkali metal or alkaline earth metal is recovered. 
     
     
         38 . A method as claimed in  claim 30 , in which chlorine produced at the anodes disengages from the circulating electrolyte at the top of the molten electrolyte above the active electrolysis zones between the anodes and cathodes. 
     
     
         39 . A method as claimed in  claim 38 , wherein the chlorine thus produced in the head space above the electrolyte is withdrawn from the cell to be used for various purposes.