Method for Removing/Concentrating Metal-Fog-Forming Metal Present in Molten Salt, Apparatus Thereof, and Process and Apparatus for Producing Ti or Ti Alloy by use of them

Abstract

The present invention provides a method by which a metal-fog-forming metal dissolved in one portion of “a molten salt mixture consisted of one or more of metal-fog-forming metal containing molten salts” (generally, a molten salt) can be removed and transferred to another portion of the molten salt to increase the concentration thereof. The method can hence be utilized as one of means for treating molten salts in various industrial fields in which metal-fog-forming metal-containing molten salts such as Ca or Na are handled. In particular, when the method is utilized in producing Ti by Ca reduction, the Ca dissolved in the molten salt to be fed to an electrolytic cell can be rapidly removed (recovered) and the Ca formation efficiency during the electrolysis of the molten salt can be enhanced. Consequently, Ca formation and TiCl 4 reduction in the electrolysis of the molten salt can be efficiently carried out and a stable operation on a commercial scale is possible. Thus, the method can be efficiently utilized in producing Ti or a Ti alloy by Ca reduction.

1 . A method of removing/concentrating a metal-fog-forming metal in a molten salt, comprising: holding “a molten salt mixture consisted of one or more of metal-fog-forming metal containing molten salts” (hereinafter, generally referred to as a “molten salt”) with the metal-fog-forming metal being dissolved therein both in a metal-fog-forming metal concentrating and removing regions (hereinafter, referred to as a “concentrating region” and a “removing region”, respectively) in a metal-fog-forming metal removing/concentrating vessel, the concentrating and removing regions being apart from each other; holding, in contact with the molten salt held in each of the concentrating and removing regions, a metal-fog-forming metal containing molten alloy; and applying a voltage below a decomposition voltage for the metal-fog-forming metal containing molten salt so that an electrode plate on the molten salt side within the removing region may serve as a positive (+) electrode against the molten salt side within the concentrating region, thereby causing the metal-fog-forming metal dissolved in the molten salt within the removing region to be absorbed into the molten alloy to result in the concentration thereof being decreased and, at the same time, increasing the concentration of the metal-fog-forming metal dissolved in the molten salt within the concentrating region. 
   
   
       2 . The method of removing/concentrating a metal-fog-forming metal in a molten salt according to  claim 1 , wherein the metal-fog-forming metal is Ca and the metal-fog-forming metal-containing molten salt is a Ca-containing molten salt. 
   
   
       3 . The method of removing/concentrating a metal-fog-forming metal in a molten salt according to  claim 1 , wherein the metal-fog-forming metal is Ca and the metal-fog-forming metal-containing molten salt is CaCl 2 . 
   
   
       4 . The method of removing/concentrating a metal-fog-forming metal in a molten salt according to  claim 3 , wherein the voltage to be applied is lower than 3.2 V. 
   
   
       5 . A process for producing Ti or a Ti alloy which comprises:
 a reduction step in which a CaCl 2 -containing molten salt with Ca being dissolved therein is held in a reaction vessel and said Ca in the molten salt is allowed to react with a TiCl 4 -based metal chloride to form Ti particles or Ti alloy particles in that molten salt; a separation step in which said Ti particles or Ti alloy particles are separated from the molten salt inside or outside the reaction vessel; an electrolysis step in which the molten salt taken out of the reaction vessel is electrolyzed to form Ca for increasing the Ca concentration in the molten salt; a return step in which said Ca formed by the electrolysis is introduced, either alone or together with the molten salt, into the reaction vessel; and a Ca recovery step in which while the molten salt separated in the separation step and to be sent to the electrolysis step is kept in contact with a molten alloy containing Ca and Mg, a voltage below a decomposition voltage for CaCl 2  is applied so that an electrode bar on the molten alloy side may serve as a negative (−) electrode and an electrode bar on the molten salt side as a positive (+) electrode to thereby cause the Ca dissolved in the molten salt to be absorbed into the molten alloy, and the molten salt reduced in Ca concentration is sent to the electrolysis step.   
   
   
       6 . A process for producing Ti or a Ti alloy which comprises: a reduction step in which a CaCl 2 -containing molten salt with Ca being dissolved therein is held in a reaction vessel and said Ca in the molten salt is allowed to react with a TiCl 4 -based metal chloride to form Ti particles or Ti alloy particles in the molten salt; a separation step in which said Ti particles or Ti alloy particles are separated from the molten salt inside or outside the reaction vessel; an electrolysis step in which the molten salt taken out of the reaction vessel is electrolyzed to form Ca to thereby increase the Ca concentration in the molten salt+a return step in which said Ca formed by electrolysis is introduced, either alone or together with the molten salt, into the reaction vessel; and a Ca removing/concentrating step in which a voltage below a decomposition voltage for CaCl 2  is applied so that an electrode plate on the molten salt side within a Ca-removing region serving to hold the molten salt separated in the separation step and to be sent to the electrolysis step may serve as a positive (+) electrode against an electrode plate on the molten salt side within a Ca-concentrating region separated from the Ca-removing region and serving to hold the molten salt to be sent to the reduction step, and the molten salt reduced in Ca concentration in the Ca-removing region is sent to the electrolysis step and the molten salt increased in Ca concentration in the Ca-concentrating region is sent to the reduction step. 
   
   
       7 . The process for producing Ti or a Ti alloy according to  claim 5 , wherein the voltage to be applied is lower than 3.2 V. 
   
   
       8 . The process for producing Ti or a Ti alloy according to  claim 5 , wherein the molten salt increased in Ca concentration in the electrolysis step is introduced into a regulating vessel provided with a Ca supply source, brought into contact with the Ca supply source to thereby render the Ca concentration therein constant and thereafter sent to the reduction step. 
   
   
       9 . The process for producing Ti or a Ti alloy according to  claim 5 , wherein the molten alloy increased in Ca concentration as a result of absorption of Ca in the Ca recovery step is used as the whole or part of the Ca supply source for a regulating vessel provided with a Ca supply source and intended for introducing the molten salt in the electrolytic cell thereinto and bringing the same into contact with the Ca supply source to thereby render the Ca concentration in the molten salt constant and, thereafter, feeding the molten salt into the reaction vessel. 
   
   
       10 . An apparatus for removing/concentrating a metal-fog-forming metal in a molten salt, comprising a metal-fog-forming metal removing/concentrating vessel including: a metal-fog-forming metal concentrating region (hereinafter, referred to as a “concentrating region”) that holds “a molten salt mixture consisted of one or more of metal-fog-forming metal containing molten salts” (hereinafter, generally referred to as a “molten salt) increased in the concentration of the metal-fog-forming metal dissolved therein; a metal-fog-forming metal removing region (hereinafter, referred to as a “removing region) that is separated from said concentrating region and intended for holding the metal-fog-forming metal containing molten salt decreased in the concentration of the metal-fog-forming metal dissolved therein as a result of application of a voltage below a decomposition voltage for the metal-fog-forming metal-containing molten salt via an electrode plate so that it may serve as a positive (+) electrode against the molten salt side within the concentrating region; and a molten alloy holding region for holding a metal-fog-forming metal containing molten alloy in contact with the molten salt both in the concentrating and removing regions. 
   
   
       11 . The apparatus for removing/concentrating a metal-fog-forming metal in a molten salt according to  claim 10 , wherein the metal-fog-forming metal is Ca and the metal-fog-forming metal containing molten salt is a Ca-containing molten salt. 
   
   
       12 . The apparatus for removing/concentrating a metal-fog-forming metal in a molten salt according to  claim 10 , wherein the metal-fog-forming metal is Ca and the metal-fog-forming metal containing molten salt is CaCl 2 . 
   
   
       13 . An apparatus for producing Ti or a Ti alloy, comprising: a reaction vessel for holding a CaCl 2 -containing molten salt with Ca being dissolved therein and reacting a TiCl 4 -based metal chloride that is fed into the molten salt with said Ca to cause the formation of Ti particles or Ti alloy particles therein; a separation means for separating said Ti particles or Ti alloy particles formed in the molten salt from the molten salt; an electrolytic cell which holds the molten salt after separation of said Ti particles or Ti alloy particles therefrom and is equipped with an anode and a cathode for carrying out electrolysis in the molten salt to form Ca on the cathode side; a return means for introducing the Ca formed by electrolysis, either alone or together with the molten salt, into the reaction vessel; and a Ca recovery means (a) for applying, while keeping the molten salt separated by the separation means and to be fed to the electrolytic cell in contact with a molten alloy containing Ca and Mg a voltage below a decomposition voltage for CaCl 2  so that an electrode bar on the molten alloy side may serve as a negative (−) electrode and an electrode bar on the molten salt side as a positive (+) electrode to thereby cause the Ca dissolved in the molten salt to be absorbed into the molten alloy and (b) for sending the molten salt reduced in Ca concentration to the electrolytic cell. 
   
   
       14 . An apparatus for producing Ti or a Ti alloy, comprising: a reaction vessel for (a) holding a CaCl 2 -containing molten salt with Ca being dissolved therein and (b) reacting a TiCl 4 -based metal chloride, which is fed into the molten salt, with the Ca to cause the formation of Ti particles or Ti alloy particles therein; a separation means for separating said Ti particles or Ti alloy particles formed in the molten salt from the molten salt; an electrolytic cell which holds the molten salt after separation of said Ti particles or Ti alloy particles therefrom and is equipped with an anode and a cathode for carrying out electrolysis in the molten salt to form Ca on the cathode side; a return means for introducing the Ca formed by electrolysis, either alone or together with the molten salt, into the reaction vessel; and a Ca removing/concentrating unit which comprises (a) a Ca-removing region for holding the molten salt separated in the separation step and to be fed to the electrolysis step and (b) a Ca-concentrating region being separated from the Ca-removing region and serving to hold the molten salt to be sent to the reduction step, the unit serving to apply a voltage below a decomposition voltage for CaCl 2  so that an electrode plate on the molten salt side in the Ca-removing region may serve as a positive (+) electrode against an electrode plate on the molten salt side in the Ca-concentrating region and, further, serving to send the molten salt thus reduced in Ca concentration in the Ca-removing region to the electrolysis step and the molten salt thus increased in Ca concentration in the Ca-concentrating region to the reduction step. 
   
   
       15 . The apparatus for producing Ti or a Ti alloy according to  claim 13 , further comprising a regulating vessel provided with a Ca supply source and intended for introducing the molten salt in the electrolytic cell thereinto, bringing the same into contact with the Ca supply source to thereby render the Ca concentration in the molten salt constant and, thereafter, feeding the molten salt into the reaction vessel. 
   
   
       16 . The apparatus for producing Ti or a Ti alloy according to  claim 13 , comprising a regulating vessel provided with a Ca supply source and intended for introducing the molten salt in the electrolytic cell thereinto, bringing the same into contact with the Ca supply source to thereby render the Ca concentration in the molten salt constant and, thereafter, feeding the molten salt into the reaction vessel, wherein the molten alloy increased in Ca concentration in the Ca recovery means is used as the whole or part of the Ca supply source in the regulating vessel. 
   
   
       17 . The process for producing Ti or a Ti alloy according to  claim 6 , wherein the voltage to be applied is lower than 3.2 V. 
   
   
       18 . The process for producing Ti or a Ti alloy according to  claim 6 , wherein the molten salt increased in Ca concentration in the electrolysis step is introduced into a regulating vessel provided with a Ca supply source, brought into contact with the Ca supply source to thereby render the Ca concentration therein constant and thereafter sent to the reduction step. 
   
   
       19 . The apparatus for producing Ti or a Ti alloy according to  claim 14 , further comprising a regulating vessel provided with a Ca supply source and intended for introducing the molten salt in the electrolytic cell thereinto, bringing the same into contact with the Ca supply source to thereby render the Ca concentration in the molten salt constant and, thereafter, feeding the molten salt into the reaction vessel.