Reduction method and system for high-melting-point metal oxide, using fluoride-based electrolytes

Abstract

The present disclosure relates to a metal oxide reduction method and, specifically, to a metal oxide reduction method which, in producing a high-grade alloy metal using a metal oxide as a raw material, enables operation in the atmosphere by moving away from an existing production process in an inert gas atmosphere, and is easy to commercialize and can maximize efficiency, as an eco-friendly method is used.

1 . A method of reducing metal M 1  from a metal oxide, comprising:
 forming a molten salt of a fluoride-based flux in an cell;   putting, into the cell, a metal M 2  forming an eutectic phase with the metal M 1 , and a reducing agent including a metal M 3  to produce an eutectic composition of the metal M 2  and the metal M 3 ; and   reducing the metal M 1  by reacting the metal oxide with the eutectic composition and forming a liquid metal alloy with the reduced metal M 1  and M 2 ,   wherein density of the molten salt is less than density of the eutectic composition and the metal oxide.   
     
     
         2 . The method of  claim 1 , wherein the molten salt has a volatilization rate of 10% by weight or less at 1,600° C. for 10 hours. 
     
     
         3 . The method of  claim 1 , wherein the fluoride-based flux is one or more selected from the group consisting of MgF 2 , CaF 2 , SrF 2 , and BaF 2 . 
     
     
         4 . The method of  claim 3 , wherein the fluoride-based flux is CaF 2 . 
     
     
         5 . The method of  claim 1 , wherein the metal M 1  is one or more selected from the group consisting of Ti, Zr, Hf, W, Fe, Ni, Zn, Co, Mn, Cr, Ta, Ga, Nb, Sn, Ag, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, and No. 
     
     
         6 . The method of  claim 1 , wherein the metal M 2  is one or more selected from the group consisting of Cu, Ni, Sn, Zn, Pb, Bi, Cd, and alloys thereof. 
     
     
         7 . The method of  claim 6 , wherein the metal M 2  is Cu. 
     
     
         8 . The method of  claim 1 , wherein the metal M 3  is one or more selected from the group consisting of Ca, Mg, Al, and alloys thereof. 
     
     
         9 . The method of  claim 1 , wherein the metal oxide includes one or more selected from the group consisting of M 1   x O z , and M 1   x M 3   y O z :
 wherein x and y are a real number from 1 to 3, respectively, and z is a real number from 1 to 4.   
     
     
         10 . The method of  claim 1 , wherein a process of reducing the metal M 1  by reacting the metal oxide with the eutectic composition is performed in air or in fluoride. 
     
     
         11 . The method of  claim 1 , wherein a process of reducing the metal M 1  by reacting the metal oxide with the eutectic composition is performed in a range of 900 to 1,600° C. 
     
     
         12 . The method of  claim 1 , further comprising forming slags of the molten salt and a by-product generated in a process of reducing the metal M 1  by reacting the metal oxide with the eutectic composition by adding a slag-forming additive. 
     
     
         13 . The method of  claim 12 , wherein the slag-forming additive comprises one or more selected from the group consisting of MgO, CaO, FeO, BaO, SiO 2 , and Al 2 O 3 . 
     
     
         14 . The method of  claim 12 , further comprising:
 forming a layer in which the liquid metal alloy is positioned at a bottom of the cell and separated from the eutectic composition, and continuously obtaining the liquid metal alloy through a lower portion of the cell; and   forming a distinct layer on top of the eutectic composition using the slags, and continuously removing the slags through a top of the cell.   
     
     
         15 . The method of  claim 1 , further comprising electrorefining the liquid metal alloy to produce the metal M 1 . 
     
     
         16 . A metal obtained by the method of  claim 15 . 
     
     
         17 . A metal alloy obtained by the method of  claim 1 . 
     
     
         18 . The method of  claim 17 , wherein a residual content of the metal M 3  is 0.1% by weight or less based on the total weight of the metal alloy, and a oxygen content is 1,800 ppm or less. 
     
     
         19 . A system for reducing metal M 1  from a metal oxide, comprising:
 an cell;   a molten salt of a fluoride-based flux positioned in the cell;   an eutectic composition of metal M 2  and metal M 3  positioned at a lower portion of the molten salt; and   a liquid metal alloy of the metal M 1  and the metal M 2  positioned below the eutectic composition;   wherein a density of the molten salt is smaller than a density of the metal oxide,   the metal oxide and the metal M 3  react to reduce the metal M 1 , and   the metal M 2  forms an eutectic phase with the metal M 1 .