Leaching solution and metal recovery method

Abstract

A valuable metal recovery method of recovering metals from a lithium ion battery without using complicate steps and by a relatively simple and convenient facility is intended to be provided. For attaining the purpose, lithium is leached selectively from a positive electrode active material containing a composite oxide of lithium and transition metal elements by using a solution showing a weak acidity at a pH of 4 to 7 so that the high Li/Co selectivity is high and a Li recovery rate is high, and lithium is recovered from the leaching solution. By using a solute that the acidity of the acidic solution spontaneously disappears due to evolution of a gas after leaching of lithium, neutralization step is no more required and the volume of liquid wastes is decreased.

What is claimed is: 
     
         1 . A metal recovery method of recovering metals from a positive electrode active material of a lithium ion battery containing lithium and transition metal elements, comprising:
 leaching valuable metals contained in the positive electrode active material into an acidic solution; and   recovering lithium from the acidic solution where the valuable metals are leached,   wherein the acidic solution is at pH of 4 to 7.   
     
     
         2 . A metal recovery method according to  claim 1 ,
 wherein the acidic solution contains a redox potential controller.   
     
     
         3 . A metal recovery method according to  claim 2 ,
 wherein the acidic solution further contains a pH controller.   
     
     
         4 . A metal recovery method according to  claim 2 ,
 wherein the redox potential controller comprises hydrogen peroxide.   
     
     
         5 . A metal recovery method according to  claim 2 ,
 wherein the redox potential controller comprises ozone.   
     
     
         6 . A metal recovery method according to  claim 3 ,
 wherein the pH controller comprises carbon dioxide.   
     
     
         7 . A metal recovery method according to  claim 1 ,
 wherein one of the solute of the acidic solution, the redox potential controller or the pH controller is a material that spontaneously disappears from the solution.   
     
     
         8 . A metal leaching solution of leaching metals from a positive electrode active material of a lithium ion battery containing lithium and transition metal elements,
 wherein pH of the solution is from 4 to 7 and the solute of the solution is a spontaneously disappearing solute.   
     
     
         9 . A metal recovery method of recovering metals from a positive electrode active material of a lithium ion battery containing lithium and transition metal elements, comprising:
 leaching lithium contained in the positive electrode active material into an acidic solution containing a spontaneously disappearing oxidizer and a buffer solution; and   recovering lithium from the acidic solution in which lithium is leached.   
     
     
         10 . A metal recovering method according to  claim 9 ,
 wherein the buffer solution contains a carboxylic acid and a salt thereof as a solute.   
     
     
         11 . A metal recovering method according to  claim 10 ,
 wherein the carboxylic acid is an aliphatic carboxylic acid having a carboxyl group and not containing an aromatic ring.   
     
     
         12 . A metal recovering method according to  claim 11 ,
 wherein the carboxylic acid has a number of carbon atoms of 1 to 4 (excluding carbon atoms in the carboxyl group).   
     
     
         13 . A metal recovering method according to  claim 10 ,
 wherein the carboxylic acid is an organic acid or glycine.   
     
     
         14 . A metal recovering method according to  claim 9 ,
 wherein the buffer solution contains phosphoric acid and a salt thereof as a solute.   
     
     
         15 . A metal recovering method according to  claim 9 ,
 wherein the spontaneously disappearing oxidizer comprises ozone or aqueous hydrogen peroxide.   
     
     
         16 . A metal recovering method according to  claim 9 ,
 wherein the acidic solution in the leaching step is at a pH of 4 to 7.   
     
     
         17 . A metal leaching solution of leaching metals from a positive electrode active material of a lithium ion battery containing lithium and transition metal elements,
 wherein the leaching solution contains a spontaneously disappearing oxidizer and a buffer solution and a pH of the solution is 4 to 7.