Method and system for separating rare earth elements

Patent metadata

Field	Value
Publication number	US-9435009-B2
Application number	US-201314422796-A
Country	US
Kind code	B2
Filing date	Oct 8, 2013
Priority date	Oct 10, 2012
Publication date	Sep 6, 2016
Grant date	Sep 6, 2016

Abstract

An objective of the invention is to provide a method and system for separating a particular rare earth element from a rare earth magnet at a high separation ratio and by a simple process. There is provided a rare earth separation method for separating a first and a second groups of rare earth elements contained in a magnet, the method including: a starting powder preparation step from the magnet; a magnet component oxidation heat treatment step; a rare earth oxide separation step from the magnet components oxide powder; a powder size optimization step; a chlorinating agent mixing step; a chlorination/oxychlorination heat treatment step of forming a “first group rare earth chlorides”/“second group rare earth oxychlorides” mixture; a selective dissolution step of selectively dissolving the first group rare earth chlorides in the solvent and leaving the second group rare earth oxychlorides undissolved in solid phase form; and a solid-liquid separation step.

First claim

The invention claimed is:

1. A rare earth separation method for separating rare earth elements contained in a magnet wherein said magnet includes as components a first group of rare earth elements and a second group of rare earth elements, comprising the steps of:
(a) a starting powder preparation step of preparing a starting powder from the magnet;
(b) a magnet component oxidation heat treatment step of forming a powder of oxides of the magnet components, the oxides being formed by heating or combustion at a temperature from 300 to 1000° C. in an oxidizing atmosphere;
(c) a rare earth oxide separation step of separating a rare earth oxide powder from the powder of the oxides of the magnet components, the rare earth oxide powder including first group rare earth oxides and second group rare earth oxides;
(d) a powder size optimization step of optimizing the rare earth oxide powder;
(e) a chlorinating agent mixing step of mixing the rare earth oxide powder obtained at the powder size optimization step (d) with a chlorinating agent to prepare a rare earth oxide powder-chlorinating agent mixture;
(f) chlorination/oxychlorination heat treatment step of forming a first group rare earth chlorides-second group rare earth oxychlorides mixture including first group rare earth chlorides and second group rare earth oxychlorides from the rare earth oxide powder-chlorinating agent mixture;
(g) a selective dissolution step of introducing the first group rare earth chlorides-second group rare earth oxychlorides mixture in a solvent in order to selectively dissolve the first group rare earth chlorides in the solvent and leave the second group rare earth oxychlorides undissolved in solid phase form; and
(h) a solid-liquid separation step of solid-liquid separating the solvent in which the first group rare earth chlorides are dissolved and the second group rare earth oxychlorides in the solid phase form.

2. The rare earth separation method according to claim 1 , wherein the chlorination/oxychlorination heat treatment step includes:
a chlorination heat treatment step of chlorinating all of the rare earth oxide powder in the rare earth oxide powder-chlorinating agent mixture to obtain rare earth chlorides including the first group rare earth chlorides and second group rare earth chlorides; and
a selective oxychlorination heat treatment step of oxychlorinating only the second group rare earth chlorides to form the first group rare earth chlorides-second group rare earth oxychlorides mixture, wherein
the chlorination heat treatment step is performed at a temperature at which all of the rare earth oxide powder can be chlorinated and lower than vaporization temperatures of the rare earth chlorides in a non-oxidizing atmosphere; and the selective oxychlorination heat treatment step is performed at an optimal temperature in an oxidizing atmosphere.

3. The rare earth separation method according to claim 2 , wherein the chlorinating agent is ammonium chloride; and at the optimal temperature of the selective oxychlorination heat treatment step, only the second group rare earth chlorides can be oxychlorinated and the first group rare earth chlorides cannot be oxychlorinated, and the first group rare earth chlorides exhibits a percent weight reduction per unit temperature of 1×10 −3 %/° C. or less during the selective oxychlorination heat treatment step as measured by thermogravimetric analysis during elevated temperature process.

4. The rare earth separation method according to claim 3 , wherein the chlorination heat treatment step includes: a first elementary chlorination step of reacting the rare earth oxide powder with ammonium chloride by a heat treatment at an atmospheric pressure to form ammonium chlorides of the rare earth elements; and a successive second elementary chlorination step of forming the rare earth chlorides from the ammonium chlorides of the rare earth elements by a heat treatment at a reduced pressure.

5. The rare earth separation method according to claim 1 , wherein the chlorination/oxychlorination heat treatment step is a simultaneous selective-chlorination/selective-oxychlorination heat treatment step of simultaneously forming the first group rare earth chlorides-second group rare earth oxychlorides from the rare earth oxide powder-chlorinating agent mixture all at once by a heat treatment at an optimal temperature in a non-oxidizing atmosphere.

6. The rare earth separation method according to claim 5 , wherein the chlorinating agent is ammonium chloride; and at the optimal temperature of the simultaneous selective-chlorination/selective-oxychlorination heat treatment step, only the first group rare earth oxides can be chlorinated and only the second group rare earth oxides can be oxychlorinated.

7. The rare earth separation method according to claim 6 , wherein the simultaneous selective-chlorination/selective-oxychlorination heat treatment step includes: a first step of reacting the first group rare earth oxides with ammonium chloride to form ammonium chlorides of the first group rare earth elements by a heat treatment at an atmospheric pressure; and
a successive second step of forming the first group rare earth chlorides from the ammonium chlorides of the first group rare earth elements by a heat treatment at a reduced pressure.

8. The rare earth separation method according to claim 1 , wherein the chlorinating agent is ammonium chloride; and the rare earth oxide powder is mixed with the ammonium chloride in a mixing ratio of 1 mole of the rare earth oxide powder relative to more than 6 moles to less than 20 moles of the ammonium chloride.

9. The rare earth separation method according to claim 1 , wherein the magnet further includes boron and some of the boron remains in the rare earth oxide powder obtained at the rare earth oxide separation step; and
the method further includes, between the rare earth oxide separation step and the powder size optimization step, a boron reduction step of reducing the boron remaining in the rare earth oxide powder.

10. The rare earth separation method according to claim 1 further including, between the powder size optimization step and the chlorinating agent mixing step, an additional oxidation heat treatment step of further and completely oxidizing the rare earth oxide powder obtained at the rare earth oxide separation step, wherein the additional oxidation step is carried out at a temperature higher than the temperature at which the magnet component oxidation heat treatment step is performed in an oxidizing atmosphere.

11. The rare earth separation method according to claim 1 , wherein the desirable powder size distribution obtained at the powder size optimization step has a cumulative 50 vol. % powder size of 0.5 μm or larger and a cumulative 90 vol. % powder size of 10 μm or smaller.

12. The rare earth separation method according to claim 1 , wherein the desirable powder size distribution obtained at the powder size optimization step has a cumulative 50 vol. % powder size of 0.04 μm or larger and a cumulative 90 vol. % powder size of 1.5 μm or smaller.

13. The rare earth separation method according to claim 12 , wherein the powder size optimization step includes a first milling step of providing a first desirable powder size distribution and a successive second milling step of providing a second desirable powder size distribution, and
wherein the first desirable powder size distribution obtained at the first milling step has a cumulative 50 vol. % powder size of 0.5 μm or larger and a cumulative 90 vol. % powder size of 10 μm or smaller, and
the second desirable powder size distribution obtained at the second milling ste

Assignees

• Hitachi Metals Ltd

Inventors

• Yamamoto Hiroki
• Furusawa Katsuyoshi
• Hoshi Hiroyuki
• Kikugawa Atsushi
• Miyata Motoyuki
• Murakami Hajime

Classifications

• B09B3/70

  Chemical treatment, e.g. pH adjustment or oxidation (involving an extraction step B09B3/80) · CPC title

• B09B3/40

  involving thermal treatment, e.g. evaporation (processes using mineral binders involving a melting or softening step B09B3/29; involving radiation B09B3/50) · CPC title

• C22B3/0005

  Chemistry & Metallurgy · mapped topic

• C22B7/007

  by acid leaching · CPC title

• B09B3/0016

  Operations & Transport · mapped topic