Separation of recycled rare earths

Patent metadata

Field	Value
Publication number	US-10351931-B2
Application number	US-201614996538-A
Country	US
Kind code	B2
Filing date	Jan 15, 2016
Priority date	Jan 15, 2015
Publication date	Jul 16, 2019
Grant date	Jul 16, 2019

Abstract

Extraction of rare earths from end-of-use machinery having rare earth magnets provides a closed-loop process towards recycling rare earths from commingled devices having embedded magnets such as motors, generators and disk drives. A low temperature process selectively leaches the magnet material from mixed scrap containing shredded fragments of the machinery which includes other metals such as steel and copper. Filtration separates the other metals from the leached, dissolved magnet material, which is precipitated by oxalic acid to form oxalates in powder form, suitable for use in production of new rare earth magnetic material. Leaching acid, such as HCl (hydrochloric acid), is recoverable via pyrohydrolysis, and redirected back to the leaching step for completing the closed-loop aspect.

First claim

What is claimed is:

1. A method of recovering rare earths (RE) from mixed scrap comprising:
agitating demagnetized recycling stock including magnet material to generate demagnetized mixed scrap by crushing and shredding to rupture an outer coating on the magnet material and exposing the magnet material for leaching solution contact;
selectively leaching, at room temperature, the magnet material by adding hydrochloric acid to the crushed and shredded mixed scrap for dissolving the mixed scrap in an acid solution to separate the magnet material while leaving steel and copper undissolved;
filtering undissolved metals including the steel and copper from the acid solution;
precipitating the magnet material by adding oxalic acid to the acid solution to form oxalates; and
filtering oxalates from the acid solution for forming new magnetic stock.

2. The method of claim 1 further comprising recovering HCl via pyrohydrolysis and recirculating the HCl into the leaching from mixed scrap.

3. The method of claim 1 further comprising demagnetizing the recycling stock by heating the recycling stock to at least 450° C. for at least 60 minutes, wherein agitating includes shredding and crushing the recycling stock including steel and copper to yield the mixed scrap.

4. The method of claim 1 further comprising:
crushing bonded magnets in the recycling stock sufficiently small to permit surface area contact with the HCl; and
rupturing an outer coating on coated magnets sufficient to permit HCl contact.

5. The method of claim 1 wherein the yield of new magnetic stock is at least 82% of the magnet materials present in the recycling stock.

6. The method of claim 1 wherein the selective leaching results in a solution of at least 88% pure rare earths.

7. The method of claim 1 wherein filtering the oxalates results in of rare earths in the acid solution being extracted for the new magnetic stock.

8. The method of claim 1 wherein the selective leaching is performed at room temperature absent external thermal sources.

9. The method of claim 8 wherein the acid solution is a 4 M solution of hydrochloric acid.

10. The method of claim 1 further comprising precipitating trichlorides from the solution by pyrohydrolysis after filtering the oxalates.

11. The method of claim 10 further comprising precipitating iron oxide and boron oxide.

12. The method of claim 1 wherein the rare earths include Nd (neodymium), Dy (dysprosium) and Pr (praseodymium).

Assignees

• Worcester Polytech Inst

Inventors

• Emmert Marion H
• Bandara H M Dhammika

Classifications

• Y02P10/216

  Cross-Sectional Technologies · mapped topic

• C22B1/00

  Preliminary treatment of ores or scrap · CPC title

• Y02P10/234

  Cross-Sectional Technologies · mapped topic

• C22B1/005

  Preliminary treatment of scrap (C22B1/02 - C22B1/26 take precedence) · CPC title

• Y02P10/236

  Cross-Sectional Technologies · mapped topic