Method of recovering rare-earth elements

Patent metadata

Field	Value
Publication number	US-9228248-B2
Application number	US-201214389304-A
Country	US
Kind code	B2
Filing date	Dec 7, 2012
Priority date	Mar 30, 2012
Publication date	Jan 5, 2016
Grant date	Jan 5, 2016

Abstract

Provided is a method of recovering rare-earth elements by which rare-earth elements can be recovered efficiently from a bauxite residue serving as a raw material and containing the rare-earth elements. Specifically provided is a method of recovering rare-earth elements from a raw material, the raw material being a bauxite residue produced as a by-product in a Bayer process, the method including: using a bauxite residue having a specific surface area of 35 m 2 /g or more; adding, to the raw material bauxite residue, a liquid leaching agent formed of an aqueous solution of at least one kind of mineral acid selected from sulfuric acid, hydrochloric acid, nitric acid, and sulfurous acid, thereby preparing a slurry having a liquid-solid ratio of 2 to 30 and a pH of 0.5 to 2.2; subjecting the slurry to leaching treatment of the rare-earth elements under a temperature condition of room temperature to 160° C.; subjecting the slurry after the leaching treatment to solid-liquid separation, yielding a leachate; and separating and recovering the rare-earth elements from the leachate.

First claim

What is claimed is:

1. A method of recovering rare-earth elements from a raw material, the raw material being a bauxite residue produced as a by-product in a Bayer process for separating and collecting an aluminum component from bauxite,
the method comprising:
using, as the raw material, a bauxite residue having a specific surface area of 35 m 2 /g or more;
adding an oxidizing agent to the raw material bauxite residue at a ratio of 0.1 to 0.3 equivalent weight with respect to Fe components in the bauxite residue;
adding, to the raw material bauxite residue, a liquid leaching agent formed of an aqueous solution of at least one kind of mineral acid selected from sulfuric acid, hydrochloric acid, nitric acid, and sulfurous acid, thereby preparing a slurry having a liquid-solid ratio of 2 to 30 and a pH of 0.5 to 2.2;
subjecting the slurry to leaching treatment of the rare-earth elements under a temperature condition of room temperature to 160° C.;
subjecting the slurry after the leaching treatment to solid-liquid separation, yielding a leachate; and
separating and recovering the rare-earth elements from the leachate.

2. A method of recovering rare-earth elements according to claim 1 , wherein the raw material bauxite residue comprises a bauxite residue provided from a Bayer process, which comprises using, as a raw material, bauxite powder having a specific surface area of 26 m 2 /g or more and treating the bauxite powder under a condition of a temperature of 160° C. or less.

3. A method of recovering rare-earth elements according to claim 1 , wherein the raw material bauxite residue comprises a bauxite residue provided from a Bayer process, which comprises using, as a raw material, bauxite powder having a specific surface area of 26 m 2 /g or more and treating the bauxite powder under a condition of a temperature of less than 230° C., the bauxite residue containing CaO at less than 4 mass %.

4. A method of recovering rare-earth elements according to claim 1 , wherein the raw material bauxite residue comprises a specific surface area fraction mainly comprising fine particles having a specific surface area of 35 m 2 /g or more, the specific surface area fraction being provided by applying fractionation treatment to a bauxite residue.

5. A method of recovering rare-earth elements according to claim 4 , wherein the specific surface area fraction provided by applying the fractionation treatment comprises a bauxite residue yielded by subjecting a bauxite residue to classification with a sieve having a mesh size of 38 to 400 μm and removing particles on the sieve.

6. A method of recovering rare-earth elements according to claim 1 , further comprising:
adding a pH adjuster to the slurry after the leaching treatment, thereby adjusting the pH thereof to 2.5 to 6;
subjecting the slurry after the adjusting of the pH to solid-liquid separation, yielding a leachate; and
separating and recovering the rare-earth elements from the leachate.

7. A method of recovering rare-earth elements according to claim 6 , wherein the raw material bauxite residue is used as the pH adjuster.

8. A method of recovering rare-earth elements according to claim 1 , further comprising:
prior to the separating and recovering of the rare-earth elements from the leachate, adding a pH adjuster to the leachate, thereby adjusting a pH thereof to 4 to 6;
removing hydroxides of Fe and Al precipitated owing to the adjusting of the pH by solid-liquid separation, thereby yielding a liquid; and
separating and recovering the rare-earth elements from the liquid.

9. A method of recovering rare-earth elements according to claim 8 , wherein the adjusting of the pH to 4 to 6 by adding the pH adjuster to the leachate comprises adding, to the leachate, an oxidizing agent selected from hydrogen peroxide, perchloric acid, permanganic acid, and hypochlorous acid, thereby oxidizing Fe 2+ ions into Fe 3+ ions in the leachate.

10. A method of recovering rare-earth elements according to claim 1 , wherein the separating and recovering of the rare-earth elements comprises:
adding a pH adjuster to one of the leachate yielded by the solid-liquid separation treatment and the liquid yielded by adjusting the pH of the leachate to cause Fe and Al to precipitate as hydroxides thereof, followed by solid-liquid separation to adjust the pH thereof to 7 or more; and
separating Ca, which is caused to precipitate owing to the pH adjustment, and hydroxides of the rare-earth elements by solid-liquid separation, thereby yielding and recovering a crude recovered product.

11. A method of recovering rare-earth elements according to claim 1 , wherein the separating and recovering of the rare-earth elements comprises:
adding oxalic acid to one of the leachate yielded by performing the solid-liquid separation treatment and the liquid yielded by adjusting the pH of the leachate to cause Fe and Al to precipitate as hydroxides thereof, followed by solid-liquid separation, at a ratio of a chemical equivalent weight equal to or more than that of the rare-earth elements existing therein, to cause the rare-earth elements to precipitate as oxalates thereof; and
separating the oxalates by solid-liquid separation, thereby yielding and recovering a crude recovered product comprising the rare-earth elements.

12. A method of recovering rare-earth elements according to claim 8 , wherein the separating and recovering of the rare-earth elements comprises:
adding an extractant to one of the leachate yielded by performing the solid-liquid separation treatment and the liquid yielded by adjusting the pH of the leachate to cause Fe and Al to precipitate as hydroxides thereof, followed by solid-liquid separation, the extractant being prepared by diluting an ester selected from phosphoric acid esters, phosphonic acid esters, phosphinic acid esters, thiophosphinic acid esters, and mixtures of these esters and at least one of tributyl phosphate and trioctylphosphine oxide with a solvent selected from hexane, benzene, toluene, octanol, and kerosene, which is a petroleum fraction; and
separating and recovering a crude recovered product comprising the rare-earth elements by a solvent extraction method.

13. A method of recovering rare-earth elements according to claim 12 , further comprising, prior to the separating and recovering of the crude recovered product by the solvent extraction method, removing emulsion which occurs during the adjusting of the pH of the leachate in advance by filtration.

14. A method of recovering rare-earth elements according to claim 12 , further comprising:
prior to the separating and recovering of the crude recovered product by the solvent extraction method, adjusting the pH of the leachate to 2.5 to 3.5; and
removing a resultant precipitate.

15. A method of recovering rare-earth elements according to claim 14 , wherein the adjusting of the pH performed prior to the separating and recovering of the crude recovered product by the solvent extraction method comprising adding a bauxite residue.

16. A method of recovering rare-earth elements according to claim 12 , wherein the ester used in the extractant used in the solvent extraction method comprises bis(2-ethylhexyl)hydrogen phosphate.

17. A method of recovering rare-earth elements according to claim 16 , wherein the bis(2-ethylhexyl) hydrogen phosphate used in the extractant used in the solvent extraction method has a concentration of 0.1 to 1.5 M.

18. A method of recovering rare-earth elements according to claim 12 , wherein an extraction time in the solvent extraction method

Assignees

• Nippon Light Metal Co

Inventors

• Sugita Kaoru
• Kobayashi Yasushi
• Taguchi Yoshihiro
• Takeda Satoshi
• Ota Yuji
• OJIRI Masashi
• Oda Kazuhiro
• Sano Hiroshi

Classifications

• C22B3/20

  Treatment or purification of solutions, e.g. obtained by leaching (C22B3/18 takes precedence) · CPC title

• C22B3/44

  by chemical processes (treatment or purification of solutions by liquid-liquid extraction C22B3/26, by ion-exchange extraction C22B3/42) · CPC title

• C22B59/00 Primary

  Obtaining rare earth metals · CPC title

• C22B7/007

  by acid leaching · CPC title

• C22B7/00

  Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; {Methods of a general interest or applied to the winning of more than two metals (briquetting of scrap C22B1/248; preliminary treatment of scrap C22B1/005)} · CPC title