Rare earth element recovery method

Patent metadata

Field	Value
Publication number	US-9068249-B2
Application number	US-201214363676-A
Country	US
Kind code	B2
Filing date	Dec 7, 2012
Priority date	Dec 9, 2011
Publication date	Jun 30, 2015
Grant date	Jun 30, 2015

Abstract

Provided is a method of recovering rare-earth elements, including causing rare-earth elements particularly including Nd and Dy to leach efficiently from a raw material for leaching which contains the rare-earth elements, and separating and recovering the rare-earth elements. The method of recovering rare-earth elements includes: a leaching step including performing leaching treatment of rare-earth elements in which an acidic slurry of a raw material for leaching which contains the rare-earth elements is held under a predetermined condition, and then subjecting the slurry obtained after the leaching treatment to solid-liquid separation, yielding a leachate containing the rare-earth elements; and a separation step of separating and recovering the rare-earth elements from the yielded leachate, in which: the raw material for leaching contains Ca as CaO at a ratio of 4 to 15 mass % and Ti as TiO 2 at a ratio of 2 to 13 mass % in a solid component (S); an acid aqueous solution is an acid aqueous solution of hydrochloric acid and/or nitric acid; and the leaching treatment performed in the leaching step is digestion or maceration which is performed under the heating and pressurizing conditions of a temperature of 160 to 300° C. and a pressure of 0.65 to 10 MPa, and the rare-earth elements are caused to leach together with Ca in the leaching step.

First claim

The invention claimed is:

1. A method of recovering rare-earth elements, comprising:
a leaching step including preparing a slurry by adding water to a raw material for leaching which contains rare-earth elements, followed by mixing, further adding an acid aqueous solution to the slurry, followed by mixing, to adjust a pH of the slurry, performing leaching treatment in which the rare-earth elements in the raw material for leaching are transferred into the acid aqueous solution while the slurry is held under a predetermined condition, and then subjecting the slurry, which is obtained after the leaching treatment to solid-liquid separation, thereby yielding a leachate containing the rare-earth elements; and
a separation step of separating and recovering the rare-earth elements from the leachate yielded in the leaching step, wherein:
the raw material for leaching comprises Ca as CaO at a ratio of from 4 to 15 mass % and Ti as TiO 2 at a ratio of from 2 to 13 mass % in a solid component (S) obtained by drying the raw material for leaching under drying conditions of 110° C. and 2 hours;
the acid aqueous solution comprises an acid aqueous solution which contains hydrochloric acid and/or nitric acid and adjusts the pH to from 0 to 2.7; and
the leaching treatment performed in the leaching step is digestion or maceration which is performed under heating and pressurizing conditions of a temperature of from 160 to 300° C. and a pressure of from 0.65 to 10 MPa, and the rare-earth elements in the raw material for leaching are caused to leach together with Ca in the leaching step.

2. A method of recovering rare-earth elements according to claim 1 , wherein the digestion or maceration in the leaching step is performed until a dissolution ratio of Ca contained in the raw material for leaching reaches 90 mass % or more.

3. A method of recovering rare-earth elements according to claim 1 , wherein the raw material for leaching comprises a bauxite residue produced as a by-product in a Bayer process for collecting an aluminum component from bauxite by using an aqueous solution of sodium hydroxide.

4. A method of recovering rare-earth elements according to claim 3 , wherein the bauxite residue comprises rare-earth elements as oxides thereof at a ratio of from 500 to 10,000 ppm in a solid component (S) obtained by drying the bauxite residue under drying conditions of 110° C. and 2 hours.

5. A method of recovering rare-earth elements according to claim 3 , wherein the slurry obtained by adding the acid aqueous solution to the bauxite residue has a liquid-solid ratio (L/S) of a liquid component (L) and a solid component (S) of from 2 to 10 and a pH value of from 0 to 2.7.

6. A method of recovering rare-earth elements according to claim 3 , further comprising adding an oxidizing agent into the slurry prepared by adding the acid aqueous solution to the bauxite residue, at a ratio of from 0.1 to 1 equivalent weight with respect to an Fe component in the bauxite residue.

7. A method of recovering rare-earth elements according to claim 6 , wherein the oxidizing agent added into the slurry is a hydrogen peroxide solution or a perchloric acid aqueous solution.

8. A method of recovering rare-earth elements according to claim 1 , further comprising:
adjusting a pH of the leachate yielded in the leaching step to from 4 to 6 by adding a pH adjuster to the leachate;
removing, by solid-liquid separation, hydroxides of Fe and Al precipitated owing to the adjusting of the pH; and
subjecting a resultant liquid to the separation step.

9. A method of recovering rare-earth elements according to claim 8 , wherein the adjusting of the pH to from 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 to oxidize Fe 2+ ions into Fe 3+ ions in the leachate.

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

11. A method of recovering rare-earth elements according to claim 10 , further comprising separating the crude recovered product into each element by dissolving the crude recovered product in an acid aqueous solution and carrying out a solvent extraction method which uses an extractant 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 tributyl phosphate and/or trioctylphosphine oxide with a solvent selected from hexane, benzene, toluene, and kerosene.

12. A method of recovering rare-earth elements according to claim 11 , wherein the separation of the crude recovered product into the each element by the solvent extraction method comprises a countercurrent multistage solvent extraction method.

13. A method of recovering rare-earth elements according to claim 1 , wherein the separation step of the rare-earth elements comprises:
adding oxalic acid to the leachate yielded in the leaching step or to a liquid yielded by adjusting a 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 to recover the rare-earth elements as a crude recovered product.

14. A method of recovering rare-earth elements according to claim 1 , wherein the separation step of the rare-earth elements comprises:
adding an extractant to the leachate yielded in the leaching step or to a liquid yielded by adjusting a 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 tributyl phosphate and/or trioctylphosphine oxide with a solvent selected from hexane, benzene, toluene, octanol, and kerosene; and
separating and recovering the rare-earth elements by a solvent extraction method.

15. A method of recovering rare-earth elements according to claim 14 , further comprising, prior to the separation step by the solvent extraction method, removing emulsion which occurs during the adjusting of the pH of the leachate in advance by filtration.

16. A method of recovering rare-earth elements according to claim 14 , further comprising:
prior to the separation step by the solvent extraction method, adjusting the pH of the leachate to from 2.5 to 3.5; and
removing the resultant precipitate.

17. A method of recovering rare-earth elements according to claim 16 , wherein the adjusting of the pH performed prior to the separation step by the solvent extraction method comprises adding a bauxite residue.

18. A method of recovering rare-earth elements according to claim 14 , wherein the extractant

Assignees

• Nippon Light Metal Co

Inventors

• Sugita Kaoru
• Ota Yuji
• Taguchi Yoshihiro
• Takeda Satoshi

Classifications

• B09B3/70

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

• B09B3/80

  involving an extraction step · CPC title

• C22B3/065

  Nitric acids or salts thereof · CPC title

• C22B3/10

  Hydrochloric acid {, other halogenated acids or salts thereof} · CPC title

• C22B3/0067

  Chemistry & Metallurgy · mapped topic