Systems and processes for recovery of high-grade rare earth concentrate from acid mine drainage

Patent metadata

Field	Value
Publication number	US-2021017625-A1
Application number	US-202016795471-A
Country	US
Kind code	A1
Filing date	Feb 19, 2020
Priority date	Jul 17, 2019
Publication date	Jan 21, 2021
Grant date	—

Abstract

In one aspect, the disclosure relates to a continuous process for treating acid mine drainage while simultaneously recovering a high-grade rare earth preconcentrate suitable for extraction of commercially valuable rare earth oxides. In a further aspect, the preconcentrate is from about 0.1% to 5% rare earth elements on a dry weight basis. In another aspect, the disclosure relates to a method for processing the preconcentrate to generate a pregnant leach solution that does not form gels or emulsions and is suitable for processing via solvent extraction. In another aspect, the disclosure relates to a system and plant for carrying out the disclosed process. In still another aspect, the disclosure relates to a composition containing rare earth elements produced by the process disclosed herein. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present disclosure.

First claim

1 . A method for producing a pregnant leach solution (PLS), the method comprising the following steps:
a. contacting a raw material containing rare earth elements (REEs) with a first base to form waste solids and an aqueous phase and discarding the waste solids; b. contacting the aqueous phase with a second base to form an REE-enriched preconcentrate and an effluent and discharging the effluent; c. contacting the REE-enriched preconcentrate with an acid to form an acidic preconcentrate; d. filtering the acidic preconcentrate to form an acidic filtrate; and e. contacting the acidic filtrate with a third base and filtering to form a pregnant leach solution;
wherein the pregnant leach solution is enriched in REEs and essentially free of solids.

2 . The method of claim 1 , wherein the raw material is raw acid mine drainage (AMD), an AMD precipitate (AMDp), or an enriched AMD precipitate (eAMDp).

3 . The method of claim 1 , wherein contacting the raw material with the first base changes the pH of the aqueous phase to from about 4.0 to about 4.5.

4 . The method of claim 1 , wherein the first base comprises NaOH, KOH, ammonia, ammonium hydroxide, calcium pellets, quicklime, lime slurry, or a combination thereof.

5 . The method of claim 1 , wherein contacting the aqueous phase with the second base changes the pH of the aqueous phase to from about 8.0 to about 8.5.

6 . The method of claim 1 , wherein the second base comprises NaOH, KOH, ammonia or an ammonium compound, calcium pellets, quicklime, lime slurry, or a combination thereof.

7 . The method of claim 1 , wherein the contacting the REE-enriched preconcentrate with the acid changes the pH of the REE-enriched preconcentrate to from about 0.7 to about 3.0.

8 . The method of claim 1 , wherein the acid comprises hydrochloric acid, nitric acid, sulfuric acid, or a combination thereof.

9 . The method of claim 1 , wherein step (c) further comprises contacting the REE-enriched preconcentrate and the acid with a reducing agent.

10 . The method of claim 1 , wherein contacting the acidic filtrate with the third base changes the pH of the acidic filtrate to from about 2.8 to about 3.0.

11 . The method of claim 1 , wherein the third base comprises MgO, NaOH, KOH, ammonia or ammonium hydroxide, calcium pellets, quicklime, lime slurry, or a combination thereof.

12 . The method of claim 1 , wherein step (e) further comprises oxidizing the acidic filtrate.

13 . The method of claim 12 , wherein the acidic filtrate is oxidized mechanically, electrochemically, with an oxidizing agent, or a combination thereof.

14 . The method of claim 13 , wherein the oxidizing agent is hydrogen peroxide.

15 . The method of claim 1 , further comprising a step for recovering scandium between steps (a) and (b), the step for recovering scandium comprising contacting the aqueous phase with a fourth base, thereby forming a scandium-enriched solid concentrate, and removing the scandium-enriched solid concentrate from the aqueous phase.

16 . The method of claim 15 , wherein contacting the aqueous phase with a fourth base changes the pH of the aqueous phase to from about 4.9 to about 5.1.

17 . The method of claim 15 , wherein the fourth base comprises NaOH, KOH, ammonia or an ammonium compound, calcium pellets, quicklime, lime slurry, or a combination thereof.

18 . The method of claim 1 , further comprising adding a flocculating agent, a coagulating agent, or both in any of steps (a), (b), or (c).

19 . The method of claim 1 , wherein following step (e), the method further comprises subjecting the pregnant leach solution to solvent extraction to produce a refined rare earth resource comprising at least 50% REEs.

20 . A pregnant leach solution (PLS) enriched in REEs and essentially free of solids, produced by the method comprising the following steps:
a. contacting a raw material containing REEs with a first base to form waste solids and an aqueous phase and discarding the waste solids; b. contacting the aqueous phase with a second base to form an REE-enriched preconcentrate and an effluent and discharging the effluent; c. contacting the REE-enriched preconcentrate with an acid to form an acidic preconcentrate; d. filtering the acidic preconcentrate to form an acidic filtrate; and e. contacting the acidic filtrate with a third base and filtering to form a pregnant leach solution.

Assignees

• Univ West Virginia

Inventors

• Ziemkiewicz Paul
• Noble Aaron
• Vass Chris

Classifications

• Y02P10/20

  Recycling · CPC title

• C22B3/3846

  Phosphoric acid, e.g. (O)P(OH)3 · CPC title

• C22B3/22

  by physical processes, e.g. by filtration, by magnetic means {, or by thermal decomposition} (treatment or purification of solutions by liquid-liquid extraction C22B3/26) · CPC title

• C22B59/00

  Obtaining rare earth metals · CPC title

• C22B3/06

  in inorganic acid solutions {, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions} · CPC title