Acid digestion processes for recovery of rare earth elements from coal and coal byproducts

Patent metadata

Field	Value
Publication number	US-2017356067-A1
Application number	US-201715617589-A
Country	US
Kind code	A1
Filing date	Jun 8, 2017
Priority date	Jun 8, 2016
Publication date	Dec 14, 2017
Grant date	—

Abstract

A system for recovering rare earth elements from coal ash includes a leaching reactor, an ash dryer downstream of the leaching reactor, and a roaster downstream of the ash dryer that is cooperatively connected to both the leaching reactor and the ash dryer. Coal ash is mixed with an acid stream such that rare earth elements present in the coal ash are dissolved in the acid stream, thereby creating (i) a leachate containing the rare earth elements and (ii) leached ash. The leachate is heated to obtain acid vapor and an acid-soluble rare earth concentrate. Mixing of the coal ash with the acid stream can occur in a leaching reactor and heating of the leachate can occur in a roaster. The acid-soluble rare earth concentrate can be fed to a hydrometallurgical process to separate and purify the rare earth elements.

First claim

1 . A method of recovering rare earth elements, vanadium, cobalt, or lithium from coal ash, the method comprising:
mixing coal ash with an acid stream such that rare earth elements, vanadium, cobalt, or lithium present in the coal ash are dissolved in the acid stream, thereby creating (i) a leachate containing the rare earth elements, vanadium, cobalt, or lithium, and (ii) leached ash; and heating the leachate to obtain acid vapor and a concentrate containing the rare earth elements, vanadium, cobalt, or lithium.

2 . The method of claim 1 , wherein the acid stream is a nitric acid stream.

3 . The method of claim 1 , further comprising treating the coal ash with a basic solution prior to mixing the coal ash with the acid stream.

4 . The method of claim 3 , further comprising:
separating the coal ash from the basic solution to obtain the coal ash and a leach solution; adding a zeolite seed to the leach solution; and heating the leach solution to obtain a zeolite material.

5 . The method of claim 3 , further comprising milling the coal ash while the coal ash is treated with the basic solution.

6 . The method of claim 1 , further comprising separating the leachate and the leached ash.

7 . The method of claim 6 , further comprising drying the leached ash.

8 . The method of claim 7 , wherein residual acid in the leached ash is recovered as acid vapor that is condensed and recycled to the acid stream.

9 . The method of claim 1 , wherein the acid vapor obtained from heating the leachate is condensed and recycled to the acid stream.

10 . The method of claim 1 , wherein the leachate is heated to a temperature of about 150° C. to about 200° C.

11 . The method of claim 1 , further comprising feeding the concentrate to a hydrometallurgical process to separate and purify the rare earth elements, vanadium, cobalt, or lithium.

12 . A system for recovering rare earth elements, vanadium, cobalt, or lithium from coal ash, the system comprising:
a leaching reactor for creating (i) a leachate containing the rare earth elements, vanadium, cobalt, or lithium, and (ii) leached ash; an ash dryer downstream of the leaching reactor for receiving the leached ash; and a roaster downstream of the leaching reactor for receiving the leachate.

13 . The system of claim 12 , further comprising a solid-liquid separation device downstream of the leaching reactor for separating the leached ash and the leachate from each other, wherein the ash dryer and the roaster are downstream of the solid- liquid separation device.

14 . The system of claim 12 , further comprising a condenser downstream of the roaster, the condenser receiving acid vapor from the roaster.

15 . The system of claim 14 , further comprising an absorption column downstream of the condenser, the absorption column receiving (A) an acid solution from the condenser, and (B) acid vapor from the condenser or the ash dryer or the leaching reactor.

16 . The system of claim 15 , wherein the leaching reactor receives a recovered acid feed from the absorption column.

17 . The system of claim 12 , further comprising a caustic tank upstream of the leaching reactor for pretreating the coal ash before the coal ash enters the leaching reactor.

18 . The system of claim 17 , further comprising a ball mill upstream of the leaching reactor or the caustic tank for reducing the particle size of the coal ash before the coal ash enters the leaching reactor.

19 . The system of claim 17 , wherein the caustic tank further includes a ball mill for reducing the particle size of the coal ash during pretreatment before the coal ash enters the leaching reactor.

20 . A method of recovering rare earth elements, vanadium, cobalt, or lithium from coal, comprising:
dissolving coal in a first solvent to dissolve organic material in the coal and create a slurry containing coal ash enriched with rare earth elements, vanadium, cobalt, or lithium; separating the coal ash from the first solvent; removing residual organic material from the coal ash; and recovering the rare earth elements, vanadium, cobalt, or lithium from the coal ash.

21 . The method of claim 20 , wherein the first solvent is a bio-based hydrogen transfer solvent.

22 . The method of claim 20 , wherein the residual organic material is removed from the coal ash by washing the coal ash with a second solvent that is different from the first solvent; or
wherein the residual organic material is removed from the coal ash by burning the coal ash at a temperature of about 300° C. to about 600° C.

23 . The method of claim 20 , further comprising separating the coal ash into fractions, containing the rare earth elements, vanadium, cobalt, or lithium before recovering the rare earth elements, vanadium, cobalt, or lithium from the coal ash;
wherein the fractions are separated by density using a sink/float analysis, or by particle size by successively screening the coal ash, or by particle size by air classifiers or cyclones, or by chemical leaching.

24 . The method of claim 23 , wherein the chemical leaching uses a mineral base, an inorganic salt, or a mineral acid, or wherein the chemical leaching is performed by acid digestion.

25 . The method of claim 23 , further comprising a calcination step before the chemical leaching.

26 . The method of claim 20 , further comprising purifying the rare earth elements, vanadium, cobalt, or lithium in a solvent extraction circuit to separate individual elements after recovering the rare earth elements from the coal ash, vanadium, cobalt, or lithium.

27 . A method of making a zeolite, comprising:
adding a zeolite seed to a leach solution containing silicon and aluminum; and heating the leach solution to obtain the zeolite.

28 . The method of claim 27 , wherein the leach solution is made by:
mixing coal ash with a basic stream, thereby creating (i) a leach solution containing silicon and aluminum, and (ii) leached ash; and separating the leach solution from the leached ash.

29 . The method of claim 27 , wherein the leach solution is heated at a temperature of about 100° C. to about 200° C., and for a time of about 12 hours to about 96 hours.

Assignees

• Battelle Memorial Institute

Inventors

• Peterson Rick
• Heinrichs Michael
• Gadkari Vinay V
• Taha Rachid
• Winecki Slawomir
• Argumedo Darwin

Classifications

• C22B3/02

  Apparatus therefor · CPC title

• C22B1/005

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

• C22B7/02

  Working-up flue dust · CPC title

• C22B59/00 Primary

  Obtaining rare earth metals · CPC title

• C22B3/065

  Nitric acids or salts thereof · CPC title