U.S. patent application number 17/012858 was filed with the patent office on 2022-03-10 for process for extraction of recoverable rare earth elements (ree) using organic acids and chelating compounds.
The applicant listed for this patent is United States Department of Energy. Invention is credited to Mark L. McKoy, Scott Montross, Thomas J. Tarka, Circe Verba, Jonathan Yang.
Application Number | 20220074019 17/012858 |
Document ID | / |
Family ID | |
Filed Date | 2022-03-10 |
United States Patent
Application |
20220074019 |
Kind Code |
A1 |
Verba; Circe ; et
al. |
March 10, 2022 |
Process for Extraction of Recoverable Rare Earth Elements (REE)
Using Organic Acids and Chelating Compounds
Abstract
One or more embodiments relates to a process for extracting Rare
Earth Elements (REEs) from REE-bearing underclays, claystones,
shales, coal-mining waste, and waste coal. In at least one
embodiment the process includes contacting the REE-bearing
underclays, claystones, shales, coal-mining waste, and waste coal
with an Organic Acid Solution (OAS) comprising at least one organic
acid and at least one ionic salt at a predetermined ambient
temperature and predetermined pH; and separating the REE from the
REE-bearing underclays, claystones, shales, coal-mining waste, and
waste coal, forming REE+Yttrium (REY) concentrate.
Inventors: |
Verba; Circe; (Albany,
OR) ; McKoy; Mark L.; (Bruceton Mills, WV) ;
Tarka; Thomas J.; (Pittsburgh, PA) ; Montross;
Scott; (Albany, OR) ; Yang; Jonathan;
(Corvallis, OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
United States Department of Energy |
Washington |
DC |
US |
|
|
Appl. No.: |
17/012858 |
Filed: |
September 4, 2020 |
International
Class: |
C22B 3/16 20060101
C22B003/16; C22B 59/00 20060101 C22B059/00; C22B 3/22 20060101
C22B003/22 |
Goverment Interests
STATEMENT OF GOVERNMENT SUPPORT
[0001] The United States Government has rights in this invention
pursuant to an employer/employee relationship between the inventors
and the U.S. Department of Energy, operators of the National Energy
Technology Laboratory (NETL) and site support contractors at NETL.
Claims
1. A process for extracting Rare Earth Elements (REEs) from
REE-bearing underclays, claystones, shales, coal-mining waste, and
waste coal the process comprising: contacting the REE-bearing
underclays, claystones, shales, coal-mining waste, and waste coal
with an Organic Acid Solution (OAS) comprising at least one organic
acid and at least one ionic salt at a predetermined ambient
temperature and predetermined pH; and separating the REE from the
REE-bearing underclays, claystones, shales, coal-mining waste, and
waste coal, forming REE+Yttrium (REY) concentrate.
2. The process of claim 1 where separating the REE from the
REE-bearing underclays, claystones, shales, coal-mining waste, and
waste coal further comprises performing at least one of
solid-liquid separating, filtering, drying and calcinating.
3. The process of claim 1 wherein the ambient temperature is above
the freezing point of the OAS and below 35.degree. C.
4. The process of claim 1 wherein the predetermined pH is between
about 2 and 6.
5. The process of claim 4 wherein the predetermined pH is between
about 4 and 5.
6. The process of claim 1 wherein the OAS solution comprising the
at least one organic acid and the at least one ionic salt follows
the formula c (ionic salt)=0.5 mol/L and c (organic acid)=0.1 mol/L
where c (ionic salt) is the concentration of ionic salt and c
(organic acid) is the concentration of organic acid, the OAS
solution having a pH ranging between about 2 and 6.
7. The process of claim 1 wherein the process is selected from the
group comprising ex-situ heap recovery (ESHR) from clay-rich
materials, ex-situ processing plant recovery from clay-rich
materials and in-situ recovery (ISR) from clay-rich materials.
8. A process for extracting Rare Earth Elements (REEs) from
REE-bearing materials consisting of underclays, claystones, shales,
coal-mining waste, and waste coal, the process comprising:
contacting the REE-bearing materials with an Organic Acid Solution
(OAS) comprising at least one organic acid and at least one ionic
salt at a predetermined ambient temperature <35.degree. C. and a
predetermined pH between about 2 and 6; performing at least one of
solid-liquid separating, filtering, drying and calcinating; and
separating the REE from the REE-bearing materials, forming
REE+Yttrium (REY) concentrate.
9. The process of claim 8 where separating the REE from the
REE-bearing materials further comprises performing at least one of
solid-liquid separating, filtering, drying and calcinating.
10. The process of claim 8 wherein the predetermined pH is about
5.
11. The process of claim 8 wherein the OAS solution comprising the
at least one organic acid and the at least one ionic salt follows
the formula c (ionic salt)=0.5 mol/L and c (organic acid)=0.1 mol/L
where c (ionic salt) is the concentration of ionic salt and c
(organic acid) is the concentration of organic acid.
12. The process of claim 8 wherein the specific REE-bearing
materials are selected from the group comprising clay rich
materials, coal-mining wastes, co-mined materials, undisturbed
sedimentary layers, open pits, and underground mines.
13. The process of claim 8 wherein the process is selected from the
group comprising ex-situ heap recovery (ESHR) from clay-rich
materials, ex-situ processing plant recovery from clay-rich
materials and in-situ recovery (ISR) from clay-rich materials.
14. An Organic Acid Solution (OAS) comprising: at least one organic
acid; and at least one ionic salt, where the OAS solution follows
the formula c (ionic salt)=0.5 mol/L and c (organic acid)=0.1 mol/L
where c (ionic salt) is the concentration of ionic salt and c
(organic acid) is the concentration of organic acid, the OAS
solution having a pH ranging between about 2 and 6.
15. The OAS solution of claim 14 having a pH ranging between about
4 and 6.
16. The OAS solution of claim 14 having a pH of about 5.
17. The OAS solution of claim 14 further comprising at least one
chelating compound.
18. The OAS solution of claim 14 further comprising at least one
surfactant, inorganic acid, colloid, and biocide.
19. The OAS solution of claim 14 where the at least one organic
solution is selected from the group comprising citric acid, acetic
acid, indole-3-acetic acid, gluconic acid and malic acid.
20. The OAS solution of claim 14 where the at least one salt is
selected from the group comprising (NH.sub.4).sub.2SO.sub.4, NaCl
and NaH.sub.2PO.sub.4.
21. The OAS solution of claim 17 where the chelating compound is
selected from the group comprising carboxylic acid from acetate,
citrate, and formate.
Description
FIELD OF THE INVENTION
[0002] Embodiments relate to a process for extracting Rare Earth
Elements (REE) for sedimentary rocks and waste streams. More
specifically embodiments relate to a process for extraction of REE
in underclays, claystones, shales, coal-mining wastes, and waste
coal using organic acids, salts and/or chelating compounds.
BACKGROUND
[0003] Rare earth elements (REE) are necessary for the advancement
of technological and energy applications. China currently controls
the world's supply and the prices of REEs. With limited
economically viable domestic REE resources, supply remains a major
concern for the United States. Efforts to secure a domestic source
of REE require the development of efficient, cost-effective, and
environmentally friendly methods for REE extraction from naturally
occurring materials (e.g., mined from geologic formations),
recycled products (e.g., end-of-life electronics containing REEs),
and/or waste streams (e.g., coal-related by-products). Sedimentary
deposits have an increased resource potential as they are often
easier to mine or extract from, compared to crystalline rocks, and
natural processes have often concentrated the REEs or put them into
forms that are easier to extract.
[0004] Current methods and technologies either use hot (commonly
90-400.degree. C.) inorganic acids to extract REEs from ore and
other sources or use relatively strong (sometimes hot) bases and
salts. For most methods, physical processes are used to concentrate
the REE-bearing minerals before acids or bases are applied. And
prior to this, mining, crushing and/or fine grinding are commonly
performed. Large concentrations of undesirable elements (e.g.,
aluminum, iron, silicon), which complicate the refinement of the
extracted REEs into salable products, are often extracted along
with the REEs by these current practices. Given radioactive Thorium
is commonly found in rare-earth minerals, Thorium is commonly
extracted inadvertently, leading to costly handling and disposal
problems. All of this extraction, handling and processing
contributes to high unit costs for REEs.
[0005] Numerous, specific problems with existing commercial
processes have to be overcome: Use of strong acids or bases, with
the associated hazards to workers and the environment, and
increased capital costs. Heating the ore to high temperatures
(typically 90.degree. C. to 400.degree. C.), but suffers from the
associated costs of heating fuels, worker hazards, environmental
impacts, and capital costs. Co-extraction of large concentrations
of unwanted elements (including radioactive Thorium) that have to
be separated from the desired REEs, are limited by the associated
multi-step processing costs (e.g., for infrastructure, energy),
worker hazards, waste handling. Inability of U.S. producers of REEs
to compete in an open market with China, with its low REE prices
and ability to manipulate the world's REE market. Society's (in the
U.S.) aversion to additional mining, and to mineral processing
technologies that are viewed as hazardous to workers and the
environment; permitting costs; ES&H compliance costs.
Beneficial use of materials that are currently viewed as wastes
(e.g., coal preparation plant reject materials) or as opportunities
lost (e.g., shale layers and underclays that could be co-mined with
the coal but are currently avoided).
[0006] In China, nearly 10,000 tons of rare earth oxide (REO)
concentrate are produced annually from weathered "elution-deposits"
derived from lateritic weathering of granitic rock. In-situ
solution mining yields .sup..about.200 tons of REE annually at a
recovery rate of 70% using inorganic acids. Despite the efficacy in
extracting REEs from a variety of ore bodies, inorganic acids are
commonly used, such as hydrochloric (HCl), nitric (HNO.sub.3), and
sulfuric (H.sub.2SO.sub.4) acids, and pose significant challenges
to worker safety, wastes management and environmental impacts.
Additionally, strong inorganic acids dissolve a variety of gangue
minerals, leading to unwanted products at high concentrations in
the pregnant leach solution (PLS) that hinder the removal and
purification of the REEs into salable product.
[0007] The REE-enrichment of the Chinese clay deposits resulted
from natural weathering, leaching, transport and accumulation
processes that could perhaps form the basis for a commercial
process designed to selectively extract and enrich REEs from
certain source rocks. This could be accomplished either in a
processing plant or via in-situ techniques. In 2015, researchers at
the University of California at Berkeley reported that fungi were
observed to extract REEs from monazite (a REE-bearing phosphate
that is relatively resistant to breakdown), while leaving
radioactive Thorium in place. This report triggered discussions at
NETL in 2015 on the potential for combining the observations from
UC-Berkeley with the Chinese geologist's descriptions of the
suspected origins of REE-rich clay deposits currently being mined
in China, to make a new, nature-inspired, commercial REE extraction
process for coal-related clay-rich rocks, such as underclays and
shale partings in coal layers.
[0008] One recently published method of leaching includes the use
of a variety of acids in solution (HCl, H.sub.3PO.sub.4,
H.sub.2SO.sub.4, HNO.sub.3, H.sub.2CO.sub.3, halogen oxoacids, and
carboxylic acids) to leach REEs from coal at 20.degree.
C.-100.degree. C. for 60 hours. This method was limited to coal and
was not mentioned as possibly working on clay-rich materials
associated with coal.
[0009] A need exists in the art for extracting REE from sedimentary
rocks and waste streams. More specifically a need exists for
extracting REE in underclays, claystones, shales, coal-mining
wastes, and waste coal. This can be accomplished using organic
acids, salts and/or chelating compounds.
SUMMARY
[0010] One or more embodiments relates to a process for extracting
Rare Earth Elements (REEs) from REE-bearing underclays, claystones,
shales, coal-mining waste, and waste coal. In at least one
embodiment the process includes contacting the REE-bearing
underclays, claystones, shales, coal-mining waste, and waste coal
with an Organic Acid Solution (OAS) comprising at least one organic
acid and at least one ionic salt at a predetermined ambient
temperature and predetermined pH; and separating the REE from the
REE-bearing underclays, claystones, shales, coal-mining waste, and
waste coal, forming REE+Yttrium (REY) concentrate.
[0011] Additional embodiments relate to a process for extracting
REEs from REE-bearing materials consisting of underclays,
claystones, shales, coal-mining waste, and waste coal. The process
includes contacting the REE-bearing material with an OAS comprising
at least one organic acid and at least one ionic salt at a
predetermined ambient temperature <35.degree. C. and
predetermined pH between about 2 and 6; and performing at least one
of solid-liquid separating, filtering, drying and calcinating. The
process further includes separating the REE from the REE-bearing
material, forming REE+Yttrium (REY) concentrate.
[0012] In one or more embodiments the process may further include
performing at least one of solid-liquid separating, filtering,
drying and calcinating. In at least one embodiment, the ambient
temperature is above the freezing point of the OAS and below
35.degree. C. and/or the predetermined pH is between about 2 and 6,
more specifically between about 4 and 5, and exemplary about 5.
[0013] In at least one embodiment of the process, the OAS solution
comprising the at least one organic acid and the at least one ionic
salt follows the formula c (ionic salt)=0.5 mol/L and c (organic
acid)=0.1 mol/L where c (ionic salt) is the concentration of ionic
salt and c (organic acid) is the concentration of organic acid and
the OAS solution having a pH ranging between about 2 and 6.
[0014] Other embodiments include an OAS having at least one organic
acid; and at least one ionic salt, where the OAS solution follows
the formula c (ionic salt)=0.5 mol/L and c (organic acid)=0.1 mol/L
where c (ionic salt) is the concentration of ionic salt and c
(organic acid) is the concentration of organic acid, the OAS
solution having a pH ranging between about 2 and 6. The OAS
solution may have a pH ranging between about 4 and 6, more
specifically about 5.
[0015] One or more embodiments of the OAS solution may include a
chelating compound selected from the group including carboxylic
acid from acetate, citrate, and formate. The OAS solution may
include at least one surfactant, inorganic acid, colloid, or
biocide. In embodiments of the OAS solution, the at least one
organic solution is selected from the group comprising citric acid,
acetic acid, indole-3-acetic acid, gluconic acid and malic acid.
The OAS solution may include at least one salt selected from the
group comprising (NH.sub.4).sub.2SO.sub.4, NaCl and
NaH.sub.2PO.sub.4.
[0016] The following documents are incorporated herein by reference
in their entirety: [0017] 1. Brisson, V., Zhuang, W. Q., &
Alvarex-Cohen, A. (2015) Bioleaching of Rare Earth Elements from
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S., Cole, P. M., Craig, W. M., & Feather, A. M. (1996). The
recovery of rare earth oxides from a phosphoric acid by-product.
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[0022] 6. Mudd, G. (2001). Critical review of acid in situ leach
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(2016). Review on hydrometallurgical recovery of rare earth metals.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The invention together with the above and other objects and
advantages will be best understood from the following detailed
description of the preferred embodiment of the invention shown in
the accompanying drawings, wherein:
[0041] FIG. 1 depicts a flow diagram illustrating a process for
extracting REEs from REE-bearing materials;
[0042] FIG. 2 depicts a flow diagram illustrating a process for
ex-situ heap recovery from waste coal;
[0043] FIG. 3 depicts a flow diagram illustrating a process for
in-situ extraction/recovery;
[0044] FIG. 4 illustrates one possible extraction method applied in
advance of underground mining; and
[0045] FIG. 5 illustrates one possible extraction method applied in
advance of a pit mine.
DETAILED DESCRIPTION
[0046] The foregoing summary, as well as the following detailed
description of certain embodiments of the present invention, will
be better understood when read in conjunction with the appended
drawings.
[0047] The following detailed description should be read with
reference to the drawings in which similar elements in different
drawings are numbered the same. The drawings, which are not
necessarily to scale, depict illustrative embodiments and are not
intended to limit the scope of the invention.
[0048] One or more embodiments relate to a process for extracting
Rare Earth Elements (REE) for sedimentary rocks and waste streams.
More specifically embodiments relate to a process for extraction of
REE in underclays, claystones, shales, coal-mining wastes, and
waste coal using organic acids, salts and/or chelating
compounds.
[0049] One embodiment relates to a process of using organic acids
and salts, in combination with chelating compounds in some cases
(where the chelating compound includes one or more of carboxylic
acid from acetate, citrate, and/or formate), for extracting REEs
and certain other critical metals (e.g., Sc, Co, Ni) in clay-rich
sedimentary rock as well as certain coal-related waste streams. A
particularly attractive resource is the clay-rich rock below coal
beds, known as underclays or "seat rock", as well as clay-rich rock
above coal beds.
[0050] The weathering of REE-rich host rocks leads to the formation
of aluminosilicate-rich clay deposits. REE ions are mobilized,
transported, and can accumulate within clay-rich soil or sediments.
These clay-rich ore deposits contain elevated concentrations of
ion-adsorbed REEs with the balance existing in colloids (e.g., Fe,
Mn-oxides) and crystalline minerals (e.g., REE-phosphates). In the
geologic past, the weathering of REE-rich igneous rocks led to the
formation of aluminosilicate-rich clays in soils and laterites.
[0051] As these deposits subsequently eroded, the REE-pregnant
clays may have later deposited in the deltas such as those of the
ancient Appalachian Basin where the clay layers, sand layers and
peat layers became coal-bearing strata. In other cases, the REE
ions were likely mobilized, transported (perhaps in chelated form
or absorbed into colloids), and accumulated within clay-rich soil
or delta deposits. REEs deposited in coal-forming peats may have
subsequently mobilized vertically (either up or down, depending on
hydrologic gradients) to absorb within clay-rich sediments below or
above the coals, leading to further enrichment of these layers.
Today these clay-rich deposits can contain up to 80-90% of their
REEs in various adsorbed states (exchangeable, colloid, mineral).
Organic acids offer a promising, selective extraction solution for
REEs in clay-rich rocks. The optimum leaching conditions of REEs
from ion-absorbed clays and other exchangeable phases is pH 4 to 5
using an ionic lixiviant and moderate temperatures (<35.degree.
.degree. C.).
[0052] It should be appreciated that reverse engineering
nature--using dilute leaching agents, transport mediators, and
concentrators found in nature--reduces hazards to workers and the
environment Embodiments of the present invention minimizes
contaminates extracted (such as Al, Fe, As, U, Th) and wastes.
Temperature ranges of the present invention are suitable for
ambient surface conditions (ranging between about 20.degree.
C.-35.degree. C.); but other temperatures are contemplated. The use
of organic acids is more economical by reducing conventional mining
and processing costs (e.g., mining, crushing and grinding, heating
fuel, multiple process steps), and encourages reusing coal refuse
or coal mining reject materials.
[0053] This process is applicable to other geological material and
REE bearing ore, including ex-situ heap leaching operations,
specifically applying solution as a liquid or constituents in a
powder form to low-grade ores, in addition to mechanical plant
processing (tank leaching, vat leaching, autoclave leaching).
Embodiments of the invention may be used with other metal ores with
large adsorbed/easily accessible component (e.g., chrysocolla
concretions for heap leaching copper operations).
[0054] FIG. 1 depicts a flow chart illustrating a process,
generally designated 10, for extracting REEs from REE-bearing
materials. The process 10 includes contacting the REE-bearing
material with an Organic Acid Solution (OAS) 12. In at least one
embodiment, OAS includes at least one organic acid and at least one
ionic salt at a predetermined ambient temperature and predetermined
pH. The method further includes separating the REE from the
REE-bearing material 14, forming REE+Yttrium (REY) concentrate. In
at least one embodiment of process 10, separating the REE from the
REE-bearing material further includes performing at least one of
solid-liquid separating, filtering, drying and calcinating.
[0055] Process 10 further includes having the ambient temperature
above the freezing point of the OAS and below 35.degree. C.
(ranging between about 20.degree. C.-35.degree. C. for example).
Further, in at least one embodiment, the predetermined pH is
between about 2 and 6, more likely between about 4 and 5, in one
preferred embodiment about 5. In at least one embodiment the OAS
solution comprising the at least one organic acid and the at least
one ionic salt follows the formula c (ionic salt)=0.5 mol/L and c
(organic acid)=0.1 mol/L where c (ionic salt) is the concentration
of ionic salt and c (organic acid) is the concentration of organic
acid and the OAS solution having a pH ranging between about 2 and
6. In at least one embodiment of the process 10 the specific
REE-bearing materials are selected from the group comprising clay
rich materials, coal-mining wastes, co-mined materials, undisturbed
sedimentary layers, open pits, and underground mines. In one or
more embodiments of the process the group comprises ex-situ heap
recovery (ESHR) from clay-rich materials, ex-situ processing plant
recovery from clay-rich materials and in-situ recovery (ISR) from
clay-rich materials.
[0056] The use of organic acids with salts may potentially increase
the recovery of REE from clay-rich rocks by: (a) maintaining a
balanced charge on clay surfaces and increasing cation exchange
capacity, (b) selectively dissolving certain matrix rock
constituents and increasing pore space connectivity and
transmissivity of fluids, and solubilizing phosphate-bound REEs (at
least from the surfaces of these mineral grains). Organic acid
leaching may be used to extract REEs from porous and permeable rock
and certain coal wastes; that salts (particularly monovalent salts)
usually facilitate the extractions, that chelating compounds may be
beneficially used in certain instances to inhibit re-absorption and
further may facilitate separation of REE from the pregnant
leachate; and that the reasonable range of parameters of the
process allow this process to overcome the problems listed in the
prior section of this ROI.
[0057] In one or more embodiments the process may apply to REE
extraction in at least three common modes: 1) ex-situ heap recovery
(ESHR) from clay-rich materials (including coal-mining wastes and
co-mined materials): 2) ex-situ processing plant recovery from
clay-rich materials (including coal-mining wastes and co-mined
materials), and 3) in-situ recovery (ISR) from clay-rich materials
(including in-situ extractions in undisturbed sedimentary layers,
open pits or underground mines). Use of clay-rich coal-related
wastes and underclay deposits may reduce environmental impacts and
wastes and allow existing waste piles to be beneficially used,
while subsequently reducing life-cycle costs.
[0058] Embodiments of the process selectively removes the REEs and
certain other critical metals of interest using organic acid
solutions (OAS=aqueous solutions containing various single acids or
combinations of acids: citric, acetic, and indole-3-acetic,
gluconic, or malic acids) amended with a monovalent or divalent
salt (e.g., ammonium sulfate, (NH.sub.4).sub.2SO.sub.4,sodium
chloride, NaCl), or sodium dihydrogen phosphate
(NaH.sub.2PO.sub.4). The components used in each OAS solution
follow the general formula: c (salt)=0.5 mol/L, c (organic
acids)=0.1 mol/L; where c=concentration of the selected salt [e.g.,
NaCl or (NH.sub.4).sub.2SO.sub.4)] or organic acids in the
extraction solution. The basic process involves: Contacting an
organic acid solution (OAS) with a clay-rich REE-source material
(ore) to leach out REEs and certain other potentially useful
elements. This process applies to geologic rock formations and
waste products (e.g., coal high in clay, mudstone, or shale). The
contact may be static (e.g., batch) or dynamic (e.g., flow through
vessels). The contact may continue through time if the extraction
process is economical, although the highest extraction rate usually
occurs at or near the initiation of the contact between OAS and
ore. Temperatures in the system must be above the freezing point of
the OAS and typically, but not necessarily, below 35.degree. C.
Fluid pressures in the system may be atmospheric, reduced or
elevated--the system is not expected to be highly sensitive to
fluid pressure unless acid gases (e.g., CO.sub.2 or H.sub.2S),
whether natural or introduced, significantly influence the system
(e.g., carbonic acid solution of minerals along flow pathways
inside ore body or ore particles).
[0059] In one or more embodiments, the OAS contains a single
organic acid or any combination of organic acids in aqueous form,
may include one or more salts, and may include one or more
chelating compounds, surfactants, inorganic acids (usually in small
concentrations), colloids, biocides, and other agents. The OAS
solution input into the system preferably (but not necessarily) has
a pH between 2 and 6, optimally at pH=5. Small amounts of inorganic
acid or base may be used to adjust the solution pH. The following
organic acids have been found to increase the extraction of REEs:
citric, acetic, and indole-3-acetic, gluconic, or malic acids.
Nd.sup.3++jCH.sub.3COO.sup.-=Nd(OOCCH.sub.3).sub.j.sup.(3-j)+,
j=1,2,3 generalized complexation reaction between a representative
REE (Nd) and citric acid. In one or more embodiments the salts have
been found to facilitate the extraction of REEs:
(NH.sub.4).sub.2SO.sub.4, NaCl, or NaH.sub.2PO.sub.4. It should be
appreciated that the following salts may also facilitate the
extraction of REEs by liberating or dispersing clay particles.
Ideally, added salts provide monovalent cations to the solution for
purposes of ion substitution at the sorption sites, clay mineral
interlayer sites, and crystal lattice sites of REEs. It is also
believed that the salts neutralize some of the surface force
charges promoting adsorption and encourage dispersion of clay
particles, allowing for more complete contact with the leachate
solution. Clay-Ln+3MX=Clay-M3+LnX.sub.3. Generalized ion-exchange
reaction between a lanthanide adsorbed to clay surface and a
monovalent salt, MX (i.e., (NH.sub.4).sub.2SO.sub.4 or NaCl).
Extraction of the REEs from the pregnant leach solution (PLS) into
salable products as rare earth oxides (REO) may then proceed
through a variety of processes fairly well-established in
industrial practice. Solvent extraction using organic solvents such
as di-(2-ethylhexyl) phosphoric acid (D2EHPA),
ethylenediaminetetraacetic acid (EDTA), tributyl phosphate, and
kerosene have been shown to effectively recover the REEs from the
PLS. These solvents selectively chelate/complex the REEs and allow
for the separation of the REEs from base cations such as Fe and Al
through the separation of the organic from the aqueous phases.
Electrochemical methods may also be applied whereby a current
passed through a solution induces electromigration of the REEs to
the anode, where further collection and processing may continue.
Certain gases and inorganic acids may be natural occurring (e.g.,
microbial CO.sub.2) or pre-existing (e.g., sulfuric acid in
pre-existing mines) within the system or may be introduced into the
OAS or introduced separately from the OAS, with these either
providing no benefit or various benefits (e.g., sulfuric acids from
mines that also liberate REEs from ore; introduction of O.sub.2 gas
to facilitate sulfuric acid generation with consequent release of
REEs; introduction of CO.sub.2 to produce a mild carbonic acid that
improves permeability of the ore). Alternative versions of the
basic process would include using various combinations of organic
acids, inorganic acids, salts, gases, chelating compounds,
surfactants and concentrating substances tailored to maximize the
extraction efficiency versus costs for a specific ore or target
REE-bearing material. Testing and tailoring should be done in
advance or at the beginning of every extraction project.
Experimental Studies
[0060] Experiments conducted with 10:1 liquid-solid at 22.degree.
C. for 24 hours at pH=5 demonstrate that 0.1M citrate and 0.5M
sodium chloride released comparable REE concentrations compared to
0.5M (NH.sub.4)2504 (exchangeable fraction)+1M HCl (colloid
fraction)+1.2M H.sub.2SO.sub.4 (mineral fraction at 70.degree. C.)
treatments which is about 33% of the total REY in the clay sample
not tied to phosphate minerals. Experiments conducted with 10:1
liquid-solid at 22.degree. C. for 24 hours at pH=5 demonstrate that
0.1M Indole-3-acetic acid treatments (with either 0.5M NaCl)
demonstrate the potential use of the organic acid as a selective
treatment to remove REE without disturbing the mineral structure
and release of Al, Si, and other difficult elements to process such
as U and Th. Final pH similar to initial pH (5-5.2). Experimental
flow through tests performed at 25.degree. C., and
.sup..about.2,000 psi pore pressure, and a fluid flow rate ranging
0.03-0.05 ml/min with 0.1M sodium citrate, and 0.5M NaCl for up to
24 hours. Most size fractions (e.g. 20, 100, 230 mesh) of underclay
sample make no difference to the amount of REEs extracted after
organic acid treatment. Isolated clay particles (<0.002 mm) have
an increased extraction efficiency. Characterization of Appalachian
Basin underclay demonstrates that >55% of the underclay is made
of clay identified as halloysite, kaolinite, smectite, illite with
non-clay phases being quartz, K-feldspar, carbonates (calcite,
siderite), and ilmenite based on quantitative x-ray diffraction.
REE mineral phases included apatite
(Ca.sub.5(PO.sub.4).sub.3(F,Cl,OH)), rhabdophane and monazite (Ce,
La, Nd--PO.sub.4), xenotime (Y--PO.sub.4), crandallite
(CaAl.sub.3(PO.sub.4)(PO.sub.3OH)(OH).sub.6). Sequential digest of
underclay powders indicates that REEs are predominantly bound in
residual phases that are not extractable by ion exchange alone. The
high recovery by HCl digestion indicates a high proportion of REE
is bound to carbonates or Fe/Mn oxides.
Ex-Situ Heap Recovery (ESHR) Example:
[0061] FIG. 2 depicts a flow chart illustrating a process,
generally designated 100, for ex-situ heap recovery from waste coal
where coal feedstock that is not grade quality for combustion and
contains >300 ppm of REE+Yttrium (REY) may be considered for
ex-situ heap leaching in accordance with one embodiment.
[0062] This ex-situ recovery process 100 includes the use of coal
wastes as feedstock with greater than 300 ppm of rare earth
elements and Yttrium (REY) to extract REEs using an ion exchange
process including dilute organic acids and monovalent salt(s). In
at least one embodiment the process 100 is conducted at ambient
temperatures, as higher temperatures are not required to leach
REEs. In this embodiment process 100 utilizes an acid to dry coal
ratio ranging from 1:10 to 1:100 (g/mL) and constant pH by
buffering using conjugate acid/base pairs to maintain the desired
pH (4-5).
[0063] As illustrated in FIG. 2, the ex-situ recovery process 100
includes the use of coal wastes as mined rock coal/rock as
feedstock 112. In process 100 the material is crushed 114, and
separated by density separation 116 and/or magnetic separation 118.
The process 100 determines if the material is grade quality 120. If
the material is grade quality, it is provided to plant feed system
122.
[0064] If the material is not grade quality, the process determines
if the material is greater than 300 ppm of REE and Yttrium (REY)
124. A portion of process 100 is generally referred to as process
150. In process 150, the organic acid and salt solution 152 contact
the materials and perform an ion exchange process 154. Process 150
than determines if additional Lixiviant is needed 156. If more
lixiviant is needed an additional ion exchange is performed.
[0065] Once reacted for the desired time (e.g., 24 hours), the
material undergoes a solid-liquid separation 158 where the solids
would be disposed of in a tailings pond 160. The leachate solution
undergoes subsequent drying (or calcining) 162 forming REY
concentrate 164. Batch benchtop experiments after 24 hours leached
up to 35% of the REE concentration (ion absorbed clay fraction
only) from the bulk material with limited release of base cations
(common metals), which are considered contaminants to down-stream
REE-oxide purification processes (See Table 1). This concentration
is equivalent to that extracted by harsh, inorganic acids used by
industry. Because there is limited iron, aluminum or silica
release, there is no need for oxidation or an oxidizing agent to be
added to the leachate thus limiting need for settling or
filtrations. Using additional sorbent technologies is another
method to further concentrate the REE by extracting REE from the
leachate. Other elements and compounds--such as cobalt, copper,
scandium, nickel that have high value can also be collected from
the leachate.
TABLE-US-00001 TABLE 1 % of Final Al Si Fe U + Th Trey Total
Composition pH (ug/g) (ug/g) (ug/g) (ug/g) (ug/g) Rey
NH.sub.4SO.sub.4 5.0 0.5 132.0 0.1 0.0 20.3 7.5 HCL 1 5522.9 3500.6
5686.0 1.3 51.2 18.9 H.sub.2SO.sub.4 0.8 2169.5 1996.6 3923.0 1.8
18.4 6.8 .SIGMA.SEQ1-3 7692.9 5629.1 9609.1 3.1 89.9 33.2 Citrate +
NaCl (RS-2) 3.5 1854.7 1178.6 309.0 1.2 85.2 31.5 NaCL Only (Post
RS-2) 5.0 92.6 0.0 73.6 0.1 3.9 1.5 .SIGMA. R52-3 1947.3 1178.6
382.6 1.3 89.1 33.0 Citrate + NH.sub.4SO.sub.4 5.1 1143.2 837.0
169.0 0.9 7.3 2.7 Citrate Only 5.2 1411.0 924.0 208.0 1.0 18.3
6.7
[0066] Table 1 depicts concentrations of Al, Si, Fe, U+Th, and
total REE+Y (REY) recovered from Flint underclay sample from the
Middle Kittanning (West Virginia) using various leaching solutions
as compared to typical sequential leaching using inorganic
acids.
In-Situ Recovery (ISR) Example:
[0067] FIG. 3 depicts a flow diagram illustrating a process,
generally designated 200, for in-situ extraction/recovery either in
an open pit 210 or underground mine 212, in advance of mining. If
the source contains greater than 300 ppm of REE+Yttrium (REY) or
other critical metals 214 may be considered for in-situ recovery
using either liquid or hot gas ion exchange. In-situ recovery and
extraction efficiency (ISR) techniques could be deployed wherever a
REE-bearing layer is underlain by a layer with at least a modest
permeability. In either an open pit mine 210 or an underground mine
212, the mine floor may serve as the leachate injection point or
injection production wells could be drilled and used for REE
extraction in advance of mining.
[0068] The IRS efficiency for REE from geologic materials is
heavily influenced by the permeation of extraction fluids into the
rock matrix. In-situ extraction of REEs will drastically reduce
costs by eliminating the need for grinding, crushing and
conventional mining methods. Use of dilute leaching agents,
transport mediators, concentrators, etc., commonly found in nature
may reduce the environmental impacts and wastes, furthering
reducing the life-cycle costs. One or more embodiments may include:
Drill horizontal injection well(s) through the coal seam; and/or at
a location vertically below the injection well(s) drill horizontal
production well(s) through sandstones (or other permeable strata)
immediately beneath the REE-bearing underclay or targeted ore
layer.
[0069] FIG. 3 further determines whether the REY is greater than
300 ppm of rare earth elements and Yttrium (REY) 214, then the
process may include drilling. FIG. 3 illustrates wells 218
including injection wells 220 and extraction wells 222 The
injection well 220 for example has a casing which could be
perforated where it lies within the coal bearing strata to
facilitate distribution of the injected fluid throughout the area
surrounding the injection well(s). Likewise, a production well may
have perforated casing where it lies within the permeable layer
serving the collection of leachate from the underclay or ore
layer(s) above. Small-scale hydraulic stimulation of the coal seam
could be used to enhance the permeability of the coal seam cleats.
Injection of dilute aqueous leaching agents and flushing fluid
(OAS, containing organic acids and other compounds) through the
injection wells into the coal bed, where it can begin to permeate
downwards. And, 3) pump periodically from the horizontal production
well beneath the underclays to create a pressure gradient that
facilitates gathering the leachate permeating through the
underclay. The localized pressure differentials will control and
limit the spread and movement the leaching solution and flushing
fluid enriched in REEs such that the collateral impacts would be
minimized.
[0070] Process 200 includes a portion generally referred to as
process 230. In process 230, the organic acid and salt 232 contact
the materials and perform an ion exchange process 234 with the
option to include additional liquid agents 236 and/or hot gas 238.
Material from the wells 218 is filtered 240. The filtered material
240 undergoes subsequent drying or calcining 242 forming REY
concentrate 246. Calcination/drying 242 also yields critical metals
244 (e.g. Sc, Co, Ni). REY concentrate 246. Gangue minerals
(Al.sub.2O.sub.3, Fe.sub.2O.sub.3) 248 may be released or produced,
which may be disposed 250. Bench top experiments after 24 hours
contained up to 35% of the REE from the bulk material with limited
release of base cations (common gangue metals), which are
considered contaminants to down-stream REE-oxide purification
processes (See Table 1).
[0071] FIG. 4 illustrates one possible extraction in-situ recovery
(ISR) method, generally designated 300 in advance of underground
mining, where the REE is extracted using perforated injection and
production wells. FIG. 4 includes coal bed 310, underlays 312 and
interbedded basal unit 314. The injection well casing 316 is
perforated (See enlarged portion 318) where it lies within the coal
bearing strata 310 to facilitate distribution of the injected fluid
throughout the area surrounding the injection well(s). Likewise,
the production well 324 has a casing 320, a perforated casing for
example (See enlarged portion 322), where it lies within the
permeable layer or below the interbedded basal unit 326 serving the
collection of leachate from the underclay or source material above.
Small-scale hydraulic stimulation of the coal seam may be used to
enhance the permeability of the coal seam cleats; Injection of
dilute aqueous leaching agents and flushing fluid (OAS, containing
organic acids and other compounds) through the injection wells into
the coal bed, where it can begin to permeate downward; and, pump
periodically from the horizontal production well beneath the
underclays to create a pressure gradient that facilitates gathering
the leachate permeating through the underclay. The localized
pressure differentials will control and limit the spread and
movement the leaching solution and flushing fluid enriched in REEs
such that the collateral impacts would be minimized.
[0072] FIG. 5 illustrates in-situ recovery at a pit mine, generally
designated 400, which includes extracting REEs in advance of open
pit mining. FIG. 5 includes coal bed 410, underlays 412 and
interbedded basal unit 414. The injection well casing 416 is
perforated (See enlarged portion 418) where it lies within the coal
bearing strata 410 to facilitate distribution of the injected fluid
throughout the area surrounding the injection well(s). Likewise
production casing 420, a multi-string casing for example (See
enlarged portion 422), lies below the coal bed 410 serving the
collection of leachate in the underclay 412, above the interbedded
basal unit 414.
[0073] One or more embodiments of the process discussed about
advantageously use organic acids to enable the extraction of
exchangeable, or weakly bonded (i.e., adsorbed or surface force
bonded), REE ions from basal planar surfaces of clay minerals as
well as liberation of non-exchangeable (stronger bonded) REE ions
present as oxides at a pH ranging from 2 to 6.
[0074] It should be appreciated that the selective approach of
using pH 5 buffered organic acid solutions amended with ionic salts
(e.g., (NH.sub.4)2504 or NaCl) is designed to facilitate the
extraction of the ion-exchangeable REE fraction from the clay via
cation exchange.
[0075] In one or more embodiments, NaCl may be used to create a
neutral charge surface on the clay to enhance ion exchange.
Additional chelation compounds may be used to keep mobilized REEs
from easily re-adsorbing before being brought out of the source
material or ore. One or more embodiments may use concentrating
compounds to further concentrate REEs, where the chelating compound
may include one or more of carboxylic acid from acetate, citrate,
and/or formate. Embodiments of the present invention may be used in
geological formations or other engineered waste products containing
other critical metals (e.g., Sc, Ni, Co).
[0076] In-situ leaching may be performed either before conventional
mining, after conventional mining, or having no association with
conventional mining. Alternative versions of the basic process
would include using various combinations of organic acids,
inorganic acids, salts, chelating compounds, concentrating
substances and surfactants tailored to maximize the extraction
efficiency versus costs for a particular ore or target REE-bearing
material. Testing and tailoring should be done in advance of or at
the beginning of every extraction project. All natural REE-sources
are different, at least at the submicroscopic level where chemical
reactions, chemical bonds, and surface forces (responsible for
sorption) are of greatest importance.
[0077] One or more anticipated uses include heap leaching, vat/tank
or process train leaching, in-situ leaching, and uranium mining
applications
[0078] Having described the basic concept of the embodiments, it
will be apparent to those skilled in the art that the foregoing
detailed disclosure is intended to be presented by way of example.
Accordingly, these terms should be interpreted as indicating that
insubstantial or inconsequential modifications or alterations and
various improvements of the subject matter described and claimed
are considered to be within the scope of the spirited embodiments
as recited in the appended claims. Additionally, the recited order
of the elements or sequences, or the use of numbers, letters or
other designations therefor, is not intended to limit the claimed
processes to any order except as may be specified. All ranges
disclosed herein also encompass any and all possible sub-ranges and
combinations of sub-ranges thereof. Any listed range is easily
recognized as sufficiently describing and enabling the same range
being broken down into at least equal halves, thirds, quarters,
fifths, tenths, etc. As a non-limiting example, each range
discussed herein can be readily broken down into a lower third,
middle third and upper third, etc. As will also be understood by
one skilled in the art all language such as up to, at least,
greater than, less than, and the like refer to ranges which are
subsequently broken down into sub-ranges as discussed above. As
utilized herein, the terms "about," "substantially," and other
similar terms are intended to have a broad meaning in conjunction
with the common and accepted usage by those having ordinary skill
in the art to which the subject matter of this disclosure pertains.
As utilized herein, the term "approximately equal to" shall carry
the meaning of being within 15, 10, 5, 4, 3, 2, or 1 percent of the
subject measurement, item, unit, or concentration, with preference
given to the percent variance. It should be understood by those of
skill in the art who review this disclosure that these terms are
intended to allow a description of certain features described and
claimed without restricting the scope of these features to the
exact numerical ranges provided. Accordingly, the embodiments are
limited only by the following claims and equivalents thereto. All
publications and patent documents cited in this application are
incorporated by reference in their entirety for all purposes to the
same extent as if each individual publication or patent document
were so individually denoted.
[0079] All numeric values are herein assumed to be modified by the
term "about", whether or not explicitly indicated. The term "about"
generally refers to a range of numbers that one of skill in the art
would consider equivalent to the recited value (e.g., having the
same function or result). In many instances, the terms "about" may
include numbers that are rounded to the nearest significant
figure.
[0080] The recitation of numerical ranges by endpoints includes all
numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,
3.80, 4, and 5).
[0081] One skilled in the art will also readily recognize that
where members are grouped together in a common manner, such as in a
Markush group, the present invention encompasses not only the
entire group listed as a whole, but each member of the group
individually and all possible subgroups of the main group.
Accordingly, for all purposes, the present invention encompasses
not only the main group, but also the main group absent one or more
of the group members. The present invention also envisages the
explicit exclusion of one or more of any of the group members in
the claimed invention.
* * * * *
References