WO2025034582A1 - Triazacoronene-based metal organic frameworks and rare earth separation processes - Google Patents

Abstract

Embodiments of the present disclosure generally relate to processes for separating rare earth element (REE) metals from a feedstock. Embodiments of the present disclosure also generally relate to a new class of metal organic frameworks. In an embodiment, a process for separating an REE metal from a feedstock is provided. The process includes introducing a metal organic framework (MOF) to an aqueous feedstock to form a water-insoluble REE-MOF complex. The process may further include performing electrochemistry on an aqueous mixture comprising the water-insoluble REE-MOF complex. Embodiments described enable selective capture and release of REE metals.

Description

Triazacoronene-Based Metal Organic Frameworks and Rare Earth Separation Processes

GOVERNMENT RIGHTS

[0001] This invention was made with government support under DMR-2118592 awarded by the National Science Foundation. The government has certain rights in the invention.

FIELD

[0002] Embodiments of the present disclosure generally relate to processes for separating rare earth element (REE) metals from a feedstock. Embodiments of the present disclosure also generally relate to a new class of metal organic frameworks (MOFs).

BACKGROUND

[0003] REE metals are utilized in various products and manufacturing processes, including permanent magnets, catalysts, fiber optics, and phosphor displays, wind turbines, cell phones, and electric vehicles, among other modern technologies. The United States depends on foreign sources for processing and purification of REE metals, representing a significant vulnerability for the U.S. supply chain, which could be mitigated by developing a domestic manufacturing industry to extract and purify REE resources. However, conventional technologies for extraction and separation of REE metals, especially from each other, can be inefficient, energy-intensive, complex, and produce sizeable amounts of hazardous waste due to the use of toxic reagents and solvents. These problems result in domestic permitting and regulatory challenges and represent a significant commercial barrier for domestic mining and refining of REE metals.

[0004] Conventional technologies for industrial-scale REE separation are based on solvent extraction schemes. In a solvent extraction process, an aqueous feedstream containing the REE metals is brought into contact with an immiscible, organic extractant stream containing ligands which bind to the REE metals, encouraging transfer between phases. After allowing the system to equilibrate, REE metals are distributed between the two phases based on the strength of ligand binding and the solvation energies for relevant species in each phase. In a solvent exchange process, the extractant phase is typically a hydrophobic organic solvent (for example, kerosene or dodecane) containing lipophilic ligands. Commonly, the employed ligands are hard Lewis bases, such as phosphoric or carboxylic acids which undergo proton exchange at the interface (for example, di-(2-ethylhexyl)phosphoric acid, HDEHP). In addition, selective adsorption of REE metals within a zinc MOF/graphene oxide nanocomposite have been reported. This interlayer-confined strategy does show good separation selectivity but only produces a capture technique without a release strategy.

[0005] There is a need for new processes for separating REE metals from a feedstock. There is also a need for new class of MOFs.

SUMMARY

[0006] Embodiments of the present disclosure generally relate to processes for separating REE metals from a feedstock. Embodiments of the present disclosure also generally relate to a new class of MOFs. Embodiments described herein enable extraction, separation, and/or purification of rare earth elements from a feedstock such as produced water, among other complex feedstocks and crude mixtures. The inventors found that MOFs may be utilized to complex, or capture, an REE. The complexed, or captured, REE may then be released by electrochemistry. Relative to conventional solvent extraction technologies, embodiments described herein are more efficient, less energy intensive, and produce less waste. Unlike conventional technologies that show only capture of REE metals using MOFs but no release of the REE metals, embodiments described herein can enable both capture and release of REE metals. The capture and release, according to embodiments of the present disclosure, may be selective.

[0007] In an embodiment, a REE metal separation process is provided. The process includes (a) providing an aqueous feedstock comprising one or more REE metals, at least one of the one or more REE metals is in the form of a first REE complex comprising a first REE metal coordinated to a first anion. The process further includes (b) contacting the aqueous feedstock comprising with a metal organic framework (MOF) under conditions effective to form a mixture comprising a second REE complex comprising: the first REE metal coordinated to the MOF, the first anion and the MOF being different.

[0008] In another embodiment, a process is provided. The process includes (a) introducing a first metal organic framework (MOF), as a solid, to an aqueous feedstock comprising one or more REE metals to form a first water-insoluble REE-MOF complex comprising a first REE metal coordinated to the first metal organic framework. The process further includes (b) isolating the first water-insoluble REE-MOF complex; and

(c) forming an aqueous mixture comprising the first water-insoluble REE-MOF complex isolated and a redox mediator. The process further includes (d) applying a first electric field to the aqueous mixture to form a composition comprising: a solid phase comprising the first MOF; and a liquid phase comprising the first REE metal. The process further includes (e) isolating the liquid phase from the composition; and (f) applying a second electric field to the liquid phase to precipitate a solid comprising the first REE metal. The process further includes (g) recovering the solid comprising the first REE metal from the liquid phase.

[0009] In another embodiment, a water-insoluble composition is provided. The water-insoluble composition includes a REE metal. The water-insoluble composition further includes a MOF coordinated to or complexed with the REE metal, the MOF comprising: a plurality of triazacoronene subunits, each triazacoronene subunit coupled to another triazacoronene subunit by a Group 1-14 metal of the periodic table of the elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, may admit to other equally effective embodiments. [0011] FIG. 1 shows a space-filling model of an example multi-pore MOF according to at least one embodiment of the present disclosure.

[0012] FIG. 2A is a flowchart showing selected operations of a REE metal separation process according to at least one embodiment of the present disclosure.

[0013] FIG. 2B is a flowchart showing selected operations of a REE metal separation process according to at least one embodiment of the present disclosure.

[0014] FIG. 2C is a generalized schematic flow diagram illustrating processes described herein corresponding to operational areas or units in a processing plant for separating a REE metal according to at least one embodiment of the present disclosure.

[0015] FIG. 2D is a generalized schematic flow diagram illustrating processes described herein corresponding to operational areas or units in a processing plant for separating a REE metal according to at least one embodiment of the present disclosure.

[0016] FIG. 3 powder X-ray diffraction pattern of an example MOF according to at least one embodiment of the present disclosure.

[0017] FIGS. 4A and 4B show an electrochemical scheme for liberation of REE metals from REE-MOFs according to at least one embodiment of the present disclosure.

[0018] FIG. 5A shows an electrochemical cell for electrolysis according to at least one embodiment of the present disclosure.

[0019] FIG. 5B shows an overlay of ultraviolet-visible spectra comparing absorption of a resulting electrolyte after electrolysis to a similar solution prepared via dissolution with hydrochloric acid.

[0020] Figures included herein illustrate various embodiments of the disclosure. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

[0021] Embodiments of the present disclosure generally relate to new processes for separating REE metals from a feedstock. Embodiments of the present disclosure also generally relate to a new class of MOFs. Embodiments described herein enable recovery and separation of REE metals from feedstocks efficiently with minimal waste and in an economical manner. In various embodiments, task-specific MOFs — which include triazacoronene ligands (or nodes) — may be utilized to complex and extract an REE from a feedstock. After complexation, electrochemical methods may then be used to release the REE. The combination of MOFs and electrochemistry allow for the selective separation of REE metals.

[0022] MOFs are three-dimensional (3D) porous crystalline materials with infinite lattices synthesized from ionic salts or polydentate organic ligands with coordinationtype connections. Their structures are flexible and can be tuned by variation of the salts or ligands, which are commonly referred to as linkers or nodes. Rare-earth MOFs have been reported and a numerous ligands have been used for REE coordination. Although MOFs with zeolitic structures have been reported for several d-block metals, this structural motif is not as easily obtained with f-block metals (e.g., rare earths). This is a consequence of the high coordination numbers and diverse coordination environments presented by f-block metals, making it difficult to form a 4-coordinate (or 4-connected) nodes common to zeolitic topologies”. Selective adsorption of REE metals within a zinc MOF/graphene oxide nanocomposite have been reported. This interlayer-confined strategy shows good separation selectivity but only produces a capture technique without a release strategy.

[0023] As described above, conventional technologies for REE extraction from feedstocks are environmentally problematic, expensive, and energy inefficient. In contrast, and relative to conventional technologies, embodiments described herein enable extraction, separation, and purification of REE metals from complex mixtures and feedstocks at lower costs, with higher energy efficiency and more environmentally friendly.

[0024] Embodiments of the present disclosure generally relate to a new class of MOFs. The MOFs may be classified as organic-inorganic hybrid materials. The MOFs may include a plurality of inorganic nodes and a plurality of organic nodes. The inorganic node, also referred to as an inorganic subunit, may include a metal cluster or a metal, or combinations thereof. The organic node, also referred to as an organic subunit or a tri azacoronene subunit, may include a heterocyclic compound, a carboxylate, or combinations thereof. The structure and/or function of MOFs described herein to capture and/or release REE metals can be tailored by, for example, the design of organic nodes with specific lengths, geometries, and functional groups. The inorganic node can also dictate properties of the MOF. For example, the bond between the metal and the organic node can be labile, thereby impacting stability of the MOF.

[0025] The inorganic node of MOFs described herein may include any suitable metal such as a Group 1-14 metal of the periodic table of the elements, such as a Group 2 to Group 13 metal element, such as Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd, Al, V, Cr, Fe Ga, In, Ti, Zr, Hf, or combinations thereof, among others, such as a Group 11 or Group 12 metal element, such as Zn, Cu, or combinations thereof. The inorganic node may further include a ligand such as a functional group comprising at least one element from Group 13-17 of the periodic table of the elements.

[0026] The organic node may be, or include, a triazacoronene unit represented by formula (I):

wherein: each R¹ of formula (I) is, independently, hydrogen, an unsubstituted hydrocarbyl, a substituted hydrocarbyl, or a functional group comprising at least one element from Group 13-17 of the periodic table of the elements; each R² of formula (I) is, independently, hydrogen, an unsubstituted hydrocarbyl, a substituted hydrocarbyl, or a functional group comprising at least one element from Group 13-17 of the periodic table of the elements;

X of formula (I) is CH or N; and y of formula (I) is the number of R² groups, and when y is greater than 1, R² on the individual aromatic ring can be the same or different.

[0027] Each of R¹ or R² of formula (I) may be, independently, linear or branched, saturated or unsaturated, cyclic or acyclic, monocyclic or polycyclic, aromatic or not aromatic. Regarding saturation, one or more of R¹ and R² of formula (I) may be, independently, fully saturated, partially unsaturated, or fully unsaturated.

[0028] As used herein, an “unsubstituted hydrocarbyl” refers to a group that consists of hydrogen and carbon atoms only. Non-limiting examples of unsubstituted hydrocarbyl include an alkyl group having from 1 to 100 carbon atoms, such as from 1 to 40 carbon atoms, such as from 2 to 32 carbon atoms, such as from 4 to 28 carbon atoms, such as from 6 to 24 carbon atoms, such as from 8 to 18 carbon atoms or from 8 to 24 carbon atoms, such as from 10 to 16 carbon atoms, such as from 12 to 14 carbon atoms, or from 8 to 40 carbon atoms, such as from 10 to 30 carbon atoms, such as from 12 to 24 carbon atoms, such as from 14 to 22 carbon atoms, such as methyl, ethyl, n- propyl, isopropyl, n-butyl, iso-butyl, sec-butyl, and tert-butyl, pentyl, hexyl, heptyl, octyl, ethyl-2-hexyl, isooctyl, nonyl, n-decyl, isodecyl, or isomers thereof; a cycloaliphatic group having from 3 to 20 carbon atoms such as, for example, cyclopentyl or cyclohexyl; an aromatic group having from 6 to 20 carbon atoms such as, for example, phenyl or naphthyl; or any combination thereof. As used herein, “substituted hydrocarbyl” refers to an unsubstituted hydrocarbyl in which at least one hydrogen of the unsubstituted hydrocarbyl has been substituted with at least one heteroatom or heteroatom-containing group, such as one or more elements from Group 13-17 of the periodic table of the elements, such as halogen (F, Cl, Br, or I), O, N, Se, Te, P, As, Sb, S, B, Si, Ge, Sn, Pb, and the like, such as C(O)R*, C(C)NR*₂, C(O)OR*, NR*2, OR*, SeR*, TeR*, PR*2, AsR*₂, SbR*₂, SR*, SOx (where x = 2 or 3), BR*₂, SiR*3, GeR*3, SnR*3, PbR*3, and the like, where R* is, independently, hydrogen or unsubstituted hydrocarbyl, or where at least one heteroatom has been inserted within the unsubstituted hydrocarbyl.

[0029] When an R group (e.g., R¹ and/or R², or other R group described herein) is a functional group comprising at least one element from Group 13-17 of the periodic table of the elements, the R group may be halogen (F, Cl, Br, or I), O, N, Se, Te, P, As, Sb, S, B, Si, Ge, Sn, Pb, and the like, such as C(O)R*, C(C)NR*₂, C(O)OR* (e.g., ester), NR*2, OR*, SeR*, TeR*, PR*2, AsR*2, SbR*2, SR*, SOx (where x = 2 or 3), BR*2, SiR*3, GeR*3, SnR*3, PbR*3, and the like, where R* is, independently, hydrogen or unsubstituted hydrocarbyl, or where at least one heteroatom has been inserted within the unsubstituted hydrocarbyl.

[0030] Each of R¹ and R² of formula (I) may be, independently, an unsubstituted hydrocarbyl having 1 to 100 carbon atoms, such as 1 to 40 carbon atoms, such as 1 to 20 carbon atoms. Non-limiting examples of R¹ of formula (I) may include an alkyl group having from 1 to 40 carbon atoms such as n-butyl, iso-butyl, sec-butyl, and tertbutyl, pentyl, hexyl, heptyl, octyl, ethyl-2-hexyl, isooctyl, nonyl, n-decyl, isodecyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, heneicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl, nonacosyl, or isomers thereof.

[0031] Each of R¹ and R² of formula (I) may be, independently, hydrogen, hydroxyl (-OH), alkoxyl (-OR*), halogen (F, Cl, Br, or I), carboxyl (-CO2H), amine (-NH2), alkylamine (-NR*₂), nitro (-NO2), ester (-C(O)R*), phosphoryl (-P(O)(OR*)₂), sulfonyl (-SO3R*), or amide (-C(O)NHR*), where R* is hydrogen, a C1-C20 unsubstituted hydrocarbyl or a C1-C20 substituted hydrocarbyl, and when more than one R¹ of Formula (I) is present each R* can be the same or different. R* can be a hydrogen, a Cl -CIO unsubstituted hydrocarbyl (such as a C1-C6 unsubstituted hydrocarbyl, such as methyl, ethyl, propyl, butyl, pentyl, or hexyl), or a Cl -CIO substituted hydrocarbyl). Additionally, or alternatively, each R² of Formula (II) can be, independently, a C1-C20 unsubstituted hydrocarbyl or a C1-C20 substituted hydrocarbyl, such as a Cl -CIO unsubstituted hydrocarbyl or a Cl -CIO substituted hydrocarbyl, such as a C1-C6 unsubstituted hydrocarbyl or a C1-C6 substituted hydrocarbyl. [0032] In some embodiments, at least one R¹ and/or at least one R² may be an ionizable group such as carboxyl (-CO2H), sulfonyl (-SO3H), amine (-NH2), alkylamine (-NR*2), peptide, phosphorous-containing group (-P(O)(OR*)2), combinations thereof, among others.

[0033] In some embodiments, at least one R¹ and/or at least one R² may be in the form of an ion or neutral species. Such ionic and neutral species can include halogens, amines, hydroxyls, carboxyls, peptides, ammoniums, oniums, alkanes, alkenes, silanes, sulfonyls, or phosphates.

[0034] In some embodiments, at least one R¹ of formula (I) is a halogen, such as fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).

[0035] In some embodiments, at least one R¹ of formula (I) is an alkoxy (-OR*) group, wherein R* is a C1-C20 unsubstituted hydrocarbyl or a C1-C20 substituted hydrocarbyl, and when more than one R¹ of Formula (I) is present, each R* can be the same or different. R* can be a Cl -CIO unsubstituted hydrocarbyl, such as a C1-C6 unsubstituted hydrocarbyl, such as methyl, ethyl, propyl, butyl, pentyl, or hexyl.

[0036] y of formula (I) may be an integer such as 1, 2, 3, or 4. When y of formula (I) is greater than 1, R² on the individual aromatic ring can be the same or different.

[0037] R¹ and/or R² of formula (I) may be chosen to adjust the water solublity/insolubility properties of the MOF. For example, more ionic charge in the MOF may lead to greater water solubility. Additionally, or alternatively, R¹ and/or R² may be selected for their ionic strength in binding a REE metal, their steric impact on binding a REE metal, or combinations thereof.

[0038] As further described below, the MOFs include a plurality of inorganic nodes (also referred to as inorganic subunits) and plurality of triazacoronene subunits (also referred to as organic nodes or organic subunits). The tri azacoronene subunits may be represented by formula (IA) or formula (IB):

[0039] R¹, R², X, and y of formula (IA) and formula (IB) may be the same as those described above with respect to formula (I).

[0040] The wavy bonds of formula (IA) and formula (IB) represent a connection to an inorganic subunit (comprising a metal (M) and ligand (L), described below), or inorganic subunit, of the MOF. The inorganic subunit may be further bonded to another organic subunit. The organic and inorganic subunits may be bonded by, for example, covalent bonds, coordination bonds, or ionic bonds, such as covalent bonds.

[0041] As shown by formula (IA) and formula (IB), the MOFs may be constructed using the “X” group or an R² group. For example, with respect to formula (IA), and when X=N (pyridine ring), X may be bonded to the inorganic subunit. Here, the metal M of the inorganic subunit may be bonded via a wavy bond to the nitrogen atom (X) of a first triazacoronene subunit and bonded via a wavy bond to the nitrogen atom (X) of a second triazacoronene subunit. That is, a single inorganic subunit bonds to two organic subunits.

[0042] As another example, with respect to formula (IB), and when X=CH, an R² may be bonded to the inorganic subunit. Here, the metal M of the inorganic subunit may be bonded via a wavy bond to a R² group of a first tri azacoronene subunit and bonded via a wavy bond to a R² group of a second tri azacoronene subunit. Again, a single inorganic subunit bonds to two organic subunits. For example, R² may be an oxygen containing group or a nitrogen containing group such as an OH group, a carboxylic acid, or an amine, among others. Such nitrogen- and oxygen-containing groups may bond to the metal (M) of the inorganic subunit.

[0043] Triazacoronenes of formula (I) may be formed by a Pictet-Spengler reaction of a triphenylene amine of formula (II) and an aromatic aldehyde of formula (III) as shown in Scheme 1 A.

Scheme 1A

[0044] The Pictet-Spengler reaction generally involves attack of the triphenylene amine (I) on substituted benzaldehydes, when X=CH, or substituted pyridines, when X=N, to form imine linkages followed by cyclization to produce new rings. Subsequent dehydrogenation forms the aromatic pyridine ring. Generally, the Pictet-Spengler reaction involves condensation of the amines with an aldehyde followed by ring closure.

[0045] Depending on the synthetic route to tri azacoronene of formula (I), each R¹ of formula (II) may be the same as R¹ of formula (I). Likewise, each R² and X of formula (III) may be the same as R² and X of formula (I). As described above, X may be CH or N. When X=CH, the aromatic aldehyde of Formula (II) can be referred to as a benzaldehyde or benzaldehyde derivative. When X=N, the aromatic aldehyde of Formula (II) can be referred to as a pyridine or pyridine derivative. [0046] Triphenylene amines of formula (II) may be produced in three steps from various catechol derivatives via Scholl reaction, nitration, and reduction of the resulting trinitro in excellent yields such that the triphenylene amines (for example, with R = OMe) may be made in gram-scale quantities. These OMe groups may be replaced prior to (or after) reaction with the other functional groups to, for example, alter non-water- soluble properties of the tri azacoronene nodes.

[0047] Various aromatic aldehydes of formula (III) may be utilized to form triazacoronenes and corresponding MOFs some of which are shown in Table 1. As shown, various pyridine substrates (X=N) and phenyl substrates (X=CH) may be used to form aromatic aldehydes. S3a and S3b are amides, S4a and S4b are diamides, S9a and S9B are esters, and SlOa and SI Ob are diesters. R* Table 1 may be a hydrogen or an unsubstituted hydrocarbyl described herein.

Table 1

[0048] Some of these pyridine and phenyl substrates (aromatic aldehydes) shown in Table 1 are commercially available (for example, Sla, S3a, S3b) or may be synthesized by known procedures (S2a, S2b, Sib). Other aromatic aldehydes shown in Table 1 may be formed by various non-limiting methods as shown in Schemes 2-4.

Scheme 2

[0049] In Scheme 2, an aromatic aldehyde 2-A, such as 3 -bromotoluene (A=H) or 3, 5 -bromotoluene (A=Br), or the corresponding pyridines, may be lithiated and subsequently treated with an electrophile such as CO2 or CISO3H, or undergo a palladium catalyzed carbonylation or phosphonation to produce modified toluenes 2- B. For modified toluene 2-B, E may be CO2H, SO3H, PO3H2, P(O)(OR*)2, amide (CONHR*), ester (COR*), or H as described above, where each R* is, independently, a hydrogen or unsubstituted hydrocarbyl. Oxidation of the methyl group of 2-B produces the benzaldehyde structures or pyridine aldehyde structures 2-C, where E may be CO2H, SO3H, PO3H2, P(O)(OR*)₂, amide (CONHR*), ester (COR*), or H, where each R* is, independently, a hydrogen or unsubstituted hydrocarbyl. In Scheme 2, X is N or CH.

[0050] An alternative to forming the aromatic aldehydes is shown in Scheme 3. As shown, chelidamic acid (4-oxo-l//-pyridine-2,6-dicarboxylic acid) 3-A is reacted with phosphorus pentabromide (PBrs) in a solvent such as methanol to form bromopyridine 3-B. The bromopyridine may then be formylated followed by hydrolysis to form diacid 3-C.

[0051] Alternatively, monoesters and diesters (such as R is Me, Et, Pr, or tBu esters) of bromobenzene or bromopyridines are commercially available and can be formylated using butyllithium/dimethylformamide (BuLi/DMF). Alternatively, and as shown in Scheme 4, the use of 3,5-dibromosalicylaldehyde 4- A may involve protection of the phenolic OH to OR to form structure 4B (where R is a protecting group). The bromines of 4-B may be lithiated and subsequently treated with an electrophile such as CO2 or CISO3H, or undergo a palladium catalyzed carbonylation or phosphonation to produce variations of X=CH nodes (Slc-S9c, except that R is a protecting group in Scheme 4). Deprotection, to convert OR in structure 4-C to an OH group may occur after formation of the triazacoronene (organic node). E in Scheme 4 is CO2H, SO3H, PO3H2, P(O)(OR*)2, amide (CONHR*), ester (COR*), or H, where each R* is, independently, a hydrogen or unsubstituted hydrocarbyl.

Scheme 4

Pd catalysis

[0052] After forming the triazacoronenes, MOF s may be constructed by reaction of the tri azacoronene with an inorganic subunit precursor, such as ZnBn, CuBrc, or other inorganic subunit precursor. MOFs may be made from the self-assembly of triazacoronenes (graphene-like nodes).

[0053] MOFs described herein may be represented by formula (IVA), formula (IVB), and/or formula (IVC):

wherein, in formula (IVA), formula (IVB), and formula (IVC): each R¹ is, independently, hydrogen, an unsubstituted hydrocarbyl, a substituted hydrocarbyl, or a functional group comprising at least one element from Group 13-17 of the periodic table of the elements; each R² is, independently, hydrogen, an unsubstituted hydrocarbyl, a substituted hydrocarbyl, or a functional group comprising at least one element from Group 13-17 of the periodic table of the elements; each M is, independently, a Group 1-14 metal of the periodic table of the elements, such as a Group 3-13 metal of the periodic table of the periodic table of the elements; each L is, independently, a ligand, such as a functional group comprising at least one element from Group 13-17 of the periodic table of the elements; w is the number of L, for example, 1, 2, 3, or 4; y is the number of R² groups, and when y is greater than 1, R² on the individual aromatic ring can be the same or different;

X is CH or N; and the wavy bonds represent a connection to another inorganic subunit (comprising M and L), this inorganic subunit bonded to another organic subunit.

[0054] R¹, R², and y of formula (IVA), formula (IVB), and formula (IVC) may be the same as those described above with respect to formula (I).

[0055] Ligand L of formula (IVA), formula (IVB), and formula (IVC) may be a functional group comprising at least one element from Group 13-17 of the periodic table of the elements, the R group may be halogen (F, Cl, Br, or I), O, N, Se, Te, P, As, Sb, S, B, Si, Ge, Sn, Pb, and the like, such as C(O)R*, C(C)NR*₂, C(O)OR* (e.g., ester), NR*2, OR*, SeR*, TeR*, PR*2, AsR*2, SbR*2, SR*, SOx (where x = 2 or 3), BR*2, SiR*3, GeR*3, SnR*3, PbR*3, and the like, where R* is, independently, hydrogen or unsubstituted hydrocarbyl, or where at least one heteroatom has been inserted within the unsubstituted hydrocarbyl. In at least one embodiment, L is a halide.

[0056] M and L, together, make up the inorganic subunit of the MOF. M may be any suitable metal such as a Group 1-14 metal of the periodic table of the elements, such as a Group 2 to Group 13 metal element, such as Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd, Al, V, Cr, Fe Ga, In, Ti, Zr, Hf, or combinations thereof, among others, such as a Group 11 or Group 12 metal element, such as Zn, Cu, or combinations thereof.

[0057] In formula (IVA), formula (IVB), and formula (IVC), certain R² groups are shown to bond with M. A different R² group on the aromatic rings may be used to bond with M. Any suitable combinations of R² groups on different tri azacoronene subunits may be used to bond with M. [0058] MOFs described herein may include a single pore. The pore may be defined by a ring comprising any suitable number of organic subunits (triazacoronenes) and any suitable number of inorganic subunits, such six organic subunits and six inorganic subunits.

[0059] For example, the MOF of formula (IVA), formula (IVB), and formula (IVC) comprises a single pore. The single pore is a hexagonal pore defined by six organic subunits and six inorganic subunits. The wavy bonds shown in of formula (IVA), formula (IVB), and formula (IVC) represent a connection to another inorganic subunit and a tri azacoronene subunit such that the MOF may comprise a plurality of pores. An example of such a multi-pore MOF 100 is shown in FIG. 1. The multi -pore MOF 100 shown in FIG. 1 includes five pores. Multi -pore MOFs can have any suitable numbers of pores, such as 1, 2, 3, 4, 5, 10, or more. The multi-pore MOF 100 also shows that each pore may be a hexagonal pore. The hexagonal pore may be defined by a ring comprising any suitable number of organic subunits and any suitable number of inorganic subunits, such as six organic subunits and six inorganic subunits. The MOF, whether a single pore or a multi-pore, may be water insoluble.

[0060] The single-pore MOFs and multi-pore MOFs may have a highly ordered nanopore structure and can have the ability to selectively incorporate functionality (e.g., varying R groups, X groups, metals, ligands, etc.) within those pores. MOFs described herein may be two-dimensional MOFs or three-dimensional (3D) MOFs having a unique combination of properties, such as electronic conductivity, filtration properties, metal (e.g., REE metal) binding properties, or combinations thereof, among other properties.

[0061] The MOFs described herein may be water insoluble. The MOFs may be added as solids to feedstocks comprising REE metals. Due to their unique combination of properties, the REE metals may be utilized to selectively separate REE metals from feedstocks comprising REE metals.

[0062] Embodiments of the present disclosure generally relate to new processes for separating REE metals from a feedstock. The MOFs described above may be utilized to selectively complex, or capture an REE from the feedstock to form an MOF -REE, and electrochemical methods may be utilized to release the REE from the MOF-REE. Processes described herein enable REE extraction, separation, and/or purification of complex feedstocks comprising one or more REE metals.

[0063] Feedstocks from which REE metals are extracted or separated (also referred to as REE metal-containing feedstocks) by embodiments described herein, may include any suitable feedstock. Any suitable aqueous feedstocks may be used. Suitable feedstocks may include, but are not limited to, produced water, slurried coal, coal mine tailings, or combinations thereof.

[0064] In some embodiments, which may be combined with other embodiments, REE metals may be extracted or separated from produced water. Produced water is water that exists in subsurface formations and is brought to the surface during oil and gas exploration and production, as well as the production of unconventional sources such as coal bed methane, tight sands, and gas shale, among others. Produced water may contain soluble and non-soluble oil/organics, suspended solids, dissolved solids, and various chemicals used in oil and gas production processes. Produced water also includes REE metals. The concentration of constituents and the volume of produced water can differ dramatically depending on the type and location of the petroleum product. Produced water accounts for the largest waste stream volume associated with oil and gas production.

[0065] REE metal-containing feedstocks include at least one REE metal, including scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). In the REE metal-containing feedstocks, the REE metals may be present as, for example, oxides (rare earth oxides (REOs)), carbonates (rare earth carbonates), hydroxides (rare earth hydroxides), phosphates (rare earth phosphates), or combinations thereof, among others.

[0066] FIG. 2A is a flowchart showing selected operations of a REE separation process 200 according to at least one embodiment of the present disclosure. Embodiments and implementations of process 200 may be combined with other embodiments and implementations described herein. For example, one or more operations or implementations of process 200 may be combined with one or more operations or implementations of process 210 (FIG. 2B).

[0067] Process 200 may include providing an aqueous feedstock comprising one or more REE metals at operation 202; and contacting the aqueous feedstock with a MOF, such as a MOF described herein, to form a mixture at operation 204. Process 200 may be used to selectively extract an REE metal from a complex feedstock and form a REE- MOF complex.

[0068] At operation 202, at least one of the REE metal present in the aqueous feedstock may be in the form of a first REE complex comprising a first REE metal coordinated to, or complexed with, a first anion. At operation 204, a mixture is formed by the introduction of the MOF with the aqueous feedstock. In addition, contact of the MOF with the aqueous feedstock enables the MOF to coordinate to, or complex with, the first REE metal to form a second REE complex present in the mixture. As described herein, the MOF utilized for operation 204 may be selected to coordinate a certain REE metal instead of other REE metals. That is, the aqueous feedstock may include a second REE metal that is different from the first REE metal. Like the first REE metal, the second REE metal may be in the form of an REE complex with an anion. Here, the MOF is adapted to selectively complex or coordinate the first REE metal over the second REE metal. The MOF may be adapted to bind a specific REE more strongly. For example, an MOF that selectively binds neodymium may be used or an MOF that selectively binds cerium may be utilized.

[0069] The second REE complex formed at operation 204 includes the first REE metal coordinated to, or complexed with, the MOF. The second REE complex may be water insoluble. Because of, for example, the water insolubility of the second REE complex, the second REE complex may be isolated from the mixture.

[0070] Referring back to the selectivity of the MOF, selection of, for example, the chemical functional groups (e.g., R¹ and/or R²) of the triazacoronenes (organic subunits), the metal (M) of the inorganic subunit, or combinations thereof, may be used to effect and enable selectivity in terms of the REE separated from the feedstock. Here, alteration of the donor atom (e.g., an R group such as R¹ and/or R²) may be used to affect polarizability, denticity, the pK_a range of the REE binding sites (those ionizable functional groups present on the organic subunits), steric hindrance, and/or saturated binding sites of the MOF, among other properties. Additionally, or alternatively, R¹ and/or R² of the organic subunit, the metal of the inorganic subunit, or combinations thereof, may be used to change the pore size of the MOF, the ionic strength of the MOF, and/or the size-exclusivity of the MOF. Overall, selection of the R¹ and/or R² of the organic subunit, the metal of the inorganic subunit, or combinations thereof, may be adapted to bind a specific REE metal more strongly than another REE metal, such that the MOF selectively separates a specific REE metal from feedstocks comprising more than one REE metal.

[0071] A concentration of the MOF in the mixture in operation 204 may be from about 0.001 molar (M) to about 10 M, such as from about 0.01 M to about 8 M, such as from about 0.1 M to about 5 M, such as from about 0.5 M to about 2.5 M, such as from about 0.75 M to about 2 M, such as from about 1 M to about 1.5 M.

[0072] FIG. 2B is a flowchart showing selected operations of a process 210 for separating one or more REE metals according to at least one embodiment of the present disclosure. Process 210 enables capture and release of an REE metal from complex mixtures. For example, process 210 may be used to selectively separate or extract an REE metal from a complex feedstock. Embodiments and implementations of process 210 may be combined with other embodiments and implementations described herein. For example, one or more operations or implementations of process 210 may be combined with one or more operations or implementations of process 200 (FIG. 2A).

[0073] Process 210 may begin with introducing a first MOF to an aqueous feedstock to form a first water-insoluble REE-MOF complex at operation 212. The first MOF introduced with the aqueous feedstock may be a solid. The aqueous feedstock may include one or more REE metals. The first water-insoluble REE-MOF complex includes a first REE metal coordinated to, or complexed with, the first MOF. Operation 212 may be performed by, for example, providing an aqueous feedstock comprising one or more REE metals (for example, operation 202); and contacting the aqueous feedstock with a MOF, such as a MOF described herein, (for example, operation 204). Operations 202 and 204 are described above. As described herein, the first MOF may be adapted or configured to selectively complex or coordinate the first REE metal. Concentrations of the MOFs used for operation 212 are also described above.

[0074] Process 210 may further include isolating the first water-insoluble REE- MOF complex at operation 214. Here, the first water-insoluble REE-MOF complex is present as a solid in a mixture that includes the aqueous feedstock. The isolation process of operation 214 may be performed by any suitable isolation or separation technique, such as solid-liquid separation techniques including mechanical or gravity separation, such as filtration, vacuum filtration, centrifugation, decanting, decanting centrifugation, settling, combinations thereof, among other techniques. For example, the mixture having the first water-insoluble REE-MOF complex, as a solid, may be filtered to isolate the first water-insoluble REE-MOF complex. Optionally, after isolating the first water-insoluble REE-MOF complex, the liquid feedstock having a lower concentration of the first REE metal may be processed using a second MOF to isolate a second REE metal as described below.

[0075] Process 210 may further include operation 216, which includes forming an aqueous mixture comprising a redox mediator and the first water-insoluble REE-MOF complex isolated at operation 214. Any suitable redox mediator, also referred to herein as a sacrificial oxidant, may be utilized. Suitable redox mediators may include those redox mediators that allow release of the REE metal (e.g., operation 218) and precipitation of a solid comprising the first REE metal (e.g., operation 222) in different operations. By forcing the process to occur stepwise, bulk pH changes can be induced that separate the REE-MOF structures.

[0076] A non-limiting example of a redox mediator includes sodium triiodide (Nab), iron species (for example, ferrocene methanol, ferricyanide (Fe(CN)e)), or combinations thereof, among others. The redox mediator allows liberation of REE ions. Here, the first water-insoluble REE-MOF complex may be added to a solution comprising the redox mediator and water. Additionally, or alternatively, aqueous mixture may be made by adding the redox mediator as a solid or a solution to the first water-insoluble REE-MOF complex. Additionally, or alternatively, water may be added to the first water-insoluble REE-MOF complex, and the redox mediator may be added as a solid or a solution to form the aqueous mixture. The water may be fresh or recycled.

[0077] Process 210 may further include applying a first electric field to the aqueous mixture at operation 218. The electric field serves as a source of electrons. The application of the electric field lowers the pH of the aqueous mixture at the anode. Because REE-MOF formation is dependent on pH, lowering the pH causes (i) the release of the first REE metal from the first water-insoluble REE-MOF complex and (ii) precipitation of the first MOF as solid products. These solid products may be in the form of neutral species or salts (e.g., sodium salts). Accordingly, application of the first electric field to the aqueous mixture at operation 218 results in formation of a composition that includes a solid phase comprising the first MOF and a liquid phase that includes the first REE metal.

[0078] Operation 218 may be performed by immersing conducting electrodes — an anode and a cathode — in the aqueous mixture and applying an electric field (a voltage or bias voltage) between the conducting electrodes. The electric field applied to the aqueous mixture may have a voltage that is from about -10 V to about +10 V, such as from about -8 V to about +8 V, such as from about -8 V to about +8 V, such as from about -6 V to about +6 V, such as from about -4 V to about +4 V, such as from about -2 V to about +2 V, such as from about -1 V to about +1 V. These voltages and voltage ranges are measured against a standard hydrogen electrode (SHE).

[0079] Process 210 may further include isolating or separating the liquid phase comprising the first REE metal from the composition at operation 220. The solid phase comprising the first MOF may also be isolated or separated at operation 220. Isolation or separation of the first REE metal present in the liquid phase from the first MOF present in the solid phase may be performed by any suitable isolation or separation technique. Suitable techniques include solid-liquid separation techniques such as mechanical or gravity separation, such as filtration, vacuum filtration, centrifugation, decanting, decanting centrifugation, settling, combinations thereof, among other techniques. Optionally, the first MOF, no longer complexed or coordinated with the first REE metal may be recycled or re-used. [0080] After operation 220, the first REE metal is present in the liquid phase. The first REE metal may be present as ions in the liquid phase. The liquid phase may still contain sufficient amounts of redox mediator, though an additional amount of redox mediator may be added to the liquid phase. Process 210 may further include applying a second electric field to the liquid phase. The electric field serves as a source of electrons. The application of the electric field at operation 222 raises the pH of the liquid phase at the cathode, causing precipitation of a solid (and water-insoluble) comprising the first REE metal. The solid comprising the first REE metal may be in the form of a complex such as a REE oxide, a REE hydroxide, a REE carbonate, a REE chloride, a REE phosphate, or other suitable complex. For example, the solid comprising the first REE metal may be recovered as hydroxide products. The solid comprising the first REE metal is different from the REE-MOF complex. Application of the second electric field at operation 222 may be performed in the same or similar manner as that performed at operation 218, with appropriate selection of the voltage. Suitable voltages and voltage ranges useful for operation 222 are described above with respect to operation 218.

[0081] The electrochemical precipitation of operation 222 results in the formation of another composition that includes a solid phase (which includes the solid comprising the first REE metal) and a liquid phase. The solid REE complex, e.g., the REE oxide, hydroxide, carbonate, chloride, phosphate, or other species may be isolated, separated, or otherwise recovered from the liquid phase at operation 224. Recovery of the solid REE complex at operation 224 may be performed by any suitable isolation or separation technique. Suitable techniques include solid-liquid separation techniques such as mechanical or gravity separation, such as filtration, vacuum filtration, centrifugation, decanting, decanting centrifugation, settling, combinations thereof, among other techniques. Optionally, the liquid phase may be recycled or re-used.

[0082] By utilizing embodiments described herein, REE metals may be recovered in an on-demand fashion which recycles the MOFs for later use and requires no additional net input of chemical reagents.

[0083] As described above, and after isolating the first water-insoluble REE-MOF complex, the liquid feedstock having a lower concentration of the first REE metal may be processed. Processing of this first REE metal-depleted feedstock may include repeating operations 212-224 to recover a second solid comprising a second REE metal, the second REE metal being different from the first REE metal. For example, a second MOF may be added to the feedstock having a lower concentration of the first REE metal to form a second water-insoluble REE-MOF complex comprising the second REE metal coordinated to, or complexed with, the second MOF. As described herein, the second MOF may be adapted or configured to selectively complex or coordinate the second REE metal. Following isolation (e.g., operation 214) and introduction with a redox mediator (e.g., operation 216), an electrochemical operation (e.g., operation 218) is performed to liberate the second REE metal from the second water-insoluble REE- MOF complex and precipitate the second MOF as a solid. Following isolation of the liquid phase (e.g., operation 220), the liquid phase containing the second REE metal is then subjected to another electrochemical operation to precipitate a second solid comprising the second REE metal.

[0084] Further processing of the aqueous feedstock may be used to selectively capture and release other REE metals by, for example, appropriate selection of MOFs.

[0085] Various process parameters may be utilized with embodiments described herein, including cell geometry, electrode material/geometry, oxygen sensitivity, current density, or combinations thereof, among others.

[0086] With respect to cell geometry, for example, anode and cathode compartments utilized for operation 218 and/or operation 222 may be separated. When separated, any suitable separator may utilized such as porous glass frits or fluorocarbon polymer such as Nafion solution.

[0087] With respect to electrode material/geometry, and at operation 218 and/or operation 222, the achievable current density and power input may be dictated by the size and kinetic properties of the electrodes employed. Here, a variety of form factors and electrode materials may be utilized. Example electrode materials may include carbon, platinum, or indium tin oxide (ITO). The electrode materials and form factors may be adjusted to determine, for example, an appropriate tradeoff between electrode cost and power input. [0088] With respect to oxygen sensitivity, one or more operations of process 200 and process 210 may be performed under an inert atmosphere such as nitrogen or argon. The use of an inert atmosphere may be used to remove dissolved oxygen species that can interfere with various operations.

[0089] With respect to the current density, the applied current density may be adjusted to, for example, prevent or at least mitigate undesirable side reactions.

[0090] Embodiments of the present disclosure also relate to a composition comprising a REE metal and a MOF organic framework. As used herein, a “composition” may include component(s) of the composition, reaction product(s) of two or more components of the composition, a remainder balance of remaining starting component(s), or combinations thereof.

[0091] The REE metal of the composition may be bonded to, e.g., coordinated to or complexed with, the MOF. The MOF of the composition may be any suitable MOF such as those described herein. For example, the MOF may include a plurality of organic subunits (tri azacoronene subunits) and a plurality of inorganic subunits. The inorganic subunit may include a Group 1-14 metal, such as a Group 3-13 metal of the periodic table of the elements. The MOF may include a hexagonal pore defined by a ring comprising any suitable number of organic subunits and any suitable number of inorganic subunits, such as six organic subunits and six inorganic subunits. The composition may be water-insoluble.

[0092] FIG. 2C and FIG. 2D are generalized schematic flow diagram illustrating various embodiments of processes described herein corresponding to operational areas or units in plants 230 and 250 for processing a REE metal-containing feedstock, respectively. Processes 200 and 210 may be performed in both of the plants. However, plant 230 and plant 250 are utilized for illustrative purposes only and are not intended to limit the scope of processes described herein such as processes 200 and 210. Embodiments and implementations of plant 230 and plant 250 may be combined with other embodiments described herein.

[0093] Plant 230 includes a stage 1 unit 232 and a stage 2 unit 234. The stage 1 unit 232 may include any suitable apparatus to form a REE-MOF complex and any suitable apparatus to perform electrochemistry to liberate the first REE metal into a liquid phase (for example, operations 212-220). The stage 2 unit 234 may include any suitable apparatus to perform electrochemistry on the liquid phase to precipitate a solid comprising the first REE metal (for example, operations 222-224).

[0094] An aqueous feedstock travels through line 231 and into the stage 1 unit 232. Because the aqueous feedstock includes a mixture of REE metals, a specific REE metal may be targeted by utilization of a specific MOF. At the stage 1 unit 232, a first MOF may be introduced with the aqueous feedstock to form a first water-insoluble REE- MOF complex. The first water-insoluble REE-MOF complex may be isolated and the liquid phase (aqueous feedstock comprising a lower concentration of the first REE metal) may exit the stage 1 unit 232 via line 238. The isolated first water-insoluble REE-MOF complex may be introduced with a redox mediator (in solution) to form an aqueous mixture. A first electric field is applied to the aqueous mixture to form a composition comprising a solid phase (comprising the first MOF) and a liquid phase comprising the first REE metal. A lowering in the pH of the aqueous mixture caused by application of the first electric field liberates the first REE metal (e.g., as ions) into the liquid phase from the water-insoluble REE-MOF complex. The liquid phase and the solid phase may be separated. Although not shown, the solid phase comprising the first MOF may be recycled and reused.

[0095] The liquid phase comprising the first REE metal exits the stage 1 unit 232 and travels via line 236 to the stage 2 unit 234. At the stage 2 unit, a second electric field is applied to the liquid phase comprising the first REE metal (e.g., as ions). Application of the second electric field causes precipitation of a solid comprising the first REE metal, which may be in the form of a complex such as REE oxide, a REE hydroxide, a REE carbonate, a REE chloride, a REE phosphate, or other suitable complex. The solid comprising the first REE metal may exit the stage 2 unit 234 via line 240. Line 242 may be utilized to recycle the redox mediator solution.

[0096] FIG. 2D shows a sequencing batch reactor design, plant 250, to isolate multiple REE metals from an aqueous feedstock. Plant 250 includes REE metal separation nodes 251a, 251b, and 251c (collectively, REE metal separation node 251). Each REE metal separation node is used to separate different REE metals from the aqueous feedstock. For example, REE metal separation node 251a may be utilized to separate Ce, REE metal separation node 251b may be utilized to separate Nd, and REE metal separation node 251c may be utilized to separate Dy.

[0097] Each REE metal separation node 251 includes a stage 1 unit — stage 1 unit 232a, stage 1 232b, and stage 1 232c, respectively (collectively, stage 1 unit 232). Each REE metal separation node 251 includes a stage 2 unit — stage 2 units 234a, 234b, and 234c, respectively (collectively, stage 1 unit 234). Each node further includes a line for carrying the aqueous feedstock between units — line 238a, line 238b, and line 238c (collectively, line 238). Each REE metal separation node 251 includes a line for carrying the liquid phase comprising the first REE from the stage 1 unit 232 to the stage 2 unit 234 — line 236a, line 236b, and line 236c (collectively, line 236). Each REE metal separation node 251 includes a line through which a solid comprising the individual REE metal exits the stage 2 unit 234 — line 240a, line 240b, and line 240c (collectively, line 240). Each REE metal separation node 251 includes a line 242 to carry the redox mediator solution from the stage 2 unit 234 to the stage 1 unit 232: line 242a, line 242b, and line 242c, collectively, line 242.

[0098] In this example, an aqueous feedstock (such as produced water) enters REE metal separation node 25 la for separating a specific REE metal. The aqueous feedstock contains more than one REE metal, and in this example, three or more REE metals. Here, a specific REE metal (such as cerium, Ce) is targeted/complexed with a specific MOF. For example, a first MOF is introduced with the aqueous feedstock at stage 1 unit 232a to form a water-insoluble Ce-MOF complex. The water-insoluble Ce-MOF complex may be isolated and the liquid phase (aqueous feedstock comprising a lower concentration of Ce metal) may exit the stage 1 unit 232a via line 238a. That is, the resulting aqueous feedstock minus the targeted REE metal — Ce metal in this example — is transferred to stage 1 unit 232b of REE metal separation node 251b where a second REE metal, for example, neodymium (Nd), may be separated.

[0099] At the stage 1 unit 232a, the isolated water-insoluble Ce-MOF complex may be introduced with a redox mediator such as Nab (in solution) to form an aqueous mixture. A first electric field is applied to the aqueous mixture to form a composition comprising a solid phase (comprising the first MOF) and a liquid phase comprising the Ce metal. A lowering in the pH of the aqueous mixture caused by application of the first electric field liberates the Ce metal (e.g., as ions) into the liquid phase from the water-insoluble Ce-MOF complex. The liquid phase and the solid phase may be separated. Although not shown, the solid phase comprising the first MOF may be recycled and reused.

[0100] The liquid phase comprising the Ce metal exits the stage 1 unit 232 and travels via line 236a to the stage 2 unit 234a. At the stage 2 unit 234a, a second electric field is applied to the liquid phase comprising the Ce metal (e.g., as ions). Application of the second electric field causes precipitation of a solid comprising the Ce metal, which may be in the form of a complex such as a Ce metal hydroxide, a Ce metal oxide, a Ce metal carbonate, a Ce metal chloride, a Ce metal phosphate, or other suitable complex. The solid comprising the Ce metal may exit the stage 2 unit 234a via line 240a. Line 242a may be utilized to recycle the redox mediator solution.

[0101] As described above, the aqueous feedstock minus the Ce metal travels to the REE metal separation node 251b where the Nd metal may be separated. Separation of the Nd metal and formation of the solid comprising the Nd metal at REE metal separation node 251b may be performed in a similar manner as separation of the Ce metal and formation of the solid comprising the Ce metal. Separation of the Nd metal at REE metal separation node 251b utilizes a second MOF that is different from the first MOF. The water-insoluble Nd-MOF complex may be isolated and the liquid phase (aqueous feedstock comprising a lower concentration of Ce metal and Nd metal) may exit the stage 1 unit 232b via line 238b. That is, the resulting aqueous feedstock minus the targeted REE metal — Ce metal and Nd metal in this example — is transferred, via line 238b, to stage 1 unit 232c of REE metal separation node 251c where a third REE metal, for example, dysprosium (Dy), may be separated. At REE metal separation node 25 lb, operations are also performed on the water-insoluble Nd-MOF complex to obtain a solid comprising the Nd metal (e.g., a Nd metal hydroxide) exiting the line 240b.

[0102] Separation of the Dy metal and formation of the solid comprising the Nd metal at REE metal separation node 251c may be performed in a similar manner as separation of the Ce metal and formation of the solid comprising the Ce metal. Separation of the Dy metal at REE metal separation node 251c utilizes a third MOF that is different from the first MOF and the second MOF. The water-insoluble Dy-MOF complex may be isolated and the liquid phase (aqueous feedstock comprising a lower concentration of Ce metal, Nd metal, and Dy metal) may exit the stage 1 unit 232c via line 238c. That is, the resulting aqueous feedstock minus the targeted REE metal — Ce metal, Nd metal, and Dy metal in this example — is transferred, via line 238c, to another stage 1 unit where another REE metal is separated. Accordingly, the process may continue to a subsequent batch reactor. Although plant 250 illustrates a separation of, for example, Ce metal, Nd metal, and/or Dy metal from a feedstock (produced water comprising REE metals), other REE metals can be separated by utilizing embodiments described herein.

[0103] Embodiments described herein can enable selective capture and release of various REE metals by utilizing MOFs and electrochemistry. Embodiments of the present disclosure enable REE metal extraction and separation from complex feedstocks comprising one or more REE metals.

[0104] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use embodiments of the present disclosure, and are not intended to limit the scope of embodiments of the present disclosure. Efforts have been made to ensure accuracy with respect to numbers used but some experimental errors and deviations should be accounted for.

Examples

[0105] Synthesis of example tri azacoronenes and MOFs that include triazacoronenes were performed. Processes for separating a REE metal were also performed.

[0106] Example tri azacoronene: Triazacoronene S20 was formed from a triphenylene amine of formula (II) (wherein R¹⁼0Me) and 4-pyridinecarboxaldehyde.

[0107] Example MOF: MOF S21 was formed from reaction of ZnBrc with a tri azacoronene of formula (I) where R¹⁼OMe and R²=H.

[0108] MOF S21 is a water insoluble MOF. MOF S21 was characterized by powder X-ray diffraction (pXRD), with the pXRD shown in FIG. 3. The XRD indicates that MOFs described herein may be formed using triazacoronenes.

Example Electrochemical Recovery of REE metals from REE-MOFs

[0109] This example describes the electrochemical methods utilized to release REE metals from REE-MOFs. For this example, a MOF is designed to complex Ce metal from an aqueous feedstock. The MOF has functional groups (e.g., R¹ and/or R²) that exhibit Bronsted-Lowry acid-base behavior.

[0110] For a trivalent REE metal species, complexation by the MOF (e.g., operation 212) may be described according to the following equilibrium described in Equation 1 :

wherein: represents an REE metal in solution (Ln = lanthanide); and H_nAⁿ~⁶ represents the node structure with the specified degree of protonation.

[OHl] Due to its Bronsted-Lowry behavior, the availability of suitable MOF species depends on the pH of the solution. One factor is the equilibrium between HAf ~

and H₂A^~_q) species described in Equation 2:

[0112] Considering these reactions, the concentration of free

species may be expected to follow Equation 3 :

wherein: FA is the formal (total) concentration of MOF species (or functional group thereof) present in solution. Inspection of Equation 3 reveals that [Ln³⁺] reaches a minimum at pH = pK_a and increases at higher or lower pH values.

[0113] Accordingly, and as described herein, the inventors utilize an electrochemical reaction scheme to exploit this pH dependence of REE-MOF formation to liberate REE metals and recycle MOFs for further use. After recovery, the waterinsoluble REE-MOF products are introduced into an aqueous solution containing Nab or other suitable sacrificial oxidant.

[0114] Electrolysis (via, for example, operation 218) is then carried out to lower the pH of the solution according to Equations 4-6:

(Eq. 6) wherein: SHE refers to standard hydrogen electrode and E° refers to standard electrode potential.

[0115] The pH drop resulting from this reaction scheme can result in (a) the liberation of free Ln³⁺ ions and (b) the precipitation of MOF species as solid products (for example, MOF species comprising neutral tri azacoronene molecules or their sodium salts). This can be described via Equation 7:

[0116] After removal of the solid MOF species, REE metals are recovered as, for example, hydroxide products through a similar electrochemical scheme (e.g., operation 222 and 224). The reactions involved include those described in Equations 8-10:

[0117] Due to the resulting pH increase, REE species are precipitated due to hydroxide formation according to Equation 11 :

[0118] Considering these steps together, the overall electrochemical change to the system is water-splitting as shown in Equation 12:

[0119] Referring back to the redox mediator (Nah, or h/E), a purpose of the redox mediator species is to allow the reaction to occur in successive steps (note that the overall cell voltage is thermodynamically consistent with water splitting and just the sum of the voltages required for each step).

[0120] By forcing this process to occur stepwise as described herein, bulk pH changes are induced that separate the REE-MOF structures shown in Equation 13:

wherein: H⁺ is added and H₆A is collected in stage 1 unit 232; and OH~ and Ln(0H)₃(_s) is collected in stage 2 unit 234.

[0121] Using this approach as described by embodiments of the present disclosure, REE metals may be recovered from the REE-MOFs in an on-demand fashion which recycles MOFs for later use and involves no additional net input of chemical reagents.

[0122] This REE metal (Ln) liberation process is illustrated graphically in FIGS. 4 A and 4B. Specifically, FIG. 4 A shows free Ln³⁺ concentration in solutions of varying pH in the presence of 1 M MOF species with varying Kf values. Here, the key pKa differentiating H2A⁴ and HA⁵ species is taken to be 4. A decrease in pH increases the free Ln³⁺ concentration, liberating REE metals from the MOF structure. FIG. 4B shows free Ln³⁺ concentration (1 mM initial concentration) as a function of different pH values calculated according to literature K_sp (solubility product constant) values for Ln(OH)3 species. Curves for the entire Lanthanide (Ln) series are shown with lanthanum (La) and lutetium (Lu) labeled. Here, an increase in the pH can result in precipitation of solid Ln(OH)3 products. [0123] In the stage 1 unit 232, water oxidation at the anode results in lowering of the solution pH and dissolution of the REE-MOF structure. The resulting increase in free Ln³⁺ concentration is illustrated in FIG. 4A. While both increasing or decreasing the solution pH can disrupt the REE-MOF structure, decreasing the pH may be utilized to completely dissociate REE metals from the MOF species and precipitate the node precursors for later use.

[0124] In the stage 2 unit 234, H⁺ reduction (or more accurately described as H2O reduction at higher pH values) can raise the solution pH, ultimately resulting in precipitation of REE metals as hydroxide products, or other solid REE metal products. This is illustrated in FIG. 4B. It is noted that both stage 1 unit 232 and the stage 2 unit 234 in the liberation process may provide an additional opportunity for REE metal separation if, for example, the input REE-MOF contains a mixture of REE metals. As shown in FIGS. 4A and 4B, the pH utilized to drive each stage of this process is dictated by equilibrium constants which vary for each REE employed: proportionality constant (Kf) values describing REE-MOF formation in the stage 1 unit 232 and K_sp values describing hydroxide salt formation in the stage 2 unit 234. Such capabilities may be utilized to help ensure the overall REE metal separation processes described herein is successful when, for example, selectivity is difficult to achieve through MOF formation alone.

Example REE metal separation

[0125] FIG. 5A shows a bench-scale set-up for processes described herein to liberate and recover REE metals. Specifically, FIG. 5A shows a separated electrochemical cell containing an electrochemical cell containing an I2/I electrolyte (redox mediator) in the cathode chamber and an inert potassium nitrate (KNO3) electrolyte in the anode chamber. Solid MOF is added to the anode chamber. Prior to hydrolysis, the color of the redox mediator was a dark yellow while the KNO3 electrolyte solution is clear. After hydrolysis the solid product (REE-MOF) is dissolved due to the lowered pH in the anode chamber and the color of the electrolyte changed from clear to yellow (not shown) following the electrolysis. This indicated that the electrolysis liberated and released the REE metals. [0126] FIG. 5B shows an overlay of Ultraviolet-visible (UV-Vis) spectra comparing the absorption of the resulting electrolyte to a similar solution prepared by dissolution with hydrochloric acid (HC1). The spectra are identical except from the slight differences in the background absorption due to the presence of nitrate ion (NCb ) in the electrolyte. The apparatus shown in FIG. 5 A was used to produce solid Ln(OH)3 products prepared by embodiments described herein such as solid neodymium(III) hydroxide (Nd(OH)3) products, solid cerium(III) hydroxide (Ce(OH)3) products, and solid yttrium(III) hydroxide (Y(0H)3) products prepared according to embodiments of the present disclosure. Overall, FIGS. 5A-5B indicate that embodiments described herein may be utilized to selectively separate REE metals from feedstocks. That is, REE catch and release processes described herein enable successful REE extraction and separation from complex mixtures.

Embodiments Listing

[0127] The present disclosure provides, among others, the following embodiments, each of which can be considered as optionally including any alternate embodiments:

[0128] Clause 1. A REE metal separation process, comprising:

(a) providing an aqueous feedstock comprising one or more REE metals, at least one of the one or more REE metals is in the form of a first REE complex comprising a first REE metal coordinated to a first anion; and

(b) contacting the aqueous feedstock comprising with a metal organic framework (MOF) under conditions effective to form a mixture comprising a second REE complex comprising: the first REE metal coordinated to the MOF, the first anion and the MOF being different.

[0129] Clause 2. The process of Clause 1, wherein a concentration of the MOF in the mixture formed in (b) is from about 0.001 M to about 10 M.

[0130] Clause 3. The process of any one of Clause 1 or Clause 2, wherein: the aqueous feedstock comprises a second REE metal different from the first REE metal; and the MOF is adapted to selectively complex the first REE metal over the second REE metal. [0131] Clause 4. The process of any one of Clauses 1-3, wherein the aqueous feedstock comprises produced water, slurried coal, coal mine tailings, or combinations thereof.

[0132] Clause 5. The process of any one of Clauses 1-3, wherein the MOF comprises a plurality of inorganic subunits and a plurality of triazacoronene subunits.

[0133] Clause 6. The process of any one of Clauses 1-3, wherein the MOF comprises at least one hexagonal pore comprising six tri azacoronene units.

[0134] Clause 7. The process of Clause 6, wherein each triazacoronene unit of the hexagonal pore is coupled to another triazacoronene unit of the at least one hexagonal pore by a Group 1-14 metal of the periodic table of the elements, such as a Group 3-13 metal.

[0135] Clause 8. The process of any one of Clause 6 or Clause 7, wherein each tri azacoronene subunit is represented by formula (IA) or formula (IB):

wherein, in formula (IA) and formula (IB): each R¹ is, independently, hydrogen, an unsubstituted hydrocarbyl, a substituted hydrocarbyl, or a functional group comprising at least one element from Group 13-17 of the periodic table of the elements; each R² is, independently, hydrogen, an unsubstituted hydrocarbyl, a substituted hydrocarbyl, or a functional group comprising at least one element from Group 13-17 of the periodic table of the elements; X is CH or N; y is the number of R² groups, and when y is greater than 1, R² on an individual aromatic ring can be the same or different; and the wavy bonds represent a connection to an inorganic subunit of the MOF.

[0136] Clause 9. The process of Clause 8, wherein: at least one R² of formula (IA) or formula (IB) is hydroxyl (-OH), alkoxyl (-OR*), halogen (F, Cl, Br, or I), carboxyl (-CO2H), amine (-NH2), alkylamine (- NR*₂), nitro (-NO2), ester (-C(O)R*), phosphoryl (-P(O)(OR*)2), sulfonyl (-SO3R*), or amide (-C(O)NHR*), wherein R* is a hydrogen, a C1-C20 unsubstituted hydrocarbyl, or a C1-C20 substituted hydrocarbyl; and each R² of formula (IA) or formula (IB) being the same or different.

[0137] Clause 10. The process of any one of Clause 8 or Clause 9, wherein at least one R² of formula (IA) or formula (IB) is selected from hydroxyl, alkoxyl, halogen, carboxyl, amide, phosphoryl, or sulfonyl.

[0138] Clause 11. The process of any one of Clauses 8-10, wherein X of formula (I A) or formula (IB) is N.

[0139] Clause 12. The process of any one of Clauses 8-11, wherein: at least one R¹ of formula (IA) or formula (IB) is an ionizable functional group; or at least one R¹ of formula (IA) or formula (IB) is a functional group that alters the at least one hexagonal pore, the functional group selected from the group consisting of a neutral species, a positively charged species, a negatively charged species, or combinations thereof.

[0140] Clause 13. The process of any one of Clauses 8-128, wherein: at least one R¹ of formula (IA) or formula (IB) is an alkoxy (-OR*) group, wherein R* is a C1-C20 unsubstituted hydrocarbyl or a C1-C20 substituted hydrocarbyl; and when more than one R¹ of formula (IA) or formula (IB) is -OR*, each R* is the same or different.

[0141] Clause 14. The process of any one of Clauses 8-13, wherein at least one R¹ of Formula (III) is a methoxy (-OMe) group.

[0142] Clause 15. The process of any one of Clauses 8-14, wherein: at least one R¹ of formula (IA) or formula (IB) is a Ci-Ce alkyl, Ci-Ce ester, or Ci-Ce amide; and when more than R¹ of formula (IA) or formula (IB) is present, each R¹ is the same or different. [0143] Clause 16. A process for separating one or more REE metals from a mixture, the process comprising:

(a) forming a first aqueous mixture comprising one or more REE metals and a first metal organic framework (MOF), at least one REE of the one or more REE metals is in the form of a first water-insoluble REE-MOF complex comprising a first REE metal and a first metal organic framework (MOF);

(b) isolating the first water-insoluble REE-MOF complex from the first aqueous mixture;

(c) forming a second aqueous mixture comprising the first water-insoluble REE-MOF complex isolated and a redox mediator; and

(d) applying a first electric field to the second aqueous mixture to form a composition comprising: a solid phase comprising the first MOF; and a liquid phase comprising the first REE metal.

[0144] Clause 17. The process of Clause 16, wherein the applying the first electric field to the second aqueous mixture comprises applying a bias voltage between conducting electrodes immersed in the second aqueous mixture.

[0145] Clause 18. The process of any one of Clause 16 or Clause 17, wherein the first electric field that is applied to the second aqueous mixture is from about -10 V to about +10 V.

[0146] Clause 19. The process of any one of Clauses 16-18, wherein the first MOF is adapted to selectively complex the first REE metal.

[0147] Clause 20. The process of any one of Clauses 16-19, further comprising: isolating the solid phase from the composition; and isolating the liquid phase from the composition.

[0148] Clause 21. The process of Clause 20, wherein, after the isolating the liquid phase from the composition, the process further comprises applying a second electric field to the liquid phase to precipitate a first water-insoluble complex comprising the first REE metal, the first water-insoluble complex different from the first waterinsoluble REE-MOF complex.

[0149] Clause 22. The process of Clause 21, wherein, after the (b) isolating the first water-insoluble REE-MOF complex from the aqueous mixture, the process further comprises: introducing a second MOF to the first aqueous mixture having a lower concentration of the first REE metal to form a second water-insoluble REE-MOF complex comprising: a second REE metal coordinated to the second MOF, wherein the second REE metal is different from the first REE metal, and wherein the second MOF is different from the first MOF.

[0150] Clause 23. The process of Clause 22, further comprising: performing operations on the second water-insoluble REE-MOF complex to remove the second MOF from the second water-insoluble REE-MOF complex, and to precipitate a second water-insoluble complex comprising the second REE metal, the second water-insoluble complex different from the second water-insoluble REE-MOF complex.

[0151] Clause 24. A process, comprising:

(a) introducing a first metal organic framework (MOF), as a solid, to an aqueous feedstock comprising one or more REE metals to form a first water-insoluble REE-MOF complex comprising a first REE metal coordinated to the first metal organic framework;

(b) isolating the first water-insoluble REE-MOF complex;

(c) forming an aqueous mixture comprising the first water-insoluble REE- MOF complex isolated and a redox mediator;

(d) applying a first electric field to the aqueous mixture to form a composition comprising: a solid phase comprising the first MOF; and a liquid phase comprising the first REE metal;

(e) isolating the liquid phase from the composition;

(f) applying a second electric field to the liquid phase to precipitate a solid comprising the first REE metal; and

(g) recovering the solid comprising the first REE metal from the liquid phase.

[0152] Clause 25. The process of Clause 24, wherein the liquid phase is recycled back to the aqueous feedstock.

[0153] Clause 26. The process of any one of Clause 24 or Clause 25, wherein: the aqueous feedstock comprises a second REE metal; and after recovering the solid comprising the first REE metal, the process further comprises:

(h) introducing a second MOF, as a solid, to the aqueous feedstock having a lower concentration of the first REE metal to form a second water-insoluble REE-MOF complex; and

(i) repeating operations (a)-(g) to recover a solid comprising the second REE metal, wherein: the second REE metal is different from the first REE metal; and the second MOF is different from the first MOF.

[0154] Clause 27. The process of any one of Clauses 24-26, wherein: the (d) applying the first electric field results in decreasing the pH of the aqueous mixture, dissolution of the first water-insoluble REE-MOF complex, and liberation of the first REE metal; and the (f) applying the second electric field results in increasing the pH of the liquid phase and the precipitation of the solid comprising the first REE metal.

[0155] Clause 28. The process of any one of Clauses 24-27, wherein: the first electric field that is applied to the aqueous mixture is from about -10 V to about +10 V; and/or the second electric field that is applied to the liquid phase is from about -10 V to about +10 V.

[0156] Clause 29. A composition, comprising: a REE metal; and a MOF coordinated to or complexed with the REE metal, the MOF comprising: a plurality of triazacoronene subunits, each triazacoronene subunit coupled to another triazacoronene subunit by a Group 1-14 metal of the periodic table of the elements.

[0157] Clause 30. The composition of Clause 29, wherein the MOF is represented by the MOF recited in any one of Clauses 5-15.

[0158] Clause 31. The composition of any one of Clause 29 or Clause 30, wherein the composition is water-insoluble.

[0159] Clause 32. The composition of any one of Clauses 29-31, wherein the MOF comprises at least one hexagonal pore defined by a ring comprising six triazacoronene subunits.

[0160] In the foregoing, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the disclosure. Furthermore, although embodiments of the disclosure may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the disclosure. Thus, the foregoing aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the disclosure” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).

[0161] As is apparent from the foregoing general description and the specific aspects, while forms of the aspects have been illustrated and described, various modifications can be made without departing from the spirit and scope of the present disclosure. Accordingly, it is not intended that the present disclosure be limited thereby. Likewise, the term “comprising” is considered synonymous with the term “including.” Likewise whenever a composition, an element or a group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “Is” preceding the recitation of the composition, element, or elements and vice versa, such as the terms “comprising,” “consisting essentially of,” “consisting of’ also include the product of the combinations of elements listed after the term.

[0162] References cited herein are incorporated by reference herein in their entirety to indicate the state of the art as of their publication or filing date and it is intended that this information can be employed herein, if needed, to exclude specific embodiments that are in the prior art.

[0163] For purposes of this present disclosure, and unless otherwise specified, all numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and consider experimental error and variations that would be expected by a person having ordinary skill in the art. For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. For example, the recitation of the numerical range 1 to 5 includes the subranges 1 to 4, 1.5 to 4.5, 1 to 2, among other subranges. As another example, the recitation of the numerical ranges 1 to 5, such as 2 to 4, includes the subranges 1 to 4 and 2 to 5, among other subranges. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. For example, the recitation of the numerical range 1 to 5 includes the numbers 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, among other numbers. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

[0164] As used herein, reference to an R group (for example, R¹, R², and R*, or other R group), alkyl, substituted alkyl, hydrocarbyl, substituted hydrocarbyl, aromatic, or compound name, etc. without specifying a particular isomer (such as butyl) expressly discloses all isomers (such as n-butyl, iso-butyl, sec-butyl, and tert-butyl). For example, reference to an R group having 3 or more carbon atoms expressly discloses all isomers thereof. When a compound is described herein such that a particular isomer, enantiomer or diastereomer of the compound is not specified, for example, in a formula or in a chemical name, that description is intended to include each isomer and enantiomer of the compound described individual or in any combination.

[0165] As used herein, the indefinite article “a” or “an” shall mean “at least one” unless specified to the contrary or the context clearly indicates otherwise. For example, embodiments comprising “a metal organic framework” include embodiments comprising one, two, or more metal organic frameworks, unless specified to the contrary or the context clearly indicates only one metal organic framework is included.

[0166] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

Claims What is claimed is:

1. A REE metal separation process, comprising:

(a) providing an aqueous feedstock comprising one or more REE metals, at least one of the one or more REE metals is in the form of a first REE complex comprising a first REE metal coordinated to a first anion; and

(b) contacting the aqueous feedstock comprising with a metal organic framework (MOF) under conditions effective to form a mixture comprising a second REE complex comprising: the first REE metal coordinated to the MOF, the first anion and the MOF being different.

2. The process of claim 1, wherein a concentration of the MOF in the mixture formed in (b) is from about 0.001 M to about 10 M.

3. The process of claim 1, wherein: the aqueous feedstock comprises a second REE metal different from the first REE metal; and the MOF is adapted to selectively complex the first REE metal over the second REE metal.

4. The process of claim 1, wherein the aqueous feedstock comprises produced water, slurried coal, coal mine tailings, or combinations thereof.

5. The process of claim 1, wherein the MOF comprises a plurality of inorganic subunits and a plurality of tri azacoronene subunits.

6. The process of claim 1, wherein the MOF comprises at least one hexagonal pore comprising six triazacoronene units.

7. The process of claim 6, wherein each triazacoronene unit of the hexagonal pore is coupled to another triazacoronene unit of the at least one hexagonal pore by a Group 1-14 metal of the periodic table of the elements.

8. The process of claim 6, wherein each triazacoronene subunit is represented by formula (IA) or formula (IB):

(IB), wherein, in formula (IA) and formula (IB): each R¹ is, independently, hydrogen, an unsubstituted hydrocarbyl, a substituted hydrocarbyl, or a functional group comprising at least one element from Group 13-17 of the periodic table of the elements; each R² is, independently, hydrogen, an unsubstituted hydrocarbyl, a substituted hydrocarbyl, or a functional group comprising at least one element from Group 13-17 of the periodic table of the elements;

X is CH or N; y is the number of R² groups, and when y is greater than 1, R² on an individual aromatic ring can be the same or different; and the wavy bonds represent a connection to an inorganic subunit of the MOF.

9. The process of claim 8, wherein: at least one R² of formula (IA) or formula (IB) is hydroxyl (-OH), alkoxyl (- OR*), halogen (F, Cl, Br, or I), carboxyl (-CO2H), amine (-NH2), alkylamine (-NR*2), nitro (-NO2), ester (-C(O)R*), phosphoryl (-P(0)(0R*)2), sulfonyl (-SO3R*), or amide (-C(O)NHR*), wherein R* is a hydrogen, a C1-C20 unsubstituted hydrocarbyl, or a C1-C20 substituted hydrocarbyl; and each R² of formula (IA) or formula (IB) being the same or different.

10. The process of claim 8, wherein at least one R² of formula (IA) or formula (IB) is selected from hydroxyl, alkoxyl, halogen, carboxyl, amide, phosphoryl, or sulfonyl.

11. The process of claim 8, wherein X of formula (IA) or formula (IB) is N.

12. The process of claim 8, wherein: at least one R¹ of formula (IA) or formula (IB) is an alkoxy (-OR*) group, wherein R* is a C1-C20 unsubstituted hydrocarbyl or a C1-C20 substituted hydrocarbyl; and when more than one R¹ of formula (IA) or formula (IB) is -OR*, each R* is the same or different.

13. The process of claim 8, wherein: at least one R¹ of formula (IA) or formula (IB) is a Ci-Ce alkyl, Ci-Ce ester, or Ci-Ce amide; and when more than R¹ of formula (IA) or formula (IB) is present, each R¹ is the same or different.

14. A process, comprising:

(a) introducing a first metal organic framework (MOF), as a solid, to an aqueous feedstock comprising one or more REE metals to form a first water-insoluble REE- MOF complex comprising a first REE metal coordinated to the first metal organic framework;

(b) isolating the first water-insoluble REE-MOF complex;

(c) forming an aqueous mixture comprising the first water-insoluble REE-MOF complex isolated and a redox mediator;

(d) applying a first electric field to the aqueous mixture to form a composition comprising: a solid phase comprising the first MOF; and a liquid phase comprising the first REE metal;

(e) isolating the liquid phase from the composition;

(f) applying a second electric field to the liquid phase to precipitate a solid comprising the first REE metal; and

(g) recovering the solid comprising the first REE metal from the liquid phase.

15. The process of claim 14, wherein the liquid phase is recycled back to the aqueous feedstock.

16. The process of claim 14, wherein: the aqueous feedstock comprises a second REE metal; and after recovering the solid comprising the first REE metal, the process further comprises:

(h) introducing a second MOF, as a solid, to the aqueous feedstock having a lower concentration of the first REE metal to form a second water-insoluble REE-MOF complex; and

(i) repeating operations (a)-(g) to recover a solid comprising the second REE metal, wherein: the second REE metal is different from the first REE metal; and the second MOF is different from the first MOF.

17. The process of claim 14, wherein: the (d) applying the first electric field results in decreasing the pH of the aqueous mixture, dissolution of the first water-insoluble REE-MOF complex, and liberation of the first REE metal; and the (f) applying the second electric field results in increasing the pH of the liquid phase and the precipitation of the solid comprising the first REE metal.

18. The process of claim 14, wherein: the first electric field that is applied to the aqueous mixture is from about -10 V to about +10 V; and the second electric field that is applied to the liquid phase is from about -10 V to about +10 V.

19. A water-insoluble composition, comprising: a REE metal; and a MOF coordinated to or complexed with the REE metal, the MOF comprising: a plurality of tri azacoronene subunits, each triazacoronene subunit coupled to another tri azacoronene subunit by a Group 1-14 metal of the periodic table of the elements.

20. The composition of claim 19, wherein the MOF comprises at least one hexagonal pore defined by a ring comprising six triazacoronene subunits.