CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No, 62/296,728, filed Februar - 18, 2016, which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Coal fly ash is generated during the process of coal combustion and is comprised of fine particles that are transported from the boiler with the flue gas. Coal fly ash contains several valuable metals such as germanium and rare earth elements (REE). In die United States 50-80 million tons of coal fly ash is produced annually by- several hundred coal-fired power plants. Less than one-half of this coal fly ash is beneficially used; the remainder is stored in wet environments to produce pond coal fly- ash or in dry landfills.

[0003] Accordingly, there is a need for compositions, methods and systems that can leach and extract the valuable metals from coal fly ash, such as pond coal fly ash. Such a composition, method and system are disclosed herein.

SUMMARY

[0004] Disclosed herein is a method comprising the steps of: a) mixing a first pond coal fly ash and a first ionic liquid, thereby leaching germanium from the first pond coal fly ash and producing a second pond coal fly ash and a first mixture comprising the first ionic liquid and the leached germanium; b) separating the first mixture from the second pond coai fly ash; and c) mixing a first brine with the second pond coal fly ash, thereby leaching iron and one or more rare earth elements from the second pond coal fly ash and producing a third pond coal fly ash and a second mixture comprising the first brine and the leached iron and one or more rare earth elements.

[0Θ05] Also disclosed herein is a composition comprising a first pond coal fly ash and a first ionic liquid. In one aspect, the first composition further comprises germanium. [0006] Also disclosed herein is a composition comprising a second pond coal fly ash and a first brine.

[00Θ7] Also disclosed herein is a composition comprising a second ionic liquid and a second mixture comprising a first brine and one or more rare earth elements.

[0008] Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

DETAILED DESCRIPTION OF THE FIGURES

[0009] These and other features of the preferred embodiments of the invention will become more apparent in the detailed description in which reference is made to the appended drawings wherein:

[0010] FIG. 1 shows a flow diagram of a method disclosed herein using conventional materials for leaching an extraction of Ge and REE.

[0011] FIG. 2 shows a flow diagram of a method disclosed herein using ionic liquids and a waste water treatment brine for leaching an extraction of Ge and REE.

[0012] FIG. 3 shows results of Cd leaching.

[0013] FIG. 4 shows results of Ba leaching.

[0014] FIG. 5 shows a flow diagram, of a disclosed integrated method herein.

DETAILED DESCRIPTION

[0015] The present invention can be understood more readily by reference to the following detailed description, examples, drawings, and claims, and their previous and following description. However, before the present devices, systems, and/or methods are disclosed and described, it is to be understood that tins invention is not limited to the specific devices, systems, and/or methods disclosed unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. [0016] The following description of the invention is provided as an enabling teaching of the invention in its best, currently known embodiment. To tins end, those skilled in the relevant art will recognize and appreciate that many changes can be made to the various aspects of the invention described herein, while still obtaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits of the present invention can be obtained by selecting some of the features of the present invention without utilizing other features. Accordingly, those who work in the art will recognize that many modifications and adaptations to the present invention are possible and can even be desirable in certain circumstances and are a part of the present invention. Thus, the following description is provided as illustrative of the principles of the present invention and not in limitation thereof.

[0017] It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

Although any devices and methods similar or equivalent to those described herein can be used in the practice or testing of the present invention, example methods and materials are now described.

[0018] As used in the specification and in the claims, the term "comprising" can include the aspects "consisting of" and ' ^" consisting essentially of." Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In this specification and in the claims, which follow, reference will be made to a number of terms which shall be defined herein.

[0019] As used in the specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a subject" includes two or more subjects.

[0020] As used herein, the terms "about" and "at or about" mean that the amount or value in question can be the value designated some other value approximately or about the same. It is generally understood, as used herein, that it is the nominal value indicated ±10% variation unless otherwise indicated or inferred. The term is intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art.

|0021] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as "about" that particular value in addition to the value itself. For example, if the value "10" is disclosed, then "about 10" is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[0022] The term "pond coal fly ash," as used herein, refers to coal fly ash that has been wet disposed, for example, been wet disposed in a pond, a so called ash pond. The coal fly ash is typically transported as a wet coal fly ash slurry from the collection point, for example a coal plant, to an ash pond where it is disposed. The coal fly ash in the slurry settles out and deposits at the bottom of the ash pond. The water in the pond can either: (a) be treated and disposed, (b) be evaporated over time, and/or (c) be infiltrated into the ground. In some cases, transport water in the wet coal fly ash slurry can be flue gas desulfurization wastewater. Pond coal fly ash has a decrease in crystallinity and an increase in the amorphous phase as compared to coal fly ash. This reduction in crystallinity provides for an increase in the ability to leach metals, such as germanium and REE, from the pond coal fly ash. The composition and method disclosed herein provide means to leach metals, such as germanium and REE, from pond coal fly ash. In one aspect, the pond coal fly ash has been wet disposed for at least 1 y ear before the composition and method disclosed herein are used and/or performed on the pond coal fly ash . In one aspect, the pond coal fly ash has been wet disposed from 1 year to 50 years before the composition and method disclosed herein are used and/or performed on the pond coal fly ash. Pond coal fly ash and weathered coal fly ash are used inte changeably herein. [0023] The terms "first," "first pond coal fly ash," "second," "second pond coal fly ash," "third," "third pond coal fly ash," and the like, where used herein, do not denote any order, quantity, or importance, and are used to distinguish one element from another, unless specifically stated otherwise.

|0024] Moreover, it is to be understood that unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; and the number or type of aspects described in the specification.

1. Method, Composition, and System

[0025] Bituminous coals contain roughly 10% ash content on a dry basis.

Combustion of bituminous coal produces bottom ash (-20% of total) and Class F fly ash (-80% of total). Bottom ash is removed from the bottom of the boiler. Coal fly ash is captured by particulate control devices such as electrostatic precipitators or bag houses. Coal fly ash is conveyed from the particulate control device in wet or diy form depending on the plant configuration. The ash can be sold directly to fly ash marketers for use in commercial applications such as a cement or concrete additive; -30-50% of coal fly ash produced in the United States is used commercially. If not used commercially, the ash is conveyed to a wet ash pond or dry landfill storage area which can be onsite or offsite depending on the plant configuration. A portion of the ash produced annually eventually becomes pond coal fly ash, which is stored in ash ponds.

[0026] Disclosed herein are compositions and methods for leaching and selectively extracting Ge and REE from pond coal fly ash. The distribution of these elements across silicate and non-silicate phases differs. Also, the silicate/non-silicate metal distribution has significant impact on the ability to leach metals from pond coal fly ash. Elements strongly associated with the silicate phase typically leach less than elements associated with the non-silicate phase. Elements in the silicate are typically more difficult for leachants to access because of the low solubility of the silicate phase itself. Pond coal fly ash contains a higher non-silicate phase as compared to fresh coal fly ash.

|0Θ27] Germanium is not associated with the silicate phase of coal fly ash (Querol, X., J. et al. Fuel, 1995. 74(3): p. 331-343). Researchers have suggested that Ge is associated with sphalerite, a metal consisting of Zn, Fe, and S (Querol, X., J. et al. Fuel, 1995. 74(3): p. 331-343). Researchers also suggest that the dominant chemical forms of Ge in coal fly ash are GeS, GeS ₂ , and GeC (Querol, X., J. et al. Fuel, 1995. 74(3): p. 331-343; Reynolds, J.E. and E.L. Coltrinari, Chloride Leach Process for Recovering Metal Values in the Presence of Arsenic. 1981, Hazen Research, Inc.; Hernandez- Exposito, A., et al, Chemical Engineering Journal, 2006. 118(1-2): p. 69-75;

Chimenos, J.M., et al., Fuel, 2013. 112: p. 450-458.). Coal fly ash produced from an integrated gasification and combined cycle (IGCC) plant in Spain contained high levels of soluble GeS ₂ and Ge0 ₂ (Querol, X., J. et al. Fuel, 1995. 74(3): p. 331 -343; Reynolds, J.E. and E.L. Coltrinari, Chloride Leach Process for Recovering Metal Values in the Presence of Arsenic. 1981, Hazen Research, Inc.; Hernandez-Exposito, A., et al., Chemical Engineering Journal, 2006, 118(1-2): p. 69-75; Chimenos, J.M., et al, Fuel, 2013. 112: p. 450-458.). Other classes of coal fly ash, such as class F fly ash, do not contain equally high levels of soluble forms of Ge as compared with the IGCC ash from Spain. However, it is evident that Ge in class F fly ash will be more mobile than elements heavily associated with the glassy silicate phase.

[0028] In one aspect, the pond coal fly ash disclosed herein is derived from class F fly ash.

|0029] All REEs behave similarly during the combustion process due to minimal differences in their properties. REEs are non-volatile elements and are strongly associated with the glassy silicate phase in newly produced (fresh) coal fly ash (Franus, W., et al., Environmental Science and Pollution Research, 2015. 22(12): p. 9464-9474; Hower, J.C., et al., Coal Combustion and Gasification Products, 2013. 5: p. 73-78). REEs are also homogenously distributed throughout the silicate phase of newly produced coal fly ash (Hower, J.C., et al, Coal Combustion and Gasification Products, 2013. 5: p. 73-78). Accordingly, the entire glassy silicate phase must be leached in order to recover 100% of the REEs present in fresh coal fly ash (Hower, J.C., et al.. Coal Combustion and Gasification Products, 2013. 5: p. 73-78). [0030] Weathering of coal fly ash, i.e. the process of producing pond fly coal ash, impacts the distribution of metals in coal fly ash and their leachmg properties.

Weathering produces physical, chemical, and metal ogical changes in coal fly ash produced from Victorian brown coal through hydration, carbonation, and dissolution (Hosseini, T., et al., Hydrometallurgv, 2015. 157: p. 22-32 ). These secondary reactions change the characteristics of coal fly ash, which are the properties found in pond coal fly ash. These changes include an increased presence of amorphous species, hydrated compounds, and carbonates. The amorphous species in coal fly ash increased from 3.75% by weight in fresh coal fly ash to 62.1% for the weathered coal fly ash (i.e. pond coal fly ash) (Hosseini, T., et al., Hydrometallurgv, 2015. 157: p. 22-32 ). Crystalline metals (including silicates) are converted to amorphous states through the weathering process. The crystalline quartz concentration in pond coal fly ash is insignificant. Accordingly, essentially all of the silicate in the pond fly coal ash is amorphous, which allows for REE to be leached from the pond fly coal ash.

[0031] As such, REEs can be leached from pond fly coal ash at higher efficiency than from fresh coal fly ash (Hosseini, T., et al., Hydrometallurgy, 2015. 157: p. 22- 32). It is believed that the conversion of the crystalline metals to amorphous states resulted in higher leaching efficiency. Hie amorphous metals are easier to break down compared to the highly crystalline metals. The conversion of crystalline silicate metals to amorphous silicate can aid in the breakdown of the silicate phase to mobilize REEs in the disclosed composition and method.

[0032] FIG. 1 shows an approach to recovering Ge and REEs, which requires the use of acids and organic solvents. FIG. 2 shows a non-limiting aspect of the disclosed method and composition for extracting Ge and leaching REEs from pond coal fly ash. The disclosed composition and method, in one aspect, do not involve the use of organic solvents or acids. Instead ionic liquids and high ionic strength brine concentrates, such as a flue gas desulfurization brine produced in a waste water treatment processes to remove sulfur from a flue gas, are used.

[0033] Disclosed herein is a method comprising the steps of: a) mixing a first pond coal fly ash and a first ionic liquid, thereby leaching germanium from the first pond coal fly ash and producing a second pond coal fly ash and a first mixture comprising the first ionic liquid and the leached germanium; b) separating the fi rst mixture from the second pond coal fly ash; and c) mixing a first brine with the second pond coal fly ash, thereby leaching iron and one or more rare earth elements from the second pond coal fly ash and producing a third pond coal fly ash and a second mixture comprising the first brine and the leached iron and one or more rare earth elements,

|0Θ34] Accordingly, also disclosed herein is a composition comprising a first pond coal fly ash and a first ionic liquid. The ratio of ionic liquid: coal fly ash could vary from 1 :9 to 1 : 1 by mass, in one aspect, the first composition further comprises germanium.

[0035] In one aspect, the first pond coal fly ash has been weathered for at least 1 year, such as for example, from about 1 to 50 years. The second pond coal fly ash contains less germanium as compared to the first pond coal fly ash due to the leaching process of germanium from the first pond coal fly ash. In one aspect, at least 80% of germanium is leached from, first pond coal fly ash. In one aspect, the first pond coal fry ash is derived from class F fly ash. Class F fly ash has a Ge and REE concentration as shown in Table 1. Table 2 shows an example of the process streams for the method disclosed herein assuming 50% of the ionic liquids can be recovered and reused.

TABLE 1 - Source of Ge and EEs in Coal Fly Ash,

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Valuable element in wind turbine

Pr 26.0 95255 325 16 735 2%

magnets and vehicle batteries

TABLE 2 - Process Stream Mass Flows.

Note - Table 2 assumes 1,000,000 tons of Class F Weathered Coal Fly Ash Processed and 50% recover}' of ionic liquids for reuse.

[0036] In step b), the first mixture comprising the first ionic liquid and the leached germanium is separated from the second pond coal fly ash. The first mixture

comprising the first ionic liquid and the leached germanium can then be further

processed to extract the germanium from the first mixture. To minimize cost and use of materials, the method can further comprise regenerating and recycling the first ionic liquid once it has been used to leach the Ge from pond coal fly ash. The regeneration and recycling of the first ionic liquid can be done by contacting the ionic liquid with an aqueous acid phase to extract germanium and other metal contaminants.

[0037] In step c), a first brine is mixed with the second pond coal fly ash, thereby leaching iron and one or more rare earth elements from the second pond coal fly ash and producing a third pond coal fly ash and a second mixture comprising the first brine and the leached iron and one or more rare earth elements. The second mixture comprising the first brine and the leached iron and one or more rare earth elements can then be further processed to remove iron from the second mixture. Thus, in one aspect, the method further comprises adding an iron precipitating agent to the second mixture, thereby precipitating and removing at least a portion of the iron from the second mixture. In one aspect, the iron precipitating agent is an agent that increases the pH of the second mixture, thereby precipitating the iron in the form of iron hydroxide. Iron precipitating agents are known in the art. Non-limiting examples of iron precipitating agents include, but are not limited to, sodium carbonate, ammonium hydroxide, ammonia, calcium carbonate, sodium hydroxide, and calcium hydroxide.

[0038] In one aspect, the first brine is a flue gas desulfurization brine that has been pretreated to remove heavy metals. Flue gas desulfurization brines are known in the art and are typically produced when a limestone slurry is contacted with flue gas to remove SO ₂ . Along with SO ₂ , salts and metals are also removed from the flue gas (Huang, Y.H., et al. Water Science & Technology, 2013. 67.1: p. 16-23). These salts (Na÷, Ca ²⁺ , Mg ⁺ , Cf, and SO ₄ ^" ) accumulate in the flue gas desulfurization brine. Flue gas desulfurization brines are known to have high concentrations of CI ^" , which assist in the leaching of the REEs from the second pond coal fly ash. Significant quantities of As, Cd, Cr, Hg, and Se are also scrubbed and accumulate in the system (Huang, Y.H., et al. Water Science & Technology, 2013. 67.1: p. 16-23). These heavy rnetals are substantially removed from the flue gas desulfurization brine before being used in the methods disclosed herein. The flue gas desulfurization brine utilized in the method can contain a CF concentration of at least about 80,000 mg L, such as from about 80,000 rng/L to about 500,000 mg/L.

[0039] The purpose of mixing the first brine with the second pond coal fly ash is to increase the dissolution of amorphous silicate and to mobilize REEs from the surface of pond coal fly ash. In one aspect, the method is performed using a flue gas desulfurization brine, which is a waste product already available onsite. The use of a flue gas desulfurization brine improves the yield of the method and the overall process economics. The use of the flue gas desulfurization brine is beneficial to the zero liquid discharge (ZLD) approaches that are gaining significant interest from the coal-fired power industry. Zero liquid discharge options are attractive because of the elimination of an environmental discharge of metals and salts, maximization of water recovery for reuse, and certainty regarding the ability to meet future regulatory requirements. The disadvantages of the approach are high capital and operating costs, and management of the high salt residuals.

[0040] Most ZLD strategies include a volume reduction step to produce a concentrated flue gas desulfurization brine. Potential volume reduction technologies for flue gas desulfurization brine include traditional evaporators and crystallizers, wastewater spray dryers, brine concentrators, and advanced membrane processes (e.g. forward osmosis, membrane distillation, etc.). For an flue gas desulfurization brine concentrated through evaporation or an advanced membrane process, the element concentrations of the water could be increased by a factor of 10 to 15.

[0041 ] The total dissolved solids of the flue gas desulfurization brine could increase to an approximate range of 100,000 to 350,000 ppm. Most often the SO ₄ ^2" are removed through precipitation as CaS0 ₄ .2H ₂ 0 and the dominant anion in the concentrated brine is CF. The benefits of a high concentration of CX in the brine can be derived from studies where saline solutions have been shown to enhance the kinetics of the dissolution of amorphous silica and quartz (lcenhower, J. P. et al., Geochimica et Cosmochimica Acta, 2000. 64(24): p. 4193-4203; Berger, G., et al ., Geochimica et Cosmochimica Acta, 1994. 58(2): p. 541 -551; Dove, P.M., Geochimica et

Cosmochimica Acta, 1999. 63(22): p. 3715-3727; Dove, P.M. et al., Geochimica et Cosmochimica Acta, 1997. 61(16): p. 3329-3340). CaCi ₂ , MgCh, and NaCl have been shown to speed the dissolution of quartz (Berger, G., et al., Geochimica et

Cosmochimica Acta, 1994. 58(2): p. 541-551 ; Dove, P.M., Geochimica et

Cosmochimica Acta, 1999. 63(22): p. 3715-3727; Dove, P.M. et al., Geochimica et Cosmochimica Acta, 1997. 61( 16): p. 3329-3340). NaCl solutions have been shown to speed the dissolution of amorphous silica; however, the author of the scientific paper on the study expects CaCh and MgCh solutions to have a similar impact as the NaCl solution (lcenhower, J. P. et al., Geochimica et Cosmochimica Acta, 2000. 64(24)).

[0042] The rate limiting step in the amorphous silica dissolution is the breaking of the Si-0 bond (Icenhower, J. P. et al., Geochimica et Cosmochimica Acta, 2000.

64(24)). It is suggested that when the solution pH is higher than approximately 3-4, cations (Ca ²⁺ , Mg ^" ' ^" , or Na ^" ) will be electrostatically attracted to the negatively charged amorphous silicate surface (icenhower, J.P. et al., Geochimica et Cosmochimica Acta, 2000. 64(24)). The cations could be positioned in the interfacial region of the amorphous silica and in position to promote hydrolysis of the Si-0 bond (Icenhower, J.P. et al., Geochimica et Cosmochimica Acta, 2000. 64(24)). The above explains the more rapid dissolution of amorphous silicate in electrolytic solutions.

[0043] It should be noted that amorphous silica dissolution kinetics increased significantly only at low NaCl additions (<0.05M) (Icenhower, J.P. et al., Geochimica et Cosmochimica Acta, 2000. 64(24)). The above implies that the rates increase until the amorphous silicate surface becomes saturated with Na ⁺ (Dove, P.M., Geochimica et Cosmochimica Acta, 1999. 63(22): p. 3715-3727). However, amorphous dissolution rates increased by a maximum factor of 21 in this study (Dove, P.M., Geochimica et Cosmochimica Acta, 1999. 63(22): p. 3715-3727). An increase in the silicate dissolution rate of that m agnitude would likely be beneficial for the breakdown of the amorphous silicate phase in pond coal fly ash to mobilize REEs. Differences likely exist in the maximum increased dissolution rate based on the dominant cation (Ca ^{i ~} versus Mg ^2"r versus Na ^'1 ) in the solution.

[0044] Also disclosed herein is a composition comprising a second pond coal fly ash and a first brine. The ratio of brine to ash could vary from 1: 1 to 1 :20. In addition, some acid and heat may be added to optimize the leaching process. The second pond coal ash has been depleted in Germanium as described above by the leaching process of the first ionic liquid.

[0045] Once at least a portion of the iron has been removed, a second ionic liquid is mixed with the second mixture, thereby extracting the leached one or more rare earth elements from the second mixture. In one aspect, the method further comprises recovering the extracted one or more rare earth elements. Recently research has been focused on development of an ionic liquid extraction process for REEs (Sun, X., et al., Talanta, 2012. 90: p. 132-137; Sun, X., et al.. Chemical Engineering Journal, 2014. 239: p. 392-398: Shen, Y, et al, Dalton Transactions, 2014. 43(26): p. 10023-10032; Dupont, D., Green Chemistry, 2015. 17(2): p. 856-868). [0046] Accordingly, also disclosed herein is a composition comprising a second ionic liquid and a second mixture comprising a first brine and one or more rare earth elements. The ratio of second ionic liquid:second mixture can vary from 1 :9 to 1 : 1 by mass.

|0047] To minimize cost and use of materials, the method can further comprise regenerating and recycling the second ionic liquid once it has been used to extract at least a portion of the leached one or more rare earth elements from the second mixture.

[0048] The regeneration and recycling of the second ionic liquid can be done by contacting the ionic liquid with an aqueous acid phase to extract rare earth elements and other metal contaminants.

[0049] The method disclosed herein, in one aspect, comprises leaching, extracting, and recovering rare earth elements. Rare earth elements are a set of seventeen chemical elements in the periodic table, specifically the fifteen ianthanides plus scandium and yttrium. In one aspect, the leached, extracted, and recovered rare earth elements in the disclosed method is selected from the group consisting of yttrium, praseodymium, neodymium, europium, and dysprosium, or a combination thereof.

[0050] In one aspect, the method disclosed herein is performed within the geographical borders of an ash producing plan site. In one aspect, the ash producing plan site comprises a coal plant. As such, the ash produced at the plant site is treated and stored to become pond coal fly ash at the location of production and also is processed in close proximity to the production site by the methods disclosed herein. As such, cost is minimized by avoiding transportation of the fresh fly ash and pond coal fly ash.

[0051] As disclosed, the method disclosed herein advantageously uses ionic liquids to leach and/or extract Ge or REEs from pond coal fly ash. Ionic liquids typically have negligible vapor pressure and are non-flammable (Vander Hoogerstraete, T., et al., Green Chemistry, 2013. 15(4): p. 919-927). Thus, unlike organic compounds, ionic liquids will not be released to the environment through volatilization (Vander Hoogerstraete, T., et al, Green Chemistry, 2013. 15(4): p. 919-927). Ionic liquids are safer to handle than organic solvents since they are non-flammable (V ander

Hoogerstraete, T., et al., Green Chemistry, 2013. 15(4): p. 919-927). Extraction processes utilizing ionic liquids are likely more friendly than conventional organic solvent extraction (Xie, F., ei al., Metals Engineering, 2014. 56: p. 10-28). However, to date, no commercial iomc liquid extraction process lias been de veloped for REEs or Ge recovery (Xie, F., et al., Metals Engineering, 2014. 56: p. 10-28).

|0Θ52] Ionic liquid extraction techniques face some challenges that must be overcome for commercialization. These challenges include high chemical costs. Large-scale production is needed to drive cost down. The present invention overcomes this by growing market demand for ionic liquids by creating a new application and market, one that would consume large quantities of ionic liquids. Coal plants produce 50-100M tons of coal fly ash year in the United States. Many of those coal plants have sequestered 10s of millions of tons (per plant) in ash ponds and dr ' landfill storage facilities over their operating life. If ionic liquids are applied to extract valuable materials from millions of tons of raw material, then the amount of ionic liquids consumed will be large enough to create new? demands that drive 1) scale-up of ionic liquid manufacturing and 2) costs down. For example, we estimate one typical 2-GW coal plant constructed in 1975 would have roughly 12 M tons of coal fly ash stored in a single ash pond. If ionic liquids are mixed at a ratio of 3:7 (ionic liquid: coal fly ash) on a continuous bases over a 30 year project life, each year of operation would consume 5M tons of ionic liquid per year at 50% recovery of the ionic liquid during regeneration.

[0053] Ionic liquids are known in the art and are salts in liquid form. Ionic liquids typically have a melting point below 100 °C. Ionic liquids contain ions, such as, a cation and an anion. In one aspect, the first ionic liquid is an ionic liquid with a phosphonic acid group, a phosphate group, or a phosphonate group as the anion group. In one aspect, the second ionic liquid is an ionic liquid with a phosphonic acid group, a phosphate group, or a phosphonate group as the anion group. In one aspect, the third ionic liquid is an ionic liquid with a phosphonic acid group, a phosphate group, or a phosphonate group as the anion group. In one aspect, the phosphate is hexafluoro phosphate. In another aspect, the phosphate is PO ₄ ^3" . In another aspect, the first ionic liquid is an ionic liquid with an imidazole derivative as the cationic group, such as an imidazo!ium group. In another aspect, the second ionic liquid is an ionic liquid with an imidazole derivative as the cationic group, such as an imidazolium group. In another aspect, the third ionic liquid is an ionic liquid with an imidazole derivative as the cationic group, such as an imidazolium group. In yet another aspect, the first ionic liquid is an ionic liquid with an imidazole derivative as the cationic group and a phosphomc acid group, a phosphate group, or a phosphonate group as the anion group. In yet another aspect, the second ionic liquid is an ionic liquid with an imidazole derivative as the cationic group and a phosphomc acid group, a phosphate group, or a phosphonate group as the anion group. In yet another aspect, the third ionic liquid is an ionic liquid with an imidazole derivative as the cationic group and a phosphonic acid group, a phosphate group, or a phosphonate group as the anion group.

[0054] In one aspect, the first ionic liquid is a different ionic liquid than the second ionic liquid. In one aspect, the first ionic liquid is the same ionic liquid than the second ionic liquid.

fOOSS] Non-limiting examples of the cation in the ionic liquids (first and second ionic liquid) disclosed herein include 3-[2-(4-nitro-phenyl)-2-oxoethyi]-l - methylimidazolium, 3-[2-(3-chlorophenyl)-2-oxoethyl]-l-methylimidazolium, 3-[2-(4- ch3orophenyl)-2~oxoetliyl]-l-methylimidazolmm, l-ethyloxy-3-[4-nitrobenzyl] imidazolium, l~me4yloxy-3~[2-(4-cli3orophenyi)-2-oxoethyl]imidazolium, 3-[2-(4- nitro-phenyl)-2~oxoethyl]-l -methylimidazolium, l-etheneoxy-3-[2,4-dichlorobenzyl] imidazolium, l-ethyloxy-3-[2,4-dichlorobenzyl] imidazolium, 3-[2-(3,4- dichloropheny 1) -2-oxoethyl ] - 1 -methylimidazolium, 1 -hydrocinnamy i- 3 -methyl imidazolium, l-nonyl-3 -methylimidazolium, l-octyl-3-ethylimidazoliun , l ,3~di-(l~ butoxymethyi)imidazolium, l-Methyl-3-(2-oxo-2-o-tolyl-emyl)-imidazolium, l-(4- met3ioxynbutyl)-3-methylimidazo3ium, l-[2-(2-methoxyethoxy)ethyl]-3-methyl imidazolium, 1,3-dibenzylimidazoiium, l-hexyl-3-methylimidazolium, 1- [2 -phenyl -2- oxyethyl]-3-methyl imidazolium, 1 -(3-cyano-propyl)-3-(2-cyano-ethyl)imidazolium, 1 - (2-Furan-2-yl-2-oxo-ethyl)-3-methylimidazolium, l-hydroxy-3-[2,4- dichlorobenzyijimidazolium, 1-benzy 1-3 -methylimidazolium, l-benzyl-3- methylimidazolium, 1-heptyl -3 -methylimidazolium, l-hexyl-3-ethylimidazolium, 1,3- dibutylimidazolium, l -(4-methoxyphenyl)-3-methylimidazolium phenemyl-3- methylimidazolium, l-methyl-3-(3-memyl-benzyl)-unidazolium, l-methyl-3-(2- metiiyi-benzyl -imidazoiium, 3-[2-(4-bromo-phenyl)-2-oxoetliyl]-l-methyl imidazolium, 1-octyl -3 -methylimidazolium , phenyletlianoyl-3-propylimidazolium , heptoxymethyi-3-methylimidazolium, 3-f2-(2-florophenyl)-2-oxoethyl]-l -methyl imidazolium, 1 -( 1 -propoxymethyl)-3-( 1 -butoxymethyl) imidazolium, 3 - [2-(4-nitro- phenyl)-2-oxoethyl]-l -methylimidazolium, 3~[2-(3-cli3orophenyl)-2~oxoethyl]~l - methylimidazolium, 3-[2-(4-chlorophenyl)-2-oxoethyl]-l-methylimidazolium, 1- ethyloxy-3-[4-nitrobenzyl] imidazolium, l-methyloxy-3-[2-(4-chlorophenyl)-2- oxoethyl]imidazolium, 3-[2-(4-nitro-phenyl)-2-oxoethyl]-l -methylimidazolium, 1- etheneoxy-3-[2,4-dichlorobenzyl] imidazolium, I -ethyloxy-3-[2,4-dichlorobenzyl] imidazolium, 3-f2-(3,4-dichlorophenyl)-2-oxoethyl]-l-methylimidazolhim, 1- hydr ocinnamy 1-3 -methyl imidazolium, 1 -nonyl-3 -methylimidazolium, i -octy 1- 3 - ethyl imidazolium, l,3-di-( l-butoxymethyl)imidazolium, i-Methyi-3-(2~oxo-2-o~to3yl- ethyl)-imidazolhim, 3-(4-Cyano-benzoyl)-l-methyl imidazolium, 3-[2-(4- Methyloxyphenyl)-2-oxoethyi |-l-metliyi imidazolium, 3-[2-(2-Metliyloxyphenyl)-2- oxoethyl]-! -methylimidazolium, i-ethyloxy~3~[2-(4-c3i3orop3ienyi)-2~

oxoethy]] imidazolium, l-hydroxy-3-(3,4,5-trimethyloxybenzyl)imidazo]ium, l-ethyl-3- [2-(4-bromo-phenyl)-2-oxoethyl]imidazolium, l-methyl-3-f2,6-(S)-dimethylocten-2- yljimidazolium, 1 -octy 3-3 -propylimidazolium, l-decyl-3-methylimidazolium, 3-[2- (l ,2~dimet3iyloxypheny3)-2~oxoethyl]-i-metliy3imidazo3ium, 3-(l , l-dimethyl-2-phenyl- 2-oxoethyl)-l -methylimidazolium, 3-f2-(3,5-dimethoxylphenyl)-2-oxoethyl]-l- methylimidazolium, 3-[2-(3,4-Dimetliyloxyphenyi)-2-oxoemyi|- l-met3iyiimidazoiium, 1 -( 3 -iionoxymethyl)-3— methylimidazolium, 3 - [2-(3 -ethoxylphenyl)-2-oxoethyl] - 1 - metiiylimidazolium, 3-[2-(4-ethoxylphenyl)-2-oxoethy]]-l-methylimidazolium, 1 -(1- amyioxymethy 3)-3 -butoxy methyl imidazolium, 1 -amy 1-3 -benzylimidazolium, 1 -( 1 - hexyioxymemyl)-3-( l-butoxymethyl) imidazolium, l-undecyl-3 -methylimidazolium, 1- (l -deeyloxymetliyl)-3~methylimidazolium, 3-[2~(3-propyioxylpheny3)-2~oxoethyl]-l - rnethyi imidazolium, 3-f2-(3-methyioxylphenyl)-2-oxoethyr|-l— ,

isopropylimidazolium, 3-[2-(2,4,6-trimethyloxyphenyl)-2— , oxoethyi |- 1- methylimidazolium, 3-[2-a-naphthyl-2 -oxoethyi] - 1 -methylimidazolium, 1 -( 1 - heptyloxymethyl)-3-(l -butoxymethyl) imidazoliumhyl), imidazolium, l-dodecyl-3- methylimidazolium, 1 -( 1 -undecyloxymethyl)-3-metiiylimidazolium, 1 -(2,2- dimethyipropionyloxy)-3-[2-(4-chloiOphenyl)-2- oxoetliyi]imidazolium, 1-(1- dodecy loxymethyl)-3 -methylimidazolium, i -tridecy 1-3 -met!iylim idazol ium , 1 - benzyloxy-3-(2,4-dichlorobenzyl)imidazolium, l-(4-Benzoyl-benzyl)-3-methyl- imidazolium, l-tetradecyl-3-methylimidazolium, 3-[2-(3-methyloxylphenyl)-2- oxoethyl] - 1 -phenylimidazolium, 1 -( 1 -nony loxymethyl)-3 -( 1 - butoxymethyl)imidazolium, l -(2-phenyletliyloxy)-3-(2,5-dichlorobenzyl)imidazolium, l-[2,4-dichlorophenylmethyloxyl]-3-[2-(4- chlorophenyl)-2-oxoethyl]imidazolium, 1- pentadecyl-3-methylimidazolium, l-phenyloxy-3-[2-(4-Dimethylamino-pheny3)-2- oxoethyl] imidazolium, l-( l-decyloxymethyl)-3-( 1-butoxy methyl)imidazolhim, 1 - hexadecyl-3 -metliylimidazolium, 1 -( 1 -decyloxymethyl)-3 -hexyl imidazolium, 1 -( 1 - undecyloxymethyl)-3-( 1 -butoxy methy3)imidazolium, 1 -( 1 -undecyloxymethyl)-3-hexyl imidazolium, l-octadecyl-3-methylimidazolium, l-cosyl-3-methylimidazolium, l-(2- (2-(2-(2-(2-(2-(2-,

(memacr 4oyloxy)emoy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)emoxy 3- ethyS imidazolium, polymer of PEOimidazolium, l,3-dihydroxy-2-bromoimidazolium, 1 ,3-dimethyl-5-chlorideimidazolium, 2,4,5-trimethyiimidazoiium, 1,2,3- trimethylimidazolium, 1,3-dimethyl-nimtrimleimidazolium, l,2-dimethyl-3- ethylimidazolium, l-ethyl-3,5-dimethylimidazolium, l -ethyl~2,3~dimethy3imidazo3ium, l,3-dimethyl-4-methylimidazolium, l ,2-methyl-3-propylimidazolium, l,2-ethyl-3- methylimidazolium, 1 -propyl -2,3 -dimethylimidazolium, l-butyl-2,3- dimethylimidazolium, 3 -butyl- 1 ,5 -dimethylimidazolium, 1 ,3 -dimethyl-2- phenylimidazolium, l-octyl-2,3-dimethylimidazolium, l ,3~dipropy3-2~

isobutylimidazolium, l-methyl-3-(2-phenyl-2-oxoethyl)-5— methoxyimidazolium, 1,2- dimethyl-3-phenylethanoyl imidazolium, l-hydroxy-2-ethyl-3-[2-(4-chloro phenyl)- 2- oxoethyl] imidazolium, l-benzyi-2-m.ethyl~3-butylimidazolium, i-benzyl-2-metliyl-3~ (3 -methyl) propylimidazolium, 1 -benzyl-2-methy]-3-amylimidazolium, l-decyl-2,3- dimethyiimidazoiium, l-methyl-2-n-heptyl-3-benzyl imidazolium, l-methyi-2-(2,2- Dimethyl-l-methylene-pi pyl)-3-(2-phenyi-2-oxyethyi) imidazolium, l-(2,2- dimetliylpropionyloxy)~2-ethyl~3-[2-(4~ehlorophenyl)~2-oxoet hyl] imidazolium, 1 ,3-di- 14-nitrobenzyioxy I -2 -methyl imidazolium, 1 ,3 -di - [4-bromobenzyloxy ] -2 -methyl imidazolium, l-phenyl-2-methy l-3-[2-(4-methoxy phenyl)-2 -oxoethyl] imidazolium, 1- benzyl-2-(2-phenyl-2-oxoethyl)-3-methylimidazolium, l,3-dibenzyl~4~(2- hydroxyethyl) imidazolium, l-benzyl-2-methyl-3-3-[2-(4-chloro phenyl)-2 -oxoethyl] imidazolium, l-phenyloxy-2-ethyl-3-| 2-(4-chloro phenyi)-cf2-oxoethyl)imidazoiium, l,2-dimethyi-3-[2-(4-NitiO-benzoic acid)-benzyl] imidazolium, l,3-di-(2,6- dicli3orobenzyloxy)-2— ethylimidazolium, l,3-di-(2,4-diehlorobenzyloxy)-2— ethylimidazolium, l,3-di-(4-bromobenzyloxy)-2-ethyl imidazolium, l-methyl-2-n- nonyl-3 -benzylimidazoli um, 1 -methyl -2 -phenyl vinyl -3 -(2-pheny 1-2— oxyethyi) imidazolium, 1 -phenylethanoyl-2-styr ene-3— methyiimidazoiium, 1 -phenemyi-2 - metliyl-3-[2-(4-chloropheny])-2 -oxoethyl] imidazolium, l-benzyl-2-methyl-3-n- decylimidazolium, l-(4-methyloxy-benzyl)-2-methyl3-|2-(4-methoxyiphenyl)-2- Oxoethyl] imidazolium, 1 -benzyl -2 -n-undecy 1-3 -metliylimidazolium, 1 -benzyloxy-2- ethyl -3 -(3 ,4,5 -trimethyloxy benzyl) irnidazoliurn, 1 -benzyl-2 -methyl-3 -n-tetradecyl imidazolium, 1 -benzyl-2-n-undecyl-3 -amy limidazoliiim, 1 ,3 -dihydroxy-2-methyl-4- bromo imidazolium, 1, 3 -dihydroxy-2 -phenyl -4-bromo imidazolium, i,3~diethy!~4,5~ diphenylimidazolium, l,3-dihydroxy-2-bromo-4,5— dimethyl imidazolium, 1,3- dimethyl-2,4,5-tri-bromo imidazolium, and 1,2, 3, 4,5 -alpha- methylimidazolium.

[0056] There could be similarities with the first and second ionic liquids.

However, the first ionic liquid will be applied to leach germanium from a solid. The second ionic liquid will be applied to conduct a liquid-liquid extraction from the second mixture. The method disclosed herein integrates with electric utility compliance strategies for coal ash storage and scrubber wastewater treatment (flue gas

desulphurization brine), see FIG. 5.

2. EXAMPLES

A. Conceptual design of composition and method

[0057] FIG. 1 shows a process of using chemistries already common in the Ge and REE metal extraction industry, which are applied to pond coal fly ash. This process relies on acid leaching and organic solvent extraction techniques common in the Ge and REE metal extraction industry. This process can be used in the future as a benchmark for a method disclosed herein, which is shown in FIG. 2. FIG. 2 shows the use of waste water treatment (WWT) (i.e. flue gas desulphurization brine) and ionic liquids as means to reduce chemical reagent costs and reduce environmental impacts of the recovery process. The processes in FIGs. 1 and 2 involve two separate leaching steps due to the potential for Ge and the REEs to be included in different phases of the pond coal fly ash.

[0058] As shown in FIG. 1 , chemistries used in conventional Ge and Rl-.f extraction processes involves: 1 . Leach Ge using oxalic acid (H2C2O4), because Ge is not present in the silicate phase, it can be leached with oxalic acid; 2. Extract Ge using an organic solvent and regenerate the solvent; 3. Mix the residual solid material from the first leaching step with acids (H2SO4, HNO3, and HF) to dissolve the silicate phase in order to leach the Pr, Y, Dy, Eu, and Nd; 4. Precipitate iron using soda ash (sodium carbonate) prior to extraction to avoid Fe interference during extraction process; 5. Extract the REEs using an organic solvent and regenerate the solvent; and 6. Mix waste from extraction process with pozzolanic agent such as Portland cement (PC), CaO, or Ca(OH)2 to solidify and stabilize waste material prior to sending to the lined landfill.

[0059] Related to the process shown in FIG. 1, oxalic acid has been shown to selectively leach Ge with low levels of impurities (Arroyo, F., et al , Gemanium and. Gallium Extraction from Gasification Fly Ash: Optimisation for Up-Scaling a Recovery Process, in 2009 World of Coal Ash (WOCA) Conference. 2009: Lexmgton, Kentucky). Oxalic add also functions as a complexation agent for Ge in the leach process (Arroyo, F., et al., Gemanium and Gallium Extraction from Gasification Fly Ash: Optimisation or Up-Scaling a Recovery Process, in 2009 World of Coal Ash (WOCA) Conference. 2009: Lexington, Kentucky). However, the oxalic acid leaching process will not break down the silicate phase; hence, REEs are assumed to remain with the residual solids from the oxalic acid leach.

[0060] Organic solvents will be evaluated for Ge recovery from the leachate. In a general organic solvent extraction process, a dissolved metal in an aqueous solution is mixed with an organic liquid containing an extractant (Vander Hoogerstraete, T., et al., Green Chemistry, 2013. 15(4): p. 919-927). The dissolved metal forms a hydrophobic complex upon contact with the extraction agent and partitions to the orga ic phase (Vander Hoogerstraete, T., et al., Green Chemistry, 2013. 15(4): p. 919-927).

Partitioning of the metal-extractant complex is based on the complexes affinity for the organic phase (Vander Hoogerstraete, T., et al., Green Chemistry, 2013. 15(4): p. 919- 927). Numerous organic solvents have been evaluated in single and multi-step processes to recover Ge from aqueous solutions including Kelex 100, LIX 26, LIX 63, H106, G315, D2EHPA, D2EHPA TBP, organo-phosphoric acids, PC-88A, Ionquest 801, and HGS98 (Nusen, S, et al, Hydrometallurgy, 2015. 151: p. 122-132).

[0061] In the second leaching step, strong acids (H2SQ4, HNO3) will be used to mobilize Eu, Dy, Nd, Y, and Pr. If REEs are not sufficiently mobilized, HF and heating will be utilized in a digestion process. Following the leaching step, an Fe(+III) precipitation step be conducted to reduce Fe(+III) interference with REE extraction (Xie, F, et al, Metals Engineering, 2014. 56: p. 10-28). Organic extraction processes have been utilized extensively for REE recovery on the commercial scale. Organic solvents including cation exchangers (carboxylic acids and phosphorous acids), chelating exchangers (β-diketones), solvating extractants (phosphorous ester), and anion exchangers (primary and quaternary amines) have all been utilized for REE recovery from leached solutions (Xie, F, et al, Metals Engineering, 2014. 56: p. 10- [0062] FIG. 2 shows a non-limiting example of a method disclosed herein. FIG. 2 shows the use of ionic liquids and brine concentrates to leach and extract Ge and REEs and involves: 1. Leaching Ge using ionic liquids; 2. Extracting Ge using an ionic liquid and regenerate the liquid; 3. Mixing the residual solid material from the first leaching step brine concentrate produced from onsite WWT processes; 4, Precipiating iron using soda ash (sodium carbonate) prior to extraction to avoid Fe interference during extraction process; 5. Extracting the REEs using an ionic liquid and regenerate the liquid; and 6. Mixing waste from extraction process with pozzolanic agent such as Portland cement (PC), CaO, or Ca(OH)2 to solidify and stabilize waste material prior to sending to the lined landfill.

B. Experimental data

|0Θ63] Rare earth elements have been recovered from ion adsorbed clays utilizing salt leaching processes (Peelman, S., et al., Leaching of Rare Earth Elements: Past and Present, in 1st European Rare Earth Resources Conference, 2014: Mekelweg, The Netherlands). Ion adsorbed clays are similar to pond coal fly ash in that they are alurnino-silicate materials (Peelman, S., et al., Leaching of Rare Earth Elements: Past and Present, in 1st European Rare Earth Resources Conference. 2014: Mekelweg, The Netherlands). The surface of these clays can contain 0.05% to 0.2% REEs

(Moldoveanu, G.A. et al. Hydrometallurgy, 2012. 117-118: p. 71-78). REE leaching strategies for ion adsorbed clay s include salt leaching with (NH4)2S04 and seawater leaching (Peelman, S., et al., Leaching of Rare Earth Elements: Past and Present, in 1st European Rare Earth Resources Conference . 2014: Mekelweg, The Netherlands;

Moldoveanu, G.A. et al. Hydrometallurgy, 2012. 117-118: p. 71 -78; Moldoveanu, G.A. et al. Hydrometallurgy, 2013. 131-132: p. 158-166). The mechanism of REE mobilization in both strategies is cation exchange (Peelman, S., et al ., Leaching of Rare Earth Elements: Past and Present, in 1st European Rare Earth Resources Conference . 2014: Mekelweg, The Netherlands; Moldoveanu, G.A. et al. Hydrometallurgy, 2012. 117-118: p. 71-78; Moldoveanu, G.A . et al. Hydrometallurgy, 2013. 131-132: p, 158- 166). The below equation shows the cation exchange reaction for the ( IT iSCk salt leach process (Peelman, S., et al., Leaching of Rare Earth Elements: Past and Present, in 1st European Rare Earth Resources Conference. 2014: Mekelweg, The Netherlands; Moldoveanu, G.A. et al. Hydrometallurgy, 2012. 117-118: p. 71-78; Moldoveanu, G.A, ei al. Hydrometallurgy, 2013. 131-132: p. 158-166): j Ai .Si .()5(OI l ) , j _:i .bLii ^! (s) + 3bNH ⁺ (aq) = i Ai .Si..O<(OH ) , j _:1 . ( H ⁴⁺ )3b(s) + bLn ³⁺ (aq) where: Α1 ₂ 8ι ₂ 0 ₅ (ΟΗ) ₄ ] is the on exchange clay (kaolinite) and Ln is the REE.

|0Θ64] Tlie impact of CI ^" salts (Ca ⁺ , Mg ²⁺ , and Na ^" ) on cationic metal leaching from a sample of pond coal fly ash was conducted. CI ^" salts (NaCl, CaCl ₂ , and MgCl ₂ ) were added to the extraction fluid specified for USEPA Method 1313 (USEPA, Method 1313 - Liquid-Solid Parti Honing as a Function of Extract pH Using a Parallel Batch Extraction Procedure. 2012). The impact of chloride salts on leachmg of Cd and Ba from, class F fly ash were significant as shown in FIGs. 3 and 4. The data shown in FIGs. 3 and 4 were conducted at the following salt concentrations: NaCl (M): 0.00, 0.15, 0.56, and 1.65; CaCl ₂ (M): 0.00, 0.16, 0.61, and 2.24; MgCl ₂ (M) - 0.00, 0.17, and 0.74.

[0065] As shown, the addition of NaCl, MgCl ₂ , and CaCl ₂ increased Cd leaching at near neutral pH. Addition of CaCl ₂ and MgCl ₂ increased Cd leaching more than addition of NaCl. It is believed that the dominant mechanism for increased Cd leaching with CF salt addition is cation exchange similar to that observed for REEs and ion adsorbed clays. No increase in Cd leaching is observed for the low pH samples because essentially all of the easily exchangeable Cd readily leaches anyway. Solubility controls leaching at low pH. For the high pH samples, salt addition did not significantly increase Cd leaching. No increase in leaching was observed due to the low solubility of Cd at high pH. Only the highest salt addition (4.4 M CI ^" ), produced an increase in leachmg.

[0066] FTG. 4 shows a trend of increased Ba leaching with salt addition at low, near neutral, and high pH. The dominant mechanism of increased Ba mobility is cation exchange. Ba exchanges with the cations per the following preference

Ca ²⁺ »Mg ²⁺ >Na ⁺ .

[0067] Differences do exist between ionic adsorbed clays and pond coal fly ash that would affect the impact of CI ^" salt addition on enhancing REE mobility. Most of the REEs in the ionic adsorbed clays are present on the surface, while REEs in pond coal fly ash are homogenously distributed through the silicate phase of the pond coal fly ash particle . Hence, REEs are not as accessible for cation exchange in the pond coal fly ash compared to the ionic adsorbed clays. However, the extreme cation

concentrations in a concentrated flue gas desulphurization brine (example: Ca = 50,000 ppm) could enhance REE leaching on the surface of the pond coal fly ash particle as the silicate phase dissolves. In addition, soils show a general cation exchange preference (although boding energies are different based on substrate) of Ca ^2_r > Mg ² ÷» Na ^1* , NH ⁴⁺ (Pickering, W ^' .F ^' ., Metal Ion Speciation— Soils and Sediments (A Review). Ore Geology Reviews, 1986. 1(1): p. 83-146). It is likely that pond coal fly ash would generally follow the same trend. Hence, it is possible that the Ca ²⁺ and Mg ² in the concentrated flue gas desulphunzation brine could be more effective in mobilizing REEs on the surface of particles than the (NlTthSCk salt leach process developed for ion adsorbed clays. The concentrated flue gas desulphunzation brine will be mixed with the second pond coal fly ash, which is a result of the Ge leach process of the first pond coal fly ash with the first ionic liquid. The second pond coal fly ash and the concentrated flue gas desulphunzation brine will be held together for a period of time before the next leachmg process of the REE with the third ionic liquid is initiated.