Recovery of metal products from mine waste

Abstract

In one aspect, the disclosure relates to methods for recovering metal compounds from mine waste, wherein the mine waste comprises at least one metal. Also disclosed herein are methods related to recovering metal compounds from acid mine drainage, wherein the acid mine drainage waste comprises at least one metal. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present disclosure.

Description

RECOVERY OF METAL PRODUCTS FROM MINE WASTECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims the benefit of U.S. Provisional Application No. 63 / 552,581 titled “RECOVERY OF METAL PRODUCTS FROM MINE WASTE” and filed on February 12, 2024 which is incorporated herein by reference in its entirety.BACKGROUND

[0002] Acid mine drainage (AMD), characterized by high levels of acidity, is a major environmental concern for mining regions worldwide. Along with its low pH, AMD typically contains elevated levels of dissolved solids such as iron, aluminum, sulfate, and toxic constituents, impacting water quality and biota in receiving waters. Various treatment processes have been developed and used to mitigate AMD impacts, resulting in large quantities of AMD sludge that require disposal. Despite improvements in AMD neutralization processes, issues such as chemical stability, leaching of toxic metals, and storage requirements hamper AMD sludge disposal. Sludge management measures such as dewatering, pretreatment, chemical stabilization, and landfill have been used to address these issues. However, high sludge handling and disposal costs (USD $23-75 per ton) represent a significant economic liability. Consequently, the feasibility of AMD treatment methods is often evaluated in terms of the quantity and quality of the produced sludge.

[0003] Considering the instability, potential environmental concerns, and high disposal cost of AMD sludge, utilization of AMD waste is an attractive management strategy. One approach to sludge utilization is to selectively extract commercially useful elements from AMD. AMD created from coal and other mining operations has been recognized as a potential source for critical minerals, heavy metals and other products. However, the presence of toxic elements such as cadmium, copper, mercury, lead and metalloids such as arsenic and selenium in the AMD sludge results in contamination from utilizing the sludge materials.

[0004] Coal mine drainage sludge has been shown to contain Fe minerals ranging from 30 to 70-percent by weight, while Al content in AMD sludge can range from 10 to 15-percent by weight. Extracting Fe and Al from AMD could reduce the sludge quantities for disposal and create a wide range of applications for value creation. As nonlimiting examples, various forms of Fe are used to remove suspended solids, phosphorus, and odor (i.e., sulfide) in water and wastewater sectors. Furthermore, selective precipitation methods can be extended to extract rare earth elements (REEs) from AMD as a first step in REE production from domestic sources. These resource recovery opportunities provide a value chain that can be created from adopting and implementing novel AMD management approaches to not only alleviate environmental and economic liabilities, but to also create valuable by-products.

[0005] Despite improvements in AMD treatment, the large volumes of sludge produced by the treatment processes and high economic costs to handle and dispose of the sludge, among other factors, necessitate further improvements in the processing and utilization of AMD sludge. Such improvements to AMD management can include reducing the overall costs of processing AMD sludge, reducing the volume of sludge for disposal, and effectively utilizing the sludge. These needs and other needs are satisfied by the present disclosure.SUMMARY

[0006] In accordance with the purpose of the disclosure, as embodied and broadly described herein, the disclosure, in one aspect, relates to methods for recovering metal compounds from mine waste, the method comprising contacting the mine waste with a first base in an amount sufficient enough to adjust the pH to a value of about 3.5 to about 4.0, thereby forming a mixture of a first aqueous phase and a first metal precipitate; separating the first metal precipitate from the first aqueous phase; contacting the first aqueous phase with a second base in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a second aqueous phase and a first solid concentrate; separating the first solid concentrate from the second aqueous phase; contacting the first solid concentrate with a first acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a third aqueous phase and a second solid concentrate; separating the third aqueous phase and the second solid concentrate; contacting the third aqueous phase with a third base in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a fourth aqueous phase and a third solid concentrate; and separating the fourth aqueous phase and the third solid concentrate; wherein the third solid concentrate comprises a second metal precipitate.

[0007] Also disclosed herein is a method to recover metal compounds from acid mine drainage (AMD), the method comprising contacting the AMD with sodium hydroxide in an amount sufficient enough to adjust the pH to a value of about 3.5 to about 4.0, thereby forming a mixture of a first aqueous phase and a first metal precipitate; separating the first metal precipitate from the first aqueous phase; contacting the first aqueous phase with sodium hydroxide in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a second aqueous phase and a second metal precipitate; separating the second metal precipitate from the second aqueous phase; contacting the second metal precipitate with hydrochloric acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a third aqueous phase and an acidic solid; separating the third aqueous phase and the acidic solid; contacting the third aqueous phase with ammonium acetate in an amount sufficient enough to adjust the pH to a value of about5.0 and 8-hydroxyquinoline, thereby forming a mixture of a fourth aqueous phase and a metal oxinate solid; and separating the fourth aqueous phase and the metal oxinate solid.

[0008] Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described aspects are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described aspects are combinable and interchangeable with one another.BRIEF DESCRIPTION OF THE FIGURES

[0009] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0010] Fig. 1 shows a representative process of selective precipitation of AMD to extract Fe products and AI(OH)3powder-based products from sludge.

[0011] Fig. 2 shows a representative process of selective precipitation to extract iron and aluminum hydroxides from AMD treatment for value creation.

[0012] FIG. 3 depicts mine drainage sources in the State of West Virginia by iron mass loading rate (solid circles).

[0013] FIG. 4 shows a chart depicting representative selective precipitation to extract iron and aluminum by raising pH to approximately 3.5 and subsequently 5. (Wei et al., 2005).

[0014] FIG. 5 shows a picture depicting two 60-gallon cone-bottom tanks previously used to extract iron sludge from an acid mine drainage source near Morgantown, WV.

[0015] FIG. 6 shows a schematic outlining representative methodology for further purifying aluminum and production of aluminum hydroxide from AMD, where processes with (*) include a selective precipitation or acidification pH adjustment step.

[0016] FIGS. 7A-7B show pictures depicting exemplary AMD coprecipitated starting input materials.

[0017] FIG. 8 shows a schematic of a representative recovery process at an AMD site and examples of value-creating applications of the recovered iron and aluminum products.

[0018] FIG. 9 shows a representative process for selective extraction of iron and aluminum for beneficial applications.

[0019] Additional advantages of the disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or can be learned by practice of the disclosure. The advantages of the disclosure 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 disclosure, as claimed.DETAILED DESCRIPTION

[0020] Many modifications and other embodiments disclosed herein will come to mind to one skilled in the art to which the disclosed compositions and methods pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosures are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.

[0021] Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0022] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure.

[0023] Any recited method can be carried out in the order of events recited or in any other order that is logically possible. That is, unless otherwise expressly stated, it is in no way intended that any method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state 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 oroperational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.

[0024] All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided herein can be different from the actual publication dates, which can require independent confirmation.

[0025] While aspects of the present disclosure can be described and claimed in a particular statutory class, such as the system statutory class, this is for convenience only and one of skill in the art will understand that each aspect of the present disclosure can be described and claimed in any statutory class.

[0026] 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. 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 the disclosed compositions and methods belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0027] Prior to describing the various aspects of the present disclosure, the following definitions are provided and should be used unless otherwise indicated. Additional terms may be defined elsewhere in the present disclosure.A. DEFINITIONS

[0028] As used herein, “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Moreover, each of the terms “by”, “comprising,” “comprises”, “comprised of,” “including,” “includes,” “included,” “involving,” “involves,” “involved,” and “such as” are used in their open, non-limiting sense and may be used interchangeably. Further, the term “comprising” is intended to include examples and aspects encompassed by the terms “consisting essentially of’ and “consisting of.” Similarly, the term “consisting essentially of’ is intended to include examples encompassed by the term “consisting of.

[0029] 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 rare earth element” includes, but is not limited to, mixtures of two or more such rare earth elements, and the like.

[0030] It should be noted that ratios, concentrations, amounts, and other numerical data can be expressed herein in a range format. 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. Ranges can be expressed herein as from “about” one particular value, and / or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms a further aspect. For example, if the value “about 10” is disclosed, then “10” is also disclosed.

[0031] When a range is expressed, a further aspect includes from the one particular value and / or to the other particular value. For example, where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure, e.g., the phrase “x to y” includes the range from ‘x’ to ‘y’ as well as the range greater than ‘x’ and less than ‘y’. The range can also be expressed as an upper limit, e.g., ‘about x, y, z, or less’ and should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘less than x’, less than y’, and ‘less than z’. Likewise, the phrase ‘about x, y, z, or greater’ should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘greater than x’, greater than y’, and ‘greater than z’. In addition, the phrase “about ‘x’ to ‘y’”, where ‘x’ and ‘y’ are numerical values, includes “about ‘x’ to about ‘y’”.

[0032] It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “about 0.1% to 5%” should be interpreted to include not only the explicitly recited values of about 0.1% to about 5%, but also include individual values (e.g., about 1 %, about 2%, about 3%, and about 4%) and the sub-ranges (e.g., about 0.5% to about 1.1 %; about 5% to about 2.4%; about 0.5% to about 3.2%, and about 0.5% to about 4.4%, and other possible sub-ranges) within the indicated range.

[0033] As used herein, the terms “about,” “approximate,” “at or about,” and “substantially” mean that the amount or value in question can be the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact but may 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 such that equivalent results or effects are obtained. In some circumstances, the value that provides equivalent results or effects cannot be reasonably determined. In such cases, it is generally understood, as used herein, that “about” and “at or about” mean the nominal value indicated ±10% variation unless otherwise indicated or inferred. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about,” “approximate,” or “at or about” whether or not expressly stated to be such. It is understood that where “about,” “approximate,” or “at or about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0034] As used herein, the term “effective amount” refers to an amount that is sufficient to achieve the desired modification of a physical property of the composition or material. For example, an “effective amount” of a buffer refers to an amount that is sufficient to achieve the desired improvement in the property modulated by the formulation component, e.g., achieving and maintaining a desired solution pH. The specific level in terms of wt% in a composition required as an effective amount will depend upon a variety of factors including the amount and type of buffer, size of processing plant (i.e., bench top, mobile, or commercial scale), amount and type of feedstock being treated, and end use of the REEs recovered during the process.

[0035] As used herein, the terms “optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0036] As used herein, the term “rare earth element” (REE), in the context of the present disclosure, refers to a composition comprising one or more rare earth elements, including one or more of a lanthanide chemical element, i.e., cerium, dysprosium, erbium, europium, gadolinium, holmium, lanthanum, lutetium, neodymium, praseodymium, samarium, scandium, terbium, thulium, ytterbium, and yttrium. The elements scandium and yttrium often occur in the same ore deposits as lanthanides and also have some similar chemical properties. Rare earth elements are useful in a variety of applications in the electronics, defense, and medical industries, as well as in other applications. An oxide of a rare earth element is a “rare earth oxide” and can be used for analytical purposes or may be useful as a component of ceramics, catalysts, and / or coatings, among other uses. It is to be understood that when referencing rareearth elements that any of the elements can be present in a zero valence or elemental state, or in an ionized or valence state associated in the art with the individual element, and all forms are understood to be collectively included within the meaning of “rare earth elements”. Moreover, it is to be understood that reference to any individual rare earth element, i.e., any one of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, including scandium and yttrium, can be present in a zero valence or elemental state, or in an ionized or valence state associated in the art with the given element, and all forms are understood to be collectively included within the meaning of reference to said element. For example, reference to “lanthanum”, “an element such as lanthanum”, “a composition comprising lanthanum”, and the like, it is understood that the reference inclusive any or all forms of lanthanum such as La0, La+1, La+2, and La+3. It is further understood that a reference to any given rare earth element is inclusive of all isotopic forms of the element.

[0037] “Critical minerals” (CMs) as used herein include minerals important to national security and the economy. REEs are a subgroup of CMs. Like REEs, CMs are considered critical minerals due to their numerous industrial uses. As used in the context of the present disclosure, certain CMs may also be purified and concentrated using the disclosed process and include one or more of the non-rare earth elements selected from cobalt, gallium, germanium, hafnium, indium, lithium, magnesium, manganese, nickel, niobium, rhenium, rubidium, tantalum, tellurium, and zinc. However, the foregoing is merely exemplary and depending upon source from which the PLS is obtained, additional or alternative CMs may be obtained. It should be noted that the U.S. Geological Survey regularly makes a determination of minerals critical to the U.S. economy, with the last list having been made publicly available on or about February 22, 2022 (e.g., see Federal Register, Vol. 87, No. 37, Thursday, February 24, 2022, p. 10381-10382 and https: / / www.usgs.gov / news / national-news- release / us-geological-survey-releases-2022-list-critical-minerals, last accessed November 30, 2023; each of which is incorporated by reference). As used in the context of the present disclosure, a CM may further include one or more mineral identified in the U.S. Geological Survey.

[0038] “Acid mine drainage” (AMD) as used herein refers to acidic water that outflows from mines such as, for example, metal mines or coal mines. In one aspect, AMD intensifies in scale and scope when construction, mining, and other activities that disturb the earth occur in and around rocks containing sulfide minerals. AMD can have high concentrations of metal ions that can cause detrimental effects to aquatic environments, especially in combination with low pH. AMD from coal mines and other sources often contains trace amounts of REEs, as well. “Acid mine drainage” as understood within the definition herein can be aqueous effluentfrom mining operations, mill tailings, overburden from mining operations, excavations, acid process waste streams, seepages, and other aqueous flows having elevated levels of metal ions and / or anions. Acid mine drainage is characterized by the presence of metals such as iron, manganese, aluminum, cadmium, cobalt, copper, lead, magnesium, molybdenum, nickel, zinc, and others. Acid mine drainage may also include undesirable anions such as sulfate, fluoride, nitrate and chloride. As used in the present application, “mine” is understood to mean active, inactive or abandoned mining operations for removing minerals, metals, ores or coal from the earth. Environmental regulations promulgated by the Environmental Protection Agency under CAA, RCRA, and CERCLA, as well as those promulgated by state and local authorities, mandate that the concentration of certain minerals and metals in specific aqueous effluents be less than the established regulatory levels.

[0039] “AMD precipitate” (AMDp) as used herein refers to a byproduct of AMD treatment. In one aspect, AMDp contains REEs but may also contain gangue metals such as, for example, iron and aluminum. In one aspect, AMDp contains from about 0.06% to about 0.1 % REE. As used herein, “enriched AMD precipitate” (eAMDp) refers to an AMD product having from about 0.1 % to about 5% REE on a dry weight basis. In another aspect, eAMDp has a lower gangue metal content then AMDp.

[0040] A “feedstock” as used herein is a raw material processed to recover REEs and other valuable components (e.g., CMs). A feedstock may be too toxic to release into the natural environment and, in one aspect, the disclosed process can remove commercially valuable components from the feedstock while simultaneously rendering the feedstock suitable for environmental release.

[0041] As used herein, “contacting” refers to the act of touching, making contact, or of bringing substances into immediate proximity.

[0042] As used herein, “decanting” or “decantation” includes pouring off a fluid, leaving a sediment or precipitate, thereby separating the fluid from the sediment or precipitate. The sediment or precipitate can be present as a slag.

[0043] As used herein, “filtering” or “filtration” refers to a mechanical method to separate solids from liquids by passing the feed stream through a porous sheet such as a paper, ceramic or metal membrane, which retains the solids and allows the liquid to pass through. This can be accomplished by gravity, pressure or vacuum (suction). The filtering effectively separates the sediment and / or precipitate from the liquid.

[0044] Unless otherwise specified, temperatures referred to herein are based on atmospheric pressure (i.e., one atmosphere).B. ABBREVIATIONS

[0045] AMD acid mine drainage

[0046] AML abandoned mine lands

[0047] SRF specific resistance to filtration

[0048] SERA Southern Extension and Research Activity

[0049] WV West VirginiaC. INTRODUCTION

[0050] In one aspect, the present disclosure relates to the recovery of high-purity metal products from mine waste. In one aspect, the mine waste can be AMD. AMD is characterized by high levels of acidity and presents a major environmental concern. AMD typically contains elevated levels of dissolved solids such as iron, aluminum, sulfate, and toxic constituents, which can impact water quality and biota in receiving waters. In one aspect, the present disclosure relates to the recovery of metal products such as iron and aluminum compounds. The recovered compounds can have a variety of uses, such as soil amendment or part of a manufactured soil or cover material, for example to support vegetation.

[0051] In a further aspect, mine waste can be a sludge material resulting from the treatment of AMD. The disclosed recovery methods can significantly reduce the amount of AMD sludge materials for disposal while generating useful products to create value for mining communities. These recovery processes provide a simple way to manage AMD and sludge material and provide a valuable use for the sludge that otherwise may result in lower capital, operational and maintenance costs for mines and municipalities. Additionally, revenue for parties liable for AMD treatment and regulatory compliance can be generated. This solution to manage AMD advances three key areas of sustainability (i.e., environmental, social, and economic) of waste management. Metal product utilization originating from AMD alleviates the burden of disposal of AMD sludge and reduces the risk of accidental release of these materials to the environment. Further, successful production of metal products creates revenue and job opportunities. Such features improve environmental justice for communities historically overburdened by mining. Broad adoption and implementation of the present methods bring about modernization of waste management infrastructure in mining regions worldwide.D. ETHODS FOR RECOVERING METAL PRODUCTS / COMPOU DS

[0052] In one aspect, the present disclosure relates to methods for recovering metal compounds from mine waste. The method can include contacting the mine waste with a first base in an amount sufficient enough to adjust the pH to a value of about 3.5 to about 4.0, thereby forming a mixture of a first aqueous phase and a first metal precipitate; separating thefirst metal precipitate from the first aqueous phase; contacting the first aqueous phase with a second base in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a second aqueous phase and a first solid concentrate; separating the first solid concentrate from the second aqueous phase; contacting the first solid concentrate with a first acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a third aqueous phase and a second solid concentrate; separating the third aqueous phase and the second solid concentrate; contacting the third aqueous phase with a third base in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a fourth aqueous phase and a third solid concentrate; and separating the fourth aqueous phase and the third solid concentrate; wherein the third solid concentrate comprises a second metal precipitate. In a further aspect, the third aqueous phase can be further contacted with 8-hydroxyquinoline (oxine), before, after, or at the same time as it is contacted with the third base. In another aspect, the method can include contacting the mine waste with a first base in an amount sufficient enough to adjust the pH to a value of about 3.5 to about 4.0, about 3.5 to about 3.8, about 3.7 to about 4.0, or about 3.6 to about 3.9. In one aspect, any one of the bases can be selected from sodium hydroxide, ammonium hydroxide, calcium hydroxide, ammonium acetate, and a combination thereof.

[0053] The method can further include washing the third solid concentrate; calcining the third solid concentrate, thereby forming a calcined solid concentrate; contacting the calcined solid concentrate with a second acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a fifth aqueous phase and a gaseous phase; separating the fifth aqueous phase from the gaseous phase; and contacting the fifth aqueous phase with a fourth base in an amount sufficient enough to adjust the pH to a value of about 5.5, thereby forming a fourth solid concentrate; wherein the fourth solid concentrate comprises the second metal precipitate. In a further aspect, the fourth solid concentrate can comprise the second metal precipitate in a weight percentage of about 70% to about 100%, about 75% to about 100%, about 80% to about 100%, about 85% to about 100%, about 90% to about 100%, about 95% to about 100%, about 70% to about 95%, about 75% to about 95%, about 80% to about 95%, or about 85% to about 95%. In a further aspect, the third solid concentrate can comprise a metal oxinate solid. In one aspect, the metal oxinate solid can be aluminum oxinate. In a further aspect, the calcined solid concentrate can comprise an aluminum compound, such as an aluminum oxide. In one aspect, the second metal precipitate can include an aluminum compound. In a further aspect, the aluminum compound is aluminum hydroxide (e.g., aluminum (III) hydroxide - AI(OH)3). In another aspect, the calcined solid concentrate can comprise a carbonate compound. The addition of an acid can dissolve the calcined solid concentrate and in one aspect, without wishing to be bound by theory, canremove the carbonate compound in the gaseous phase. In one aspect, the gaseous phase comprises carbon dioxide.

[0054] In another aspect, the calcined solid concentrate may not comprise a carbonate compound. In a further aspect, the method can further include washing the third solid concentrate; calcining the third solid concentrate, thereby forming a calcined solid concentrate; and contacting the calcined solid concentrate with a fourth base in an amount sufficient enough to adjust the pH to a value of about 5.5, thereby forming a fourth solid concentrate; wherein the fourth solid concentrate comprises the second metal precipitate. In a further aspect, the fourth solid concentrate can comprise the second metal precipitate in a weight percentage of about 70% to about 100%, about 75% to about 100%, about 80% to about 100%, about 85% to about 100%, about 90% to about 100%, about 95% to about 100%, about 70% to about 95%, about 75% to about 95%, about 80% to about 95%, or about 85% to about 95%. In a further aspect, the third solid concentrate can comprise a metal oxinate solid. In one aspect, the metal oxinate solid can be aluminum oxinate. In a further aspect, the calcined solid concentrate can comprise an aluminum compound, such as an aluminum oxide. In one aspect, the second metal precipitate can include an aluminum compound. In a further aspect, the aluminum compound is aluminum hydroxide (e.g., aluminum (III) hydroxide - Al (OH).

[0055] The first metal precipitate can include an iron compound. In one aspect, the iron compound is Fe (III) hydroxide (Fe(OH)3). Separating the first metal precipitate from the first aqueous phase can include allowing the precipitate to settle and removing all or most of the aqueous phase from the mixture of the first metal precipitate and the first aqueous phase. Following the separation, the first metal precipitate can undergo further treatment. For example, the first metal precipitate can be dewatered. In one aspect, the dewatering can include evaporation, filtration (e.g., vacuum filtration), or a combination thereof. The solid material that remains after the dewatering step can be further dried, such as by air drying or heat drying (e.g., in an oven). In another aspect, the solid material remaining after dewatering or after the additional drying steps can be crushed, ground, pulverized, milled, and the like to form particles of various sizes. The particles can optionally be sieved to separate out particles of particular sizes or in a particular size range.

[0056] The second metal precipitate can include an aluminum compound. In one aspect, the aluminum compound is aluminum hydroxide (e.g., aluminum (III) hydroxide - AI(OH)3). In one aspect, the fourth solid concentrate can comprise the second metal precipitate and an aqueous phase. In one aspect, the second metal precipitate can be separated from the aqueous phase. Separating the second metal precipitate from the aqueous phase can include allowing the precipitate to settle and removing all or most of the aqueous phase from the fourthsolid concentrate. Following the separation, the second metal precipitate can undergo further treatment. For example, the second metal precipitate can be dewatered. In one aspect, the dewatering can include evaporation, filtration (e.g., vacuum filtration), or a combination thereof. The solid material that remains after the dewatering step can be further dried, such as by air drying or heat drying (e.g., in an oven). In another aspect, the solid material remaining after dewatering or after the additional drying steps can be crushed, ground, pulverized, milled, and the like to form particles of various sizes. The particles can optionally be sieved to separate out particles of particular sizes or in a particular size range.

[0057] The method can further include contacting the second aqueous phase with a fourth base in an amount sufficient enough to adjust the pH to a value of about 7.0 to about 9.0, thereby forming a mixture of a sixth aqueous phase and a fifth solid concentrate and separating the sixth aqueous phase and the fifth solid concentrate; wherein the fifth solid concentrate comprises at least one rare earth element. The sixth aqueous phase can be suitable for release into the environment. In one aspect, the pH of the sixth aqueous phase is adjusted to about 7.0 to about 8.0 before release. In another aspect, the fifth solid concentrate can be used as a feedstock for recovery of rare earth elements and other critical minerals. Various methods for the isolation and recovery of critical minerals and rare earth elements from feedstocks can be found in U.S. Patent No. 1 1 ,827,954; U.S. Patent Application Nos. 17 / 115,128 and 17 / 706,584; and Inti. Patent Application Nos. PCT / US2020 / 042674, PCT / US2023 / 021564, and PCT / US2023 / 025623; each of which are incorporated herein by reference.

[0058] Also disclosed herein is a method to recover metal compounds from AMD. The method can include contacting the AMD with sodium hydroxide in an amount sufficient enough to adjust the pH to a value of about 3.5 to about 4.0, thereby forming a mixture of a first aqueous phase and a first metal precipitate; separating the first metal precipitate from the first aqueous phase; contacting the first aqueous phase with sodium hydroxide in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a second aqueous phase and a second metal precipitate; separating the second metal precipitate from the second aqueous phase; contacting the second metal precipitate with hydrochloric acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a third aqueous phase and an acidic solid; separating the third aqueous phase and the acidic solid; contacting the third aqueous phase with ammonium acetate in an amount sufficient enough to adjust the pH to a value of about 5.0 and 8-hydroxyquinoline (oxine), thereby forming a mixture of a fourth aqueous phase and a metal oxinate solid; and separating the fourth aqueous phase and the metal oxinate solid. In another aspect, the method can include contacting the AMD with sodium hydroxide in an amount sufficient enough to adjustthe pH to a value of about 3.5 to about 4.0, about 3.5 to about 3.8, about 3.7 to about 4.0, or about 3.6 to about 3.9.

[0059] The method can further include washing the metal oxinate solid; calcining the metal oxinate solid, thereby forming a calcined solid; contacting the calcined solid with hydrochloric acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a fifth aqueous phase and a gaseous phase; separating the fifth aqueous phase and the gaseous phase; and contacting the fifth aqueous phase with ammonium hydroxide in an amount sufficient enough to adjust the pH to a value of about 5.5, thereby forming a metal hydroxide solid. In a further aspect, the metal hydroxide solid can have a relatively high purity. In one aspect, the metal hydroxide solid can comprise the metal hydroxide in a weight percentage of about 70% to about 100%, about 75% to about 100%, about 80% to about 100%, about 85% to about 100%, about 90% to about 100%, about 95% to about 100%, about 70% to about 95%, about 75% to about 95%, about 80% to about 95%, or about 85% to about 95%. In one aspect, the metal hydroxide solid can include aluminum hydroxide. In another aspect, the metal oxinate solid can be aluminum oxinate. In a further aspect, the calcined solid can comprise an aluminum compound, such as an aluminum oxide. In another aspect, the calcined solid can comprise a carbonate compound. The addition of an acid can dissolve the calcined solid and in one aspect, without wishing to be bound by theory, can remove the carbonate compound in the gaseous phase. In one aspect, the gaseous phase comprises carbon dioxide.

[0060] In another aspect, the calcined solid may not comprise a carbonate compound. In a further aspect, the method can further include washing the metal oxinate solid; calcining the metal oxinate solid, thereby forming a calcined solid; and contacting the calcined solid with ammonium hydroxide in an amount sufficient enough to adjust the pH to a value of about 5.5, thereby forming a metal hydroxide solid. In one aspect, the metal hydroxide solid can comprise the metal hydroxide in a weight percentage of about 70% to about 100%, about 75% to about 100%, about 80% to about 100%, about 85% to about 100%, about 90% to about 100%, about 95% to about 100%, about 70% to about 95%, about 75% to about 95%, about 80% to about 95%, or about 85% to about 95%. In one aspect, the metal hydroxide solid can include aluminum hydroxide. In another aspect, the metal oxinate solid can be aluminum oxinate. In a further aspect, the calcined solid can comprise an aluminum compound, such as an aluminum oxide. In another aspect, the calcined solid can comprise a carbonate compound.

[0061] The first metal precipitate of this method can include an iron compound. In one aspect, the iron compound is Fe (III) hydroxide (Fe(OH)3). Separating the first metal precipitate from the first aqueous phase can include allowing the precipitate to settle and removing all or most of the aqueous phase from the mixture of the first metal precipitate and the first aqueousphase. Following the separation, the first metal precipitate can undergo further treatment. For example, the first metal precipitate can be dewatered. In one aspect, the dewatering can include evaporation, filtration (e.g., vacuum filtration), or a combination thereof. The solid material that remains after the dewatering step can be further dried, such as by air drying or heat drying (e.g., in an oven). In another aspect, the solid material remaining after dewatering or after the additional drying steps can be crushed, ground, pulverized, milled, and the like to form particles of various sizes. The particles can optionally be sieved to separate out particles of particular sizes or in a particular size range.

[0062] The second metal precipitate of this method can include an aluminum compound. In one aspect, the metal hydroxide solid includes aluminum hydroxide, (e.g., aluminum (III) hydroxide - AI(OH)3). The metal hydroxide solid can be in a mixture with an aqueous phase. The metal hydroxide solid can be separated from the aqueous phase, for example by allowing the solid to settle and removing all or most of the aqueous phase from the mixture. Following the separation, the metal hydroxide solid can undergo further treatment. For example, the metal hydroxide solid can be dewatered. In one aspect, the dewatering can include evaporation, filtration (e.g., vacuum filtration), or a combination thereof. The solid material that remains after the dewatering step can be further dried, such as by air drying or heat drying (e.g., in an oven). In another aspect, the solid material remaining after dewatering or after the additional drying steps can be crushed, ground, pulverized, milled, and the like in order to form particles of various sizes. The particles can optionally be sieved to separate out particles of particular sizes or in a particular size range.

[0063] The method can further include contacting the second aqueous phase with a base in an amount sufficient enough to adjust the pH to a value of about 7.0 to about 9.0, thereby forming a mixture of a sixth aqueous phase and a fifth solid concentrate and separating the sixth aqueous phase and the fifth solid concentrate; wherein the fifth solid concentrate comprises at least one rare earth element. The sixth aqueous phase can be suitable for release into the environment. In one aspect, the pH of the sixth aqueous phase is adjusted to about 7.0 to about 8.0 before release. In another aspect, the first solid concentrate can be used as a feedstock for recovery of rare earth elements and other critical minerals. Various methods for the isolation and recovery of critical minerals and rare earth elements from feedstocks can be found in U.S. Patent No. 1 1 ,827,954; U.S. Patent Application Nos. 17 / 1 15,128 and 17 / 706,584; and Inti. Patent Application Nos. PCT / US2020 / 042674, PCT / US2023 / 021564, and PCT / US2023 / 025623; each of which are incorporated herein by reference.

[0064] One example process utilizing selective precipitation to extract Fe and Al products from AMD is shown in FIG. 1. A field operation can be set up to extract Fe and Al sludge from aselected AMD source, for example, at a site that has an existing AMD treatment process already established. In regards to FIG. 1 , the process of Fe and Al extractions includes the following steps: transferring AMD feedstock to a first separator (label 1); adding enough hydrogen peroxide to the first separator to convert ferrous iron to ferric iron and adding enough base to the first separator to raise the resultant solution pH to about 3.5; separating the first solid phase and the first aqueous phase whereby the first solid phase is comprised primarily of an iron-based sludge; filtering the first aqueous phase (label 2); transferring the filtered first aqueous phase to a second separator (label 3); adding enough base to the second separator to raise the resultant solution pH to about 5; separating the second solid phase and the second aqueous phase whereby the second solid phase is comprised primarily of an aluminum based sludge; transfer the second aqueous phase to a third separator (label 4); adding enough base to the third separator to raise the resultant solution pH to about 7 to 9; separating the third solid phase and the third aqueous phase whereby the third solid phase is comprised of sludge enriched in rare earth elements and the third aqueous phase is treated effluent for discharge to a standard water treatment facility; transferring the second solid phase comprised primarily of an aluminum-based sludge to a dewatering station (label 6); transferring the water extracted from the dewatering station to the third separator; transferring the aluminum-based sludge from the dewatering station to a hopper (labels 7 and 8); transferring the aluminum-based sludge from the hopperto a dryerto produce aluminum hydroxide powder (label 9). The sludge of the third solid phase can be a potential feedstock for the recovery of rare earth elements and other critical minerals.

[0065] Fe compounds recovered using the methods disclosed herein can be used as a sorbent for removing contaminants such as phosphorous and / or toxic elements such as arsenic, selenium, and other heavy metals. In another aspect, the Fe compounds recovered can be used to control algae in fish tanks aquariums, municipal wastewater treatment, agricultural run-offs, and the like. The Al compounds recovered can be further processed and used in cement production or as flame retardants. Further details regarding the manufacturing and use of representative recovered compounds can be found Example 3. The recovered precipitates and / or solids, when not fully dried, can also be referred to as a sludge.E. REFERENCES

[0066] References are cited herein throughout using the format of author names and year published enclosed by parentheses corresponding to one or more of the following numbered references. For example, citation of the first two references immediately herein below would be indicated in the disclosure as (Abed et al., 2017; Ahmed and Lin, 2017).

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[0068] Ahmed, M. and Lin, L.-S. (2017) Ferric Reduction in Organic Matter Oxidation and Its Applicability for Anaerobic Wastewater T reatment: A Review and Future Aspects, Reviews in Environmental Science and Bio / Technology, 16(2), 273-287.

[0069] Ahmed, M„ Lin, 0., Saup, C. M., Wilkins, M. J., and Lin, L.-S. (2019) Effects of Fe / S Ratio on the Kinetics and Microbial Ecology of an Fe(lll)- dosed Anaerobic Wastewater Treatment System, J. Hazardous Materials, 5 (369), 593-600.

[0070] Ahmed, M., Saup, C. M., Wilkins, M. J., Lin, L.-S. (2020) Continuous Ferric Iron-dosed Anaerobic Wastewater Treatment: Organics Removal, Kinetics, Sludge Characteristics, and Microbial Composition, Journal of Environmental Chemical Engineering, 8, 103537.

[0071] Ahmed, M., Anwar, R., Deng, D., Garner, E., and L.-S. Lin (2021) Functional interrelationships of microorganisms in iron-based anaerobic wastewater treatment, Microorganisms, special issue Wastewater Microbiology, 9, 1039.

[0072] Alfaya, E., Iglesias, O., Pazos, M., & Sanrom'an, M. A. (2015) Environmental application of an industrial waste as catalyst for the electro-Fenton-like treatment of organic pollutants. RSC Adv. 5: 14416-14424.

[0073] Amanda, N., & Moersidik, S. S. (2019) Characterization of Sludge Generated from Acid Mine Drainage Treatment Plants. Journal of Physics 1351 .

[0074] Andersen, S. L., Flores, R. G., Madeira, V. S., Jose, H. J., & Moreira, R. F. (2012) Synthesis and Characterization of Acicular Iron Oxide Particles Obtained from Acid Mine Drainage and Their Catalytic Properties in Toluene Oxidation. Ind. Eng. Chem. Res. 51(2): 767-774.

[0075] Anwar, R., Ahmed, M., Seats, P., Huang Q., and Lin, L.-S. (2021) Prospect of Utilizing Coal Mine Drainage Sludge as an Iron Source for Value-creating Applications, Reviews in Environmental Science and Bio / Technology, 20, 679-695.

[0076] Azam HM, Finneran KT (2013) Ferric iron amendment increases Fe(lll)-reducing microbial diversity and carbon oxidation in on-site wastewater systems. Chemosphere, 90: 1435- 1443.

[0077] Buzby, K. Newton, M. A. R., Waterland, N. L., and Lin, L-S. (2021) Phosphate sorption by AMD-coated sand in a greenhouse setting. (In prep).

[0078] Chen, T., Yana, B., Lei, C., & Xiao, X. (2014) Pollution control and metal resource recovery for acid mine drainage. Hydrometallurgy 147-148: 112-119.

[0079] Cui, M., Jang, M., & Cho, S.-H. (201 1) Potential application of sludge produced from coal mine drainage treatment for removing Zn(ll) in an aqueous phase. Environmental Geochemistry and Health 33: 103-112.

[0080] Dempsey, B. A. & Jeon, B.-H. (2001) Characteristics of sludge produced from passive treatment of mine drainage, Geochemistry: Exploration, Environment, Analysis, 1 , 89-94.

[0081] Flores, R. G., Andersen, S. L., & Maia, L. K. (2012) Recovery of iron oxides from acid mine drainage and their application as adsorbent or catalyst. Journal of Environmental Management 11 1 : 53-60.

[0082] Ha, N. T„ & Anh, B. T. (2017) The removal of heavy metals by iron mine drainage sludge and Phragmites australis. 2nd Transdisciplinary Research on Environmental Problems in Southeast Asia.71. IOP Conf. Series: Earth and Environmental Science.

[0083] Kalin, M., Fyson, A., & N. Wheeler, W. (2006) The chemistry of conventional and alternative treatment systems for the neutralization of acid mine drainage. Science of The Total Environment. 366(2-3): 395-408.

[0084] Kefeni, K. K., Msagati, T. M., Maree, J. P., & Mamba, B. B. (2015) Metals and sulphate removal from acid mine drainage in two steps via ferrite sludge and barium sulphate formation. Minerals Engineering. 81 : 79-87.

[0085] Kulandaivelu, J., Gao, J., Song, Y., Shrestha, S., Li, X., Li, J., Doederer, K., Keller, J., Yuan, Z., Mueller, J.F., Jiang, G. (2019) Removal of Pharmaceuticals and Illicit Drugs from Wastewater Due to Ferric Dosing in Sewers, Environ. Sci. Technol., 53, 6245-6254.

[0086] Huang, S. and Jaffe, P. R. (2018) Isolation and characterization of an ammoniumoxidizing iron reducer: Acidimicrobiaceae sp. A6. PLoS ONE, 13(4), e0194007.

[0087] Netpradit, S., Thiravetyan, P., & Towprayoon, S. (2003) Application of waste metal hydroxide sludge for adsorption of azo reactive dyes. Water Res. 37: 763-772.

[0088] Penn, C. J., Bryant, R. B., Kleinman, P. J., & Allen, A. L. (2007) Removing dissolved phosphorus from drainage ditch water with phosphorus sorbing materials. Journal of Soil and Water Conservation 62(4): 269-276.

[0089] Rakotonimaro, T. V., Neculita, C. M., Bussiere, B., Benzaazoua, M., & Zagury, G. J. (2017) Recovery and reuse of sludge from active and passive treatment of mine drainage- impacted waters: a review. Environ Sci Pollut Res. 24: 73-91.

[0090] Rebosura Jr, M., Salehin, S, Pikaar, I., Kulandaivelu, J., Jiang, G., Keller, J., Sharma, K., Yuan, Z. (2020) Effects of in-sewer dosing of iron-rich drinking water sludge on wastewater collection and treatment systems, Wat. Res., 171 , 1 15396.

[0091] Shim, M. J., Choi, B. Y., Lee, G., Hwang, Y. H., Yang, J.-S., O'Loughlin, E. J., & Kwon, M. J. (2015) Water quality changes in acid mine drainage streams in Gangneung, Korea, 10 years after treatment with limestone. Journal of Geochemical Exploration 159: 234-242.

[0092] Shuai, W., and Jaffe, P. R. (2019) Anaerobic ammonium oxidation coupled to iron reduction in constructed wetland mesocosms, Sci Total Environ., 648, 984-992.

[0093] Sibrell, P.L., & Watten, B. J. (2003) Evaluation of sludge produced by limestone neutralization of AMD at the Friendship Hill National Historic Site. 9th Billings Land Reclamation Symposium. Billings MT: American Society of Mining and Reclamation.

[0094] Sibrell, P. L., Montgomery, G. A., Ritenour, K. L., & Tucker, T. W. (2009) Removal of phosphorus from agricultural wastewaters using adsorption media prepared from acid mine drainage sludge. Water Research 43: 2240-2250.

[0095] Tony, M. A. & Lin, L.-S. (2020a) Performance of acid mine drainage sludge as an innovative catalytic oxidation source for treating vehicle-washing wastewater, Journal of Dispersion Science and Technology, DOI No. 10.1080 / 01932691.2020.1813592.

[0096] Tony, M. A. & Lin, L.-S. (2020b) Attenuation of organics contamination in polymers processing effluent using iron-based sludge: Process optimization and oxidation mechanism, Environmental Technology, DOI No. 10.1080 / 09593330.2020.1803417. 718-727

[0097] Tony, M. A. & Lin, L.-S. (2020c) Iron recovery form acid mine drainage sludge as a Fenton source for municipal wastewater treatment, International Journal of Environmental Analytical Chemistry, DOI No. 10.1080 / 03067319.2020.1734196.

[0098] Viadero, R. C., Wei, X., & Buzby, K. (2006) Characterization and Dewatering Evaluation of Acid Mine Drainage Sludge from Ammonia Neutralization. Environmental Engineering Science 23(4): 734-743.

[0099] Wei, X., Roger C. Viadero, J., & Buzby, K. M. (2005) Recovery of Iron and Aluminum from Acid Mine Drainage by Selective Precipitation. Environmental Engineering Science 22(6).

[0100] Wei, X., & Viadero Jr., R. C. (2007) Adsorption and Precoat Filtration Studies of Synthetic Dye Removal by Acid Mine Drainage Sludge. Journal of environmental engineering 133(6): 633-640.

[0101] Wei, X., Viadero, R., & Bhojappa, S. (2008) Phosphorus removal by acid mine drainage sludge from secondary effluents of municipal wastewater treatment plants. Water Res. 42: 3275- 3284.

[0102] Yan, L, Xu, Z., Wang, X. et al. (2018) Synergistic effects of aluminum hydroxide on improving the flame retardancy and smoke suppression properties of transparent intumescent fire- retardant coatings. J Coat Technol Res, 15, 1357-1369.

[0103] Yang, Y„ Chen, T., Sumona, M„ Sen Gupta, B„ Sun, Y„ Hu, Z., Zhan, X. (2017) Utilization of iron sulfides for wastewater treatment: a critical review, Rev. Environ. Sci. Biotechnol., 16, 289-308.

[0104] Zinck, J. (2006) Disposal, reprocessing and reuse options for acidic drainage treatment sludge. 7th International Conference on Acid Rock Drainage (ICARD) (pp. 2604-2617). St. Louis MO: American Society of Mining and Reclamation (ASMR).

[0105] Alder, P.R., and P.L. Sibrell. 2003. Sequestration of phosphorus by acid mine drainage floc. Journal of Environmental Quality 32, 1122-1129.

[0106] “Sampling vegetation attributes.” Technical Reference 1734-4, Denver, Colo.: US Department of Agriculture, http: / / www.blm.gov / nstc / library / pdf / samplveg.pdf. (August 5, 2015).

[0107] “Measuring and monitoring: Plant population.” Technical Reference 1730-1 , Denver, Colo.: US Bureau of Land Management. http: / / www.blm.gov / nstc / library / pdf / MeasAndMon.pdf. (August 8, 2015).

[0108] Publications. (n.d.). SERA-17. Retrieved November 2, 2023, from https: / / sera17.wordpress.ncsu.edu / publications /

[0109] Rodrigues Silva, A., B. Watters, J. Quaranta, and L. Hopkinson. 2022. Evaluation of the use of AMD sludge as soil amendment. Proceedings of the West Virginia Academy of Science, 94(3): 17-23.

[0110] Skousen, J, A Sexstone, P Ziemkiewicz. 2000. Acid mine drainage control and treatment. Reclamation of Drastically Disturbed Lands, 2nd ed. American Society of Agronomy, Madison, Wl, 131-168.

[0111] Watters, Brady, "Exploring the Usage of Acid Mine Drainage Sludge as a Soil Amendment for Reclaimed Mine Lands" (2023). Graduate Theses, Dissertations, and Problem Reports. 11713. https: / / researchrepository.wvu.edu / etd / 11713F. ASPECTS

[0112] The following listing of exemplary aspects supports and is supported by the disclosure provided herein.

[0113] Aspect 1. A method to recover metal compounds from a mine waste, the method comprising: (a) contacting the mine waste comprising at least one metal with an oxidizingagent in an amount sufficient enough to oxidize the at least one metal; (b) contacting the mine waste with a first base in an amount sufficient enough to adjust the pH to a value of about 3.5 to about 4.0, thereby forming a mixture of a first aqueous phase and a first metal precipitate; (c) separating the first metal precipitate from the first aqueous phase; (d) contacting the first aqueous phase with a second base in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a second aqueous phase and a first solid concentrate; (e) separating the first solid concentrate from the second aqueous phase; (f) contacting the first solid concentrate with a first acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a third aqueous phase and a second solid concentrate; (g) separating the third aqueous phase and the second solid concentrate; (h) contacting the third aqueous phase with a third base in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a fourth aqueous phase and a third solid concentrate; and (i) separating the fourth aqueous phase and the third solid concentrate; wherein the third solid concentrate comprises a second metal precipitate.

[0114] Aspect 2. The method of aspect 1 , wherein the first metal precipitate comprises an iron compound.

[0115] Aspect 3. The method of aspect 1 , wherein the first metal precipitate comprises iron (III) hydroxide.

[0116] Aspect 4. The method of any one of aspects 1-3, wherein the oxidizing agent is a peroxide.

[0117] Aspect 5. The method of any one of aspects 1-4, further comprising contacting the third aqueous phase with 8-hydroxyquinoline.

[0118] Aspect 6. The method of any one of aspects 1-5, further comprising: (a) washing the third solid concentrate; (b) calcining the third solid concentrate, thereby forming a calcined solid concentrate; (c) contacting the calcined solid concentrate with a second acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a fifth aqueous phase and a gaseous phase; (d) separating the fifth aqueous phase from the gaseous phase; and (e) contacting the fifth aqueous phase with a fourth base in an amount sufficient enough to adjust the pH to a value of about 5.5, thereby forming a fourth solid concentrate; wherein the fourth solid concentrate comprises the second metal precipitate.

[0119] Aspect 7. The method of any one of aspects 1-6, wherein the second metal precipitate comprises an aluminum compound.

[0120] Aspect 8. The method of any one of aspects 1-7, wherein the second metal precipitate comprises aluminum (III) hydroxide.

[0121] Aspect 9. The method of any one of aspects 1-8, wherein the first base, the second base, and the third base are individually selected from sodium hydroxide, ammonium hydroxide, calcium hydroxide, ammonium acetate, and a combination thereof.

[0122] Aspect 10. The method of any one of aspects 1-9, further comprising: (a) contacting the second aqueous phase with a fourth base in an amount sufficient enough to adjust the pH to a value of about 7.0 to about 9.0, thereby forming a mixture of a sixth aqueous phase and a fifth solid concentrate; and (b) separating the sixth aqueous phase and the fifth solid concentrate; wherein the fifth solid concentrate comprises at least one critical mineral.

[0123] Aspect 11. The method of aspect 10, further comprising providing the fifth solid concentrate as a feedstock for recovery of critical minerals.

[0124] Aspect 12. The method of aspect 10 or aspect 11 , wherein the fourth base is selected from sodium hydroxide, ammonium hydroxide, calcium hydroxide, and any combination thereof.

[0125] Aspect 13. A method to recover metal compounds from acid mine drainage (AMD), the method comprising: (a) contacting the AMD comprising at least one metal with an oxidizing agent in an amount sufficient enough to oxidize the at least one metal; (b) contacting the AMD with sodium hydroxide in an amount sufficient enough to adjust the pH to a value of about 3.5 to about 4.0, thereby forming a mixture of a first aqueous phase and a first metal precipitate; (c) separating the first metal precipitate from the first aqueous phase; (d) contacting the first aqueous phase with sodium hydroxide in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a second aqueous phase and a second metal precipitate; (e) separating the second metal precipitate from the second aqueous phase; (f) contacting the second metal precipitate with hydrochloric acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a third aqueous phase and an acidic solid; (g) separating the third aqueous phase and the acidic solid; (h) contacting the third aqueous phase with ammonium acetate in an amount sufficient enough to adjust the pH to a value of about 5.0 and 8-hydroxyquinoline, thereby forming a mixture of a fourth aqueous phase and a metal oxinate solid; and (i) separating the fourth aqueous phase and the metal oxinate solid.

[0126] Aspect 14. The method of aspect 13, wherein the first metal precipitate comprises an iron compound.

[0127] Aspect 15. The method of aspect 13, wherein the first metal precipitate comprises iron (III) hydroxide.

[0128] Aspect 16. The method of any one of aspects 13-15, wherein the second metal precipitate comprises an aluminum compound.

[0129] Aspect 17. The method of any one of aspects 13-16, further comprising: (a) washing the metal oxinate solid; (b) calcining the metal oxinate solid, thereby forming a calcined solid; (c) contacting the calcined solid with hydrochloric acid in an amount sufficient enough to adjust the pH to a value of about 1 .0 to 2.5, thereby forming a mixture of a fifth aqueous phase and a gaseous phase; (d) separating the fifth aqueous phase and the gaseous phase; and (e) contacting the fifth aqueous phase with ammonium hydroxide in an amount sufficient enough to adjust the pH to a value of about 5.5, thereby forming a metal hydroxide solid.

[0130] Aspect 18. The method of aspect 17, wherein the metal hydroxide solid comprises aluminum hydroxide.

[0131] Aspect 19. The method of any one of aspects 13-18, further comprising: (a) contacting the second aqueous phase with a base in an amount sufficient enough to adjust the pH to a value of about 7.0 to about 9.0, thereby forming a mixture of a sixth aqueous phase and a first solid concentrate; and (b) separating the sixth aqueous phase and the fifth solid concentrate; wherein the fifth solid concentrate comprises at least one critical mineral.

[0132] Aspect 20. The method of aspect 19, further comprising providing the fifth solid concentrate as a feedstock for recovery of critical minerals.

[0133] From the foregoing, it will be seen that aspects herein are well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure.

[0134] While specific elements and steps are discussed in connection to one another, it is understood that any element and / or steps provided herein is contemplated as being combinable with any other elements and / or steps regardless of explicit provision of the same while still being within the scope provided herein.

[0135] It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

[0136] Since many possible aspects may be made without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings and detailed description is to be interpreted as illustrative and not in a limiting sense.

[0137] 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. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.

[0138] Now having described the aspects of the present disclosure, in general, the following Examples describe some additional aspects of the present disclosure. While aspects of the present disclosure are described in connection with the following examples and the corresponding text and figures, there is no intent to limit aspects of the present disclosure to this description. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the present disclosure.G. EXAMPLES

[0139] 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 the compounds, compositions, articles, devices and / or methods claimed herein are made and evaluated and are intended to be purely exemplary of the disclosure and are not intended to limit the scope of what the inventors regard as their disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric.1. EXTRACTION AND UTILIZATION OF AMD IRON AND ALUMINUM FOR VALUECREATING APPLICATIONS TO ENHANCE WASTE MANAGEMENT SUSTAINABILITY

[0140] Technical Approach'. Acid mine drainage (AMD), characterized by high levels of acidity, is a major environmental concern for mining regions worldwide (Chen et al., 2014). Along with its low pH, AMD typically contains elevated levels of dissolved solids such as iron, aluminum, sulfate, and toxic constituents (Shim et al., 2015), impacting water quality and biota in receiving waters (Chen et al., 2014). Various treatment processes have been developed and used to mitigate AMD impacts, resulting in large quantities of AMD sludge that require disposal (Amanda and Moersidik, 2019; Rakotonimaro et al., 2017; Wei et al., 2008). Despite improvements in AMD neutralization processes, some critical issues such as chemical stability, leaching of toxic metals, and storage requirements hamper AMD sludge disposal (Kalin et al., 2006). Sludge management measures such as dewatering, pretreatment, chemical stabilization, and landfill have been used to address these issues (Kefeni et al., 2015). However, high sludge handling and disposal costs (USD$23-75 per ton) represent a significant economic liability (Rakotonimaro et al., 2017) and consequently the feasibility ofAMD treatment methods is often evaluated in terms of the quantity and quality of the produced sludge (Kefeni et al., 2015).

[0141] Considering the instability, potential environmental concerns, and high disposal cost of the AMD sludge (AMDS), utilization of this waste is an attractive management strategy (Cui et al., 2011 ; Sibrell and Watten, 2003). Previous studies have shown utilization of mine drainage sludge in sorptive removal of phosphorus, heavy metals, color, and dyes (Ha and Anh, 2017; Kefeni et al., 2015; Netpradit et al., 2003; Penn et al., 2007; Sibrell et al., 2009; Wei et al., 2008; Zinck, 2006). AMDS has also been used as an iron catalyst facilitating Fenton reactions for organics oxidation (Alfaya et al., 2015; Andersen et al., 2012; Flores et al., 2012;). However, presence of toxic elements such as cadmium, copper, mercury, lead and metalloids such as arsenic and selenium in the AMD sludge causes contamination from utilizing the sludge materials.

[0142] An approach to utilizing sludge is to extract the useful elements from AMD. In particular, iron (Fe) and aluminum (Al), two predominant metals in AMD, can be extracted as hydroxides using a selective precipitation method (Wei et al., 2005). Previous studies show coal mine drainage sludge contains Fe minerals ranging from 30% to 70% by weight (Abed et al., 2017; Cui et al., 201 1 ; Viadero et al., 2006). Some passive treatment processes can generate sludge with around 95% Fe content (Rakotonimaro et al., 2017). Al content in AMD sludge has been found to range from 10 to 15 % by weight (Amanda and Moersidik, 2019; Viadero et al., 2006; Wei and Viadero Jr., 2007). Extracting these two elements from AMD treatment can greatly reduce the sludge quantities for disposal and create wide ranges of uses for value creation. For example, various forms of Fe have long been used to remove suspended solids, phosphorus, and odor ( / .e., sulfide) in water and wastewater sectors. Previous studies have also shown multi-faceted benefits of using Fe in wastewater treatment. Adding a small dose of Fe to onsite wastewater systems was found to enhance organics degradation rate and efficiency (Azam and Finneran, 2013). Recent findings showed dosing Fe to wastewater treatment produced biological sludge with higher dewatering properties (Rebosura Jr. et al., 2020), which can reduce polymer use for sludge dewatering and save costs. Another benefit is the removal of micropollutants such as toxic metals (Yang et al.,2017) and pharmaceutical compounds (Kulandaivelu et al., 2019) from wastewater by using Fe minerals. Other studies showed that certain bacteria can utilize iron in facilitating microbial reactions that remove nitrogen from wastewater (Shuai and Jaffe, 2019; Huang and Jaffe,2018). Aluminum hydroxide, AI(OH)3, is a known flame retardant (Yan et al., 2018) that has been used in various products such as spray, fire barrier paint, and powder to help reduce fire hazard. Recently, the selective precipitation procedure has been extended to extract rare earth element (REEs) from AMD as the first step of producing REEs from domestic sources. Theseresource recovery opportunities suggest a potential value chain that can be created from adopting and implementing novel AMD management approaches to not only alleviate environmental and economic liabilities but also create valuable by-products.

[0143] This example aims to systematically characterize causal linkages between various AMD treatment and sludge disposal factors and sludge properties (Anwar et al., 2021). The example is intended, at least in part, to provide a systematic understanding for developing AMD treatment and sludge disposal guidelines that would facilitate production of Fe sludge materials for specific beneficial applications. A two-stage AMD treatment method using selective precipitation can be used to generate high-purity Fe sludge for a range of beneficial applications. The analysis had a focus on extracting iron from the AMD sources in WV and estimated a total ferric iron mass loading rate to be approximately 324,000 ton / year (Anwar et al., 2021). Handling and disposal costs for this quantity of sludge were between $7.5 to $24 million per year, which could potentially be saved through extracting iron from the AMD sources. Furthermore, it has been demonstrated in the laboratory that it is feasible to use the AMD Fe innovative wastewater treatment using Fenton reactions, (Tony & Lin, 2020a, b,c), and with microbial reactions to remove organics and ammonium (Ahmed and Lin, 2017; Ahmed et al., 2019, 2020, 2021). Iron dosing in wastewater treatment can generate nutrientcontaining byproducts vivianite [Fe3(PO4)2'8H2O] and ferrous ammonium phosphate [FeNH4PO4]) that have fertilizer value and can be recovered for agricultural uses. A protocol of preparing Fe-coated sand and its use as a sorbent has also been demonstrated to reduce phosphorus loss to runoff and to serve as an on-demand phosphorous source for horticultural crops (Buzby et al., 2021).

[0144] Despite improvements in AMD treatment, the large volumes of sludge produced by the treatment processes and high economic costs to dispose of the sludge, among other factors, necessitate further improvements in the handling and further processing of AMD sludge. Such improvements to AMD management could include reducing the overall costs of processing AMD sludge, reducing the volume of sludge for disposal, and finding uses for the sludge. Herein is discussed a field demonstration of an AMD treatment approach to extract high-purity Fe and Al sludge materials, and to generate products of market quality using the extracted sludges. Overall, this AMD management approach can significantly reduce the quantities of AMD sludge for disposal and generate useful products to create value for mining communities.

[0145] Disclosed herein are selective precipitation processes to extract Fe and Al hydroxides in separate streams, and to develop sludge processing protocols to turn the extracted materials into two products (FIG. 2). In one aspect, the disclosed selective precipitation process pertains to turning the Fe sludge into Fe particles / pellets as a sorbent for removal of contaminants (e.g., phosphorus, heavy metals), and AI(OH)3powder as a flame retardant.

[0146] Selection of AMD sources. AMD sources can be selected based on a set of criteria including discharge flow, pH, metal concentrations ( / .e., high Fe and Al production rates) to extract Fe and Al while meeting regulatory discharge limits. AMD site data can be analyzed to generate maps of the AMD site. Flow rate as well as Fe and Al concentrations from the data can be used to estimate Fe and Al production rates from the AMD sources. AMD sources can then be screened based on a set of criteria including Fe / AI mass loading rates, pH, redox potential (ORP), total dissolved solids (TDS), road accessibility, and existing onsite treatment facility production rates.

[0147] Fe and Al mass loading rates from all the AMD sources can also be calculated. In addition, the dataset can be formatted as geocoded data structures and the data to be superimposed on a map of the study area. The data can be used to show a study area with AMD sources similar to FIG. 3. Results can include a shortened list of AMD sources eligible for applied field operations.

[0148] Optimize field operations for Fe and Al extraction. Field operations to extract Fe and Al sludge from a selected AMD source can rely on a selective precipitation method developed previously (Wei et al., 2005). Previous results showed selective precipitation of metals from AMD can be controlled by incrementally raising pH (FIG. 4). Specifically, the AMD pH can be raised to 3.5 to 4.0 which can selectively precipitate iron hydroxide Fe(OH)3, and then to approximately 5.0 to precipitate AI(OH)3 while other metals (including toxic elements) remain dissolved. These pH endpoints exclude other metals from the generated Fe and Al sludge and allow collection of high-purity sludge materials in separate streams.

[0149] In addition to the pH endpoints, AMD sludge characteristics also vary with the chemicals used to adjust the pH. Previous results show that resultant sludge was denser and settles faster when hydrated lime was used to precipitate Fe sludge than when sodium hydroxide was used. This affects settling time and ease of dewatering as well as chemical constituents in the sludge. Viadero et al. (2006) determined that ammonium hydroxide produced a sludge with a comparable SRF to sodium hydroxide reported by Dempsey and Jeon (2001), but lower than sodium hydroxide, hydrated lime or limestone neutralization reported by Sibrell and Watten (2003).

[0150] For the field operation, a design used to extract Fe sludge from AMD (FIG. 5) can be modified by adding an additional tank to collect sludge materials. Specifically, the operation pipes a flow of untreated AMD water to a series of three cone-bottom tank for pH adjustments using an alkaline chemical (e.g., hydrated lime). The field operations involve diverting an AMD flow to the first tank. In the first tank, ORP of the raw AMD water is monitored and, if necessary, an oxidant (e.g., hydrogen peroxide H2O2) can be added with mixing to ensure that all the Feis in the fully oxidized state ( / .e., +3). The pH can then be raised to a predetermined set point (e.g., 3.5) to selectively precipitate Fe. The chemical precipitate of Fe(OH)3can then be allowed to settle to the cone bottom for its separation from the supernatant. The supernatant can then piped to the second tank in which pH can be raised to 5 for AI(OH)3precipitation and settling. Similarly, the supernatant in the second tank can then be piped to the third tank for further pH adjustment from 7 to 8 to finish the AMD treatment and settling of the remaining sludge. The treated water can then be discharged back to the AMD stream for its treatment in an established process. Sludge characteristics can be altered using alkaline chemicals commonly used in AMD treatment such as caustic soda, hydrated lime, ammonium hydroxide, and so on separately or in combination with one another. The resultant sludge can then be characterized to determine which produces Fe and Al sludge that optimizes both physical properties (e.g., settling time and dewatering characteristics) and chemical composition (Fe and Al purity).

[0151] The field operation can then be operated as needed to generate sludge materials. The operation allows for calculation of the alkaline chemical dose for the piped AMD flow and production rates of three sludge materials - Fe(OH)3, AI(OH)3, and remaining sludge. The sludge materials can be sampled for laboratory analyses to determine solid content, Fe and Al content and purity as well as presence of other chemical elements and their concentrations. Variations in water quality of the AMD water can also be characterized and its effect on the chemical dosing, process operations, and sludge yields.

[0152] Sludge dewatering method. The generated sludge materials ( / .e., Fe, Al and remaining sludge) after separation from their supernatants are collected from a valve-controlled underdrain of the tank and transported for further processing. The dewatering properties of the sludge materials can be characterized by SRF measurements. To further dewater the sludge, a combination of filtration and evaporation can be used to dewater the sludge products. The sludge slurry can be placed in a frame with a wire mesh bottom supporting a mesh filter and allowed to drain. The frame can be refilled until it is full or until the supernatant no longer drains from the sludge. The solid can be air dried to further increase the solid content to ~60%. Solid content of the sludge materials before and after the dewatering can be measured by decantation of excess water if necessary, vacuum filtration using a Buchner funnel, then drying at 105 °C overnight.

[0153] Characterization ofFe and Al products. The dewatered sludge materials can be further processed to generate Fe and Al products for value creation. Fe particles / pellets of different controlled sizes and AI(OH)3powder can be targeted as the products. The Fe and Al products may be formed from either partially dry (>50% solids) or completely dried sludge. Partially dried sludge can be very firm and allow it to be formed into small pellets which can then becompletely dried. Alternatively, the dewatered Fe sludge can be dried in an oven at about 105°C overnight. The sludge can then be crushed if necessary and sieved to produce Fe particles of different sizes. These Fe particles can be used as a sorbent for removing contaminants such as phosphorus and toxic elements (e.g., As, Se, heavy metals). The product can have a wide range of potential applications including algae control in fish tanks and aquariums, municipal wastewater treatment, agricultural runoffs, etc.

[0154] To make AI(OH)s powder, the dewatered Al sludge can be further dewatered following the same procedure as the Fe sludge - oven dried at about 105°C overnight. The dried Al materials are then crushed into powder. A method of turning the dewatered Al sludge into its powder product using a rotary dryer can also be developed. The AI(OH)3 powder can be a market-ready material form as a flame retardant.

[0155] The sludge solids can then be characterized by their physical properties (e.g., solid content, particle size), morphology, minerology (e.g., metal (hydroxides), and chemical composition (e.g., weight %) using spectroscopic analyses including scanning electron microscope equipped with energy dispersion (SEM-EDS), X-ray powder diffraction (XRD), X- ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP) spectroscopy. In particular, the product purity can be quantified by acid digesting the products and measuring the concentrations of a suite of commonly found metals in AMD sources.

[0156] Evaluation of toxicity leaching characteristics of the residual sludge. In addition to quantifying the volume of the remaining sludge for disposal, Toxicity Characteristic Leaching Procedure (TCLP) can be conducted to examine leaching characteristics of toxic elements from the residual sludge generated from the last pH adjustment ( / .e., 7-8). The sludge material can be dewatered as described previously and then sampled via TCLP following the USEPA Method 131 1. The leachate / extractant can then be collected and analyzed for the eight toxic elements specified in the TCLP method to determine compliance of the allowable limits (Table 1).Table 1. Maximum allowable concentrations of six elements in the leachate from a Toxicity Characteristic Leaching Procedure (TCLP).

[0157] Techno-economic analysis on benefits. Techno-economic analysis (TEA) for a full- scale operation of the AMD source can be conducted using the developed Fe and Al extraction process. Specifically, the extraction operation allows estimation of Fe and Al sludge production rates from the AMD source and associated costs including those of alkaline chemical, dewatering operations (filter materials and power consumption), packaging and transportation. Potential savings resulting from the reduced quantities of AMD sludge for disposal can be estimated based on various disposal options (e.g. , impoundment, geotube, landfill). In addition, market values of the Fe and Al products can be estimated based on similar products on the market.2. EXPERIMENTAL PROTOCOL FOR AMD TREATMENT

[0158] AMD Chemical Composition. The composition of the parent rock material on AML impacts the composition of AMD and often includes iron (Fe), aluminum (Al), copper (Cu), cadmium (Cd), manganese (Mn), magnesium (Mg), and zinc (Zn) (Gray 1996, Kirby et al. 1999, and Skousen et al. 1998). In addition to the dissolved heavy metals, 17 chemically similar REE elements can also be concentrated in AMD (Verplanck et al. 2004, Zhao et al. 2007, Stewart et al. 2017).

[0159] Physical and Chemical AMD Treatment. A series of chemical reactions with metal sulfides, oxygen, and water produces ferrous iron (Fe 2+), ferric iron (Fe 3+), and acid produced AMD. The high acidity and low pH come from the reaction between ferric iron and the metal sulfate, pyrite, and is a contributing factor to the leaching of heavy metals into the environment. These elements within AMD are thus dependent on the pH of the water and cause ferric iron to precipitate out of solution.

[0160] Wei et al. (2005) utilized chemical neutralization techniques to selectively precipitate relatively pure iron and aluminum from AMD.

[0161] Aluminum (Al)-Silicon (Si) Coprecipitation. Due to the main chemical constituents being heavy metals and REEs, most of the literature does not consider silica as a contaminant when characterizing the purity of a product. Although the pH adjustment techniques can be utilized to selectively precipitate Al, the lack of characterization of coprecipitation of Al with Si can decrease the purity of the product. One focus can be to selectively recover Fe, precipitate relatively pure Al, perform a silicon removal process to separate Al from Si caused by coprecipitation, recover aluminum, and finally the production of aluminum hydroxide. Chemical techniques can also be used for resource recovery and purification of aluminum hydroxide [AI(OH)3] from AMD and other sources containing AI(OH)3to produce a product with a high yield and purity that can be commercially competitive when used as a fire retardant.

[0162] Experimental Protocols - AMD Collection and Water Sampling. Untreated AMD water sample collection occurred at the Department of Environmental Protection’s OMEGA acid mine drainage treatment site outside of Morgantown, West Virginia. Untreated AMD water was collected in 5-gallon buckets upstream before any treatment occurred, then transported back to a laboratory. The storage of all materials, unless specified, were kept at room temperature (20°C).

[0163] Experimental Protocols - Initial concentration of raw water. The starting material used in the proposed methodology included the untreated AMD, as well as a semi-dry AI(OH)3residue that was the product of a previous selective precipitation recovery experiments from the Omega AMD site. Iron was initially precipitated from Omega raw AMD water, which resulted in a semi-dry AI(OH)3residue that contained coprecipitated aluminum and silicon. The residue was rehydrated with water until a homogeneous mixture was obtained, then settled and the supernatant collected. Regardless of starting materials, the untreated AMD or AI(OH)3residue was allowed to settle, the supernatant siphoned and filtered to remove suspended solids and debris. The general water analysis of the raw Omega water was referenced by Wei et al., 2005, while the initial analysis of the targeted resources (Al, Fe) and contaminants (Si) start from the AI(OH)3residue from the Omega site. An aliquot of the filtrate was sampled for the metals (Al, Fe) and metalloid (Si) of interest.Table 2. Characteristics of raw AMD water from Omega Site as reported by Wei et al., 2005. No silicon (Si) was reported in the Raw AMD characteristics.

[0164] Experimental Protocols - Analytical Method. All samples analyzed to determine the concentration of Fe, Al, and Si were allowed to settle for a minimum of 12 hours, the supernatants collected, then filtered with a 22 pm filter under vacuum. Aqueous samples were transferred to a plastic centrifuge tube with a screw cap and diluted with a mixture of deionized water and 5% metal grade nitric acid to dissolve any remaining suspended solids. Sample concentrations were analyzed by inductively coupled plasma mass spectrometry (ICP-MS).

[0165] Experimental Protocols - Experimental Procedure. The present example focuses on the resource recovery of Fe and Al from AMD using a combination of selective precipitation and coordination chemistry techniques. The general methodology includes three main protocols: 1) Fe Recovery, 2) Silicon Separation and Removal, and 3) Aluminum Refinement and Recovery (FIG. 6). The protocols are also referenced as the Fe protocol, Si protocol, and Al protocol throughout. Titrations adjusted the pH stepwise to selectively precipitated Fe and Al. In FIG. 6, processes with (*) include a selective precipitation or acidification pH adjustment step, such that Iron (Fe) Recovery*1is the first pH adjustment step, later denoted as pHi . Recovered resources as a high purity product include iron [Fe], tris(8- hydroxyquinoline)aluminum , and aluminum hydroxide [AI(OH)3], Alkalinity steps cause the pH to rise and the dissolved metals to selectively precipitate out of solution. Acidity steps dissolve the metals back into solution at a lower pH. Table 3 outlines the titrants used within the selective precipitation method, which included Sodium Hydroxide (NaOH), Hydrochloric Acid (HCI), Ammonium Acetate (NH4CH3CO2), and Ammonium Hydroxide (NH4OH). A 12-hour minimum settling time was selected because of the known differences in settling rate and particle size between packing characteristics of metals and suspended solids within AMD. The separation between the aqueous and solid phases enabled for the resource to be selectively transferred between processes as a filtered supernatant, settled coprecipitated precipitate, or supernatant (FIG. 6). 8-hydroxyquinoline, dissolved in anhydrous ethanol, was used as a chelating agent to react with aluminum within a rare-earth concentrate ore solution (Wang et al., 2020). An example of two starting AMD materials are shown in FIGS. 7A-7B.Table 3. Processes and pH adjustment steps for the Fe protocol, Si Protocol, and Al Protocol.

[0166] Results - Equations.920.5 - 6.6Metal RecoveryAl= X 100% = 99.2 %920.5 r. — c ’-'in ’-'outPurity = X 100%E Csum(920.5 - 6.6)PurityAl=[(920.5 - 6.6) + (113.4 - 48.5) + (7.99 - 0.01)]X 10°% 92‘61 %

[0167] Results - Table.Table 4. Metal concentrations before and after titrations for an Al chelation process.3. APPLICATIONS OF AMD SLUDGE

[0168] Land Application. Costs associated with sludge management and handling are high, often several times greater than the cost of chemical treatment (Skousen et al., 2000). Alternative uses of this material, for example as soil amendment or part of a manufactured soil or cover material (e.g., Alder and Sibrell 2003, Rodrigues Silva et al. 2022, Watters 2023), may help offset these costs. This by-product can be used as a cover material to support vegetation.

[0169] A disclosed process for AMD sludge disposal is to allow it to dry and age on land, resulting in a soil-like material. Therefore, there is potential for the use in manufactured growth media or in the reclamation process. There is the opportunity of land application of AMD sludge, a waste by-product, as part of the reclamation process. Several items can be considered, including water quality impacts, the ability to support vegetation establishment and persistence, and practical application methods. Use of sludge as part of a cover system in reclamation can be characterized as follows: (1) Water quality impacts of replacing various levels of cover soil with AMD sludge; (2) Impacts of replacing various levels of cover soil withAMD sludge at plot-scale; (3) Practical land application methods at the field scale; and (4) Practical land application methods for product alternate use. AMD sludge production and storage can be managed to provide a low-cost vegetative growth media and soil fill replacement for active reclamation projects. FIG. 8 shows a schematic of a representative recovery process at an AMD site and examples of value-creating applications of the recovered iron and aluminum products

[0170] Selective Extraction of Iron and Aluminum Sludge from AMD. Iron (Fe) and aluminum (Al) hydroxides represent the bulk of the AMD sludges generated from alkaline treatment. Utilizing Fe and Al sludge materials to generate useful products can not only reduce the costs for sludge transportation and disposal but can also create value from the products. A general two-staged pH neutralization for selective extraction of iron and aluminum is illustrated in FIG. 9.

[0171] Manufacturing Aluminum and Iron Products. A combination of lab- and field-protocols can be used to produce target products (i.e., Al (hydr)oxide, granular ferric oxide, and Fe- coated sand) using Fe and Al sludges.

[0172] Iron-coated sorbents. The iron sludge can be used to coat grey sand to make Fe- coated sorbents as a nutrient management tool for horticulture production. A protocol previously developed can be used forthe sand coating. The protocol involves mixing the Fe / AI sludge (slurry) with the sand. The coated sand is then dried and cured in a muffle furnace at 550 °C. Anticipating the demand of large quantities of Fe-coated sand for beneficial applications, a rotary drum mixer with heating element can also be used to produce Fe-coated sand on site. Specifically, the air-dried sludge can be mixed with grey sand in the rotary drum and heated at different temperatures to examine the effectiveness for coating the sand. This is less labor intensive as well as decreases processing time.

[0173] Granular ferric oxide (GFO). The iron sludge can be used to make granular ferric oxide (GFO) as a phosphorus sorbent commonly for aquarium algae control and similar applications. Production of GFO particles of uniform size (e.g., 5 mm) with material strength is a possible application. The rotary drum method can be used to generate GFO. The method may involve compression of the sludge material. A protocol for producing GFO can be developed. The chemical composition of GFO can be analyzed and its adsorption capacity for phosphorus using isotherm methods.

[0174] Aluminum products. The produced Al hydroxide sludge can be transported for further dewatering and processing to generate two products: aluminum hydroxide as a flame retardant and aluminum oxide for cement production.

[0175] Utilizing AMD Products for the Agricultural Industry. AMD-coated sand can hold on to phosphorus (P) to prevent it from leaching out of the potting mix. The P retained by the sand can be released to the plant's roots to support growth. Young plants (plugs) must establish strong root systems, which require P, before transplanting.

[0176] Growing media amended with AMD-coated sand saturated with PO4(AMD-PO4sand), plain sand (PS, not coated with AMD), and commercial potting mix, as a control, can be used. The two types of sand can be incorporated at 0, 5, 10, 20, and 30%, v / v in the potting media for young plant (plug) production. The content of the essential minerals in plants and irrigation leachate can be measured. At the end of the production cycle, the germination percentage of the tray can be determined. The shoot and root biomass can be determined on a dry-weight basis. Additionally, root architecture can be examined. An optimum percentage of the AMD- PO4 sand can be determined based on the abovementioned measurements and P utilization / retention efficiency. The coated sand can provide an on-demand P source during the early stages of plant growth for quality plug production.

[0177] AMD products in hydroponic crop production. One means to expand the use of AMD sludge is with horticultural products commonly used in hydroponic production, such as rockwool, clay pebbles, and capillary mats, can be coated with AMD sludge. Various crops in the different products coated with AMD sludge can be grown for evaluation. If the coating fails, AMD-coated sand can be mixed in the capillary mats and rockwool for microgreen (seedlings) and tomato production, respectively. AMD-coated products can provide an on-demand P source and reduce algae growth. Reduction in algae growth can enhance plant productivity and reduce possible plant pathogens.

[0178] AMD can be used to coat rockwool, clay pebbles, and capillary mats. The stability of AMD on the coated substrates and P-holding capacity can be examined. If the substrate can't be coated, AMD-coated sand can be mixed into rockwool and capillary mats. In either case, the coated substrates' can encourage crop growth and development , in addition to the biomass of the shoots, mineral nutrients, and heavy metal uptake. AMD-coated products perform similarly to AMD-coated sand in potting media experiments by providing an on- demand P source, preventing P accumulation in the leachate. A reduction in algae growth can help plant production by reducing the competition for nutrient resources.

[0179] It will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Other aspects of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. It is intendedthat the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.

Claims

CLAIMSAt least the following is claimed:1 . A method to recover metal compounds from a mine waste, the method comprising:(a) contacting the mine waste comprising at least one metal with an oxidizing agent in an amount sufficient enough to oxidize the at least one metal;(b) contacting the mine waste with a first base in an amount sufficient enough to adjust the pH to a value of about 3.5 to about 4.0, thereby forming a mixture of a first aqueous phase and a first metal precipitate;(c) separating the first metal precipitate from the first aqueous phase;(d) contacting the first aqueous phase with a second base in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a second aqueous phase and a first solid concentrate;(e) separating the first solid concentrate from the second aqueous phase;(f) contacting the first solid concentrate with a first acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a third aqueous phase and a second solid concentrate;(g) separating the third aqueous phase and the second solid concentrate;(h) contacting the third aqueous phase with a third base in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a fourth aqueous phase and a third solid concentrate; and(i) separating the fourth aqueous phase and the third solid concentrate; wherein the third solid concentrate comprises a second metal precipitate.

2. The method of claim 1 , wherein the first metal precipitate comprises an iron compound.

3. The method of claim 1 , wherein the first metal precipitate comprises iron (III) hydroxide.

4. The method of claim 1 , wherein the oxidizing agent is a peroxide.

5. The method of claim 1 , further comprising contacting the third aqueous phase with 8- hydroxyquinoline.

6. The method of claim 1 , further comprising:(a) washing the third solid concentrate;(b) calcining the third solid concentrate, thereby forming a calcined solid concentrate;(c) contacting the calcined solid concentrate with a second acid in an amount sufficient enough to adjust the pH to a value of about 1 .0 to 2.5, thereby forming a mixture of a fifth aqueous phase and a gaseous phase;(d) Separating the fifth aqueous phase from the gaseous phase; and(e) contacting the fifth aqueous phase with a fourth base in an amount sufficient enough to adjust the pH to a value of about 5.5, thereby forming a fourth solid concentrate; wherein the fourth solid concentrate comprises the second metal precipitate.

7. The method of claim 1 , wherein the second metal precipitate comprises an aluminum compound.

8. The method of claim 1 , wherein the second metal precipitate comprises aluminum (III) hydroxide.

9. The method of claim 1 , wherein the first base, the second base, and the third base are individually selected from sodium hydroxide, ammonium hydroxide, calcium hydroxide, ammonium acetate, and a combination thereof.

10. The method of claim 1 , further comprising:(a) contacting the second aqueous phase with a fourth base in an amount sufficient enough to adjust the pH to a value of about 7.0 to about 9.0, thereby forming a mixture of a sixth aqueous phase and a fifth solid concentrate; and(b) separating the sixth aqueous phase and the fifth solid concentrate; wherein the fifth solid concentrate comprises at least one critical mineral.1 1 . The method of claim 10, further comprising providing the fifth solid concentrate as a feedstock for recovery of critical minerals.

12. The method of claim 10, wherein the fourth base is selected from sodium hydroxide, ammonium hydroxide, calcium hydroxide, and any combination thereof.

13. A method to recover metal compounds from acid mine drainage (AMD), the method comprising:(a) contacting the AMD comprising at least one metal with an oxidizing agent in an amount sufficient enough to oxidize the at least one metal;(b) contacting the AMD with sodium hydroxide in an amount sufficient enough to adjust the pH to a value of about 3.5 to about 4.0, thereby forming a mixture of a first aqueous phase and a first metal precipitate;(c) separating the first metal precipitate from the first aqueous phase;(d) contacting the first aqueous phase with sodium hydroxide in an amount sufficient enough to adjust the pH to a value of about 5.0, thereby forming a mixture of a second aqueous phase and a second metal precipitate;(e) separating the second metal precipitate from the second aqueous phase;(f) contacting the second metal precipitate with hydrochloric acid in an amount sufficient enough to adjust the pH to a value of about 1 .0 to 2.5, thereby forming a mixture of a third aqueous phase and an acidic solid;(g) separating the third aqueous phase and the acidic solid;(h) contacting the third aqueous phase with ammonium acetate in an amount sufficient enough to adjust the pH to a value of about 5.0 and 8-hydroxyquinoline, thereby forming a mixture of a fourth aqueous phase and a metal oxinate solid; and(i) separating the fourth aqueous phase and the metal oxinate solid.

14. The method of claim 13, wherein the first metal precipitate comprises an iron compound.

15. The method of claim 13, wherein the first metal precipitate comprises iron (III) hydroxide.

16. The method of claim 13, wherein the second metal precipitate comprises an aluminum compound.

17. The method of claim 13, further comprising:(a) washing the metal oxinate solid;(b) calcining the metal oxinate solid, thereby forming a calcined solid;(c) contacting the calcined solid with hydrochloric acid in an amount sufficient enough to adjust the pH to a value of about 1.0 to 2.5, thereby forming a mixture of a fifth aqueous phase and a gaseous phase;(d) separating the fifth aqueous phase and the gaseous phase; and(e) contacting the fifth aqueous phase with ammonium hydroxide in an amount sufficient enough to adjust the pH to a value of about 5.5, thereby forming a metal hydroxide solid.

18. The method of claim 17, wherein the metal hydroxide solid comprises aluminum hydroxide.

19. The method of claim 13, further comprising:(a) contacting the second aqueous phase with a base in an amount sufficient enough to adjust the pH to a value of about 7.0 to about 9.0, thereby forming a mixture of a sixth aqueous phase and a first solid concentrate; and(b) separating the sixth aqueous phase and the fifth solid concentrate; wherein the fifth solid concentrate comprises at least one critical mineral.

20. The method of claim 19, further comprising providing the fifth solid concentrate as a feedstock for recovery of critical minerals.

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