Methods for recovering metals from mineral waste

Abstract

The present application relates to a method for recovering at least one alkali earth metal and at least one metal from a mineral material. More specifically, the method comprises: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution and separating the impurities to form a metal-bearing solution; selectively recovering the at least one metal from the metal-bearing solution using ion-exchange resin and a spent acid solution comprising at least one alkali earth metal salts; and optionally heating the spent acid solution to recover the at least one alkali earth metal.

Description

METHODS FOR RECOVERING METALS FROM MINERAL WASTECROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims the benefit of priority of co-pending U.S. Provisional Patent Application No. 63 / 695,831 , which was filed September 17, 2024, the content of which is incorporated herein by reference in its entirety.FIELD

[0002] The present application is in the field of metallurgy. More specifically, the present application relates to recovering metals from metallurgical waste such as serpentine tailings.BACKGROUND

[0003] Mineral materials are generated during the processing of ores. For example, serpentine tailings are solid waste materials generated as a byproduct during the processing of serpentine-rich ores to produce asbestos, nickel and magnesium. The serpentine tailings mainly consist of magnesium silicate minerals, such as chrysotile, I izardite and antigorite with various amounts of other elements such as iron, aluminum and nickel.

[0004] Processing of serpentine-rich ores generates a large amount of serpentine tailings, typically at a ratio of 5 to 20 times more than the desired product, although the actual amount can be much higher depending on the ore grade. As such, the serpentine tailings require a substantial storage space. The disposal of this large volume of serpentine tailings poses significant environmental challenges because of its composition, such as chrysotile asbestos which can be hazardous if inhaled. Thus, the serpentine tailings necessitate careful handling, storage and remediation to diminish the risks of environmental contamination and human exposure. Moreover, the serpentine tailings can contain heavy metals such as nickel, chromium and iron which can contaminate ecosystems by leaching into the soil and groundwater.

[0005] The managing of serpentine tailings can incur significant costs when considering safe storage, remediation methods and environmental monitoring. Furthermore, failure to maintain appropriate storage of this serpentine mineral wastecan lead to ecological disasters. As such, serpentine tailings can be sequestered by methods such as encapsulation or geopolymerization to produce more stable forms of the material in various solid matrices. These methods also expand the volume and weight of the material which increase the storage volume needed, in addition to the stabilized solid matrix being at risk of leaching toxic components over time, resulting in a significant carbon footprint during its production. Furthermore, as serpentine ores and serpentine tailings are rich in magnesium, they can be used to sequestrate carbon by forming various stable carbonates and thus can help mitigate climate change.1However, the carbon sequestration using serpentine tailings is a costly process that necessitates large-scale and expensive infrastructure, not to mention the significant energy requirements for speeding up this relatively slow process.

[0006] As the production of nickel grows worldwide with the increasing demand for batteries and electrical vehicles, the volume of serpentine tailings is set to rise and accumulate in the coming decades. Meanwhile, the serpentine tailings generated during peak asbestos production in the mid-20thcentury have yet to be fully processed to mitigate health and environmental risks.

[0007] As such, there is a need for processes for treating mineral material, such as serpentine tailings.SUMMARY

[0008] It has been shown herein that at least one alkali earth metal and at least one metal can be recovered from a mineral material.

[0009] Accordingly, the present application includes a method for recovering at least one alkali earth metal and at least one metal from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution and separating the impurities to form a metal-bearing solution;selectively recovering the at least one metal from the metal-bearing solution using ionexchange resin and a spent acid solution comprising at least one alkali earth metal salts; and optionally heating the spent acid solution to recover the at least one alkali earth metal.

[0010] The present application further includes a method for recovering at least one metal from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution and separating the impurities to form a metal-bearing solution; selectively recovering the at least one metal from the metal-bearing solution using ionexchange resin.

[0011] Further included is a method of recovering at least one alkali earth metal and at least one metal from serpentine tailings, said method comprising: leaching the serpentine tailings with an acid solution and heating a temperature to form a solid residue and a leachate solution; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution by adjusting pH to form a metalbearing solution; selectively recovering the at least one metal and a spent acid solution comprising at least one alkali earth metal salts from the metal-bearing solution using at least one ion-exchange resin columns; heating and / or crystallizing the spent acid solution to form at least one alkali earth metal oxide; carbonating the at least one alkali earth metal oxide with CO2 or carbonic acid to form at least one alkali earth metal carbonate.

[0012] The present application also includes a method for recovering magnesium, nickel and cobalt from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue;separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution and separating the impurities to form a metal-bearing solution; selectively recovering nickel and cobalt from the metal-bearing solution using ionexchange resin and a spent acid solution comprising magnesium salts; and optionally heating the spent acid solution to recover the magnesium.

[0013] Also provided is a method of recovering magnesium, nickel and cobalt from serpentine tailings, said method comprising: leaching the serpentine tailings with a nitric acid solution and heating to form a solid residue and a leachate solution; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution by adjusting pH to form a metalbearing solution; selectively recovering nickel and cobalt from the metal-bearing solution using at least one ion-exchange resin columns and forming a spent acid solution comprising magnesium nitrate; heating the magnesium nitrate to form magnesium oxide and gaseous nitric oxide; carbonating the magnesium oxide with CO2 or carbonic acid to form magnesium carbonate; and oxidizing the gaseous nitric oxide to form nitrogen dioxide, absorbing the nitrogen dioxide in water to form and regenerate the nitric acid and optionally recirculating the nitric acid to the leaching.

[0014] Further included is a method for recovering at least one alkali earth metal and at least one metal from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; increasing the pH to precipitate impurities from the leachate solution and separating the impurities and solid residue by filtration to form a metal-bearing solution; selectively recovering the at least one metal from the metal-bearing solution using ionexchange resin or pH adjustment and filtration and forming a spent acid solution comprising at least one alkali earth metal salts; and optionally heating the spent acid solution to recover the at least one alkali earth metal.

[0015] Other features and advantages of the present application will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the application, are given by way of illustration only and the scope of the claims should not be limited by these embodiments, but should be given the broadest interpretation consistent with the description as a whole.BRIEF DESCRIPTION OF DRAWINGS

[0016] The embodiments of the application will now be described in greater detail with reference to the attached drawings in which:

[0017] FIG.1 shows a bloc diagram of an example of process for extracting a metal from a mineral waste such as serpentine tailings according to exemplary embodiments of the present disclosure.

[0018] FIG.2 shows a bloc diagram of another example of process for extracting a metal from a mineral waste such as serpentine tailings according to exemplary embodiments of the present disclosure.

[0019] FIG.3 shows a bloc diagram of another example of process for extracting a metal from a mineral waste such as serpentine tailings according to exemplary embodiments of the present disclosure.DETAILED DESCRIPTIONI. Definitions

[0020] Unless otherwise indicated, the definitions and embodiments described in this and other sections are intended to be applicable to all embodiments and aspects of the present application herein described for which they are suitable as would be understood by a person skilled in the art.

[0021] As used in this application and claim(s), the words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "include" and "includes") or "containing" (and any form of containing, such as "contain" and "contains"), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps.

[0022] The term “consisting” and its derivatives as used herein are intended to be closed terms that specify the presence of the stated features, elements, components, groups, integers, and / or steps, and also exclude the presence of other unstated features, elements, components, groups, integers and / or steps.

[0023] The term “consisting essentially of’, as used herein, is intended to specify the presence of the stated features, elements, components, groups, integers, and / or steps as well as those that do not materially affect the basic and novel characteristic(s) of these features, elements, components, groups, integers, and / or steps.

[0024] The terms "about", “substantially” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies or unless the context suggests otherwise to a person skilled in the art.

[0025] As used in the present application, the singular forms “a”, “an” and “the” include plural references unless the content clearly dictates otherwise. For example, an embodiment including “a compound” should be understood to present certain aspects with one compound, or two or more additional compounds.

[0026] In embodiments comprising an “additional” or “second” component, the second component as used herein is different from the other components or first component. A “third” component is different from the other, first, and second components, and further enumerated or “additional” components are similarly different.

[0027] The term “and / or” as used herein means that the listed items are present, or used, individually or in combination. In effect, this term means that “at least one of” or “one or more” of the listed items is used or present.

[0028] The term “suitable” as used herein means that the selection of the particular composition or conditions would depend on the specific steps to be performed, the identity of the components to be transformed and / or the specific use forthe compositions, but the selection would be well within the skill of a person trained in the art.II. Methods of the Application

[0029] It has been shown herein that at least one alkali earth metal and at least one metal can be recovered from a mineral material.

[0030] Accordingly, the present application includes a method for recovering at least one alkali earth metal and at least one metal from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution and separating the impurities to form a metal-bearing solution; selectively recovering the at least one metal from the metal-bearing solution using ion-exchange resin and a spent acid solution comprising at least one alkali earth metal salts; and optionally heating the spent acid solution to recover the at least one alkali earth metal.

[0031] The present application also includes a method for recovering at least one metal from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution and separating the impurities to form a metal-bearing solution; selectively recovering the at least one metal from the metal-bearing solution using ion-exchange resin.

[0032] In some embodiments, mineral material refers, for example, to an inorganic solid substance with a well-defined chemical composition and crystalline structure. In some embodiments, the mineral material includes a mineral waste, asbestos-containing materials and / or silicate materials.

[0033] In some embodiments, mineral waste refers, for example, to byproducts and residual materials generated from the extraction and / or processing of minerals. For example, mineral waste can originate as a byproduct from processing a mineral material in order to isolate one of its specific components. In some embodiments, the mineral waste includes serpentine tailings. In some embodiments, serpentine tailingsrefers, for example, to an industrial waste product generated during the production of asbestos, nickel or magnesium. For example, such a waste product can comprise silica, magnesium, iron, nickel, cobalt and aluminum. It can also comprise an array of other constituents such as Na, K, Cr, Cd, V, Ni, Ba, Cu, Pt, Pd, Mn, Pb, U, and / or Zn, etc.

[0034] In some embodiments, the mineral material includes at least one metal and at least one alkali earth metal. In some embodiments, alkali earth metal as used herein refers, for example, to chemical elements in the Group 2 of the periodic table. For example, an alkali earth metal can include beryllium, magnesium, calcium, strontium, barium and radium.

[0035] In some embodiments, the metal generated through the recovery method includes one or more of nickel, cobalt, copper, uranium, vanadium, zinc, cadmium, platinum or palladium.

[0036] In some embodiments, the metal generated through the recovery method includes nickel, cobalt or a combination thereof.

[0037] In some embodiments, the recovery method of a mineral material can include the generation of alkali earth metal salts. In some embodiments, alkali earth metal salt refers, for example, to ionic salts containing a chemical element in the Group 2 of the periodic table. For example, an alkali earth metal salt can include but is not limited to magnesium hydroxide, magnesium nitrate, magnesium oxide, magnesium carbonates, or a combination thereof.

[0038] In some embodiments, the alkali earth metal includes magnesium.

[0039] In some embodiments, the alkali earth metal salts include magnesium hydroxide, magnesium nitrate, magnesium oxide, magnesium carbonates, magnesium sulfate, calcium oxide, calcium hydroxide, calcium carbonates, calcium sulfate or a combination thereof. For example, the alkali earth metal salts can be in solution. For example, the alkali earth metal salts are in a solid state that includes hydrated or dehydrated forms.

[0040] In some embodiments, the solid residue refers, for example, to an insoluble deposit generated by leaching a solid material by percolating it in a liquid. For example, a solid residue can include the insoluble deposit generated by leaching and heating a mineral material to form a liquid soluble fraction.

[0041] In some embodiments, the leachate solution refers, for example, to a liquid that has dissolved and carries away some of the constituents of a solid material by being percolated through it. For example, a leachate can include a solution of dissolved metals and solid residue produced by exposing a mineral material to an acidic solution.

[0042] In some embodiments, leaching the mineral material includes using an acid solution, wherein the acid solution includes, for example, nitric acid. For example, the acid solution has a concentration of about 10% to 90% by volume, or the acid solution has a concentration of about 10% to 40% by volume, or the acid solution has a concentration of about 20% to 30% by volume.

[0043] In some embodiments, the acid solution refers, for example, to a liquid mixture of water of another solvent in which an acid has been dissolved, leading to the presence of hydrogen ions (H+) into the solution which is characterized by a pH value below 7. For example, a solution can include sulfuric acid and / or nitric acid dissolved in water.

[0044] In some embodiments, leaching the mineral material with an acid solution generates a leachate and a solid residue. For example, the solid residue can be filtered off from the leachate, thus producing a crude solution and the isolated solid residue. For example, the solid residue includes amorphous silica.

[0045] In some embodiments, the leaching includes recirculating the leachate through a hydrodynamic cavitation device.

[0046] In some embodiments, the crude solution refers, for example, to a liquid carrying dissolved metals void of solid residue. For example, a crude solution can include a leachate solution of dissolved metals that has been separated from its solid residue.

[0047] In some embodiments, processing the crude solution to generate a metal-bearing solution includes precipitation of impurities. In some embodiments, the impurities refers, for example, to unwanted substances present within a mineral material during the extraction of a specific component. The impurities include, for example, iron, aluminum, various compounds derived from iron or aluminum, or a combination thereof.

[0048] In some embodiments, precipitated impurities include iron hydroxide, aluminum hydroxide, hematite, or a combination thereof.

[0049] In some embodiments, hematite refers, for example, to a compound comprising a-Fe2O3, y-Fe2O3, [3-FeO.OH or mixtures thereof.

[0050] In some embodiments, the impurities in the crude solution can be precipitated by adjusting the pH of the crude solution.

[0051] In some embodiments, the pH of the crude solution can be adjusted by adding a pH modifier to the crude solution. For example, the pH of the crude solution can be adjusted by adding a pH modifier until the pH is about 1 to 3. As such, the metal-bearing solution generated from precipitating impurities from the crude solution has a pH of about 1 to 3, or a pH of about 1 .5 to 3. A pH modifier includes, for example, magnesium oxide, caustic soda, lime, serpentine tailings or other common pH modifiers. The magnesium oxide added as a pH modifier to the crude solution includes, for example, the magnesium oxide generated from downstream in the process by the heating of magnesium nitrate. The serpentine tailings added as a pH modifier to the crude solution includes, for example, the serpentine tailings feedstock reclaimed upstream in the current process.

[0052] In some embodiments, the metal-bearing solution refers, for example, to a liquid carrying dissolved metals void of soluble impurities. For example, a metalbearing solution can include a crude solution of dissolved metals that has been separated from its soluble impurities by various means, such as, for example, precipitation and / or hydrolysis.

[0053] In some embodiments, the composition of the metal-bearing includes nickel at a concentration of about 50 mg / L to about 5000 mg / L, or the concentration is of about 100 mg / L to about 4000 mg / L, or the concentration is of about 200 mg / L to about 3000 mg / L, or the concentration is of about 250 mg / L to about 2500 mg / L, or the concentration is of about 300 mg / L to about 1000 mg / L, or the concentration is of about 350 mg / L to about 700 mg / L.

[0054] In some embodiments, the metal-bearing includes cobalt at a concentration of about 2 mg / L to about 200 mg / L, or the concentration is of about 5 mg / L to about 175 mg / L, or the concentration is of about 10 mg / L to about 100 mg / L, or the concentration is of about 15 mg / L to about 75 mg / L, or the concentration is of about 20 mg / L to about 40 mg / L.

[0055] In some embodiments, the composition of the metal-bearing includes magnesium at a concentration of about 10 000 mg / L to about 300 000 mg / L, or the concentration is of about 25 000 mg / L to about 250 000 mg / L, or the concentration is of about 35 000 mg / L to about 200 000 mg / L, or the concentration is of about 40 000 mg / L to about 15 000 mg / L, or the concentration is of about 50 000 mg / L to about 100 000 mg / L.

[0056] In some embodiments, the metal-bearing includes cobalt is at a pH about 1 to about 4, or the pH is about 1 to about 3, or the pH is about 1 .5 to about 3, or the pH is about 2 to about 3.

[0057] In some embodiments, at least one metal is recovered from the metalbearing solution. For example, the recovering of at least one metal from the metalbearing solution includes chromatography. For example, the chromatography includes ion-exchange columns made of ion-exchange resins.

[0058] In some embodiments, the expression “ion-exchange resin” as used herein refers, for example, to a polymeric material that can exchange specific ions within its structure with other ions from a solution passed through it. For example, an ion-exchange resin can be used to selectively capture desirable ions from a solution and to elute them to isolate a specific ion. For example, an ion-exchange resin can be a cation exchange resin which exchange selectively certain cations via the functionalgroups of its polymeric structure which can include, for example, bispicolylamine (BPA) and / or iminodiacetate (IDA).

[0059] In some embodiments, the ion-exchange resins include cation-exchange resins such as weakly acidic microporous cation-exchange resins. The ion-exchange resins include, for example, high or moderate selectivity for nickel cations and cobalt cations and low selectivity for alkali cations and alkali earth metal cations, such as magnesium and calcium. The ion-exchange resins include, for example, complexation of divalent cations or trivalent cations. For example, the ion-exchange resins include bispicolylamine (BPA) functionalities or iminodiacetate (IDA) functionalities. For example, the ion-exchange resins include Lewatit™ Selective Ion Exchange resins, such as Lewatit™ TP 207 or Lewatit™ MDS TP220 BPA resin.

[0060] In some embodiments, selectively recovering the at least one metal using ion-exchange resin comprises loading the metal-bearing solution to selectively adsorb the at least one metal to the ion-exchange resin and eluting to selectively desorb the at least one metal from the ion-exchange resin and recover the at least one metal.

[0061] In some embodiments, eluting comprises a first elution at a first concentration of acid to selectively desorb a first metal and a second elution at a second concentration of acid to selectively desorb a second metal.

[0062] In some embodiments, the recovering of at least one metal includes adsorption of the at least one metal in its cationic form to the ion-exchange resin, then elution of impurities followed by elution of at least one metal cation from ion-exchange resin with an acid solution to desorb the at least one metal cation, optionally followed by a subsequent elution or elutions of one or more different metal cations from the ionexchange resin at different concentrations of the acid solution.

[0063] In some embodiments, an acid solution for elution of at least one metal includes sulfuric acid.

[0064] In some embodiments, an acid solution for elution of at least one metal includes water or at least one other solvent.

[0065] In some embodiments, to elute cobalt, a concentration of an acid solution is from about 25 g / L to about 100 g / L, or a concentration of an acid solution is from about 25 g / L to about 50 g / L, or about 50 g / L to about 100 g / L.

[0066] In some embodiments, to elute nickel, a concentration of an acid solution is from about 50 g / L to about 300 g / L, or a concentration of an acid solution is from about 100 g / L to about 200 g / L.

[0067] In some embodiments, the expression “spent acid solution” as used herein refers, for example, to an acidic solution passed through an ion-exchange resin wherein at least one or more of dissolved metals have been adsorbed by the ionexchange resin during elution.

[0068] In some embodiments, the heating of the spent acid solution comprises spray roasting, spray drying, evaporating, evaporative crystallizing, rotary kilning, fluid bed roasting or a combination thereof.

[0069] In some embodiments, the elution of the metal-bearing solution through an ion-exchange column generates a spent acid solution. For example, the spent acid solution includes at least one alkali earth metal. For example, the spent acid solution includes at least one alkali earth metal salt. For example, the spent acid solution includes magnesium nitrate.

[0070] In some embodiments, the mineral material is reduced in size prior to leaching. For example, the comminution of the mineral material is performed by crushing, grinding, micronization, high-pressure grinding rolls, attrition milling, impact milling, cutting, shearing, ultrasonic milling, cryogenic milling of the mineral material or a combination thereof. In some embodiments, the comminution of the mineral material is made using jaw crushers, gyratory crushers, impact crushers, cone crushers, roll crushers, impact crushers, ball mills, rod mills, semi-autogenous grinding mills, autogenous grinding mills, vertical roller mills, jet mills, high-pressure grinding rolls, attritors, stirred mills, hammer mills, cutter mills, shear crushers, ultrasonic mills, cryogenic mills or a combination thereof. In some embodiments, magnetic separation is used before size reduction or comminution of the mineral material.

[0071] The processes of the application have been shown to recover nickel and cobalt from a mineral material such as a mineral waste, more specifically serpentine tailings.

[0072] The present application further includes a method of recovering at least one alkali earth metal and at least one metal from serpentine tailings. The method comprises leaching the serpentine tailings with an acid solution with heating at a temperature to form a leachate solution and a solid residue. The method comprises separating the solid residue from the leachate solution to form a crude solution. The method comprises precipitating impurities from the crude solution by adjusting pH to form a metal-bearing solution. The method comprises selectively recovering the at least one metal and a spent acid solution which comprises at least one alkali earth metal salt from the metal-bearing solution using at least one ion-exchange columns. The method comprises heating and / or crystallizing the spent acid solution to form at least one alkali earth metal oxide. The method comprises carbonating the at least one alkali earth metal oxide with CO2 or carbonic acid to form at least one alkali earth metal carbonate.

[0073] In some embodiments, the magnesium nitrate generated from the method is isolated, for example, by evaporation or crystallization. In some embodiments, the isolation of the magnesium nitrate from the spent acid solution is performed by an evaporator, a spray roaster, a fluid bed roaster, an evaporative crystallizer and / or a crystallizer. The magnesium nitrate can be in a diluted form, such as solubilized in the spent acid solution. The magnesium nitrate can also be in a concentrated solution, such as following the evaporation of the spent acid solution which generates a concentrated liquor of magnesium nitrate.

[0074] In some embodiments, the free water in the magnesium nitrate can be removed by centrifugation or spray drying. The magnesium nitrate can be in a hydrated form, such as, for example, a hexahydrate or a dihydrate form.

[0075] In some embodiments, magnesium nitrate is a molten salt.

[0076] In some embodiments, the spent acid solution is heated at a temperature of about 200 °C to about 700 °C, or the heating is at a temperature of about 250 °C toabout 650 °C, or the heating is at a temperature of about 400 °C to about 600 °C, or the heating is at a temperature of about 450 °C to about 550 °C.

[0077] In some embodiments, the magnesium nitrate, as a concentrated liquor or as hexahydrate, dihydrate, dried or anhydrous crystals, either pure or in a mixture of various compounds, elements and / or impurities, is heated at a temperature of about 200 °C to about 700 °C, or the heating is at a temperature of about 250 °C to about 650 °C, or the heating is at a temperature of about 400 °C to about 600 °C, or the heating is at a temperature of about 450 °C to about 650, or the heating is at a temperature of about 450 °C to about 550 °C.

[0078] In some embodiments, the magnesium nitrate generated from the process is decomposed to produce magnesium oxide and NOx gases. For example, NOx gases include NO2 and NO.

[0079] In some embodiments, the magnesium oxide is a solid used in a carbonation process. In some embodiments, the magnesium oxide is, for example, contacted with CO2 bearing gas in a circulating fluid bed to produce solids containing magnesium carbonates. In some embodiments, the magnesium is, for example, dissolved in a mixture of carbonic acid to produce a solution of magnesium carbonate. In some embodiments, the CO2 used is removed from the atmosphere.

[0080] In some embodiments, the carbonation includes recirculating the carbonic acid and magnesium oxide mixture through a hydrodynamic cavitation device.

[0081] In some embodiments, the NOx gases are oxidized to regenerate nitric acid. For example, the oxidation of NOx gases includes air, hydrogen peroxide or oxygen gas and water. The oxidation can include generation of nitric trioxide and nitrite ions. The oxidation includes transformation of transforms NO into nitric trioxide by catalysis via the presence of aqueous nitric acid. The regenerated nitric acid can be recycled inside the process.

[0082] The present application further includes a method for recovering magnesium, nickel and cobalt from a mineral material. The method comprises leaching the mineral material with an acid solution with heating to form a leachate solution anda solid residue. The method comprises separating the solid residue from the leachate solution to form a crude solution. The method comprises precipitating impurities from the crude solution and separating the impurities to form a metal-bearing solution. The method comprises selectively recovering nickel and cobalt from the metal-bearing solution using ion-exchange resin and a spent acid solution which comprises magnesium salts. The method comprises heating the spent acid solution to recover the magnesium.

[0083] The present application further includes a method for recovering magnesium, nickel and cobalt from serpentine tailings. The method comprises leaching the serpentine tailings with a nitric acid solution with heating at a temperature to form a leachate solution and a solid residue. The method comprises separating the solid residue from the leachate solution to form a crude solution. The method comprises precipitating impurities from the crude solution by adjusting pH to form a metal-bearing solution. The method comprises selectively recovering nickel and cobalt from the metal-bearing solution using at least one ion-exchange columns and forming a spent acid solution which comprises magnesium nitrate. The method comprises heating the magnesium nitrate to form magnesium oxide and gaseous nitric oxide. The method comprises carbonating the magnesium oxide with CO2 or carbonic acid to form magnesium carbonate. The method comprises oxidizing the gaseous nitric oxide to form nitrogen dioxide, absorbing the nitrogen dioxide in water to form and regenerate the nitric acid, whereas the method comprises recirculating the nitric acid to the leaching.

[0084] The present application further includes a method for recovering at least one alkali earth metal and at least one metal from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; increasing the pH to precipitate impurities from the leachate solution and separating the impurities and solid residue by filtration to form a metal-bearing solution; selectively recovering the at least one metal from the metal-bearing solution using ion-exchange resin or pH adjustment and filtration and forming a spent acid solution comprising at least one alkali earth metal salts; and optionally heating the spent acid solution to recover the at least one alkali earth metal.In other words, this embodiment of the method of the application comprises leaving the leach residue in the solution during the removal of impurities using pH adjustment, that is not filtering the residues before precipitation. Without being bound to theory, this embodiment may lead to higher removal and easier filterability from the metal bearing solution in the filtration step, where the silica may act as a filter aid. This may allow for the use of conventional filter press to remove hydroxide impurities to very low levels rather than leaf filters.

[0085] Accordingly, the present application includes a general process of recovery of at least one metal and at least one alkali earth metal at Fig. 1 .

[0086] The process described in Fig.1 show that the serpentine tailings undergo a coarse screening (2 mm) followed by a fine screening (2 mm). The leach of the screened serpentine tailings with HNO3 produces a leachate and a solid residue that includes silicates. Leach filtration separates the silicates from the leachate, thus affording a crude solution. Impurity removal 1 of the crude solution precipitates Fe and Al hydroxides by the addition of a pH modifier, which include magnesium oxide produced in the process, serpentine tailings, caustic soda, lime or other common pH modifiers, thus affording a metal-bearing solution. Impurity removal 2 of the metalbearing solution separates residues through filtration. The filtrated residues can be reprocessed again at the leach step with the screened serpentine tailings. Mixed hydroxide precipitates (MHP) are formed from the filtered metal-bearing solution by feeding the metal-bearing solution to ion-exchange columns to selectively adsorbs metals of interest in their cationic form, such as nickel and cobalt. The magnesium, such as magnesium nitrate, is not adsorbed by the column and is eluted through directly in a spent acid solution. The metals of interest are then eluted with acid solutions of specific concentrations and are processed to generate the mixed hydroxide precipitates of nickel and cobalt. Evaporation of the spent acid solution forms magnesium nitrate. Crystallization of the magnesium nitrate forms magnesium nitrate crystals. Pyrolysis of the magnesium crystals generates magnesium oxide and NOx gases. Carbonation of the magnesium oxide with CO2 generates a magnesium carbonate precipitate in solution. Filtration of the magnesium carbonate precipitate in solution affords solid magnesium carbonate.

[0087] The present application further includes another exemplary process of recovery of at least one metal and at least one alkali earth metal at Fig. 2.

[0088] The process described in Fig. 2 shows in the top section that the feedstock undergoes screening at 2 mm, wherein the particles having a size of more than 2 mm are removed and particles having a size of less than 2 mm are processed to the next stage.

[0089] In the second section, the leaching step includes storage and pulping of screened serpentine tailings having a size of less than 2 mm, followed by HNO3 leaching to produce a leachate and a solid residue that includes amorphous silica. Leach residue filtration follows where amorphous silica is filtered off, thus affording a crude solution. The impurity removal step includes impurity removal 1 of the crude solution (optionally with addition of an impurity removal 1 thickener), followed by impurity removal 1 filtration to remove the impurity removal 1 residues, such as Fe and Al hydroxides. Following addition of impurity removal 1 thickener and / or after impurity removal 1 filtration, there may be an impurity removal 2 by an impurity removal 2 filtration to afford a metal-bearing solution while removing impurity removal 2 residues to be reintroduced to impurity removal 1 , not shown.

[0090] In the third section, the nickel recovery is an ion exchange that includes feeding the metal-bearing solution to ion-exchange columns to selectively adsorbs metals of interest in their cationic form, including nickel and cobalt, by elution with H2SO4. The magnesium, such as magnesium nitrate, is not adsorbed by the column and is eluted through directly in a spent acid solution to the next stage, while filtration of the adsorbed metals is followed by a crystallization step to yield Ni and Co, including their sulfate forms (SO4) and then drying and packaging of the Ni and Co.

[0091] In the fourth section, the spent acid solution comprising magnesium nitrate is subjected to an evaporation and crystallization to produce Mg(NO3)2.6H2O. Pyrolysis of the Mg(NO3)2.6H2O produces MgO and NOx gases, the latter of which undergoes acid regeneration of HNO3 to be recycled in the process at the second section at the HNO3 leaching step.

[0092] In a fifth section, the MgO from the fourth section undergoes a carbonation with CO2 injection and / or carbonic acid produced during the filtration as H2O & CO2(aq) mix, which generate magnesium carbonates after filtration.

[0093] A similar process is described in Fig. 3 but for the filtration in the second section to remove the amorphous silica. Specifically, the leachate produced from the HNO3 leaching is not filtered, but sent directly to impurity removal 1 and then filtration which removes the amorphous silica at this stage.EXAMPLES

[0094] The following non-limiting examples are illustrative of the present application.Example 1

[0095] Serpentine tailings were leached using a solution that is 27% nitric acid for a period of 4 hours at a temperature between 80 °C to 90 °C, at a ratio of 5 parts of solution to 1 part of serpentine tailings or around 20% of solids, which generated solid residues that were filtered from the leachate to form a crude solution.

[0096] A pH modifier was added to bring the pH of the crude solution to about 3 while the solution was not heated above 90 °C, after which iron and aluminum are precipitated from the solution as hydroxides which are then filtered out to generate a metal-bearing solution. The pH modifier was magnesium oxide generated from the process.

[0097] The metal-bearing solution was passed through ion-exchange columns which bound nickel and cobalt. The nickel and cobalt were recovered from the ionexchange columns by eluting with sulphuric acid, which generated a spent acid solution.

[0098] The spent acid solution was evaporated and underwent crystallization producing a stream of steam and solid hydrated magnesium nitrate. The steam was recompressed and recycled within the process. The solid hydrated magnesium nitrate was dehydrated with a spray dryer. The dehydrated magnesium nitrate was thendecomposed at a temperature around 450 °C, producing a stream of NOx rich gas and magnesium oxide powder.

[0099] The magnesium oxide powder was used to mineralize CO2 gas, producing a carbonate mineral which was backfilled on the mine site. The monitoring of this transformation enabled the generation of a carbon credit.

[0100] The NOx rich gas was passed through water to regenerate nitric acid for use in leaching in the process.Example 2

[0101] Serpentine tailings were leached using a solution that is 27% nitric acid for a period of 4 hours at a temperature between 80 °C to 90 °C, at a ratio of 5 parts of solution to 1 part of serpentine tailings or around 20% of solids, which generated solid residues that were filtered from the leachate to form a crude solution.

[0102] A pH modifier was added to bring the pH of the crude solution to about 3 while the solution was not heated above 90 °C, after which iron and aluminum precipitated from the solution as hydroxides which were then filtered out to generate a metal-bearing solution. The pH modifier was magnesium oxide generated from the process.

[0103] An additional pH modifier was added to bring the pH of the metal-bearing solution to about 6 while the solution was not heated above 90 °C, after which nickel and cobalt precipitated as hydroxides from the solution and are filtered out. The pH modifier included magnesium oxide generated from the process, raw serpentine tailings or other common pH modifiers such as caustic soda or lime. The extracted nickel was further purified using solvent extraction or was sold as is as a mixed hydroxide precipitate.

[0104] The remaining metal-bearing solution was evaporated and underwent crystallization producing a stream of steam and solid hydrated magnesium nitrate. The steam was recompressed and recycled within the process. The solid hydrated magnesium nitrate was dehydrated with a spray dryer. The dehydrated magnesiumnitrate was then decomposed at a temperature around 450 °C, producing a stream of NOx rich gas and magnesium oxide powder.

[0105] The magnesium oxide powder was used to mineralize CO2 gas, producing a carbonate mineral which was backfilled on the mine site. The monitoring of this transformation enabled the generation of a carbon credit.

[0106] The pyrolysis NOx rich gas produced from the roasting underwent acid regeneration by being quenched, recovered and revalorized as nitric acid.Example 3

[0107] Serpentine tailings were leached using a solution that was 27% nitric acid, or nitric acid in a range of 10 to 40%, for a period of 4 hours at a temperature between 80 °C to 90 °C, at a ratio of 5 parts of solution to 1 part of serpentine tailings or around 20% of solids, or the ratio was in a range between 3: 1 to 10: 1 of solution:solid mixture, which generated solid residues that were filtered from the leachate to form a crude solution.

[0108] A pH modifier was added to bring the pH of the crude solution to about 3 while the solution was not heated above 90 °C, after which iron and aluminum precipitated from the solution as hydroxides which were then filtered out to generate a metal-bearing solution. The pH modifier was magnesium oxide generated from the process.

[0109] The metal-bearing solution was passed through ion-exchange circuit which bound nickel and cobalt. The nickel and cobalt were recovered from the ionexchange columns by eluting with sulphuric acid, which generated a spent acid solution.

[0110] The spent acid solution was evaporated in an evaporator which generated a concentrated liquor of magnesium nitrate which was then fed to a spray roaster to form magnesium oxide and NOx gas as a pyrolysis gas. The solid magnesium oxide was collected at the roaster’s bottom and from the roaster off-gas cycloning.

[0111] The pyrolysis NOx rich gas produced from the roasting underwent acid regeneration to regenerate nitric acid for use in leaching in the process.Example 4

[0112] Serpentine tailings were leached using a solution that was 27% nitric acid, or nitric acid in a range of 10 to 40%, for a period of 4 hours at a temperature between 80 °C to 90 °C, at a ratio of 5 parts of solution to 1 part of serpentine tailings or around 20% of solids, or the ratio was in a range between 3: 1 to 10: 1 of solution:solid mixture, which generated solid residues that were filtered from the leachate to form a crude solution.

[0113] A pH modifier was added to bring the pH of the crude solution to about 3 while the solution was not heated above 90 °C, after which iron and aluminum precipitated from the solution as hydroxides which were then filtered out to generate a metal-bearing solution. The pH modifier was magnesium oxide generated from the process.

[0114] The metal-bearing solution was passed through an ion-exchange circuit which bound nickel and cobalt. The nickel and cobalt were recovered from the ionexchange columns by eluting with sulphuric acid, which generated a spent acid solution.

[0115] The spent acid solution was evaporated in an evaporative crystallizer producing magnesium nitrate hexahydrate crystals which were then melted or dried to their dihydrate form. The melted magnesium nitrate hexahydrate or magnesium nitrate dihydrate crystals were then fed to a kiln to be decomposed in solid magnesium oxide and NOx gas as a pyrolysis gas. The solid magnesium oxide was collected.

[0116] The pyrolysis NOx rich gas produced from the roasting underwent acid regeneration by being quenched, recovered and revalorized as nitric acid.Example 5

[0117] Serpentine tailings were leached using a solution that was 27% nitric acid, or nitric acid in a range of 10 to 40%, for a period of 4 hours at a temperature between 80 °C to 90 °C, at a ratio of 5 parts of solution to 1 part of serpentine tailingsor around 20% of solids, or the ratio was in a range between 3: 1 to 10: 1 of solution:solid mixture, which generated solid residues that were filtered from the leachate to form a crude solution.

[0118] A pH modifier was added to bring the pH of the crude solution to about 3 while the solution was not heated above 90 °C, after which iron and aluminum precipitated from the solution as hydroxides which were then filtered out to generate a metal-bearing solution. The pH modifier was magnesium oxide generated from the process.

[0119] The metal-bearing solution was passed through an ion-exchange circuit which bound nickel and cobalt. The nickel and cobalt were recovered from the ionexchange columns by eluting with sulphuric acid, which generated a spent acid solution.

[0120] The spent acid solution was evaporated in an evaporator generating a concentrated liquor of magnesium nitrate which was then fed to a crystallizer to form magnesium nitrate crystals. Optionally, the free water in the magnesium nitrate crystals were removed via centrifugation or spray drying. The magnesium nitrate crystals were collected and fed into a rotary kiln to be decomposed in solid magnesium oxide and NOx gas as a pyrolysis gas. The solid magnesium oxide was collected at the roaster’s bottom and from the roaster off-gas cycloning.

[0121] The pyrolysis NOx rich gas produced from the roasting underwent acid regeneration to regenerate nitric acid for use in leaching in the process.Example 6

[0122] Serpentine waste was mixed with nitric acid and water. The materials were reacted over a 6hr period at a temperature of 90°C. The solid residue was filtered and then MgO slurry was added to the filtrate to bring the pH to 1.85. Solid and liquid samples were extracted from the experiment, The elemental data was obtained using ICP analysis of the solid and liquid samples.

[0123] Table 1 shows results of the primary neutralization of leached solution post silica filtration. This was an endpoint precipitation test with a pH target of 1.85.The neutralizing agent was a 10wt% MgO slurry. Fe concentration was reduced from 5610mg / L to 33.4mg / L, while Al was reduced from 212mg / L to 116.8mg / L. This experiment was conducted at the bench scale at a facility in Quebec City, Quebec.Table 1 : Bench Scale Precipitation Test

[0124] Table 2 shows composite results from the continuous piloting operations that took place at a facility in Lakefield, Ontario. In this test, leaching conditions remained the same as the on the bench scale, however instead of filtering the silica and unleached solids, they remained in the solution during the neutralization phase. This creates a seeding effect, allowing for efficient crystal growth and therefore greater Fe and Al removal. This was also an endpoint precipitation test, however the target was reduced to pH 1 .5. A 10wt% MgO slurry was used as the neutralization agent.Table 2: Continuous Pilot Precipitation

[0125] The effect of keeping the silica in solution is seen in the Fe and Al removal results as it is often below 1 mg / L remaining. Additional benefits were observed during the filtration process. During the bench scale tests, the Fe / AI residue formed a gel-like solution, making filtration very difficult. The effect of having this residue combined with the silica allowed for an ease of filtration using standard pressure filtration techniques.

[0126] While the applicant's teachings described herein are in conjunction with various embodiments for illustrative purposes, it is not intended that the applicant's teachings be limited to such embodiments as the embodiments described herein are intended to be examples. On the contrary, the applicant's teachings described and illustrated herein encompass various alternatives, modifications, and equivalents, without departing from the embodiments described herein, the general scope of which is defined in the appended claims.REFERENCES1. Ian M. Power; Siobhan A. Wilson; Gregory M. Dippie, “Serpentinite Carbonation for CO2 Sequestration”, Elements, 2013, 9 (2), 115-121 .

Claims

WHAT IS CLAIMED IS:1 . A method for recovering at least one alkali earth metal and at least one metal from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution and separating the impurities to form a metal-bearing solution; selectively recovering the at least one metal from the metal-bearing solution using ion-exchange resin and a spent acid solution comprising at least one alkali earth metal salts; and optionally heating the spent acid solution to recover the at least one alkali earth metal.

2. A method for recovering at least one metal from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution and separating the impurities to form a metal-bearing solution; selectively recovering the at least one metal from the metal-bearing solution using ion-exchange resin.

3. The method of claim 1 or 2, wherein the mineral material is a mineral waste, asbestos-containing materials, silicate materials or a combination thereof.

4. The method of claim 3, wherein the mineral waste comprises serpentine tailings.

5. The method of any one of claims 1 to 4, wherein the mineral material comprises at least one metal and at least one alkali earth metal.

6. The method of any one of claims 1 to 5, further comprising reducing a size of the mineral material prior to the leaching.

7. The method of claim 5, further comprising subjecting the mineral material to a magnetic separation prior to size reduction.

8. The method of any one of claims 1 to 7, wherein the at least one alkali earth metal comprises magnesium.

9. The method of any one of claims 1 to 8, wherein the at least one alkali earth metal salts comprise magnesium hydroxide, magnesium nitrate, magnesium oxide, magnesium carbonates, or a combination thereof.

10. The method of any one of claims 1 to 9, wherein the at least one metal comprise nickel, cobalt, copper, uranium, vanadium, zinc, cadmium, platinum, palladium or a combination thereof.11 .The method of any one of claims 1 to 9, wherein the at least one metal comprises nickel, cobalt, or a combination thereof.

12. The method of any one of claims 1 to 11 , wherein the acid solution comprises nitric acid.

13. The method of any one of claims 1 to 12, wherein the acid solution has a concentration of about 10% to about 90% by volume.

14. The method of any one of claims 1 to 12, wherein the acid solution has a concentration of about 10% to about 40% by volume.

15. The method of any one of claims 1 to 12, wherein the acid solution has a concentration of about 20% to about 30% by volume.

16. The method of any one of claims 1 to 15, wherein the leaching is performed at a ratio in a range of about 3 : about 1 to about 10 : about 1 of acid solution to mineral material.

17. The method of any one of claims 1 to 16, wherein the leaching is performed at a ratio of about 5 : about 1 of acid solution to mineral material.

18. The method of any one of claims 1 to 17, wherein the leaching and heating of the mineral material is at a temperature of about 70 °C to about 90 °C.

19. The method of any one of claims 1 to 18, wherein the leaching and heating of the mineral material is at a temperature of about 80 °C to about 90 °C.

20. The method of any one of claims 1 to 19, wherein the separating the solid residue from the leachate solution is by filtration.21 . The method of any one of claims 1 to 20, wherein the precipitating impurities comprises adjusting a pH, hydrolysis or a combination thereof.

22. The method of claim 21 , wherein adjusting the pH is performed by a pH modifier.

23. The method of claim 22, wherein the pH modifier comprises magnesium oxide, serpentine tailings, caustic soda or lime.

24. The method of claim 22, wherein the pH modifier is magnesium oxide generated from heating the at least one alkali earth metal salt that is further recirculated.

25. The method of any one of claims 18 to 21 , wherein adjusting the pH is to a pH of about 1 to about 3.

26. The method of any one of claims 1 to 25, wherein the impurities comprise iron, aluminum or a combination thereof.

27. The method of any one of claims 1 to 25, wherein the precipitated impurities comprise iron hydroxide, aluminum hydroxide, hematite or a combination thereof.

28. The method of any one of claims 1 to 27, wherein the metal-bearing solution is at a pH of about 1 to about 3.

29. The method of any one of claims 1 to 27, wherein the metal-bearing solution is at a pH of about 1 .5 to about 3.

30. The method of any one of claims 1 to 29, wherein the ion-exchange resin comprises bispicolylamine (BPA) functionalities or iminodiacetate (IDA) functionalities.31 .The method of any one of claims 1 to 30, wherein the ion-exchange resin comprises cation-exchange resin.

32. The method of any one of claims 1 to 31 , wherein the ion-exchange resin is a weakly acidic microporous cation-exchange resin.

33. The method of any one of claims 1 to 32, wherein the selectively recovering the at least one metal using ion-exchange resin comprises at least one ionexchange resin columns.

34. The method of any one of claims 1 to 33, wherein the selectively recovering the at least one metal using ion-exchange resin comprises loading the metalbearing solution to selectively adsorb the at least one metal to the ionexchange resin and eluting to selectively desorb the at least one metal from the ion-exchange resin and recover the at least one metal.

35. The method of claim 34, wherein the eluting comprises eluting with an acid solution.

36. The method of claim 35, wherein the acid solution comprises sulfuric acid.

37. The method of claim 35 or 36, wherein the eluting comprises a first elution at a first concentration of acid to selectively desorb a first metal and a second elution at a second concentration of acid to selectively desorb a second metal.

38. The method of claim 37, wherein the first concentration is about 25 g / L to about 100 g / L and the first metal is cobalt.

39. The method of claim 37, wherein the second concentration is about 50 g / L to about 300 g / L and the second metal is nickel.

40. The method of claim 1 , wherein the heating of the spent acid solution comprises spray roasting, spray drying, evaporating, evaporative crystallizing, rotary kilning, fluid bed roasting or a combination thereof.41 . The method of claim 1 , wherein the heating of the spent acid solution is to decompose the at least one alkali earth metal salt into at least one alkali earth metal oxide.

42. The method of claim 41 , wherein the at least one alkali earth metal salt is magnesium nitrate and the heating decomposes the magnesium nitrate into magnesium oxide and gaseous nitric oxide.

43. The method of any one of claims 1 and 40 to 42, wherein the heating of the spent acid solution is at a temperature of about 450 °C to about 650 °C.

44. The method of claim 41 , further comprising carbonation of the at least one alkali earth metal oxide in the presence of a CO2 bearing gas or a carbonic acid solution to produce at least one alkali earth metal carbonate.

45. The method of claim 42, further comprising carbonation of the magnesium oxide in the presence of a CO2 bearing gas or a carbonic acid solution to form magnesium carbonate.

46. The method of claim 42, further comprising oxidation of the gaseous nitric oxide to regenerate nitric acid.

47. The method of claim 46, wherein the nitric acid is recycled to the leaching.

48. A method of recovering at least one alkali earth metal and at least one metal from serpentine tailings, said method comprising: leaching the serpentine tailings with an acid solution and heating a temperature to form a solid residue and a leachate solution; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution by adjusting pH to form a metal-bearing solution; selectively recovering the at least one metal and a spent acid solution comprising at least one alkali earth metal salts from the metal-bearing solution using at least one ion-exchange resin columns; heating and / or crystallizing the spent acid solution to form at least one alkali earth metal oxide; carbonating the at least one alkali earth metal oxide with CO2 or carbonic acid to form at least one alkali earth metal carbonate.

49. A method for recovering magnesium, nickel and cobalt from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution and separating the impurities to form a metal-bearing solution; selectively recovering nickel and cobalt from the metal-bearing solution using ion-exchange resin and a spent acid solution comprising magnesium salts; and optionally heating the spent acid solution to recover the magnesium.

50. A method of recovering magnesium, nickel and cobalt from serpentine tailings, said method comprising: leaching the serpentine tailings with a nitric acid solution and heating to form a solid residue and a leachate solution; separating the solid residue from the leachate solution to form a crude solution; precipitating impurities from the crude solution by adjusting pH to form a metal-bearing solution; selectively recovering nickel and cobalt from the metal-bearing solution using at least one ion-exchange resin columns and forming a spent acid solution comprising magnesium nitrate; heating the magnesium nitrate to form magnesium oxide and gaseous nitric oxide; carbonating the magnesium oxide with CO2 or carbonic acid to form magnesium carbonate; and oxidizing the gaseous nitric oxide to form nitrogen dioxide, absorbing the nitrogen dioxide in water to form and regenerate the nitric acid and optionally recirculating the nitric acid to the leaching.51 .A method for recovering at least one alkali earth metal and at least one metal from a mineral material, said method comprising: leaching the mineral material with an acid solution and heating to form a leachate solution and a solid residue; increasing the pH to precipitate impurities from the leachate solution and separating the impurities and solid residue by filtration to form a metalbearing solution; selectively recovering the at least one metal from the metal-bearing solution using ion-exchange resin or pH adjustment and filtration and forming a spent acid solution comprising at least one alkali earth metal salts; and optionally heating the spent acid solution to recover the at least one alkali earth metal.

52. The method of claim 51 , wherein the acid solution comprises nitric acid.

53. The method of claim 51 or 52, wherein the acid solution has a concentration of about 10% to about 90% by volume.

54. The method of claim 51 or 52, wherein the acid solution has a concentration of about 10% to about 40% by volume.

55. The method of claim 51 or 52, wherein the acid solution has a concentration of about 20% to about 30% by volume.

56. The method of any one of claims 51 to 55, wherein the leaching is performed at a ratio in a range of about 3 : about 1 to about 10 : about 1 of acid solution to mineral material.

57. The method of any one of claims 51 to 56, wherein the leaching is performed at a ratio of about 5 : about 1 of acid solution to mineral material.

58. The method of any one of claims 51 to 57, wherein the leaching and heating of the mineral material is at a temperature of about 70 °C to about 90 °C.

59. The method of any one of claims 51 to 58, wherein the leaching and heating of the mineral material is at a temperature of about 80 °C to about 90 °C.

60. The method of any one of claims 51 to 59, wherein the separating the solid residue from the leachate solution is by filtration.61 . The method of any one of claims 51 to 60, wherein increasing the pH or pH adjustment is performed by a pH modifier.

62. The method of claim 61 , wherein the pH modifier comprises magnesium oxide, serpentine tailings, caustic soda or lime.

63. The method of claim 61 , wherein the pH modifier is magnesium oxide generated from heating the at least one alkali earth metal salt that is further recirculated.

64. The method of any one of claims 18 to 21 , wherein adjusting the pH is to a pH of about 1 to about 3.

65. The method of any one of claims 51 to 64, wherein the impurities comprise iron, aluminum or a combination thereof.

66. The method of any one of claims 51 to 65, wherein the precipitated impurities comprise iron hydroxide, aluminum hydroxide, hematite or a combination thereof.

67. The method of any one of claims 51 to 66, wherein the metal-bearing solution is at a pH of about 1 to about 3.

68. The method of any one of claims 51 to 67, wherein the metal-bearing solution is at a pH of about 1 .5 to about 3.

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