Nitric acid recovery and recycling process

Abstract

Metal-containing precursor materials are contacted with an initial nitric acid solution containing a predetermined nitric acid concentration, at a predetermined temperature, and a predetermined atmospheric pressure to remove at least one valuable metal to form a nitrates solution having other metals therein. The resultant nitrate solution is transported to a converter. A sulfuric acid solution is introduced along with nitrate solution into the converter to convert the nitrates into sulfates in excess sulfuric acid solution. The formed solid sulfates and sulfuric acid are separated nitric acid solution containing a predetermined NOx concentration is recovered from the vapor stream by condensation therein.

Description

NITRIC ACID RECOVERY AND RECYCLING PROCESSTECHNICAL FIELD

[0001] The subject disclosure is directed to an improved method for recovering nitric acid as a by-product of metal processing.BACKGROUND ART

[0002] Raw metal-bearing ores, such as nickel-bearing ores, aluminum-bearing ores, and metal processing waste products, such as process tailings, red mud, fly ash, pyrite, and other similar waste materials, represent a rich source of valuable minerals. The term “ores” as used herein means oxide and sulfide ores, and other metal-bearing materials, it being understood that metals can be combined with other elements. The compositions of ores vary tremendously, even taken from the same mining site. Accordingly, many processes that extract valuable minerals from a full range of ores, including transitional ores, are known.

[0003] Unfortunately, many mineral extracting processes are very expensive, and energy intensive, and, in many instances, such processes produce substantial amounts of waste products. These waste products cannot be discarded into rivers or seas without further treatment.

[0004] Conventional treatments directed towards recovering nitric acid utilize distillation processes to recover the nitric acid from the waste in acid form or as nitrates. Distillation is somewhat practical because nitric acid can be distilled at a relatively low temperature. The recovered nitric acid can be used for various acid treatments. Unfortunately, conventional processes that recover nitric acid are considered to be less desirable due to the high energy requirement and presence of large volume of NOx gases.

[0005] The removal of the NOx gas from the nitric acid can be difficult because NOx gas is not satisfactorily absorbed in an absorbing liquor such as water, and in order to recover such NOx gas in the form of nitric acid, the NOx gas must be passed through a column packed with an oxidation catalyst to convert nitrogen monoxide to nitrogen dioxide, and for this treatment, the equipment must be enlarged and the treatment cost becomes high. Accordingly, there is a need for an improved process for recovering nitric acid from metal processing waste products.DISCLOSURE OF INVENTION

[0006] In various implementations, a method for producing a nitric acid solution is provided. Metal-containing precursor materials are contacted with an initial nitric acid solution containing apredetermined nitric acid concentration, at a predetermined temperature, and a predetermined atmospheric pressure to remove at least one valuable metal to form an intermediate solution having nitrates therein. The intermediate solution is transported to a converter. A heated concentrated sulfuric acid solution having a predetermined concentration of sulfuric acid is introduced into the converter to mix with the intermediate solution on into the converter to form a mixture in which the nitrates are converted into sulfates and a vapor stream. Nitric acid solution containing a predetermined NOx concentration is recovered. Formed solid sulfates are separated from the mixture.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a schematic diagram of an embodiment of a nitric acid recovery process in accordance with this disclosure.

[0008] FIG. 2 is a schematic diagram of a hydrometallurgy process that produces a nitrates solution stream therein.

[0009] FIG. 3 is an exemplary process in accordance with the disclosed subject matter.MODES FOR CARRYING OUT THE INVENTION

[0010] The subject disclosure is directed to an improved method for recovering an enriched nitric acid solution from a by-product of a process that extracts valuable minerals from ores and other similar source materials. Such source materials can include nickel-bearing ores, aluminum- bearing ores, process tailings, such as red mud, fly ash, pyrite, and other similar waste products. The recovered, enriched nitric acid product can be recycled for re-use in the extraction process.

[0011] Exemplary mineral extraction processes are disclosed within U.S. Patent Nos. 8,016,913 and 8,038,767 to Drinkard, Jr., the entire disclosures of which, except for any definitions, disclaimers, disavowals, and inconsistencies, are incorporated herein by reference.

[0012] The detailed description provided below in connection with the appended drawings is intended as a description of examples and is not intended to represent the only forms in which the present examples can be constructed or utilized. The description sets forth functions of the examples and sequences of steps for constructing and operating the examples. However, the same or equivalent functions and sequences can be accomplished by different examples. Unless otherwise indicated percentages are expressed by weight.

[0013] References to “one embodiment,” “an embodiment,” “an example embodiment,” “one implementation,” “an implementation,” “one example,” “an example” and the like, indicate thatthe described embodiment, implementation or example can include a particular feature, structure or characteristic, but every embodiment, implementation or example can not necessarily include the particular feature, structure or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment, implementation or example. Further, when a particular feature, structure or characteristic is described in connection with an embodiment, implementation or example, it is to be appreciated that such feature, structure or characteristic can be implemented in connection with other embodiments, implementations or examples whether or not explicitly described.

[0014] Numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments of the described subject matter. It is to be appreciated, however, that such embodiments can be practiced without these specific details.

[0015] Various features of the subject disclosure are now described in more detail with reference to the drawings, wherein like numerals generally refer to like or corresponding elements throughout. The drawings and detailed description are not intended to limit the claimed subject matter to the particular form described. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the claimed subject matter.

[0016] Conventional nitric acid recovery processes, such as the types of processes disclosed in U.S. Patent No. 6,264,909 to Drinkard, Jr., are energy intensive and inefficient. The most efficient conventional processes recover between 50% to 60% nitric acid, which must be further distilled to produce a produce of a product having a concentration of about 70% to about 99%. In contrast, the disclosed process produces a recycled nitric process that exceeds about 90% without the need for additional distillation. The disclosed processes also produce sulfates as a by-product, which is an advantage over conventional processes.

[0017] Another advantage of the disclosed process is the presence of dissolved NOx gases in the recovered nitric acid solution. The NOx component of the solution represents reduced species that, unexpectedly, can be used to reduce higher oxides in ores or in other waste products during the recycled phase of the nitric acid. This enriched, recovered nitric acid solution can include up to about 5% NOx. In some embodiments, the NOx concentration is between about 4% to about 5%.

[0018] Referring now to the drawings and, in particular, to FIG. 1 , there is shown an improved method, generally designated with the numeral 100, for recovering and for recycling an enrichednitric acid solution from a by-product from a mineral extraction process 110. The mineral extraction process 110 extracts a valuable mineral 112, such as a metal compound, from a precursor material 114, such as a feed ore.

[0019] The precursor material 114 can be in the form of raw ores and / or waste products that include valuable minerals. Exemplary raw ores include nickel-bearing ores, aluminum-bearing ores, such as bauxite or laterite. Exemplary waste products include process tailings, such as red mud, fly ash, and other similar precursor materials. Other types of suitable precursor material 114 include pyrite and nodules.

[0020] The precursor material 114 can include metals and metal compounds. Exemplary metals and compounds that include aluminum, iron, nickel, cobalt, manganese, magnesium, rare Earth elements, and scandium.

[0021] The metal extraction process 110 can include a processor 116 that receives an initial nitric acid solution 118 that is combined with the precursor material 114 to remove at least one metal compound therefrom. The processor 116 can produce the extracted metal compound 112 and a barren solution for transport to a converter 120. In this exemplary embodiment, the metal compound is of aluminum.

[0022] Alternatively, the processor 116 can produce an intermediate solution that can be transported to a finishing apparatus 122 to remove a second metal, to produce a nitrate solution for transport to the mixing converter 120. In some exemplary embodiments, the second metal is iron.

[0023] The mixing converter 120 can be any suitable mixing container suitable for receiving nitric acid solutions and other acids, such as a crystallizer. Once the mixing converter 120 receives the nitrate solution from the processor 116 and / or the finishing apparatus 122, a hot sulfuric acid solution 124 is introduced along with the nitrate solution. In this exemplary embodiment, the hot sulfuric acid solution is a about 90% to about 98% concentrated sulfuric acid solution in the temperature range of about 150°C to about 200°C. The concentrated sulfuric acid solution can be mixed with the nitrates solution to form a saturated sulfate solution. Sulfuric acid to be added in excess to hold the formed solid sulphates in the solution.

[0024] The sulfuric acid solution 124 converts nitrates within the solution into sulfates 126. The types of sulfates 126 that will be produced will depend upon the composition of the nitrates solution that is produced through the mineral extraction process 110. In this exemplary embodiment, the sulfates 126 are produced in the form of solid white product.

[0025] The composition of the sulfates 126 will also depend upon the type of alkali material that is used in the mineral extraction process 110. In some embodiments, the sulfates 126 will be calcium sulfate dihydrates (gypsum salts), magnesium sulfates (Epsom salts), calcium sulfates, manganese sulfates, cobalt sulfates, nickel sulfates, or mixtures thereof.

[0026] The converter 120 can form a slurry that includes the sulfates 126 in solid form and a liquid component. The slurry is converted in 120 in which water can be removed from the liquid component to recover a nitric acid solution therefrom at 128.

[0027] The nitric acid solution can contain a predetermined NOx concentration. In some embodiments, the predetermined NOx concentration can be up to about 5% NOx. In other embodiments, the NOx concentration can be between about 4% to about 5%. The NOx component of the nitric acid solution can be recycled in the process 116, to reduce higher oxides in precursor materials, such as the precursor materials 114.

[0028] The converter 120 can remove water from the liquid component through any suitable method. Suitable methods include producing a vapor stream and / or through solid-liquid separation. The converter 120 can include a heat exchanger. The heat exchanger can include titanium, such as a titanium liner for contacting the slurry.

[0029] The converter 120 is operated within a predetermined temperature range, so that the recovered nitric acid solution will have desirable properties. At the lower end of the temperature range, the barren solution will not form vapor. At the upper end of the temperature range, a substantial portion of the nitric acid is converted into NOx gas. In this exemplary embodiment, the liquid component is evaporated at a temperature within a range of about 120°C to about 210°C.

[0030] As indicated above, the sulfate 126 formed from this method 100 can include a mixture of sulfate compounds. A separator 130 can be used to separate the different sulfate compounds from one another.

[0031] Referring now to FIG. 2 with continuing reference to the foregoing figure, there is shown an exemplary hydrometallurgy process, generally designated with the numeral 200, for recovering valuable metals through the hydrolysis / precipitation of aluminum and other processing steps. In this exemplary embodiment, the process 200 can be the process 110 performed with the processor 116 and the finishing apparatus 124 shown in FIG. 1.

[0032] The exemplary process 200 begins by combining a nitric acid solution with precursor materials for leaching at 210. The nitric acid solution contains a predetermined concentration ofnitric acid, which can range from about 10% to about 95%. In this exemplary embodiment, the predetermined concentration is about 70%. The precursor materials are feed ores, such as the feed ores 114 shown in FIG. 1.

[0033] At 210, the precursor materials are leached with the nitric acid solution at a predetermined temperature and predetermined atmospheric pressure. In this exemplary embodiment, the predetermined temperature is within the range about 90°C to about 115°C. The predetermined atmospheric pressure is within the range of about 0.95 atmospheres to about 1.05 atmospheres. In some embodiments, the predetermined atmospheric pressure is about 1.0 atmosphere. The leaching step at 210 can be used to remove various metals from the ore into the solution. Exemplary metals include aluminum, iron, nickel, cobalt, manganese, magnesium, rare Earth elements, scandium and other metals. In this exemplary embodiment, aluminum is leached from the precursor materials.

[0034] The leaching step at 210 produces a leached solution and a residue. The leached solution with the leached metals removed therefrom is transported for iron hydrolysis at 212. The residue is washed and neutralized at 214 to produce a product at 216 that is rich in silicates. The final residue product can be used to improve soil because it includes a trace amount of nitrates.

[0035] The residue may have titanium and / or titanium compounds for certain ores that can be recovered further by a simple physical separation such as gravity. Titanium and titanium compounds can be separated from the silicates using gravity separation and the final residue can be used as fertilizer.

[0036] The solution is transported for hydrolysis at 212. The iron hydrolysis at 212 can be performed within an iron hydrolysis reactor that can operate within a temperature range of about 150°C to about 195°C to recover iron as hematite at 218 A vapor stream 220 can be directed to 222 for recovery of nitric acid 224 therein.

[0037] The iron hydrolysis reactor also produces an iron oxide product at 218 and acid is recovered via vapor stream. Most of the iron is removed at 218.

[0038] The intermediate solution can be mixed with alkali, such as calcium oxide (lime) or magnesium oxide (magnesia), at 226 to precipitate aluminum therefrom at 227.

[0039] Alternatively, the intermediate solution can be heated at 226 within a preselected temperature range to form aluminum oxide and for nitric acid recovery at 222. In this exemplaryembodiment, the temperature range can be from about 170°C to about 195°C and to recover nitric acid in the vapor stream.

[0040] The intermediate solution can be subjected to additional extraction operations at 228 to remove scandium, rare Earth elements, and other metals. The extraction operations can include ion exchange and / or solvent extraction followed by precipitation of individual elements or groups of elements as hydroxides or other compounds using alkali, such as calcium oxide (lime) and / or magnesium oxide (magnesia).

[0041] A raffinate solution from the ion exchange circuit at 228 can be sent for precipitation of a nickel, cobalt, and manganese mixed hydroxide product at 230. The mixed hydroxide product can be produced using alkali, such as calcium oxide (lime) and / or magnesium oxide (magnesia).

[0042] A barren solution 232 is produced from the extraction operations at 228 and / or the precipitation of the raffinate solution at 230. The nitrate solution 232 can be transported to converter at 120.

[0043] Referring now to FIG. 3 with continuing reference to the foregoing figures, an exemplary method, generally designated with the numeral 300, for recovering an enriched nitric acid solution for recycle is shown. The by-product is obtained from a process that utilizes nitric acid to extract valuable minerals from nickel-bearing and / or aluminum-bearing ores, process tailings, including red mud, fly ash, pyrite, and nodules as well as other similar precursor materials.

[0044] At 301, metal-containing precursor materials are contacted with an initial nitric acid solution containing a predetermined nitric acid concentration, at a predetermined temperature, and a predetermined atmospheric pressure to remove at least one valuable metal to form an intermediate solution having nitrates therein. In exemplary embodiments, the metal-containing precursor materials are ores or metal-processing waste products that are leached using a nitric acid solution that includes between about 10% nitric acid to about 95% nitric acid.

[0045] The precursor materials are leached at a temperature between about 90°C to about 115°C and at an atmospheric pressure of between about 0.9 atmospheres and 1.1 atmospheres. The precursor materials are leached to extract aluminum, iron, nickel, cobalt, manganese, magnesium, rare Earth elements, scandium and other metals into solution. The residue is washed and neutralized to produce a product that contains silicates and titanium (for certain types of ores).

[0046] The leached solution can be sent for iron hydrolysis to recover iron as hematite. The iron hydrolysis can occur within a temperature range of about 150°C to about 195°C. The reaction can produces a vapor stream that includes nitric acid, which can be recovered.

[0047] The solution that was subject to the iron hydrolysis step can be precipitated with an alkali, such as calcium oxide (lime) and / or magnesium oxide (magnesia) to obtain aluminum as a hydroxide. Alternatively, the aluminum can be separated from the solution by heating solution to a temperature range of between about 170°C to about 195°C to form aluminum oxide. In such embodiments, nitric acid can be obtained from the vapor stream.

[0048] The solution can be further processed to remove scandium, rare Earth elements, and other metals through ion exchange and / or solvent exchange reactions. Then, the elements can be precipitated as hydroxides or other compounds using alkali, such as calcium oxide (lime) and / or magnesium oxide (magnesia). Then, the raffinate solution from the ion exchange circuit can be sent for precipitation of a nickel, cobalt, and manganese mixed hydroxide product using an alkali, such as calcium oxide (lime) or magnesium oxide (magnesia).

[0049] At 302, the intermediate solution from Step 301 is transported to a converter. Then, a heated concentrated sulfuric acid solution having a predetermined concentration of sulfuric acid is introduced into the converter at 303 to mix with the intermediate solution on into the converter to form a mixture in which the nitrates are converted into sulfates and a vapor stream. In this exemplary embodiment, the sulfuric acid can be a concentrated sulfuric acid of about 90% to about 98% and in the temperature range of about 150°C to about 200°C. The hot sulfuric acid added to be in excess to the stoichiometric requirement of nitrates to sulphates conversion

[0050] At 304, nitric acid solution containing a predetermined NOx concentration is recovered. In this exemplary embodiment, the nitrates are converted to sulfates to produce a solid by-product. The solid by-product can be calcium sulfate dihydrates (gypsum salts), magnesium sulfates (Epsom salts), calcium sulfates, manganese sulfates, cobalt sulfates, nickel sulfates, or mixtures thereof. The sulfuric acid solution to be recycled.

[0051] At 305, formed solid sulfates are separated from the mixture. The method 300 is very energy efficient and can result in the recovery of about 90-99% of the nitric acid that is used to extract the metals at 301. The recovered nitric acid can be recycled back to 301 , used in other metal extraction processes, or used in other processes. The recovered nitric acid solution can includedissolved NOx gases that can enhance the efficacy and the efficiency of subsequent metal extraction processes.Supported Features and Embodiments

[0052] The detailed description provided above in connection with the appended drawings explicitly describes and supports various features of systems, apparatus, and methods for recovering enriched nitric acid from the by-products from the processing of raw ores, process tailings, fly ash, pyrite and other similar materials. By way of illustration and not limitation, supported embodiments include a method for producing a nitric acid solution, the method comprising: contacting metal-containing precursor materials with an initial nitric acid solution containing a predetermined nitric acid concentration, at a predetermined temperature, and a predetermined atmospheric pressure to remove at least one valuable metal to form an intermediate solution having nitrates therein; transporting the intermediate solution to a converter; introducing a heated concentrated sulfuric acid solution having a predetermined concentration of sulfuric acid into the converter to mix with the intermediate solution on into the converter to form a mixture in which the nitrates are converted into sulfates and a vapor stream; recovering nitric acid solution containing a predetermined NOx concentration; and separating formed solid sulfates from the mixture.

[0053] Supported embodiments include the foregoing method, wherein the metal-containing precursor materials are selected from the group consisting of raw ores, nickel-bearing ores, aluminum-bearing ores, process tailings, red mud, fly ash, pyrite, nodules, and metal-process waste materials.

[0054] Supported embodiments include any of the foregoing methods, wherein at least one valuable metal is selected from the group consisting of aluminum, iron, nickel, cobalt, manganese, magnesium, a rare Earth element, and scandium.

[0055] Supported embodiments include any of the foregoing methods, wherein the predetermined nitric acid concentration for the initial nitric acid solution is within the range of about 10% to about 95%, the predetermined temperature is within the range of about 90°C to about 115°C and the predetermined atmospheric pressure is within the range of about 0.95 atmospheres to about 1.05 atmospheres.

[0056] Supported embodiments include any of the foregoing methods, wherein the contacting step includes leaching the metal-containing precursor materials with the initial nitric acid solution to produce the valuable metal compound, a nitrate solution and a residue.

[0057] Supported embodiments include any of the foregoing methods, wherein the contacting step includes: washing the residue; and neutralizing the residue to produce at least one of silicates, titanium, and titanium compounds therefrom.

[0058] Supported embodiments include any of the foregoing methods, wherein the metalcontaining precursor materials include iron, further comprising: performing iron hydrolysis on the metal-containing precursor materials to recover the iron from the metal-containing precursor materials in the form of hematite.

[0059] Supported embodiments include any of the foregoing methods, wherein the iron is recovered within a temperature range of range of about 150°C to about 195°C.

[0060] Supported embodiments include any of the foregoing methods, wherein the iron hydrolysis produces a vapor stream and nitric acid is recovered from the vapor stream.

[0061] Supported embodiments include any of the foregoing methods, wherein the metalcontaining precursor materials include aluminum, and wherein the iron hydrolysis produces an iron-free solution, the method further comprising: precipitating the aluminum from the iron-free solution to form an aluminum hydroxide.

[0062] Supported embodiments include any of the foregoing methods, wherein the metalcontaining precursor materials include aluminum, and wherein the iron hydrolysis produces an iron-free solution, the method further comprising: heating the iron- free solution to a temperature within the range of about 170°C to about 195°C to form an aluminum oxide and a vapor stream; and recovering nitric acid from the vapor stream.

[0063] Supported embodiments include any of the foregoing methods, wherein the intermediate solution is a first intermediate solution; and wherein the contacting step removes aluminum and iron from metal-containing precursor materials to form a second intermediate solution, further comprising: extracting at least one of nickel, cobalt, manganese, magnesium, a rare Earth element, and scandium from the second intermediate solution to form a nitrate solution.

[0064] Supported embodiments include any of the foregoing methods, wherein the extracting step includes performing at least one of ion-exchange extraction and solvent extraction on the second intermediate solution.

[0065] Supported embodiments include any of the foregoing methods, further comprising: introducing an alkali into the second intermediate solution to obtain a metal product containing at least one of a rare Earth element and scandium.

[0066] Supported embodiments include any of the foregoing methods, wherein the extracting step forms a raffinate solution, further comprising: introducing an alkali into the raffinate solution to obtain a hydroxide product that includes at least one of nickel, cobalt, and manganese.

[0067] Supported embodiments include any of the foregoing methods, wherein the sulfuric acid solution is a concentrated sulfuric acid solution.

[0068] Supported embodiments include any of the foregoing methods, wherein the predetermined NOx concentration is up to about 5% NOx.

[0069] Supported embodiments include any of the foregoing methods, wherein the converter is a device selected from the group consisting of a crystallizer and a simple reactor.

[0070] Supported embodiments include any of the foregoing methods, wherein the intermediate solution converts to sulfate salts in excess sulfuric acid.

[0071] Supported embodiments include any of the foregoing methods, wherein the sulfuric acid solution forms a slurry for transporting solid components from the converter.

[0072] Supported embodiments include any of the foregoing methods, wherein water is removed from the liquid component through evaporation.

[0073] Supported embodiments include any of the foregoing methods, wherein water is removed from the liquid component using a heat exchanger.

[0074] Supported embodiments include any of the foregoing methods, wherein the heat exchanger is lined with titanium.

[0075] Supported embodiments include any of the foregoing methods, wherein the liquid component is evaporated at a temperature within a range of about 120°C to about 210°C.

[0076] Supported embodiments include any of the foregoing methods, further comprising: dissolving the solid sulfates in water to form a sulfate-rich solution; crystallizing the sulfate-rich solution to form a plurality of crystallized sulfate compounds; and separating the crystallized sulfate compounds from one another via solvent extraction to form purified sulfate salts.

[0077] Supported embodiments include a system, a kit, an apparatus, and / or means for implementing any of the foregoing methods or a portion thereof.

[0078] Supported embodiments can provide various attendant and / or technical advantages in terms of an energy efficient hydrometallurgical processing route to produce metal compounds of aluminum, nickel, cobalt, iron, rear Earth elements, scandium, magnesium and others from the solution

[0079] Supported embodiments include an energy efficient hydrometallurgical processing route that produces an inert residue of silicates with a trace of nitrates that can be used, for example, to improve soil.

[0080] Supported embodiments include an energy efficient hydrometallurgical processing route that produces an inert residue of silicates and Titanium in some ores. Titanium can be separated from the silicates using gravity separation. Resultant silicates with a trace of nitrates that can be used, for example, to improve soil.

[0081] Supported embodiments include a process that utilizes nitric acid recycle and recovery technology to recover an enriched nitric acid solution from a mineral extraction process. The technology can be used to recover and to recycle essentially all of the nitric acid used in the process.

[0082] Supported embodiments include a nitric acid recovery and recycling process that includes leaching, hydrolysis, Ion exchange , Solvent extraction ,mixed-hydroxide precipitation, nitrate to sulfate conversion, solid liquid separation, nitric acid recovery

[0083] The detailed description provided above in connection with the appended drawings is intended as a description of examples and is not intended to represent the only forms in which the present examples can be constructed or utilized. It is to be understood that the configurations and / or approaches described herein are exemplary in nature, and that the described embodiments, implementations and / or examples are not to be considered in a limiting sense, because numerous variations are possible.

[0084] Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are presented as example forms of implementing the claims.

Claims

CLAIMSWhat is claimed is:

1. A method for producing a nitric acid solution, the method comprising: contacting metal-containing precursor materials with an initial nitric acid solution containing a predetermined nitric acid concentration, at a predetermined temperature, and a predetermined atmospheric pressure to remove at least one valuable metal to form an intermediate solution having nitrates therein; transporting the intermediate solution to a converter; introducing a heated concentrated sulfuric acid solution having a predetermined concentration of sulfuric acid into the converter to mix with the intermediate solution on into the converter to form a mixture in which the nitrates are converted into sulfates and a vapor stream; recovering nitric acid solution containing a predetermined NOx concentration; and separating formed solid sulfates from the mixture.

2. The method of claim 1, wherein the metal-containing precursor materials are selected from the group consisting of raw ores, nickel-bearing ores, aluminum-bearing ores, process tailings, red mud, fly ash, pyrite, nodules, and metal-process waste materials.

3. The method of claim 1, wherein at least one valuable metal is selected from the group consisting of aluminum, iron, nickel, cobalt, manganese, magnesium, a rare Earth element, and scandium.

4. The method of claim 1 , wherein the predetermined nitric acid concentration for the initial nitric acid solution is within the range of about 10% to about 95%, the predetermined temperature is within the range of about 90°C to about 115°C and the predetermined atmospheric pressure is within the range of about 0.95 atmospheres to about 1.05 atmospheres.

5. The method of claim 1, wherein the contacting step includes leaching the metal-containing precursor materials with the initial nitric acid solution to produce the valuable metal compound, a nitrate solution and a residue.

6. The method of claim 5, wherein the contacting step includes: washing the residue; and neutralizing the residue to produce at least one of silicates, titanium, and titanium compounds therefrom.

7. The method of claim 1, wherein the metal-containing precursor materials include iron, further comprising: performing iron hydrolysis on the metal-containing precursor materials to recover the iron from the metal-containing precursor materials in the form of hematite.

8. The method of claim 7, wherein the iron is recovered within a temperature range of range of about 150°C to about 195°C.

9. The method of claim 7, wherein the iron hydrolysis produces a vapor stream and nitric acid is recovered from the vapor stream.

10. The method of claim 7, wherein the metal-containing precursor materials include aluminum, and wherein the iron hydrolysis produces an iron-free solution, the method further comprising: precipitating the aluminum from the iron- free solution to form an aluminum hydroxide.

11. The method of claim 7, wherein the metal-containing precursor materials include aluminum, and wherein the iron hydrolysis produces an iron-free solution, the method further comprising: heating the iron- free solution to a temperature within the range of about 170°C to about 195°C to form an aluminum oxide and a vapor stream; and recovering nitric acid from the vapor stream.

12. The method of claim 1, wherein the intermediate solution is a first intermediate solution; and wherein the contacting step removes aluminum and iron from metal-containing precursor materials to form a second intermediate solution, further comprising:extracting at least one of nickel, cobalt, manganese, magnesium, a rare Earth element, and scandium from the second intermediate solution to form a nitrate solution.

13. The method of claim 12, wherein the extracting step includes performing at least one of ion-exchange extraction and solvent extraction on the second intermediate solution.

14. The method of claim 12, further comprising: introducing an alkali into the second intermediate solution to obtain a metal product containing at least one of a rare Earth element and scandium.

15. The method of claim 12, wherein the extracting step forms a raffinate solution, further comprising: introducing an alkali into the raffinate solution to obtain a hydroxide product that includes at least one of nickel, cobalt, and manganese.

16. The method of claim 1, wherein the sulfuric acid solution is a concentrated sulfuric acid solution.

17. The method of claim 1, wherein the predetermined NOx concentration is up to about 5% NOx.

18. The method of claim 1 , wherein the converter is a device selected from the group consisting of a crystallizer and a simple reactor.

19. The method of claim 1 , wherein the intermediate solution converts to sulfate salts in excess sulfuric acid.

20. The method of claim 19, wherein the sulfuric acid solution forms a slurry for transporting solid components from the converter.

21. The method of claim 1, wherein water is removed from the liquid component through evaporation.

22. The method of claim 21 , wherein water is removed from the liquid component using a heat exchanger.

23. The method of claim 22, wherein the heat exchanger is lined with titanium.

24. The method of claim 21, wherein the liquid component is evaporated at a temperature within a range of about 120°C to about 210°C.

25. The method of claim 1, further comprising: dissolving the solid sulfates in water to form a sulfate-rich solution; crystallizing the sulfate-rich solution to form a plurality of crystallized sulfate compounds; and separating the crystallized sulfate compounds from one another via solvent extraction to form purified sulfate salts.

Images