Aluminium crystallization hydrometallurgy process

Abstract

Precursor materials in the form of raw ores, process tailings, fly ash, and other similar materials are leached using a nitric acid solution containing a predetermined nitric acid concentration, at a predetermined temperature, and at a predetermined atmospheric pressure to produce a leached solution and a residue. The residue is washed with a neutralizing solution to produce a byproduct therefrom. The leached solution is crystallized to obtain a mixture of nitrate crystals and a post- crystallization solution. A supernatant bleed stream is sent to a hydrolysis reactor. At least two metal compounds are extracted and precipitated from the post-crystallization solution.

Description

ALUMINIUM CRYSTALLIZATION HYDROMETALLURGY PROCESSTECHNICAL FIELD

[0001] The subject disclosure is directed to an improved method for processing raw ores, such as aluminum-bearing ores, process tailings, such as red mud, fly ash, and other similar precursor materials to recover the metal compounds contained therein.BACKGROUND ART

[0002] Raw metal-bearing ores, such as aluminum-bearing ores, represent a rich source of valuable metal compounds. 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, processes that can extract valuable metal compounds from a full range of ores, including transitional ores, is desirable.

[0003] Similarly, metal and metal oxide processes generate waste products, such as process tailings, red mud, fly ash, and other similar metallurgical waste products, also represent a rich source of valuable metal compounds. Indeed, some countries produce millions of tons of such waste materials through the production of metals and / or metal oxides. Unfortunately, conventional metal and metal oxide processing, if not conducted in a sustainable manner, will result in pollution and safety hazards. Accordingly, there is a need for more efficient and environmentally friendly techniques to extract valuable metal compounds from raw metal-bearing ores and various waste products.DISCLOSURE OF INVENTION

[0004] In various implementations, a method for obtaining recovered metal compounds from precursor materials is provided. The precursor materials are leached using a nitric acid solution containing a predetermined nitric acid concentration, at a predetermined temperature, and at a predetermined atmospheric pressure to produce a leached solution and a residue. The residue is washed with a neutralizing solution to produce a byproduct therefrom. The leached solution is crystallized to obtain a mixture of nitrate crystals and a post-crystallization solution. A supernatant bleed stream is sent to a hydrolysis reactor. At least two metal compounds are extracted and precipitated from the post-crystallization solution.

[0005] The recovered nitrate crystals can be purified via a series of wash / recrystallisation steps by using predetermined concentrated HNO3 followed by thermal decomposition to produce purified aluminum oxide product.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a flow diagram of an embodiment of a hydrometallurgy process in accordance with the disclosed subject matter.

[0007] FIG. 2 is another flow diagram illustrating a portion of the process shown in FIG. 1.

[0008] FIG. 3 is an exemplary process in accordance with the disclosed subject matter.MODES FOR CARRYING OUT THE INVENTION

[0009] The subject disclosure is directed to an improved method for processing aluminum- bearing ores, process tailings such as Red Mud and fly ash to recover the valuable metal compounds contained therein. The process can be utilized to recycle the majority of the acid used therewith.

[0010] 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.

[0011] References to “one embodiment,” “an embodiment,” “an example embodiment,” “one implementation,” “an implementation,” “one example,” “an example” and the like, indicate that the 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.

[0012] 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.

[0013] 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. Unless otherwise indicated percentages are expressed by weight.

[0014] The disclosed process includes leaching ore using nitric acid within a concentration range of about 10% to about 95% at a temperature range of about 90°C to about 115°C and at atmospheric pressure to leach valuables such as aluminum, iron, nickel, cobalt, manganese, magnesium, rare earth elements, scandium and others into the solution. In some embodiments, the concentration of the nitic acid is about 70%. In other embodiments, the concentration of the nitric acid is about 90%.

[0015] The lower limit of temperature range can be about 100°C. In some embodiments, the lower limit of the temperature range will change with the concentration of the nitric acid. As the nitric acid concentration increases, the boiling point of the nitric acid solution decreases, so that the lower limit of the temperature range can decrease.

[0016] The residue is washed and neutralized to produce a product that is rich in silicates and titanium for further recovery of titanium. The final residue can be used as a by-product for mine rehabilitation.

[0017] Aluminum is crystallized as nitrates from the solution by natural cooling of the solution and / or with combination of seeding with aluminum nitrate. Aluminum nitrate crystals are purified with a combination of a nitric acid wash and / or re-dissolution and recrystallization of aluminum nitrate by rejecting iron and other metals from the crystals into the solution. Purified aluminum nitrate crystals are decomposed, thermally, at about 150°C up to 1250°C into various forms of alumina and NOx gases that are recovered as nitric acid within the process. The forms of alumina can include AI2O3, alpha alumina, beta alumina, and gamma alumina.

[0018] A supernatant bleed stream from the crystallization circuit is sent to an iron hydrolysis reactor to recover iron as hematite at about 150°C to about 195°C. In some embodiments, the upper end of the range can be as low as about 165 °C.

[0019] Nitric acid is recovered from a vapor stream emitting therefrom. An iron-free and aluminum-free solution is processed for scandium, rare earth elements and others extraction viaion exchange and / or solvent extraction followed by precipitation of individual or groups of elements as hydroxides or other compounds.

[0020] In some embodiments, an ion exchange and / or a solvent extraction circuit can be subject to a precipitation step to form at least one of a nickel, cobalt, and manganese mixed hydroxide product.

[0021] The barren solution, after recovering the majority of the elements, is concentrated with magnesium nitrate to be thermally decomposed at about 500°C and up to about 900°C into magnesia and NOx gases, which, in turn, are converted into nitric acid.

[0022] The disclosed systems and methods represent improvements over the systems and methods 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.

[0023] Referring now to the drawings and, in particular, to FIGS. 1-2, there is shown an improved hydrometallurgy process, generally designated with the numeral 100, for recovering valuable metal compounds through the crystallization of aluminum and other processing steps. The process 100 can be used to process precursor materials in the form of raw ores and / or waste products that include valuable metal compounds. Exemplary raw ores include aluminum-bearing ores. Exemplary waste products include process tailings, such as red mud, fly ash, and other similar precursor materials.

[0024] The process 100 can be used to recover metals and metal compounds. Exemplary metal compounds include compounds that include aluminum, iron, nickel, cobalt, manganese, magnesium, rare Earth elements, and scandium.

[0025] The process 100 begins by combining a nitric acid solution 110 with precursor materials 112 for leaching at 114. The nitric acid solution 110 contains a predetermined concentration of nitric acid, which can range from about 10% to about 95%. In this exemplary embodiment, the predetermined concentration is about 70%. The precursor materials 112 are feed ores or process tailings.

[0026] At 114, the precursor materials 112 are leached with the nitric acid solution 110 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 1.05atmospheres. In this exemplary embodiment, the predetermined atmospheric pressure is about 1.0 atmosphere.

[0027] The leaching step at 114 produces a leached solution and a residue. The leached solution is transported for crystallization at 116. The crystallization step at 116 produces a mixture of nitrate crystals and solution.

[0028] Crystallization can be accomplished through any suitable means. In this exemplary embodiment, crystallization is accomplished by naturally cooling the leached solution or by seeding the leached solution with recycled aluminum nitrate crystals.

[0029] The residue from step 114 is washed with a neutralizing solution at 118 to produce a byproduct therefrom. The residue is rich in silicates and titanium, which can be recovered as the byproduct at 118.

[0030] The crystallization step at 116 can produce a supernatant bleed stream at 120 for further processing through a series 122 of steps shown in FIG. 2. The remaining solution from 120 can be recycled to the leaching step at 114 which can be utilized to recover more aluminium from the solution and certain other materials, such as scandium, at a mineral recovery step at 146.

[0031] The crystals formed at 116 are subject to purification at 126. At 126, the solution can be subject to a nitric acid wash and / or redissolution at 128 with the recrystallization. Redissolution and recrystallization can be accomplished by rejecting iron and other metals from the crystals into the solution.

[0032] The aluminum nitrate crystals within the crystallized leached solution can be thermally decomposed within a predetermined temperature range at 134 in the presence of alumina and NOx gases. The thermal decomposition will produce a high-grade alumina product at 136. In this exemplary embodiment, the predetermined temperature range is from about 150°C up to about 1250°C. The NOx components can be recovered as nitric acid.

[0033] As shown in FIG. 1, a second supernatant bleed stream 130 can be obtained from the crystallized leached solution at 126. The second supernatant blead stream 130 can be subject to further processing through the series 122 of steps shown in FIG. 2. A stream of the series 122 can be returned to the leaching step at 114 for further recycling.

[0034] Referring now to FIG. 2 with continuing reference to the foregoing figure, the processing of a supernatant bleed stream 138 is shown in more detail. The supernatant bleed stream138 can be obtained from the crystallization step at 116 and / or the purification step 126 shown inFIG. 1.

[0035] The supernatant bleed stream 138 can be directed into an iron hydrolysis reactor 140, which can operate within a temperature range of about 150°C to about 195°C to recover iron as hematite at 142. A vapor stream can be directed to 144 for recovery of nitric acid therein.

[0036] An iron-free solution can be processed for the recovery of additional metal compounds at 146, such as scandium, rare Earth elements, and other metal compounds. The recovery step at 146 produces a rich strip liquor and a barren liquor.

[0037] Magnesium oxide and nitric acid can be removed from the barren liquor at 148. Scandium, rare Earth elements, and other metal compounds can be removed from the rich strip liquor at 150.

[0038] Referring now to FIG. 3 with continuing reference to the foregoing figures, an exemplary method, generally designated with the numeral 200, for extracting metal compounds from precursor materials is shown. The precursor materials can be aluminum-bearing ores, process tailings, including red mud, and fly ash, as well as other similar precursor materials.

[0039] At 201, the precursor materials are leached using a nitric acid solution containing a predetermined nitric acid concentration, at a predetermined temperature, and at a predetermined atmospheric pressure to produce a leached solution and a residue. The leaching step can be performed using nitric acid of about 10% to about 95%. The predetermined temperature can range from about 90°C to about 115 °C. The leaching step can be used to obtain aluminum, iron, nickel, cobalt, manganese, magnesium, rare Earth elements, scandium and other materials into the solution. In some embodiments, the lower limit of the temperature range can be higher (i.e., about 100°C) depending upon the concentration of the nitric acid.

[0040] At 202, the residue is washed with a neutralizing solution to produce a byproduct therefrom. The residue, which contains silicates and titanium, can be obtained after the leaching step is performed at 201 for washing and neutralization to recover titanium product and mine rehabilitation residue.

[0041] At 203, the leached solution to obtain a mixture of nitrate crystals and a postcrystallization solution. In this step, aluminum is crystallized as nitrates from the solution by natural cooling and / or with the seeding with a recycled aluminum nitrate crystals.

[0042] Then, the aluminum nitrate crystals are purified with a combination of nitric acid wash and / or redissolution and recrystallization. The redissolution and recrystallization can be achieved by rejecting iron and other metals from the crystals into the solution. The aluminum nitrate crystals can be high purity aluminum nitrate crystals.

[0043] At 204, the high purity aluminum nitrate crystals can be decomposed, thermally, within a temperature range of about 150°C to about 1250°C into alumina and NOx gases. The NOx gases can be recovered as nitric acid. The thermal decomposition step can produce various forms of alumina, such as AI2O3, alpha alumina, beta alumina, and gamma alumina. The first metal compound produced being high grade Alumina.

[0044] At 205, a supernatant bleed stream is sent to a hydrolysis reactor. In this exemplary embodiment, the hydrolysis reactor can be the iron hydrolysis reactor 140 shown in FIG. 2. The iron hydrolysis reactor 140 can operate within a temperature range of about 150°C to about 195 °C to recover iron as hematite at 142 shown in FIG. 2. The iron hydrolysis reactor 140 can produce a vapor stream that can be directed to recover nitric acid therein.

[0045] At 206, a metal compound is extracted and precipitated from the solution. In this exemplary embodiment, the metal compound can be scandium. The precipitation step at 206 will produce a solution that is iron-free and aluminum-free because the iron is removed at 205 and the aluminum is removed at 203.

[0046] At 207, another metal compound is extracted and precipitated from the solution. In this exemplary embodiment, the solution is iron-free and aluminum-free from steps 203 and 205. The extraction step can be performed using any suitable extraction step, such as ion exchange extraction and / or solvent extraction to recover valuable metals, such as scandium, nickel, cobalt, manganese, in hydroxide form. The compounds are precipitated as individual elements, metal hydroxides, and / or other compounds.

[0047] Optionally, the barren solution, after being subject to steps 205-207, will be rich in magnesium and / or magnesium nitrate to form a raffinate solution. The raffinate solution can be sent from the ion exchange circuit for thermal decomposition at around about from 500°C up to 900°C to form magnesium compounds, nitric acid, and NOx gases.

[0048] In some embodiments, the magnesium compound product can be a nickel, cobalt, and manganese mixed hydroxide product. The NOx gases can be converted into nitric acid. The recovered nitric acid is recycled for use in Step 201.Supported Features and Embodiments

[0049] The detailed description provided above in connection with the appended drawings explicitly describes and supports various features of systems, apparatus, and methods for processing precursor materials, such as raw ores, process tailings, fly ash, and other similar materials to recover metal compounds therein through hydrometallurgy. By way of illustration and not limitation, supported embodiments include a method for obtaining recovered metal compounds from precursor materials comprising: leaching the precursor materials using a nitric acid solution containing a predetermined nitric acid concentration, at a predetermined temperature, and at a predetermined atmospheric pressure to produce a leached solution and a residue; washing the residue with a neutralizing solution to produce a byproduct therefrom; crystalizing the leached solution to obtain a mixture of nitrate crystals and a solution; first metal compound produced being high grade Alumina, sending a supernatant bleed stream to a hydrolysis reactor; extracting and precipitating multiple metal compounds sequentially from the solution.

[0050] Supported embodiments include the foregoing method, wherein the precursor materials are selected from the group consisting of raw ores, aluminum-bearing ores, process tailings, red mud, fly ash, and metal-process waste materials.

[0051] Supported embodiments include any of the foregoing methods, wherein the first metal compound is high grade alumina and the other metal compounds are selected from the group consisting of iron, nickel, cobalt, manganese, magnesium, a rare Earth element, and scandium.

[0052] Supported embodiments include any of the foregoing methods, wherein the predetermined nitric acid concentration 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.

[0053] Supported embodiments include any of the foregoing methods, wherein the byproduct is a material selected from the group consisting of a silicate and a titanium compound.

[0054] Supported embodiments include any of the foregoing methods, wherein the nitrate crystals are aluminum nitrate crystals.

[0055] Supported embodiments include any of the foregoing methods, wherein the crystallization step is performed by naturally cooling the leached solution.

[0056] Supported embodiments include any of the foregoing methods, wherein the crystallization step is performed by seeding the leached solution with recycled aluminum nitrate crystals.

[0057] Supported embodiments include any of the foregoing methods, further comprising: purifying the aluminum nitrate crystals.

[0058] Supported embodiments include any of the foregoing methods, wherein the purifying step includes: washing the aluminum nitrate crystals with a nitric acid solution.

[0059] Supported embodiments include any of the foregoing methods, wherein the purifying step includes: redissolving and recrystallizing the aluminum nitrate crystals through the rejection of metal from the crystals into the leached solution.

[0060] Supported embodiments include any of the foregoing methods, wherein the metal is iron.

[0061] Supported embodiments include any of the foregoing methods, further comprising: thermally decomposing the aluminum nitrate crystals at a temperature within the range of about 150°C to about 1250°C to produce high grade alumina and NOx gases with the NOx being recovered as nitric acid.

[0062] Supported embodiments include any of the foregoing methods, wherein the hydrolysis reactor is an iron hydrolysis reactor for recovering iron as hematite.

[0063] 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.

[0064] Supported embodiments include any of the foregoing methods, wherein the hydrolysis reactor produces a vapor stream; and wherein nitric acid is recovered from the vapor stream.

[0065] Supported embodiments include any of the foregoing methods, wherein the extracting step is selected from the group consisting of an ion exchange extraction step and a solvent extraction step.

[0066] Supported embodiments include any of the foregoing methods, wherein the precipitation step is performed after the extracting step to extract the recovered metal compounds as hydroxide compounds.

[0067] Supported embodiments include any of the foregoing methods, wherein the extracting step is an ion exchange extraction step that produces a mixed hydroxide product from a raffinate solution.

[0068] Supported embodiments include any of the foregoing methods, wherein the mixed hydroxide product includes at least one of nickel, cobalt, and manganese.

[0069] Supported embodiments include any of the foregoing methods, further comprising: concentrating the barren solution with magnesium nitrate; thermally decomposing the barren solution at a thermal decomposition temperature to form magnesia and NOx gases; and converting the NOx gases into nitric acid.

[0070] Supported embodiments include a system, a kit, an apparatus, and / or means for implementing any of the foregoing methods or a portion thereof.

[0071] Supported embodiments can provide various attendant and / or technical advantages in terms of an energy efficient hydrometallurgical processing route of producing critical minerals / metals such as aluminum, nickel, cobalt, iron, rear Earth elements, scandium, magnesium and others from the leached solution and titanium product from the residue.

[0072] Supported embodiments include a hydrometallurgical process that uses nitric acid recycle and recovery technology. The technology can be used to recycle the majority of the acid used in the process.

[0073] Supported embodiments include a hydrometallurgical process that utilizes leaching, crystallization, hydrolysis, ion exchange, solvent extraction, precipitation, thermal decomposition, solid liquid separation, and gravity separation / magnetic separation.

[0074] 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.

[0075] 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 obtaining recovered metal compounds from precursor materials comprising: leaching the precursor materials using a nitric acid solution containing a predetermined nitric acid concentration, at a predetermined temperature, and at a predetermined atmospheric pressure to produce a leached solution and a residue; washing the residue with a neutralizing solution to produce a byproduct therefrom; crystalizing the leached solution to obtain a mixture of nitrate crystals and a postcrystallization solution; sending a supernatant bleed stream to a hydrolysis reactor; and extracting and precipitating at least two metal compounds from the post-crystallization solution.

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

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

4. The method of claim 1 , wherein the predetermined nitric acid concentration 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 byproduct is a material selected from the group consisting of a silicate and a titanium compound.

6. The method of claim 1, wherein the nitrate crystals are aluminum nitrate crystals.

7. The method of claim 6, wherein the crystallization step is performed by naturally cooling the leached solution.

8. The method of claim 6, wherein the crystallization step is performed by seeding the leached solution with recycled aluminum nitrate crystals.

9. The method of claim 6, further comprising: purifying the aluminum nitrate crystals.

10. The method of claim 9, wherein the purifying step includes: washing the aluminum nitrate crystals with a nitric acid solution.

11. The method of claim 9, wherein the purifying step includes: redissolving and recrystallizing the aluminum nitrate crystals through the rejection of a plurality of metals from the crystals into the leached solution.

12. The method of claim 11, wherein the plurality of metals includes iron.

13. The method of claim 9, further comprising: thermally decomposing the aluminum nitrate crystals at a temperature within the range of about 150°C to about 1250°C to produce high grade alumina and NOx gases with the NOx being recovered as nitric acid.

14. The method of claim 1, wherein the hydrolysis reactor is an iron hydrolysis reactor for recovering iron as hematite.

15. The method of claim 14, wherein the iron is recovered within a temperature range of range of about 150°C to about 195°C.

16. The method of claim 14, wherein the hydrolysis reactor produces a vapor stream; and wherein nitric acid is recovered from the vapor stream.

17. The method of claim 1, wherein the extracting step is selected from the group consisting of an ion exchange extraction step and a solvent extraction step.

18. The method of claim 16, wherein the precipitation step is performed after the extracting step to extract the recovered metal compounds as hydroxides.

19. The method of claim 16, wherein the extracting step is an ion exchange extraction step that produces a mixed hydroxide product from a raffinate solution.

20. The method of claim 19, wherein the mixed hydroxide product includes at least one of nickel, cobalt, and manganese.

21. The method of claim 1, further comprising: concentrating the barren solution with magnesium nitrate; thermally decomposing the barren solution at a thermal decomposition temperature to form magnesia and NOx gases; and converting the NOx gases into nitric acid.

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