Methods of extracting rare earth elements from olivine containing ores

Abstract

The disclosure relates to methods of processing ore comprising one or more olivines. The methods can comprise : roasting the ore to form a calcine thereby converting one or more olivines to one or more magnetic materials, the roasting comprising: a temperature between 800 °C and 1000 °C a roasting time between 60 and 120 minutes; and an airflow up to 1.5 L / min / kg; and magnetically separating one or more magnetic materials from the calcine.

Description

METHODS OF EXTRACTING RARE EARTH ELEMENTS FROM OLIVINE CONTAINING ORESCROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims the benefit of priority co-pending U.S. Provisional Patent Application No. 63 / 729,989, filed on December 10, 2024, the content of which is incorporated herein by reference in its entirety.FIELD OF THE DISCLOSURE

[0002] The disclosure relates to methods and processes for producing and recovering rare earth elements (REE), and more particularly to systems and methods for extracting rare earth elements from ore and mineral concentrates that contain olivines.BACKGROUND OF THE DISCLOSURE

[0003] Rare Earth Elements (REE) are a set of seventeen metallic elements, including the fifteen (15) lanthanoids ranging in atomic number from 57 to 71 on the periodic table. They further include scandium having atomic number 21 and yttrium having atomic number 39.

[0004] Given their unusual physical and chemical properties such as magnetic and optical properties, REE are necessary components of numerous products across a wide range of applications, especially in high-tech consumer products such as cellular telephones, computer hard drives, electric and hybrid vehicles, flat-screen monitors and televisions, displays and many other electronic, optical and other technologies.

[0005] In the United States, the principal uses for scandium in 2020 were in aluminum- scandium alloys and solid oxide fuel cells (SOFCs). Other uses for scandium included ceramics, electronics, lasers, and lighting. However, commercial applications of scandium continue to be limited by the absence of reliable, secure, stable, long-term production of the metal.

[0006] Scandium and yttrium are metals associated with REE because their chemical and physical similarities to lanthanoids. Scandium is known for not occurring in economic concentrations or in the same geological settings as the lanthanoids and yttrium.

[0007] Scandium lacks affinity for common ore-forming anions; therefore, it is widely dispersed in the lithosphere and forms solid solutions with low concentrations in more than 100 minerals. As a result, Scandium remains only sparsely available and accordingly, even in applications where the use of scandium would be advantageous, industry has been forced to turn to more readily available alternatives. For example, the use of scandium-aluminum alloys in aerospace applications is advantageous because of the lower specific gravity of scandium-aluminum alloys versus the more widely used titanium aluminum alloys. In a commercial airline fleet, this difference in specific gravity may also translate into substantial fuel savings in the course of a year. Moreover, scandium-aluminum alloys are comparable in strength to titanium-aluminum alloys and are actually less expensive to produce on a cost of raw materials basis. However, despite these advantages, the use of scandium-aluminum alloys remains limited due to low scandium availability.

[0008] Despite being difficult to refine, scandium is abundant in the earth's crust. Indeed, scandium is a 50th most common element on earth, and is comparable in abundance to cobalt. However, as explained above, scandium is distributed sparsely, and occurs only in trace amounts in many scandium-bearing ores. Thortveitite and kolbeckite are the primary mineral sources of scandium, and thortveitite, euxenite, and gadolinite are this element's only known concentrated mineral sources. Thortveitite can contain up to 45% of scandium (in the form of scandium (III) oxide), though the mineral is somewhat rare. Hard-rock type ferrosyenite, mineralization containing ferromagnesian minerals, including scandium-bearing silicates such as pyroxenes and amphiboles, are also a good source of Scandium and REEs.

[0009] REEs do not occur naturally as metallic elements, but their strong affinity for oxygen causes them to form mostly as their respective oxides (REOs). Because oftheir reactivity, it is difficult to refine the rare earths to a pure form. Due to their chemical similarity, it is even more difficult to separate them into individual elements or compounds.

[0010] Rare Earth Oxides (REO) minerals occur in a variety of geological environments. They are generally found in hard rock deposits or in placer sands and are of primary or secondary origin, respectively. The composition of the REO minerals is strongly influenced by the presence of carbonates and phosphates.

[0011] Some processes and methods for recovering scandium are known in the art. Historically, scandium has been produced as byproduct material in China (iron ore, rare earths, titanium, and zirconium), Canada (titanium), Kazakhstan (uranium), the Philippines (nickel), Russia (apatite and uranium), and Ukraine (uranium). In the United States, scandium is produced primarily from the scandium-yttrium silicate mineral thortveitite and from byproduct leach solutions from uranium operations. Scandium may also be recovered as a by-product from bauxite residue, titanium, zirconium, cobalt, and nickel process streams.

[0012] Thus, some processes and methods for extracting scandium from feedstocks are known. For example, US Patent Application 2012 / 0207656 provides for an “acid bake” method for extracting scandium values from scandium-containing ores. However, acid bake processes have not been very effective in recovering scandium from pyroxene and amphibole group scandium-bearing minerals such as hedenbergite and ferrohornblende because the acid treatment at high temperature (250°C - 300°C) has proven to be ineffective in liberating scandium from the silicate matrix of these minerals, resulting in very low recovery rate.

[0013] Applications of pressure leaching are known in the art in the processing of aluminum. The Bayer process, invented in 1887, is used for producing pure alumina (AL2O3), wherein aluminum-bearing bauxite ores convert to sodium aluminate (NaALC ) in the presence of caustic (NaOH). Such a reaction, depending on the bauxite mineralogy, is performed at temperatures of 1430 °C and pressures of about 4.20 Atm, and required the use of pressure vessels, also known as digesters.

[0014] High Pressure Acid Leach (HPAL) has also been used to recover Scandium contained in nickel oxide ores. For example, US Patent 9,399,804 provides a method for recovering scandium comprising the leaching step of obtaining a leachate and leach residue by solid-liquid separation under high temperature and high pressure after charging a nickel oxide ore containing scandium, aluminum and chromium into a pressure vessel with sulfuric acid, the neutralization step of obtaining a neutralized sediment and a post-neutralization solution by adding a neutralizer to the leachate, the sulfuration step of, by adding a sulfidizing agent to the post-neutralization solution, separating the liquid into nickel sulfide and a post- sulfuration solution, the ion exchange step of obtaining a scandium eluent by bringing the post-sulfuration solution into contact with a chelate resin to adsorb the scandium on the chelate resin, the solvent extraction step of obtaining a stripping solution by bringing the scandium eluent into contact with an extraction agent, the scandium precipitation step of obtaining precipitates by adding a neutralizer or oxalic acid to the stripping solution, and the roasting step of obtaining scandium oxide by drying and roasting the precipitates. However, this process requires oxide nickel as a starting material for extracting Scandium, and it is not optimal for extracting and recovering Scandium from ore and mineral concentrates that contain scandium-bearing silicates. Although this method has been proven effective for processing lateritic ores for the recovery of nickel, cobalt and associated scandium as a by-product, the HPAL method for recovering Scandium from hard-rock type mineralization containing Scandium-bearing pyroxenes and amphiboles has not been shown to be effective.

[0015] Other methods for recovering scandium from ores are also known. For example, US Patent 9,982,325 provides a method for recovering scandium values from scandium-containing ores.

[0016] Due to frequent impurity presence, a significant amount of ore needs to be processed to recover a modest amount of scandium. There is accordingly a need for improved processes for ore processing and scandium recovery.SUMMARY OF THE DISCLOSURE

[0017] According to a broad aspect, a method of removing one or more olivines from ore, comprises roasting the ore to form a calcine thereby converting the one or more olivines to one or more magnetic materials, the roasting comprising a temperature between 800 °C and 1000 °C, a roasting time between 60 and 120 minutes, and airflow up to 1 .5 L / min / kg, and magnetically separating the one or more magnetic materials from the calcine.

[0018] In embodiments, olivines comprise fayalite and the one or more magnetic materials comprise magnetite.

[0019] In embodiments, the temperature is between 850 °C and 950 °C.

[0020] In embodiments, the temperature is about 850 °C.

[0021] In embodiments, the airflow is 1.5 L / min / kg, and / or the retention time is about 60 minutes.

[0022] In embodiments, the ore comprises scandium.

[0023] In embodiments, the calcine comprises one or more rare earth elements, and the method further comprises forming a feedstock comprising the calcine, leaching the feedstock in an alkali solution at a first temperature for a predetermined duration and at a given pressure to produce a leachate slurry, the leaching in the alkali solution being a High Pressure Caustic leaching, extracting a solid residue from the leachate slurry, leaching of the solid residue in a mineral acid to form a primary leach solution, and extracting the rare earth elements from the primary leach solution.

[0024] In embodiments, the rare earth elements comprise scandium.

[0025] In embodiments the extracting comprises extracting scandium to thereby produce a raffinate solution; and the method further comprises precipitating the rare earth elements in the raffinate solution to form a mixed rare earth element carbonate.

[0026] In embodiments, the mixed rare earth element carbonate has a purity of between 42 wt-% to 45wt-% rare earth elements.

[0027] In embodiments, the method further comprises extracting the rare earth elements from the mixed rare earth element carbonate by solvent extraction.

[0028] In embodiments, extracting the rare earth elements comprises precipitating the scandium with magnesium oxide to form a crude scandium cake, re-leaching the crude scandium cake in a mineral acid to form a releach solution, and recovering high purity scandium from the releach solution by solvent extraction.

[0029] In embodiments, the high purity scandium has a purity between 95% and 99.9%.

[0030] In embodiments, the method further comprises, prior to precipitating the scandium, reducing iron in a ferric state Fe3+to a ferrous state Fe2+.

[0031] In embodiments, the method further comprises, following the precipitating of the scandium, oxidizing the iron in the ferrous state iron to the ferric state, precipitating the ferric state iron to form a scandium-and-iron-depleted solution, and precipitating the rare earth elements in the scandium-and-iron-depleted solution with at least one of magnesium carbonate and sodium carbonate to form a mixed rare earth element carbonate.

[0032] In embodiments, the oxidizing is carried out using air.

[0033] In embodiments, the method comprises at least one of: a first temperature between 180°C and 280°C, a predetermined duration of the caustic leaching between 60 minutes and 180 minutes, and a given pressure between 9.87 ATM and 39.48 ATM.

[0034] In embodiments, the method further comprises at least one of transforming one or more fluorides and phosphates to water-soluble compounds and removing the water-soluble compounds from the leachate slurry, regenerating an alkali reagent following the high-pressure caustic leaching and providing the alkali reagent soregenerated to the alkali solution, regenerating the mineral acid and providing the mineral acid so regenerated to the leaching of the solid residue step, and cooling the leachate slurry to a second temperature of about 80 °C.

[0035] In embodiments, the feedstock has a solid content between 10 wt-% and 45 wt-%.

[0036] In embodiments, the feedstock further comprises rare-earth-element- bearing silicate minerals, and the method further comprises destroying a silicate matrix of the rare-earth-element-bearing silicate minerals by forming water-soluble sodium silicate.DETAILED DESCRIPTION OF THE DISCLOSURE

[0037] Variants, examples and preferred embodiments of the disclosure are described hereinbelow. When numerical figures or units are used herein, it is to be understood that minor variations, such as within 15%, remain within the description of embodiments as would be understood by a person of skill in the art. This remains the case even if the terms “about”, “approximately” or “around” are used or not used in this description, figures or claims.

[0038] References to process steps such as but not limited to extraction, precipitation, conversion and others are to be construed as being directed to at least a portion of the material to which the process step is applied. Accordingly, the present disclosure is not limited to 100% or substantially 100% conversion, extraction, precipitation or others.

[0039] References to rare earth elements are to be construed to include scandium and yttrium. References to rare earth elements are furthermore to be construed to include their compounds, including but not limited to oxides.

[0040] Referring now to Figure 1 , an exemplary process for purifying a scandium- containing material, the material comprising ferrous impurities such as olivines, comprisesproviding an ore comprising one or more olivines (101 ), roasting the ore (102) and, following the roasting, magnetically separating (103) at least a portion of the magnetic impurities from the roasted material. The separation may be carried out using appropriate magnetic separation methods including but not limited to passing the roasted material in proximity to a magnetic source such that ferrous or other magnetic impurities are attracted to the magnetic source while non-magnetic scandium is kept in the process stream.

[0041] In general, scandium extraction and / or purification processes comprise leaching steps which are susceptible to contamination by ferrous minerals and / or materials. As an example, olivines may comprise ferrous components and are often found in scandium-containing ore. Notably, the mineral fayalite, having a general formula Fe2SiO4 may account for more than 10% of an ore’s content. Fayalite is generally paramagnetic, making it an unsuitable candidate for magnetic separation from other ore components. Taking into account scandium’s low content in ore, generally below 0.1 %, the overall scandium to iron content in ore may be below 1 part per 100.

[0042] Fayalite may oxidize to form hematite and / or magnetite, such as during a roasting step. Depending on the roasting conditions, the fayalite will first oxidize to magnetite. Further oxidation of magnetite will yield hematite, a non-magnetic or very weakly magnetic mineral.

[0043] Accordingly, controlling processing conditions to maximize magnetite yield while minimizing magnetite conversion to hematite will improve the effectiveness of a preleaching magnetic separation step and thereby reduce valuable element loss attributable to ferrous contaminants during the leaching stage.EXAMPLES

[0044] Two scandium concentrates from the Crater Lake deposit (Met 1 sample and Met 2 sample) were received for a batch oxidizing / roasting testwork program. Samples as-received were already dried and ground non-magnetic products from wethigh-intensity magnetic separation test (WHIMS). Upon receipt, the two samples were inventoried, each homogenized and split into 200 g test charges.

[0045] The Met 1 sample assayed 357 g / t Sc, slightly higher than Met 2 sample at 292 g / t Sc. The assay results are shown in Table 1 . The two samples also contained a significant amount of other rare earth elements.Table 1

[0046] Semi-quantitative X-ray Diffraction (XRD) analyses for Met 1 and Met 2 head samples are shown in Table 2.Table 2

[0047] The Met 2 sample was comprised of moderate amounts of hedenbergite (17.8%), ferrohornblende (20.4%), albite (14.6%), biotite (13.0%), and fayalite (15.1 %), with minor levels of microcline (5.2%), clinochlore (3.4%), fluorapatite (3.1 %), ilmenite (2.5%), and titanomagnetite (1.3%). The Met 1 sample was similar in composition, but contained less fayalite in its mineralogical composition, at approximately 7%.

[0048] Previous high-definition mineralogical analysis revealed that scandium was hosted primarily by hedenbergite (~82%) and ferrohornblende (~18%), at about 0.05% and 0.03%, respectively. Fayalite did not contain any scandium in its crystal structure, but since it accounted for a significant amount of the iron distribution, it is removed at least in part before hydrometallurgical leaching.

[0049] The susceptible magnetics in the Met 1 and Met 2 head samples were assessed by Davis Tube and Satmagan testing, and the results are shown in Table 3.Table 3

[0050] Five batch roasting tests were carried out on the Met 2 sample only, due to its higher fayalite content.

[0051] The roasting testwork was carried out on a 200g Met 2 sample using an RF- 1200X-4R high temperature tube furnace. The samples were charged to the tubed and tube ends were equipped to provide a gas and to allow gas to exit the tube to a water bubbler vented to the plant scrubber. Loaded tubes were placed in the horizontal split tube furnace, rotated and heated. Once a target temperature was achieved, gas (e.g. air) was provided at a set rate. After a predetermined time, the samples were cooled down and recovered. If necessary, roasted samples were pulverized if sintered, and homogenized.

[0052] To prove the concept of olivine (or fayalite) transformation into magnetite and investigate the effect of roasting conditions on the efficiency of its oxidation, the air flowrate, roasting temperature and retention time were varied in 5 batch roasting tests. Roasting temperatures ranging from 800°C to 1000°C were examined. Higher than 1000°C will likely melt the fayalite, while lower than 800°C will likely provide insufficient heat for the geochemical reaction to occurwithin a reasonable period of time (120 minutes or less).

[0053] The calcines produced under different oxidized roasting conditions were assessed sequentially by semi-quantitative XRD characterization and by Davis Tube testing.

[0054] The test conditions, along with along fayalite content and magnetite to hematite ratios and calcine characterization results by XRD and Davis tube tests are shown in Table 4. Magnetite ratios include magnetite and titano-magnetite (Mag + Ti- Mag).Table 4

[0055] The mineral fayalite can be converted into an iron oxide by oxidizing roasting at 800 - 1000°C. Temperature and retention time were significant driving factors for fayalite oxidation. Air flowrate was also important for controlling the magnetite / hematite formation during the roasting process.

[0056] The fayalite conversion rate was significantly enhanced with increasing temperature. Scandium loss to the magnetic product also correlated with temperature changes. Air supply should be sufficient to oxidize the fayalite to magnetite, but not so much as to further oxidize the magnetite to hematite. Based on current test data, the following bulk kiln roasting conditions were close to optimum: 850°C or 900°C roasting temperature, 60 to 120 minutes retention time, and 1.5 L / min / kg air flowrate.

[0057] Table 5 presents susceptible magnetics in the obtained calcine, alongside the scandium distribution in the magnetic calcine fraction as a percentage of overall calcine scandium content.Table 5

[0058] The content, by weight, of selected minerals in the post-roasting calcines as determined by XRD is shown in Table 6.

[0059] As can be seen from Table 6, roasting at a high temperature (1000 °C) for 120 minutes resulted in a high hematite content (9.2 wt%) compared to other roasting conditions (approximately 5-6 wt%) while yielding the highest fayalite conversion (approximately 1 wt% fayalite in the calcine).

[0060] It was apparent from the test results in Tables 4 to 6 that fayalite can be converted into iron oxides by oxidizing roasting at 800 - 1000°C. Temperature and retention time were the driving forces for fayalite oxidation, and air flowrate was also important for controlling the formation of magnetite and hematite.

[0061] As can be seen in Table 4, fayalite conversion over a retention time of 20 minutes was minor. Retention times of 60 and 120 minutes achieved significant fayalite conversion, evidenced by a lower wt% of fayalite in the calcine.

[0062] As shown in Table 5, roasting between 850 °C and 1000 °C at a retention time greater than 20 minutes yielded the highest proportion of susceptible magnetics (above 25 wt%) in the calcines among the five tested conditions. Accordingly, roasting between 850 °C and 1000 °C with a retention time above 20 minutes, such as about 60 or about 120 minutes can be a suitable pre-leaching step to reduce ferrous and other magnetic material content in ore. For example, reducing ore processing requirements by 25% or more may reduce leaching fluid use, improve the extraction process’ energy efficiency and / or reduce effluent and waste stream volume.

[0063] Referring to Figure 2, a table showing detailed mass balances as determined by Davis Tube testing for the calcines obtained in the roasting tests described above is presented. As can be seen in Figure 2, scandium loss to the magnetic fraction also increased with increasing temperature. For example, sample RT#5 yielded a scandium loss of 9.2% of the total scandium content to the magnetic fraction, whereasRT#2 resulted in a 12.2% loss. This may be due to the phase transformation of some of the Sc-bearing ferrohornblende to highly magnetic iron oxide at higher roasting temperatures.

[0064] Compared with RT#1 and RT#2, it was apparent that approximately one hour retention time at 1000°C is needed to fully oxidize fayalite into iron oxide minerals. Increased retention time, however, does not necessarily result in increased conversion. For example, RT#3 yielded lower fayalite oxidation at 800 °C despite an increased retention time of 2 hours.

[0065] Air supply, expressed as air flowrate for the same retention time and as air volume (total) for different retention times controls the reduction or oxidization of iron oxides during the roasting process. The air supply should be appropriate to oxidize the fayalite to magnetite, but not so much as to further oxidize magnetite to hematite. This estimation was evaluated by the ratio of Mag+Ti-Mag to Hematite. As can be seen in Table 4, the higher the volume of air supplied, the lower the ratio of Mag+Ti-Mag to Hematite.

[0066] In order to minimize scandium losses, a lower temperature (800-850 °C) combined with longer roasting retention time (up to 120 minutes) may provide an appropriate increase in susceptible magnetics while minimizing scandium losses. For example, suitable roasting conditions may include roasting at 850°C or 900°C roasting temperature, from about 60 to about 120 minutes retention time, and about 1.5 L / min / kg airflowrate. For example, roasting may be carried out at 850 °C for 120 minutes at an air flowrate of 1 .5 L / min / kg.

[0067] Satmagan tests were carried out on the Met 2 head sample and five Met 2 calcines. The correlations of magnetic Fe% from Satmagan with mag wt% from Davis Tube and magnetite from XRD analysis are shown in Figures 3 and 4.

[0068] As Figures 3 and 4 show, susceptible magnetics data from the Satmagan test was well correlated with data from more precise Davis Tube testing and XRDanalysis. Accordingly, Satmagan may be used to quickly characterize the calcines produced by roasting.DOWNSTREAM PROCESSING

[0069] The calcines obtained from the method 100 may be further processed to extract REEs or other valuable minerals, elements and / or compounds therefrom. In Figures 5 to 7, mineral processing comprises the olivine removal from ore described above for at least a portion of the minerals provided to the processes of Figures 5 to 7.

[0070] Referring now to Figure 5, a block diagram shows a method of extracting REEs and / or scandium from ore, a calcine, REE and / or scandium-bearing feedstock and / or scandium / REE bearing mineral concentrate may comprise: providing the ore, the calcine, the REE and / or scandium bearing feedstock and / or scandium / REE bearing mineral concentrate; leaching the ore, the calcine, the REE and / or scandium bearing feedstock and / or the scandium / REE bearing mineral concentrate in an alkali solution at a first temperature for a predetermined duration and at a given pressure to produce a leachate slurry; extracting a solid residue from the leachate slurry; leaching of the solid residue in a mineral acid to form a primary leach solution; and extracting REE and / or scandium from the primary leach solution.

[0071] In embodiments, the method may comprise forming a feedstock with the calcine. Accordingly, the feedstock so formed would become at least a portion of the REE- bearing feedstock. For example, the feedstock formed with the calcine may be mixed with other feedstocks, such as recycled process streams or one or more different supplies of REE or scandium-bearing feedstock, such as feedstock formed from ores low in ferrous materials.

[0072] It is understood that the ore processed according to the method 100 may be an ore comprising one or more REEs in their elemental, oxide and other forms, and may or may not comprise scandium. Accordingly, the method 100 and further downstreamprocessing steps may be carried out for extracting any REE or valuable element and / or compound from ore by leaching.

[0073] The alkali solution may comprise an alkali reagent selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate, and combinations thereof.

[0074] The alkali solution may be provided at a dosage of between 500 g / kg and 2000 g / kg of calcine, ore, and / or REE and / or scandium bearing feedstock.

[0075] The caustic leach may be a batch, semi-batch or continuous process. For example, the caustic leach may be carried out in a stirred tank, in a plug flow reactor, or in any suitable equipment.

[0076] The leachate slurry may be a caustic leach slurry.

[0077] The method may comprise regenerating and recycling the alkali reagent.Regeneration may be carried out using chemical and / or electrochemical methods, and may comprise additional steps such as removing sulphur, phosphorus and compounds thereof.

[0078] The leachate slurry may be cooled down to a second temperature of about 80°C prior to further processing. Cooling of the slurry may benefit solid-liquid separation steps and further leaching steps by broadening the range of materials that may be used downstream, as the equipment will not have to withstand high temperatures resulting from caustic leaching. The heat left over from caustic leaching may be recycled. For example, one or more output streams from the caustic leaching step may be provided to one or more heat exchangers prior to further processing.

[0079] The leachate slurry may be provided to a solid-liquid separation step, for example a filtration step, to recover a solid residue. The solid residue may be washed with water.

[0080] The feedstock may comprise a solid content between 10 wt-% and 45 wt-%. In general, higher solid content feedstocks may cause blockages and / or fouling of equipment. It is understood, however, that up to 100% solid content feedstock is within the scope of this disclosure, for example a pulverized solid feedstock provided in an acceptable manner, for example through a hopper, and mixed with appropriate amounts of water and leach reagents to achieve a predetermined solid content leach batch in the leach tank or autoclave.

[0081] The first temperature may be between 180°C and 280°C. For example, the first temperature may be about 250°C.

[0082] The predetermined duration of the caustic leaching may be between about 60 minutes and 180 minutes

[0083] The given pressure may be above atmospheric pressure For example, the given pressure may be between 1.5 and 50 ATM, for example between 8 ATM and 40 ATM, for example between 9.87 ATM and 39.48 ATM.

[0084] The leaching in the alkali solution may be a High Pressure Caustic (HPC) leaching.

[0085] The HPC leaching may be performed in a reaction vessel or in an autoclave. The vessel or autoclave may be configured to stir or otherwise agitate the mixture of feedstock and leach solution.

[0086] The HPC leaching may comprise transforming the REE and / or scandium to insoluble hydroxides, which would then be present as solids in the leachate slurry. The separation of the solid residue from the leachate slurry may be conducted in a thickener, a vacuum filter, a pressure filter, a rotary filter, or combinations thereof. Other appropriate filtering techniques will be apparent to a skilled person.

[0087] The method may comprise destroying the silicate matrix of the Sc-bearing silicate minerals by forming water soluble sodium silicate thereby liberating Scandium and / or REEs.

[0088] The method may comprise transforming fluorides and phosphates to water soluble compounds and removing fluorides and phosphates from the leachate slurry. The fluorides and fluoride containing minerals may be removed prior to leaching of the solid residue in the mineral acid.

[0089] The mineral acid may be selected from the group consisting of Hydrochloric acid (HCI), Sulphuric acid (H2SO4), Nitric acid (HNO3), Hydrobromic acid (HBr), Perchloric acid (HCIO4), Hydroiodic acid (HI), and suitable mixtures thereof. While HCI is shown as the leaching mineral acid in the Figures, it is understood that other acceptable mineral acids and combinations thereof may be used.

[0090] The mineral acid may be at a concentration of 5 to 20 wt-% of the mixture of solid residue and acid. The leaching of the solid residue may comprise stirring for about 60 minutes. The leaching of the solid residue may be performed at an acid leach temperature between 20°C and 30°C for a period of 15 to 1200 minutes. For example, the acid leaching may have a duration between 60 to 1200 minutes. The leaching of the solid residue may be performed at 1 ATM. The leaching of the solid residue may be performed while stirring or otherwise agitating the mixture.

[0091] The REE and / or the scandium may be extracted from the primary leach solution by precipitation, solvent extraction, ion exchange extraction, or a combination thereof.

[0092] A raffinate solution may be generated after extracting the REE and / or scandium from the primary leach solution. For example, the scandium and / or REEs may be extracted using solvent extraction, thereby producing a raffinate solution.

[0093] The mineral acid may be regenerated. Following the acid leaching, the primary leach solution may be processed to recover scandium and / or other REEs andthen fed to a regeneration step. For example, HCI may be regenerated using suitable HCI regeneration processes including but not limited to electrolytic regeneration, hydrogen chloride absorption, pyrohydrolysis, chemical oxidation and hydrothermal regeneration. The regenerated HCI, or another regenerated mineral acid, may be recycled to the acid leaching step.

[0094] The method may further comprise adding a suitable reducing agent, e.g., metallic iron powder to reduce ferric iron (Fe3+) to ferrous iron (Fe2+), between leaching of the solid residue and extracting REE and / or scandium from the primary leach solution.

[0095] The scandium contained in the primary leach solution may be precipitated as a crude scandium cake by adjusting the solution pH to about 3.5 by adding a neutralizing agent such as magnesium oxide (MgO), sodium hydroxide (NaOH), lime, or a combination thereof.

[0096] A scandium depleted solution comprising iron in its ferrous state and having a pH of about pH 3.5 may be formed.

[0097] The crude scandium cake precipitate may be re-leached in a mineral acid as described above and / or suitable mixtures thereof to form a scandium -rich releach solution. For example, the crude scandium cake precipitate may be re-leached in hydrochloric acid to form a scandium-rich releach solution.

[0098] The Scandium-rich releach solution may be purified further with precipitation, solvent extraction, ion exchange, or a combination thereof, to extract scandium and / or a scandium oxide product having a purity of 95% to 99.9%.

[0099] Referring now to Figure 6, a block diagram illustrates an embodiment of a method for extracting rare-earth oxides (REO) from ore, calcines, REE and / or scandium bearing feedstock, the method comprising: providing the ore, calcine or REE and / or scandium bearing feedstock; HPC leaching the ore, calcine, REE and / or scandium bearing feedstock in an alkali solution at a first temperature for a predetermined duration and at a given pressure to produce a leachate slurry; extracting a solid residue from theleachate slurry; leaching of the solid residue in a mineral acid to form a primary leach solution, from which scandium is extracted to thereby produce a raffinate solution; precipitating the REE remaining in the raffinate solution to form a mixed REE-carbonate; and extracting the REO from the mixed REE-carbonate.

[0100] The raffinate solution may be produced using solvent extraction.

[0101] The REE precipitation may be performed by using sodium carbonate, to form a mixed REE-carbonate. The mixed REE-carbonate may be further processed to separate Rare-Earth Oxides (REO) from contaminants and / or from each other. For example, the REE and / or REO may be extracted from the mixed REE carbonate for further processing and purification. For example, the REO may be extracted from the mixed REE-carbonate by solvent extraction to produce separated REO.

[0102] The method may further comprise adding a metallic iron powder to reduce ferric iron (Fe3+) into ferrous iron (Fe2+), between leaching of the solid residue and precipitating the REE remaining in the raffinate solution.

[0103] After adding the metallic iron powder, the method may further comprise adding a neutralizing agent such as magnesium oxide (MgO), sodium hydroxide (NaOH), lime, or a combination thereof, to adjust the pH of the primary leach solution to about pH 3.5 to thereby form a crude scandium cake precipitate.

[0104] The scandium-depleted solution may be contacted with air, oxidizing ferric iron (Fe3+) into ferrous iron (Fe2+), forming a ferric precipitate and producing a scandium and iron depleted solution.

[0105] A mixed REE carbonate product may be precipitated, for example by adding magnesium carbonate, sodium carbonate, ammonium carbonate or combinations thereof to the scandium and iron depleted solution and / or to the raffinate solution, raising the pH to about pH 5-6. The mixed REE-carbonate so obtained may have a purity of 42 wt% to 45 wt% REE.

[0106] In another embodiment, there is disclosed a process for producing Rare Earth Elements (REE) and / or scandium from ore and / or REE and / or scandium bearing feedstock, the method comprising: providing the ore and / or the REE and / or scandium bearing feedstock; leaching the ore and / or the REE and / or scandium bearing feedstock in an alkali solution at a first temperature for a predetermined duration and at a given pressure to produce a leachate slurry, wherein the leaching in the alkali solution is a High Pressure Caustic (HPC) leaching; extracting a solid residue from the leachate slurry; leaching of the solid residue in a mineral acid to form a primary leach solution; and extracting REE and / or scandium from the primary leach solution.

[0107] The Scandium extracted therefrom may have a purity from 95% to 99.9%, for example 99%, or 99.9%

[0108] The REE and / or scandium may be extracted from the primary leach solution by precipitation, solvent extraction (SX), ion exchange (IX), or a combination thereof.

[0109] Referring now to Figure 7, a block diagram illustrates an embodiment of a method for extracting scandium, rare-earth elements, and / or rare-earth oxides (REO) from ore, calcine, and / or REE and / or scandium bearing feedstock, the method comprising: providing the REE and / or scandium bearing feedstock; leaching the REE and / or scandium bearing feedstock in an alkali solution at a first temperature for a predetermined duration and at a given pressure to produce a leachate slurry, wherein the leaching in the alkali solution is a High Pressure Caustic (HPC) leaching; extracting a solid residue from the leachate slurry; leaching of the solid residue in a mineral acid to form a primary leach solution, wherein ferric iron (Fe3+) is reduced to its ferrous state (Fe2+) in the presence of the mineral acid and the scandium contained in the primary leach solution is precipitated with magnesium oxide (MgO) to form a crude scandium cake. The ferric iron (Fe3+) is reduced to its ferrous state (Fe2+) to prevent co-precipitation with scandium. The crude scandium cake is then re-leached in a mineral acid and high purity scandium is recovered from the scandium releach solution by solvent extraction.

[0110] Still referring to Figure 7, there is provided a further step where the ferrous iron (Fe2+) is oxidized with air and precipitated in its ferric state (Fe3+) to form an iron- depleted solution. A mixed REE carbonate is formed by precipitating the REE remaining in the scandium and iron depleted solution, for example with magnesium carbonate, sodium carbonate, ammonium carbonate, or a combination thereof. The mixed REE carbonate may be further processed to recover and / or separate REEs and / or REOs as described above.

[0111] The ferrous iron (Fe2+) in the scandium-depleted solution may be oxidized and precipitated in the form of ferric iron (Fe3+) by re-oxidation with air, to thereby produce a scandium and iron depleted solution.

[0112] While exemplary embodiments have been described above, it is understood that combinations of the processing steps outlined above may be implemented without departing from the principles disclosed herein. Accordingly, scandium and / or REE recovery processes may be implemented with or without ferric iron reduction, with or without mixed-REE-carbonate precipitation, with or without ferrous iron precipitation, and with or without acid and / or alkali regeneration.

Claims

CLAIMS1 . A method of processing ore comprising one or more olivines, comprising: roasting the ore to form a calcine thereby converting one or more olivines to one or more magnetic materials, the roasting comprising: a temperature between 800 °C and 1000 °C a roasting time between 60 and 120 minutes; and an airflow up to 1 .5 L / min / kg; and magnetically separating one or more magnetic materials from the calcine.

2. The method according to claim 1 , wherein the olivines comprise fayalite and the one or more magnetic materials comprise magnetite.

3. The method according to claim 1 or 2, wherein the temperature is between 850 °C and 950 °C.

4. The method according to claim 1 or 2, wherein the temperature is about 850 °C.

5. The method according to any one of claims 1 to 4, wherein at least one of: the airflow is 1.5 L / min / kg; and the retention time is about 60 minutes.

6. The method according to claim 1 , wherein the ore comprises scandium.

7. The method according to claim 1 , wherein the calcine comprises one or more rare earth elements, further comprising: forming a feedstock comprising the calcine; leaching the feedstock in an alkali solution at a first temperature for a predetermined duration and at a given pressure to produce a leachate slurry; wherein the leaching in the alkali solution is a High Pressure Caustic (HPC) leaching;extracting a solid residue from the leachate slurry; leaching of the solid residue in a mineral acid to form a primary leach solution; and extracting the rare earth elements from the primary leach solution.

8. The method according to claim 7, wherein the rare earth elements comprise scandium.

9. The method according to claim 8, wherein the extracting the rare earth elements comprises extracting scandium to thereby produce a raffinate solution; further comprising: precipitating the rare earth elements in the raffinate solution to form a mixed rare earth element carbonate.

10. The method according to claim 9, wherein the mixed rare earth element carbonate has a purity of between 42 wt-% to 45 wt-% rare earth elements.

11. The method according to claim 9, further comprising separating the rare earth elements from the mixed rare earth element carbonate by solvent extraction.

12. The method according to claim 8, wherein the extracting the rare earth elements comprises: precipitating the scandium with magnesium oxide to form a crude scandium cake; re-leaching the crude scandium cake in a mineral acid to form a releach solution; and recovering high purity scandium from the releach solution by solvent extraction.

13. The method according to claim 12, wherein the high purity scandium has a purity between 95% and 99.9%.

14. The method according to claim 12, further comprising, prior to precipitating the scandium, reducing iron in a ferric state Fe3+to a ferrous state Fe2+.

15. The method according to claim 14, further comprising, following the precipitating the scandium: oxidizing the iron in the ferrous state iron to the ferric state; precipitating the ferric state iron to form a scandium-and-iron-depleted solution; and precipitating the rare earth elements in the scandium-and-iron-depleted solution with at least one of magnesium carbonate, sodium carbonate and ammonium carbonate to form a mixed rare earth element carbonate.

16. The method according to claim 15, wherein the oxidizing is carried out using air.

17. The method according to claim 7, wherein at least one of: the first temperature is between 180°C and 280°C; the predetermined duration of the caustic leaching is between 60 minutes and 180 minutes; and the given pressure is between 9.87 ATM and 39.48 ATM.

18. The method according to claim 7, further comprising at least one of: transforming one or more fluorides and phosphates to water soluble compounds and removing the water soluble compounds from the leachate slurry; regenerating an alkali reagent after the high-pressure caustic leaching and providing the alkali reagent so regenerated to the alkali solution; regenerating the mineral acid and providing the mineral acid so regenerated to the leaching of the solid residue step; and cooling the leachate slurry to a second temperature of about 80 °C.

19. The method according to claim 7, wherein the feedstock has a solid content between 10 wt-% and 45 wt-%.

20. The method according to claim 7, wherein the feedstock further comprises rare- earth-element-bearing silicate minerals, further comprising destroying a silicate matrix of the rare-earth-element-bearing silicate minerals by forming water-soluble sodium silicate.

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