HIGH PRESSURE CAUSTIC LEACH METHODS AND PROCESSES FOR RECOVERY OF SCANDIUM AND RARE-EARTH OXIDES

Abstract

Despite the abundance of scandium, its commercial applications continue to be limited by the absence of reliable, secure, stable and long-term production. The subject-matter disclosed herein provides for a method for extracting Rare Earth Elements (REE), scandium and/or Rare-Earth Oxides (REO) from ore and mineral concentrates, the method comprising: providing Rare Earth Elements (REE) and/or scandium bearing feedstock; a high-pressure caustic (HPC) leaching step, comprising leaching the feedstock in an alkali solution at a first temperature for a target period of time 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; extracting scandium and/or REE from the primary leach solution; and/or precipitating REE remaining in the raffinate to form a mixed REE-carbonate to thereby facilitate the extraction of REO.

Claims

1. A method of extracting Rare Earth Elements (REE) and/or scandium from ore, REE and/or scandium bearing feedstock and/or scandium/REE bearing mineral concentrate, the method comprising: providing the ore, the REE and/or scandium bearing feedstock and/or scandium/REE bearing mineral concentrate; leaching the ore, 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 target 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; separating 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.

2. The method of claim 1, wherein the alkali solution comprises an alkali reagent selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate.

3. The method of claim 1, wherein the alkali solution is provided at a dosage of 500 g per kg to 2000 g per kg of REE and/or scandium bearing feedstock.

4. The method of claim 1, wherein, between leaching the ore and/or the REE and/or scandium bearing feedstock in an alkali solution and separating a solid residue from the leachate slurry, the method comprises regenerating and recycling the alkali reagent.

5. The method of claim 1, wherein, between leaching the ore and/or the REE and/or scandium bearing feedstock in an alkali solution and separating a solid residue from the leachate slurry, the leachate slurry is cooled down to a second temperature of about 80° C. to ambient temperature.

6. The method of claim 1, wherein, between leaching the ore and/or the REE and/or scandium bearing feedstock in an alkali solution and separating a solid residue from the leachate slurry, the solid residue is washed with water.

7. The method of claim 1, wherein leaching the REE and/or scandium bearing feedstock comprises a solid content of 10 to 45 wt-%.

8. The method of claim 1, wherein the first temperature is between 180° C. and 280° C.

9. The method of claim 1, wherein the target duration of the caustic leach is between 60 minutes and 180 minutes.

10. The method of claim 1, wherein the given pressure is between 9.87 ATM and 39.48 ATM.

11. The method of claim 10, wherein the HPC leaching is performed in a reaction vessel or in an autoclave.

12. The method of claim 1, wherein extracting the solid residue from the leachate slurry is conducted in a vacuum or pressure filter.

13. The method of claim 1, wherein, between separating the solid residue and leaching of the solid residue, the method comprises destroying the silicate matrix of the Sc-bearing silicate minerals by forming water soluble sodium silicate thereby liberating Scandium and/or REEs.

14. The method of claim 1, wherein, between extracting of the solid residue and leaching of the solid residue, the method comprises transforming fluorides and phosphates to water soluble compounds and removing fluorides and phosphates from the leachate slurry.

15. The method of claim 14, wherein fluorides and fluoride containing minerals are removed prior to leaching of the solid residue in the mineral acid.

16. The method of claim 1, wherein the mineral acid is selected from the group consisting of Hydrochloric acid (HCl), Sulphuric acid (H.sub.2SO.sub.4), Nitric acid (HNO.sub.3), Hydrobromic acid (HBr), Perchloric acid (HClO.sub.4), Hydroiodic acid (HI), and suitable mixtures thereof having a concentration between 5 to 20 wt-%.

17. The method of claim 1, wherein leaching of the solid residue comprises stirring for a period of 60 to 1200 minutes at a second temperature between 20° C. and 30° C. and at 1 ATM.

18. The method of claim 1, wherein the REE and/or the scandium is extracted from the primary leach solution by precipitation, solvent extraction, ion exchange extraction or a combination thereof.

19. The method of claim 1, wherein, between leaching of the solid residue and extracting REE and/or scandium from the primary leach solution, the method comprises the regenerating and recycling the mineral acid.

20. The method of claim 1, wherein Rare-Earth Oxides (REO) are extracted from the primary leach solution by forming a mixed REE-carbonate in the presence of sodium carbonate (Na.sub.2CO.sub.3).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration example embodiments thereof and in which:

[0052] FIG. 1—represents a block diagram illustrating the method of recovering scandium according to one embodiment of the present invention.

[0053] FIG. 2—represents a block diagram illustrating the method of recovering scandium according to one embodiment of the present invention, wherein rare earth elements (REE) that remain in the solvent extraction raffinate are precipitated with sodium carbonate to extract Rare-Earth Oxides (REO).

[0054] FIG. 3—represents a process flow diagram illustrating the method of recovering scandium and REE according to one embodiment of the present invention, wherein a crude scandium cake is produced followed from a first redox reaction of iron (from Fe.sup.3+ to Fe.sup.2+) and the precipitation of scandium by adding a neutralizing agent such as magnesium oxide (MgO), sodium hydroxide (NaOH), lime, or a combination thereof), and wherein mixed REE carbonate is produced for Scandium and/or REO extraction, followed from a second redox reaction of iron (from Fe.sup.2+ to Fe.sup.3+), and the precipitation of the remaining REE by the addition potassium carbonate (K.sub.2CO.sub.3), ammonium carbonate ((NH.sub.4).sub.2CO.sub.3), magnesium carbonate (MgCO.sub.3) and/or sodium carbonate (Na.sub.2CO.sub.3), or a combination thereof.

DETAILED DESCRIPTION OF EMBODIMENTS

[0055] Variants, examples and preferred embodiments of the invention 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.

[0056] In an embodiment, there is disclosed a method of extracting Rare Earth Elements (REE) and/or scandium from ore, REE and/or scandium bearing feedstock and/or scandium/REE bearing mineral concentrate, the method comprising: providing the ore, the REE and/or scandium bearing feedstock and/or scandium/REE bearing mineral concentrate; leaching the ore, 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 target 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.

[0057] Referring now to FIG. 1, a block diagram illustrates an embodiment of a method for extracting Mineral concentrates, 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 target 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.

[0058] The alkali solution may comprise an alkali reagent selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate.

[0059] The alkali solution may be provided at a dosage of 500 g per kg to 2000 g per kg of REE and/or scandium bearing feedstock.

[0060] The leachate slurry may be a caustic leach slurry.

[0061] The method may comprise regenerating and recycling the alkali reagent.

[0062] The leachate slurry may be cooled down to a second temperature of about 80° C.

[0063] The solid residue may be washed with water.

[0064] The REE and/or scandium bearing feedstock may comprise a solid content of 10 to 45 wt-%.

[0065] The first temperature may be between 180° C. and 280° C.

[0066] The target duration of the caustic leaching may be between about 60 minutes and 180 minutes.

[0067] The given pressure may be between 9.87 ATM and 39.48 ATM.

[0068] The leaching in the alkali solution may be a High Pressure Caustic (HPC) leaching.

[0069] The HPC leaching may be performed in a reaction vessel or in an autoclave.

[0070] 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.

[0071] The method may comprise transforming fluorides and phosphates to water soluble compounds and removing fluorides and phosphates from the leachate slurry.

[0072] The fluorides and fluoride containing minerals may be removed prior to leaching of the solid residue in the mineral acid.

[0073] The mineral acid may be selected from the group consisting of Hydrochloric acid (HCl), Sulphuric acid (H.sub.2SO.sub.4), Nitric acid (HNO.sub.3), Hydrobromic acid (HBr), Perchloric acid (HClO.sub.4), Hydroiodic acid (HI), and suitable mixtures thereof.

[0074] The mineral acid may be at a concentration of 5 to 20 wt-%.

[0075] The leaching of the solid residue may comprise stirring for about 60 minutes.

[0076] The leaching of the solid residue may be performed at a second temperature between 20° C. and 30° C. for a period of 15 to 1200 minutes, preferably 60 to 1200 minutes.

[0077] The leaching of the solid residue may be performed at 1 ATM.

[0078] The leaching of the solid residue may be performed while stirring.

[0079] The REE and/or the scandium may be extracted from the primary leach solution by precipitation, solvent extraction or ion exchange extraction, or a combination thereof.

[0080] The method of any one of claims 1 to 23, wherein, between leaching of the solid residue and extracting REE and/or scandium from the primary leach solution, the method comprises the regenerating and recycling the mineral acid.

[0081] A raffinate solution may be generated after extracting the REE and/or scandium from the primary leach solution.

[0082] The HPC leaching may comprise transforming the REE and/or scandium to insoluble hydroxides.

[0083] The insoluble hydroxides may be present in the leachate slurry.

[0084] The separation of the solid residue from the leachate slurry may be conducted in a thickener, and/or vacuum or pressure filter.

[0085] 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.

[0086] After adding the metallic iron powder, the method may further comprise adding a neutralizing agent such as sodium hydroxide (NaOH), lime or magnesium oxide (MgO) to adjust the pH of the primary leach solution to about pH 3.5 to thereby form a crude scandium cake precipitate.

[0087] The crude scandium cake precipitate may be re-leached in a mineral acid selected from the group consisting of Hydrochloric acid (HCl), Sulphuric acid (H.sub.2SO.sub.4), Nitric acid (HNO.sub.3), Hydrobromic acid (HBr), Perchloric acid (HC10.sub.4), Hydroiodic acid (HI), and suitable mixtures thereof to form a scandium-rich releach solution.

[0088] The crude scandium cake precipitate is re-leached in hydrochloric acid to form a scandium-rich releach solution.

[0089] The scandium-rich releach solution may be purified with, precipitation, solvent extraction or ion exchange, or a combination thereof, to thereby extract scandium oxide product having a purity of 95% to 99.9% and producing a scandium-depleted solution.

[0090] The scandium oxide product may have a purity of 99.9%.

[0091] In another embodiment, there is further disclosed a method for extracting rare-earth oxides (REO) from ore, REE and/or scandium bearing feedstock and/or scandium/REE bearing mineral concentrate, the method comprising: providing the ore, REE and/or scandium bearing feedstock and/or scandium/REE bearing mineral concentrate; leaching the ore, REE and/or scandium bearing feedstock and/or scandium/REE bearing mineral concentrate in an alkali solution at a first temperature for a target 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, 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.

[0092] Referring now to FIG. 2, a block diagram illustrates an embodiment of a method for extracting rare-earth oxides (REO) from ore 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 target 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, 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.

[0093] The alkali solution may comprise an alkali reagent selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate.

[0094] The alkali solution may be provided at a dosage of 500 g per kg to 2000 g per kg of REE and/or scandium bearing feedstock.

[0095] The first temperature may be between 180° C. and 280° C.

[0096] The first temperature may preferably be about 250° C.

[0097] The target duration of the caustic leaching may be between about 60 minutes and 180 minutes.

[0098] The given pressure is between 9.87 ATM and 39.48 ATM.

[0099] The method may comprise transforming fluorides and phosphates to water soluble compounds and removing fluorides and phosphates from the leachate slurry.

[0100] The fluorides and fluoride containing minerals may be removed prior to leaching of the solid residue in the mineral acid.

[0101] The mineral acid may be selected from the group consisting of Hydrochloric acid (HCl), Sulphuric acid (H.sub.2SO.sub.4), Nitric acid (HNO.sub.3), Hydrobromic acid (HBr), Perchloric acid (HClO.sub.4), Hydroiodic acid (HI), and suitable mixtures thereof.

[0102] The raffinate solution may be produced using solvent extraction.

[0103] The REE precipitation may be performed by using sodium carbonate. The mixed REE-carbonate may be further processed in a REE separation plant to obtain Rare-Earth Oxides (REO).

[0104] The method may further comprise adding a metallic iron powder to reduce ferric iron (Fe.sup.3+) into ferrous iron (Fe.sup.2+), between leaching of the solid residue and precipitating the REE remaining in the raffinate solution.

[0105] 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.

[0106] The crude scandium cake precipitate may be re-leached in a mineral acid selected from the group consisting of Hydrochloric acid (HCl), Sulphuric acid (H.sub.2SO.sub.4), Nitric acid (HNO.sub.3), Hydrobromic acid (HBr), Perchloric acid (HClO.sub.4), Hydroiodic acid (HI), and suitable mixtures thereof to form a scandium-rich releach solution.

[0107] The crude scandium cake precipitate may be re-leached in hydrochloric acid to form a scandium-rich releach solution.

[0108] The scandium-rich releach solution may be purified with solvent extraction to thereby extract scandium oxide product having a purity of 95% to 99.9% and producing a scandium-depleted solution.

[0109] The scandium oxide product may preferably have a purity of 99.9%.

[0110] The scandium-depleted solution may be contacted with air oxidizing ferric iron (Fe.sup.3+) into its ferrous iron (Fe.sup.2+) forming a ferric precipitate and producing a scandium and iron depleted solution.

[0111] The mixed REE carbonate product may be precipitated by adding the magnesium carbonate (MgCO.sub.3) and/or sodium carbonate (Na.sub.2CO.sub.3) to the scandium and iron depleted solution and/or to the raffinate solution raising the pH to about pH 5-6.

[0112] The mixed REE-carbonate may have a purity of 42 to 45% REE.

[0113] The REE and/or REO may be extracted from the mixed REE carbonate for further processing and purification.

[0114] 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 target 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.

[0115] In embodiments, there is further 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 target 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, wherein the Scandium extracted may have a purity from 95% to 99.9%.

[0116] The Scandium extracted may have a purity of 99.9%.

[0117] The REE and/or scandium may be extracted from the primary leach solution by precipitation, solvent extraction (SX), and ion exchange (IX), or a combination thereof.

[0118] The alkali solution may comprise an alkali reagent selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate.

[0119] The alkali solution may be provided at a dosage of 500 g per kg to 2000 g per kg of REE and/or scandium bearing feedstock.

[0120] The first temperature may be between 180° C. and 280° C.

[0121] The first temperature may preferably be about 250° C.

[0122] The target duration of the caustic leaching may be between about 60 minutes and 180 minutes.

[0123] The given pressure may be above atmospheric pressure and preferably between 9.87 ATM and 39.48 ATM.

[0124] The process may comprise transforming fluorides and phosphates to water soluble compounds and removing fluorides and phosphates from the leachate slurry.

[0125] The fluorides and fluoride containing minerals may be removed prior to leaching of the solid residue in the mineral acid.

[0126] The mineral acid may be selected from the group consisting of Hydrochloric acid (HCl), Sulphuric acid (H.sub.2SO.sub.4), Nitric acid (HNO.sub.3), Hydrobromic acid (HBr), Perchloric acid (HClO.sub.4), Hydroiodic acid (HI), and suitable mixtures thereof.

[0127] The mineral acid may be Hydrochloric acid (HCl).

[0128] In another embodiment, there is further provided a process for producing Rare-Earth Oxides (REO) from ore 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 target 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, 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, wherein the mixed REE-carbonate may have a purity of 42 to 45% REE.

[0129] The REO may be extracted from the mixed REE-carbonate by solvent extraction in a separation facility to produce separated REO.

[0130] The alkali solution may comprise an alkali reagent selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate.

[0131] The alkali solution is provided at a dosage of 500 g per kg to 2000 g per kg of REE and/or scandium bearing feedstock.

[0132] The first temperature may be between 180° C. and 280° C.

[0133] The first temperature may preferably be about 250° C.

[0134] The target duration of the caustic leaching may be between about 60 minutes and 180 minutes.

[0135] The given pressure may be between 9.87 ATM and 39.48 ATM.

[0136] The process may comprise transforming fluorides and phosphates to water soluble compounds and removing fluorides and phosphates from the leachate slurry.

[0137] The fluorides and fluoride containing minerals may be removed prior to leaching of the solid residue in the mineral acid.

[0138] The mineral acid may be selected from the group consisting of Hydrochloric acid (HCl), Sulphuric acid (H.sub.2SO.sub.4), Nitric acid (HNO.sub.3), Hydrobromic acid (HBr), Perchloric acid (HClO.sub.4), Hydroiodic acid (HI), and suitable mixtures thereof.

[0139] The mineral acid may be Hydrochloric acid (HCl).

[0140] Referring now to FIG. 3, a block diagram illustrates an embodiment of a method for extracting scandium, rare-earth elements, and/or rare-earth oxides (REO) from ore 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 target 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 (Fe.sup.3+) is reduced to its ferrous state (Fe.sup.2+) 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 (Fe.sup.3+) is reduced to its ferrous state (Fe.sup.2+) 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.

[0141] Still referring to FIG. 3, there is provided a step wherein the ferrous iron (Fe.sup.2+) is oxidized with air and precipitated in its ferric state (Fe.sup.3+), forming a mixed REE carbonate by precipitating the REE remaining in the scandium and iron depleted solution with magnesium carbonate (MgCO.sub.3) and/or sodium carbonate (Na.sub.2CO.sub.3), or a combination thereof; thereby allowing the extraction of REO from the mixed REE-carbonate.

[0142] The alkali solution may comprise an alkali reagent selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate.

[0143] The alkali solution may be provided at a dosage of 500 g per kg to 2000 g per kg of REE and/or scandium bearing feedstock.

[0144] The first temperature may be between 180° C. and 280° C.

[0145] The first temperature may preferably be about 250° C.

[0146] The target duration of the caustic leaching may be between about 60 minutes and 180 minutes.

[0147] The given pressure is between 9.87 ATM and 39.48 ATM.

[0148] The method may comprise transforming fluorides and phosphates to water soluble compounds and removing fluorides and phosphates from the leachate slurry.

[0149] The fluorides and fluoride containing minerals may be removed prior to leaching of the solid residue in the mineral acid.

[0150] The mineral acid may be selected from the group consisting of Hydrochloric acid (HCl), Sulphuric acid (H.sub.2SO.sub.4), Nitric acid (HNO.sub.3), Hydrobromic acid (HBr), Perchloric acid (HClO.sub.4), Hydroiodic acid (HI), and suitable mixtures thereof.

[0151] The iron present in the primary leach solution as ferric iron (Fe.sup.3+) may be reduced to its ferrous state (Fe.sup.2+) by the addition of metallic iron powder, thereby avoiding co-precipitation with the scandium.

[0152] 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.

[0153] A scandium depleted solution comprising iron in its ferrous state (Fe.sup.2+) and having a pH of about pH 3.5 may be formed.

[0154] The precipitated crude scandium cake may be re-leached in a mineral acid selected from the group consisting of Hydrochloric acid (HCl), Sulphuric acid (H.sub.2SO.sub.4), Nitric acid (HNO.sub.3), Hydrobromic acid (HBr), Perchloric acid (HClO.sub.4), Hydroiodic acid (HI), and suitable mixtures thereof to form a scandium-rich releach solution.

[0155] The precipitated crude scandium cake may be re-leached preferentially in hydrochloric acid to form a scandium-rich releach solution.

[0156] The Scandium-rich releach solution may be purified further with precipitation, solvent extraction, ion exchange, or a combination thereof, to extract scandium oxide product having a purity of 95% to 99.9%.

[0157] The scandium oxide product may have a purity of 99.9%.

[0158] The ferrous iron (Fe.sup.2+) in the scandium-depleted solution may be oxidized and precipitated in the form of ferric iron (Fe.sup.3+) by re-oxidation with air, to thereby produce a scandium and iron depleted solution.

[0159] A mixed REE carbonate product may be precipitated from the scandium and iron depleted solution by raising the pH to about pH 5-6 with the addition of magnesium carbonate (MgCO.sub.3), potassium carbonate (K.sub.2CO.sub.3), ammonium carbonate ((NH.sub.4).sub.2CO.sub.3),and/or sodium carbonate (Na.sub.2CO.sub.3), or a combination thereof.

[0160] The mixed REE-carbonate may have a purity of 42 to 45% REE.

[0161] REE and/or REO may be extracted from the mixed REE carbonate for further processing and purification.

EXAMPLES

[0162] The chemical composition of mineral concentrates used in the tests is presented in Table 1. The test conditions for the high-pressure caustic leach (stage 1), and the mineral acid leach of the caustic residue (stage 2), and their metallurgical balances are provided in tables 2 and 3, respectively.

Testing High Pressure Caustic (HPC) Leaching—2

[0163] A scandium/REE mineral concentrate weighing 150 g (grade provided below in Table 1), produced from MET01 ore sample with magnetic separation was added to an autoclave together with 100 g of reagent liquor to target a pulp density of 60% solids by weight. The reagent liquor is made of 60 g of 100% sodium hydroxide (NaOH) dissolved in water at caustic addition rate of 0.4 ton NaOH per ton of mineral concentrate. The slurry consisting of mineral concentrate and NaOH solution was agitated in an autoclave while being heated to a target temperature of 250° C. The slurry was kept at the target temperature for a period of 120 minutes to allow the dissolution of silicate minerals. After 120 minutes, the slurry was cooled to about 80° C., and then filtered in a vacuum filter to separate the caustic leach solution from the Sc/REE containing-residue. The residue was thoroughly washed with water. The mass and volume of the leach liquor (including wash solution) were determined to be 1352.6 g, and 1320 ml respectively. The mass of the wet residue was measured, as well as its mass after drying. Aliquots of the leach liquor and dry residue were taken for chemical analysis. The metallurgical balance of the caustic dissolution (stage 1) for this test showed that 31.4% of Si was dissolved while only 2.8% Sc and 0.3% of REE deported to the caustic leach liquor. The test conditions, chemical analysis of the leach liquor and residue, and the caustic leach metallurgical balance are presented in Tables 2A, 2B and 2C.

[0164] A 20 g aliquot of residue from HPC2 test was added to a 180 ml of 20% HCl solution in a glass reactor, equipped with an agitator to target a pulp density of 10% solids by weight. The slurry was leached at ambient temperature for a period of 60 minutes, after which it was filtered in a pressure filter to recover the Sc/REE-bearing primary leach solution (PLS). The acid leach cake was washed thoroughly with water. The volume and mass of the acid leach liquor were determined, the mass of the wet cake, as well and its mass after drying were measured. Samples of the leach liquor and cake were chemically analyzed. A metallurgical balance for the acid leach step (stage 2 of the process), showed 70% of scandium and 89.7% of REE were extracted into the hydrochloric acid leach liquor (see Tables 3A, 3B et 3C). The leach solution was further processed for the recovery of scandium and the rare earth elements.

Testing High Pressure Caustic (HPC) Leaching—5

[0165] A bench scale test was conducted in HPC5 with 150 g of MET01 mineral concentrate using the same procedure described above for HPC2 test, but used 200 g of caustic solution to target a pulp density of 43% solids by weight. The caustic lixiviant contained 120 g of 100% NaOH (0.8 ton of NaOH per ton of mineral concentrate). The test was conducted at 180° C., for a period of 120 minutes. The metallurgical balance for the caustic cracking stage showed 26.7% dissolution of silicates, with 1.3% Sc and 0.3% REE deportment to caustic solution.

[0166] The residue from the caustic decomposition stage 1 was leached in hydrochloric acid at 10% pulp density, and ambient temperature for 1200 minutes (20 hours). The mass balance indicated that 67% of scandium and 87.3% of the rare earth elements were recovered into the leach solution (see Tables 3A, 3B et 3C).

Testing High Pressure Caustic (HPC) Leaching—7

[0167] Another high-pressure caustic leach test was conducted with 100 g of MET01 mineral concentrate, and 230 g of caustic solution, containing 138 g of 100% NaOH, (or 1.38 ton of NaOH per ton of mineral concentrate) to target 30% pulp density. The test was conducted at 220° C., for 120 minutes using similar procedure described above. The metallurgical balance for the caustic dissolution step of the process showed 37.8% decomposition of silicates, 10% Sc, and 1% REE dissolution.

[0168] Residue from stage 1 of the process was leached in a 20% HCl solution for 60 minutes at ambient temperature and a pulp density of 10%. Scandium deportment to acid leach liquor was 90.7%, while REE recovery was 93.4% (see Tables 3A, 3B et 3C).

Testing High Pressure Caustic (HPC) Leaching—8

[0169] Another bench scale HPC leach, followed by a hydrochloric acid leach of the caustic leach cake with identical conditions to those in HPC7 test was conducted using a MET02 mineral concentrate sample as feed (see Table 1 for the chemical composition of feedstock and Tables 2A, 2B and 2C for the test conditions).

[0170] At the caustic leach step, 22.5% Si decomposition was achieved with 12.2% Sc and 1.1% REE dissolution. The metallurgical balance for the hydrochloric acid leach of the caustic cake achieved 83.7% and 83.1% recovery respectively for Sc and REE (see Tables 3A, 3B et 3C).

Testing High Pressure Caustic (HPC) Leaching—9

[0171] A bench scale test was conducted on MET01 mineral concentrate at conditions similar to HPC7 except that the caustic addition rate was 1 ton NaOH per ton of mineral concentrate. The caustic leach material balance showed a 36.3% silicates decomposition, 8.3% Sc and 0.9% REE dissolution rates. The HCl leach achieved 88.5% Sc and 90.3% REE recovery to acid leach liquor.

Testing Crude Scandium Cake and REE Carbonate Precipitation

[0172] A series of bench scale precipitation tests were conducted on the primary leach solution obtained from HPC7 HCl leach test to precipitate crude scandium cake, iron and mixed REE carbonate at various pH. The ferric iron in the primary leach solution obtained from HPC7 HCl leach test was reduced to the ferrous state with the addition of metallic iron powder to avoid Fe co-precipitation with Sc. The pH of the solution was then adjusted to pH 3.5 with the addition of magnesium oxide (MgO). The precipitated crude Sc cake was recovered following a solid/liquid separation step. To precipitate iron from the Sc-depleted liquor, the iron was re-oxidized from Fe.sup.2+ to Fe.sup.3+. The rare earth elements were then precipitated from the Sc and Fe depleted liquor with the addition of sodium carbonate at pH 6. About 96 wt.-% of Sc in the primary leach solution was precipitated as crude Sc cake at pH 3.5 and 97% of Fe in solution was precipitated as an iron precipitate after re-oxidation. 66% of REE in the primary leach solution was recovered into a mixed REE carbonate product.

[0173] The chemical composition of mineral concentrates used in the tests is presented in Table 1. The test conditions for the high-pressure caustic leach (stage 1), and the hydrochloric acid leach of the caustic residue (stage 2), and their metallurgical balances are provided in Tables 2 and 3 respectively. The precipitation test results and metallurgical balance are presented in Table 4.

TABLE-US-00001 TABLE 1 Feedstock Composition Sample Met 1 Met 2 Name Unit Mineral Concentrate Mineral Concentrate SiO.sub.2 [wt.-%] 44.4 41.9 Al.sub.2O.sub.3 [wt.-%] 7.5 6.9 Fe.sub.2O.sub.3 [wt.-%] 26.9 31.4 TiO.sub.2 [wt.-%] 1.8 2.2 K.sub.2O [wt.-%] 2.5 2.2 Na.sub.2O [wt.-%] 2.3 2.0 CaO [wt.-%] 10.0 8.6 MgO [wt.-%] 2.5 2.6 BaO [wt.-%] 0.05 0.07 MnO.sub.2 [wt.-%] 1.02 1.19 P.sub.2O.sub.5 [wt.-%] 1.03 1.24 ZrO.sub.2 [wt.-%] 0.56 0.73 Sc [mg/kg] 381 244 Total rare [mg/kg] 3363 2747 earth elements

TABLE-US-00002 TABLE 2A High Pressure Caustic Leach (HPC Stage 1) Test Conditions Table 2A - High Pressure Caustic Leach Test Conditions Parameters Unit HPC2 HPC5 HPC7 HPC 8 HPC 9 Feed type Met1 Met1 Met1 Met2 Met1 Sample Mineral Mineral Mineral Mineral Mineral Concentrate Concentrate Concentrate Concentrate Concentrate Mass feed g 150 150 100 100 100 Leaching type NaOH NaOH NaOH NaOH NaOH agent Mass NaOH g  60 120 138 138 100 (100%) Mass g 100 200 230 230 230 reagent liquor

TABLE-US-00003 TABLE 2A High Pressure Caustic Leach Test Conditions Parameters Unit HPC2 HPC5 HPC7 HPC 8 HPC 9 Leaching min 120 120 120 120 120 time Leaching ° C. 250 180 220 220 220 temperature Slurry solid wt.-% 60 43 30 30 30 content Type of filter vacuum vacuum pressure pressure pressure

TABLE-US-00004 TABLE 2B High Pressure Caustic Leach (HPC Stage 1) - Chemical Analysis Table 2B - High Pressure Caustic Leach Chemical Analysis HPC2 HPC5 HPC7 HPC8 HPC9 Residue Solution Residue Solution Residue Solution Residue Solution Residue Solution Elem. [mg/kg] [mg/l] [mg/kg] [mg/l] [mg/kg] [mg/l] [mg/kg] [mg/l] [mg/kg] [mg/l] Na 81,000 14,000 122000 60000 94000 18470 114000 12200 91000 15000 Mg 15,000 <1 13000 <1 15000 0.4 12000 <0.1 15000 0.2 Al 39,000 79 37000 350 35000 120 26000 160 37000 83 Si 150,000 6,800 129000 11000 129000 1800 120000 1000 130000 2100 P 4,500 26 3600 170 3400 27 2300 68 3800 19 K 14,000 920 7000 3500 5000 510 2000 450 7000 540 Ca 76,000 13 68000 <1 80000 0.2 55000 1.4 79000 0.7 Fe 190,000 12 180000 9.4 200000 4.2 220000 0.6 200000 2 Zr 4100 <1 2400 <1 3300 0.1 5500 <0.1 3300 0.1 Sc 355 <1 330 <1 390 <1 251 <0.1 390 <1 ΣREE 3937 <1 3643.8 1141.5 4281.5 <1 3231 <0.1 3955 <1

TABLE-US-00005 TABLE 2C High Pressure Caustic Leach (HPC Stage 1) - Metallurgical Balance Table 2C - High Pressure Leach Metallurgical Balance HPC2 HPC5 HPC7 HPC8 HPC9 Rmng Ext Rmng Ext Rmng Ext Rmng Ext Rmng Ext in to in to in to in to in to residue solution residue solution residue solution residue solution residue solution Elem. [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-] Na 36.5 63.5 31.3 68.7 10.5 89.5 21.1 78.9 14.7 85.3 Mg 99.9 0.1 100.0 0.0 99.7 0.3 99.7 0.3 99.8 0.2 Al 98.0 2.0 95.9 4.1 87.0 13.0 82.3 17.7 92.7 7.3 Si 68.6 31.4 72.4 27.6 62.2 37.8 77.5 22.5 63.7 36.3 P 94.5 5.5 82.6 17.4 74.3 25.7 49.2 50.8 85 15 K 60.2 39.8 30.9 69.1 18.4 81.6 11.3 88.7 26.9 73.1 Ca 99.8 0.2 100.0 0.0 99.9 0.1 99.9 0.1 100 0 Fe 99.9 0.1 100.0 0.0 99.9 0.1 100.0 0.0 100 0 Zr 99.8 0.2 99.8 0.2 99.9 0.1 99.9 0.1 99.9 0.1 Sc 97.2 2.8 98.7 1.3 90.0 10.0 87.8 12.2 91.7 8.3 ΣREE 99.7 0.3 99.9 0.1 99.0 1.0 98.9 1.1 99.1 0.9

TABLE-US-00006 TABLE 3A Hydrochloric Acid Leach (HPC Stage 2) - Test Conditions Table 3A - Hydrochloric Acid Leach Test Conditions HPC2 HPC5 HPC7 HPC8 HPC9 Parameters Unit HCl HCl HCl HCl HCl Feed type Residue Residue Residue Residue Residue Sample from from from from from HPC2 HPC5 HPC7 HPC8 HPC9 Mass feed g 20 20 20 20 20 Reagent HCl HCl HCl HCl HCl (20%) (20%) (20%) (20%) (20%) Volume ml 180  180  180  180  180  reagent Leaching min 60 1200  60 60 60 time Leaching ° C. ambient ambient ambient ambient ambient temperature Volume for ml 180  180  180  180  180  leach Solid wt.-% 10 10 10 10 10 content Type of filter pressure pressure pressure pressure pressure

TABLE-US-00007 TABLE 3E Hydrochloric Acid Leach (HPC Stage 2) - Chemical Analysis Table 3B - Hydrochloric Acid Leach Chemical Analysis HPC2-HCl HPC5-HCl HPC7-HCl HPC8-HCl HPC9-HCl Residue Solution Residue Solution Residue Solution Residue Solution Residue Solution Elem. [mg/kg] [mg/l] [mg/kg] [mg/l] [mg/kg] [mg/l] [mg/kg] [mg/l] [mg/kg] [mg/l] Na 4,000 2,600 10000 3300 9600 4200 18100 5000 11000 4300 Mg 8,000 410 9000 340 4100 870 4600 510 5000 630 Al 12,000 1,200 14000 970 12000 1700 10000 1000 17000 1400 Si 322,000 280 294000 140 310000 490 220000 240 285000 83 P 2,000 120 1100 97 2400 150 2000 80 3100 120 K 4,000 370 5000 240 5800 300 3600 80 6000 260 Ca 38,000 1,900 43000 1600 16000 4300 19000 2400 35000 29000 Fe 80,000 6,300 90000 4700 60000 12000 120000 11500 60000 9000 Zr 10100 4 8000 <1 9500 3.8 12100 1.9 8700 3.5 Sc 298 10 280 7.8 125 21 50 9.4 100 16 ΣREE 931 116 1100 103.3 784.1 192.5 775.6 139.4 760 148

TABLE-US-00008 TABLE 3C Hydrochloric Acid Leach (HPC Stage 2) - Metallurgical Balance Table 3C - Hydrochloric Acid Leach Metallurgical Balance HPC2-HCl HPC5-HCl HPC7-HCl HPC8-HCl HPC9-HCl Rmng. Ext Rmng. Ext Rmng. Ext Rmng. Ext Rmng. Ext in to in to in to in to in to residue solution residue solution residue solution residue solution residue solution Elem. [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] Na 2.2 97.8 4.0 96.0 3.8 96.2 11.7 88.3 5.1 94.9 Mg 21.9 78.1 26.6 73.4 98.6 1.4 99.4 0.6 99.1 0.9 Al 12.6 87.4 16.5 83.5 10.9 89.1 26.8 73.2 20.2 79.8 Si 94.3 5.7 96.6 3.4 91.6 8.4 97.1 2.9 98.6 1.4 P 19.3 80.7 13.4 86.6 21.7 78.3 47.7 52.3 35.0 65.0 K 13.5 86.5 22.2 77.8 25.1 74.9 62.2 37.8 32.5 67.5 Ca 22.3 77.7 26.9 73.1 99.6 0.4 99.9 0.1 99.9 0.1 Fe 15.4 84.6 20.8 79.2 8.0 92.0 27.6 72.4 12.2 87.8 Zr 97.6 2.4 99.1 0.9 97.7 2.3 99.6 0.4 98.1 1.9 Sc 30.0 70.0 33.0 67.0 9.3 90.7 16.3 83.7 11.5 88.5 ΣREE 10.3 89.7 12.7 87.3 6.6 93.4 16.9 83.1 9.7 90.3

TABLE-US-00009 TABLE A Crude Scandium Cake and REE Carbonate Precipitation Crude Sc Cake and REE Carbonate Precipitation Grade Recovery Crude Crude Sc Fe REE Barren Sc Iron REE Barren Cake Precipitate Carbonate Solution Cake Precipitate Carbonate Solution Elements [mg/kg] [mg/kg] [mg/kg] [mg/l] [wt.-%] [wt.-%] [wt.-%] [wt.-%] Na 2900 13000 12000 5850 1.3 15.7 1.2 81.8 Mg 59000 64000 98000 48300 3.4 9.8 1.2 85.6 Al 75000 2200 2200 0.3 92.1 7.3 0.6 0 Si 1400 30 22 0.4 93.5 5.4 0.3 0.8 P 3600 20 <1 <0.1 98.4 1.5 0 0.1 K 280 770 550 350 0.9 2.4 1 95.7 Ca 2300 5600 20000 4000 1.8 0.2 3.3 94.7 Fe 16000 289000 42000 0.6 2 96.9 1.1 0 Zr 200 7.5 1.6 <0.1 79.5 8 0.1 12.3 Sc 1000 3.7 6.5 <0.1 95.9 1 0.1 3 ΣREE 1226 365 20983 3.1 17.9 14.3 66.4 1.4

[0174] Mineral concentrates prepared from MET02 sample was used for HPC tests PC1, PC2 and PC3. The chemical composition of the mineral concentrates is presented in Table 5. The test conditions for the high-pressure caustic leach (stage 1), and the mineral acid leach of the caustic residue (stage 2), and their metallurgical balances are provided in tables 6 and 7, respectively.

Testing High Pressure Caustic (HPC) Leaching—PC1-AL1

[0175] A MET02 PP1+PP2 scandium/REE mineral concentrate weighing 500 g (grade provided below in Table 5), was added to a 2 L autoclave together with 690 g of 100% sodium hydroxide dissolved in water at caustic addition rate of 1.38 tons NaOH per ton of mineral concentrate and a target a pulp density at 30% solids by weight. The slurry consisting of mineral concentrate and NaOH solution was agitated in an autoclave while being heated to a target temperature of 250° C. The slurry was kept at the target temperature for a period of 120 minutes to allow the dissolution of silicate minerals. After 120 minutes, the slurry was cooled to about 80° C., and then filtered in a vacuum filter to separate the caustic leach solution from the Sc/REE containing-residue. The residue was thoroughly washed with water. The mass and volume of the leach liquor (including wash solution) were determined to be 4409.0 g, and 3758.7 ml respectively. The mass of the wet residue was measured to be 598.9 g, and its mass after drying was 389.7 g. Aliquots of the leach liquor and dry residue were taken for chemical analysis. The metallurgical balance of the caustic dissolution (stage 1) for this test showed that 58.2% of Si and 37.9% of Al were dissolved while only 4.4% Sc and 4.9% of neodymium (Nd) (a proxy element used for the REE) deported to the caustic leach liquor. The test conditions, chemical analysis of the leach liquor and residue, and the caustic leach metallurgical balance are presented in Tables 6A, 6B and 6C.

[0176] A 300 g sample of residue from PC1 test was added to a 2477 ml of 20% HCl solution in a glass reactor, equipped with an agitator to target a pulp density of 10% solids by weight. The slurry was leached at ambient temperature for a period of 60 minutes, after which it was filtered in a pressure filter to recover the Sc/REE-bearing primary leach solution (PLS). The acid leach cake was washed thoroughly with water. The volume and mass of the acid leach liquor were determined, the mass of the wet cake, as well and its mass after drying were measured. Samples of the leach liquor and cake were chemically analyzed. A metallurgical balance for the acid leach step (stage 2 of the process), showed 93.2% of scandium and 91.2% of REE were extracted into the hydrochloric acid leach liquor (see Tables 7A, 7B et 7C).

Testing High Pressure Caustic (HPC) Leaching—PC2-AL2

[0177] A bench scale test was conducted in PC2 with 500 g of MET02 PP1+PP2 mineral concentrate using the same procedure described above for PC1 test, but at leaching temperature of 220° C., for a period of 120 minutes. The metallurgical balance for the caustic cracking stage showed 46.6% dissolution of silicates with 34.7% Al, 0.9% Sc and 2.3% Nd deportment to caustic solution.

[0178] A 300 g sample of the residue from the caustic decomposition stage 1 in test PC2 was leached in 2477 ml of 20% hydrochloric acid solution at 10% pulp density, and ambient temperature for 60 minutes (AL2). The mass balance showed that 84.6% of scandium and 88.6% of the rare earth elements were recovered into the leach solution (see Tables 7A, 7B et 7C).

Testing High Pressure Caustic (HPC) Leaching—PC3-AL3.1/AL3.2

[0179] Another high-pressure caustic leach test was conducted with 6.0 Kg of MET02 PP3+PP4 mineral concentrate, and 14 Kg of caustic solution, containing 8.28 Kg of 100% NaOH, (or 1.38 ton of NaOH per ton of mineral concentrate) to target 30% pulp density in a 20 L autoclave. The test was conducted at 250° C., for 120 minutes using similar procedure described above. The metallurgical balance for the caustic dissolution step of the process showed zero percent scandium dissolution, 57.8% decomposition of silicates, 27.6% Al and 6.9% Nd dissolution.

[0180] A 300 g of residue from stage 1 of the process (PC3 tests) was leached in a 20% HCl solution for 60 minutes at ambient temperature and a pulp density of 10% (AL3.1 test). Scandium deportment to acid leach liquor was 96.3%, while REE recovery was 95.3% (see Tables 7A, 7B et 7C).

[0181] Another 300 g of residue from PC3 test was leached in a 20 g/L HCl solution for 60 minutes at ambient temperature and a pulp density of 10% (AL3.2 test). The scandium recovery to the PLS was 62.3%, and REE extraction was 95.8% (see Tables 7A, 7B et 7C).

TABLE-US-00010 TABLE 5 Composition of MET02 Mineral Concentrate Sample MET02 MET02 Name Unit PP1 + PP2 PP3 + PP4 SiO.sub.2 [wt-%] 42.5 42.7 Al.sub.2O.sub.3 [wt-%] 6.99 7.04 Fe.sub.2O.sub.3 [wt-%] 28.9 29.0 MgO [wt-%] 2.61 2.64 CaO [wt-%] 8.29 8.35 Na.sub.2O [wt-%] 2.33 2.33 K.sub.2O [wt-%] 2.25 2.25 TiO.sub.2 [wt-%] 1.9 1.92 P.sub.2O.sub.5 [wt-%] 1.33 1.33 MnO [wt-%] 0.94 0.94 Sc [wt-%] 0.03 0.03 Nd [wt-%] 0.06 0.07

TABLE-US-00011 TABLE 6A High Pressure Caustic Leach Test Conditions for MET02 Concentrate Parameters Unit PC1 PC2 PC3 Feed Sample type Met2 Met2 Met2 PP1 + PP2 PP1 + PP2 PP3 + PP4 Mineral Mineral Mineral Concentrate Concentrate Concentrate Mass feed g 500 500 500 Leaching agent type NaOH NaOH NaOH Mass NaOH (100%) g 690 690 690 Mass reagent liquor g 1167 1167 1167 Leaching time min 120 120 120 Leaching temperature ° C. 250 220 250 Slurry solid content wt.-% 30 30 30 Type of filter vacuum vacuum vacuum

TABLE-US-00012 TABLE 6B High Pressure Caustic Leach - Chemical Analysis PC1 PC2 PC3 Residue Solution Residue Solution Residue Solution Element mg/kg mg/L mg/kg mg/L mg/kg mg/L Na 91,248 N/A 76,411 N/A 94,958 432000 Mg 18,815 N/A 18,272 N/A 19,719 49.6 Al 29,479 6720 28,844 5160  35,195 8280 Si 106,575 7000 126,675 10160  109,847 5140 P 3,884  534 3,404 354 4,626 740 K 747 N/A 2,823 N/A 1,245 23000 Ca 69,682 N/A 67,109 N/A 82,189 <18 Fe 245,498 N/A 228,013 N/A 212,625 266 Ti 12,946 N/A 12,826 N/A 15,583 <0.4 Sc 368 N/A 355 N/A 439 <0.2 ΣREE 4017 N/A 3964 N/A 4581 <1.0 N/A—Assay not available

TABLE-US-00013 TABLE 6C High Pressure Caustic Leach - Metallurgical Balance PC1 PC2 PC3 Rmng in Ext to Rmng in Ext to Rmng in Ext to residue solution residue solution residue solution Element wt-% wt-% wt-% wt-% wt-% wt-% Mg 93 7 97 3 95 5 Al 62 38 65 35 72 28 Si 42 58 53 47 42 58 P 52 48 49 51 61 39 K 3 97 13 87 5 95 Ca 92 8 95 5 100 0 Fe 95 5 94 6 80 20 Ti 89 11 94 6 100 0 Sc 96 4 99 1 100 0 Nd 95 5 98 2 93 7

TABLE-US-00014 TABLE 7A Hydrochloric Acid Leach (HPC Stage 2) - Test Conditions Parameters Unit PC1 AL1 PC2 AL2 PC3 AL3.1 PC3 AL3.2 Feed Sample type Residue Residue Residue Reside from PC1 from PC2 from PC3 from PC3 Mass feed g 300 300 300 300 Reagent HCl (20%) HCl (20%) HCl (20%) HCl (20 g/L) Volume reagent ml 2477 2477 2477 2477 Leaching time min 60 60 60 60 Leaching ° C. ambient ambient ambient ambient temperature Solid content wt.-% 10 10 10 10 Type of filter vacuum vacuum vacuum vacuum

TABLE-US-00015 TABLE 7B Hydrochloric Acid Leach - Chemical Analysis PC1-ALI PC2 AL2 PC3 AL3.1 PC3 AL3.2 Residue Solution Residue Solution Residue Solution Residue Solution Element mg/kg mg/l mg/kg mg/l mg/kg mg/l mg/kg mg/l Na 8,606 11,500 4,525 9,020 3,783 12,700 1,929 16,800 Mg 2,472 2,510 6,754 1,880 1,146 2,690 2,111 3,430 Al 11,008 4,010 9,685 3,100 2,646 5,000 1,641 6,380 Si 293,082 N/A 313,649 N/A 353,848 N/A 185,104 N/A P 3,971 347 1,484 364 5,761 341 4,844 348 K 996 50 4,815 101 1,162 97 996 107 Ca 7,719 9,480 17,367 7,260 2,859 10,200 1,501 14,500 Fe 33,153 31,100 69,243 24,400 16,996 24,700 259,487 10,700 Ti 17,561 823 18,999 534 19,059 981 25,472 148 Sc 71 47 137 38 54 53 388 37 ΣREE 803 520 650 425 377 529 284 751

TABLE-US-00016 TABLE 7C Hydrochloric Acid Leach - Metallurgical Balance PC1-ALl PC2 AL2 PC3 AL3.1 PC3 AL3.2 Rmng in Ext to Rmng in Ext to Rmng in Ext to Rmng in Ext to residue solution residue solution residue solution residue solution Element wt-% wt-% wt-% wt-% wt-% wt-% wt-% wt-% Na 3.3 96.7 2.4 97.6 1.2 98.8 0.9 99.1 Mg 4.6 95.4 14.8 85.2 1.8 98.2 4.6 95.4 Al 13.1 86.9 13.4 86.6 2.3 97.7 2.0 98.0 Si 96.7 3.3 98.9 1.1 97.2 2.8 71.8 28.2 P 36.0 64.0 17.4 82.6 37.6 62.4 44.6 55.4 K 46.9 53.1 68.1 31.9 28.2 71.8 34.1 65.9 Ca 3.9 96.1 10.3 89.7 1.0 99.0 0.8 99.2 Fe 4.7 95.3 12.1 87.9 2.4 97.6 52.0 48.0 Ti 47.7 52.3 59.2 40.8 36.9 63.1 69.7 30.3 Sc 6.8 93.2 15.4 84.6 3.7 96.3 37.7 62.3 ΣREE 8.8 91.2 11.4 88.6 4.7 95.3 4.2 95.8

[0182] The above description of the embodiments should not be interpreted in a limiting manner since other variations, modifications and refinements are possible within the scope of the present invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed invention. The scope of the invention is defined in the appended claims and their equivalents.