US-12617693-B2 - 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.

Inventors

• Yemi OYEDIRAN
• Daniel RISCHE
• Christian Graf

Assignees

• IMPERIAL MINING GROUP LIMITED

Dates

Publication Date

20260505

Application Date

20221206

Claims (17)

1. 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, wherein the given pressure is between 9.87 ATM and 39.48 ATM, the HPC leaching is performed in a reaction vessel or in an autoclave, and the leaching of the solid residue in a mineral acid comprises stirring for a period of 60 to 1200 minutes at a second temperature between 20° C. and 30° C. and at 1 ATM.
2. 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. 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 the ore, the REE and/or scandium bearing feedstock, and/or scandium/REE bearing mineral concentrate.
4. 4 . The method of claim 1 , wherein, between leaching the ore, the REE and/or scandium bearing feedstock, and/or scandium/REE bearing mineral concentrate in an alkali solution and separating the solid residue from the leachate slurry, the method comprises regenerating and recycling the alkali solution.
5. 5 . The method of claim 1 , wherein, between leaching the ore, the REE and/or scandium bearing feedstock, and/or scandium/REE bearing mineral concentrate in an alkali solution and separating the solid residue from the leachate slurry, the leachate slurry is cooled down to a second temperature of about 80° C. to ambient temperature.
6. 6 . The method of claim 1 , wherein, between leaching the ore, the REE and/or scandium bearing feedstock, and/or scandium/REE bearing mineral concentrate in an alkali solution and separating the solid residue from the leachate slurry, the solid residue is washed with water.
7. 7 . The method of claim 1 , wherein leaching the REE and/or scandium bearing feedstock comprises a slurry solid content of 10 to 45 wt %.
8. 8 . The method of claim 1 , wherein the first temperature is between 180° C. and 280° C.
9. 9 . The method of claim 1 , wherein the target duration of the HPC leaching is between 60 minutes and 180 minutes.
10. 10 . The method of claim 1 , wherein separating the solid residue from the leachate slurry is conducted in a vacuum or pressure filter.
11. 11 . The method of claim 1 , wherein, between separating the solid residue and leaching of the solid residue in the mineral acid, the method comprises destroying a silicate matrix of REE and/or scandium bearing silicate minerals by forming water soluble sodium silicate thereby liberating Scandium and/or REE.
12. 12 . The method of claim 1 , wherein, between separating of the solid residue and leaching of the solid residue in the mineral acid, the method comprises transforming fluorides and phosphates to water soluble compounds and removing the water soluble compounds from the leachate slurry.
13. 13 . The method of claim 12 , wherein fluorides and fluoride containing minerals are removed prior to transforming into water soluble compounds.
14. 14 . The method of claim 1 , wherein the mineral acid is selected from the group consisting of Hydrochloric acid (HCl), Sulphuric acid (H 2 SO 4 ), Nitric acid (HNO 3 ), Hydrobromic acid (HBr), Perchloric acid (HClO 4 ), Hydroiodic acid (HI), and suitable mixtures thereof having a concentration between 5 to 20 wt %.
15. 15 . The method of claim 1 , wherein the REE the scandium is extracted from the primary leach solution by precipitation, solvent extraction, ion exchange extraction or a combination thereof.
16. 16 . The method of claim 1 , wherein, between the leaching of the solid residue and extracting REE and/or scandium from the primary leach solution, the method comprises regenerating and recycling the mineral acid.
17. 17 . 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 2 CO 3 ).

Description

CROSS-REFERENCE This application claims priority to U.S. Provisional Application No. 63/265,176 filed on Dec. 9, 2021 (“HIGH PRESSURE CAUSTIC LEACH METHODS AND PROCESSES FOR RECOVERY OF SCANDIUM AND RARE-EARTH OXIDES”), which is entirely incorporated herein by reference. FIELD The invention relates to methods and processes for producing and recovering rare earth elements (REE), and more particularly to systems and methods for extracting and recovering scandium, and separated rare-earth oxides (REO) from ore and mineral concentrates that contain scandium such as in the form of silicates. BACKGROUND 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. Given their unusual physical and chemical properties such as magnetic and optical properties, REE are necessary components of more than 200 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 and defense applications such as electronic displays, guidance systems, lasers, and radar and sonar systems. 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, lighting, and radioactive isotopes. However, commercial applications of scandium continue to be limited by the absence of reliable, secure, stable, long-term production of the metal. 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. 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 in this application has been thwarted by the low availability of scandium. 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 the only known concentrated mineral sources of this element. 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. REEs do not occur naturally as metallic elements, but given their strong affinity for oxygen, this causes them to form mostly as their respective oxides (REOs). Because of their 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. Rare Earth Oxides (REO) minerals occur in a variety of geological environments. In general, they are found in hard rock deposits or in placer sands and are of primary or secondary origin, respectively. Composition of the REO minerals is strongly influenced by the presence of carbonates and phosphates. Some processes and methods for the recovery of 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 preferentially neither mined, nor recovered from process streams or mine tailings. Scandium is produced primarily from the scandium-yttrium silicate mineral thortveitite