SOLUBILIZATION OF SCANDIUM FROM FLUORIDE BEARING MATERIALS

Abstract

A method of selectively removing scandium from a scandium and fluoride-containing feed material includes providing the scandium-containing feed material, acid leaching the scandium-containing feed material with at least one acid in a presence of at least one of an aluminum or iron containing salt to form a scandium containing stream, and purifying the scandium containing stream to form a scandium compound end product.

Description

FIELD OF THE INVENTION

The present invention relates generally to selectively recovering scandium from solid materials, and more particularly to solubilizing scandium from fluoride bearing materials.

BACKGROUND

Scandium has gained importance for the use of scandium-stabilized zirconia as a high efficiency electrolyte in solid oxide fuel cells. Applications of scandium also include use of scandium oxide (Sc₂O₃) to make high-intensity discharge lamps, and scandium-aluminum alloys that are used for minor aerospace industry components, baseball bats, and bicycle frames.

Due to limitations in mining and availability, scandium is currently only produced in small quantities. While the element occurs in many ores, it is only present in trace amounts; there are no known, easily-extractable deposits of minerals containing high scandium content. Thus, conventional acid recovery processes may be unsuitable for processing fluoride containing scandium ores. As commercial uses for scandium continue to expand, there exists the need for the development of improved methods to selectively recover scandium from readily available sources, such as ores in which a fluoride is present.

SUMMARY

An embodiment relates to a method of selectively removing scandium from a scandium-containing feed material which includes providing the scandium-containing feed material, acid leaching the scandium-containing feed material with at least one acid in a presence of at least one of an aluminum or iron containing salt to form a scandium containing stream, and purifying the scandium containing stream to form a scandium compound end product.

Another embodiment relates to a method of selectively removing scandium from a scandium fluoride containing slurry, comprising adding an aluminum containing salt to the scandium fluoride containing slurry to form at least one aluminum fluoride complex and causing the scandium fluoride to dissolve, removing the at least one aluminum fluoride complex from the slurry to provide a scandium containing stream, and purifying the scandium containing stream to form a scandium compound end product.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing, which is incorporated herein and constitutes part of this specification, illustrates exemplary aspects of the invention. Together with the general description given above and the detailed description given below, the drawing serves to explain features of the invention.

FIG. 1 is a process flow diagram illustrating an overview of the steps in a method of recovering scandium oxide from a solid material according to an embodiment.

FIG. 2 is a process flow diagram illustrating an overview of the steps in another method of recovering scandium oxide from a solid material according to another embodiment.

DETAILED DESCRIPTION

As used herein, selective removal of an ion or compound generally refers to methods to facilitate the removal of the ion or compound from solutions or suspensions (e.g., slurries). As used herein, the selective removal of scandium generally refers to methods to facilitate the removal of scandium (III) ions (Sc³⁺) or scandium-containing compounds from a solution or suspension.

As used herein, solvent extraction refers to extracting a substance from one liquid phase (e.g., an aqueous solution) into a different liquid phase (e.g., an organic solvent) based on the relative solubility of the substance in each of the phases.

Scandium oxide, and more particularly scandium (III) oxide, is described herein as the end product of the various embodiment methods. However, scandium(III) oxide is given merely as an example, and the methods described herein may be used in the production of other useful products, including, but not limited to, non-stoichiometric scandium oxide, scandium(III) chloride (ScCl₃), scandium(III) hydroxide (Sc(OH)₃), scandium(III) oxalate (Sc₂(C₂O₄)₃) and scandium(III) carbonate (Sc(CO₂)₃). One or more of the above scandium compounds may also reduced to produce scandium metal. These products are collectively referred to herein as “scandium compound end products”.

The present inventors realized that while scandium is normally quite soluble in a highly acidic solution (pH<2), it precipitates as scandium fluoride (ScF₃) when fluoride is present in the acidic solution. Scandium fluoride is not a desirable intermediate product for forming scandium oxide for commercial uses.

The present inventors have discovered that the addition of aluminum containing salts, such as AlCl₃, Al₂(SO₄) or aluminum hydroxide, or iron containing salts, such as FeCl₂, FeCl₃ or Fe₂(SO₄)₃, to the solution reduces or prevents the precipitation of scandium salts. If applicable, the aluminum or iron based salts can also be added as hydrated salts, such that the aluminum containing salts can comprise AlCl₃, Al₂(SO₄) or aluminum hydroxide with or without waters of hydration. The aluminum and/or iron in solution preferentially form complexes with fluorine relative to scandium, reducing the amount of free fluorine in solution, thereby increasing the concentration of scandium that can stay in solution. By keeping the scandium in solution, the scandium can be recovered in a subsequent purification step, such as a solvent extraction or ion exchange process step.

A method for the selective recovery of scandium from a waste acid stream according to a first embodiment is illustrated in FIG. 1. In the method 100, scandium-containing feed material 102, such as a scandium containing ore, sand or tailings from another mineral recovery process, is provided to a first reactor vessel 104. The first reactor vessel 104 may be an acid leaching reactor, such as a tank in which an acid leaching process takes place.

An acid solution 106 is also added to the first reactor vessel 104. The acid solution 106 is typically an aqueous leaching solution and may include one or more acids. Suitable acids include, but are not limited to hydrochloric acid, sulfuric acid and nitric acid. Preferably, the acid solution has a pH of 2 or less, such as 1 to 2.

An aluminum containing salt or an iron containing salt is also added. In an embodiment, the aluminum containing salt or an iron containing salt may be added to the scandium-containing feed material 102. Alternatively, the aluminum containing salt or an iron containing salt may be dissolved in the acid solution 106. In another embodiment, the aluminum containing salt or an iron containing salt is separately added to the first reactor vessel 104.

In an embodiment, an atomic ratio of aluminum or iron added to fluorine in the first reactor is greater than or equal to 3, such as 3 to 20. In an embodiment, the atomic ratio of aluminum or iron to scandium in the first reactor is greater than or equal to 2, such as 2 to 15. For example, if the aluminum salt is added to the first reactor vessel, then for low fluoride containing feed materials, the atomic ratio of aluminum to scandium can be 2 to 3, while for high fluoride containing feed materials, the atomic ratio of aluminum to scandium can be 10 to 12. In one embodiment, a filter may be located between the two vessels to remove undissolved solids, such as silicates.

A scandium containing stream 110, which can be a scandium containing solution or a slurry (e.g., flowable suspension containing inert undissolved solids) exits one portion of the first reactor vessel 104. In an embodiment, an amount of aluminum or iron in the first reactor vessel 104 is sufficient to prevent or reduce scandium precipitation from the scandium containing stream 110. Tailings 108 comprising non-soluble rocks and minerals are removed from the first reactor vessel 104 by any suitable method, such filtration or by removal from another portion of the first reactor vessel 104. The tailings 108 may be discarded, processed further to recovery other valuable elements, or recycled to the front end of the acid leaching reactor if they still contain sufficient scandium.

The scandium containing stream 110 may then be passed to second reactor vessel 112. The second reactor vessel 112 may be a purification reactor, such as a tank or ion exchange column, in which the scandium containing stream 110 is purified. That is, the scandium containing stream 110 may be treated to remove other (non-scandium) soluble elements in the scandium containing stream 110. Other soluble elements include, but are not limited to, zirconium and titanium. The other soluble elements may be removed by any suitable process, such as solvent extraction, ion exchange and/or stripping. In an embodiment, the scandium containing stream 110 may be mixed with a scrubbing agent 114 to form a separable compound 116. For example, zirconium preferentially reacts with oxalic acid (H₂C₂O₄), for example, about 0.3-1.5 M, preferably about 1.1 M H₂C₂O₄, to form the separable oxalate compound 116 that may be separated from the scandium containing stream 110. Titanium preferentially reacts with sulfuric acid (e.g., 0.5-5M H₂SO₄) and hydrogen peroxide (e.g., 2-10%, e.g., 5% H₂O₂) to form a separable titanium sulfate compound 116 (e.g., TiO(SO₄)₂²⁻). Removal of the soluble elements as the separable compound 116 provides in a purified scandium containing stream 118 exiting the second reactor vessel 112.

In an embodiment, the purified scandium containing stream 118 is a purified loaded organic phase of a solvent extraction process. A strip solution may then be added to the purified loaded organic phase to unload scandium. The strip solution may be, for example, a sodium hydroxide (NaOH) solution. Sc³⁺ ions may be unloaded from the loaded organic phase and into an aqueous phase with Na⁺ and OH⁻, from which solid scandium hydroxide (Sc(OH)₃) may precipitate out of solution. Alternatively, the second reactor vessel 112 may be an ion exchange column which is used to extract the purified scandium containing stream 118.

As discussed above, the scandium hydroxide may then be leached to extract scandium ions from the filter cake. Then, the extracted sodium ions may be precipitated out of solution as a scandium oxalate product from the filtrate. The scandium oxalate product may be calcined and dried to make a product containing scandium oxide (e.g., Sc₂O₃) or another scandium compound end product.

In an embodiment, impurities may be removed with solvent extraction, such as, cross-current solvent extraction. In embodiments, the scandium-containing stream may be an aqueous phase and the solvent stream may be an organic phase. In an embodiment, cross-current solvent extraction may be performed as a multistage process using a cross-current array. A multistage cross-current array may contain multiple extraction units, for example two to six, such as three extraction units in series. In an embodiment, the extraction units in an array may be mixing tanks or settlers, or mixer-settler units. In another embodiment, extraction units may be centrifugal extractors that mix and separate in the same unit. In another embodiment, the extraction units may be separatory funnels.

Methods for the selective recovery of scandium, e.g., scandium compound end products from fluoride bearing materials are provided. The steps of the various embodiments may be combined with other scandium recovery processes, such as described in U.S. patent application Ser. No. 14/151,177, filed Jan. 9, 2014, which issued as U.S. Pat. No. 9,102,999, hereby incorporated by reference. The steps of the various embodiments may include: solvent extraction (e.g., cross-current solvent extraction) to load at least one stage (e.g., multiple stages) of an organic phase with scandium ions (e.g., Sc³⁺) from a solution, stripping scandium (e.g., in the form of Sc(OH)₃) from the organic phase and precipitation and filtration of scandium hydroxide (e.g., Sc(OH)₃).

As discussed in U.S. patent application Ser. No. 14/151,177, the scandium hydroxide may then be leached to extract scandium ions from the filter cake. The extracted sodium ions may then be precipitated out of solution as a scandium oxalate product from the filtrate. The scandium oxalate product may be calcined and dried to make a product containing scandium oxide (e.g., Sc₂O₃). Byproducts of some or all of these steps may be recycled back for use in different steps of the process, or may be converted back into a starting reactant for use in a different step of the process.

In an alternative second embodiment method 200 illustrated in FIG. 2, fluoride solubility is enhanced prior to scandium acid leaching. Solid materials 202 containing scandium and fluoride are initially provided to a pre-reactor 204 and are acid leached with an acid 206 at a mild pH of 3 to 5, (e.g. about 4) in the presence of an aluminum salt, such as aluminum chloride or aluminum sulfate.

At mildly acidic pH, scandium solubility is severely limited by the solubility of scandium hydroxide. However, at mildly acidic conditions, aluminum solubility is not significantly impaired. Thus, aluminum fluoride 208 can form preferentially to scandium fluoride at mildly acidic pH to decrease the fluorine content available for forming scandium fluoride.

Filtration (or other suitable solid/liquid separation technique, such as settling/decanting, centrifugation, etc.) of the slurry of scandium (still as solids) and fluoride (primarily in the liquid as aluminum fluoride complexes, e.g., AlF_4-6) allows the scandium to be segregated from the fluoride 208. The fluoride wash step may be repeated/scaled up by just adding more water and aluminum salt, such as AlCl₃.

Subsequent acid leaching of the fluoride depleted raw material 102 which are provided from the pre-reactor 204 to the acid leaching reactor 104 frees scandium solids.

For example, after removing the aluminum fluoride 208 from the pre-reactor 204, the remaining scandium containing solid 102 may be acid leached in the acid leaching reactor 104 in a highly acidic solution, such as a solution having a pH of 2 or less, such as 1-2 using hydrochloric, sulfuric and/or nitric acid to recover the scandium compound end products, as described above with respect to the first embodiment.

Thus, in this alternative embodiment, the step of acid leaching includes two substeps. A first acid leaching substep in the pre-reactor 204 uses an acid having a pH between 3 and 5 to form and remove an aluminum fluoride 208 complex. A subsequent second acid leaching substep in the acid leaching reactor 104 uses the at least one acid having a pH of 2 or less to form the scandium containing stream 110.

In another alternative embodiment, if some or all of the scandium has precipitated as ScF₃, the scandium can be recovered from the ScF₃ precipitate with the addition of Al and/or Fe salts to the ScF₃ containing slurry. The Al and/or Fe form complexes with the fluorine, causing the ScF₃ precipitate to dissolve. In this manner the ScF₃ precipitate slurry can be made into a clear solution from which scandium is subsequently recovered as scandium compound end products. This approach can be used to solubilize scandium from any material in which scandium fluoride precipitation is an issue.

Thus, in this alternative embodiment, a method of selectively removing scandium from a scandium fluoride containing slurry includes adding an aluminum containing salt to the scandium fluoride containing slurry to form at least one aluminum fluoride complex and causing the scandium fluoride to dissolve, removing the at least one aluminum fluoride complex from the slurry to provide a scandium containing stream (e.g., solution or slurry), and purifying the scandium containing stream to form a scandium compound end product.

As is understood in the art, not all equipment or apparatuses are shown in the figures. For example, one of skill in the art would recognize that various holding tanks and/or pumps and/or filters may be employed in the present method.

The foregoing method descriptions and the process flow diagrams are provided merely as illustrative examples and are not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As will be appreciated by one of skill in the art the steps in the foregoing embodiments may be performed in any order. Words such as “then,” “next,” etc. are not intended to limit the order of the steps; these words are simply used to guide the reader through the description of the methods. Although process flow diagrams may describe the steps as a sequential process, many of the steps can be performed in parallel or concurrently.

Any reference to claim elements in the singular, for example, using the articles “a,” “an” or “the” is not to be construed as limiting the element to the singular.

The preceding description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein.

Claims

1. A method of selectively removing scandium from a scandium-containing feed material, comprising:

providing the scandium-containing feed material;

acid leaching the scandium-containing feed material with at least one acid in a presence of at least one of an aluminum or iron containing salt to form a scandium containing stream; and

purifying the scandium containing stream to form a scandium compound end product.

2. The method of claim 1, wherein the at least one of the aluminum containing salt or the iron containing salt is added to the scandium-containing feed material prior to the step of acid leaching.

3. The method of claim 1, wherein the at least one of the aluminum containing salt or the iron containing salt is dissolved in a solution comprising the least one acid.

4. The method of claim 1, wherein the at least one of the aluminum containing salt or the iron containing salt is separately added to a reactor vessel in which the acid leaching takes place.

5. The method of claim 1, wherein the at least one acid is selected from at least one of hydrochloric acid, sulfuric acid and nitric acid.

6. The method of claim 1, wherein the scandium compound end product comprises scandium hydroxide, scandium oxide, scandium chloride, scandium oxalate or scandium carbonate.

7. The method of claim 1, wherein the step of purifying comprises at least one of solvent extraction, ion exchange and stripping.

8. The method of claim 1, wherein the scandium-containing feed material comprises a solid material containing fluorine which forms a complex with aluminum ions or iron ions during the acid leaching.

9. The method of claim 8, wherein an amount of aluminum or iron in a reactor vessel in which the acid leaching takes place is sufficient to prevent scandium precipitation.

10. The method of claim 1, wherein the step of acid leaching the scandium-containing feed material with at least one acid takes place in the presence of the aluminum containing salt.

11. The method of claim 10, wherein the aluminum containing salt is AlCl3 with or without waters of hydration.

12. The method of claim 10, wherein the aluminum containing salt comprises Al2(SO4) with or without waters of hydration, or aluminum hydroxide with or without waters of hydration.

13. The method of claim 10, wherein an atomic ratio of aluminum to fluorine is greater than or equal to 3 in a reactor vessel in which the acid leaching takes place.

14. The method of claim 13, wherein the atomic ratio of aluminum to scandium in the reactor vessel in which the acid leaching takes place is greater than or equal to 2.

15. The method of claim 10, wherein the at least one acid has a pH of 2 or less during the step of acid leaching.

16. The method of claim 10, wherein the step of acid leaching comprises:

a first acid leaching substep using an acid having a pH between 3 and 5 to form and remove an aluminum fluoride complex; and

a subsequent second acid leaching substep using the at least one acid having a pH of 2 or less to form the scandium containing stream.

17. A method of selectively removing scandium from a scandium fluoride containing slurry, comprising:

adding an aluminum containing salt to the scandium fluoride containing slurry to form at least one aluminum fluoride complex and causing the scandium fluoride to dissolve;

removing the at least one aluminum fluoride complex from the slurry to provide a scandium containing stream; and

purifying the scandium containing stream to form a scandium compound end product.

18. The method of claim 17, wherein the aluminum containing salt is AlCl3 with or without waters of hydration.

19. The method of claim 17, wherein the aluminum containing salt is Al2(SO4) with or without waters of hydration.

20. The method of claim 17, wherein:

the scandium compound end product comprises scandium hydroxide, scandium oxide, scandium chloride, scandium oxalate or scandium carbonate; and

the step of purifying comprises at least one solvent extraction, ion exchange and stripping.