Methods of recovering scandium from titanium residue streams

A method for selectively removing scandium from a scandium-containing feed solution includes contacting the scandium-containing feed solution with a solvent stream in plural stages using cross current extraction, in which the solvent is loaded with at least a portion of the scandium from the feed solution, and/or ion exchange, and separating the loaded solvent from remaining scandium-containing feed solution.

FIELD OF THE INVENTION

The present invention relates generally to selectively recovering scandium from extractive metallurgy waste, and more particularly to extracting and recovering scandium from waste acid streams generated from titanium processing.

BACKGROUND

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. Currently, only a few mines, located in Russia, Ukraine and China, produce scandium, and in each case it is made as a byproduct from the extraction of other elements and sold as scandium oxide.

In particular, 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. 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.

SUMMARY OF THE INVENTION

An embodiment method of selectively removing scandium from a scandium-containing feed solution includes: transferring scandium ions from an aqueous phase to an organic phase, in which a loaded organic phase is created; scrubbing the loaded organic phase with an acidic solution; stripping scandium ions from the loaded organic phase into an aqueous phase, in which a loaded aqueous phase is created; and separating the scandium ions from the loaded aqueous phase by providing the loaded aqueous phase to an ion exchange apparatus.

Another embodiment method of selectively removing scandium from a scandium-containing feed solution includes: contacting the scandium-containing feed solution with a solvent stream in plural stages using cross-current extraction, in which the solvent is loaded with at least a portion of the scandium from the scandium-containing feed solution; and separating the loaded solvent from remaining scandium-containing feed solution.

An embodiment method of producing a scandium-containing product from a titanium- and scandium-containing acid solution stream includes producing at least 2.0 kg/h, preferably 2.0-2.9 kg/h, such as 2.8 kg/h, of the product comprising at least 99 wt % Sc2O3per 125,000 L/h of the acid solution stream.

Another embodiment method of selectively removing scandium from a scandium-containing feed solution includes contacting the scandium-containing feed solution with at least one ion exchange resin, in which the at least one ion exchange resin is loaded with at least a portion of the scandium from the scandium-containing feed solution; providing an eluent solution to the at least one ion exchange resin, in which scandium is unloaded into an eluate stream; and converting the unloaded scandium in the eluate stream to a solid scandium oxide product.

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. 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.

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.

As used herein, titanium processing refers to extraction or refinement of titanium products, such as titanium dioxide (TiO2) (e.g., by the sulfate process or chloride process), titanium sponge, and/or other titanium products for commercial use from titanium-containing ore. For example, titanium dioxide is commonly extracted from ilmenite using the sulfate method, which produces a waste stream containing dilute sulfuric acid. Another example is the extraction of titanium dioxide from rutile or leucoxene using the chloride method, which produces a waste stream containing hydrochloric acid. In an embodiment, the waste stream (e.g., liquor) from titanium dioxide processing may be hydrolytic solution (i.e., dissolved ions in solution) that contains approximately 15-20 mg/L scandium, with other impurities such as zirconium (Zr), titanium (Ti), iron (Fe) and silicon dioxide (SiO2). In a preferred embodiment, scandium may be directly extracted from the effluent waste liquor from titanium dioxide processing. The embodiments described herein are equally applicable to artificially prepared waste streams that simulate the waste liquor from titanium processing, and to other salt solutions.

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), and scandium(III) oxalate (Sc2(C2O4)3). These products are collectively referred to herein as “scandium compound end products”.)

Methods for the selective recovery of scandium, e.g., scandium compound end products, for example, in the form of scandium oxide from titanium processing waste streams are provided. 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 ions from the organic phase; precipitation and filtration of scandium hydroxide (e.g., Sc(OH)3); leaching scandium ions from the filter cake; precipitation of a scandium oxalate product from the filtrate; and calcination and drying a product containing scandium oxide (e.g., Sc2O3). According to the preferred embodiments, byproducts 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.

A method for the selective recovery of scandium from a waste acid stream according to an embodiment is illustrated inFIG. 1. In method100, scandium may be removed in a multi-stage cross-current solvent extraction process from a waste liquor generated during titanium dioxide (e.g., TiO2) refinement by the sulfate method.

In the various embodiments, cross-current solvent extraction is performed by feeding a scandium-containing stream and a solvent stream into an extraction unit. In preferred embodiments, the scandium-containing stream may be an aqueous phase, i.e., a waste acid liquor stream containing scandium ions, and the solvent stream may be an organic phase.

In a preferred 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.

In steps102a-102c, a waste acid stream101containing many species in solution, including scandium, may be contacted and mixed with an extractant and an organic liquid at a phase ratio of 1:2 to 1:10, such as 1:5, organic to aqueous (O:A). The organic liquid may be, for example, a high flash point kerosene (e.g., laboratory grade kerosene) or another organic with similar properties (e.g., hexane). In a preferred embodiment, an extractant is also mixed with the waste acid stream and the organic phase. The extractant may be one of a number of commercially available reagents. Examples of such extractants may include, but are not limited to bis(2 ethylhexyl)hydrogen phosphate (DEHPA) (CAS Number 4971-47-5), and tributyl phosphate (TBP) (CAS Number 126-73-8).

The extractant reacts with a portion of the scandium ions in the aqueous phase to form a Sc-extractant complex that is more soluble in the organic liquid than in the aqueous phase. In a preferred multistage cross-current process, the aqueous raffinate103a,103bfrom one extraction unit in steps102a-102cis fed to the next unit as the aqueous feed, while multiple cross-current streams of the barren (i.e., fresh or unloaded) organic phase105a-105care provided to extraction units to contact the aqueous feed, without feeding the loaded organic into the next extraction unit. Thus, barren organic phase is provided to each unit, while the aqueous phase flows from one unit to the next in series in the cross-current extraction process. Each successive extraction stage removes a portion of the remaining scandium ions in the aqueous phase into the organic phase107a-107c. In a preferred embodiment, solvent extraction may include three cross-current stages, steps102a-102c. However, other embodiments may include more than three stages, or may include fewer than three stages. In contrast, in a counter-current extraction process, the loaded organic phase is provided from one extraction unit to the next unit in series in an opposite direction to the aqueous phase flow between the units.

Thus, in an embodiment, the scandium-containing feed solution101is contacted with a barren first solvent stream105ain a first stage102a. The first solvent stream105ais loaded with at least a portion of the scandium from the feed solution. The loaded first solvent107ais separated from the remaining scandium-containing feed solution103afrom the first stage102a.

The first stage is followed by contacting the remaining scandium-containing feed solution103afrom the first stage102awith a barren second solvent stream105bin a second stage102b. The second solvent stream105bis loaded with at least a portion of the scandium from the remaining scandium-containing feed103afrom the first stage102a. The loaded second solvent107bis separated from remaining scandium-containing feed solution103bfrom the second stage102b.

Then, in a third stage102c, the remaining scandium-containing feed solution103bfrom the second stage102bis contacted with a barren third solvent stream105c. The third solvent stream105cis loaded with at least a portion of the scandium from the remaining scandium-containing feed103bfrom the second stage102b. The loaded third solvent107cis separated from the remaining scandium-containing feed solution103cfrom the third stage102c.

This embodiment may include more than three stages described above. The first, second and third stages102a-102cin this embodiment may be performed respectively in first, second, and third extraction units, connected in series to form a cross-current array.

At the end of steps102a-102c, the spent aqueous solution103cmay be scrubbed using, for example, a dual media filter or a coalescer, to recover any organic phase that was carried through the extraction, step104. The aqueous raffinate may be collected, for example, into a waste holding tank, step106. Any recovered organic phase can be recycled so that it can be used in steps105a-105c.

The cumulative loaded organic phase107from steps102a-102cis then purified in a series of scrubbing steps. The scrubbing steps may also be conducted using a cross current process.

In an example embodiment, the loaded organic phase107may be provided to a zirconium scrubbing process, step108. An example scrubbing agent for removal of Zr impurities may be, but is not limited to, oxalic acid (H2C2O4)109, for example, about 0.3-1.5 M, preferably about 1.1 M H2C2O4, to remove Zr in the form of a zirconium(IV) oxalate compound (Zr(C2O4)32−)111. Zr scrubbing using oxalic acid may proceed according to the following reaction:
Zr(SO4)2·xHR+3H2C2O4→Zr(C2O4)32−+6H++2SO42−+xHR  (eq. 1),

where R represents the organic liquid. Alternative scrubbing agents that may be used include, for example, hydrofluoric acid (HF) or hydrochloric acid (HCl).

In step110, the loaded organic107S may be provided to a titanium scrubbing process. In an example embodiment, sulfuric acid (e.g., 0.5-5M H2SO4) and hydrogen peroxide (e.g., 2-10%, e.g., 5% H2O2)113may be used as scrubbing agents to remove titanium impurities115. Titanium scrubbing using sulfuric acid and hydrogen peroxide may proceed according to the following reaction:
TiOSO4·xHR+SO42−+H2O2→TiO(SO4)22−+H2O+xHR  (eq. 2),

where R represents the organic liquid. Other impurities that may be removed by further optional scrubbing stages (not shown for clarity inFIG. 1) may include, for example, iron (Fe) and manganese (Mn).

The spent scrubbing agents containing the impurities111,115from steps108and110may also contain recoverable, usable compounds. For example, one of the compounds that may be present in the spent sulfuric acid and hydrogen peroxide used for titanium scrubbing in step110is titanium oxysulfate (TiOSO4)115. Titanium oxysulfate, which can be used as a mordant in dyeing processes, may be recovered from the spent scrubbing agent and used and/or sold for use in a pigment plant.

In step112, a strip solution117may be added to the purified loaded organic phase107P to unload scandium. The strip solution may be, for example, a sodium hydroxide (NaOH) solution. Sc3+ions may be unloaded from the organic phase107P and into an aqueous phase119with Na and OH−, from which Sc(OH)3may precipitate out of solution. Stripping scandium from the organic phase107P using a NaOH strip solution may proceed according to the following reaction:
HSc(SO4)2·xHR+8NaOH→Sc(OH)3↓+2Na2SO4+xNaR  (eq. 3).

In an embodiment, the unloaded organic (i.e., barren organic121) liquid may be recycled back to the extraction units, step114, to be incorporated in the organic phase105a-105cfor the solvent extraction stages in steps102a-102c. Extractant123can be added to barren organic121and recovered organic from step104to form the organic phase105a-105c. Sc(OH)3may be separated from the aqueous solution119using any suitable techniques. In an example embodiment, Sc(OH)3precipitate125may be separated from the aqueous phase119in a clarifier. In another embodiment, a centrifuge may be used to separate the precipitated Sc(OH)3125from solution119. In a preferred embodiment, the aqueous solution119containing Sc(OH)3precipitate may be fed into a filter (e.g., a vacuum filter) to produce a filter cake of Sc(OH)3125, step116. The filtrate solution may be recovered in a tank, and, in step118, sodium hydroxide117may be recycled back to the strip solution used in step112to unload scandium ions from the organic phase107P. In an embodiment, the resulting filter cake may contain, for example, 70-90 wt % Sc(OH)3, thereby yielding 30-40 wt % scandium. The components which make up the other 10-30 wt % of the resulting filter cake may be, for example, residual TiO2, NaOH, and/or rare earth elements.

In step120, the filter cake125may be leached with an acid127to dissolve the Sc, producing an outflow filtrate solution129with scandium ions. In a preferred embodiment, the leaching acid127may be, but is not limited to, hydrochloric acid (HCl). Waste acid stream131contains Ti(OH)4to a pigment plant.

In step122, the filtrate solution129may be contacted with an organic phase124in a solvent extraction process. The organic phase124may be an organic extractant, such as P350 (dimethylheptyl methyl phosphate), in an organic solvent, such as high flash point kerosene. The solvent extraction in step122may be carried out, for example, in a conventional solvent extraction plant using mixer-settlers in single or multi stage (up to 3 stages). As a result of step122, the organic phase124may be loaded with scandium ions from the filtrate solution129. The aqueous raffinate from the solvent extraction may be collected, for example, into a waste holding tank in step123.

In step126, the loaded organic phase from the solvent extraction in step122may be stripped with water128, and the stripped organic130may be recycled to a mixer for reuse in the solvent extraction in step122. In step134, oxalic acid132may be added to a scandium-containing aqueous phase created from the stripping of the loaded organic phase in step122, and a resulting scandium oxalate precipitate may be recovered by filtration. The waste acid solution135from the filtration step may be discarded or reused.

In step136, the Sc2(C2O4)3in the filtered scandium oxalate precipitate may be dried of excess moisture and calcinated (i.e., heated to convert Sc2(C2O4)3to Sc2O3) at 700-800 degrees Celsius to obtain a scandium compound end product137(e.g., a scandium oxide solid composition) that has a composition of at least 99 wt %, such as around 99 to 99.9 wt % scandium oxide.

Thus, as described above, cross-current extraction and/or scrubbing result in a higher scandium recovery percent than counter-current extraction and/or scrubbing because cross-current extraction and/or scrubbing requires fewer repetitions or steps than comparable counter-current process. Since each extraction and/or scrubbing stage cycle inevitably loses a small amount of scandium, using a lower cycle number cross-current extraction and/or scrubbing results in a lower scandium loss and lower process cost than comparable counter-current methods.

FIG. 2illustrates an alternative embodiment method to recover Sc2O3from a titanium processing waste stream, which uses cross-current solvent extraction and an ion exchange apparatus.

In method200, steps102-121are performed as discussed above with respect toFIG. 1. Then, in step204, scandium containing loaded aqueous solution129may be loaded into a stationary phase adsorbent by providing the aqueous phase to a cationic exchange resin, such as in one or more chromatography columns. An example of an ion exchange resin that may be used is Lewatit TP207, supplied by Bayer AG, which is a weakly acidic, macroporous-type ion exchange resin with chelating iminodiacetate groups that selectively removes heavy metal cations.

In step208, scandium ions may be eluted from the loaded ion exchange resin209. In a preferred embodiment, a hydrochloric acid eluent211may be provided to the one or more loaded columns to unload the scandium from the resin209. Scandium ions may be displaced on the resin209by H+ions, and the resulting eluate213contains scandium chloride (ScCl3) in solution. Thus, steps204and208replace steps122and126in the method ofFIG. 1. In step210, the ScCl3eluate213may be provided to a mixer with a solution of oxalic acid (H2C2O4)215to cause scandium oxalate (Sc2(C2O4)3) to precipitate out of solution. In step212, the resulting solution containing scandium oxalate ((Sc2(C2O4)3) precipitates may be fed into a filter (e.g., a vacuum filter) to obtain a scandium oxalate (Sc2(C2O4)3) product217. In step214, the scandium oxalate (Sc2(C2O4)3) product217may be calcinated (i.e., heated to convert the oxalate to oxide) and excess moisture removed by drying to obtain a scandium compound end product237having a composition of at least 90 wt % Sc2O3, such as 93-95 wt % Sc2O3, e.g., around 96 wt % Sc2O3. In step216, the unloaded (i.e., barren) ion exchange resin209U may be regenerated for use in repeated cycles. For example, regeneration may be done by providing the column containing the ion exchange resin209U with a solution of hydrochloric acid (HCl)219to create the regenerated resin209R which is then loaded with additional loaded aqueous solution129.

FIG. 3illustrates an alternative embodiment method to recover Sc2O3from a titanium processing waste stream, which uses a series of ion exchange columns.

In step302, a waste acid stream304(e.g., liquor) from titanium dioxide processing may be loaded into a stationary phase adsorbent by providing the stream to one or more cationic exchange resins305. The waste acid stream304may be a direct waste acid stream, or may be an output scandium containing aqueous solution119inFIG. 1or119A inFIG. 2In an embodiment, the waste acid stream304may be provided to multiple ion exchange columns that are in series, such as two or more, for example two to five, such as three ion exchange columns. As discussed above, the waste acid stream produced from titanium processing may be an aqueous stream containing hydrochloric acid. In various embodiments, the waste acid stream may contain approximately 15-40 mg/L scandium, as well as a high concentration of other metal ions, for example, iron (Fe), zirconium (Zr), vanadium (V), aluminum (Al), magnesium (Mg), manganese (Mn), and/or titanium (Ti).

Examples of ion exchange resins that may be used to make the ion exchange columns include ion exchange resins that contain sulfur-based and/or phosphorus-based ligands and/or chelating functional groups in ion exchange resins that are selective for scandium. In particular, commercially available ion exchange resins that may be used in the various embodiments include, but are not limited to, Lewatit® TP207or TP260, Diphonix®, MonoPhos™, Water Treatment Polymer D402 macroporous aminophosphonic resin, and/or other commercially available ion exchange resins. Loading the ion exchange resins with scandium ions from the waste acid stream in various embodiments may proceed according to the following equation:
3R′H+SO+→R′3Sc+3H+(eq. 4),
where R′ represents a cationic exchange resin, producing loaded resins306. The use of plural (e.g., three) ion exchange columns in series may enable loading of at least 80% (e.g., 81-85%, such as 85%) of the scandium ions in the waste acid stream304. Preferably, an ion exchange resin in the various embodiments has a high selectivity for scandium ions over iron (III) ions.

In step308, an eluent310may be provided to the one or more loaded resins306to unload the scandium ions. In the various embodiments, the eluent310may be a solution having a logarithmic measure of the acid dissociation constant (pKa) that is greater than or equal to −2, such as pKaof −2 to 12. In other words, the eluent is a weak acid, a neutral solution, or a base. Example eluents310that may be used include ethylenediaminetetraacetic acid (“EDTA”), sodium carbonate (Na2CO3), 1-hydroxyethylidene 1,1-diphosphonic acid (“Phos 6”), and/or other eluents which provide displacement ions, such as H+, Na+, etc. on the loaded resins306. Scandium ions may be displaced on the resin306by H+or Na2+, ions, with the resulting eluate312solution containing scandium salts in solution. In an embodiment in which the eluent310is EDTA, the elution of scandium ions may proceed according to the following reaction:
R′3Sc+H4EDTA→4H++3R′+[Sc(EDTA)]−(eq. 5),
where R′ represents a cationic exchange resin. In various embodiments, the concentration of scandium in the eluate may be at least 800 mg/L, such as 800-1,000 mg/L. Thus, the scandium concentration in the eluate (i.e., the elution product)312may be greater than 25 times, such as 30-67 times that of the initial waste acid stream (i.e., 15-40 mg/L scandium). In the various embodiments, the eluate312may be a solution of a scandium-containing complex, for example, a scandium carbonate, a scandium hydroxide, and/or other scandium-containing complex depending on the eluent used.

In various embodiments, the loaded resin may also be washed with appropriate agents to remove various impurities co-extracted onto the resins (not shown).

In step314, the scandium-containing eluate312may be subjected to post-processing steps to convert the eluted scandium to a solid scandium compound end product316containing greater than 40 wt %, such as 40-50 wt %, Sc2O3. In the various embodiments, the post-processing of step314may involve neutralizing the scandium-containing complex in the eluate312using mineral acids, such as hydrochloric acid or sulphuric acid324. In step318, solid scandium oxide precipitate319may be recovered from the neutralized slurry by filtration. In step320, the precipitated solid scandium oxide compound may be dried of excess moisture and calcinated at 700-800 degrees Celsius to obtain a solid refined product322containing at least 95 wt % Sc2O3, such as 95-99.9 wt % Sc2O3.

In various embodiments, the ion exchange resins may be regenerated for use in repeated cycles, which may involve any of a variety of solutions depending on the composition of the resin. For example, in step309, the unloaded (i.e., barren) ion exchange resin may be washed by providing water311to the column containing the ion exchange resin to displace the eluent, and to wash the unloaded (i.e., barren) ion exchange resin. In step326, a solution of hydrochloric acid (HCl)328may be provided to the column containing the washed resin in order to create a regenerated resin330, which may be provided back for loading with waste acid stream304to use in the ion exchange of step302.

In various embodiments, a complexing agent may be added to the eluent to enhance separation factors preferentially for scandium may be added. For example, citric acid-ammonium citrate ((NH4)2C6H6O7) are described in the prior art as enhancing separation of rare earth metals. Additional complexing agents may include, but are not limited to, Ethylenediaminetetraacetic acid (EDTA), (2-Hydroxyethyl) ethylenediaminetriacetic acid (HEDTA), Diethylene triamine pentacetic acid (DTPA) and 1,2-Cyclohexanediamine tetraacetic acid (DCTA), all of which show high stability over wide ranges of pH and high separation factors.

In another embodiment, the separation process may involve the use of simulating moving bed chromatography (SMB) instead of traditional chromatography columns204and208. In this manner, the separation process may be continuously and performed, as an effective alternative to repetitions of single batch processes. Thus, in one embodiment, an ion exchange apparatus may be a moving bed ion exchange apparatus. In another embodiment, the ion exchange apparatus may comprise one or more static ion exchange columns.

RESULTS

Table 1 below illustrates the amounts in g/L of scandium and various impurities in the process feeds of an embodiment method described above with respect toFIG. 1. Measurements were taken for the initial waste acid feed101of a titanium processing plant refining TiO2using a sulfate process, and in the raffinate103dfollowing three cross-current solvent extraction stages102a-102cto determine the percentages of scandium and impurities that were extracted into the organic phase107.

The data in Table 1 show that 97 wt % of the scandium initially present in the TiO2waste acid stream101was extracted in the cumulative loaded organic phase107through the three stages102a-102cof cross-current solvent extraction. Thus, at least 90 wt %, such as 95-97 wt %, is removed in steps102a-102c.

Table 2 below provides data for the amount of scandium and various impurities that were measured before (in the loaded organic107) and after (in the scrub organic107S) a zirconium scrubbing step108in which oxalic acid (H2C2O4)109was used the scrubbing agent.

The data show that the use of oxalic acid1009was effective for scrubbing Fe from the organic phase107, as well as for Zr scrubbing. Thus, at least 90 wt %, such as 90-96 wt %, of Zr and Fe may be removed in step108.

Table 3 below provides data for the amount of scandium and various impurities measured before (in the loaded organic107) and after (in the scrub organic107S) titanium scrubbing in step110with sulfuric acid (e.g., 5M H2SO4) and hydrogen peroxide (e.g., 5% H2O2)113as scrubbing agents:

Thus, following the two scrubbing steps, concentrations of each impurity (e.g., Ti, Fe, Zr, etc.) measured in the organic phase were at or below 2 wt % (e.g., 0.2-2 wt %). At least 95 wt % Ti, such as 99-99.9 wt % Ti, may be removed in step110.

Table 4 below provides the amount of scandium oxide and other compounds that were measured before and after the cross-current solvent extraction and in the subsequent process streams for the production of each stage of cross-current solvent extraction and the subsequent process streams for production of Sc2O3.

Thus, 5 kg/h of 99.9 wt % Sc(OH)3cake125is produced from a Ti-containing waste acid stream101having a flow rate of 125,000 L/h. In other words, at least 4.5 kg/h (e.g., 4.5 to 5 kg/hr) of at least 99 wt % (such as 99-99.9 wt %) Sc(OH)3cake125is produced per 125,000 L/h of a Ti-containing waste acid stream101. The calcined and dried scandium oxide product forms at least 2 kg/h (e.g., 2 to 2.9 kg/h), such as at least 2.8 kg/h of the scandium oxide solid product per 125,000 L/h of the waste acid stream101.

FIG. 4illustrates a loading profile for scandium in ion exchange columns of an embodiment method described above with respect toFIG. 3. A waste acid feed304from a titanium processing plant was provided to three ion exchange columns305arranged in series, each containing a Monophos™ cationic exchange resin. Measurements of the concentrations of scandium loaded in the three columns are shown as a function of time. As shown inFIG. 4, the second column (Column B) may be loaded with at least 30 mg/L (e.g., 30-31 mg/L) of scandium after 200 minutes.

FIG. 5illustrates elution profiles of titanium, scandium and iron (III) ions in an eluate312, from elution of loaded ion exchange columns306, having the loading profile shown inFIG. 4, with a sodium carbonate eluent310. Measurements of the concentrations of titanium, scandium and iron (III) ions eluted into solution are each shown as a function of time.

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 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.