Vanadium extraction

Abstract

A method for extracting vanadium(V) from a source comprising vanadium, the method comprising (a) leaching the source comprising vanadium with a composition comprising a compound of formula (I) wherein R1, R2, R3 and R4 are each independently a C1-10 hydrocarbyl group; and wherein A+ is N+ or P+; wherein the composition further comprises an oxidising agent; and wherein said leaching extracts some of the vanadium from the source comprising vanadium to provide extracted vanadium(V); and (b) recovering the extracted vanadium(V).

Description

[0001]Vanadium Extraction Field The present disclosure relates to a method for extracting vanadium(V) from a source comprising vanadium. The present disclosure relates more particularly to a method of extracting vanadium(V) that includes recovering the extracted vanadium(V), optionally during electrodialysis. Background Vanadium is utilised in the steel industry to make metal alloys for rebar and structural steel, as well as in aircraft. Vanadium can lighten steel by up to 30 % and boost its strength by up to 100 % when it is added in modest amounts. Currently, the steel and titanium industries account for more than 90 % of the use of vanadium produced worldwide. More recently, vanadium redox flow batteries (VRFBs) have gained significant attention because of their long cycle life, full discharge ability, low running cost, fast response, environmental credentials, and non- flammability. The global energy storage market is increasing rapidly due to increasing deployment to national grids of solar and wind energy sources that are inherently intermittent, requiring buffer storage. Therefore, the global effort towards clean energy technology is anticipated to increase demand for vanadium greatly. Conventional vanadium refining begins with roasting the feedstock with sodium salts such as sodium carbonate and sodium chloride at high temperatures to produce water-soluble vanadium species, followed by a process involving ammonium polyvanadate or metavanadate precipitation to separate solid vanadium(V) species from the aqueous phase. This seemingly simple vanadium processing method comes at the cost of emitting hazardous gases, such as sulfur oxides into the atmosphere in addition to the production of hazardous tailings which is inherent to the salt-roasting water-leaching processing method. Moreover, the release of vanadium(V) to the environment potentially can be hazardous. Unfortunately, limited attention has been given to vanadium(V) toxicity and there are limited studies on vanadium geochemistry relative to similar trace metals despite being classified as a potentially toxic metal. The most recent research on vanadium pollution and health risks in marine ecosystems revealed that children are at the highest health risk. Thus, the primary production of vanadium has severe environmental impacts while being highly susceptible to political and geopolitical decisions due to being concentrated in specific regions. Therefore, it is of great importance to identify alternative approaches to produce vanadium from more available sources such as the secondary source gasifier ash to secure circular economy implementation, as well as to expand the vanadium supply chain network. Summary According to a first aspect, there is provided a method for extracting vanadium(V) from a source comprising vanadium, the method comprising: (a) leaching the source comprising vanadium with a composition comprising a compound of formula (I): wherein R1, R2, R3 and R4 are each independently a C1-10 hydrocarbyl group; and wherein A+is N+or P+wherein the composition further comprises an oxidising agent; and wherein said leaching extracts some of the vanadium from the source comprising vanadium to provide extracted vanadium(V); and (b) recovering the extracted vanadium(V). According to a second aspect, there is provided a compound of formula: H4(Me4N)2V10O28.5H2O According to a third aspect, there is provided a compound of formula: H3(Me4N)3V10O28.6H2O According to a fourth aspect, there is provided a compound of the second or third aspect obtained or obtained by the method of the first aspect. According to a fifth aspect, there is provided use of composition comprising a compound of formula (I): (I) wherein R1, R2, R3 and R4 are each independently a C1-10 hydrocarbyl group; and wherein A+is N+or P+to extract vanadium(V) from a source comprising vanadium. Description of the Figures Figure 1 shows the X-ray diffraction pattern of H4(Me4N)2V10O28.5H2O. Figure 2 shows the X-ray diffraction pattern of H3(Me4N)3V10O28.6H2O. Definitions The term “at least one” is synonymous with “one or more”, i.e. one, two, three, four, five, six, or more. As used herein the term “about” generally encompasses or refers to a range of values that one skilled in the art would consider equivalent to the recited values (i.e. having substantially the same function or result and / or achieving those in the same way). Where the term “about” is used in relation to a numerical value, it can represent (in increasing order of preference) a 10%, 5%, 2%, 1 % or 0% deviation from that value. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components. The term “consisting essentially of or “consists essentially of means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. Typically, when referring to compositions, a composition consisting essentially of a set of components will comprise less than 5% by weight, typically less than 3% by weight, more typically less than 1 % by weight of non-specified components. The term “consisting of” or “consists of” means including the components specified but excluding addition of other components. Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to encompass or include the meaning “consists essentially of or “consisting essentially of”, and may also be taken to include the meaning “consists of” or “consisting of”. For the avoidance of doubt, wherein amounts of components in a composition are described in wt. % or “% by weight”, this means the weight percentage of the specified component in relation to the whole composition referred to. For example, “the gasifier ash comprises from about 10% to about 60%, by weight, of elemental vanadium”, means that from 10 to 60% by weight of gasifier ash is provided by the elemental vanadium. Throughout this specification, the term “solution” is used to define a liquid mixture in which a solute is uniformly distributed within a solvent. Unless otherwise stated, the solvent comprises water, i.e. the solution is an aqueous solution. Detailed Description Vanadium extraction by acids such as sulfuric acid, requires organic liquid-liquid extraction steps and a large amount of sulfuric acid to recover the extracted vanadium from the organic solvent. The oxidative ammonium polyvanadate precipitation step also requires further purification of the vanadium. However, alkaline leaching offers a simpler approach to extracting vanadium, although aluminium oxide and silicon oxide present major challenges when it comes to purification of vanadium(V) from sodium-vanadium systems. A desilication process is required to reduce the silica concentration in the solution which results in a decrease in the extraction yield while adding process complexity. Additionally, the desilication process typically takes a long time due to the slow formation of the (Si-O-Al).xH2O compounds. It is one aim of the present invention, amongst others, to provide a method for extracting vanadium that addresses at least one disadvantage of the prior art, whether identified here or elsewhere, or to provide an alternative to existing methods. For instance, it may be an aim of the present invention to provide a method for extracting vanadium which is able to extract vanadium in high purity, without the dissolution of aluminium and silicon oxides. According to aspects of the present invention, there is provided a method for extracting vanadium(V) from a source comprising vanadium and a use as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows. According to a first aspect, there is provided a method for extracting vanadium(V) from a source comprising vanadium, the method comprising: (a) leaching the source comprising vanadium with a composition comprising a compound of formula (I): wherein R1, R2, R3 and R4 are each independently a C1-10 hydrocarbyl group; and wherein A+is N+or P+; wherein the composition further comprises an oxidising agent; and wherein said leaching extracts some of the vanadium from the source comprising vanadium to provide extracted vanadium(V); and (b) recovering the extracted vanadium(V) . The method is suitably performed in the order of (a) followed by (b). It has been found that the method disclosed herein may, for example, be used to refine gasifier ash that contains over 20 elements to ultrapure (such as at least 99 wt. %, such at least 99.5 wt. %) V2O5 which is highly desirable for vanadium redox flow batteries. Moreover, it has been found that the method disclosed herein may be used in a closed liquid loop, with solid feedstock and energy (electrical and heat) inputs, no ongoing chemical input, and solid V2O5 outputs. It has also been found that the by-products of the method are hydrogen and oxygen, which themselves are considered as valuable side products. The method disclosed herein may, for example, be performed in one undivided electrochemical reactor for oxidation operating at atmospheric temperature and pressure, and one membrane-divided electrochemical reactor for electrodialysis, operating at near-ambient temperature and pressure. These reactors are scalable reactors, facilitating the production of highly pure V2O5. The method disclosed herein may be implemented as one-pot extraction and purification of vanadium(V), without any co-extraction of aluminium or silicon oxides. The electrolysis of the vanadium- rich liquid allows simultaneous solvent and vanadium(V) recovery. The method uses only water and optionally produces hydrogen and oxygen as by-products. As no other by-products are produced, there is no need for wastewater treatment. The source comprising vanadium may additionally or alternatively be referred to herein as the source of vanadium. The source of vanadium may be an industrial or environmental source of vanadium. The source of vanadium may comprise vanadium compounds of a variety of sources and oxidation states. Vanadium compounds vary greatly depending on the source of the feedstocks. The mineralogical sources contain vanadium within the spinel structures of chromium, specifically in compositions like (Fe,Mg,Mn)(V,Cr)2O4 or (Fe,Mn)2(V,Ti)O4. Some compounds are introduced during the production of the secondary vanadium source. For example, Ca2V2O7can be found if the feedstocks were from the production of iron and steel as limestone is one of the key consumables in steel production. Refinery feedstocks however may contain NaVO3.H2O, VOSO4(H2O)6, FeVO4, VO2 or in general a mixture of cations and vanadate such as (Mg, Ca, Na, K, Fe)-V2O7.xH2O. The industrial or environmental source of vanadium may be selected from, for example, bottom or fly ash, petroleum boiler ash, gasifier ash, alumina slag, and spent catalysts from sulfuric acid production units. The industrial or environmental source of vanadium may comprise at least about 10% by weight, suitably at least about 15% by weight, for example at least about 20% by weight or at least about 25% by weight, for example at least about 30% by weight, such as about 35% by weight, of elemental vanadium. Methods of determining the amount of elemental vanadium are known in the art. For example, the amount of vanadium may be determined by inductively coupled plasma mass spectrometry (ICP-MS). Suitably the industrial or environmental source is gasifier ash. The composition of gasifier ash can vary depending on the type of feedstock (i.e., the material being gasified) and the specific gasification process used. Gasifier ash typically contains compounds such as silica, alumina, iron, calcium oxide, potassium, sodium, sulfur, chlorine, trace metals such as zinc and copper, carbon, and various minerals, such as Ca3V2O8, Ca2V2O7, Ca(VO3)2, Ni3V2O8, Fe2V4O13, FeVO4and Fe(VO3)2. The gasifier ash may comprise at least about 10 % by weight, suitably at least about 15 % by weight, for example at least about 20 % by weight or at least about 25 % by weight, for example at least about 30 % by weight, such as about 35 % by weight, of elemental vanadium. Suitably the gasifier ash comprises from about 10% to about 60%, by weight, of elemental vanadium, such as from about 15% to about 55%, by weight, for example from about 20% to about 50%, by weight, such as from about 25 % to about 45 %, by weight, for example from about 35 % to about 45 % by weight. The source comprising vanadium may be a metal-containing ore comprising vanadium. In contrast to metals like copper, nickel, or zinc, vanadium does not tend to accumulate in concentrated deposits. This is due to the close resemblance between the V3+and Fe3+cations, which leads to vanadium being typically present in small quantities within iron minerals. One such vanadium mineral, coulsonite (FeV2O4), forms a series with chromite (FeCr2O4) and magnetite (Fe3O4). The majority of vanadium production occurs through the extraction of titanomagnetites, either directly from titanomagnetite ores / concentrates or indirectly from the slag produced during the smelting of these ores. Titanomagnetite ores are typically associated with mafic igneous rocks and are found in substantial quantities. The method of the first aspect comprises leaching the source comprising vanadium with a composition comprising a compound of formula (I): wherein R1, R2, R3 and R4 are each independently a C1-10 hydrocarbyl group; and wherein A+is N+or P+; R1, R2, R3 and R4 may each be the same. R1, R2, R3 and R4 may each be different. As used herein, the term ‘hydrocarbyl’ is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having predominantly hydrocarbon character. Examples of hydrocarbyl groups include: (i) hydrocarbon groups, that is, aliphatic (which may be saturated or unsaturated, linear or branched, e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, and aromatic-, aliphatic-, and alicyclic-substituted aromatic substituents, as well as cyclic substituents wherein the ring is completed through another portion of the molecule (e.g., two substituents together form a ring); (ii) substituted hydrocarbon groups, that is, substituents containing non-hydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbon nature of the substituent (e.g., halo (especially chloro and fluoro), hydroxy, alkoxy, keto, acyl, cyano, mercapto, alkylmercapto, amino, alkylamino, nitro, nitroso, and sulphoxy); (iii) hetero substituents, that is, substituents which, while having a predominantly hydrocarbon character, in the context of this invention, contain other than carbon in a ring or chain otherwise composed of carbon atoms. Heteroatoms include sulphur, oxygen, nitrogen and encompass substituents such as pyridyl, furyl, thienyl and imidazolyl. Suitably R1, R2, R3 and R4 are each independently an unsubstituted C1-10 alkyl group. Suitably R1, R2, R3 and R4 are each independently a substituted C1-10 alkyl group, wherein the substituents are selected from halo (especially chloro and fluoro), hydroxy, alkoxy, keto, acyl, cyano, mercapto, alkylmercapto, amino, alkylamino, nitro, nitroso, and sulphoxy. Suitably R1, R2, R3 and R4 are each independently an unsubstituted C1-10 aryl group. Suitably R1, R2, R3 and R4are each independently a substituted C1-10aryl group, wherein the substituents are selected from halo (especially chloro and fluoro), hydroxy, alkoxy, keto, acyl, cyano, mercapto, alkylmercapto, amino, alkylamino, nitro, nitroso, and sulphoxy. R1, R2, R3and R4may each independently be an unsubstituted C1-10alkyl group, suitably an unsubstituted C1-9 alkyl group, for example an unsubstituted C1-8 alkyl group, or an unsubstituted C1-7 alkyl group, such as an unsubstituted C1-5 alkyl group. Suitably, R1, R2, R3 and R4 may each independently be an unsubstituted C1-5 alkyl group. Suitably, R1, R2, R3 and R4 are each the same. In one example, R1, R2, R3 and R4 are each butyl. The compound of formula(I) is suitably tetrabutyl phosphonium hydroxide or tetrabutyl ammonium hydroxide. Suitably, R1, R2, R3 and R4 are each propyl. Suitably, R1, R2, R3 and R4 may each independently be ethyl. In one example, R1, R2, R3 and R4 are each methyl. The compound of formula (I) is suitably tetramethyl ammonium hydroxide (TMA) or tetramethyl phosphonium hydroxide. The composition is suitably an aqueous composition, and suitably further comprises water. The compound of formula (I) is suitably water-soluble. The compound of formula (I) is suitably water-soluble at room temperature. Water-soluble is used in its typical sense to refer a compound that can dissolve in water. The United States Pharmacopeia (USP) has established the definitions below to define solubility: Descriptive terms Approximate volume of solvent in mL / g of substance Very soluble less than 1 Easily soluble from 1 to 10 Soluble from 10 to 30 Sparingly soluble from 30 to 100 Slightly soluble from 100 to 1,000 Very slightly soluble from 1,000 to 10,000 Practically insoluble more than 10,000 The compound of formula (I) is suitably soluble in water. The compound of formula (I) may be easily soluble in water. In the method of the first aspect, the composition further comprises an oxidising agent. The oxidising agent is suitably provided to oxidise vanadium compounds with oxidation states below 5 produced by thermal treatment of the carbonaceous vanadium-containing feed material, back to vanadium(V). The oxidising agent may be any suitable oxidising agent. For example, the oxidising agent may be any oxidising agent meeting the thermodynamic criterion of its equilibrium electrode potential EOx / Red > EVV / VIV. Examples of suitable oxidising agents include, but are not limited to, oxygen (O2); hydrogen peroxide (H2O2); potassium permanganate (KMnO4); sodium chlorate (NaClO3); chlorine (Cl2); sodium hypochlorite (NaClO); nitric acid (HNO3); peroxyacetic acid (PAA); potassium iodate (KIO3); bromine (Br2); iodine (I2); ozone (O3); sodium peroxide (Na2O2); peroxides (such as organic peroxides); permanganates (e.g., potassium permanganate, sodium permanganate); and persulfates (e.g., ammonium persulfate, sodium persulfate). The oxidising agent may comprise chlorite (ClO2-), chlorate (ClO3-) and / or hypochlorite anions (ClO-). For example, the oxidising agent may be selected from the group consisting of sodium chlorite, sodium chlorate, sodium hypochlorite, hypochlorous acid and potassium chlorate. The oxidising agent may also be selected from ‘active chlorine’ (Cl2 (aq), Cl3-, HClO, ClO-), active bromine or active iodine. By ‘active’, we mean to refer to chlorine, bromine or iodine that is readily available to perform oxidation. The composition may comprise more than one oxidising agent. Optionally (a) leaching the source comprising vanadium, for example the industrial or environmental sample, is under an elevated temperature, for example from about 50°C to about 120°C, such as from about 80°C to about 100°C. Optionally, (a) leaching the source comprising vanadium is not under autoclaving conditions. The method may further comprise: (a2) separating the extracted vanadium(V) into liquid and solids, optionally by centrifugation or vacuum filtration. Suitably (a2) occurs after (a) and before (b). Methods of separating the extracted vanadium(V) into liquids and solids may be any conventional solid- liquid separation means known in the art, such as by centrifugation and vacuum filtration. Separating the extracted vanadium(V) into liquids and solids suitably provides solid extracted vanadium(V) and a solution comprising extracted vanadium(V) (also referred to herein as the extracted vanadium(V) solution), i.e. the method may further comprise (a2) separating the extracted vanadium(V) into solid extracted vanadium(V) and a solution comprising extracted vanadium(V). The method may further comprise making the solid extracted vanadium(V) into a solution and enriching said solution with vanadium(V) to form an enriched vanadium(V) solution. This may be performed to increase the vanadium(V) concentration in the solution to a desired value. The enriched vanadium(V) solution may be contacted with ammonium chloride to form a precipitate of ammonium metavanadate. The ammonium metavanadate may be decomposed into vanadium(V) oxide. The method of the first aspect comprises: (b) recovering the extracted vanadium(V) . Suitably (b) involves recovering the extracted vanadium(V) as a precipitate, optionally during electrodialysis. Suitably, the extracted vanadium(V) is recovered during electrodialysis, wherein the electrodialysis is performed in an electrodialysis cell comprising: an anolyte comprising the extracted vanadium(V) solution; and a catholyte; and a cation-permeable membrane. The catholyte suitably comprises a compound of formula (I), as described herein. Suitably (b) involves precipitating the extracted vanadium(V) in the anolyte e.g. by electrolytic acidification induced by water oxidation. Suitably (b) involves regenerating the compound of formula (I) in the catholyte e.g. by electrodialysis coupled to water reduction. In one example the catholyte comprises tetramethyl ammonium hydroxide. In one example the catholyte comprises tetrabutyl phosphonium hydroxide. Any suitable cation-permeable membrane may be used. Examples of such membranes include NafionTM(DuPont Inc.), such as NafionTM424andNafionTM324. The cation-permeable membrane enables the selective migration of cations from anolyte to catholyte (such as the selective migration of TMA+), while enabling cathodic water reduction to hydrogen and hydroxide ions, which are precluded from the reverse transport process by the cation-permeable membrane. Suitably the electrodialysis cell further comprises a supporting electrolyte in the anolyte. Any suitable supporting electrolyte may be used. Suitable supporting electrolytes include acids having a pH of from 2 to 6. For example, the supporting electrolyte may be sulfuric acid. Suitably the electrodialysis cell further comprises tetramethyl ammonium hydroxide in the catholyte. The method may further comprise: (c) admixing the solution comprising extracted vanadium(V) with a further compound such as an ammonium salt, optionally ammonium sulfate, to form a precipitate, for example ammonium metavanadate. Suitably (c) occurs after (b). The further compound may be an ammonium salt. Any suitable ammonium salt may be used. Suitably the ammonium salt is ammonium chloride. Suitably the ammonium salt is ammonium sulfate. The further compound may be an acid. Any suitable acid may be used. Suitably the acid is hydrochloric acid, sulfuric acid or phosphoric acid. Suitably, the further compound, such as an ammonium salt, optionally ammonium salt, is admixed with the solution comprising extracted vanadium(V) until a pH of about 7 is reached. Admixture of the solution comprising extracted vanadium(V) and a further compound such as an ammonium salt, optionally ammonium sulfate, forms a precipitate. The precipitate is suitably a compound comprising ammonium and vanadium(V). Suitably the precipitate is ammonium metavanadate (NH4VO3). The method may further comprise: (d) decomposing the precipitate formed in (b) and / or (c) into vanadium(V) oxide. Methods of decomposing are known in the art. For example, the precipitate may be decomposed into vanadium(V) oxide (V2O5) by thermal decomposition The method may involve precipitation of an organo-vanadium compound in the anode chamber and / or deposited onto the anode. Suitably, using the same electrochemical equipment and depending on the anolyte bulk pH, an organo-vanadium compound may be deposited onto the anode or precipitated in the anode chamber. The organo-vanadium compound may be H4(Me4N)2V10O28.5H2O or H3(Me4N)3V10O28.6H2O. The organo-vanadium compound may be decomposed into vanadium(V) oxide. Thus, in one example, the method of the first aspect comprises: (a) leaching the industrial or environmental sample comprising vanadium with a composition comprising tetramethyl ammonium hydroxide, wherein said leaching extracts some of the vanadium from the industrial or environmental sample to provide a solution comprising extracted vanadium; `(a2) separating the solution comprising extracted vanadium into liquid and solids to provide solid extracted vanadium(V) and a solution comprising extracted vanadium(V); (b) recovering the extracted vanadium(V) as a principate during an electrodialysis process; (c) admixing the solution comprising extracted vanadium(V) with an ammonium salt, optionally ammonium sulfate to form a precipitate; and (d) decomposing the precipitates formed in (b) and / or (c) into vanadium(V) oxide. Suitably, the extracted vanadium may be vanadium(V) oxide. The vanadium(V) oxide may have a purity of at least about 95 wt.%, such as at least about 97 wt.%, for example at least about 99 wt.%. The purity of the extracted vanadium may be measured using inductively coupled plasma mass spectrometry (ICP- MS). According to a second aspect, there is provided a compound of formula H4(Me4N)2V10O28.5H2O The compound of the second aspect may comprise XRD peaks with the following characteristic peaks at 2θ at about 9.05°± 0.20°; about 9.32 °± 0.20°; about 10.19 °± 0.20°; about 10.91°± 0.20°; about 11.42°± 0.20°; about 12.37°± 0.20°; about 14.44 °± 0.20°; about 15.37°± 0.20°; about 16.00°± 0.20°; about 19.99°± 0.20°; about 22.86 °± 0.20°; about 24.09°± 0.20°; about 25.59°± 0.20°; about 28.05°± 0.20°; about 44.41 °± 0.20°; and about 50.43°± 0.20°. According to a third aspect, there is provided a compound of formula H3(Me4N)3V10O28.6H2O The compound of the third aspect may comprise XRD peaks with the following characteristic peaks at 2θ at about 7.90°± 0.20°; about 8.11°± 0.20°; about 8.85°± 0.20°; about 9.17°± 0.20°; about 9.57°± 0.20°; about 11.00°± 0.20°; about 11.80°± 0.20°; about 12.18°± 0.20°; about 13.12°± 0.20°; about 14.41°± 0.20°; about 15.30°± 0.20°; about 16.02°± 0.20°; about 17.93°± 0.20°; about 19.76°± 0.20°; about 21.83°± 0.20°; about 24.46°± 0.20°; about 25.02°± 0.20°; about 26.97°± 0.20°; about 27.89°± 0.20° and about 29.29°± 0.20°. The compounds of the second and third aspects have a general formula of Hx(Me4N)yV10O28.zH2O. XPS may be used to determine the ratio of x to y. TGA may be used to determine the water content. According to a fourth aspect, there is provided a compound according to the second or third aspect obtained or obtainable by the method of the first aspect. According to a fifth aspect, there is provided use of a composition comprising a compound of formula (I): wherein R1, R2, R3 and R4 are each independently a C1-10 hydrocarbyl group; and wherein A+is N+or P+to extract vanadium(V) from a source of vanadium. The source of vanadium and the composition comprising a compound of formula (I) are as described in relation to the first aspect. Suitably the compound of formula (I) is water-soluble as described in relation to the first aspect. In particular, the composition comprising a compound of formula (I) may further comprise an oxidising agent, as described in relation to the first aspect. Suitably, there may be provided use of a composition comprising a compound of formula (I): wherein R1, R2, R3 and R4 are each independently a C1-10 hydrocarbyl group; and wherein A+is N+or P+; and an oxidising agent, to extract vanadium(V) from a source of vanadium. Suitably, the use of the fifth aspect provides vanadium in the form of vanadium(V) oxide having a purity of at least about 95 wt.%, such as at least about 97 wt.%, for example at least about 99 wt.%. Features described above in relation to one of the foregoing aspects apply equally, mutatis mutandis, to the other aspects. For example, features described above in relation to the method of the first aspect of the invention apply equally to the use according to the fifth aspect, mutatis mutandis. Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims. The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention as set out herein are also to be read as applicable to any other aspect or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each exemplary embodiment of the invention as interchangeable and combinable between different exemplary embodiments. Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Therefore unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. Examples 20 g of the gasifier ash containing ca. 39 wt% elemental vanadium was added to 200 ml 2.78 M tetramethylammonium hydroxide solution. Herein, 4 g sodium chlorite was added as the oxidising agent. To eliminate sodium ions impurity from the process, active chlorine or ClOxcompounds could be directly in the solution instead. The solution was then heated to 90 °C for 540 minutes while being mixed. The liquid and the solids were separated by the conventional means such as centrifugation or vacuum filtration.82% vanadium(V) recovery can be achieved oxidatively, and 63% vanadium(V) recovery can be achieved non-oxidatively. The resulting solution was used as a feedstock for the electrochemical recovery process. 1 ml sulfuric acid (11 M) was added as a supporting electrolyte to a 120 ml tetramethylammonium hydroxide solution containing 0.89 M vanadium(V). The solution was then poured into the anode chamber of the electrochemical reactor. At the beginning of the experiment, the catholyte contained 23 mM tetramethylammonium hydroxide to provide ionic conductivity. The anolyte solution was electrolyzed to near-neutral pH. The resulting solution was mixed with an ammonium salt such as ammonium sulfate until white precipitates of ammonium metavanadate were formed. Optionally ammonium metavanadate can be decomposed thermally to >99 wt.% V2O5 and NH3 + H2O. The recovered ionic liquid was removed from the cathode chamber and was set aside to be recycled in the vanadium(V) leaching process. 1 ml sulfuric acid (11 M) was added as a supporting electrolyte to a 120 ml tetramethylammonium hydroxide solution containing 0.89 M vanadium(V). The solution was then poured into the anode chamber of the electrochemical reactor. The catholyte at the beginning of the experiment contained 23 mM tetramethylammonium hydroxide for the initial ionic conductivity. The anolyte solution was electrolyzed to pH 2 at which a compound containing vanadium and the ionic liquid cation (an organo- vanadium compound) was precipitated in the anode chamber. Similar compounds may be deposited onto the anode. Either of the organo-vanadium compounds can be decomposed thermally to >99% V2O5 and gaseous products, depending on the nature of the ionic liquid. As an alternative approach, the organo-vanadium compounds were mixed with an ammonium sulfate salt solution until white precipitates of ammonium metavanadate were formed. Optionally ammonium metavanadate can be decomposed to >99% V2O5 and NH3 + H2O. The recovered ionic liquid was removed from the cathode chamber and was set aside to be recycled in the vanadium(V) leaching process. The organo-vanadium compounds formed in Example 3 were filtered and dried under room temperature. XRD data were collected from the X’Pert 3 XRD machine. The XRD patterns of the organo-vanadium compounds formed in Example 3 are shown in Figures 1 and 2. Figure 1 shows the X-ray diffraction pattern of H4(Me4N)2V10O28.5H2O. Table 1 Pos. [°2θ] Height [cts] FWHM Left [°2θ] d-spacing [Å] Rel. Int. [%] 9.0478 2036.46 0.1571 9.76611 72.72 9.3175 2800.49 0.1571 9.48403 100.00 10.1865 448.29 0.1571 8.67680 16.01 10.9057 2671.32 0.1571 8.10616 95.39 11.4151 1079.51 0.1571 7.74553 38.55 12.3740 228.62 0.1571 7.14736 8.16 14.4417 269.14 0.1571 6.12837 9.61 15.3706 263.35 0.1571 5.76002 9.40 15.9999 245.98 0.1571 5.53486 8.78 19.9854 234.41 0.1571 4.43918 8.37 22.8621 199.67 0.1571 3.88669 7.13 24.0907 269.14 0.1571 3.69118 9.61 Pos. [°2θ] Height [cts] FWHM Left [°2θ] d-spacing [Å] Rel. Int. [%] 25.5891 651.17 0.1571 3.47835 23.25 28.0463 379.12 0.1571 3.17893 13.54 44.4078 164.94 0.1571 2.03835 5.89 50.4309 188.10 0.1571 1.80811 6.72 The peaks shown in Figure 1 are summarised in Table 1. Figure 2 shows the X-ray diffraction pattern of H3(Me4N)3V10O28.6H2O. Table 2 Pos. [°2θ] Height [cts] FWHM Left [°2θ] d-spacing [Å] Rel. Int. [%] 7.8979 1387.78 0.0050 11.18524 41.63 8.1148 1831.51 0.0062 10.88679 54.93 8.8535 2357.47 0.0050 9.98001 70.71 9.1720 2286.81 0.0050 9.63412 68.59 9.5702 2517.19 0.0050 9.23417 75.50 11.0035 3333.99 0.0050 8.03429 100.00 11.7998 844.63 0.0050 7.49382 25.33 12.1808 933.65 0.0062 7.26029 28.00 13.1203 218.09 0.0062 6.74244 6.54 14.4101 335.85 0.0062 6.14173 10.07 15.2968 261.48 0.0062 5.78764 7.84 16.0203 718.53 0.0050 5.52784 21.55 17.9315 235.14 0.0062 4.94275 7.05 19.7630 298.19 0.0062 4.48862 8.94 21.8335 298.19 0.0062 4.06743 8.94 24.4613 277.17 0.0062 3.63609 8.31 25.0188 718.53 0.0062 3.55633 21.55 26.9705 547.94 0.0062 3.30324 16.43 27.8865 649.11 0.0062 3.19678 19.47 29.2940 168.56 0.0062 3.04631 5.06 peaks shown in Figure 2 are summarised in Table 2. Example 4 For a continuous process, tetramethylammonium hydroxide solution containing 0.89 M vanadium(V) was continuously added to the anode chamber. The anolyte pH was maintained at near-neutral. The resulting anolyte solution was mixed with an ammonium salt such as ammonium sulfate until white precipitates of ammonium metavanadate were formed. Optionally ammonium metavanadate can be decomposed thermally to >99% V2O5 and NH3 + H2O. Continuously, the regenerated ionic liquid was removed, and water was added to the cathode chamber. Example 5 This example was to maximise the recovery of the vanadium(V) from the residue. 10 g of the post- reaction solid (residue) was mixed with 100 ml methanol at room temperature for half an hour. The solids and the liquid were separated by the conventional means. The solution was recycled 4-5 times to enrich the vanadium(V) content of the methanol solution. Concentrated ammonium chloride in methanol was added slowly to the recycled solution until no further white precipitates of ammonium metavanadate were formed. Optionally ammonium metavanadate can be decomposed thermally to >99% V2O5 and NH3+ H2O. Example 6 Descriptions of Reaction 1 - Reaction 17 are listed below: 1. Half reaction for the oxidation of the mixed (lower oxidation state) vanadium oxides to vanadium(V) 2. Half reaction for the reduction of hypochlorite to chloride 3. Overall redox reaction 4. Vanadium(V) dissolution at high pH 5. Chlorine generation at the anode 6. Water reduction at the cathode 7. Chemical reaction between the dissolved chlorine species and water 8. Hypochlorous acid dissociation reaction 9. Vanadium pentoxide dissolution reaction 10. Water oxidation reaction at the anode 11. Vanadium(V) condensation reaction 12. Water reduction at the cathode 13. Overall electrolytic process 14. Ammonium metavanadate precipitation reaction 15. Calcination reaction of ammonium metavanadate to vanadium pentoxide 16. Ammonia recovery 17. Overall vanadium recovery process The method involved mixing the ash in an electrochemical reactor containing a stainless steel AISI 316 cathode and Ti / RuO2anode, in the presence of tetramethylammonium chloride (TMA+Cl-). Under pH 9- 10, tetramethylammonium hypochlorite (TMA+ClO-) was produced that oxidised the lower oxidation state vanadium oxide (Reaction 1 and Reaction 2). The produced TMA+Cl- was converted back to TMA+ClO- in situ to complete the loop (Reactions 5 - 8). Subsequently, the pH of the solution was increased to >14 via a concentrated tetramethylammonium hydroxide solution and vanadium(V) was leached into the solution (Reaction 4 and Reaction 9). The leach liquor was sent to the membrane-divided electrochemical reactor in which H4TMA2V10O28 deposits were formed onto the surface of the anode. The deposits that formed between pH 5-6 were then removed mechanically and subsequently suspended in ammonia-methanol solution to eliminate the TMA+ions from the vanadate. The NH4VO3was then calcined at 550 °C to produce ultra-pure vanadium pentoxide. Undivided reactor Oxidation2Reaction 1 M+ −x V2O (s) → V O + 2 M + 2 ex5 2 5where M is a concomitant cation Reduction TMA ClO + H − −2O + 2 e → TMA Cl + 2OH Reaction 2Overall2M VO + T+ −Reaction 3 x2 MA ClO + H O → VO + TMA Cl + 2MOH x5 2 2 5V2O5 Reaction 4 V2O5 + 6 TMA OH → 2 [TMA]3 [VO4] (aq) + 3 H2Odissolution In-situ oxidation reaction Anode 2Cl− → Cl2 + 2e−Reaction 5 Cathode 2H2O + 2e− → 2OH− + H2 Reaction 6Electrolyte Reaction 7HOCl OCl− Reaction 8V2O5 Leaching:+Reacti 30 OH− + 5 V2O5 s, ash → 30 TMA+ + 10 VO3−on 9 30 TMA + ( ) 4 + 15 H2OAnode Reaction 10 14 H2O → 7 O2 + 28 + 28e− (pH ~6) Reaction 11 Cathode: Reactio 2O + 28 e−n 12 28 H → 14 H2 + 28 OH− Electrolytic30 TMA+ + 10 VO3−4 + 30 H2O →Reaction 13 Process:H4TMA2V1 O (s)+14 H (g) + 7 O (g)+ 28 TMA+ + 28 OH−0 28 2 2Ammonia Reaction 14 H4TMA2V10O28(s) + 10 NH4OH → 10 NH4VO3(s) + 2 TMA OH + 6 H2Oexchange Calcination at10 NH4VO3 → 5 V2O5 + 10 NH3 + 2H2O Reaction 15550oC Ammonia Reaction 16 recovery 10 NH3 + 10 H2O → 10 NH4OHOverall^^ ^^^^^^^^ + ^^^^ ^^^^^^ → ^^^^ ^^^^(^^) + ^^.^^ ^^^^ (^^)+ ^^ ^^^^^^^^Process Reaction 17 Example 7 For electrolysis with anode (a) redox couple (O|R) and cathode (c) redox couple (O’|R’), the reactor potential difference (U): has components due to thermodynamic equilibrium electrode potentials (E), activation and transport overpotentials (^) at anode (a) and cathode (c), and ohmic potential losses due to current I flowing through phase i of conductivity ^i with path length di and cross-sectional area Ai. The negative sign by convention signifies an anti-spontaneous process. The specific electrical energy consumption (kW h tTMA+-1) of the process per tonne of product TMA+with molar mass MTMA+(84 g mol-1) by reaction (22) with electron stoichiometry ^e,TMA+, unity in this case: Equation 19 depends linearly on the reactor potential difference U, and inversely on the charge yield (Φe^^^^^^+ ; equation 25) of the required reaction (22), i.e. transport of TMA+ions in competition with H+ions through the cation-permeable membrane; F represents the Faraday constant (96485 A s mol-1). Hence, the objective of the electrochemical reactor is selective migrational transport of TMA+ions from anolyte to catholyte through the cation-permeable membrane, across which the electric field strength (^^) provides the driving force. Transport rates may be approximated by the Nernst-Planck equation for the flux density: In which the last term, due to convective flow, can be assumed to be negligible within a membrane. Though the first term implies migrational transport rates increase linearly with the electric field strength across the membrane, rates are limited ultimately by mass transport to, rather than through, membranes. Current densities greater than those limited by mass transport rates result in decreased charge yields (Φe^^^^^^+ ; equation 25), and hence increased specific electrical energies (equation 19) and costs, which dominate running costs of the process and specific V2O5 product costs. Application of an electric field requires external pairs of electrodes, at which electrochemical oxidation, at anodes, and reduction at cathodes occur. In the absence of electro-active species in aqueous electrolyte solutions, those reactions will be water oxidation to oxygen and protons by reaction (21) and reduction to hydrogen and hydroxide ions by reaction (26). This requires an equilibrium potentialdifference (Δ^^ = ^^^^2⁄ ^^2^^ − ^^^^2^^⁄ ^^2 ) of 1.23 V at 298 K in equation (18), in addition to the non-equilibriumcontributions, due to the current, to the reactor potential difference U. The corresponding process chemistry is described by reactions (21-33) below, with a net overall reaction (33). However, by feeding hydrogen evolved from cathodes to (gas diffusion) anodes, at which it can be oxidised to protons by reaction (34), the absence of oxygen evolution removes the equilibrium potential differences requirement, decreasing the operating reactor potential difference (equation 18) and hence decreasing the specific electrical energy consumption, according to equation (19). The corresponding process chemistry is described by reactions (34-46) below, with a net overall reaction (46). V2O5 Recovery Process Chemistry by Electrodialysis with Water SplittingAnode: 14^^ ^^ → 7^^ (^^)+2 + −2 2 8^^ + 28^^ Reaction 21Cation permeable membrane:Maximise: Φ^^^^^^+(TMA+(anolyte) → TMA+(catholyte)); jTMA+ Reaction 22Minimise: [(1 − Φ + + +^^^^^^+)(H (anolyte) → H (catholyte))]; jH Reaction 23Current densities: jtotal = jTMA++ jH+Equation 24 Charge yield for TMA+: Equation 25 Cathode: 28^^2^^ + 28^^− → 14^^2(^^) + 28^^^^−Reaction 26Leaching: 30TMA+ + 30OH− + 5V O (s, ash) → 30TM+3−2 5 A+10VO4 + 15H2O Reaction 27Homogeneous solution (3 < pH < 6): 10VO3− +4 + 30TMA + 28H+ → H4TMA2V10O28(s) + 12H2O + 28TMA+Reaction 28 Overall Electrolytic Process:30TMA+ + 10VO3−+30H O → H TMA ( ) ( ) + −4 2 4 2V10O28(s)+14H2 g + 7O2 g + 28TMA + 28OH Reaction 29Ammonium Vanadate PrecipitationH4TMA2V10O28(s) + 10NH+4 + 10OH− → 10NH4VO3(s)+2[TMA++OH−] + 6H2O Reaction 30Ammonium Vanadate Calcination at 550oC / V2O5 Production 10NH4VO3 → 5V2O5(c, pure) + 10NH3(^^) + 5H2O Reaction 31Recycling Ammonia by Aqueous Absorption 10NH3(^^) + 10H2O → 10[NH+ −4 + OH ] Reaction 32Overall Process Chemistry:5V2O5(s,ash)+14H2O → 5V2O5(c,pure)+14H2 + 7^^2 Reaction 33Alternative V2O5 Recovery Process Chemistry by Electrodialysis with Hydrogen Oxidation Gas Diffusion AnodeGas Diffusion Anode: 15^^2(^^) → 30^^+ + 30^^− Reaction 34Cation permeable membrane:Maximise: Φ + +( ) +( ) +^^^^^^ (TMA anolyte → TMA catholyte ); jTMA Reaction 35Minimise: (1 − Φ^^^^^^+)(H+(anolyte) → H+(catholyte)); jH+ Reaction 36Current densities: jtotal = jTMA++ jH+Reaction 37 Charge yield for TMA+: Reaction 38 Cathode: 30H2O + 30e− → 15H2(g) + 30OH−Reaction 39Leaching: 30TMA+ + 30OH− + 5V2O5(s, ash) → 30TMA++10VO3−4 + 15H2O Reaction 40Homogeneous solution (3 < pH < 6): 10VO3−4 + 30TMA+ + 28H+ → H4TMA2V10O28(s) + 12H2O + 28TMA+Reaction 41 Overall Electrolytic Process:30TMA+ + 10VO3−+16H O → H TMA V O (s)+ 28T + −4 2 4 2 10 28 MA + 28OH Reaction 42Ammonium Vanadate PrecipitationH4TMA2V10O28(s) + 10NH+4 + 10OH− → 10NH4VO3(s)+2[TMA++OH−] + 6H2O Reaction 43Ammonium Vanadate Calcination at 550oC / V2O5 Production 10NH4VO3 → 5V2O5(c, pure) + 10NH3 + 5H2O Reaction 44Recycling Ammonia by Aqueous Absorption 10NH3(^^) + 10H2O → 10[NH+4 + OH−] Reaction 45Overall Process Chemistry: 5V2O5(s,ash) → 5V2O5(c,pure) Reaction 461 g sodium vanadate was mixed with 15 ml solution containing 1 M total sulfate and 2.78 M total tetramethylammonium cations balanced with hydroxide ions. Mixing until no solids were left in the vial. approximately 35 ml methanol was added to the solution while mixing until white crystals of sodium sulfate were formed. The methanol was removed by rotary evaporation and the resulting solution was used to recover highly pure vanadium as explained in Example 4. This work was supported by the Engineering and Physical Sciences Research Council [grant numbers EP / P51052X / 1 and EP / X52556X / 1 ].

Claims

Claims 1. A method for extracting vanadium(V) from a source comprising vanadium, the method comprising: (a) leaching the source comprising vanadium with a composition comprising a compound of formula (I):wherein R1, R2, R3 and R4 are each independently a C1-10 hydrocarbyl group; and wherein A+is N+or P+; wherein the composition further comprises an oxidising agent; and wherein said leaching extracts some of the vanadium from the source comprising vanadium to provide extracted vanadium(V); and (b) recovering the extracted vanadium(V) .

2. The method according to claim 1, wherein the source comprising vanadium is (a) an industrial or environmental source of vanadium, optionally, wherein the industrial or environmental source is selected from bottom or fly ash, petroleum boiler ash, gasifier ash, alumina slag, and spent catalysts from sulfuric acid production units, suitably wherein the industrial or environmental source is gasifier ash; or (b) a metal ore comprising vanadium.

3. The method according to claim 1 or claim 2, wherein R1, R2, R3 and R4 are each the same, optionally wherein R1, R2, R3 and R4 are each independently an unsubstituted C1-10 alkyl group, suitably wherein R1, R2, R3 and R4 are each methyl or wherein R1, R2, R3 and R4 are each butyl.

4. The method according to any preceding claim, wherein the compound of formula (I) is tetrabutyl phosphonium hydroxide.

5. The method according to any of claims 1-4, wherein the compound of formula (I) is tetramethyl ammonium hydroxide.

6. The method according to any preceding claim, wherein the oxidising agent comprises chlorite, chlorate or hypochlorite, for example sodium chlorite, sodium chlorate or sodium hypochlorite.

7. The method according to any preceding claim, wherein the oxidising agent is selected from active chlorine, active bromine, active iodine, or ClOx.

8. The method according to any preceding claim, wherein (a) leaching the industrial or environmental sample is under an elevated temperature, for example from about 50°C to about 120°C, such as from about 80°C to about 100°C.

9. The method according to any preceding claim, further comprising: (a2) separating the extracted vanadium into liquid and solids, optionally by centrifugation or vacuum filtration.

10. The method according to any preceding claim, wherein (b) involves precipitating the extracted vanadium(V) during electrodialysis, suitably wherein the electrodialysis is performed in an electrodialysis cell comprising: an anolyte comprising a solution comprising extracted vanadium(V); and a catholyte, and a cation-permeable membrane.

11. The method according to any preceding claim, wherein the catholyte comprises a compound of formula (I), suitably tetramethyl ammonium hydroxide.

12. The method according to claim 10 or 11, wherein the electrodialysis process further comprises a supporting electrolyte in the anolyte, suitably sulfuric acid.

13. The method according to any preceding claim, further comprising (c) admixing the solution comprising extracted vanadium(V) with an ammonium salt, optionally ammonium sulfate, to form a precipitate, for example ammonium metavanadate.

14. The method according to claim 13, further comprising(d) decomposing the precipitate into vanadium(V) oxide.

15. The method according to any preceding claim, wherein an organo-vanadium compound is precipitated in the anode chamber and / or deposited onto the anode, optionally, wherein the organo-vanadium compound is H4(Me4N)2V10O28.5H2O or H3(Me4N)3V10O28.6H2O; and / or optionally, wherein the organo-vanadium compound is decomposed into vanadium(V) oxide.

16. The method according to claim 9, wherein the solid extracted vanadium(V) is made into a solution and enriched with vanadium to form an enriched vanadium solution.

17. The method according to claim 17, wherein the enriched vanadium(V) solution is contacted with ammonium sulfate to form a precipitate of ammonium metavanadate.

18. The method according to claim 18, wherein the ammonium metavanadate is decomposed into vanadium(V) oxide.

19. The method of any preceding claim, comprising: (a) leaching the industrial or environmental sample comprising vanadium with a composition comprising tetramethyl ammonium hydroxide and sodium hydroxide, wherein said leaching extracts some of the vanadium from the industrial or environmental sample to provide a solution comprising extracted vanadium; ` (a2) separating the solution comprising extracted vanadium into liquid and solids; (b) recovering the extracted vanadium(V) liquid as a precipitate comprising vanadium(V) during an electrodialysis process; (c) admixing the solution comprising extracted vanadium(V) with an ammonium salt, optionally ammonium sulfate, to form a precipitate; and (d) decomposing the precipitates formed in (b) and / or (c) into vanadium(V) oxide.

20. The method according to any of claims 15, 18 or 19, wherein vanadium(V) oxide has a purity of at least about 95 wt.%, such as at least about 97 wt.%, for example at least about 99 wt.%.

21. A compound of formula H4(Me4N)2V10O28.5H2O 22. A compound of formula H3(Me4N)3V10O28.6H2O 23. The compound according to claim 21 or claim 22 obtained or obtainable by the method of any of claims 1 to 20.

24. Use of composition comprising a compound of formula (I):wherein R1, R2, R3 and R4 are each independently a C1-10 hydrocarbyl group; and wherein A+is N+or P+to extract vanadium(V) from a source of vanadium.

25. The use according to claim 24, wherein the compound of formula (I) is water-soluble.

26. The use according to claim 24 or claim 25, wherein vanadium is extracted in the form of vanadium(V) oxide having a purity of at least about 95 wt.%, such as at least about 97 wt.%, for example at least about 99 wt.%.

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