FIELD

[0001] The disclosed innovations are in the field of chemical and physical mineral processing techniques, particularly methods for processing of petroleum coke fly ash to extract vanadium values.

BACKGROUND

[0002] The refining of oil products, including heavy oils and bitumen, results in the production of significant volumes of petroleum coke as a by-product. By design, petroleum cokes tend to concentrate crude oil constituents such as metals and sulfur, leaving the oil products recovered from refining relatively free from these elements. Petroleum cokes are accordingly a potential source of metal values, but extraction of these values can be made more challenging by the nature of the matrix of materials in various petroleum cokes.

[0003] Significant volumes of petroleum coke are burned as fuel, converting much of the carbonaceous content of the coke into carbon dioxide and using heat from the exothermic reaction to produce useful energy. The solid material remaining after combustion is known as ash, and can be taken out of the combustion unit at different points. For example, bottom, middle and fly ash. Fly ash is the lightest material and can be collected by solid/gas separator equipment. Bottom ash is coarse enough to be collected directly from the reactor.

[0004] The ash products from petroleum coke combustion contain heavy metals present in the original coke material. In addition, silica and some uncombusted carbon units can also be present. One element that has been found in high concentration in ash products from petroleum coke combustion is vanadium.

[0005] Vanadium is a valuable metal used as an alloying element to make high strength steel. Vanadium can also be used in solution form (soluble salt) in the manufacture of flow batteries for energy storage. The unique and valuable properties of vanadium make vanadium highly sought after.

[0006] A wide variety of approaches have been suggested for the recovery of vanadium values from a wide variety of source materials (see Gupta and Krishnamurthy (1992), Extractive Metallurgy of Vanadium, Process Metallurgy 8, Elsevier Science Publishers B.V.). The treatment of ash materials from petroleum coke combustion to recover metal values, such as vanadium, molybdenum and gallium, has for example been reported in US Patent 4,966,761 , briefly commercialized by the patentee Carbovan. Processes of this kind, when implemented on a commercial scale, may make use of significant quantities of relatively high-cost alkali hydroxides, and may face challenges in metal extraction from solutions that contain relatively high amounts of silica. Similarly, US Patent 4,536,374 describes a soda ash roasting and water leach process, involving significant energy inputs in the roasting process, as is the case with conventional NaCI salt roasting processes that produce soluble sodium metavanadate prior to leaching (see Holloway, Preston Carl “Vanadium Recovery from Oil Sands Fly Ash” [Masters Thesis], University of Alberta, 2003). Particular challenges have been described in extracting vanadium from a petroleum coke fly ash that is characterized by high silicon and aluminum contents, in which metal values are reportedly retained in a glassy silica-alumina matrix, necessitating the use of a high temperature roasting of the fly ash in the presence of sodium chloride and water vapor - in part to inhibit silicon dissolution during a subsequent alkali leach (Gomez- Bueno, C.O., Spink, D.R. & Rempel, G.L. Extraction of vanadium from Athabasca tar sands fly ash. Metall Mater Trans B 12, 341-352 (1981).

SUMMARY

[0007] Methods are provided for treating challenging petroleum coke ash or ash concentrates that include a significant concentration of silicon and aluminum compounds. The methods make use of an alkali hydroxide pressure leach and do not require salt pre-roasting. Following leaching, the overall consumption of alkali hydroxide is mitigated in a subsequent base treatment of the leachate. The base treatment, for example with lime, may be carried out so as to precipitate silica from the leachate solution and, with a solid/liquid separation, produce a regenerated alkali hydroxide solution for recirculation and use in the pressure leach step. This may be carried out so that the vanadium-containing solution produced by the base treatment is largely free of silica, facilitating subsequent steps of vanadium recovery. Further, the vanadium-containing silica-depleted solution may be recycled to the alkali hydroxide pressure leach, to build the concentration of vanadium without adding to the silicate load in the leaching and base treatment circuit. [0008] An acidulation step may be provided downstream of the leaching and base treatment circuit, with a high-pH input solution made up of one or both of the vanadium-loaded leachate solution and/or the vanadium-containing silica-depleted solution from the base treatment stage. Acid treatment of this high-pH acidulation input solution will further precipitate residual silicate. Following a solid/liquid separation of the acid-precipitated silica from acidulation, vanadium values may be recovered from the resulting neutralized vanadium recovery solution.

[0009] The vanadium recovery solution, with or without acidulation, may for example be further subjected to a vanadium oxidation step to convert dissolved vanadium species to dissolved vanadium (V) oxoanion species in an oxidized vanadium recovery solution. The oxidized vanadium recovery solution may in turn be subjected to a vanadium solvent extraction (VSX) step to load vanadium species into a pregnant organic phase, and separating the pregnant organic phase from a spent vanadium recovery solution. Vanadium may be stripped from the pregnant organic phase into an aqueous sodium or ammonium vanadate solution, to provide a stripped organic phase that is recycled to the VSX step. Ammonium metavanadate may then be precipitated from the sodium or ammonium vanadate solution by addition of ammonium sulfate. The ammonium metavanadate may in turn be calcined to provide a vanadium pentoxide product.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a process flow diagram illustrating a process for extracting vanadium values from petroleum coke ash and/or a petroleum coke ash concentrate.

[0011] Figure 2 is a line graph illustrating vanadium (V) and silica (Si) concentrations with increasing lime addition in a base treatment of a vanadium leachate.

[0012] Figure 3 is a speciation diagram for vanadium species.

[0013] Figure 4 is a graph illustrating an extraction isotherm and McCabe Thiele Diagram for vanadium recovery. DETAILED DESCRIPTION

[0014] As illustrated in Figure 1, processes are provided for recovering vanadium values from a petroleum coke (petcoke) ash material, such as petroleum coke ash and/or petroleum coke ash concentrates, including materials derived from combustion of a bitumen coke feedstock. The petcoke ash material may for example comprise 1-10 wt% V2O5, or less than 10, 9, 8 or 7 wt%. The petcoke ash material may also be characterized as containing less than 1 wt% NaVCb, this being indicative that the material has not been subjected to NaCI roasting, because a NaCI roast would convert vanadium oxides in the ash to sodium metavanadate. [0015] The petcoke ash material may also be characterized by relatively high aluminum and silicon contents, for example being materials in which aluminum and silicon are the two most abundant metals, and/or where wherein silicon and aluminum form an aluminosilicate matrix in the petcoke ash. The petcoke ash may for example comprise at least 5 wt%, 10 wt% or 15 wt% S1O2, and/or at least 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% or 8 wt% AI2O3.

[0016] As illustrated, the petcoke ash material may be subjected to pressure leaching in an alkali hydroxide leach solution, for example having a concentration of an alkali hydroxide, such as NaOH, of between 0.5M and 5M. Leaching may for example be carried out at a leaching temperature of from 100°C to 300°C and a leaching pressure above atmospheric pressure during an effective leaching residence time, for example a residence time of less than 24 hours. Leaching conditions may be maintained so that the pressure leaching extracts at least 5%, 10%, 15%, 20% or 25% of the silicon in the petcoke ash, for example as sodium silicate (Na2SiC>3), and extracts at least 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% of the vanadium in the petcoke ash into a vanadium leachate solution leaving a solid leach residue. The vanadium leachate solution may then be separated from the solid leach residue in a solid/liquid (S/L) separation. As shown in Figure 1, the underflow from the S/L separation may go to a solids washing step.

[0017] As shown in Figure 1 , the vanadium leachate solution may be treated with a base, such as lime (Ca(OH)2) in a base treatment step so as to precipitate a silica-solid base-treatment-tailing material and produce a vanadium-containing silica-depleted solution comprising a regenerated alkali hydroxide. The concentration of silica in the vanadium-containing silica-depleted solution may for example be <1 , 2, 3, 4 or 5 g/L. The vanadium leachate solution may be characterized as having an initial dissolved vanadium content, and the base treatment conditions may be arranged so that no more than 1 wt% of the initial dissolved vanadium content of the vanadium leachate solution reports to the silica- solid base-treatment-tailing material. The silica-solid base-treatment-tailing material may then be separated from the vanadium-containing silica-depleted solution in a solid/liquid separation.

[0018] At least a portion of the regenerated alkali hydroxide in the vanadium- containing silica-depleted solution may be recirculated to pressure leaching, thereby offsetting alkali hydroxide consumed in the solubilisation of silicates. This recirculation will also have the beneficial effect of increasing the vanadium concentration of the vanadium-containing silica-depleted solution.

[0019] Vanadium values may be recovered from the vanadium-containing silica- depleted solution directly, or following a step of acidulation (as shown in Figure 1). Acidulation of the vanadium-containing silica-depleted solution prior to recovering vanadium values involves treatment of the vanadium-containing silica-depleted solution with an acid. The vanadium-containing silica-depleted solution may for example be mixed with an acid leachate from primary treatment of vanadium ores or concentrates. Acidulation may be carried out so as to precipitate an acid- precipitated-silica-solid tailing material and produce a neutralized vanadium- containing silica-depleted solution, in accordance with the following reactions:

2NaOH + H2SO4 Na ₂ S0 ₄ + 2H ₂ 0

Na ₂ SiC>3 + H ₂ S04 Na ₂ S04 + Si0 ₂ + H ₂ 0 [0020] The acid-precipitated silica may then be separated from the neutralized vanadium-containing silica-depleted solution by solid/liquid separation.

[0021] Prior to pressure leaching, the petcoke ash material may be subjected to a carbon floatation step, to separate a buoyant carbon tails fraction from a vanadium-containing solid floatation residue which is then directed to pressure leaching.

[0022] The recovery of vanadium values may involve a vanadium oxidation (VO) process, for example with a peroxide at elevated temperatures, or with other oxidants such as h SOs (Caro’s acid), NaS ₂ Oe (sodium persulfate), NaOCI (sodium hypochlorite), chlorine, ozone, SOVair (including variations other than the sodium salts, such as for example K, Mg or Ca salts). The VO process may accordingly be carried out so as to convert dissolved vanadium species to dissolved vanadium(v) oxoanion species in an oxidized vanadium recovery solution, as follows:

2V02 + H2O2 + H2SO4 = (V0 ₂ ) ₂ S04+ 2H2O.

[0023] In some embodiments, there may be some further oxidation and precipitation of iron that occurs during the VO process, in accordance with the following reaction, in which case any solids formed may be removed by clarification prior to solvent extraction of vanadium:

2FeS0 ₄ + H2O2 + 4H ₂ 0 = 2Fe(OH) ₃ +2H ₂ S0 ₄ .

[0024] In the VO process, vanadium species may form a range of polynuclear species, see Figure 3, while maintaining vanadium in the +5 oxidation state. For example a 10-V polynuclear species as shown below:

5(V02) ₂ S0 ₄ + 8H2O = (H ⁺ ) ₄ (H ₂ VIO028 ⁴ -) + 5H2SO4.

[0025] The oxidized vanadium recovery solution may then be subjected to a vanadium solvent extraction (VSX) process, to load vanadium species into a pregnant organic phase. In select embodiments, a tertiary amine, such as Alamine 336, may be used as the solvent, for example in a suitable diluent such as a kerosene. The tertiary amine, such as Alamine 336, may for example be conditioned with sulfuric acid solution prior to vanadium extraction. Alamine 336 has the formula (NR3), where the R groups represent hydrocarbon groups of 8 and 10 carbons respectively in about a 60 /40 ratio. Representing the conditioned Alamine 336 as NR3H ⁺ (HS04 ) the use of the conditioned Alamine 336 to extract vanadium may be represented as follows:

• Loading:

4(NR ₃ H ⁺ (HS0 ₄ -)) + (H ⁺ ) ₄ (H ₂ VIO028 ⁴ -) = (NR ₃ H ⁺ )4(H ₂ VIO028 ⁴ -) + 4H ₂ S0 ₄ .

[0026] In practice, the amine protonation, acid consumption and vanadium extraction reactions are complex. In general terms, vanadium +5 in aqueous solution exists primarily as the VCV cation at low pH and as the VCV anion at high pH. In the pH range 2 - 6 the main species is the orange decavanadate ion [VioCtes ^{' 6} ], which can exist in several protonated forms. These vanadium +5 oxyanions are readily extracted by protonated amines. Maximum loading tests suggest that the primary anion extracted is [VIO025 (OH)3] ³ , in a process that may be represented as follows:

[0027] The pregnant loaded organic phase may be washed and/or scrubbed with water or dilute acid or a vanadium +5 salt solution (for example) to remove any entrained aqueous solution or co-extracted impurities (including iron which may be loaded as a separate species or incorporated in the polynuclear vanadium species). [0028] The pregnant organic phase may then be separated from a spent vanadium recovery raffinate. In a V-stripping step, vanadium may be stripped, for example with sodium carbonate or aqueous ammonia, from the pregnant organic phase into an aqueous sodium or ammonium vanadate solution, which may contain sodium sulfate or ammonium sulfate derived from residual bisulfate loading of the solvent extraction chemical (e.g. Alamine 336). The stripping reaction with sodium carbonate solution may accordingly include:

• Vanadium stripping

(NR ₃ H ⁺ )4(H ₂ VIOC>28 ⁴ -) + 5Na ₂ C0 ₃ = 2.5Na ₄ V ₄ 0i2 + 3H ₂ 0 + 5C0 ₂ (g) + 4(NR ₃ ); and,

• Sulfate Stripping

(NR ₃ H ⁺ (HS0 ₄ -)) + Na ₂ C0 ₃ = Na ₂ S0 ₄ + C0 (g) + (NR ₃ ).

[0029] The stripped organic phase may, if necessary (which may not be the case where there is sufficient acid in the feed solution to SX to protonate the amine prior to decavanadate loading), then be conditioned and recycled to the VSX process:

(NR ₃ ) + H ₂ S0 ₄ = (NR ₃ H ⁺ (HS0 ₄ -)).

[0030] In a precipitation step, ammonium metavanadate may then be precipitated from the sodium vanadate solution, for example by addition of ammonium sulfate. In the event that there is an excess of iron in the strip solution, the strip solution may be heated and aged for a period of time for the iron to precipitate from solution. The precipitate may then be filtered, and the solution advanced to ammonium metavanadate precipitation:

5(NH ₄ ) ₂ S0 ₄ + 2.5Na ₄ V ₄ 0i2 = 10NH ₄ VO ₃ + 5Na ₂ S0 ₄ . [0031] The ammonium metavanadate (AMV) may then optionally be filtered and washed to remove entrained impurities (including sodium) and then treated in a calcination process, to provide a calcined vanadium pentoxide product:

2NH4VO3 = V2O5 + 2NHs(g) + H ₂ 0(g).

EXAMPLES

Example 1 : Caustic Leaching

[0032] Caustic leaching of a bitumen-derived petcoke bottom ash was carried out at 150 °C for 2 hours with an oxygen overpressure of 75 psig (the oxygen overpressure is an optional aspect of the present processes). A sample of 50 g of ash that was pulverized to 100% passing 37 microns was added to 1.11 L of 80 g/L NaOH solution. The caustic leach extracted 80% of the vanadium and 44.9% of the silicon. The reaction of caustic with silica/silicates produces soluble sodium silicate (Na2SiC>3). This exemplifies the consumption of caustic to solubilize silicates, and the resulting presence in the leach solution of silicates that are potential foulants when advancing the leachate solution to vanadium recovery by solvent extraction or ion exchange.

Example 2: Caustic Leaching with Base Treatment

[0033] Caustic leaching of a bitumen-derived petcoke bottom ash was carried out using higher strength solutions than in Example 1. The leach was carried out with 310 g of pulverized ash (-37 pm) at 20% solids (1240 g of solution containing 8% NaOH). After 2 hours of leaching, 76.4% vanadium extraction and 28.1% silica extraction were achieved. The vanadium concentration in the leachate was 7.27 g/L and the silica concentration was 14.9 g/L. These results illustrate that a high strength vanadium solution can be produced, but again with relatively high dissolved silica content and the attendant consumption of NaOH due to formation of Na2Si03. [0034] This leach solution was treated by sequentially adding lime to the solution to precipitate silica and regenerate NaOH. The reaction is Na2Si03 + Ca(OH)2 CaSi03 + 2NaOH. The graph in Figure 2 shows the results of this base treatment. The lime addition was added based on the stoichiometric addition of Ca(OH)2 to precipitate silica, phosphorus and aluminum. The concentrations of these three elements in the leachate were 14.9 g/L Si, 0.05 g/L Al and 0.254 g/L P. The main reaction is therefore the formation of calcium silicate. The removal of silica to below 1000 mg/L (1 g/L) was achieved with 100% stoichiometric hydrated lime addition. The vanadium concentration in solution was substantially unaffected by lime addition until an excess of lime was added. Use of an excess of lime leads to the formation of a calcium vanadate precipitate, and would accordingly result in loss of vanadium with the solid silica tails product. Hence, over addition of lime is undesirable.

Example 3: Carbon Floatation

[0035] Carbon flotation from a sample of mixed ash was carried out. The tailing (the unfloated material) was collected and combined for the purpose of alkali hydroxide leaching.

[0036] The results indicate that carbon can be floated to high recovery, and vanadium in the tailings is amenable to caustic leaching. The initial mixed ash was 2.46% V2O5 and 57.2% C®, the mixed ash concentrate was 5.13% V2O5 and 0.4% C®. The extraction of the mixed ash and the mixed ash concentrate were exemplified using the foregoing conditions of 308 g of solid added to 1200 g of 8% NaOH solution at 150 °C for 2 hours. The vanadium extraction was slightly higher (82% versus 80%) for the mixed ash concentrate. The silica extraction was reversed at 13% for the mixed ash and 10% for the mixed ash concentrate. These results illustrate that many types of petcoke ash material can be leached using the methods disclosed herein, and the presence of carbon does not adversely impact the vanadium extraction.

Example 4: Solvent Extraction of Vanadium

[0037] This Example illustrates the efficacy of solvent extraction of dissolved vanadium using the tertiary amine Alamine 336.

[0038] Tertiary amines soluble in a hydrocarbon diluent can be protonated to form a large organic cation in the organic phase. This large organic cation can then ion pair with metal anions in an aqueous phase to form organic soluble cation anion complexes thereby moving the metal containing ion from the aqueous phase into the organic phase. By vigorously mixing the respective tertiary amine containing organic phase with the respective metal anion containing aqueous phase over a range of organic to aqueous volumes ratios, then allowing the phases to separate and analyzing the resulting organic and aqueous phases for the metal of interest one can generate data for an extraction isotherm that is a function of the conditions under which the data was generated, which will be unique and representative of results under those conditions. With the extraction isotherm, it is possible to computationally model extractions, including modeling an advancing organic phase flow, an advancing aqueous phase flow and the extraction stage efficiencies, reflected in a McCabe Thiele diagram that allows the prediction of the degree of recovery of the metal of interest under the conditions used to generate the isotherm, for example with one, two or more counter current stages of extraction.

[0039] Vanadium in the plus 5 oxidation state will form vanadium-oxygen complex anions over a wide pH range, and these vanadium-oxygen complex anions can be extracted by tertiary amines. To model this behaviour in the context of the present processes, isotherm data was generated using an organic solution that contained 1 Volume % of Alamine 336 (a tertiary amine available from BASF) in the hydrocarbon diluent Aromatic 150 ND. The organic solution was vigorously contacted twice with a fresh 1.5 g/L sulfuric acid solution to give a fully protonated Alamine 336 solution. Fresh fully protonated Alamine 336 organic solution was then vigorously contacted over a range of organic to aqueous volumes with fresh aqueous solution containing 1.65 g/L V in the +5 oxidation state, about 5 g/L ferric iron and other metals, including trace amounts of molybdenum. Contact was for 10 minutes total to assure equilibrium and the temperature was 45 °C. An equilibrium pH of 1 .5 for the aqueous phase was targeted. Mixing was stopped late in the total mixing time with the aqueous phase showing a pH of 1.35 to 1.4 and a small amount of NaOH was added and stirring again started to raise the pH to 1.5. This was repeated again to get a final pH of 1 .5. After the phases were allowed to separate a final time the pH of each aqueous phase was determined. Then filtered samples of the respective organic and aqueous phases were subjected to vanadium analysis to give the isotherm data in Table 1. Table 1 : Isotherm Points for Vanadium Extraction

[0040] The isotherm data was used to generate a McCabe Thiele diagram, assuming an advance organic to advance aqueous flow of 1/1 , with 100% stage efficiency. The extraction isotherm along with the McCabe Thiele diagram for vanadium recovery for two counter current stages of extraction is shown in Figure 4. The McCabe Thiele diagram illustrates that approximately 84% vanadium recovery from an aqueous solution having 1 .65 g/L vanadium at a pH of 1.5 when using a 1 volume % solution of Alamine 336 in an aromatic diluent at 45 °C in a solvent extraction plant with two counter current extraction stages.

Example 5: Vanadium Stripping

[0041] This Example illustrates the effective stripping of vanadium from an Alamine 336 solvent. This was illustrated using 8 liters of a 1 volume % solution of Alamine 336 in Aromatic 150 ND, which was vigorously contacted twice with a fresh 1.5 g/L sulfuric acid solution for at least 2 minutes. This protonated 1 volume % Alamine 336 solution was next vigorously contacted for 10 minutes with an aqueous vanadium leach solution which was generated by pressure leaching a vanadium oxide ore, as described herein, and then using hydrogen peroxide to oxidize all the vanadium to the +5 oxidation state. The resulting vanadium loaded organic phase contained 960 mg/L V, with iron and molybdenum as impurities. This vanadium loaded organic solution was batch stripped with 200 ml of a solution containing 100 g/L of sodium carbonate at an organic/aqueous ratio of 1 . After each contact of the strip solution with the fresh vanadium loaded organic phase, the pH of the recovered vanadium strip solution was raised from about 9 back to pH 11 with the addition of sodium carbonate.

[0042] The vanadium concentration of the stripped organic was less than 1 mg/L indicating essentially complete stripping of the vanadium using sodium carbonate at a pH about 9 or greater. The final volume of the initial strip solution was 214 ml, and before crystallization or precipitation it contained 34.6 g/L V, ~1.7 g/L Fe, 110 g/L sodium and 102 mg/L molybdenum and it had a pH > 9.

Example 6: Crystallization of Ammonium Metavanadate [0043] This Example illustrates the effective crystallization of ammonium metavanadate (AMV) from a strip liquor prepared as described in Example 5. After sitting, the strip liquor produced in Example 5 showed signs of spontaneous crystallization and precipitation. The crystals and solids were filtered from the strip liquor and then washed with deionized water. The crystals dissolved in the wash water for the most part, leaving behind on the filter paper a small amount of red/brown precipitate. The resulting solids/crystal wash water was analyzed, with the result that it was found to contain 8.2 g/L vanadium, 325 mg/L Fe, 29.9 g/L sodium and 25.6 mg/L molybdenum - indicating that some of the stripped vanadium crystallized over time and was dissolved in the wash water.

[0044] The filtered strip liquor contained 33.3 g/L V, 1.65 g/L Fe, 89.4 g/L sodium and 97 mg/L molybdenum, and it had a pH of 10.1. This solution was subjected to iron removal by heating the solution to 95 °C for 7 hours to yield a solution containing 36.4 g/L, 117 g/L Na and 992 mg/L Fe, pH = 9.92. The pH of this solution was adjusted to 10.5 with NaOH and then brought back to -95-100 °C for about 6 hours. During heating the liquor eventually turned partially cloudy, and upon filtration to produce clear vanadium containing strip solution, a small amount of red solids were left on the filter paper. The final clear vanadium de-ironed strip solution contained 42.3 g/L V, 142 g/L Na and 126 mg/L Fe and showed a loss of volume due to evaporation.

[0045] Ammonium metavanadate was precipitated from a 79 ml sample of the final clear de-ironed solution above as follows. The 79 ml sample was stirred at 35 °C and then a 6-fold excess of ammonium sulfate on a mole basis was added slowly over about a 3-hour period while maintaining a pH of 8 by addition of sulfuric acid. The resulting solution was stirred and cooled overnight at room temperature. [0046] The crystals formed in the reaction vessel were then filtered to produce 15.4 grams of AMV. The filtrate solution contained 872 mg/L of vanadium.

Example 7: Calcination of AMV

[0047] The 15.4 g of AMV produced in Example 6 were calcined at 500°C for 3 hours, resulting in 12.2 g of calcine (21% weight loss). The initial calcined product was high in Na and the following wash sequence was used to reduce the Na content. The calcine was re-pulped with 200 ml of hot deionized water for 30 minutes at temperature and then filtered. It was then re-pulped with deionized water at pH by addition of sulfuric acid, mixed well for 30 minutes and then filtered. A final displacement wash was done on the filter cake using deionized water.

[0048] The thrice washed calcine showed 49.7% V, 1.82% Na, 0.09% Fe and 0.02 % Al as the major constituents. Direct conversion of the V to V2O5 suggests 88.7% V2O5, while a 100% minus impurities analysis suggests 97 - 98 % V2O5. [0049] The washes removed about 92% of the Na in the original calcine and around a third of the Fe, the bulk of which was handled in the first hot water wash. The next two washes acted as polishing steps.

[0050] An alternative to washing the calcine would be to wash the AMV with a solution of about 450 g/L ammonium sulfate in deionized water several times prior to calcination. High purity AMV may in turn be produced by recrystallization.

INCORPORATED REFERENCES

[0051] Citation of references herein is not an admission that such references are prior art to the present invention. Any priority document(s) and all publications, including but not limited to patents and patent applications, cited in this specification, and all documents cited in such documents and publications, are hereby incorporated herein by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein and as though fully set forth herein. Although various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. Terms such as “exemplary” or “exemplified” are used herein to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “exemplified” is accordingly not to be construed as necessarily preferred or advantageous over other implementations, all such implementations being independent embodiments. Unless otherwise stated, numeric ranges are inclusive of the numbers defining the range, and numbers are necessarily approximations to the given decimal. The word "comprising" is used herein as an open-ended term, substantially equivalent to the phrase "including, but not limited to", and the word "comprises" has a corresponding meaning. As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a thing" includes more than one such thing. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.