WO2021119728A1

WO2021119728A1 - Recovery of vanadium from slag materials

Info

Publication number: WO2021119728A1
Application number: PCT/AU2020/051337
Authority: WO
Inventors: David Robinson; Mark Daniel Urbani
Original assignee: Avanti Materials Ltd
Priority date: 2019-12-19
Filing date: 2020-12-08
Publication date: 2021-06-24
Also published as: EP4077751A1; AU2020408368A1; CN115427592A; CL2022001643A1; EP4077751A4

Abstract

A method for the recovery of vanadium from a vanadium containing feed stream, the method comprises: subjecting the vanadium containing feed stream to an acid leach step to form a slurry including a pregnant leach solution that comprises dissolved vanadium and a solid residue; passing the product of the leach step to a solid/liquid separation step to produce a pregnant leach solution that comprises dissolved vanadium; contacting the pregnant leach solution with a reducing agent to reduce one or more species in the pregnant leach solution; passing the pregnant leach solution to a precipitation step in which the solution pH is increased to precipitate a vanadium product; and recovering the vanadium product from the solution.

Description

Recovery of Vanadium from Slag Materials

TECHNICAL FIELD

[0001] The present invention relates to a method for the recovery of vanadium from slag materials. In particular, the method of the present invention is adapted to recover vanadium from steel slag through hydrometallurgical processing.

BACKGROUND ART

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0003] Vanadium is most prominently found within magnetite iron ore deposits and is typically present in slags generated during iron recovery processes. To recover vanadium, the slags are typically processed with the so-called ‘salt roast process’. In the salt roast process, the vanadium slag is mixed with alkali salts and subjected to a roast to produce sodium metavanadate. These vanadium values are subsequently leached with water. Vanadate values are then precipitated from the leach solution as ammonium metavanadate or ammonium polyvanadate. The high temperature roast step is highly energy intensive and so the vanadium tenor in the slag needs to be at a particular level to make the process economical.

[0004] A number of different hydrometallurgical process have been employed to process the slags for the recovery of vanadium. Such processes typically comprise an acid leach step in order to extract vanadium into solution. The main issue faced with the recovery of vanadium by hydrometallurgical means is that other metals species such as iron and titanium are typically co-extracted with the vanadium during the acid leach step. The separation of vanadium from a leach solution that also comprises dissolved iron species poses a significant challenge. Most processes by which this can be achieved are uneconomical. Both vanadium and iron can be found in multiple oxidation states and degrees of coordination with varying leach systems and the mixture of species containing these elements alone can be quite complex. In addition, many of the leach solutions containing vanadium and iron will contain a myriad of other impurities including manganese, chrome, calcium, sodium silica and aluminium. These impurities will need to be considered in the recovery process. As a consequence, many traditional separation techniques and established reagents are unable to cleanly separate vanadium from iron. In order to address this problem, most processes require that the leach solution is first treated to remove these impurities, particularly iron and titanium, before vanadium can be extracted. This adds complexity and overall cost to processes.

[0005] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

SUMMARY OF INVENTION

[0006] In accordance with a first aspect of the present invention, there is provided a method for the recovery of vanadium from a vanadium containing feed stream, the method comprises: subjecting the vanadium containing feed stream to an acid leach step to form a slurry including a pregnant leach solution that comprises dissolved vanadium and a solid residue; passing the product of the leach step to a solid/liquid separation step to produce a pregnant leach solution that comprises dissolved vanadium; contacting the pregnant leach solution with a reducing agent to reduce one or more species in the pregnant leach solution; passing the pregnant leach solution to a precipitation step in which the solution pH is increased to precipitate a vanadium product; and recovering the vanadium product from the solution.

[0007] In one form of the present invention, the method further comprises the step of: directing the vanadium product to a purification circuit to product a purified vanadium product. [0008] The method of the present invention is preferably adapted to recover vanadium products from slag materials that result from the steel industry. In addition to vanadium, such materials will contain iron, along with other species such as titanium. The method of the present invention allows for a vanadium product to be directly precipitated from the pregnant leach solution without the need to first remove iron species from the pregnant leach solution. This is advantageous where the vanadium recovery is targeted as the separate impurity removal steps are not required prior to the recovery of vanadium.

[0009] In one form of the present invention, the vanadium containing feed stream comprises a steel slag. Throughout this specification, unless the context requires otherwise, the term “steel slag” will be understood to refer to the slag byproduct of a steel manufacturing process. As would be appreciated by a person skilled in the art, when an iron containing material is exposed to high temperatures, impurities or gangue material are separated from the molten metal and are removed as a slag. This slag is subsequently cooled and a solid material is formed.

[0010] In one form of the present invention, the leach step the leachate used in the acid leach step is sulphuric acid, hydrochloric acid or carbonic acid.

[0011] In one embodiment of the present invention, the method further comprises the step of: subjecting the feed stream to a pretreatment process. prior to the step of subjecting the feed stream to the leach step.

[0012] In one form of the present invention, the pre-treatment process comprises a screening step to remove oversize particles.

[0013] Preferably, the pre-treatment process comprises one or more size reduction steps. More preferably, the one or more size reduction steps comprise one or more of a crushing step, a grinding step and a milling step.

[0014] In one form of the present invention, the pre-treatment process comprises one or more beneficiation steps. Preferably, the one or more beneficiation steps include one or more of a gravity classification step, a magnetic classification step and a floatation step. [0015] In one form of the present invention, the feed stream is subjected to a pre-leach step, prior to the leach step. Preferably, the preleach step comprises the contact of the feed stream with water to produce a preleach slurry. More preferably, the preleach slurry is subjected to a thickening step to increase the solid concentration.

[0016] In one form of the present invention, the step of: subjecting the feed stream to a leach step to form a slurry including a pregnant leach solution that comprises dissolved vanadium and a solid residue, more specifically comprises subjecting the feed stream to a leach step in one or more leach reactors. Preferably, the step comprises subjecting the feed stream to a leach step in two or more leach reactors. More preferably, the step comprises subjecting the feed stream to a leach step in three or more leach reactors. More preferably, the step comprises subjecting the feed stream to a leach step in four or more leach reactors. More preferably, the step comprises subjecting the feed stream to a leach step in five or more leach reactors.

[0017] In one form of the present invention, the step of subjecting the feed stream to a leach step is conducted at atmospheric pressure.

[0018] In one form of the present invention, the step of subjecting the feed stream to a leach step is conducted at elevated temperature.

[0019] In one form of the present invention, the solid/liquid separation step comprises the treatment of the slurry in a counter current decantation (CCD) circuit. In one embodiment, the CCD circuit comprises two or more thickeners arranged in series. In one embodiment, the CCD circuit comprises three or more thickeners arranged in series. In one embodiment, the CCD circuit comprises four or more thickeners arranged in series. In one embodiment, the CCD circuit comprises five or more thickeners arranged in series. In one embodiment, the CCD circuit comprises six or more thickeners arranged in series. In one embodiment, the CCD circuit comprises seven or more thickeners arranged in series.

[0020] In an alternative form of the present invention, the solid/liquid separation step comprises the treatment of the slurry in a filtration device. Preferably, the filtration device is a belt filter. [0021] Preferably, the step of contacting the pregnant leach solution with a reducing agent will reduce substantial proportion of ferric ions present in the pregnant leach solution to ferrous ions. In one embodiment, at least 95% of the ferric ions present in solution are reduced to ferrous ions. In one embodiment, at least 96% of the ferric ions present in solution are reduced to ferrous ions. In one embodiment, at least 97% of the ferric ions present in solution are reduced to ferrous ions. In one embodiment, at least 98% of the ferric ions present in solution are reduced to ferrous ions. In one embodiment, at least 99% of the ferric ions present in solution are reduced to ferrous ions.

[0022] In one form of the present invention, the step of contacting the pregnant leach solution with a reducing agent will target a solution Eh of < 250 mV against a Ag/AgCI reference electrode.

[0023] In one form of the present invention, the precipitation step comprises contacting the pregnant leach solution with a pH modifier to increase the pH of the solution. Preferably, the pH modifier is an alkaline substance. More preferably, the pH modifier is selected from one or more of magnesium carbonate, sodium bicarbonate and sodium carbonate.

[0024] In one form of the present invention, the precipitation step comprises increasing the solution pH to at least 4. In one form of the present invention, the precipitation step comprises increasing the solution pH to at least 4.1. In one form of the present invention, the precipitation step comprises increasing the solution pH to at least 4.2. In one form of the present invention, the precipitation step comprises increasing the solution pH to at least 4.3. In one form of the present invention, the precipitation step comprises increasing the solution pH to at least 4.4. In one form of the present invention, the precipitation step comprises increasing the solution pH to at least 4.5.

[0025] In one form of the present invention, the precipitation step comprises increasing the solution pH to between 4 and 5. In one form of the present invention, the precipitation step comprises increasing the solution pH to between 4.1 and 5. In one form of the present invention, the precipitation step comprises increasing the solution pH to between 4.2 and 5. In one form of the present invention, the precipitation step comprises increasing the solution pH to between 4.3 and 5. In one form of the present invention, the precipitation step comprises increasing the solution pH to between 4.4 and 5. In one form of the present invention, the precipitation step comprises increasing the solution pH to between 4.5 and 5.

[0026] In one form of the present invention, the precipitation step is conducted prior to the recovery of iron values from the pregnant leach solution.

[0027] In one form of the present invention, the precipitation step is conducted prior to the recovery of titanium values from the pregnant leach solution.

[0028] In one form of the present invention, the step of recovering the vanadium product comprises passing the slurry formed in the precipitation step to solid liquid separation step to produce a solid vanadium product and a barren solution. Preferably, the solid vanadium product is washed prior to further processing.

[0029] In one form of the present invention, the purification circuit more specifically comprises a salt roast step, a leach step and an ammonium metavanadate precipitation step. Preferably, the purification circuit further comprises a V2O5 production step.

[0030] In an alternative form of the present invention, the purification circuit more specifically comprises an acid leach step and a vanadium solvent extraction step. Preferably, the vanadium solvent extraction step will recover vanadium as a vanadyl sulphate solution.

[0031] In an alternative form of the present invention, the purification circuit more specifically comprises an ammoniacal leach step, a vanadyl product precipitation step and calcination step.

[0032] In accordance with a further aspect of the present there is provided a vanadium product produced by the process described above.

[0033] In accordance with a further aspect of the present invention, there is provided a purified vanadium product produced by the process described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

Figure 1 is a flowsheet of the process to recover a vanadium product; and

Figure 2 is flowsheet of various purification routes that may be utilised to purify the vanadium product produced in Figure 1 .

DESCRIPTION OF EMBODIMENTS

[0035] The method of the present invention relates to the recovery of vanadium from a vanadium containing feed stream. In a very broad sense, the method comprises the steps of: subjecting the vanadium containing feed stream to a leach step step to form a slurry including a pregnant leach solution that comprises dissolved vanadium and a solid residue; passing the product of the leach step to a solid/liquid separation step to produce a pregnant leach solution that comprises dissolved vanadium; contacting the pregnant leach solution with a reducing agent to reduce one or more species in the pregnant leach solution; passing the pregnant leach solution to a precipitation step in which the solution pH is increased to precipitate a vanadium product; and recovering the vanadium product from the solution.

[0036] The recovered vanadium product comprises a fairly high V2O5 component amongst other precipitated solids. In one embodiment, the recovered vanadium product comprises at least 10% vanadium.

[0037] The method the present invention is suitable to recover vanadium from steel slags. As would be appreciated by a person skilled in the art, steel slags comprise a large proportion of iron species. These iron species, along with other metal impurities, will be co-extracted into the leach solution during the leach step. These impurities will need to be considered in the recovery process. The process of the present invention provides a method by which a vanadium product can be selectively precipitated over iron species present in the pregnant leach solution, thereby permitting the recovery of vanadium directly from the pregnant leach solution without the need to first remove/recover iron.

[0038] In Figure 1 , there is shown a method for the recovery of vanadium 10 in accordance with an embodiment of the present invention. In this embodiment, a feed stream 12 is subjected to a pre-treatment process 14 to render the feed stream suitable for further processing.

[0039] In the embodiment shown in the figures, the feed stream 12 is first directed to a primary crusher 16 to break up large pieces of the feed stream 12 for further processing. The resulting material from the primary crusher is directed to a primary grinder 18 to reduce the particle size of the feed stream 12. The material resulting material is directed to screen 20 and any oversize material 22 is directed to a tertiary crusher 24 before being redirected to the primary grinder 18.

[0040] In one embodiment, the screen has a mesh size of between 75 pm and 500 pm.

[0041] The ground material 26 is directed to secondary grinding stage 28 to further reduce the particle size. The resulting material is directed to a cyclonic separator 30 and any oversize particles 32 are recycled back to the secondary grinding stage 28. As would be appreciated, by a person skilled in the art, the cyclonic separator 30 could be replaced with other particle size separation devices, such as for example a screen.

[0042] In one embodiment, the secondary grinding stage will reduce the particle size of the feed stream to the below 150 pm. In one embodiment, the secondary grinding stage will reduce the particle size of the feed stream to the below 140 pm. In one embodiment, the secondary grinding stage will reduce the particle size of the feed stream to the below 130 pm. In one embodiment, the secondary grinding stage will reduce the particle size of the feed stream to the below 120 pm. In one embodiment, the secondary grinding stage will reduce the particle size of the feed stream to the below 110 pm. In one embodiment, the secondary grinding stage will reduce the particle size of the feed stream to the below 100 pm. In one embodiment, the secondary grinding stage will reduce the particle size of the feed stream to the below 90 pm. In one embodiment, the secondary grinding stage will reduce the particle size of the feed stream to the below 80 pm.

[0043] The processed feed stream is directed to a pre-leach step (not shown) where it is contacted with water to produce a pre-leach slurry 34. The slurry 34 is then directed to a thickening step 36 to remove excess water and produce a concentrated leach feed stream 38. The inventors have found that the pre-leach step will help remove excess lime and other water soluble materials from the feed stream and consequently reduce leachate consumption in the later leach step. The solids content of the leach feed stream is controlled to a target solids content. The target solids content is dependent on the grade of the feed material and is manipulated such that sufficient water is present in the discharge from the leach to maintain all soluble salts in solution.

[0044] Preferably, the target solids content in the leach feed stream is between 5% and 40% by weight. More preferably, the target solids content in the leach feed stream is between 20% and 30% by weight. The inventors have found that the preferred target solids content in the leach feed stream is depended on the grade of the feedstock. Generally speaking, the higher the feedstock grade, the lower the target solids content.

[0045] The concentrated leach feed stream is directed to a leach circuit 40 where it is contacted with a leachate to leach vanadium and other metals into solution. In the embodiment shown in Figure 1 , the leach step is an acid leach step and the leachate is sulfuric acid 42. The leach circuit 40 comprises a number of leach reactors arranged in series. Sulfuric acid 42 is added to the leach reactors in sufficient excess to maintain a free acid concentration.

[0046] Whilst a tank leach process is described above, it is envisaged that the person skilled in the art may select from any leaching circuit available in the art to achieve the same effect.

[0047] In one embodiment, the concentration of the sulphuric acid is in the range of the range of 10% to 60% (w/w). In one embodiment, the concentration of the sulphuric acid is in the range of the range of 20% to 50% (w/w).

[0048] The leach can be exothermic and is typically operated at elevated temperature of 45-105°C with or without the addition of heat. [0049] The leach step will produce a leach slurry 44 that comprises a pregnant leach solution containing dissolved vanadium and other soluble metals, together with a residue of undissolved material. The leach step 40 will also result in the precipitation of calcium sulfate with varying degrees of hydration and this will form part of the slurry 44. The amount of calcium in the feed stream 12 will determine the amount of calcium sulfate that is produced.

[0050] The leach slurry 44 is directed to a solid liquid separation step to separate any solids from the pregnant leach solution. In the embodiment shown in Figure 1 , the slurry 44is directed to a counter current decantation (CCD) circuit 46. In the CCD circuit 46, the slurry 44 is washed in a series of thickeners until the majority of the dissolved metals are removed. To maximise recovery, the slurry 44 is directed into the first thickener and the wash solution is directed to the final thickener. The underflow and overflow flow counter current to one another. A flocculent 48 may be added to one or more of the thickeners to aid in the separation process. The overflow 49 from the first thickener is directed to further processing to recover metals. The underflow 50 of the final thickener, contains a high calcium sulfate content which can be recovered for sale. The inventors have found that the use of the CCD circuit 46 is advantageous as it involves multiple solid washing stages. This will ensure that a significant amount of the soluble metals will be separated from the solids that are produced during the leach step. As discussed above, calcium sulfate will be produced during the leach reaction. The use of the CCD circuit 46 will substantially clean this solid, allowing for the possibility of subsequent use.

[0051] Whilst the embodiment shown in the figures comprises a CCD circuit 46, it is envisaged that other solid liquid separation process may be utilised. For example, the slurry may be directed to a filtration step, using a belt filter or other filtration devices. The filtration step would preferably also include a wash step.

[0052] The pregnant leach solution 49 is directed to a reduction step 52 where it is contact with a reducing agent 54. The step of contacting the pregnant leach solution 49 with a reducing agent 54 will reduce substantial proportion of ferric ions present in the pregnant leach solution to ferrous ions.

[0053] Any reducing agent which will act to reduce a substantial portion of the ferric ions present in the pregnant leach solution to ferrous will be suitable for use. In one embodiment, the reducing agent is a metal powder. Preferably, the metal power is iron. In one embodiment, the reducing agent is selected from sodium sulfite, sodium metabisulphite and sulphur dioxide.

[0054] Preferably, sufficient reducing agent is added to reduce the solution Eh of < 250 mV against a Ag/AgCI reference electrode.

[0055] Following the reduction step 52, the pregnant leach solution is directed to a precipitation step 56, where the pH of the solution is increased to precipitate a vanadium product. As the reduction step 52 reduces the ferric species to ferrous ion, the increase in pH will precipitate vanadium products with a high degree of selectivity over iron and other impurity metal ions in the solution.

[0056] In one embodiment, the pH of the solution is increased by the addition of a pH modifier 58. Preferably, the pH modifier 58 is an alkaline substance. In one embodiment, the pH modifier 58 is selected from one or more of sodium bicarbonate and sodium carbonate.

[0057] In one embodiment of the present invention, the pH is increased to above 3. In one embodiment of the present invention, the pH is increased to above 3.5. In one embodiment of the present invention, the pH is increased to above 4.

[0058] In one embodiment of the present invention, the pH is increased to between 3 and 4.5. In one embodiment of the present invention, the pH is increased to between 3.5 and 4.5. In one embodiment of the present invention, the pH is increased to between 4 and 4.5.

[0059] The resulting slurry 60 is directed to a solid liquid separation step 62 to recover the precipitated vanadium products 64. In one embodiment, the solid liquid separation 62 step comprises a filtration step to recover the vanadium product 64. Preferably, the recovered vanadium product 64 is washed to remove and entrained iron other impurities.

[0060] The filtrate 66 from the solid liquid separation step 62 is a ferrous sulfate solution comprising dissolved impurity metals. The filtrate 66 is directed to a neutralisation circuit 68 where it is contacted with a neutralising agent, such as lime 70, to increase the solution pH and precipitate an iron rich calcium sulfate residue and an aqueous effluent. The residue 72 is recovered in solid liquid separations step 74 and directed to disposal.

[0061] The vanadium product 64 contains mixture of vanadium oxides and hydroxides with varying degrees of hydration. In one embodiment, the vanadium product 64 contains approximately 10% to 40% V2O5 equivalent. The vanadium product 64 may be dried and sold as a final product. Alternatively, the vanadium product 64 can be directed to a purification circuit to increase the vanadium purity.

[0062] In Figure 2, three alternative purification circuits are shown.

[0063] In a first embodiment, the purification circuit is more specifically comprises a salt roast step 78, a leach step 80 and a precipitation step 82. In the salt roast step 78, the vanadium product 64 is roasted at elevated temperature in the presence of a salt 84. In one embodiment, the salt is an alkaline or alkaline earth salt, preferably sodium carbonate. The amount of salt in the roast step is dependent on the vanadium content. In one embodiment, at least 5% w/w salt is added to the vanadium product 64. Where the vanadium product 64 comprises approximately 18% vanadium, approximately 7-8% w/w salt is added to the vanadium product 64.

[0064] In one embodiment, the roast step 78 is conducted at a temperature of at least 1 ,000 °C.

[0065] In one embodiment, the residence time of the roast step 78 is at least 1 hour.

[0066] The roasted product is directed to the leach step 80 to dissolve vanadium species. Preferably, the leach step comprises to contact of the roasted product with water.

[0067] In one embodiment, the leach step is conducted at a temperature of at least 70°C.

[0068] In one embodiment, the leach step is conducted for a residence time of at least 1 hour.

[0069] The vanadium-containing aqueous solution can be treated by known processes to recover vanadium. In one embodiment, aluminium sulfate is first added to the warm vanadium solution to facilitate silica (and alumina) removal. Following filtration, the purified vanadium solution is treated with ammonium sulfate in precipitation step 82 to precipitate ammonium metavanadate 86. The ammonium metavanadate may then be separated and subjected to a calcination step to produce solid V2O5.

[0070] In a second embodiment 88, the purification circuit comprises an acid leach step 90 to leach vanadium into solution. The pregnant leach solution is directed to a solvent extraction step 92 to recover vanadium. For most efficient separation of vanadium from iron the higher oxidation states of vanadium and iron are preferred in solution. Optimisation of acid strength and oxidant addition is required to economically effect this oxidation and phosphine oxides (e.g. Cyanex 923) or amine reagents (e.g. Alamine 336) can be used to selectively extract vanadium. Preferably, the vanadium solvent extraction step will recover vanadium as a vanadyl sulphate solution 94.

[0071] In a third embodiment 96, the purification circuit comprises an ammoniacal leach step 98 where it is contacted with an alkaline leachant to leach vanadium into solution. Preferably, the alkaline leachant is selected from NaHCC>3 or NFUOH. The pregnant leach solution is directed to a precipitation step 100 where is contacted with an ammonium species to precipitate NH4VO3. The resulting precipitate can be recovered and directed to a calcination step 102 to produce a V2O5 product 104.

Example 1

[0072] A steel slag sample was sourced from a steel production plant. A chemical assay of the material was conducted and the material was shown to contain 2.46% V, 17.9% Fe and 0.72% Ti.

[0073] The material was subjected to a sulphuric acid leach step using 50% sulfuric acid and 22% solids (1800 kg/t acid addition). The leach was conducted at a temperature of 100 °C. The leach curve is provided in Figure 3. As will be noted, the leach kinetics were rapid and extractions high (>99% V). The resulting leach solution was separated from the solids and a chemical analysis was performed on each. The leach liquor contained 10.4 g/L V, 78 g/L Fe and 2.8 g/L Ti. The final residue contained 25.8% Ca, 4.0% Si, 100 ppm V, 1000 ppm Fe and 200 ppm Ti.

Example 2 [0074] A sample of composite steel slag (400g) was added to 400gpl sodium carbonate (made up in Perth scheme water) at a pulp density of 15% solids by weight and agitated in a glass reactor. Hydrogen peroxide was added periodically to maintain an Eh close to zero. The test was maintained at 90°C for twelve hours. No kinetic samples were taken. The test was terminated after twelve hours and the pulp filtered, assayed and stored. The results are shown in Table 1 :

Table 1 Mass Vanadium Titan rum | Iron

[0075] The leach was successful, achieving a moderately high vanadium extraction. The addition of peroxide was hampered due to the addition at a high temperature resulting in flashing off oxygen gas. The mass gain was significant (50%), as expected, as a result of carbonate formation.

Example 3

[0076] A steel slag sample was subjected to a sulphuric acid leach and the filtrate was separated. Iron powder was added to the leach liquor. An Eh <250mV Ag/AgCI was targeted. The solution pH was increased to 4 with the addition lime to precipitate a vanadium product. Essentially complete vanadium precipitation was achieved (99.6%) to a high-grade precipitate (18.3% V).

Example 4

[0077] An investigation into the possible routes for purification was undertaken on the precipitated product of Example 3. A sample was leached was leached with 150gpl sodium carbonate at 90°C for six hours. The leach resulted in approximately 20% mass loss. Vanadium was leached, however the extraction was considerably lower than anticipated (19.8%). No impurities (iron and titanium) were present in the leach solution.

[0078] Based on the results of the sodium carbonate leach of a vanadium precipitate, the leach was repeated in the presence of an oxidant to promote extraction. Addition of peroxide was completed in stages. The initial Eh was -390mV and was increased to >0. The Eh continued to fall and was topped up after 2h. The vanadium extraction increased considerably (70.1%) as did the mass loss (~39%). Again there was minimal impurities present in the leachate.

[0079] The test was repeated at 400gpl sodium carbonate. The test improved on previous results showing an 83.5% extraction. The results are shown in Table 2.

Table 2

JR026 Sodium carbonate «flth oxidant j 70.1 | 12.2 | 3 j 3

Example 5

[0080] The vanadium product from Example 3 was subjected to a salt roast process to determine the effectiveness of this method to purify the vanadium product.

[0081] The head sample was 16% V (details below) and in a first pass at SRL 10% w/w Na2C03 was used as the salt addition and the test performed as follows:

• Roast temperature of 1200 deg C and residence time 2 hours

• Water leach done at 90 deg C and residence time of 2 hours

[0082] The second SRL test was performed under identical operating conditions with a further 10% w/w Na2C03 addition.

[0083] The results are shown in Table 3. Overall the extraction of vanadium was around 97 % and a total salt addition of amounts to an equivalent to 11 .5 % w/w (this much higher than a usual SRL operation due to the very high V level in the feed). Table 3: Solids Assays

[0084] The water leach from the above were combined and AMV and then V2O5 produced using standard methods and chemistry. The analytical composition of the product V2O5 from the SRL process on this high V intermediate showed 54.8 % V with major impurity being silica which may be an artefact from grinding the product prior to assay.

Example 6

[0085] A vanadium product was subjected to an alkaline leach process to determine the effectiveness of this method to purify the vanadium product.

[0086] 84% of V in a 400g sample of high V intermediate dissolved into 11 of sodium carbonate solution (made from 400 g of sodium carbonate dissolved in 11 of water) while adding 112 g of 30% H202, held at 90 °C for 12 hours. Equivalent deportment of iron and titanium to the PLS was less than 1% of that in the high V intermediate feed

[0087] This V PLS can be processed through ammonium metavanadate precipitation and V2O5 production using standard methods.

[0088] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. A method for the recovery of vanadium from a vanadium containing feed stream, the method comprises: subjecting the vanadium containing feed stream to an acid leach step to form a slurry including a pregnant leach solution that comprises dissolved vanadium and a solid residue; passing the product of the leach step to a solid/liquid separation step to produce a pregnant leach solution that comprises dissolved vanadium; contacting the pregnant leach solution with a reducing agent to reduce one or more species in the pregnant leach solution; passing the pregnant leach solution to a precipitation step in which the solution pH is increased to precipitate a vanadium product; and recovering the vanadium product from the solution.

2. A method according to claim 1 , wherein the method further comprises the step of: directing the vanadium product to a purification circuit to product a purified vanadium product.

3. A method according to claim 2, wherein the purification circuit comprises a salt roast step, a leach step and an ammonium metavanadate precipitation step.

4. A method according to claim 2, wherein the purification circuit comprises an acid leach step and a vanadium solvent extraction step

5. A method according to claim 2, wherein the purification circuit comprises an ammoniacal leach step, a vanadyl product precipitation step and calcination step.

6. A method according to any one of the preceding claims, wherein the method further comprises the step of: subjecting the feed stream to a pretreatment process, prior to the step of subjecting the feed stream to the leach step.

7. A method according to any one of the preceding claims, wherein the feed stream is subjected to a pre-leach step, prior to the leach step.

8. A method according to any one of the preceding claims, wherein the step of contacting the pregnant leach solution with a reducing agent will reduce substantial proportion of ferric ions present in the pregnant leach solution to ferrous ions.

9. A method according to any one of the preceding claims, wherein the step of contacting the pregnant leach solution with a reducing agent will target a solution Eh of < 250 mV against a Ag/AgCI reference electrode.

10. A method according to any one of the preceding claims, wherein the reducing agent is selected from a metal powder, sodium sulfite, sodium metabisulphite and sulphur dioxide.

11. A method according to any one of the preceding claims, wherein the precipitation step comprises contacting the pregnant leach solution with a pH modifier to increase the pH of the solution.

12. A method according to any one of the preceding claims, wherein the precipitation step comprises increasing the solution pH to at least 3.