CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present patent application claims the benefits of priority of U.S. Provisional Patent Application No. 62/905,740 entitled “PROCESS FOR THE RECOVERY OF VANADIUM OXIDES FROM VARIOUS MATERIALS”, and filed at the United States Patent and Trademark Office on September 25, 2019, the content of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a chemical process for the recovery of vanadium oxides in a high purity form from various differing feedstocks, particularly from iron-bearing solutions.

BACKGROUND OF THE INVENTION

[0003] Most vanadium compounds and metal are obtained via a multistep process that begins with the roasting of crushed ore with sodium chloride (NaCl) or sodium carbonate (soda ash, Na2C03) at about 850°C. The sodium metavanadate so-formed (NaVCri) can then be recovered by water leaching, and vanadium recovered from the resultant solution via conventional precipitation methods as trioxide, pentoxide or AMV (ammonium metavanadate).

[0004] One such process is described in US patent 4,477,416 by J.B. Goddard, entitled “Salt Roasting of Vanadium Ore in the Presence of Carbon”, and issued October 16 ^th , 1984. The main disadvantage of such a process, in addition to its requiring a high roasting temperature, is that the roasting conditions are ideal for forming a variety of chlorinated hydrocarbons, and it is therefore environmentally undesirable.

[0005] Leaching of vanadium from ores and other feed materials such as spent hydrodesulphurisation catalysts is well known with both hydrochloric acid and sulphuric acid. Typically, the vanadium is recovered from the leach solution by one of sulphide precipitation, ammonium salt precipitation, solvent extraction or ion exchange methods. [0006] Li Zeng and Chu Yong Cheng, in an article entitled “A Literature Review of the Recovery of Molybdenum and Vanadium from Spent Hydrodesulphurisation Catalyst”, published in Hydrometallurgy, Volume 98 (2009), pages 10-20, have reviewed all of the above methods of both recovering vanadium and molybdenum from solutions, and in separating the two elements. Particular emphasis was placed on solvent extraction methods.

[0007] A further article by the same authors entitled “Recovery of Molybdenum and Vanadium from Synthetic Sulphuric Acid Leach Solutions of Spent Hydrodesulphurisation Catalysts Using Solvent Extraction”, published in Hydrometallurgy, Volume 101 (2010), pages 141-147, describes a process wherein the highest oxidation state (+5) of vanadium and molybdenum (+6) can be recovered using the commercially-available solvent extraction reagent LIX ^® 63 (systematic name 5,8-diethyl-7-hydroxydodecane-6-oxime). Vanadium and molybdenum are subsequently separated from the caustic strip solution by selective precipitation. A disadvantage of this process is that both metals have to be in their highest oxidation state, thereby stressing the organic reagent with a very high oxidation-reduction potential, leading to appreciable oxidation and degradation of the reagent. The high oxidation state is necessary to prevent co-extraction of any iron present in the leach solution.

[0008] A similar process has been described by Pingwei Zhang et al., in an article entitled “Extraction and Selective Stripping of Molybdenum (VI) and Vanadium (IV) from Sulfuric Acid Solution Containing Aluminum (III), Cobalt (II), Nickel (II) and Iron (III) by LIX 63 in Exxsol D80”, published in Hydrometallurgy, Volume 41 (1996), pages 45-53. It is noticeable that in this process, the oxidation-reduction potential is lower, with vanadium being in a lower (+4) oxidation state. This is feasible, since there is actually very little iron present in the leach solution feeding the solvent extraction process, and hence its presence is very much less of a problem compared to the process described in the preceding paragraph. However, the extraction efficiency of vanadium (IV) is somewhat less than it is for vanadium (V).

[0009] Li Zeng, Qinggang Li and Liansheng Xiao, in an article entitled “Extraction of Vanadium from the Leach Solution of Stone Coal Using Ion Exchange Resin”, published in Hydrometallurgy, Volume 97 (2009), pages 194-197, describe a process very similar to that described in paragraph 0006, but using a resin instead of a solvent extraction reagent. Again, vanadium has to be in its highest oxidation state for the process to be effective. [0010] The foregoing processes all take measure to ensure that iron is neither present in the solution (the salt roast process), or that process conditions are adjusted to allow solvent extraction to take place. However, in making these adjustments, the oxidation-reduction potential has to be so high that it is deleterious to the organic reagents being used. Most of the above work has been conducted in sulphate media, but it can be assumed that in chloride media, because of the higher reactivity of chloride solutions, these degradation effects will be enhanced, and this is, in fact, exactly what applicant has found to be the case. The efficiency of the LIX ^® 63 reagent dropped rapidly from 100% in cycle 1 to <40% by cycle 5.

[0011] More recently, Benedikt Nowak and Herbert Weissenbaeck, in U.S. Patent Application No. 2019/0093194, published on March 28, 2019 and entitled “Process for the Separation of Vanadium”, describe a method of separating vanadium from iron-bearing solutions. This process oxidises iron and vanadium in solution with oxygen in an autoclave, and maintains the level of acid in solution very low, wherein vanadium and iron solids will precipitate. As noted, the process requires an autoclave to effect oxidation and precipitation. [0012] In light of the foregoing, there is a need for a new process which is able to recover vanadium in a pure form from liquors containing iron, particularly in a chloride medium, and without recourse to a very complicated solvent extraction process requiring a high oxidation- reduction potential.

SUMMARY OF THE INVENTION [0013] In accordance with a broad aspect of the present invention, a new process for recovering vanadium in a highly pure form is disclosed.

[0014] The invention is first directed to process for the recovery of a vanadium compound from a feed material comprising vanadium and iron compounds, the process comprising the steps of: a) leaching the feed material in a chloride medium to obtain a vanadium/iron-bearing leach solution; b) heating the vanadium/iron-bearing leach solution until at least a portion of the iron and vanadium compounds contained in the solution precipitates as solids; c) separating the solids containing iron and vanadium compounds from the solution; d) leaching the solids with a strong base solution for selectively dissolving the vanadium compounds from the solids; and e) precipitating the vanadium compounds from the strong base solution for recovering the vanadium compounds in a substantially pure form.

[0015] According to a preferred embodiment, the feed material may further comprise titanium compounds, step a) of the process then consisting in leaching the feed material in the chloride medium to obtain a vanadium/iron/titanium-bearing leach solution. The process then further comprises, after step a), the step of hydrolytically removing said titanium compounds as a titanium dioxide compound from said vanadium/iron/titanium-bearing leach solution.

[0016] According to a preferred embodiment, the process further comprises, after or conjointly to the leaching step d), the step of recovering the solids containing iron compounds.

[0017] According to a preferred embodiment, the feed material is derived from a titaniferous magnetite ore; from an ilmenite ore; from a primary vanadium ore; from an intermediate product, such as a titanium alloy baghouse dust, spent catalyst or fly ash; or a combination thereof.

[0018] According to a preferred embodiment, in step a), the chloride media may comprise magnesium chloride, zinc chloride, calcium chloride, ferric chloride, sodium chloride, potassium chloride, or a combination thereof, optionally combined with hydrochloric acid.

[0019] According to a preferred embodiment, in step a), the chloride media comprises hydrochloric acid, optionally combined with magnesium and/or zinc.

[0020] According to a preferred embodiment, the step b) of heating the iron-bearing leach solution is performed at a temperature of between about 160 and about 190°C, preferably of between about 180 and 190°C.

[0021] According to a preferred embodiment, in step e), between about 30% and about 90% of the iron and vanadium contained in the iron-bearing leach solution is precipitated, preferably between about 30% and about 70%, and more preferably about 50%. [0022] According to a preferred embodiment, in step d), the strong base comprises caustic soda (a.k.a. sodium hydroxide) solution having a concentration of between about 2% and about 20 % by weight, preferably of about 10% by weight.

[0023] According to a preferred embodiment, the step d) of leaching the solids with a strong base solution is performed at a temperature of between about 20 and about 100°C, preferably of between about 90 and about 100°C.

[0024] According to a preferred embodiment, step e) of precipitating the vanadium from the strong base solution is achieved by raising the pH of the solution to about 6.0-6.5, at a temperature of about 60-65°C, with the addition of ammonium chloride in such amount that the NH4CI/V ratio is approximately 10. Preferably, the pH is raised using ammonia.

[0025] If aluminium is present in the feed material, when the pH is initially raised to about 6.0- 6.5, aluminium hydroxide solids will form, which are preferentially removed before the addition of ammonium chloride.

[0026] According to a preferred embodiment, any feed materials wherein the vanadium may be solubilised into a chloride medium along with iron and other metals, and containing economic values of vanadium may be used. These include, but are not limited to, vanadium bearing titaniferous magnetite and ilmenite ores, primary vanadium ores such as might be found in Madagascar or South America, spent oil refining catalysts such as hydrodesulphurisation catalysts, fly ash emanating from coal-fired power stations, and titanium alloy baghouse dusts.

[0027] Advantageously, the process according to the present invention is able to recover vanadium in a pure form from liquors containing substantial amounts of iron, and optionally titanium, and without recourse to a very complicated solvent extraction process and high oxidation-reduction potentials. The resulting vanadium oxide is obtained in a form of high- purity and without the production of red mud.

[0028] Other and further aspects and advantages of the present invention will be better understood upon reading of the illustrative embodiments about to be described and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice. BRIEF DESCRIPTION OF THE DRAWING

[0029] The above and other aspects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawings in which:

[0030] Figure 1 is a flowchart illustrating the process according to preferred embodiments of the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0031] A novel hydrochloric acid-based process for recovering vanadium in a highly pure form is disclosed. Although the invention is described in terms of specific illustrative embodiments, it is to be understood that the embodiments described herein are by way of example only and that the scope of the invention is not intended to be limited thereby.

[0032] The terminology used herein is in accordance with definitions set out below.

[0033] As used herein % or wt.% means weight % unless otherwise indicated. When used herein % refers to weight % as compared to the total weight percent of the phase or composition that is being discussed.

[0034] By "about", it is meant that the value of weight %, time, pH, volume or temperature can vary within a certain range depending on the margin of error of the method or device used to evaluate such weight %, time, pH, volume or temperature. A margin of error of 10% is generally accepted.

[0035] The description which follows, and the embodiments described therein are provided by way of illustration of an example of particular embodiments of principles and aspects of the present invention. These examples are provided for the purposes of explanation and not of limitation, of those principles of the invention. In the description that follows, like parts and/or steps are marked throughout the specification and the drawing with the same respective reference numerals.

[0036] Referring to Figure 1, there is shown a schematic representation of a hydrochloric acid- based flowsheet, wherein the vanadium is dissolved along with iron and other impurities. [0037] The feed material 10, which may be, for example, but is not limited to a vanadium bearing titaniferous magnetite or ilmenite, is leached 11 in a recycled acidic chloride medium to dissolve predominantly all of the vanadium. Under these conditions, a significant proportion of the iron content will also dissolve. Additionally, other elements such as titanium, magnesium, aluminium and calcium may also dissolve. In a separate embodiment which is not shown in Figure 1, if calcium is present in the feed material, sulphuric acid may also be added to the leach in order to precipitate any calcium as calcium sulphate, which may be in the form of gypsum, hemi-hydrate or anhydrite, with the former phase preferred.

[0038] Also, if the feed material further comprise titanium compounds, leaching the feed material in the chloride medium allows obtaining a vanadium/iron/titanium-bearing leach solution. The process then further comprises, after step a), or before the heating/precipitation step b), the step of hydrolytically removing said titanium compounds as a titanium dioxide compound from said vanadium/iron/titanium-bearing leach solution.

[0039] The inventors have also invented a new process for the removal of titanium compounds from a feed liquor, as disclosed in provisional application No. U.S. 62/915,093 filed on October 15, 2019 and subsequent patent applications claiming priority thereof, the content of which being incorporated herein by reference. Such a process can be adapted and used for hydrolytically removing titanium dioxide from said vanadium/iron/titanium-bearing leach. The removing process comprises, for instance: i. leaching said vanadium/iron/titanium-bearing leach solution with a first HC1 solution having a hydrochloric acid content of 20% by weight or more, to obtain a first leachate comprising iron compounds and a magnetic concentrate comprising titanium dioxide; ii. leaching the magnetic concentrate comprising titanium dioxide with a second HC1 solution having a hydrochloric acid content of 20% by weigh or more, in the presence of a reductant, to obtain a second leachate comprising titanium dioxide and a solid residue; iii. removing the solid residue; and iv. hydrolysing the second leachate in presence of an oxidant to obtain pure titanium dioxide and HC1 solution. [0040] The recycled acidic medium comprises the acidic fdtrate 19 and acidic vapours 12 generated during the subsequent precipitation step 16 of iron and vanadium.

[0041] Any suitable leaching mechanism 11, such as atmospheric or pressurised stirred tank reactors, or with a prior calcining step, may be employed. Those skilled in the art will be able to achieve vanadium dissolution by one of these methods. This step is described merely as a means of obtaining a solution containing at least vanadium and iron.

[0042] The leaching conditions are generally determined such that ideally the maximum vanadium dissolution occurs. The principal chemical reactions for a titaniferous magnetite are as shown in reactions (1), (2) and (3).

Fe ₃ 04 + 8HC1 2FeCb + FeCh + 4H ₂ 0 (1)

V2O3 + 2HC1 2VOC1 + H2O (2)

V2O5 + 6HC1 2VOC13 + 3H ₂ 0 (3)

Similar reactions take place for other materials, such as magnesium, contained in the feed material.

[0043] Solid-liquid separation 13 may be effected by any convenient means, such as, but not limited to, flocculation and thickening, countercurrent decantation, fdter press or vacuum belt fdter. The solids 14 from the leach will be predominantly silica and calcium sulphate (if calcium is present), and as such are environmentally benign and may be disposed of as landfill.

[0044] The oxidation-reduction potential, well known as the ORP of the solution 15 is first adjusted to ensure that all of the vanadium is in the pentavalent state. This may be achieved by the addition of a suitable oxidant such as, but not limited to hydrogen peroxide. The temperature of the solution 15 from solid/liquid separation is raised to 160-190°C, preferably 170-180°C via any suitable means familiar to those skilled in the art. This causes the precipitation of at least a portion of the iron and vanadium as their respective oxides, according to reactions (4) and (5) shown below. As the temperature is raised, acidic vapours 12 are generated, which are recycled directly to the leaching circuit 11. The vapours are absorbed directly into the leaching slurry in order to extract their maximum heating value and to maintain the circuit water balance. 2FeCls + 3¾0 Fe ₂ 0 ₃ + 6HC1 (4)

2VOC13 + 3H ₂ 0 V ₂ Os + 6HC1 (5)

[0045] Growing the particles may be achieved through seeding by recycling a portion of the solids 20 up to 20% to the precipitation reactor, the optimum amount of recycling depending on the size of particle required.

[0046] It has been discovered that by allowing the particles 20 to grow in size to >2 microns, preferably >5 microns, and more preferably >20 microns, that hematite and vanadium oxide form separate, discreet phases and not a solid solution, such that the vanadium particles can be readily re-dissolved in a caustic solution, leaving the coarse hematite particles behind. The overall reactions taking place are shown in reactions (4) and (5), although it is understood that there is a quite complicated reaction pathway to arrive at the final, steady state.

[0047] Depending on the composition of the leach solution, only a portion of the dissolved iron and vanadium are precipitated in order to maintain the fluidity of the precipitation slurry, with the balance being recycled to the leaching stage. Preferably, 20-70% of the dissolved iron and vanadium is precipitated, more preferably 30-50%, the actual amount depending on the concetration of the metals in the incoming solution. If there is a significant amount of a non- hydroly sable chloride, such as magnesium or zinc, then up to 100% of the iron amy preferably be precipitated. Any aluminium present will also hydrolyse and precipitate as its oxide.

[0048] In this process, the combined hematite and vanadium solids 20 are removed from the slurry 17 via means of a suitable filter 18. The liquid phase 19 is recycled to the acid leaching reactor in order to recover its heat, re-use the contained acid and to maintain the water balance of the circuit. If impurities, such as magnesium, base metals or potassium, build up in this liquor, a bleed may be taken to control such impurities.

[0049] The combined hematite and vanadium solids are subjected to a caustic leach 21 under atmospheric conditions, at a temperature of 20-100°C, preferably 90-100°C. The vanadium particles are dissolved, forming a sodium metavanadate liquor, whereas the hematite particles remain unchanged. Since the hematite particles are coarse to start with, they do not a form a “red mud” typical of other caustic leach processes, but rather the slurry may be readily and rapidly fdtered on any suitable solid-liquid separation device 23. The hematite solids 24 are benign, and may be disposed of in a landfill. Alternatively, the hematite solids are sufficiently pure and uniform to merit being regarded as feed for a steel plant or for a pigment process.

[0050] The sodium metavanadate solution generated in this manner is essentially pure, and vanadium may be recovered by any method familiar to those skilled in the art, but especially via the precipitation of ammonium metavanadate (AMV, NH4VO3). Precipitation can be achieved for instance by raising the pH of the solution to about 6.0-6.5, for instance with ammonia, at a temperature of about 60-65 °C. If aluminium is present in the solution, it will precipitate under these conditions as Al(OH)3 solids and may be removed. Thereafter, ammonium chloride is added in such amount that the NH4CI/V ratio is approximately 10. AMV has a value on its own, but may be calcined under appropriate conditions familiar to those skilled in the art to either vanadium trioxide (V2O3) or vanadium pentoxide (V2O5).

[0051] The process will now be illustrated by way of examples. These examples are provided for illustration of certain embodiments of the invention, and are not intended as limitations thereof.

Example 1

[0052] The filtrate from a miniplant run on a titaniferous magnetite ore containing significant amounts of vanadium was heated up to 190°C. The results of the test are shown in

[0053]

[0054] Table 1, where it can be seen that predominantly all of the iron and vanadium, together with a small amount of manganese, reported to the solids phase, with the other elements remaining in the liquid phase.

[0055] Table 1. Behaviour of Elements in Hydrolysis and Acid Regeneration Test

[0056] Example 1 demonstrates the effectiveness of the technique in selectively recovering both iron and vanadium from a complex chloride leach solution into a clean solids phase, and that, if desired, 100% of the iron and vanadium in the feed may be recovered. It is preferred, however, to partially recover the iron and vanadium, and recycle the liquid phase. It makes the process easier in that if the recovery is run to completion, the system will dry out, so it is easier to recycle some liquid.

Example 2

[0057] The solids precipitate from Example 1 were leached at 100°C fortwo hours in a solution of 5% caustic soda, at a solids loading of 2.5%. No iron or manganese was detected in the caustic filtrate solution, and 70% of the vanadium was dissolved.

[0058] This example demonstrates that vanadium may be then be effectively separated from the iron solids, generating a caustic solution containing the vanadium, which may be recovered by any suitable method.

Example 3

[0059] A sample of dust from the processing of a titanium alloy containing 95% Ti, 3% V and traces of A1 was leached in hydrochloric acid. The amount of feed material added to the acid was such to give a titanium concentration in solution of 30-35 g/L, with the actual final value being 33 g/L. The ORP of the filtrate was adjusted to 100 mV versus Pt-Ag/AgCl electrode, and hydrolysed at 80°C in order to precipitate all of the titanium as titanium dioxide hydrate. The filtrate obtained after titanium removal contained 3 g/L Vanadium, and the ORP of the solution was adjusted with hydrogen peroxide to a level ensuring that all of the V was in its pentavalent state, giving the classic colour of such vanadium solutions. The pH was raised with caustic soda to 6.5, whereupon a white precipitate of aluminium hydroxide was formed. After the precipitate was removed by filtration, ammonium chloride was added and ammonium metavanadate was precipitated.

[0060] This example demonstrated the recovery of vanadium from solutions containing high levels of titanium, but no iron.

[0061] While illustrative and presently preferred embodiments of the invention have been described in detail hereinabove, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.