Methods of extracting vanadium and producing vanadium pentoxide

Abstract

This disclosure concerns a method of extracting vanadium, comprising mixing carbon soot ash with a leaching agent and an oxidising agent in a polar solvent in order to form a mixture and reacting the mixture in order to form vanadium 5 (V) ions; filtrating the mixture in order to separate a vanadium leachate from a leached ash; and purifying the vanadium leachate in order to obtain a vanadium filtrate. A weight ratio of carbon soot ash to polar solvent is about 1:2 to about 1:10. A mole ratio of leaching agent to oxidising agent is about 2:0.3 to about 2:2. This disclosure concerns a method of producing vanadium pentoxide.

Description

[0001]

[0002] Methods of Extracting Vanadium and Producing Vanadium Pentoxide

[0003] Technical Field

[0004] The present invention relates, in general terms, to methods of extracting vanadium and producing vanadium pentoxide.

[0005] Background

[0006] Over the past few years, the annual worldwide production of vanadium is estimated to hover around 100,000 metric tons, with a notable uptrend observed from 2018 to 2022. Due to its physical properties such high tensile strength, hardness, and fatigue resistance, Vanadium has been deployed widely in the iron and steel industry, and it plays a unique role in the manufacturing of alloys. In addition, it has huge potential in the renewable energy industry, as vanadium-based redox flow batteries (RFBs) could possibly become one of the leading energy storage solutions in the future.

[0007] According to the European Union and U.S. Department of the Interior, vanadium belongs to the categories 'critical raw materials' and 'critical minerals', which means it possess high economic importance and is susceptible to supply chain disruption. Vanadium market size is to increase more than one-fold from 2023 to 2033, reaching US$ 105.4 Billion. This suggests that its demand will rise, thus it is essential to ramp up production in order to have sufficient supply. Looking at the current sources of vanadium, approximately 70% of this material is derived from the slag generated during steel production while extraction from Heavy Petroleum Fuel (HPF) accounted for only 8% of the total demand in 2021.

[0008] It would be desirable to overcome or ameliorate at least one of the abovedescribed problems.

[0009] Summary

[0010] The present disclosure provides a method of extracting vanadium, comprising: a) mixing carbon soot ash with a leaching agent and an oxidising agent in a polar solvent in order to form a mixture and reacting the mixture in order to form vanadium (V) ions; b) filtrating the mixture in order to separate a vanadium leachate from a leached ash; and c) purifying the vanadium leachate in order to obtain a vanadium filtrate; wherein a weight ratio of carbon soot ash to polar solvent is about 1 :2 to about 1: 10; and wherein a mole ratio of leaching agent to oxidising agent is about 2:0.3 to about 2:2.

[0011] In some embodiments, the carbon soot ash comprises vanadium with a weight percent of at least 12 wt% relative to the carbon soot ash.

[0012] In some embodiments, the polar solvent is an aqueous medium.

[0013] In some embodiments, the leaching agent is selected from metal hydroxide, carbonate salt, or a combination thereof.

[0014] In some embodiments, the oxidising agent is selected from percarbonate salt, hydrogen peroxide or a combination thereof.

[0015] In some embodiments, when the leaching agent is metal hydroxide and the oxidising agent is hydrogen peroxide, the mole ratio of leaching agent to oxidising agent is about 2:0.4 to about 2: 1.

[0016] In some embodiments, when the leaching agent is metal hydroxide and the oxidising agent is hydrogen peroxide and percarbonate salt, the mole ratio is about 2:0.4:0.1 to about 2:0.4: 1.

[0017] In some embodiments, a weight ratio of carbon soot ash to leaching agent and oxidising agent is about 1 :0.5 to about 1: 1.2

[0018] In some embodiments, the mixture of step a) is reacted at a temperature of about 50°C to about 100°C, and for a duration of about 2 h to about 24 h.

[0019] In some embodiments, the mixture of step a) is characterised by a pH of about 8 to about 13.

[0020] In some embodiments, the vanadium leachate comprises vanadium (V) ions and at least one impurity, wherein a weight percent of vanadium (V) ions is about 60 wt% to about 90 wt% relative to the total weight of vanadium (V) ions and the at least one impurity.

[0021] In some embodiments, the purification step comprises adjusting a pH of the vanadium filtrate to about 8 to about 11.

[0022] In some embodiments, the purification step comprises mixing the vanadium filtrate with an absorbent; wherein a weight ratio of adsorbent and vanadium leachate is about 1 :5 to about 1 :200.

[0023] In some embodiments, the mixture of vanadium filtrate and absorbent is mixed at a temperature of about 50°C to about 100°C, and for a duration of about 20 min to about 24 h.

[0024] In some embodiments, the absorbent is selected from activated aluminium oxide, magnesium hydroxide, or a combination thereof.

[0025] In some embodiments, a weight ratio of activated aluminium oxide to magnesium hydroxide is about 1 : 1 to about 1 :4.

[0026] In some embodiments, the activated aluminium oxide is characterised by a pore size of about 1 nm to about 10 nm.

[0027] In some embodiments, the vanadium filtrate is characterised by a purity of at least 99.5%.

[0028] In some embodiments, the purification step comprises filtrating the vanadium leachate.

[0029] In some embodiments, the method further comprises a step of precipitating the vanadium (V) ions in the presence of a precipitating agent.

[0030] In some embodiments, the precipitating agent is an ammonium salt.

[0031] In some embodiments, the precipitating agent is dispersed in a solution, wherein the solution comprising about 20 wt% to about 40 wt% of the precipitating agent.

[0032] In some embodiments, the method further comprising a step of calcinating the vanadium filtrate in order to produce vanadium pentoxide.

[0033] In some embodiments, the calcination is performed at a temperature of about 300°C to about 700°C, and for a duration of about 2 h to about 8 h.

[0034] The present disclosure also provides a method of producing vanadium pentoxide, comprising: a) mixing carbon soot ash with a leaching agent and an oxidising agent in a polar solvent in order to form a mixture and reacting the mixture in order to form vanadium (V) ions; b) filtrating the mixture in order to separate a vanadium leachate from a leached ash; c) purifying the vanadium leachate in order to obtain a vanadium filtrate; d) precipitating the vanadium (V) ions as a vanadium (V) salt; and e) calcinating the vanadium (V) salt in order to produce vanadium pentoxide; wherein a weight ratio of carbon soot ash to polar solvent is about 1 :2 to about 1: 10; and wherein a mole ratio of leaching agent to oxidising agent is about 2:0.3 to about 2:2.

[0035] In some embodiments, the vanadium filtrate and / or vanadium pentoxide is characterised by a purity of at least about 99.2%.

[0036] In some embodiments, the vanadium filtrate and / or vanadium pentoxide is characterised by a Al impurity of less than about 0.4%.

[0037] In some embodiments, the vanadium filtrate and / or vanadium pentoxide is characterised by a Si impurity of less than about 0.4%.

[0038] In some embodiments, the vanadium filtrate and / or vanadium pentoxide is characterised by an absence of Fe, S, Na, or a combination thereof.

[0039] In some embodiments, the vanadium pentoxide is characterised by a particle size of less than 600 nm.

[0040] The present disclosure also provides a vanadium (V) solution and / or vanadium pentoxide obtained by the method as disclosed herein.

[0041] The present disclosure also provides a vanadium (V) solution and / or vanadium pentoxide as disclosed herein.

[0042] Brief description of the drawings

[0043] Embodiments of the present invention will now be described, by way of non limiting example, with reference to the drawings in which:

[0044] Figure 1 shows TEM images of (a) Carbon soot ash, (b) Leached ash and (c) Vanadium pentoxide.

[0045] Figure 2 shows SEM images of (a) Carbon soot ash, (b) Leached ash and (c) Vanadium Pentoxide.

[0046] Figure 3 shows FT-IR spectrum of (a) Carbon soot ash, (b) Leached ash and (c) Vanadium pentoxide.

[0047] Figure 4 shows XRD patterns of (a) Carbon soot ash, (b) Leached ash and (c)

[0048] Vanadium pentoxide

[0049] Figure 5 shows effect of catalysts on carbon soot ash leaching.

[0050] Figure 6A shows removal efficiencies of C and D at different temperatures on carbon soot ash.

[0051] Figure 6B shows removal efficiencies of C and D at different time on carbon soot ash.

[0052] Figure 7 shows removal efficiencies of different solid-to-liquid ratios.

[0053] Figure 8A shows removal efficiencies of different ratios of hydrogen peroxide in C.

[0054] Figure 8B shows removal efficiencies of different ratios of sodium percarbonate in D.

[0055] Figure 9 shows effect of pH on impurities removal efficiency.

[0056] Figure 1OA shows removal efficiencies of different adsorbents.

[0057] Figure 1OB shows effect of weight ratios on adsorbents (activated AI2O3: Mg(OH)2).

[0058] Figure 11 shows effect of a precipitating agent (ammonium sulphate) on precipitation.

[0059] Detailed description

[0060] The present disclosure is predicated on the understanding that solid carbon-rich residue from petroleum refining is a highly underutilized source of vanadium which offers substantial potential to help meet the global demand in the near future.

[0061] Carbon soot and ash (or carbon soot ash) are undesirable by-products from the combustion and gasification of carbon-based materials, typically fossil fuel. Common methods of dealing with them includes landfill and disposal via incineration. As vanadium is an organometallic complex, it can be found in all crude oils, and its content varies from less than 1% to 60% in carbon soot. Being one of the most troublesome metals present, it is regarded as toxic and has the capability to inflict a variety of injuries, especially respiratory effects, once it is inhaled into the body. During the landfill and incineration of carbon soot, particular matters that contains vanadium will be released into the environment, resulting in devastating consequences to the public health.

[0062] The removal of vanadium from carbon soot not only eliminates its adverse health effects, but also contributes significantly to the global demand.

[0063] In a typical process, vanadium extraction involves three major steps: roasting, leaching, and precipitation. Roasting vanadium slag with different additives yields various oxidation states of vanadium ions. These can then be dissolved by leaching agents, such as sulfuric acid, water or carbonates. Subsequently, vanadium is separated from the leaching solution through precipitation.

[0064] Gradient oxidation roasting-acid leaching (GORA) process has been introduced to extract vanadium from stone coal. It involves two roasting stages conducted at 650°C and 850°C, which facilitate the formation of a porous structure, enhancing the subsequent leaching reactions. While this method removes the need for additives, the necessity for high temperatures is a significant drawback. To address this, microwave oxidation roasting has been proposed for recycling vanadium from slag. Microwave heating to temperatures between 500°C and 550°C may assist in breaking down the dense slag structures, improving extraction rates. Apart from roasting with heat, another approach involves the mechano-chemical activation of vanadium-bearing shale with NaF as activator.

[0065] The activation treatment reduces the energy barrier on the surface, accelerating its dissolution and thereby increasing leaching efficiency to 90% at temperature of 95°C. Although the process temperature is significantly lowered, the use of chemical activators poses resource wastage issue. To mitigate this, a study on the use of iron (III) oxide-assisted mechano-chemical activation suggests that the chemical activator can be replaced with vanadium tailings waste, eliminating the need for extra resources. However, the large accumulation of vanadium tailings not only causes a loss of vanadium as a resource but also leads to environmental pollution.

[0066] The requirement for a leaching agent in the subsequent leaching step is also problematic due to its potential environmental harm upon disposal. To tackle this issue, leaching agents which are more eco-friendly are introduced. For example, citric acid has been explored for extracting vanadium from gasifier slag, achieving up to 98.8% recovery at 75°C. However, gypsum formation decreases recovery rates over time. Besides chemical leaching, bioleaching has gained attention as well. Studies have been conducted on the use of microorganisms like Acidithiobacillus ferrooxidans and Shewanella oneidensis MR-1 to extract Vanadium from raw minerals and vanadium tailings. However, bioleaching yields a relatively low efficiency of 59% and has a long reaction duration. Ultrasonic-aided leaching has been tested. Studies on recovering vanadium from leaching tailings enhanced by ultrasound in H2SO4 - H2O2 system uses the effect of ultrasound to decompose H2O2 into »OH radicals. This provides higher oxidation potential, thus accelerating the reaction process and achieving a leaching efficiency of 72%. However, the use of a strong base is hazardous in nature and requires additional clean up steps. Apart from extracting vanadium from slags and tailings, some studies have explored the potential of leaching vanadium from spent catalyst. Research have been conducted on the leaching of vanadium from spent hydrodesulfurization (HDS) catalysts and selective catalytic reduction (SCR) catalysts. These methods allow the utilization of secondary resources to obtain vanadium while eliminating the potential environmental harm from catalyst disposal. However, they require additional leaching agents, implying increased resource consumption.

[0067] After leaching, separating and precipitating are crucial to ensure the extraction efficiency and purity of vanadium. Various techniques have been put forward to separate vanadium from different impurities, typically other metals. For instance, a polymer inclusion membrane electrodialysis process (PIMED) have been proposed to separate vanadium from molybdenum in acidic sulphate leaching solution. Such separation is based on the difference in affinities between the metal ions and carrier. For iron impurities, a study suggests using citric acid as complexing agent to separate vanadium from iron (III) in the leaching solution, achieving over 80% extraction in a low pH environment. However, membrane electrodialysis is an expensive process, and is not suitable for scaling up to an industrial scale. Another route for separation and selective extraction of vanadium from leaching solution is sucrose reduction-HzCh selective oxidation method. This method utilizes the difference in redox properties to separate vanadium from chromium. Vanadium (V) is first reduced, then selectively oxidized with H2O2, and eventually calcined to V2O5. Although pure vanadium can be extracted at an extraction ratio of 93.8%, the complexity of this method poses a challenge for execution.

[0068] While various modifications have been made in all three steps of the vanadium extraction process, the main issues remain: low extraction efficiency, potential environmental harm, the requirement for high temperature, resource wastage, and high complexity.

[0069] In some embodiments, the present disclosure is directed to vanadium extracted from carbon soot ash via leaching using a green reagent, achieving an efficiency greater than 95%. This method is straightforward, and it incorporates a leaching agent and an oxidising agent for the oxidation step, minimizing the loss of oxidizing reagents. Additionally, the process operates at a low temperature, effectively reducing the need for heat, and minimizing the loss of carbon materials to near zero. Furthermore, the resulting vanadium has less than 1% impurity from other metals, allowing for the retrieval of high-purity vanadium.

[0070] The present disclosure provides a method of extracting vanadium, comprising : a) mixing carbon soot ash with a leaching agent and an oxidising agent in a polar solvent in order to form a mixture and reacting the mixture in order to form vanadium (V) ions; b) filtrating the mixture in order to separate a vanadium leachate from a leached ash; and c) purifying the vanadium leachate in order to obtain a vanadium filtrate.

[0071] The method extracts and converts V3+and V4+ions into V5ions. This occurs at least in step a). As will be discussed herein, through the interplay of the leaching agent and oxidising agent, V5+ions may be preferentially retained in the leachate while minimising the wt% of dissolved impurities, thus improving its extraction.

[0072] Carbon soot ash refers to the fine black particulate matter that is produced as a by-product of the incomplete combustion of carbon-based fuels, such as wood, coal, or oil. The key components of carbon soot ash are carbon soot and ash. Carbon soot consists of fine, black carbon particles that are the result of incomplete combustion. Ash refers to the non-combustible mineral residues that remain after the carbon-based fuel has been burned. Ash can contain various inorganic compounds, such as silicates, aluminates, and metal oxides, depending on the composition of the original fuel. Carbon soot ash is typically produced in processes like domestic wood burning, industrial furnaces, and vehicle engines. It can be a significant source of air pollution and can contribute to environmental issues such as smog, acid rain, and respiratory health problems.

[0073] In some embodiments, the carbon soot ash is derived from oil refinery carbon waste. The carbon soot ash produced from oil refineries contains about 12 to 30 weight percentage of V. The carbon soot ash also comprises metals like aluminium, nickel, iron, titanium, chromium, cobalt, zinc and manganese in various quantities, which may interfere the vanadium extraction process. The presently disclosed method avoids (or at least minimises) the interference from these metals from the extraction of vanadium.

[0074] In some embodiments, the carbon soot ash comprises vanadium with a weight percent of at least 12 wt% relative to the carbon soot ash. In other embodiments, vanadium is at least 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, or 25 wt%. In some embodiments, the weight percent is about 12 wt% to about 40 wt%, about 15 wt% to about 40 wt%, about 15 wt% to about 35 wt%, about 15 wt% to about 30 wt%, or about 15 wt% to about 25 wt%.

[0075] A polar solvent is a type of solvent in which the molecules have an uneven distribution of electrons, resulting in a partial positive and partial negative charge within the molecule. This polarity allows the solvent to effectively dissolve other polar or ionic substances. Examples of polar solvents include, but is not limited to, water, ethanol, acetone, dimethyl sulfoxide, and formamide.

[0076] In some embodiments, the polar solvent is an aqueous medium. This allows for the method to be scalable and sustainable.

[0077] The term 'aqueous medium' used herein refers to a water based solvent or solvent system, and which comprises of mainly water. Such solvents can be either polar or non-polar, and / or either protic or aprotic. Solvent systems refer to combinations of solvents which resulting in a final single phase. Both 'solvents' and 'solvent systems' can include, and is not limited to, pentane, cyclopentane, hexane, cyclohexane, benzene, toluene, dioxane, chloroform, diethylether, dichloromethane, tetra hydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, formic acid, butanol, isopropanol, propanol, ethanol, methanol, acetic acid, ethylene glycol, diethylene glycol or water. Water based solvent or solvent systems can also include dissolved ions, salts and molecules such as amino acids, proteins, sugars and phospholipids. Such salts may be, but not limited to, sodium chloride, potassium chloride, ammonium acetate, magnesium acetate, magnesium chloride, magnesium sulfate, potassium acetate, potassium chloride, sodium acetate, sodium citrate, zinc chloride, HEPES sodium, calcium chloride, ferric nitrate, sodium bicarbonate, potassium phosphate and sodium phosphate.

[0078] In some embodiments, a weight ratio of carbon soot ash to polar solvent is about 1 :2 to about 1 : 10. This allows vanadium to be extracted cleanly from carbon soot ash. In other embodiments, the weight ratio is about 1 :2 to about 1 :9, about 1 :2 to about 1 :8, about 1 :2 to about 1:7, or about 1 :2 to about 1 :6. In other embodiments, the weight ratio is about 1 :3 to about 1 :6.

[0079] A leaching agent refers to a solvent or a chemical used to selectively extract a desired substance from a solid or liquid mixture. In some embodiments, the leaching agent is selected from metal hydroxide, carbonate salt, or a combination thereof. The metal may be a Group 1 metal. In some embodiments, the leaching agent is selected from sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate or a combination thereof. In other embodiments, the leaching agent is sodium hydroxide.

[0080] In some embodiments, a concentration of the leaching agent in the polar solvent is about 0.5M to 5M. In other embodiments, the concentration is about 0.5M to about 4.5M, about 0.5M to about 4M, about 0.5M to about 3.5M, or about 0.5M to about 3M. In other embodiments, the concentration is about IM to about 3M. In other embodiments, the concentration is about 2M.

[0081] In some embodiments, a weight ratio of carbon soot ash to leaching agent is about 1 :0.1 to about 1 :0.8, about 1 :0.1 to about 1 :0.7, about 1 :0.1 to about

[0082] 1 :0.6, about 1 :0.1 to about 1 :0.5, about 1 :0.2 to about 1 :0.5, or about 1 :0.3 to about 1 :0.5. In some embodiments, a weight ratio of carbon soot ash to leaching agent is about 1 :0.4 to about 1 :0.5.

[0083] In some embodiments, the oxidising agent is selected from percarbonate salt, hydrogen peroxide or a combination thereof. In some embodiments, the oxidising agent is selected from sodium percarbonate, hydrogen peroxide or a combination thereof. In some embodiments, the oxidising agent is a combination of sodium percarbonate and hydrogen peroxide. The oxidising agent oxidises vanadium ions to vanadium (V) ions. Without wanting to be bound by theory, it is believed that vanadium (V) ions are stable in the polar solvent and do not re-associate with the carbon soot ash, thereby improve its extraction.

[0084] In some embodiments, a concentration of the oxidizing agent in the polar solvent is about 0.2M to about IM. In some embodiments, a concentration of the oxidizing agent is about 0.2M to about 0.9M, about 0.2M to about 0.8M, about 0.2M to about 0.7M, about 0.2M to about 0.6M, about 0.3M to about 0.6M, or about 0.4M to about 0.6M. In some embodiments, a concentration of the oxidizing agent is about 0.6M.

[0085] In some embodiments, a concentration of percarbonate salt in the polar solvent is about 0.1 M to about 1 M, about 0.1 M to about 0.9 M, about 0.1 M to about 0.8 M, about 0.1 M to about 0.7 M, about 0.1 M to about 0.6 M, about 0.1 M to about 0.5 M, about 0.1 M to about 0.4 M, or about 0.1 M to about 0.3 M. In some embodiments, a concentration of percarbonate salt is about 0.2 M.

[0086] In some embodiments, a concentration of hydrogen peroxide in the polar solvent is about 0.1 M to about 1 M, about 0.1 M to about 0.9 M, about 0.1 M to about 0.8 M, about 0.1 M to about 0.7 M, about 0.1 M to about 0.6 M, or about 0.1 M to about 0.5 M. In some embodiments, a concentration of hydrogen peroxide is about 0.4 M.

[0087] In some embodiments, a concentration of percarbonate salt in the polar solvent is about 0.2 M and a concentration of hydrogen peroxide is about 0.4 M. Percarbonate salt is an addition salt of hydrogen peroxide and sodium carbonate that provides a solid source of hydrogen peroxide. When dissolved in water, the percarbonate salt liberates hydrogen peroxide. As peroxide slowly decomposes over time, this allows the concentration of peroxide to be maintained for a long duration.

[0088] It was found that some of the interfering metals like iron, aluminium and nickel are amphoteric and can dissolve in both acid and base. The interfering metals interferes with the process by reacting with peroxide, thus less peroxide is available for converting V3+to V5+. Furthermore, the reacted interfering metals may also attach to the vanadium species and mask the vanadium species from reacting with the leaching agent and oxidising agent. In combination, this reduces the extraction efficiency. It was found that apart from regenerating peroxide, the percarbonate salt supresses interfering ions like iron, aluminium and nickel by forming complex compounds with them through redox and ligand exchange reactions. This prevents the interfering ions from consuming the oxidizing agents, allowing more oxidizing agents to be directed toward vanadium ions, thereby increasing vanadium leaching efficiency. As shown in Figure 5, a combination of sodium hydroxide and hydrogen peroxide in C achieves an 84% vanadium removal efficiency from ash due to their high oxidizing capacity. The addition of sodium percarbonate in D further boosts the efficiency to 95% by reducing the impact of interfering ions on the oxidation of vanadium.

[0089] In some embodiments, a mole ratio of leaching agent to oxidising agent is about 2:0.3 to about 2:2. In other embodiments, the mole ratio is about 2:0.3 to about 2: 1.8, about 2:0.3 to about 2 : 1.6, about 2 :0.3 to about 2: 1.5, or about 2:0.3 to about 2: 1.4. In other embodiments, the mole ratio is about 2:0.4 to about 2: 1.4.

[0090] In some embodiments, when the leaching agent is metal hydroxide and the oxidising agent is hydrogen peroxide, the mole ratio of leaching agent to oxidising agent is about 2:0.4 to about 2: 1. In other embodiments, the mole ratio is about 2:0.4 to about 2:0.9, about 2:0.4 to about 2:0.8, about 2:0.4 to about 2:0.7, about 2:0.4 to about 2:0.6, or about 2:0.4 to about 2:0.5.

[0091] In some embodiments, when the leaching agent is metal hydroxide and the oxidising agent is hydrogen peroxide, the mole ratio of leaching agent to oxidising agent is at least about 2:0.4.

[0092] In some embodiments, when the leaching agent is metal hydroxide and the oxidising agent is hydrogen peroxide and percarbonate salt, the mole ratio is about 2: 0.4: 0.1 to about 2:0.4: 1. In other embodiments, the mole ratio is about 2:0.4:0.1 to about 2:0.4:0.9, about 2:0.4:0.1 to about 2:0.4:0.8, about

[0093] 2:0.4:0.1 to about 2:0.4:0.7, about 2:0.4:0.1 to about 2:0.4:0.6, about

[0094] 2:0.4:0.1 to about 2:0.4:0.5, about 2:0.4:0.1 to about 2:0.4:0.4, about

[0095] 2:0.4:0.1 to about 2:0.4:0.3, or about 2:0.4:0.1 to about 2:0.4:0.2. In some embodiments, when the leaching agent is sodium hydroxide and the oxidising agent is hydrogen peroxide and sodium percarbonate, the mole ratio is about 2:0.4:0.1.

[0096] In some embodiments, a mole ratio of hydrogen peroxide to percarbonate salt is about 4: 1 to about 4: 10. In other embodiments, the mole ratio is about 4: 1 to about 4:9, about 4: 1 to about 4:8, about 4: 1 to about 4:7, about 4:1 to about 4:6, about 4:1 to about 4:5, about 4: 1 to about 4:4, about 4: 1 to about 4:3, or about 4: 1 to about 4:2.

[0097] In some embodiments, a weight ratio of carbon soot ash to leaching agent and oxidising agent is about 1 :0.5 to about 1 : 1.2, about 1 :0.5 to about 1 : 1.1, about 1:0.5 to about 1 : 1, about 1 :0.5 to about 1 :0.9, about 1 :0.5 to about 1 :0.8, or about 1 :0.6 to about 1 :0.8. In some embodiments, a weight ratio of carbon soot ash to leaching agent and oxidising agent is about 1:0.65 to about 1:0.75.

[0098] In some embodiments, the mixture of step a) is reacted at a temperature of about 50°C to about 100°C. In other embodiments, the temperature is about 50°C to about 90°C, about 50°C to about 80°C, about 50°C to about 70°C, or about 50°C to about 60°C.

[0099] In some embodiments, the mixture of step a) is reacted for a duration of about 2 h to about 24 h. In other embodiments, the duration is about 2 h to about 20 h, about 2 h to about 18 h, about 2 h to about 16 h, about 2 h to about 14 h, about 2 h to about 12 h, about 2 h to about 10 h, or about 4 h to about 10 h.

[0100] In some embodiments, the mixture of step a) is characterised by a pH of about 7.5 to about 13. In other embodiments, the pH is about 8 to about 13, about 9 to about 13, about 10 to about 13, or about 11 to about 13.

[0101] In some embodiments, step a) is characterised by a removal or leaching efficiency of at least 80%. In other embodiments, the removal efficiency is at least about 85%, about 90% or about 95%.

[0102] The mixture may be mechanically agitated at any stirring speed without a significant difference in leaching efficiency.

[0103] Through the selective use of a leaching agent and oxidising agent in a polar solvent, the extraction of vanadium from carbon soot ash is optimised. Vanadium ions are converted into V5+ions, which remains solvated in the polar solvent. By modulating the pH via the leaching agent, other impurity metals may be precipitated and removed with the leached ash.

[0104] The mixture is filtered in order to separate the vanadium leachate from the leached ash. A sintered filter may be used. For example, a 0.45 pm filter paper may be used.

[0105] In some embodiments, the vanadium leachate comprises vanadium (V) ions and at least one impurity. The impurity may be an element or ion which is deemed undesirable. In some embodiments, the at least one impurity is an element selected from aluminium, iron, silicon, sulphur, sodium, or a combination thereof. In some embodiments, the at least one impurity is an element selected from aluminium, iron, silicon, or a combination thereof.

[0106] In some embodiments, the vanadium (V) ions is about 60 wt% to about 90 wt% relative to the vanadium leachate (excluding the solvent). This percentage may be determined using elemental analysis. In other embodiments, the vanadium (V) ions is about 60 wt% to about 85 wt%, about 60 wt% to about 80 wt%, or about 60 wt% to about 75 wt%.

[0107] In some embodiments, the vanadium (V) ions is about 2 wt% to about 30 wt% relative to the vanadium leachate (including the solvent). In other embodiments, the wt% is about 4 wt% to about 30 wt%, about 5 wt% to about 30 wt%, about 6 wt% to about 30 wt%, about 8 wt% to about 30 wt%, about 10 wt% to about 30 wt%, about 12 wt% to about 30 wt%, about 14 wt% to about 30 wt%, about 16 wt% to about 30 wt%, about 18 wt% to about 30 wt%, about 20 wt% to about 30 wt%, or about 25 wt% to about 30 wt%.

[0108] In some embodiments, the vanadium leachate (excluding the solvent) comprises less than about 6 wt% of impurities. In other embodiments, the vanadium leachate comprises less than about 5 wt%, 4 wt%, 3 wt% or 2 wt% of impurities. The impurities may be a metal ion. The metal ion may be from a metal selected from aluminium, nickel, iron, titanium, chromium, cobalt, zinc and manganese.

[0109] In some embodiments, the vanadium leachate (including the solvent) comprises less than about 6 wt% of impurities. In other embodiments, the vanadium leachate comprises less than about 5 wt%, 4 wt%, 3 wt%, 2 wt%, or 1 wt% of impurities.

[0110] In some embodiments, the purification step comprises adjusting a pH of the vanadium filtrate. The pH may be adjusted to a range from about 7 to about 11, or about 8 to about 11. In other embodiments, the pH is adjusted to a range from about 9 to about 10. In other embodiments, the pH is adjusted to about pH 9.

[0111] The vanadium leachate may have a high pH. In some embodiments, the pH is adjusted by adding an acid. The acid may be selected from sulphuric acid, hydrochloric acid, nitric acid, or a combination thereof.

[0112] In some embodiments, the purification step comprises mixing the vanadium filtrate with an absorbent. The absorbent is a material or substance that has the ability to absorb or trap the at least one impurity. This may be via entrapment within the porous structure of the absorbent, via physical or chemical interaction with the at least one impurity.

[0113] In some embodiments, the absorbent is selected from aluminium oxide, magnesium oxide, magnesium sulphate, magnesium hydroxide, calcium hydroxide or a combination thereof. In some embodiments, the absorbent is selected from activated aluminium oxide, magnesium hydroxide, or a combination thereof.

[0114] Activated aluminium oxide, also known as activated alumina, is a type of aluminium oxide that has been treated to increase its surface area and porous structure. It is believed that activated AI2O3 has a high repulsion for vanadium ions, thus does not absorb vanadium ions.

[0115] It was further found that the combination of activated aluminium oxide and magnesium hydroxide achieves the high removal efficiency for impurities, with 99% for Al3+and 95% for Si4-. Additionally, it displays the lowest disruption of vanadium ions at 1.3%. In contrast, other adsorbents (such as Ca(OH)2, have more than 10 % of vanadium loss during the purification step.

[0116] In some embodiments, the activated aluminium oxide is characterised by a surface area of about 100 m2 / g to about 500 m2 / g. In other embodiments, the surface area of about 150 m2 / g to about 500 m2 / g, about 200 m2 / g to about 500 m2 / g, about 250 m2 / g to about 500 m2 / g, about 300 m2 / g to about 500 m2 / g, about 350 m2 / g to about 500 m2 / g, or about 40 m2 / g to about 500 m2 / g.

[0117] In some embodiments, the activated aluminium oxide is characterised by a pore size of about 1 nm to about 50 nm. In other embodiments, the pore size is about 1 nm to about 45 nm, about 1 nm to about 40 nm, about 1 nm to about 35 nm, about 1 nm to about 30 nm, about 1 nm to about 25 nm, about 1 nm to about 20 nm, about 1 nm to about 15 nm, about 1 nm to about 10 nm, or about 1 nm to about 8 nm. In other embodiments, the pore size is about 1 nm to about 6 nm, or about 5 nm to about 6 nm.

[0118] In some embodiments, a weight ratio of adsorbent and vanadium leachate is about 1 : 1000 to about 100:1000, about 1 :1000 to about 90: 1000, about 1: 1000 to about 80: 1000, about 1: 1000 to about 70: 1000, about 1: 1000 to about 60: 1000, about 1: 1000 to about 50: 1000, about 1: 1000 to about 40: 1000, about 1 : 1000 to about 30: 1000, or about 1 : 1000 to about 20: 1000. In other embodiments, the weight ratio is about 2:1000 to about 20: 1000. In other embodiments, the weight ratio is about 1 :5 to about 1 :200, about 1 :5 to about 1: 150, about 1 :5 to about 1: 100, about 1 :5 to about 1:80, about 1:5 to about 1:60, about 1 : 10 to about 1:60, about 1 :20 to about 1 :60, about 1 :30 to about 1:60, about 1 :40 to about 1 :60, or about 1 :50 to about 1 :60.

[0119] In some embodiments, the absorbent is a combination of activated aluminium oxide and magnesium hydroxide. In some embodiments, the magnesium hydroxide is dispersed within a porous structure of the activated aluminium oxide. In some embodiments, a weight ratio of activated aluminium oxide to magnesium hydroxide is about 4:1 to about 1 :4. In other embodiments, the weight ratio is about 4: 1 to about 1 : 1, about 3: 1 to about 1: 1, about 2:1 to about 1: 1, about 1.5: 1 to about 1: 1. In other embodiments, the weight ratio is about 1 :1 to about 1 :4, about 1: 1 to about 1:3, about 1: 1 to about 1 :2, or about 1 : 1 to about 1 :1.5. In other embodiments, the weight ratio is about 1.5:2.

[0120] In some embodiments, the mixture of vanadium filtrate and absorbent is mixed at a temperature of about 50°C to about 100°C. In other embodiments, the temperature is about 50°C to about 90°C, about 50°C to about 80°C, about 50°C to about 70°C, or about 50°C to about 60°C.

[0121] In some embodiments, the mixture of vanadium filtrate and absorbent is mixed for a duration of about 20 min to about 24 h. In other embodiments, the duration is about 20 min to about 20 h, about 20 min to about 18 h, about 20 min to about 16 h, about 20 min to about 14 h, about 20 min to about 12 h, about 20 min to about 10 h, about 20 min to about 8 h, about 20 min to about 6 h, about 20 min to about 5 h, about 20 min to about 4 h, about 20 min to about 3 h, or about 20 min to about 2 h. In other embodiments, the duration is about 30 min to about 2 h or about 1 h to about 2 h.

[0122] During this step, the pH may be maintained at about 8 to about 10. In other embodiments, the pH of the process is maintained at about 8 to about 10.

[0123] In some embodiments, the purification step comprises filtrating the vanadium leachate. The use of an absorbent and / or adjusting the pH may cause the at least one impurity to precipitate. The filtration will thus separate the absorbent and / or the precipitation.

[0124] In some embodiments, the vanadium filtrate is characterised by a purity of at least 99%. In some embodiments, the vanadium filtrate is characterised by a purity of more than about 99%. In this regard, of the metal ions present in the vanadium filtrate, 99% is vanadium ions. In other embodiments, the purity is at least least 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, or 99.9%.

[0125] In some embodiments, the method further comprises a step of precipitating the vanadium (V) ions. The vanadium (V) ions may be in the vanadium filtrate, or in the filtrate from the purification step as discussed above.

[0126] In some embodiments, the vanadium (V) ions is precipitated in the presence of a precipitating agent. In some embodiments, the precipitating agent is an ammonium salt. The precipitating agent may be selected from ammonium sulphate, ammonium chloride, or a combination thereof.

[0127] In some embodiments, the precipitating agent is a solid. In some embodiments, the precipitating agent is dispersed in a solution, wherein the solution comprising about 20 wt% to about 40 wt% of the precipitating agent. In other embodiments, the weight percent is about 22 wt% to about 40 wt%, about 24 wt% to about 40 wt%, about 26 wt% to about 40 wt%, about 28 wt% to about 40 wt%, about 30 wt% to about 40 wt%, about 32 wt% to about 40 wt%, or about 35 wt% to about 40 wt%.

[0128] In some embodiments, the vanadium (V) ions is precipitated in the presence of ammonium sulphate. The ammonium sulphate may be provided as a 30 wt% solution to the vanadium leachate.

[0129] In some embodiments, the precipitating agent is added in excess of the amount of vanadium in the vanadium leachate. For example, the precipitating agent may be in excess by about 0.1 times to about 100 times. For example, 1 L of vanadium leachate may be mixed with 1 L of 30 wt% ammonium sulfate solution. When vanadium is about 20 wt% of the vanadium leachate, the ammonium sulfate is about 1.5 times that of the vanadium.

[0130] In some embodiments, the precipitation step is performed at an ambient temperature. In some embodiments, the precipitation step is performed at a temperature of about 15°C to about 40°C. In other embodiments, the temperature is about 15°C to about 38°C, about 15°C to about 36°C, about 15°C to about 34°C, about 15°C to about 32°C, about 15°C to about 30°C, about 15°C to about 28°C, about 15°C to about 26°C, about 15°C to about 24°C, or about 15°C to about 22°C.

[0131] In some embodiments, the precipitation step performed for a duration of about 10 min to about 24 h. In other embodiments, the duration is about 20 min to about 24 h, about 20 min to about 20 h, about 20 min to about 18 h, about 20 min to about 16 h, about 20 min to about 14 h, about 20 min to about 12 h, about 20 min to about 10 h, about 20 min to about 8 h, about 20 min to about 6 h, about 20 min to about 5 h, about 20 min to about 4 h, about 20 min to about 3 h, or about 20 min to about 2 h. In other embodiments, the duration is about 30 min to about 2 h.

[0132] In some embodiments, the precipitated vanadium (V) salt is dried at an ambient temperature. In some embodiments, the precipitated vanadium (V) salt is dried at a temperature of about 50°C to about 100°C. In other embodiments, the temperature is about 60°C to about 100°C, about 70°C to about 100°C, about 80°C to about 100°C, or about 90°C to about 100°C.

[0133] In some embodiments, the precipitated vanadium (V) salt is dried for a duration of about 1 h to about 24 h. In other embodiments, the duration is about 1 h to about 20 h, about 1 h to about 18 h, about 1 h to about 16 h, about 1 h to about 14 h, about 1 h to about 12 h, about 1 h to about 10 h, about 1 h to about 8 h, about 1 h to about 6 h, about 1 h to about 5 h, about 1 h to about 4 h. In other embodiments, the duration is about 3 h to about 5 h.

[0134] In some embodiments, the method further comprising a step of calcinating the vanadium filtrate in order to produce vanadium pentoxide. In some embodiments, the method further comprises a step of calcinating the precipitated vanadium (V) salt. In some embodiments, the method further comprises a step of calcinating the dried vanadium (V) salt.

[0135] In some embodiments, the calcination is performed at a temperature of about 300°C to about 700°C. In other embodiments, the temperature is about 350°C to about 700°C, about 400°C to about 700°C, about 400°C to about 650°C, about 400°C to about 600°C, or about 400°C to about 550°C. In other embodiments, the temperature is about 400°C to about 500°C.

[0136] In some embodiments, the calcination is performed for a duration of about 2 h to about 8 h. In other embodiments, the duration is about 2 h to about 7 h, about 2 h to about 6 h, or about 2 h to about 5 h. In other embodiments, the duration is about 3 h to about 5 h.

[0137] The present disclosure also provides a method of producing vanadium pentoxide, comprising: a) mixing carbon soot ash with a leaching agent and an oxidising agent in a polar solvent in order to form a mixture and reacting the mixture in order to form vanadium (V) ions; b) filtrating the mixture in order to separate a vanadium leachate from a leached ash; c) purifying the vanadium leachate in order to obtain a vanadium filtrate; d) precipitating the vanadium (V) ions as a vanadium (V) salt; and e) calcinating the vanadium (V) salt in order to produce vanadium pentoxide.

[0138] In some embodiments, the vanadium filtrate and / or vanadium pentoxide is characterised by a purity of at least about 99.2%. In other embodiments, the purity is at least about 99.3%, about 99.4%, about 99.5%, about 99.6%, about 99.7%, about 99.8%, or about 99.9%.

[0139] In some embodiments, the vanadium filtrate and / or vanadium pentoxide is characterised by a Al impurity of less than about 0.4%. In other embodiments, the purity is less than about 0.35%, about 0.2%, about 0.15%, about 0.1%, about 0.09%, about 0.08%, about 0.07%, about 0.06%, about 0.05%, about 0.04%, about 0.03%, about 0.02%, or about 0.01%.

[0140] In some embodiments, the vanadium filtrate and / or vanadium pentoxide is characterised by a Si impurity of less than about 0.4%. In other embodiments, the purity is less than about 0.35%, about 0.2%, about 0.15%, about 0.1%, about 0.09%, about 0.08%, about 0.07%, about 0.06%, about 0.05%, about 0.04%, about 0.03%, about 0.02%, or about 0.01%.

[0141] In some embodiments, the vanadium filtrate and / or vanadium pentoxide is characterised by an absence of Fe, S, Na, or a combination thereof.

[0142] The vanadium pentoxide may be obtained as nanoparticles. In some embodiments, the vanadium pentoxide is characterised by a particle size of less than 600 nm. In some embodiments, the vanadium pentoxide is characterised by a particle size of about 200 nm to about 600 nm, about 220 nm to about 600 nm, about 240 nm to about 600 nm, about 260 nm to about 600 nm, about 280 nm to about 600 nm, about 300 nm to about 600 nm, about 300 nm to about 580 nm, about 300 nm to about 560 nm, about 300 nm to about 540 nm, about 300 nm to about 520 nm, or about 300 nm to about 500 nm.

[0143] The present disclosure also provides a vanadium (V) solution obtained by the method as disclosed herein. The present disclosure also provides a vanadium (V) solution as disclosed herein.

[0144] The present disclosure also provides vanadium pentoxide obtained by the method as disclosed herein. The present disclosure also provides vanadium pentoxide as disclosed herein.

[0145] Examples

[0146] Material Characterization

[0147] The morphology of carbon soot ash, leached ash and vanadium precipitate were examined using a Field-Emission Scanning Electron Microscopy (FE-SEM, JSM- 7610FPIus, JEOL) at an accelerating voltage of 100-200 kV. This was complemented by a high-resolution transmission electron microscope (FETEM) (JEM-2100F) at an accelerating voltage of 200 kV. For the elemental analysis of ash and vanadium precipitate, solid samples were digested using strong acids, then analysed with an inductively coupled plasma optical emission spectrometer (ICP-OES, iCAP 6200, ThermoFisher) to identify various cations. ThermoFisher Scientific Thermo FlashSmart CHNS Elemental Analyser was used to evaluate the CHNS content, calibrated with sulfanilamide standards. The sample, precisely weighed into tin capsules, was heated to 950 °C with a 3-second oxygen injection. Subsequently, the analytes of interest, namely N2, CO2, H2O, SO2, were detected by a thermal conductivity detector. The attenuated total reflectance- infra red (ATR-IR) spectra of ash and Vanadium precipitate were computed by an ATR-IR spectrometer (Perkin Elmer, Spectrum Two) in the scan range of 4000-400 cm-1. Functional groups were determined using Fourier Transform Infra-red (FTIR, Bruker Vertex 70) spectroscopy at a resolution of 2 cm-1with 64 scans. X-ray diffraction (XRD) patterns were recorded using a Bruker D8 Advance X-ray diffractometer using CuKa radiation as the X-ray source. The evaluation of the crystallographic structures of ash was done using high angle diffractograms, which were recorded in the 20 range from 10° to 80° in 0.02° steps with a count time of 20 seconds at each point.

[0148] General Methodology

[0149] Carbon soot ash was mixed with a leaching agent and oxidizing agent in a polar solvent to form a mixture. The mixture was heated for certain period of time, such as from at 50°C to 80°C for 4 to 10 hours. Filtration was employed to separate the leached ash from the resulting vanadium leachate, which mainly contained vanadium along with impurities such as aluminium, iron and silicon. Acid (such as sulphuric acid, hydrochloric acid, and nitric acid or a combination thereof) was added to the vanadium leachate to obtain a certain pH or the pH is adjusted to 9-10, and adsorbent was dosed into the leachate at certain weight ratio. The mixture was heated for certain period of time, such as 50°C to 80°C for 30 min to 2 hours. Subsequent filtration was employed to remove impurities (Al, Si, Fe) in the form of mixed metal oxide. The resulting filtrate achieved a high purity sodium vanadate solution, with vanadium purity levels ranging from 99.5% to 99.9%. Precipitating agent (such as ammonium sulphate, and ammonium chloride or a combination thereof) was added to the filtrate and stirred for certain period of time (such as from 30 min to 2 h) to facilitate the formation of a white precipitate (ammonium vanadate), which was filtered out. The precipitate was then subjected to drying at 80°C for 5 hours, followed by calcination at 400°C for 4 hours to yield high-purity vanadium pentoxide.

[0150] Carbon soot ash may be mixed with leaching agent, oxidizing agent and water. The weight ratio of carbon soot ash and water may be 1:3 to 1 :6.

[0151] The leaching agent may be provided to the carbon soot ash in solvent at a concentration of IM to 3M. The leaching agent may be provided at 2 M. The concentration of the leaching agent in the solvent may be about The leaching agent may be selected from sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate or a combination thereof.

[0152] The concentration of the oxidizing agent in the solvent may be 0.01 M to 1 M. The concentration may be about 0.1 M to about 0.8 M, or about 0.2 M to about 0.6 M. The oxidizing agent may be selected from sodium percarbonate and hydrogen peroxide or a combination thereof. The concentration of hydrogen peroxide may be about 0.4 M. The concentration of sodium percarbonate may be about 0.2 M.

[0153] The adsorbent may be selected from aluminium oxide, magnesium oxide, magnesium sulphate or a combination thereof. The weight ratio of adsorbent and leachate may be 2: 1000 to 20: 1000.

[0154] The precipitating agent may be in pure solid form, or in solution form that contains 20 wt% - 40 wt% of precipitating agent.

[0155] The drying process may be conducted at 80°C to 100°C for about 3 to 5 hours.

[0156] The calcination process may be conducted at 400°C to 500°C for about 3 to 5 hours.

[0157] Characterization of (a) Carbon soot ash, (b) Leached ash and (c) Vanadium pentoxide

[0158] Figure 1 and Figure 2 present images obtained from TEM and SEM analyses of three materials: (a) Carbon soot ash, (b) Leached ash and (c) Vanadium pentoxide. The morphologies of these materials are evaluated.

[0159] The images reveal that the particles of all the materials exhibit significant aggregation. Both carbon soot ash and leached ash display indefinite morphologies, characterized by a variety of shapes and sizes. In contrast, vanadium pentoxide demonstrates a bead-like morphology. The beads are aggregated into small groups, with all the beads being similar and uniform in size. Investigations show that the bead sizes are consistently less than 500 nm, with a range between 300-500 nm, precluding their classification as nanoparticles.

[0160] The synthesized vanadium pentoxide shows a uniform size and shape, making it particularly suitable for various applications, notably as a catalyst. This uniformity is clearly evidenced in the TEM and SEM images.

[0161] Figure 3 presents the FT-IR spectra of (a) Carbon soot ash, (b) Leached ash and (c) Synthesized vanadium pentoxide (V2O5). The spectra of the ash display broad peaks at 3250 cm and 1600 cm , corresponding to the stretching and bending vibrations of -OH from water. Additionally, a peak at 1100 cm4is observed, which is due to the asymmetric stretching vibration of Si-O-Si, while a peak near 950 cm4indicates the presence of Metal-OH / Metal-O vibrations. Peaks below 750 cm4can be attributed to the vibrational modes of metal-O.

[0162] In the leached ash, the intensities of all the previously mentioned peaks in ash are decreased due to the leaching process. As for the synthesized V2O5, two prominent peaks at 1040 cm4and 850 cm4are observed. The sharp peak at 1040 cm4is associated with the V-O-V bridged oxygen vibrations, while the broad peak between 800 cm1to 900 cm4is resultant of the V=O vibrations in vanadium pentoxide.

[0163] Table 1. CHNS content for (a) Carbon soot ash, (b) Leached ash and (c) Vanadium pentoxide. ND= not detected

[0164] Table 2. ICP-OES results for metals content in (a) Carbon soot ash, (b) Leached ash and (c) Vanadium pentoxide. ND= not detected

[0165] Table 1 and Table 2 present the results for CHNS analysis and ICP-OES analysis. Table 1 shows that the CHNS elements are absent in the synthesized vanadium pentoxide while Table 2 suggests Al and Si impurities are present in small quantities in vanadium pentoxide. The purity of synthesized vanadium pentoxide may be up to 99.9%.

[0166] Fig. 4 illustrates the XRD patterns of (a) Carbon soot ash, (b) Leached ash and (c) Synthesized vanadium pentoxide. The carbon soot ash shows a larger number of peaks due to the presence of various metal oxides, which cannot be differentiated as some peaks of metal oxides overlap at same position. After leaching, the leached ash exhibits fewer peaks because the metal oxides, mainly vanadium oxides, are extracted from the ash and this results in only three peaks at 22.0°, 26.0°, and 36.0°(2e), corresponding to the (100), (101), and (110) reflections of silica in quartz form, respectively. The reduction in the number of peaks from (a) to (b) shows that vanadium oxides are effectively leached out of the ash.

[0167] The XRD pattern for (c) shows peaks corresponding to vanadium pentoxide, which match well with the JCPDS card no. 00-041-1426 for V2O5. The sharp and intense peaks at 15.6°, 20.30°, 21.1° and 26.0° (2e) correspond to the diffraction planes (200), (001), (101) and (110) of the orthorhombic phase of V2O5. This indicates the absence of other vanadium oxide forms, such as V3+and V4+. The purity of the vanadium pentoxide is further confirmed from CHNS and ICP-OES (Table 1 and 2), showing a purity level of approximately 99.9%.

[0168] Effect of Catalysts on Ash Leaching

[0169] Carbon soot ash contains various metals such as vanadium, nickel, aluminium, iron and silica. Among these, vanadium is particularly valuable, and it is present at 21-25% in ash. It is extracted through base leaching using various catalysts (leaching agent and / or oxidising agent).

[0170] Figure 5 illustrates the different catalysts used and their respective vanadium removal efficiencies. Four catalysts are employed, namely A, B, C, and D. A comprises solely of hydrogen peroxide (H2O2) while B only uses sodium hydroxide NaOH. C and D employ combinations of reagents, with C consisting of sodium hydroxide and hydrogen peroxide, and D containing sodium hydroxide, hydrogen peroxide, and sodium percarbonate. An increasing trend in removal efficiency is observed from A to D, with D achieving up to 95%.

[0171] Firstly, results for A and B in Figure 5 show that pure hydrogen peroxide and sodium hydroxide achieve removal efficiencies of 20% and 70% respectively. In C, these two reagents are combined, increasing efficiency to 84%. This increase is attributed to the enhanced oxidizing capacity. In an alkaline environment facilitated by sodium hydroxide, hydrogen peroxide undergoes decomposition due to its unstable peroxide bond. As a result, hydroxyl radicals (•OH) are produced. These oxygen-centred radicals are among the most powerful oxidizing agents, and they break the bond in the ash to increase vanadium extraction. Additionally, these radicals oxidize vanadium ions, increasing their oxidation state. Vanadium ions in a higher oxidation state exhibit increased solubility in alkaline solutions, thereby improving leaching efficiency.

[0172] Moving on, the result for D in Figure 5 suggests the addition of sodium percarbonate to C further increases removal efficiency to 95%. Apart from the high oxidizing capacity produced by sodium hydroxide and hydrogen peroxide, the percarbonate present supresses the interfering ions like iron, aluminium and nickel. It does so by forming complex compounds with them through redox and ligand exchange reactions. This prevents the interfering ions from consuming the oxidizing agents, allowing more oxidizing agents to be directed toward vanadium ions, thereby increasing vanadium leaching efficiency.

[0173] Based on Figure 5, a combination of sodium hydroxide and hydrogen peroxide in C achieves an 84% vanadium removal efficiency from ash due to their high oxidizing capacity. The addition of sodium percarbonate in D further boosts the efficiency to 95% by reducing the impact of interfering ions on the oxidation of vanadium.

[0174] Effect of Time and Temperature

[0175] Figure 6A and Figure 6B illustrate the effect of temperature and time on the vanadium removal efficiency of C and D. These two catalysts are selected for their high efficiency due to strong oxidizing capacity.

[0176] Figure 6A shows the efficiencies of these catalysts at different temperatures. The graph reveals an upward trend in removal efficiency with increasing temperature for both catalysts. At room temperature, both catalysts exhibit efficiencies below 80%. The efficiencies reach their peak levels at 50°C, with C reaching 85% and D achieving over 95% efficiency. Further increase in temperature resulted in insignificant changes of efficiencies. The observed increase in efficiencies is attributed to several factors. Higher temperatures facilitate the breakdown of aggregated ash particles into smaller particles, thereby exposing a larger surface area and providing more active sites for vanadium ion leaching. Vanadium ions in ash exist in various oxidation states, with V5+being highly soluble in alkaline mediums. At room temperature, D is unable to convert all vanadium ions in ash to V5-despite its high oxidizing capacity. As temperature reaches 50°C, D gains sufficient energy to achieve this conversion, thereby reaching maximum efficiency. Additionally, higher temperatures reduce the viscosity of the leaching solution, enhancing mass transfer between the ash and catalyst during oxidation. This results in the formation of more V5+ions. The increased temperature also raises the concentration of oxidizing species (»OH radicals), ensuring a sufficient supply to maintain a high oxidizing capacity in the solution.

[0177] Figure 6B shows the efficiencies of C and D over different leaching duration. Both catalysts exhibit increased removal efficiencies as duration increases, with C peaking at 85% efficiency at 12 hours, while D peaks at over 95% efficiency at 4 hours. The significant difference in peak times is due to the presence of interfering metal ions in C. These interfering ions utilize the active oxidative species along with vanadium ions, reducing vanadium leaching efficiency. In contrast, D contains percarbonate, which prevents interfering ions from reacting with the oxidizing species. As a result, D has a lower activation energy, enabling a more rapid reaction rate compared to C.

[0178] Furthermore, Figure 6B shows that the removal efficiencies of both catalysts maintained consistent up to the 24-hour mark. This levelling off suggests the vanadium ions in the leachate are stable and will not be re-adsorbed back into the ash over the next 24 hours. Such stability ensures that vanadium ions can be extracted from the leachate without interference.

[0179] Figure 6A and Figure 6B show that the removal efficiencies of both C and D peak at the temperature of 50°C. C requires 12 hours to reach optimum efficiency, whereas D achieves this in 4 hours. In both cases, the leached vanadium ions remain stable and dissolved in the leachate for up to 24 hours.

[0180] Effect of Solid-to-Liquid Ratio (Ash : Water containing catalyst)

[0181] Figure 7 shows the effect of the solid-to-liquid ratio (S / L ratio) on the vanadium removal efficiency using D. In this context, the solid refers to carbon soot ash, while the liquid represents the solvent. The concentration of D is kept constant. For example, a ratio of 1 :5 refers to 1 g ash to 5 ml solvent (water) containing 2M NaOH, a ratio of 1 :6 refers to 1 g ash to 6 ml solvent (water) containing 2M NaOH, and a ratio of 1 :7 refers to 1 g ash to 7 ml solvent (water) containing 2M NaOH. The S / L ratio is a parameter in this leaching study. As shown in Figure 7, an upward trend is observed in removal efficiency with increasing S / L ratios. The efficiency begins at approximately 72% for a 1 :3 ratio, increases to 82% for a 1 :4 ratio, and peaks at 95% with a 1 : 5 ratio. Beyond this peak, the efficiency plateaus, with no further increase observed at higher ratios.

[0182] In the leaching process, efficient collisions between the solid ash and liquid catalyst are necessary for enhanced efficiency. These collisions are facilitated by the movement of particles between the solid liquid phase through diffusion. The S / L ratio plays a vital role in diffusion as it affects mass transfer across the stagnant boundary layer. Increasing S / L ratio results in a steeper concentration gradient between the solid and liquid phases, thereby increasing mass transfer and leaching efficiency. At a low S / L ratio, the leached vanadium from the ash saturates the leachate, preventing the remaining vanadium ions from dissolving further. In contrast, at a S / L ratio of 1 : 5, the solution has sufficient capacity to dissolve all vanadium ions, thereby reaching maximum efficiency of 95%. Above the ratio of 1 : 5, no increase in removal efficiency is observed, indicating that D has attained its maximum efficiency regardless of S / L ratio.

[0183] Based on Figure 7, it can be concluded that a 1 : 5 S / L ratio is the optimum ratio for leaching. This ratio will be implemented in industrial applications to achieve maximum efficiency with minimal resource usage.

[0184] Effect of Hydrogen Peroxide and Sodium Percarbonate in sodium hydroxide

[0185] Figure 8A and 8B show the effect of hydrogen peroxide and sodium percarbonate on the vanadium removal efficiencies of C and D. In this study, the concentration of sodium hydroxide is maintained at 2M as this concentration has been evaluated to be optimal for the leaching process.

[0186] Figure 8A investigates the optimal concentration of hydrogen peroxide for C within the 0.1M to 1.0M range. The data indicates an upward trend in removal efficiency with increasing hydrogen peroxide concentration from 0.1M to 0.4M. A peak efficiency of 84% is obtained at 0.4M, and no further efficiency gains is observed at higher concentrations. The limitation in efficiency is likely due to the rapid decomposition of hydrogen peroxide and the consumption of resulting •OH radicals by interfering metal ions in carbon soot ash. Fe2+may be the primary ions which utilize these free radicals by conducting Fenton reaction. The mechanism of Fenton reaction suggests that Fe2+catalyse the breakdown of hydrogen peroxide into »OH radicals, subsequently reacting with these radicals to oxidize into Fe3+.

[0187] Figure 8B introduces sodium percarbonate as a co-catalyst to enhance the efficiency observed in Figure 8A. The combination of chemical reagents (sodium hydroxide, hydrogen peroxide and sodium percarbonate) constitutes D. Figure 8B aims to identify the optimal sodium percarbonate concentration for D within the 0.1M to 1.0M range. Based on Figure 8A, it can be inferred that the optimal concentration ratio of sodium hydroxide to hydrogen peroxide is 2:0.4 (M). Thus, this concentration is maintained in Figure 8B. As shown in the graph, the addition of percarbonate increases the overall efficiency, achieving 88% efficiency at 0.1M and a peak efficiency of 96% at 0.2 M. This improvement is attributed to the masking effect of sodium percarbonate on Fe2-ions, rendering them inactive for oxidation. Consequently, fewer Fe2+ions consume the oxidation species, allowing more »OH radicals to oxidize V3+to V5+in a Fentonlike reaction. V5+remains stable in alkaline medium as sodium vanadate.

[0188] Further increases in sodium percarbonate concentration beyond 0.2M lead to fluctuations in efficiency below 96%. This drop in efficiency is primarily due to excessive carbonate blocking the interaction between V3+ions and hydrogen peroxide.

[0189] Overall, Figure 8A and Figure 8B show that the optimal concentration ratio for D is 2:0.4:0.2 (M). This ratio maximizes removal efficiency within the cost- effective range of 0.1M to 1.0M, supporting high yield and low resource usage for industrial applications.

[0190] Effect of pH on Impurities Removal (Aluminium and Silicon)

[0191] The leaching process using D results in a leachate that contains metal impurities, primarily Al3+and Si4+. The concentrations of Al3+and Si4+are around 600mg / L and 300mg / L, respectively, accounting for 2% and 1% of the leachate concentration relative to vanadium. These metal impurities limit the vanadium purity to 97%. To enhance the vanadium purity to 99.5% and above, it is necessary to remove these impurities without affecting the vanadium ions. This can be achieved by adjusting the pH of the leachate and incorporating adsorbents.

[0192] Figure 9 illustrates the effect of pH on the removal efficiencies of Al3+and Si4+ions from the leachate. Removal efficiencies at both low and high pH extremes are poor due to the high solubility of ions, thus these conditions are omitted. The figure displays efficiencies for pH values ranging from 6 to 11, where significant removal efficiencies are observed. As shown in Fig. 9, the removal efficiencies of Al3+is consistently higher than Si4+across all pH conditions. This higher efficiency is attributed to the formation of insoluble hydroxide AI(OH)s by Al3+, while Si4+forms soluble silicate ions instead.

[0193] In Figure 9, both metal impurities exhibit increasing removal efficiencies from pH 6 to pH 9, with Al3+having a slight decline at pH 10. Al3+reaches efficiencies of 60% and 53% at pH 9 and 10 respectively, whereas Si4+achieves a peak efficiency of 30% at pH 9. A steep drop for Al3+is observed after pH 10, due to the dissolution of AI(OH)s in highly alkaline environments.

[0194] Based on these observations, pH 9 is identified as the optimal pH for the removal of metal impurities. This pH level will be used in further studies involving the addition of adsorbents to the leachate.

[0195] Effect of Adsorbents for the Removal of Al and Si from Leachate

[0196] The removal of impurities from the leachate is facilitated by various adsorbents. In this study, these adsorbents are investigated using different weight ratios. The pH condition is maintained at 9 as it is evaluated to be the optimal environment by previous studies. Figure 10A shows the efficiency of different adsorbents, while Figure 10B demonstrates the effect of weight ratios on their performance.

[0197] Figure 10A presents five types of adsorbents: Ca(OH)2, AI2O3, activated AI2O3 (porous form), Mg(OH)2 and a combination of activated AI2O3 and Mg(OH)2. These adsorbents are selected for their widespread use in water treatment to remove heavy metals. The aim is to identify adsorbents that effectively remove Al3+and Si4+without disturbing vanadium ions in the leachate. Data from Figure 10A indicate that all adsorbents exhibit higher removal efficiency for Al3+compared to Si4+. Among them, Ca(OH)2 shows the lowest removal efficiency at around 65% for Al3+and 33% for Si4+. In comparison, AI2O3, activated AI2O3, and Mg(OH)2 are more efficient, attaining over 70% for Al3+and above 50% for Si4+. The increase in efficiency is attributed to the formation of insoluble aluminium silicate, which precipitates out of the leachate. Regarding vanadium disruption, both Ca(OH)2 and AI2O3 exhibit high vanadium adsorption at around 8%, whereas activated AI2O3 and Mg(OH)2 maintain disruption efficiency below 2%, likely due to high repulsion for vanadium ions.

[0198] Figure 10A shows that the combination of activated AI2O3 and Mg(OH)2 achieves the highest removal efficiency for impurities, with 99% for Al3+and 95% for Si4+. Additionally, it displays the lowest disruption of vanadium ions at 1.3%. The high efficiency is primarily due to the porous nature of activated alumina, which accommodates the Mg(OH)2 species in the pores, forming a hybrid adsorbent. The hybrid adsorbent captures the Al3+and Si4+ions, subsequently diffusing them into the pores to form magnesium aluminium silicate. The strong interaction of activated alumina traps the resultant magnesium aluminium silicate, leading to high removal efficiency.

[0199] Based on Figure 10A, a combination of AI2O3 and Mg(OH)2 constitutes the most effective adsorbent. Figure 10B evaluates the optimal weight ratio of activated AI2O3 to Mg(OH)2, so that removal efficiencies can be optimized. Using equal weights of AI2O3 and Mg(OH)2 results in the removal efficiency of 94% for Al3+and 90% for Si4+. By adjusting weight ratios, the highest removal efficiency is observed at a ratio of 1.5:2, achieving 99% efficiency for Al3+and 95% for Si4-. This is attributed to the porous capacity of activated AI2O3, allowing uniform distribution of Mg(OH)2 particles in the pores. It is possible that changes in the proportions of the two reagents cause the collapse of the active sites in the hybrid adsorbent structure, thereby reducing efficiency.

[0200] Findings from Figure 10A and Figure 10B suggest that the combination of activated AI2O3 to Mg(OH)2 exhibits the highest efficiency for the removal of Al3+and Si4+impurities among the adsorbents studied. The weight ratio of 1.5:2 demonstrates optimal efficiency within a cost-effective range, making it suitable for industrial use.

[0201] Precipitation of Ammonium Vanadate from Leachate

[0202] Vanadium is extracted from high-purity vanadium leachate as ammonium vanadate through precipitation using an ammonium sulphate solution. In this study, different weight percentages of ammonium sulphate solution, ranging from 10% to 30%, are employed for the precipitation of vanadium. The goal is to achieve 100% precipitation. Figure 11 illustrates the different precipitation efficiencies observed.

[0203] As shown in Figure 11, precipitation efficiency increases with higher weight percentages, achieving 99.23% of vanadium precipitation using 30% ammonium sulphate solution at room temperature within 30 minutes. The ammonium vanadate obtained from this process is calcined at different temperatures to produce vanadium pentoxide. The optimal calcination temperature is evaluated to be 500 °C for 4 hours in an air atmosphere. The XRD analysis for the resulting V2O5 is presented in Figure 4, with the peaks confirming the product's identity. Additionally, the purity of the synthesized V2O5 reaches 99.9%, as confirmed with ICP-OES (Table 2).

[0204] Conclusion

[0205] It has been found that vanadium can be effectively extracted from carbon soot ash with high purity in the form of vanadium pentoxide. The extraction procedure begins with leaching using a combination of sodium hydroxide, hydrogen peroxide and sodium percarbonate as leaching agents (catalysts). This method extracts vanadium from carbon soot ash with over 95% efficiency at 50°C within 4 hours. An optimal solid-to-liquid ratio of 1:5 and weight ratios of 2:0.4:0.2 for sodium hydroxide, hydrogen peroxide and sodium percarbonate, respectively, are recommended for industrial applications. After leaching, metal impurities are effectively removed from the leachate using a combination of activated AI2O3 and Mg(OH)2 at a weight ratio of 1.5:2 in an alkaline condition of pH 9. Finally, vanadium is precipitated out from the leachate using a 30% ammonium sulphate solution, achieving a purity above 99.9%. Characterization techniques indicate that the vanadium pentoxide produced through this process has promising applications in the field of energy and environmental applications.

[0206] It will be appreciated that many further modifications and permutations of various aspects of the described embodiments are possible. Accordingly, the described aspects are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

[0207] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0208] Throughout this specification and the claims which follow, unless the context requires otherwise, the phrase "consisting essentially of", and variations such as "consists essentially of" will be understood to indicate that the recited element(s) is / a re essential i.e. necessary elements of the invention. The phrase allows for the presence of other non-recited elements which do not materially affect the characteristics of the invention but excludes additional unspecified elements which would affect the basic and novel characteristics of the method defined.

[0209] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

Claims1. A method of extracting vanadium, comprising: a) mixing carbon soot ash with a leaching agent and an oxidising agent in a polar solvent in order to form a mixture and reacting the mixture in order to form vanadium (V) ions; b) filtrating the mixture in order to separate a vanadium leachate from a leached ash; and c) purifying the vanadium leachate in order to obtain a vanadium filtrate; wherein a weight ratio of carbon soot ash to polar solvent is about 1 :2 to about 1: 10; and wherein a mole ratio of leaching agent to oxidising agent is about 2:0.3 to about 2:2.

2. The method according to claim 1, wherein the carbon soot ash comprises vanadium with a weight percent of at least 12 wt% relative to the carbon soot ash.

3. The method according to claim 1 or 2, wherein the polar solvent is an aqueous medium.

4. The method according to any one of claims 1 to 3, wherein the leaching agent is selected from metal hydroxide, carbonate salt, or a combination thereof.

5. The method according to any one of claims 1 to 4, wherein the oxidising agent is selected from percarbonate salt, hydrogen peroxide or a combination thereof.

6. The method according to any one of claims 1 to 5, wherein when the leaching agent is metal hydroxide and the oxidising agent is hydrogen peroxide, the mole ratio of leaching agent to oxidising agent is about 2:0.4 to about 2: 1.

7. The method according to any one of claims 1 to 6, wherein when the leaching agent is metal hydroxide and the oxidising agent is hydrogen peroxide and percarbonate salt, the mole ratio is about 2:0.4:0.1 to about 2:0.4: 1.

8. The method according to any one of claims 1 to 7, wherein a weight ratio of carbon soot ash to leaching agent and oxidising agent is about 1 :0.5 to about 1 : 1.2.

9. The method according to any one of claims 1 to 8, wherein the mixture of step a) is reacted at a temperature of about 50°C to about 100°C, and for a duration of about 2 h to about 24 h.

10. The method according to any one of claims 1 to 9, wherein the mixture of step a) is characterised by a pH of about 8 to about 13.

11. The method according to any one of claims 1 to 10, wherein the vanadium leachate comprises vanadium (V) ions and at least one impurity, wherein a weight percent of vanadium (V) ions is about 60 wt% to about 90 wt% relative to the total weight of vanadium (V) ions and the at least one impurity.

12. The method according to any one of claims 1 to 11, wherein the purification step comprises adjusting a pH of the vanadium filtrate to about 8 to about 11.

13. The method according to any one of claims 1 to 12, wherein the purification step comprises mixing the vanadium filtrate with an absorbent; wherein a weight ratio of adsorbent and vanadium leachate is about 1:5 to about 1 :200.

14. The method according to claim 13, wherein the mixture of vanadium filtrate and absorbent is mixed at a temperature of about 50°C to about 100°C, and for a duration of about 20 min to about 24 h.

15. The method according to claim 13 or 14, wherein the absorbent is selected from activated aluminium oxide, magnesium hydroxide, or a combination thereof.

16. The method according to claim 15, wherein a weight ratio of activated aluminium oxide to magnesium hydroxide is about 1: 1 to about 1 :4.

17. The method according to claim 15 or 16, wherein the activated aluminium oxide is characterised by a pore size of about 1 nm to about 10 nm.

18. The method according to any one of claims 1 to 16, wherein the vanadium filtrate is characterised by a purity of at least 99.5%.

19. The method according to any one of claims 1 to 18, wherein the purification step comprises filtrating the vanadium leachate.

20. The method according to any one of claims 1 to 19, wherein the method further comprises a step of precipitating the vanadium (V) ions in the presence of a precipitating agent, wherein the precipitating agent is an ammonium salt.

21. The method according to claim 20, wherein the precipitating agent is dispersed in a solution, wherein the solution comprising about 20 wt% to about 40 wt% of the precipitating agent.

22. The method according to any one of claims 1 to 21, wherein the method further comprising a step of calcinating the vanadium filtrate in order to produce vanadium pentoxide, wherein the calcination is performed at a temperature of about 300°C to about 700°C, and for a duration of about 2 h to about 8 h.

23. A method of producing vanadium pentoxide, comprising:a) mixing carbon soot ash with a leaching agent and an oxidising agent in a polar solvent in order to form a mixture and reacting the mixture in order to form vanadium (V) ions; b) filtrating the mixture in order to separate a vanadium leachate from a leached ash; c) purifying the vanadium leachate in order to obtain a vanadium filtrate; d) precipitating the vanadium (V) ions as a vanadium (V) salt; and e) calcinating the vanadium (V) salt in order to produce vanadium pentoxide; wherein a weight ratio of carbon soot ash to polar solvent is about 1 :2 to about 1: 10; and wherein a mole ratio of leaching agent to oxidising agent is about 2:0.3 to about 2:2.

24. The method according to any one of claims 1 to 23, wherein the vanadium filtrate and / or vanadium pentoxide is characterised by a purity of at least about 99.2%.

25. The method according to any one of claims 1 to 24, wherein the vanadium filtrate and / or vanadium pentoxide is characterised by a Al impurity of less than about 0.4%.

26. The method according to any one of claims 1 to 25, wherein the vanadium filtrate and / or vanadium pentoxide is characterised by a Si impurity of less than about 0.4%.

27. The method according to any one of claims 1 to 26, wherein the vanadium filtrate and / or vanadium pentoxide is characterised by an absence of Fe, S, Na, or a combination thereof.

28. The method according to any one of claims 1 to 27, wherein the vanadium pentoxide is characterised by a particle size of less than 600 nm.

29. A vanadium (V) solution and / or vanadium pentoxide obtained by the method according to any one of claims 1 to 28.

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