Method for preparing high-purity vanadium chemicals from vanadium raw materials having high molybdenum contents
Patent Information
- Application Number
- EP2022772454
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2022-08-29
- Publication Date
- 2025-07-09
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Abstract
Description
[0001] Process for the production of high-purity vanadium chemicals from vanadium raw materials with high molybdenum contents
[0002] The invention relates to a process for producing high-purity vanadium chemicals from vanadium raw materials with high molybdenum contents.
[0003] Regarding the background of the invention, it should be noted that its objective is to develop a chemical separation process for the selective extraction of molybdenum from alkali vanadate solutions, particularly from sodium vanadate solutions with high neutral salt contents. This process is intended to be applied prior to the precipitation of vanadium in order to be able to use vanadium raw materials with high molybdenum contents for the production of high-purity vanadium chemicals. These high-purity vanadium chemicals meet the requirements for use in the catalyst and aviation industries, as well as as energy storage materials.
[0004] The raw materials used for this purpose can be spent catalysts and gasification residues from the petrochemical industry.
[0005] The necessity of such a separation process is that molybdenum is leached from the aforementioned raw materials with the same efficiency as vanadium and partially precipitated together with vanadium. If vanadium precipitation takes place before molybdenum precipitation, the higher the molybdenum content in the raw material, the more the vanadium chemicals are contaminated with molybdenum. This makes the use of vanadium chemicals for the aforementioned applications impossible. In detail, the relevant state of the art offers various techniques for extracting molybdenum from vanadate solutions, namely precipitation, ion exchange, or liquid-liquid extraction - see L. Zeng, CY Cheng, A literature review of the recovery of molybdenum and vanadium from spent hydrodesulphurisation catalysts, Part IP. Separation and purification, Hydrometallurgy, 2009, 98, 10-20 and TH Nguyen, MSLee, A review on the separation of molybdenum, tungsten, and vanadium from leach liquors of various resources by solvent extraction, Geosystem Engineering, 2016, 19, 247-259.
[0006] For example, the selective extraction of molybdenum from a vanadate solution by precipitation could only be achieved after the vanadium content in the mother liquor had been reduced by a prior precipitation and the remaining vanadium had been reduced to tetravalent vanadium with sulfur dioxide at 80°C to 90°C. The precipitation of molybdic acid then took place at a strongly hydrochloric acid pH below 1.1 - see ZR Llanos, GF Provoost, WG Deering, FJ Debaene, Integrated process for the recovery of metals and fused alumina from spent catalysts, Patent US 5702500A, 1997.
[0007] WO 2007 / 020338 A2 discloses the initial precipitation of vanadium from a purified sodium vanadate solution containing 25.3 g / L molybdenum and 2.1 g / L vanadium, obtained from a raw material containing 9.7% molybdenum and 1.5% vanadium, at 90°C using ammonium chloride at a pH of 7-8. This precipitates 1.5% molybdenum and more than 95% vanadium. Taking into account the added volume of ammonium chloride solution, a clarified solution containing 18.7 g / L molybdenum and less than 0.08 g / L vanadium is ultimately obtained, from which molybdenum is precipitated as calcium molybdate using a calcium chloride solution at a pH of 7-8 and 90°C. The amount of calcium chloride solution is obviously added all at once, unless otherwise disclosed in this document.When an alkali vanadate solution containing more vanadium than molybdenum is treated in the same way, in contrast to the solution in WO 2007 / 020338 A2, a significant amount of calcium metavanadate will precipitate alongside calcium molybdate, despite the lower solubility of calcium molybdate stated in CN 132 1782 A. The reason for this is that in solutions with high concentrations of various salts (such as calcium molybdate, calcium metavanadate, sodium metavanadate, and sodium sulfate), the precipitation of the minority component calcium molybdate is kinetically inhibited due to the salting-in effect and even fails to occur completely below a certain molybdenum content. In contrast, the precipitation of the majority component calcium metavanadate is kinetically favored despite its higher solubility, since the salting-in effect is less pronounced for components with higher concentrations.If the precipitation of the kinetically preferred calcium metavanadate is not explicitly inhibited by the reaction procedure, as would be the case when using the process described in WO 2007 / 020338 A2, the selectivity of molybdenum over vanadium is significantly altered in favor of vanadium. Therefore, more molybdenum remains in the precipitation liquor, thus impairing the purity of subsequent products such as ammonium metavanadate or vanadium pentoxide.
[0008] In the vanadium extraction process according to the aforementioned CN 132 1782 A, calcium molybdate, calcium metavanadate, and sodium metavanadate are present as solids due to the calcium roasting used in the presence of sodium sulfate before an ammonium carbonate solution is added for dissolution. This results in selective dissolution of calcium metavanadate over calcium molybdate and no selective precipitation of molybdenum from an alkali vanadate solution. Simply using the indication of the lower solubility of calcium molybdate compared to calcium metavandate from CN 132 1782 A for selective molybdenum removal only leads to success with solutions whose vanadium content is significantly lower than their molybdenum content, since competing precipitation of calcium metavanadate cannot be suppressed.In contrast, the mere indication of the lower solubility of calcium molybdate compared to calcium metavanadate in solutions with higher vanadium than molybdenum contents and simultaneously high neutral salt contents does not lead to the necessary selective molybdenum extraction for the production of high-purity vanadium chemicals. Therefore, monitoring the reaction kinetics is all the more necessary in such solutions.
[0009] These examples demonstrate that it is known to precipitate molybdenum from solutions from which vanadium has previously been precipitated and significantly depleted. However, to the best of our knowledge, there are no reports of successful selective precipitation of molybdenum from vanadate solutions with higher vanadium contents than molybdenum and simultaneously high neutral salt contents, where competing precipitation of vanadium must be suppressed.
[0010] In ion exchange systems, hexavalent molybdenum and pentavalent vanadium are adsorbed and eluted equally, so no separation occurs. This is used for the complete purification of waste liquors and is only economically viable for small vanadium and molybdenum contents (0.1 g / L - 1 g / L). Ion exchange effectively separates molybdenum from tetravalent vanadium only in the strongly acidic range (pH 1), which in turn requires the initial reduction of vanadium with sulfites – see L. Zeng, CY Cheng, op. cit.
[0011] The most widely used method for extracting molybdenum from vanadate solutions is liquid-liquid extraction - see L. Zeng, CY Cheng, op. cit., TH Nguyen, MS Lee, op. cit. and US 5 431 892 A. Although molybdenum extraction from vanadate solutions with similar vanadium and molybdenum contents (approx. 10 g / L each) can yield vanadium chemicals with high purities - see US 5 431 892 A - this method is, however, technically very complex due to the use of organophosphorus or alkylamine-based extraction agents dissolved in organic solvents such as kerosene or xylene and the subsequent back-extraction with ammonia water and very expensive due to the use of specialty chemicals. In addition, the extraction of molybdenum from these vanadate solutions takes place in the strongly acidic, usually hydrochloric acid pH range.For example, the organophosphorus extraction agents di-(2-ethylhexyl)phosphoric acid (D2EHPA) dissolved in kerosene - see RK Biswas, Recovery of vanadium and molybdenum from heavy oil desulphurization waste catalyst, Hydrometallurgy, 1985, 14, 219-230 - or trioctylphosphine oxide (TOPO) - see YA El-Nadi, NS Awwad, AA Nayl, A comparative study of vanadium extraction by Aliquot 336 from acidic and alkaline media with application to spent catalyst International Journal of Mineral Processing, 2009, 92, 115-120 - can be used, which separate cationic molybdenum from vanadium species at pH < 1. Molybdenum must then be separated using ammonia water. When using D2EHPA, a second organic phase may form due to increased viscosity, which makes the reusability of the extraction agent more difficult - see P. Zhang, K.Inoue, Recovery of metal values from spent hydrodesulfurization catalysts by liquid-liquid extraction, Energy & Fuels, 1995, 9, 231-239. Higher-valent amines such as trioctylamine (TOA), Alamin 336 dissolved in toluene - see MA Olazabal, MM Orive, LA Fernandez, JM Madariaga, Selective extraction of vanadium (V) from solutions containing molybdenum (VI) By Ammonium Salts Dissolved In Toluene, Solvent Extraction and Ion Exchange, 1992, 10, 623-635 - or TOA in combination with tributyl phosphate (TBP) - see HI Kim, KW Lee, D. Mishra, KM Yi, JH Hong, MK Jun, HK Park, Separation and recovery of vanadium from leached solution of spent residue hydrodesulfurization (RHDS) catalyst using solvent extraction, Journal of Industrial and Engineering Chemistry, 2014, 20, 4457-4462 - extract molybdenum at pH < 1 only via tetravalent vanadium species, which must first be produced by sulfites or sulfur dioxide.
[0012] What all these known extraction processes have in common is that the vanadium contents in the solutions to be treated are similar to or lower than the high molybdenum contents (usually < 1 g / L vanadium and 1-10 g / L molybdenum).
[0013] Based on the described problem, the invention is based on the object of providing a simpler, environmentally friendly, yet highly effective process for the selective extraction of molybdenum from alkali vanadate solutions with particularly high molybdenum contents and, in contrast, even higher vanadium contents, as well as high neutral salt contents, for the production of high-purity vanadium chemicals. This object is achieved by a process having the features of patent claim 1, in which molybdenum is selectively precipitated via vanadium from alkali vanadate solutions by applying the following process steps:
[0014] - Providing a molybdenum-containing alkali vanadate solution at a maximum temperature of 70 °C, preferably about 60 °C,
[0015] - adding calcium hydroxide as a precipitant in portions while keeping the pH constant between 6 and 7 with acid,
[0016] - Mixing the solution,
[0017] - Solid-liquid separation of the resulting suspension, and
[0018] - Further processing of the low-molybdenum alkali vanadate solution into a high-purity vanadium chemical with a molybdenum content of maximum 500 ppm.
[0019] The process according to the invention solves the central problem of avoiding competitive precipitation of vanadium during the treatment of alkali vanadate solutions with higher vanadium contents than the molybdenum contents and simultaneously high neutral salt contents. This is achieved by, on the one hand, precisely controlling the kinetics of the reactions taking place and, on the other hand, ensuring that the correct vanadium and molybdenum species are present in solution throughout the entire precipitation process. Thus, the kinetics of the reaction to calcium metavandate are controlled by the portionwise addition of calcium hydroxide, i.e., slowed down to such an extent that the thermodynamically favored product calcium molybdate, which is kinetically inhibited by the salting-in effect, is nevertheless preferentially formed (thermodynamic reaction control). For example, with rapid addition, the kinetically favored product calcium metavanadate would always precipitate if there was an excess of vanadium.Adjusting the pH between each lime addition prevents the precipitation reaction from drifting into the basic pH range, ensuring that as little calcium metavanadate as possible and predominantly the more soluble calcium decavanadate is present, which ultimately supports the selective precipitation of calcium molybdate. In addition, the lower pH limit should also be controlled due to the equilibrium shift between molybdate and heptamolybdate. Drifting below pH 6.2 should be avoided, as otherwise the molybdate content shifts in favor of heptamolybdate. However, only the molybdate ions can form the less soluble calcium molybdate, whereas calcium heptamolybdate is very soluble. If the molybdate content decreases with decreasing pH, precipitation of the remaining molybdate no longer occurs due to the predominant salting-in effect.Due to the above circumstances, a pH value in the range between 6.2 and 6.9 is preferable (claim 8).
[0020] Only by combining these two steps of portionwise addition of calcium hydroxide and maintaining a constant pH value are the selectivities of molybdenum over vanadium achieved according to the invention from solutions with, in particular, higher vanadium than molybdenum contents and, at the same time, high neutral salt contents possible, so that only in this way can high-purity vanadium chemicals with a molybdenum content of maximum 500 ppm be obtained.
[0021] Further preferred developments of the process according to the invention are specified in the dependent claims. In principle, the object of the invention is thus achieved by precipitating molybdenum, for example as calcium molybdate (CaMoCL) - see claim 2 - from alkali vanadate solutions with higher vanadium than molybdenum contents and simultaneously high neutral salt contents, wherein the molybdenum content is at least 6.5 g / L and the neutral salt content, in particular the sodium sulfate content, is preferably in the range of 70 g / L to 120 g / L - see claim 3. The precipitation of molybdenum takes place before the precipitation of vanadium - see claim 4. This occurs up to a residual solubility of molybdenum of 1 g / L to 2 g / L, which guarantees the consistent production of high-purity vanadium chemicals with a molybdenum content of a maximum of 500 ppm from the above-mentioned raw materials. The application of this process makes the use of raw materials with high molybdenum contents possible.
[0022] The precipitation of molybdenum as calcium molybdate is achieved in an aqueous medium without the addition of organic additives - see claim 6 - by gradually adding a stoichiometric amount of calcium hydroxide with respect to molybdenum - see claim 5. The pH can be kept constant by portionwise dosing of sulfuric acid - see claim 7. Under the conditions mentioned, molybdenum is precipitated over vanadium with a selectivity of 85% to 90%, which is expressed by the molar molybdenum / vanadium ratio in calcium molybdate of 85:15 to 90:10. Precipitation of sparingly soluble calcium sulfate is negligible. The achievable purities of calcium molybdate allow its sale as a product to the molybdenum industry.
[0023] This process according to the invention thus enables the production of the mentioned high-purity vanadium chemicals from vanadium raw materials with high molybdenum contents, such as spent catalysts, preferably vanadium-containing Ni-Mo catalysts, or vanadium-containing residues from petroleum refineries - see claim 9.
[0024] A significant advantage of the invention over the prior art is that molybdenum can be extracted from alkali vanadate solutions with significantly higher vanadium contents (approx. 35 g / L - 50 g / L) than molybdenum contents (approx.
[0025] 7 g / L - 10 g / L) and simultaneously high neutral salt contents, can be selectively extracted by precipitation as calcium molybdate. According to the invention, the precipitation of molybdenum can take place before the precipitation of vanadium, so that the molybdenum content is already constantly reduced to a low level (1 g / L to 2 g / L) in the mother liquor for the subsequent precipitation of ammonium metavanadate (AMV). As a result, the production of high-purity vanadium chemicals with a molybdenum content of up to 500 ppm from raw materials with high molybdenum contents is made possible by a molybdenum precipitation reaction as a purification step—also different from the state of the art.
[0026] By applying the process according to the invention, the ion exchange process and liquid-liquid extraction can be avoided, which represents an additional economic, safety, and environmentally relevant advantage compared to the prior art. The precipitation of molybdenum as calcium molybdate from alkali vanadate solutions takes place exclusively in an aqueous medium and in the plant-friendly, slightly acidic to neutral pH range of 6 to 7. Only inexpensive, non-toxic calcium hydroxide, which is harmless in terms of occupational safety and the environment, and small amounts of sulfuric acid are used in this invention. Furthermore, the use of calcium hydroxide does not result in problematic contamination of the high-purity vanadium chemicals with chloride ions, as would be the case with calcium chloride. Cross-contamination of the vanadium chemicals and wastewater streams with organic substances is excluded.Chemical-intensive pH jumps and oxidation or reduction processes are eliminated when using this process. Complex extraction and stripping processes or equipment are also eliminated; only a heatable stirred vessel is required. In addition, the CaMoO4 precipitation at approximately 60°C requires less energy than, for example, the precipitation of molybdic acid at 80°C to 90°C and the precipitation of calcium molybdate at 90°C reported in WO 2007 / 020338 A2. The temperature range of approximately 60°C preferred according to the invention can be set between 58 and 62°C.
[0027] Further features, details and advantages of the invention will become apparent from the following description of embodiments.
[0028] Example 1
[0029] In this example, 1 liter of a sodium vanadate solution (NaV solution) is obtained by leaching a roasted Ni-Mo catalyst with 18.7% V and 2.4% Mo. The NaV solution, containing 8.5 g / L molybdenum, 42.8 g / L vanadium, and 105 g / L sodium sulfate, was heated to 60°C. A total of 6.55 g of calcium hydroxide (anhydrous), stoichiometric with respect to molybdenum, was then added. The calcium hydroxide was added in four portions of 1.64 g each at intervals of 20 minutes. Between the additions of the calcium hydroxide portions, the pH was kept constant at 6.4 by slowly adding concentrated sulfuric acid (96%). After the last portion was added and the pH adjusted, the suspension was stirred at 60°C for five hours. During the stirring period, the pH was checked and, if necessary, readjusted to 6.4. The precipitate was filtered and washed with water.Ammonium sulfate was added to the molybdenum-poor sodium vanadate solution at a pH of 8 to 9, and the mixture was stirred for two hours. The precipitated ammonium metavanadate (AMV) was filtered and washed with water. As an alternative to AMV, precipitation in the pH range of 2 to 3 can yield an ammonium polyvanadate (APV) or a sodium polyvanadate (NPV), and a sodium ammonium vanadate (NAV) in the pH range of 5 to 6. Vanadium pentoxide V2O5 can be routinely produced from AMV or APV by calcination in air, vanadium dioxide VO2 by calcination with mild reducing agents such as natural gas, or vanadium trioxide V2O3 by calcination with hydrogen. Table 1 shows the contents of molybdenum, vanadium and sulfur in the sodium vanadate solution before and after molybdenum removal, the contents in the precipitate calcium molybdate and the contents of the ammonium metavanadates (AMV) obtained from the respective NaV solutions.
[0030] Tab. 1 : Molybdenum, vanadium and sulfur contents of the NaV solutions before and after Mo removal, of the calcium molybdate and of the AMV without and with Mo removal. Example 1 shows that the NaV solution with 8.5 g / L Mo and 42.8 g / LV contains 0.8 g / L Mo and 42.6 g / LV after applying the described process. The precipitate, calcium molybdate, contains Mo and V in a molar ratio of 88:12, which reflects the selectivity of the process. The AMV subsequently precipitated from the molybdenum-poor NaV solution contains 0.008% Mo (corresponding to 0.010% Mo in V2O5; 0.011% Mo in VO2; and 0.013% Mo in V2O3). The AMV without prior molybdenum removal contains 0.051% Mo (corresponding to 0.065% Mo in V2O5; 0.073% Mo in VO2; and 0.080% Mo in V2O3). This example demonstrates that the inventive process for selective molybdenum removal from sodium vanadate solutions is successful, enabling the production of high-purity vanadium chemicals such as AMV from raw materials with high molybdenum contents (2.4% Mo). This example also shows that the precipitation of calcium molybdate is selective compared to the possible precipitation of calcium sulfate.
[0031] Example 2
[0032] In this example, 1 liter of a sodium vanadate solution (NaV solution) is obtained by leaching a roasted Ni-Mo catalyst with 13.5% V and 5.5% Mo. The NaV solution, containing 7.9 g / L molybdenum, 36.3 g / L vanadium, and 79 g / L sodium sulfate, was heated to 60°C. A total of 6.09 g of calcium hydroxide (anhydrous), stoichiometric with respect to molybdenum, was then added. The calcium hydroxide was added in four portions of 1.52 g each, each at intervals of 20 minutes. Between the additions of the calcium hydroxide portions, the pH was kept constant at 6.8 by slowly adding concentrated sulfuric acid (96%). After the last portion was added and the pH was adjusted, the suspension was stirred at 60°C for five hours. During the stirring period, the pH was checked every hour and readjusted to 7.0 if necessary. The precipitate was filtered and washed with water.Ammonium sulfate was added to the molybdenum-poor sodium vanadate solution at a pH of 8 to 9, and the mixture was stirred for two hours. The precipitated ammonium metavanadate (AMV) was filtered and washed with water. As an alternative to AMV, precipitation in the pH range of 2 to 3 can yield an ammonium polyvanadate (APV) or a sodium polyvanadate (NPV), and a sodium ammonium vanadate (NAV) can be obtained in the pH range of 5 to 6. Vanadium pentoxide V2O5 can be routinely produced from AMV or APV by calcination in air, vanadium dioxide VO2 by calcination with mild reducing agents such as natural gas, or vanadium trioxide V2O3 by calcination with hydrogen.
[0033] Table 2 shows the contents of molybdenum, vanadium and sulfur in the sodium vanadate solution before and after molybdenum removal, the contents in the precipitate calcium molybdate and the contents of the ammonium metavanadates (AMV) obtained from the respective NaV solutions:
[0034] Tab. 2: Molybdenum, vanadium and sulfur contents of the NaV solutions before and after Mo removal, of the calcium molybdate and of the AMV without and with Mo removal. Example 2 shows that the sodium vanadate solution with 7.9 g / L Mo and 36.3 g / LV contains 2.2 g / L Mo and 35.9 g / LV after applying the described process. The precipitate, calcium molybdate, contains Mo and V in a molar ratio of 83:17, which reflects the selectivity of the process. The AMV subsequently precipitated from the molybdenum-poor sodium vanadate solution contains 0.009% Mo (corresponding to 0.012% Mo in V2O5; 0.013% Mo in VO2; and 0.014% Mo in V2O3), whereas the AMV without prior molybdenum removal contains 0.075% Mo (corresponding to 0.096% Mo in V2O5; 0.107% Mo in VO2; and 0.117% Mo in V2O3). This example proves that the inventive method of selective molybdenum removal from sodium vanadate solutions is successful and thus enables the production of high-purity vanadium chemicals such as AMV from raw materials with high molybdenum contents (5.5% Mo).This example also shows that the precipitation of calcium molybdate is selective compared to a possible precipitation of calcium sulfate.
Claims
Patent claims 1. A process for the production of high-purity vanadium chemicals from vanadium raw materials with high molybdenum contents, characterized in that molybdenum is selectively precipitated via vanadium from alkali vanadate solutions, comprising the following process steps: - Providing a molybdenum-containing alkali vanadate solution at a maximum temperature of 70 °C, preferably about 60 °C, - adding calcium hydroxide as a precipitant in portions while keeping the pH constant between 6 and 7 with acid, - Mixing the solution, - Solid-liquid separation of the resulting suspension, and - Further processing of the low-molybdenum alkali vanadate solution into a high-purity vanadium chemical with a molybdenum content of maximum 500 ppm.
2. Process according to claim 1, characterized in that the precipitation of molybdenum takes place in the form of one or more molybdenum-containing calcium compounds, preferably as calcium molybdate.
3. Process according to claim 1 or 2, characterized in that the alkali vanadate solution provided has a higher vanadium content than molybdenum content and at the same time a high neutral salt content, the molybdenum content being at least 6.5 g / L.
4. Process according to one of the preceding claims, characterized in that the precipitation of molybdenum takes place before the precipitation of vanadium from the alkali vanadate solution.
5. Process according to one of the preceding claims, characterized in that the portionwise addition of calcium hydroxide is carried out stoichiometrically with respect to molybdenum in at least four steps within a period of 90 minutes.
6. Process according to one of the preceding claims, characterized in that the precipitation of the molybdenum-containing calcium compound takes place in an aqueous medium without the addition of organic auxiliaries.
7. Process according to one of the preceding claims, characterized in that the pH value is kept constant in this range by portionwise dosing of sulfuric acid.
8. Process according to one of the preceding claims, characterized in that the pH is kept constant in a range from 6.2 to 6.
9.
9. Process according to one of the preceding claims, characterized in that the vanadium raw materials with high molybdenum contents are spent catalysts, preferably vanadium-containing Ni-Mo catalysts, or vanadium-containing residues from petroleum refineries.