Method for producing high purity vanadium chemicals from high molybdenum content vanadium feedstock

Abstract

A process for producing a high purity vanadium chemical from a vanadium feedstock having a high molybdenum content wherein molybdenum is selectively precipitated with respect to vanadium from an alkaline vanadate solution by the following process steps: providing an alkaline vanadate solution containing molybdenum at a temperature of at most 70 DEG C, preferably about 60 DEG C, the invention relates to a method for producing a vanadium chemical, comprising the steps of:-adding calcium hydroxide as a precipitating agent in batches while keeping the pH constant between 6 and 7 using an acid,-mixing the solutions,-subjecting the resulting suspension to solid-liquid separation, and-further treating the low-molybdenum alkaline vanadate solution to produce a high-purity vanadium chemical with a molybdenum content of at most 500 ppm.

Description

Technical Field

[0001] The present invention relates to a method for producing high-purity vanadium chemicals from vanadium raw materials with a high molybdenum content. Background Art

[0002] With regard to the background of the present invention, it should be noted that its purpose is to develop a chemical separation method for selectively extracting molybdenum from alkaline vanadate solutions, in particular from sodium vanadate solutions with a high neutral salt content. This method will be used before vanadium precipitation in order to be able to use vanadium raw materials with a high molybdenum content to produce high-purity vanadium chemicals. These high-purity vanadium chemicals meet the requirements for use in the catalyst and aviation industries and as energy storage materials.

[0003] Raw materials used for this purpose may be spent catalysts and gasification residues from the petrochemical industry.

[0004] This separation method is required because molybdenum is leached from the above raw materials with the same efficiency as vanadium and partially precipitates with the vanadium. If vanadium precipitation occurs before molybdenum precipitation, the higher the molybdenum content in the raw materials, the more the vanadium chemicals will be contaminated with molybdenum. This makes the vanadium chemicals unusable for the above applications.

[0005] Specifically, the relevant prior art provides various techniques for extracting molybdenum from vanadate solutions, namely precipitation, ion exchange or liquid-liquid extraction - see L. Zeng, CY Cheng, "Literature Review on Recovery of Molybdenum and Vanadium from Waste Hydrodesulfurization Catalysts, Part II: Separation and Purification", "Hydrometallurgy", 2009, 98, pp. 10-20, and TH Nguyen, MS Lee, "A Review on Separation of Molybdenum, Tungsten and Vanadium from Leachates from Different Resources by Solvent Extraction", "Geosystems Engineering", 2016, 19, pp. 247-259.

[0006] For example, selective extraction of molybdenum from vanadate solutions by precipitation is possible only after the vanadium content of the mother liquor has been reduced by a previous precipitation process and the remaining vanadium has been reduced to tetravalent vanadium with sulfur dioxide at a temperature of 80°C to 90°C. Then, molybdic acid is precipitated in strong hydrochloric acid at a pH value below 1.1 - see ZR Lanos, GFP Provoost, WG Deering, FJ Debaene, "Integrated process for recovery of metals and molten alumina from spent catalysts", patent US 5702500A, 1997.

[0007] From WO 2007 / 020338 A2 it is known to first precipitate vanadium from a purified sodium vanadate solution at 90° C. using ammonium chloride at a pH of 7-8, this solution containing 25.3 g / L of molybdenum and 2.1 g / L of vanadium, this solution being obtained from a raw material containing 9.7% molybdenum and 1.5% vanadium. This results in the precipitation of 1.5% of molybdenum and more than 95% of vanadium. Taking into account the volume of ammonium chloride solution added, a clear solution containing 18.7 g / L of molybdenum and less than 0.08 g / L of vanadium is finally obtained, and the molybdenum is precipitated as calcium molybdate using a calcium chloride solution at a pH of 7-8 and 90° C. In the absence of any contrary disclosure in the publication, it is evident that this amount of calcium chloride solution is added all at once. If the alkaline vanadate solution (the content of vanadium in the solution is more than platinum) different from WO 2007 / 020338 A2 is handled in the same manner, although the solubility of calcium molybdate is lower as described in CN1321782A, in addition to calcium molybdate, a considerable amount of calcium metavanadate can also be precipitated. This is because, in a solution containing multiple high-concentration salts (such as calcium molybdate, calcium metavanadate, sodium metavanadate and sodium sulfate), due to the salting-out effect, the precipitation of the minority component calcium molybdate is kinetically suppressed, and if the molybdenum content is lower than a certain level, precipitation does not even occur completely. In contrast, because the salting-out effect has a smaller impact on the composition with higher concentration, although the solubility of calcium metavanadate is higher, the precipitation of the main component calcium metavanadate is kinetically preferred. If the reaction process does not clearly suppress the precipitation of the preferred calcium metavanadate kinetically, as in the case of using the method described in WO 2007 / 020338A2, molybdenum will be significantly changed relative to the selectivity of vanadium, which is conducive to vanadium. Therefore, more molybdenum remains in the precipitate, thereby affecting the purity of subsequent products (such as ammonium metavanadate or vanadium pentoxide, etc.).

[0008] In the vanadium extraction process of CN1321782A above, before adding ammonium carbonate solution for dissolution, calcium molybdate, calcium metavanadate and sodium metavanadate exist in solid form in the presence of sodium sulfate due to the use of calcium roasting. This results in the selective dissolution of calcium metavanadate relative to calcium molybdate, rather than the selective precipitation of molybdenum from the alkaline vanadate solution. If molybdenum is selectively removed only based on the indication of the lower solubility of calcium molybdate relative to calcium metavanadate in CN1321782A, this is only applicable to solutions with a vanadium content significantly lower than the molybdenum content, because the competitive precipitation of calcium metavanadate cannot be suppressed. In contrast, it is only shown that the lower solubility of calcium molybdate relative to calcium metavanadate cannot achieve the selective molybdenum extraction required for the production of high-purity vanadium chemicals in solutions with a vanadium content higher than the molybdenum content and a high neutral salt content at the same time. If such solutions exist, it is more necessary to control the reaction kinetics.

[0009] These examples show that it is known to precipitate molybdenum from solutions that have previously been precipitated with vanadium and are significantly depleted. However, according to current knowledge, there are no reports of successful selective precipitation of molybdenum from vanadate solutions that have a higher vanadium content than molybdenum and that also have a high content of neutral salts, in which case the competitive precipitation of vanadium needs to be suppressed.

[0010] In ion exchange systems, hexavalent molybdenum and pentavalent vanadium are equally adsorbed and eluted, so no separation occurs here. This is used for complete purification of wastewater, but is only economically feasible when the vanadium and molybdenum contents are low (0.1 g / L-1 g / L). With the help of ion exchange, molybdenum can be effectively separated from tetravalent vanadium only in the strongly acidic range (pH 1), which in turn requires the use of sulfite to reduce the vanadium - see L. Zeng, CY Cheng, ibid.

[0011] The most widely used method for extracting molybdenum from vanadate solutions is liquid-liquid extraction - see L. Zeng, CY Cheng, supra, TH Nguyen, MS Lee, supra, and US 5431892A. By extracting molybdenum from vanadate solutions with similar vanadium and molybdenum contents (about 10 g / L each), high-purity vanadium chemicals can be obtained - see US 5431892A. However, due to the use of organophosphorus or alkylamine-based extractants dissolved in organic solvents (such as kerosene or xylene) and subsequent back extraction with ammonia, this method is technically very complex and very costly due to the use of special chemicals. In addition, molybdenum is extracted from these vanadate solutions in a strongly acidic state (usually in the pH range of hydrochloric acid). For example, the organophosphorus extractant di-(2-ethylhexyl)phosphoric acid (D2EHPA) dissolved in kerosene—see RK Biswas, Recovery of vanadium and molybdenum from spent catalysts from heavy oil desulfurization, Hydrometallurgy, 1985, 14, pp. 219–230—or trioctylphosphine oxide (TOPO)—see YA El-Nadi, NS Awwad, AA Nayl, Comparative study of vanadium extraction from acidic and alkaline media by Aliquat 336 and its application to spent catalysts, International Journal of Mineral Processing, 2009, 92, pp. 115–120—can be used to separate cationic molybdenum from vanadium species at pH < 1. Ammonia must then be used to separate the molybdenum. If D2EHPA is used, a second organic phase may be formed due to increased viscosity, which makes it difficult to reuse the extractant - see P. Zhang, K. Inoue, "Recovery of metal values ​​from spent hydrodesulfurization catalysts by liquid-liquid extraction", Energy & Fuels, 1995, 9, pp. 231-239.High amines such as trioctylamine (TOA), alamin 336 dissolved in toluene - see MAO Lazabal, MM Orive, LA Fernandez, JM Madariaga, "Selective Extraction of Vanadium (V) from Molybdenum (VI)-Containing Solutions by Ammonium Salts Dissolved in Toluene", Solvent Extraction and Ion Exchange, 1992, 10, pp. 623-635 - or a combination of TOA and tributyl phosphate (TBP) - see HI Kim, KW Lee, D. Mishra, KMYi, JH Hong, MK Jun, HK Park, "Separation and Recovery of Vanadium from Leachate of Waste Residue Hydrodesulfurization (RHDS) Catalyst Using Solvent Extraction", Journal of Industrial and Engineering Chemistry, 2014, 20, pp. 4457-4462 - can only extract molybdenum via tetravalent vanadium species at pH <1, and the tetravalent vanadium species must first be prepared using sulfite or sulfur dioxide.

[0012] All these known extraction methods have in common that the vanadium content of the solution to be treated is similar to or lower than the high molybdenum content (usually <1 g / L for vanadium and 1-10 g / L for molybdenum). Summary of the invention

[0013] Based on the above problems, the object of the present invention is to provide a simpler, environmentally friendly and efficient method for selectively extracting molybdenum from an alkaline vanadate solution, which has a high molybdenum content and a relatively high vanadium content and a high neutral salt content at the same time, so as to produce high-purity vanadium chemicals.

[0014] This object is achieved by a process having the features of claim 1, wherein molybdenum is selectively precipitated relative to vanadium from an alkaline vanadate solution by applying the following process steps:

[0015] - providing an alkaline vanadate solution containing molybdenum at a temperature of up to 70° C., preferably about 60° C.,

[0016] - calcium hydroxide is added in batches as a precipitant while the pH is kept constant between 6 and 7 using acid,

[0017] - mixed solution,

[0018] - solid-liquid separation of the resulting suspension, and

[0019] - Further processing of the low-molybdenum alkaline vanadate solution to produce high-purity vanadium chemicals with a molybdenum content of up to 500 ppm.

[0020] The method of the present invention solves the main problem of avoiding competitive precipitation of vanadium when treating alkaline vanadate solutions with a vanadium content higher than the molybdenum content and a high neutral salt content by controlling the kinetics of the ongoing reaction in a clear manner and by ensuring that the correct vanadium and molybdenum species are present in the solution throughout the precipitation process. The reaction kinetics of the formation of calcium metavanadate are controlled by adding calcium hydroxide in batches (in other words, in a slowed manner) so that the thermodynamically favorable product calcium molybdate is still formed preferentially (thermodynamic reaction control) despite the kinetic inhibition of the salting-out effect. For example, if added quickly, the kinetically favorable product calcium metavanadate will always precipitate in the case of an excess of vanadium. The pH value is adjusted between each addition of lime to prevent the precipitation reaction from entering the alkaline pH range, so that the calcium metavanadate is as little as possible, mainly the more soluble calcium decavanadate, which ultimately contributes to the selective precipitation of calcium molybdate. In addition, due to the shift in the equilibrium between molybdate and heptamolybdate, the lower limit of pH should also be controlled. It is best to avoid pH values ​​below 6.2 here, otherwise the proportion of molybdate will shift in favor of heptamolybdate. However, only molybdate ions can form calcium molybdate which is not easily soluble, while calcium heptamolybdate is very soluble. If the proportion of molybdate decreases with decreasing pH, the remaining molybdate will no longer precipitate due to the general salting-out effect. Due to the above, the pH value is preferably between 6.2 and 6.9 (claim 8).

[0021] Only by combining the two steps of adding calcium hydroxide in batches and maintaining a constant pH value can the selectivity of molybdenum for vanadium according to the present invention be achieved from a solution having a higher vanadium content than a molybdenum content and a high neutral salt content, and only in this way can a high-purity vanadium chemical with a molybdenum content of up to 500 ppm be obtained.

[0022] Further advantageous developments of the method according to the invention are set forth in the dependent claims.

[0023] Therefore, the present invention mainly aims at obtaining molybdenum by precipitating molybdenum, such as calcium molybdate (CaMoO 4 ) - see claim 2. The object of the invention is achieved primarily by precipitating molybdenum from an alkaline vanadate solution having a higher vanadium content than molybdenum content and a simultaneously high neutral salt content, the molybdenum content being at least 6.5 g / L, and the neutral salt content, in particular sodium sulfate content, preferably being 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. The precipitation of molybdenum is carried out until the residual solubility of molybdenum is 1 g / L to 2 g / L, which ensures the continuous production of high-purity vanadium chemicals with a molybdenum content of up to 500 ppm from the above raw materials. Only by applying this method is it possible to use such a raw material with a high molybdenum content.

[0024] The precipitation of molybdenum as calcium molybdate is carried out in an aqueous medium without the addition of organic auxiliary substances - see claim 6. The precipitation of molybdenum as calcium molybdate is carried out by incremental addition of a certain amount of calcium hydroxide relative to the stoichiometric amount of molybdenum - see claim 5. The pH value can be kept constant by batchwise metering of sulfuric acid - see claim 7. Under the above conditions, molybdenum is precipitated with a selectivity of 85% to 90% relative to vanadium, which is expressed by a molar ratio of molybdenum to vanadium in the calcium molybdate of 85:15 to 90:10. The precipitation of sparingly soluble calcium sulfate is negligible. The achievable purity of calcium molybdate allows its sale as a product in the molybdenum industry.

[0025] Therefore, the process of the present invention makes it possible to produce the above-mentioned high-purity vanadium chemicals from vanadium raw materials with a high molybdenum content (such as spent catalysts, preferably vanadium-containing Ni-Mo catalysts, or vanadium-containing residues from refineries) - see claim 9.

[0026] The decisive advantage of the present invention over the prior art is that molybdenum can be selectively extracted by precipitation as calcium molybdate from alkaline vanadate solutions having a significantly higher vanadium content (about 35 g / L-50 g / L) than molybdenum content (about 7 g / L-10 g / L) and a high neutral salt content. According to the present invention, the precipitation of molybdenum can be carried out before the precipitation of vanadium, so that the molybdenum content in the mother liquor used for the subsequent precipitation of ammonium metavanadate (AMV) has been continuously reduced to a low level (1 g / L to 2 g / L). Therefore, unlike the prior art, high-purity vanadium chemicals with a molybdenum content of up to 500 ppm can be produced from raw materials with a high molybdenum content by means of a molybdenum precipitation reaction as a purification step.

[0027] By using the method of the present invention, ion exchange methods and liquid-liquid extraction can be avoided, which constitutes an additional difference with respect to the prior art and has additional economic, safety and environmental advantages. Molybdenum is precipitated as calcium molybdate only in aqueous media and in weakly acidic to neutral alkaline vanadate solutions in the pH range of 6 to 7, which is gentle on the system. Only calcium hydroxide, which is cheap, non-toxic and unobjectionable in terms of occupational safety and the environment, and a small amount of sulfuric acid are used in the present invention. In addition, if calcium hydroxide is used, high-purity vanadium chemicals will not be contaminated with chloride ions as when calcium chloride is used. The possibility of cross-contamination of vanadium chemicals and wastewater streams with organic substances is excluded. When using this method, chemical-intensive pH jumps and oxidation or reduction processes can be avoided. Similarly, complex extraction and stripping methods or units can also be omitted; only a heatable stirring tank is required. In addition, CaMoO at about 60°C 4The energy required for precipitation is less than, for example, the energy required for precipitating molybdic acid at 80 to 90° C. and calcium molybdate at 90° C. as reported in WO 2007 / 020338 A2. The preferred temperature range of about 60° C. according to the invention may be between 58 and 62° C.

[0028] Further features, details and advantages of the invention will become apparent from the following description of embodiments. DETAILED DESCRIPTION

[0029] Example 1

[0030] In this example, 1 liter of sodium vanadate solution (NaV solution) was obtained by leaching from a calcined Ni-Mo catalyst with 18.7% V and 2.4% Mo. The NaV solution contained 8.5 g / L molybdenum, 42.8 g / L vanadium and 105 g / L sodium sulfate and was heated to 60°C. Then, a total of 6.55 g of calcium hydroxide (anhydrous) was added, which was equivalent to the stoichiometric amount relative to molybdenum. Calcium hydroxide was added in four portions of 1.64 g each, with an interval of 20 minutes each. Between the additions of calcium hydroxide, the pH was kept constant at 6.4 by slowly metering concentrated sulfuric acid (96%). After adding the last portion and adjusting the pH, the suspension was stirred at 60°C for five hours. During stirring, the pH was checked and adjusted to 6.4 if necessary. The precipitate was filtered and washed with water. At a pH of 8 to 9, ammonium sulfate was added to the low sodium molybdate solution and stirred for two hours. The precipitated ammonium metavanadate (AMV) is filtered and washed with water. As an alternative to AMV, ammonium polyvanadate (APV) or sodium polyvanadate (NPV) can be obtained by precipitation in the pH range of 2 to 3, and sodium ammonium vanadate (NAV) can be obtained by precipitation in the pH range of 5 to 6. Vanadium pentoxide (V pentoxide) can be conventionally produced from AMV or APV by calcination in an air atmosphere. 2 O 5 ), vanadium dioxide (VO 2) can be produced by calcination using natural gas and other mild reducing agents. 2 ), or vanadium trioxide (V 2 O 3 Table 1 shows the molybdenum, vanadium and sulfur contents in the sodium vanadate solution before and after the removal of molybdenum, the molybdenum, vanadium and sulfur contents in the precipitate (calcium molybdate), and the molybdenum, vanadium and sulfur contents in the ammonium metavanadate (AMV) obtained from the corresponding NaV solution:

[0031] Table 1: Molybdenum, vanadium and sulfur contents in NaV solution before and after molybdenum removal, calcium molybdate and ammonium metavanadate (AMV) without and with molybdenum removal.

[0032]

[0033] Example 1 shows that after applying the described method, a NaV solution containing 8.5 g / L Mo and 42.8 g / L V contained 0.8 g / L Mo and 42.6 g / L V. The precipitated calcium molybdate contained Mo and V in a molar ratio of 88:12, which reflects the selectivity of this method. The ammonium metavanadate (AMV) subsequently precipitated from the low-molybdenum NaV solution contained 0.008% Mo (equivalent to V 2 O 5 0.010% Mo, VO 2 0.011% Mo and V 2 O 3 The AMV without prior removal of molybdenum contains 0.051% Mo (equivalent to V 2 O 5 0.065% Mo, VO 2 0.073% Mo and V 2 O 3 This example shows that the method of the present invention for selectively removing molybdenum from a sodium metavanadate solution is successful and that high purity vanadium chemicals, such as ammonium metavanadate (AMV), can be produced from a high molybdenum content (2.4% Mo) feedstock. This example also shows that the precipitation of calcium molybdate is selective over possible calcium sulfate precipitation.

[0034] Example 2

[0035] In this example, 1 liter of sodium vanadate solution (NaV solution) was obtained by leaching from a calcined Ni-Mo catalyst with 13.5% V and 5.5% Mo. The NaV solution contained 7.9 g / L molybdenum, 36.3 g / L vanadium and 79 g / L sodium sulfate and was heated to 60°C. Then, a total of 6.09 g of calcium hydroxide (anhydrous) was added, which was equivalent to the stoichiometric amount relative to molybdenum. Calcium hydroxide was added in four portions of 1.52 g per portion, with an interval of 20 minutes each. Between the addition of each portion of calcium hydroxide, the pH value was kept constant at 6.8 by slowly metering concentrated sulfuric acid (96%). After adding the last portion and adjusting the pH value, the suspension was stirred at 60°C for five hours. During stirring, the pH value was checked every hour and adjusted to 7.0 if necessary. The precipitate was filtered and washed with water. When the pH value was 8 to 9, ammonium sulfate was added to the low sodium molybdate solution and stirred for two hours. The precipitated ammonium metavanadate (AMV) was filtered and washed with water. As an alternative to AMV, ammonium polyvanadate (APV) or sodium polyvanadate (NPV) can be obtained by precipitation in the pH range of 2 to 3, and sodium ammonium vanadate (NAV) can be obtained by precipitation in the pH range of 5 to 6. Vanadium pentoxide (V pentoxide) can be conventionally produced from AMV or APV by calcination in an air atmosphere. 2 O 5 ), vanadium dioxide (VO 2) can be produced by calcination using natural gas and other mild reducing agents. 2 ), vanadium trioxide (V 2 O 3 ).

[0036] Table 2 shows the molybdenum, vanadium and sulfur contents in the sodium vanadate solution before and after the removal of molybdenum, the molybdenum, vanadium and sulfur contents in the precipitate (calcium molybdate), and the molybdenum, vanadium and sulfur contents in the ammonium metavanadate (AMV) obtained from the corresponding NaV solution:

[0037] Table 2: Molybdenum, vanadium and sulfur contents in sodium metavanadate solution before and after molybdenum removal, calcium molybdate and ammonium metavanadate (AMV) without and with molybdenum removal.

[0038]

[0039] Example 2 shows that after applying the described method, a sodium vanadate solution containing 7.9 g / L Mo and 36.3 g / L V contained 2.2 g / L Mo and 35.9 g / L V. The precipitated calcium molybdate contained Mo and V in a molar ratio of 83:17, which reflects the selectivity of this method. The ammonium metavanadate (AMV) subsequently precipitated from the low molybdate sodium vanadate solution contained 0.009% Mo (equivalent to V 2 O 5 0.012% Mo in VO 20.013% Mo and V 2 O 3 0.014% Mo in AMV), while AMV without prior molybdenum removal contains 0.075% Mo (equivalent to V 2 O 5 0.096% Mo in VO 2 0.107% Mo and V 2 O 3 This example shows that the method of the present invention for selectively removing molybdenum from a sodium vanadate solution is successful and that high purity vanadium chemicals, such as ammonium metavanadate (AMV), can be produced from a high molybdenum content (5.5% Mo) feedstock. This example also shows that the precipitation of calcium molybdate is selective over possible calcium sulfate precipitation.

Claims

1. A method for producing high-purity vanadium chemicals from vanadium raw materials with a high molybdenum content, characterized in that: Molybdenum is selectively precipitated relative to vanadium from an alkaline vanadate solution by the following process steps: - providing an alkaline vanadate solution containing molybdenum at a temperature of up to 70° C., preferably about 60° C., - calcium hydroxide is added in batches as a precipitant while the pH is kept constant between 6 and 7 using acid, - mixed solution, - solid-liquid separation of the resulting suspension, and - Further processing of the low-molybdenum alkaline vanadate solution to produce high-purity vanadium chemicals with a molybdenum content of up to 500 ppm.

2. The method according to claim 1, characterized in that The molybdenum is precipitated in the form of one or more molybdenum-containing calcium compounds, preferably calcium molybdate.

3. The method according to claim 1 or 2, characterized in that: The alkaline vanadate solution provided has a vanadium content higher than a molybdenum content and at the same time a high neutral salt content, with a molybdenum content of at least 6.5 g / L.

4. A method according to any preceding claim, characterised in that The precipitation of molybdenum occurs prior to the precipitation of vanadium from the alkaline vanadate solution.

5. A method according to any preceding claim, characterised in that Calcium hydroxide is added in at least four steps over a period of 90 minutes, in a stoichiometric amount relative to molybdenum.

6. A method according to any preceding claim, characterised in that The precipitation of the molybdenum-containing calcium compound is carried out in an aqueous medium without the addition of organic auxiliary substances.

7. A method according to any preceding claim, characterised in that The pH was kept constant within this range by metering sulfuric acid in portions.

8. A method according to any preceding claim, characterised in that The pH value was maintained in the range of 6.2 to 6.

9.

9. A method according to any preceding claim, characterised in that The vanadium raw material with a high molybdenum content is a spent catalyst, preferably a vanadium-containing Ni-Mo catalyst, or a vanadium-containing residue from an oil refinery.

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