Method for circularly and efficiently extracting vanadium in waste SCR (Selective Catalytic Reduction) denitration catalyst

Abstract

The invention provides a method for circularly and efficiently extracting vanadium in a waste SCR denitration catalyst, and belongs to the technical field of nonferrous metallurgy and waste catalyst recycling. The method comprises the following steps: firstly, pretreating the waste SCR denitration catalyst to obtain waste SCR denitration catalyst powder; mixing the waste SCR denitration catalyst powder with an organic solvent, then carrying out a leaching reaction, and after the reaction is finished, cooling and separating to obtain a leaching solution; then the leachate is returned to a leaching reaction for circular treatment, and vanadium-rich liquid is obtained; and finally, the vanadium-rich liquid is subjected to a hydrothermal reaction, and VO2 is obtained. According to the method, the operation process and equipment are simple, and the utilization efficiency of oxalic acid in the waste SCR catalyst leaching process can be effectively improved; according to the technological process and the addition of oxalate, the selectivity of oxalic acid can be effectively improved, and good economic benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of nonferrous metal metallurgy and waste catalyst recycling, and in particular to a method for cyclically and efficiently extracting vanadium from waste SCR denitration catalysts. Background Art

[0002] In coal-fired power plants, V2O5-WO3 / TiO2 catalysts are commonly used SCR catalysts. As the catalysts are used for a longer time, alkali metals, ammonium salts, and heavy metals will cause catalyst poisoning, coal ash will cause catalyst micropore blockage, and high operating temperatures will cause catalyst sintering. A large amount of waste SCR denitration catalysts are produced every year. Recycling waste SCR denitration catalysts and extracting useful metal materials (vanadium, tungsten, titanium, etc.) from them is a common way to dispose of waste SCR denitration catalysts.

[0003] The patented methods for recovering vanadium from waste flue gas denitrification catalysts disclosed in China mainly include acid leaching, alkaline leaching and alkaline roasting. Among them, the acid leaching conditions are mild, the cost is low, the vanadium leaching efficiency is high, and it is suitable for large-scale application. Oxalic acid in acid leaching, as a good reducing agent and complexing agent, can effectively improve the leaching efficiency of vanadium in waste SCR catalysts. Oxalic acid can form a water-soluble complex with vanadium in the waste SCR catalyst, thereby separating vanadium from the solid structure of the catalyst and allowing it to enter the leaching solution. The vanadium in the leaching solution is enriched by evaporation, ion exchange or extraction, and then ammonium salt precipitation, filtration and roasting methods are used to obtain V2O5.

[0004] Patent CN106011472A discloses a method for recovering vanadium from waste SCR denitration catalysts using reducing organic acids, and extracts precious metal vanadium from waste catalysts by roasting, acid leaching and concentrated crystallization. Patent CN108642271B discloses a novel method for producing vanadium dioxide from vanadium-containing shale without ammonium precipitation, and adds oxalic acid or oxalate to vanadium-rich solution, and then reacts at 180-250°C for 6-10 hours to obtain a vanadium dioxide product. In these existing technologies, the process of leaching vanadium from waste SCR catalysts with oxalic acid has problems such as low oxalic acid utilization efficiency and high impurity content in the leachate, which is not conducive to enrichment.

[0005] Based on this, it is very important to provide a method for enriching vanadium in the leaching solution with high oxalic acid utilization efficiency. Summary of the invention

[0006] The purpose of the present invention is to provide a method for cyclically and efficiently extracting vanadium from waste SCR denitration catalysts, so as to solve the technical problems in the prior art of low oxalic acid utilization efficiency and high impurity content in the leachate which is not conducive to enrichment.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for cyclically and efficiently extracting vanadium from a discarded SCR denitration catalyst, comprising the following steps:

[0009] 1) Pre-treating the waste SCR denitration catalyst to obtain waste SCR denitration catalyst powder;

[0010] 2) mixing the waste SCR denitration catalyst powder and the organic solvent to carry out a leaching reaction, cooling and separating after the reaction to obtain a leaching solution;

[0011] 3) returning the leaching solution to step 2) for cyclic treatment to obtain vanadium-rich solution;

[0012] 4) The vanadium-rich solution is subjected to a hydrothermal reaction to obtain VO2.

[0013] Furthermore, the organic solvent is an oxalic acid-oxalate solution, and the ratio of the amount of oxalic acid to the amount of oxalate in the oxalic acid-oxalate solution is 14 to 18:1;

[0014] The concentration of oxalic acid in the oxalic acid-oxalate solution is 0.3-0.5 mol / L.

[0015] Further, the pretreatment includes ultrasonic cleaning, drying and crushing of the waste SCR denitration catalyst;

[0016] The ultrasonic cleaning time is 20 to 40 minutes, the drying temperature is 80 to 120° C., and the drying time is 8 to 16 hours.

[0017] Furthermore, the particle size of the waste SCR denitration catalyst powder is 100-325 meshes.

[0018] Furthermore, the leaching reaction temperature is 70-95° C., the leaching reaction time is 3-9 hours, and the liquid-to-solid ratio is 10-25 mL / g.

[0019] Furthermore, the mass concentration of vanadium in the vanadium-rich solution is 0.85-1.6 g / L.

[0020] Furthermore, the temperature of the hydrothermal reaction is 150-200° C., and the time of the hydrothermal reaction is 6-10 hours.

[0021] Beneficial effects of the present invention:

[0022] (1) The present invention recycles the leaching solution, greatly improving the quality of vanadium leached per unit mass of oxalic acid, and effectively improving the utilization efficiency of oxalic acid;

[0023] (2) In the present invention, during the leachate circulation process, elements such as aluminum, silicon and tungsten are limited by solubility. As the number of leaching times increases, the leaching rate drops sharply, which effectively reduces the proportion of impurities while increasing the vanadium concentration in the leachate, achieving a preliminary enrichment effect;

[0024] (3) The waste SCR denitration catalyst of the present invention contains a variety of metal oxides. The addition of oxalate to provide reactants for the oxalic acid solution will not increase the acidity of the solution, thereby effectively improving the average leaching efficiency of vanadium and the selectivity of oxalic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The process flow chart of the method for cyclically and efficiently extracting vanadium from waste SCR denitration catalysts of the present invention;

[0026] Figure 2 is a graph showing the variation of the leaching efficiency of each element with the number of leaching times in Example 1 of the present invention;

[0027] Figure 3 is a graph showing the variation of the leaching efficiency of each element with the number of leaching times in Example 2 of the present invention;

[0028] Figure 4 This is a graph showing the variation of the leaching efficiency of each element with the number of leaching times in Comparative Example 1 of the present invention;

[0029] Figure 5 This is a graph showing the change in vanadium leaching efficiency with leaching times in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0030] The present invention provides a method for cyclically and efficiently extracting vanadium from a discarded SCR denitration catalyst, comprising the following steps:

[0031] 1) Pre-treating the waste SCR denitration catalyst to obtain waste SCR denitration catalyst powder;

[0032] 2) mixing the waste SCR denitration catalyst powder and the organic solvent to carry out a leaching reaction, cooling and separating after the reaction to obtain a leaching solution;

[0033] 3) returning the leaching solution to step 2) for cyclic treatment to obtain vanadium-rich solution;

[0034] 4) The vanadium-rich solution is subjected to a hydrothermal reaction to obtain VO2.

[0035] In the present invention, the organic solvent is an oxalic acid-oxalate solution, and the ratio of the amount of oxalic acid to the amount of oxalate in the oxalic acid-oxalate solution is 14 to 18:1, preferably 15 to 17:1, and more preferably 16:1;

[0036] The concentration of oxalic acid in the oxalic acid-oxalate solution is 0.3-0.5 mol / L, preferably 0.35-0.45 mol / L, and more preferably 0.4 mol / L.

[0037] In the present invention, the pretreatment includes ultrasonic cleaning, drying and crushing of the waste SCR denitration catalyst;

[0038] The ultrasonic cleaning time is 20 to 40 minutes, preferably 25 to 35 minutes, and more preferably 30 minutes; the drying temperature is 80 to 120°C, preferably 90 to 110°C, and more preferably 100°C; the drying time is 8 to 16 hours, preferably 10 to 14 hours, and more preferably 12 hours.

[0039] In the present invention, the particle size of the spent SCR denitration catalyst powder is 100 to 325 meshes, preferably 120 to 300 meshes, and more preferably 150 to 250 meshes.

[0040] In the present invention, the leaching reaction temperature is 70-95°C, preferably 75-92°C, and more preferably 80-90°C; the leaching reaction time is 3-9h, preferably 4-8h, and more preferably 5-7h; the liquid-to-solid ratio is 10-25mL / g, preferably 12-23mL / g, and more preferably 15-20mL / g.

[0041] In the present invention, the mass concentration of vanadium in the vanadium-rich solution is 0.85 to 1.6 g / L, preferably 0.88 to 1.5 g / L, and more preferably 0.9 to 1.3 g / L.

[0042] In the present invention, the temperature of the hydrothermal reaction is 150-200° C., preferably 160-190° C., and more preferably 170-180° C.; the time of the hydrothermal reaction is 6-10 h, preferably 7-9 h, and more preferably 8 h.

[0043] In the present invention, the principle of the method of the present invention is that the waste SCR catalyst contains a variety of metal oxides. Due to the acidity and complexing ability of oxalic acid, leaching of vanadium will lead to leaching of other elements, which is not conducive to the subsequent further extraction of vanadium. Therefore, the present invention adopts a cyclic leaching process. During the circulation process, the presence of impurity elements in the leachate will effectively inhibit the subsequent leaching of impurity elements, and the addition of oxalate solution increases the reactants while reducing the acidity of the solution, further improving the selectivity of oxalic acid.

[0044] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0045] The waste SCR catalyst used in the embodiment of the present invention is a waste catalyst from a coal-fired power plant, wherein the mass fraction of each element is as follows:

[0046] element Ti W V Ca Al Fe Si Content / wt.% 53.86 4.1 0.52 1.04 0.9 0.04 2.55

[0047] The rest is oxygen.

[0048] Example 1

[0049] 100g of waste SCR denitration catalyst was precipitated for 30min, then dried at 100℃ for 12h, and finally crushed in a ball mill to obtain waste SCR denitration catalyst powder with a particle size of 180 mesh; the waste SCR denitration catalyst powder with a liquid-solid ratio of 20mL / g was mixed with oxalic acid-sodium oxalate solution, the concentration of oxalic acid was 0.4mol / L, the molar ratio of oxalic acid to sodium oxalate was 16:1, and the mixture was subjected to leaching reaction at 90℃ for 6h. After the reaction was completed, the mixture was cooled, and the cooled product was separated by filtration to obtain a leachate and a filter residue, the main component of the filter residue was anatase TiO2; the leachate was returned to the leaching reaction for recycling treatment to obtain a vanadium-rich solution with a vanadium mass concentration of 0.9g / L; finally, the vanadium-rich solution was subjected to a hydrothermal reaction at 180℃ for 8h, and then filtered to obtain VO2.

[0050] Example 2

[0051] 1000g of waste SCR denitration catalyst was ultrasonically cleaned for 30min, then dried at 100℃ for 12h, and finally crushed in a ball mill to obtain waste SCR denitration catalyst powder with a particle size of 180 mesh; the waste SCR denitration catalyst powder with a liquid-solid ratio of 20mL / g was mixed with oxalic acid-sodium oxalate solution, the oxalic acid concentration was 0.4mol / L, the molar ratio of oxalic acid to sodium oxalate was 16:1, and the mixture was subjected to leaching reaction at 90℃ for 6h. After the reaction was completed, the mixture was cooled, and the cooled product was separated by filtration to obtain a leachate and a filter residue, the main component of the filter residue was anatase TiO2; the leachate was returned to the leaching reaction for recycling treatment to obtain a vanadium-rich solution with a vanadium mass concentration of 0.9g / L; finally, the vanadium-rich solution was subjected to a hydrothermal reaction at 180℃ for 8h, and then filtered to obtain VO2.

[0052] Comparative Example 1

[0053] Compared with Example 1, other conditions are the same, except that sodium oxalate is not added in Comparative Example 1, and oxalic acid in the same amount as the sodium oxalate in Example 1 is added.

[0054] Comparative Example 2

[0055] Compared with Example 1, Comparative Example 2 only performed one leaching reaction.

[0056] Comparative Example 3

[0057] Compared with Example 1, other conditions are the same, except that in Comparative Example 3, oxalic acid is not added, and sodium oxalate in an amount equal to that of oxalic acid in Example 1 is added.

[0058] The VO2 prepared in each comparative example 1 to 2 of Examples 1 to 2 was analyzed, and the mass fractions of vanadium, aluminum, silicon and tungsten in the VO2 product were calculated. The calculation results are shown in Table 1.

[0059] Table 1 Mass fractions of vanadium, aluminum, silicon and tungsten in VO2 products

[0060] Mass fraction (%) vanadium aluminum silicon Tungsten Example 1 40.34 6.95 0.21 0.68 Example 2 39.72 6.97 0.36 0.96 Comparative Example 1 38.60 7.01 0.20 0.76 Comparative Example 2 23.48 15.04 6.59 13.35

[0061] It can be seen from the above embodiments that the present invention provides a method for cyclically and efficiently extracting vanadium from waste SCR denitration catalysts. First, the waste SCR denitration catalyst is pretreated to obtain waste SCR denitration catalyst powder; then, the waste SCR denitration catalyst powder is mixed with an organic solvent and subjected to a leaching reaction. After the reaction is completed, the mixture is cooled and separated to obtain a leachate; then, the leachate is returned to the leaching reaction cycle to obtain a vanadium-rich liquid; finally, the vanadium-rich liquid is subjected to a hydrothermal reaction to obtain VO2. As can be seen from Table 1, the VO2 products obtained in Example 1, Example 2 and Comparative Example 1 have a higher purity, and the mass fraction of vanadium is between 38 and 41%, which is significantly improved compared to Comparative Example 2. This is because during the cyclic leaching process of the leachate, the leaching of the main impurity elements aluminum, silicon and tungsten is subject to greater solubility limitations, thereby improving the purity of vanadium in the leachate, and the purity of vanadium in the final VO2 product is also improved. Figure 2 and Figure 4 It can be seen that when sodium oxalate is added during the oxalic acid cycle leaching of the waste SCR catalyst, the average leaching efficiency of vanadium is significantly improved from 69.08% to 77.37%, and the leaching efficiency of the impurity elements silicon, aluminum and tungsten does not change much. Figure 3 It can be seen that after increasing the processing amount of waste SCR catalyst to 1000g, the average vanadium leaching efficiency does not change much. Figure 5 It can be seen that when sodium oxalate is used alone to leach the waste SCR catalyst, the weak alkaline solution is not conducive to the chemical dissolution of vanadium oxides, and the average vanadium leaching efficiency is greatly reduced.

[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for cyclically and efficiently extracting vanadium from waste SCR denitration catalysts, characterized in that: The following steps are involved: 1) Pre-treating the waste SCR denitration catalyst to obtain waste SCR denitration catalyst powder; 2) mixing the waste SCR denitration catalyst powder and the organic solvent to carry out a leaching reaction, cooling and separating after the reaction to obtain a leaching solution; 3) returning the leaching solution to step 2) for cyclic treatment to obtain vanadium-rich solution; 4) The vanadium-rich solution is subjected to a hydrothermal reaction to obtain VO2.

2. The method for cyclically and efficiently extracting vanadium from waste SCR denitration catalysts according to claim 1, characterized in that: The organic solvent is an oxalic acid-oxalate solution, and the ratio of oxalic acid to oxalate in the oxalic acid-oxalate solution is 14-18:1; The concentration of oxalic acid in the oxalic acid-oxalate solution is 0.3-0.5 mol / L.

3. The method for cyclically and efficiently extracting vanadium from waste SCR denitration catalyst according to claim 1, characterized in that: The pretreatment includes ultrasonic cleaning, drying and crushing of the waste SCR denitration catalyst; The ultrasonic cleaning time is 20 to 40 minutes, the drying temperature is 80 to 120° C., and the drying time is 8 to 16 hours.

4. The method for cyclically and efficiently extracting vanadium from waste SCR denitration catalysts according to claim 1 or 3, characterized in that: The particle size of the waste SCR denitration catalyst powder is 100-325 meshes.

5. The method for cyclically and efficiently extracting vanadium from waste SCR denitration catalyst according to claim 1 or 2, characterized in that: The leaching reaction temperature is 70-95° C., the leaching reaction time is 3-9 hours, and the liquid-to-solid ratio is 10-25 mL / g.

6. The method for cyclically and efficiently extracting vanadium from waste SCR denitration catalysts according to claim 5, characterized in that: The mass concentration of vanadium in the vanadium-rich solution is 0.85-1.6 g / L.

7. The method for cyclically and efficiently extracting vanadium from waste SCR denitration catalysts according to claim 6, characterized in that: The temperature of the hydrothermal reaction is 150-200° C., and the time of the hydrothermal reaction is 6-10 hours.

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