Method for co-removing chromium and silicon from sodium-containing vanadium solution by selective reduction

Abstract

A method for co-removing chromium and silicon from a sodium-containing vanadium solution by selective reduction. The method comprises: adjusting the pH value of a sodium-containing vanadium solution such that the pH value of the system solution is 10.5-11.5 at 60°C to obtain a pretreated sodium-containing vanadium solution; adding a preset amount of reducing agent to the pretreated sodium-containing vanadium solution at a time for reduction reaction; adding a silicon removal agent to a reaction system at the last stage of the reduction reaction for reaction to obtain a first intermediate reaction solution, carrying out solid-liquid separation on the first intermediate reaction solution, washing a solid phase with water, and then combining the solid phase with a filtrate to obtain an impurity removal solution; and carrying out an oxidation purification treatment on the impurity removal solution to obtain a purified solution. In the present invention, under specific concentration and pH conditions of a sodium-containing solution, vanadium mainly exists in the form of a pyrovanadate, shows relatively low oxidizability and stable properties, and is not prone to reducing. Even if a small part of vanadium is reduced, vanadium still remains as a vanadite in the solution, while a chromate is selectively reduced into chromium hydroxide, thereby completing the separation of vanadium and chromium in the form of a chromium hydroxide precipitate.

Description

A method for selective reduction of chromium and silicon by sodium vanadium solution

[0001] This application claims priority to Chinese Patent Application No. 202410917163.X, filed on July 9, 2024, entitled “A Method for Selective Reduction of Chromium and Silicon by Sodium Vanadium Solution”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of vanadium extraction technology, and more particularly to a method for selective reduction of chromium and silicon by sodium vanadium solution. Background Technology

[0003] Vanadium is a very rare metallic element, primarily used in the steel industry to improve the strength and toughness of steel products. In recent years, its applications in non-steel sectors have become increasingly widespread, such as the booming energy storage field, where vanadium-based cathode materials and all-vanadium redox flow batteries are increasingly mature in research and application. It also has numerous applications in chemical catalysis, pharmaceuticals, metallic vanadium, vanadium alloys, and titanium alloys. The characteristics of vanadium's applications in non-steel sectors dictate that the quality requirements for vanadium oxide are very high. The sodium roasting of vanadium slag followed by water leaching remains the most widely used vanadium extraction process. Due to the properties of vanadium and chromium, the sodium leaching solution generally contains a certain amount of chromium. During the vanadium precipitation process, chromium inevitably enters the vanadium product to some extent, thus reducing its quality. Therefore, it is necessary to reduce the chromium content in the vanadium solution, thereby reducing the amount of chromium entering the vanadium product and improving its quality to meet diverse market demands. The industry commonly uses vanadium intermediate precipitates such as APV, AMV, and SAV for secondary vanadium precipitation to remove chromium from vanadium products, or uses weakly acidic or weakly alkaline vanadium solutions for chromium removal. These methods generally result in large amounts of wastewater, high vanadium loss, and high costs.

[0004] For example, the literature "Study on Removal of Chromium Impurities from Vanadium Solution by Sodium Sulfide Reduction Method" uses Na₂S as a reducing agent and NaOH as a precipitating agent to study the effects of reducing agent dosage, temperature, reaction time, precipitation time, and solution pH on the removal of chromium impurities and the vanadium loss rate. Experiments show that the optimal reaction conditions are: Na₂S addition of 4 times the theoretical amount, reaction temperature of 60℃, reaction time of 2 hours, precipitation time of 2 hours, and solution pH of 11 during the reaction. Under these conditions, the chromium removal rate reaches 94%, while the vanadium loss rate is controlled at 14%.

[0005] Therefore, existing technologies still need improvement. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a method for selective reduction of chromium and silicon using sodium vanadium solution, thereby resolving the technical issues present in the existing sodium vanadium chromium and silicon co-removal techniques.

[0007] To address the aforementioned technical problems, some embodiments of the present invention disclose a method for selective reduction of chromium and silicon using sodium vanadium chloride solution, comprising:

[0008] Step 1: Adjust the pH value of the vanadium sodium solution so that the pH value of the system solution is 10.5-11.5 at 60℃, or 11.3-12.7 at 20℃-25℃, to obtain the pretreated vanadium sodium solution;

[0009] Step 2: Add a predetermined amount of reducing agent to the pretreated vanadium sodium solution at once to carry out a reduction reaction;

[0010] Step 3: At the end of the reduction reaction, add a desiliconizing agent to the reaction system to carry out the reaction and obtain the first intermediate reaction solution;

[0011] Step 4: Perform solid-liquid separation on the first intermediate reaction solution, wash the solid phase with water and add it to the filtrate to obtain the purified solution;

[0012] Step 5: The impurity removal solution is subjected to oxidation purification treatment to obtain a purified solution.

[0013] In some embodiments, it also includes:

[0014] Step 6: Dilute the purified solution to a vanadium content of 25g / L-35g / L, adjust the pH to 5.0-6.0, and set the temperature to 20-70℃ before adding ammonium salt;

[0015] Step 7: After adjusting the pH value to 2.0-2.3, heat to 90-100℃ and maintain the temperature for reaction, then perform solid-liquid separation to obtain APV.

[0016] In some embodiments, in step six, the amount of ammonium salt added is TV / ammonium sulfate = 1.2 to 2.0 by mass.

[0017] In some embodiments, it also includes:

[0018] Step 6: Adjust the pH of the purified solution to 9.0-9.5 and the temperature to 20-40℃, then add ammonium salt;

[0019] Step 7: After reacting at 10-40℃, perform solid-liquid separation to obtain AMV.

[0020] In some embodiments, in step six, the amount of ammonium salt added is TV / ammonium sulfate = 2.5 to 5.0 by mass.

[0021] In some embodiments, in step one,

[0022] If the pH value of the system solution is greater than 11.5 at 60℃, sulfuric acid is added to the system solution to adjust the pH value.

[0023] If the pH value of the system solution is less than 10.5 at 60℃, sodium hydroxide is added to the system solution to adjust the pH value, and the reaction must be carried out for 10 to 60 minutes after adding sodium hydroxide.

[0024] Preferably, the pH value of the system solution at 60°C is 10.6 to 11.0.

[0025] In some embodiments, in step two, the reducing agent is sodium hydrosulfide or sodium sulfide, and the amount of reducing agent added is Cr / S = 0.75 to 1.3 by molar ratio. The pH value of the reaction system at 60°C is 10.5 to 11.5, the reaction temperature is 60°C to 95°C, and the reaction time is 30 min to 90 min.

[0026] Preferably, in step two, the amount of reducing agent sodium hydrosulfide or sodium sulfide added is Cr / S = 0.85 to 1.0 by molar ratio, the reaction temperature is 60°C to 85°C, and the reaction time is 30 min to 60 min.

[0027] In some embodiments, in step three, the silicon remover is aluminum sulfate, and the amount of silicon remover added is Al / Si = 0.4 to 0.8 by molar ratio. The reaction temperature is 60-95°C, and the reaction time is 30-40 min.

[0028] In some embodiments, in step four, the residue obtained after solid-liquid separation is washed once with clean water at 20°C to 60°C, and the washing filtrate is added to the residue removal liquid. The washing water volume is the same as the water volume carried away by the residue removal liquid, ensuring that the volume of the residue removal liquid is equal to the volume of the vanadium sodium chloride solution.

[0029] Preferably, in step four, the first intermediate reaction liquid obtained after the reaction is completed is subjected to solid-liquid separation without being allowed to stand.

[0030] In some embodiments, in step five, the oxidant for the oxidation purification treatment is hydrogen peroxide with a mass concentration of 25% to 50%, and the amount added is H2O2 / Cr = 1 to 2.5 by molar ratio. The pH value of the reaction system at 60°C is 10.8 to 12.0, the reaction temperature is 30°C to 95°C, and the reaction time is 10 min to 60 min.

[0031] Preferably, in step five, the pH value of the reaction system at 60°C is 10.8 to 11.5, the temperature range is 60°C to 85°C, and the reaction time is 20 min to 30 min.

[0032] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0033] This invention provides a method for selective reduction of chromium and silicon in vanadium sodium solution. Under specific concentration and pH conditions, vanadium in the sodium sodium solution primarily exists as pyrovanadate, which has low oxidizing power, is stable, and is not easily reduced. Even if a small portion is reduced, vanadium remains in the solution as vanadate, while chromate is selectively reduced to chromium hydroxide, thus achieving vanadium-chromium separation through chromium hydroxide precipitation. At the end of the selective reduction reaction, aluminum salt is added to the reduction system, reacting with silicon in the vanadium solution to form aluminum silicate. The aluminum silicate and chromium hydroxide mutually adsorb, flocculate, and co-precipitate, significantly enhancing the chromium and silicon removal efficiency. After purification, the purified solution precipitates low-chromium and low-silicon vanadium intermediates APV and AMV. This invention features high chromium removal rate, high silicon removal rate, low vanadium loss, and a short process flow. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 is a pH and potential range diagram of the selective reduction chromium removal method of vanadium sodium solution for selective reduction of chromium and silicon co-removal disclosed in some embodiments of the present invention.

[0036] Figure 2 is a pH and potential range diagram of the selective reduction chromium removal method of vanadium sodium solution for selective reduction of chromium and silicon co-removal disclosed in some embodiments of the present invention.

[0037] Figure 3 is a graph showing the relationship between redox potential and time during the reduction of chromium and silicon in a method for selective reduction of chromium and silicon using vanadium sodium solution disclosed in some embodiments of the present invention.

[0038] Figure 4 is a graph showing the pH change over time during the reduction of chromium and silicon in a method for selective reduction of chromium and silicon using vanadium sodium solution disclosed in some embodiments of the present invention.

[0039] Figure 5 is a graph showing the relationship between the oxidation potential of vanadium solution and pH in a method for selective reduction of chromium and silicon by sodium vanadium solution as disclosed in some embodiments of the present invention.

[0040] Figure 6 is a graph showing the relationship between the oxidation potential of vanadium solution and temperature in a method for selective reduction of chromium and silicon by sodium vanadium solution as disclosed in some embodiments of the present invention.

[0041] Figure 7 shows the effect of temperature on the chromium and silicon removal efficiency and vanadium loss during the selective reduction of vanadium sodium solution in a method for selective reduction of vanadium sodium solution to remove chromium and silicon, as disclosed in some embodiments of the present invention.

[0042] Figure 8 shows the effect of time on the chromium and silicon removal efficiency and vanadium loss during the selective reduction of vanadium sodium solution in a method for selective reduction of vanadium sodium solution to remove chromium and silicon, as disclosed in some embodiments of the present invention.

[0043] Figure 9 shows the effect of pH on the chromium removal efficiency and vanadium loss during the selective reduction of vanadium-sodium solution for chromium-silicon co-removal, as disclosed in some embodiments of the present invention.

[0044] Figure 10 shows the effect of the reducing agent addition coefficient on the chromium and silicon removal efficiency during the selective reduction of vanadium sodium solution in a method for selective reduction of chromium and silicon co-removal disclosed in some embodiments of the present invention.

[0045] Figure 11 shows the effect of the aluminum addition coefficient on the silicon removal efficiency and vanadium loss during the selective reduction of vanadium-sodium solution in a method for selective reduction of vanadium-sodium solution to remove chromium and silicon, as disclosed in some embodiments of the present invention.

[0046] Figure 12 shows the effect of the aluminum addition coefficient on the sedimentation effect of the impurity residue during the selective reduction of vanadium sodium solution for the co-removal of chromium and silicon, as disclosed in some embodiments of the present invention.

[0047] Figure 13 is a diagram showing the oxidation effect of the impurity removal solution in a method for selective reduction of chromium and silicon by sodium vanadium solution disclosed in some embodiments of the present invention;

[0048] Figure 14 is a flowchart of a method for selective reduction of chromium and silicon by sodium vanadium solution according to some embodiments of the present invention. Detailed Implementation

[0049] The embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of this disclosure by way of example, but should not be used to limit the scope of this disclosure. This disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0050] These embodiments are provided to make the disclosure thorough and complete, and to fully express the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​set forth in these embodiments should be interpreted as exemplary only and not as limiting.

[0051] It should be noted that, in the description of this disclosure, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationship, are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0052] Furthermore, the terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. "Vertical" is not strictly vertical, but within the permissible margin of error. "Parallel" is not strictly parallel, but within the permissible margin of error. Terms such as "including" or "contains" mean that the element preceding the word encompasses the element listed after the word, and do not exclude the possibility of encompassing other elements as well.

[0053] It should also be noted that, in the description of this disclosure, unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this disclosure depending on the specific circumstances. When a particular device is described as being located between a first device and a second device, an intermediary device may or may not be present between the particular device and the first or second device.

[0054] All terms used in this disclosure have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0055] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0056] As shown in Figure 14, some embodiments of this invention disclose a method for selective reduction of chromium and silicon in vanadium sodium solution. Under specific concentration and pH conditions, vanadium in the sodium sodium solution mainly exists in the form of pyrovanadate, which has low oxidizing power, stable properties, and is not easily reduced. Even if a small portion is reduced, vanadium remains in the solution as vanadate, while chromate is selectively reduced to chromium hydroxide, thus completing the vanadium-chromium separation as chromium hydroxide precipitate. At the end of the selective reduction reaction, aluminum salt is added to the reduction system, reacting with silicon in the vanadium solution to form aluminum silicate. The aluminum silicate and chromium hydroxide mutually adsorb, flocculate, and co-precipitate, significantly promoting the chromium and silicon removal effects of the system. This invention can easily reduce Cr in the vanadium solution from 3000 mg / L to 1 mg / L, Si < 20 mg / L, and vanadium loss rate < 2%. After purification, the purified solution can precipitate low-chromium and low-silicon vanadium intermediate precipitates APV and AMV.

[0057] The method includes the following steps:

[0058] a. Pretreatment of sodium vanadium leaching solution (sodium vanadium leaching solution);

[0059] b. Adding a reducing agent to the pretreatment solution for selective reduction and chromium removal;

[0060] c. Add a silicon remover to the reduction system to perform silicon-chromium co-precipitation;

[0061] d. The impurity removal solution is purified to obtain a vanadium-precipitated purified solution;

[0062] e. Prepare vanadium intermediate precipitates APV or AMV from the purified solution.

[0063] The composition requirements for sodium vanadium chloride solution are shown in Table 1 below.

[0064] Table 1

[0065] In the above embodiments, the vanadium concentration in the vanadium sodium solution in step a should be controlled at 30 g / L to 60 g / L, preferably 35 g / L to 50 g / L, and the pH of the vanadium sodium solution should be controlled at 10.5 to 11.5 (pH measured at 60°C; if measured at 20°C to 25°C, the pH should be increased by 0.8 to 1.2 from 10.5 to 11.5, mainly because the higher the temperature of the vanadium sodium solution system, the lower the pH is, and the change is non-linear), preferably 10.6 to 11.0. Experiments have shown that a pH higher than the above range will cause the chromium-containing solid particles in the chromium removal solution to become smaller, which is not conducive to sedimentation and filtration. A further increase in pH will cause some Cr(OH)3 to dissolve, making it impossible to achieve efficient vanadium-chromium separation, which is not conducive to the chromium removal process. If the pH of the vanadium sodium solution in step a is less than 10.5 at 60°C, sodium hydroxide needs to be added to adjust the pH to ≥ 10.5. After adding sodium hydroxide, the reaction should last for 10 min to 60 min, preferably 20 min to 40 min, to allow vanadium to fully polymerize in the solution, so that vanadium exists mainly in the form of pyrovanadate in the solution. If the pH of the vanadium sodium solution in step a is greater than 11.5 at 60°C, sulfuric acid needs to be added to adjust the pH to ≤ 11.5. If the pH is too high, the solubility of chromium hydroxide will increase, making it impossible to effectively separate vanadium and chromium.

[0066] In step b, the reducing agent is sodium hydrosulfide and sodium sulfide, preferably sodium hydrosulfide. The reducing agent addition coefficient Cr / S = 0.75-1.3 (molar ratio), preferably Cr / S = 0.85-1.0. The reaction pH is 10.5-11.5 (measured at 60℃), the reduction temperature is 60℃-95℃, preferably 60℃-85℃, and the reduction time is 30min-90min, preferably 30min-60min. In step b, the reducing agent is added all at once. After the reducing agent is added, the pH of the solution system will rise rapidly, further improving the selective reduction and removal of chromium of the entire system.

[0067] In step c, the desiliconizing agent is aluminum sulfate, and the addition coefficient is Al / Si = 0.4–0.8 (molar ratio). Because some silicon is carried away during the reduction and removal of chromium, and excessive addition of aluminum sulfate will significantly lower the pH of the system, which is detrimental to the selective reduction and removal of chromium, appropriately lowering the pH at the end of the reduction and removal process can enhance the separation effect of vanadium and chromium. In step c, the reaction temperature of the desiliconizing agent is 60℃–95℃, and the reaction time is 10 min–60 min, preferably 30 min–40 min, until the reaction is complete. The settling time is 0–48 h, preferably 0–12 h. In the mixed system of chromium hydroxide and aluminum silicate, the adverse effects of pH and settling time on the desiliconization effect are weakened. That is, a better desiliconization effect can be achieved under high pH and no settling conditions, and the filterability of the impurity residue is greatly increased. After solid-liquid separation in step c, the impurity residue is washed once with clean water at 20℃–60℃. The washing filtrate is added to the impurity removal liquid. The washing water volume is the amount of water carried away by the impurity residue, ensuring that the volume of the impurity removal liquid is approximately equal to the volume of the vanadium liquid before impurity removal.

[0068] In step d, an oxidant is used for oxidation and purification. The oxidant is 25% to 50% hydrogen peroxide, and the amount added is H2O2 / Cr = 1 to 2.5 (molar ratio). The reaction pH is 10.8 to 12.0 (at 60°C), preferably 10.8 to 11.5. The reaction temperature is 30°C to 95°C, preferably 60°C to 85°C. The reaction time is 10 min to 60 min, preferably 20 min to 30 min.

[0069] If APV is precipitated in step e, the solution needs to be diluted to V = 25 g / L to 35 g / L. The pH is adjusted to 5.0 to 6.0 for the first time at a temperature of 20℃ to 70℃. After adjusting the pH, ammonium salt is added at a ratio of TV / ammonium sulfate of 1.2 to 2.0 (mass ratio), preferably 1.2 to 1.6 (mass ratio). Then, a second pH adjustment is performed at 2.0 to 2.3. The temperature is then raised to 90℃ to 100℃ and held for 45 to 90 minutes. After solid-liquid separation, high-quality APV is obtained.

[0070] If AMV is precipitated in step e, the purification solution does not need to be diluted. Adjust the pH to 9.0-9.5 and the pH temperature to 20℃-40℃. After adjusting the pH, add ammonium salt. The amount of ammonium salt added is TV / ammonium sulfate = 2.5-5.0 (mass ratio). Keep it at 10℃-40℃ for 120min-240min. After solid-liquid separation, high-quality AMV is obtained.

[0071] Experiments have shown that the selective reduction method for chromium and silicon removal using vanadium sodium solution disclosed in this invention can reduce the Cr concentration in the solution from 3.2 g / L to 0.002 g / L, a reduction of more than 1000 times. Under high pH conditions, it can reduce the Si concentration from 0.8 g / L to 0.03 g / L, with a chromium removal rate greater than 99.5% and a silicon removal rate greater than 93.3%. The vanadium loss is approximately 2.41%-2.55%.

[0072] During the reduction and removal of chromium, the pH and redox potential need to be controlled within region A of Figure 1 to ensure that vanadium exists in the solution in ionic form, while chromium in the system precipitates out as Cr(OH)3 (as shown in region B of Figure 2), thus achieving vanadium-chromium separation in the solution system. Figure 3 shows the relationship between the redox potential and time during the selective reduction and co-removal of chromium and silicon using sodium vanadium chloride solution. Combined with Figure 1, this reflects that the redox potential in the actual operation matches the theoretical range. Figure 4 shows the relationship between the pH and time during the selective reduction and co-removal of chromium and silicon using sodium vanadium chloride solution. Combined with Figure 1, this reflects that the pH in the actual operation matches the theoretical range. The combination of Figures 1, 2, 3, and 4 demonstrates that the actual potential and pH in the selective reduction and co-removal of chromium and silicon using sodium vanadium chloride solution match the theoretical values, indicating the excellent performance of the chromium removal agent. Figure 5 shows the relationship between the oxidation potential of the solution system and pH. As shown in Figure 5, the oxidation potential of vanadium in the solution decreases with increasing pH, indicating that the higher the pH, the lower the oxidizing power of vanadium, the more stable the vanadium's existing form, the less easily V is reduced during chromium removal, the better the V-Cr selectivity, and the lower the vanadium loss. Figure 6 shows the relationship between the oxidation potential of the solution system and temperature. As shown in Figure 6, the oxidation potential of vanadium in the solution decreases with increasing temperature, indicating that the higher the solution temperature, the lower the oxidizing power of vanadium, the more stable the vanadium's existing form, the less easily V is reduced during chromium removal, the better the V-Cr selectivity, and the lower the vanadium loss. Figure 7 shows the effect of temperature on the chromium and silicon removal efficiency and vanadium loss during the selective reduction of chromium and silicon. As shown in Figure 7, a water bath temperature ≥70℃ (solution temperature 60℃) results in good chromium removal efficiency and low vanadium loss. Figure 8 shows the effect of time on the removal efficiency of chromium and silicon and vanadium loss during the selective reduction of chromium and silicon. As shown in Figure 8, the Cr concentration in the purified solution can be reduced to 0.006 g / L when the reaction time is 30 min, while the vanadium loss begins to increase after 60 min. Figure 9 shows the effect of pH on the removal efficiency of chromium and silicon during the selective reduction of chromium and silicon. As shown in Figure 9, the selective reduction of chromium using sodium vanadium solution requires a higher pH; a lower pH results in a lower chromium removal rate and a greater vanadium loss. Figure 10 shows the effect of the reducing agent addition coefficient on the removal efficiency of chromium and silicon during the selective reduction of chromium and silicon. As shown in Figure 10, the chromium concentration in the purified solution can be reduced from approximately 1 g / L to less than 0.1 g / L when the chromium removal agent dosage coefficient increases from 0.7 to 1.0, and the silicon and chromium show a synergistic effect. Figure 11 shows the effect of the aluminum addition coefficient on the removal efficiency of silicon and vanadium loss during the selective reduction of chromium and silicon. As shown in Figure 11, an increase in the aluminum addition coefficient leads to a decrease in Si concentration in the purified solution, while the aluminum addition coefficient has no obvious effect on vanadium loss. Figure 12 shows the effect of aluminum addition coefficient on the sedimentation effect of impurity removal residue during selective reduction of chromium and silicon. Figure 13 shows the oxidation effect of the impurity removal solution. As can be seen from Figures 12 and 13, adding aluminum sulfate will lower the pH value of the purification solution, which is conducive to the sedimentation of silicon and chromium. Without the addition of aluminum sulfate, there are more suspended solids in the purification solution, which are difficult to clarify and the suspended solids pass through the filter during filtration (the number under the beaker is the aluminum addition coefficient).The purification solution is colorless after complete oxidation; its yellowish-brown color is mainly due to vanadate, while the sodium vanadium solution is yellow primarily due to chromate. Under higher pH conditions, vanadium is reduced to vanadate, existing in solution as ionic ions, which does not increase vanadium loss.

[0073] Example 1

[0074] 400 mL of the above vanadium sodium solution was measured using a graduated cylinder. The composition is shown in Table 1.1. The vanadium concentration of the solution was 39.39 g / L, and the pH of the vanadium sodium solution was 10.5 (measured at 60℃). Sodium hydrosulfide (containing 32% water) was used as the reducing agent, with a reducing agent addition coefficient of Cr / S = 1.0 (molar ratio) of 1.56 g. The reaction pH was 10.5 (measured at 60℃), the reduction temperature was 63℃, and the reduction time was 60 min. The reducing agent was added all at once. Aluminum sulfate was used as the desiliconizing agent, with a desiliconizing agent addition coefficient of Al / Si = 0.8 (molar ratio) of 2.97 g. The reaction temperature was 60℃, the reaction time was 30 min, and the settling time after the reaction was 0 h. After solid-liquid separation, the residue was washed once with clean water at 26℃. The washing filtrate was added to the impurity removal solution, and the washing water volume was 80 mL, ensuring that the volume of the impurity removal solution was approximately equal to the volume of the vanadium solution before impurity removal. Oxidation purification was carried out using an oxidant, which was 30% hydrogen peroxide, with an addition amount of 4.24 mL of H2O2 / Cr = 2 (molar ratio). The reaction pH was 10.8 (at 60℃), the reaction temperature was 60℃, and the reaction time was 30 min. The purified solution contained Cr < 1 mg / L, Si = 0.02 g / L, and vanadium loss of 1.4%.

[0075] The purified solution was used to precipitate APV. The solution was diluted to V = 30 g / L, totaling 200 mL. The pH was adjusted to 5.0 for the first time at 60℃. After the pH was adjusted, ammonium salt was added at a ratio of TV / ammonium sulfate = 1.2 (mass ratio) = 7.2 g. Then, the pH was adjusted to 2.0 for the second time. The temperature was then raised to 95℃ and held for 60 min. After solid-liquid separation, high-quality APV was obtained. The composition is shown in Table 1.2 below.

[0076] Table 1.1

[0077] Precipitate AMV without diluting the purification solution. Use 200 mL of solution, adjust the pH to 9.0, and set the pH temperature to 30°C. After adjusting the pH, add ammonium salt at a ratio of TV / ammonium sulfate of 2.5 (mass ratio) of 19.41 g. Incubate at 30°C for 180 min. The high-quality AMV obtained after solid-liquid separation is shown in Table 1.3.

[0078] Table 1.3

[0079] Example 2

[0080] Measure 400 mL of the above vanadium sodium solution using a graduated cylinder. The composition is shown in Table 2.1. The vanadium concentration of the vanadium solution is 49.04 g / L. The pH of the vanadium sodium solution is 10.1 (measured at 60℃). Therefore, sodium hydroxide needs to be added to adjust the pH to 10.8. After adding sodium hydroxide, the reaction time must be 30 min. Sodium sulfide (sodium sulfide nonahydrate) is used as the reducing agent. The reducing agent addition coefficient Cr / S = 0.85 (molar ratio) is 4.98 g. The reaction pH is 10.8 (measured at 60℃), the reduction temperature is 85℃, and the reduction time is 30 min. The reducing agent is added all at once. Aluminum sulfate is used as a silicon remover, with a silicon remover addition coefficient Al / Si = 0.6. The molar ratio was 2.21 g. The reaction temperature of the silicon removal agent was 80℃, the reaction time was 30 min, and the standing time after the reaction was 12 h. After solid-liquid separation, the residue was washed once with clean water at 20℃. The washing filtrate was added to the purification solution, and the washing water volume was 90 mL, ensuring that the volume of the purification solution was approximately equal to the volume of the vanadium solution before purification. Oxidation purification was carried out using an oxidant, which was 30% hydrogen peroxide. The amount added was 5.88 mL of H2O2 / Cr = 2.5 (molar ratio). The reaction pH was 11.1 (at 60℃), the reaction temperature was 60℃, and the reaction time was 30 min. The Cr in the purified solution was <1 mg / L, Si = 0.01 g / L, and the vanadium loss was 1.6%.

[0081] The purified solution was used to precipitate APV. The solution was diluted to V = 30 g / L, totaling 200 mL. The pH was adjusted to 6.0 for the first time at 70℃. After the pH was adjusted, ammonium salt was added at a ratio of TV / ammonium sulfate = 1.6 (mass ratio) = 9.6 g. Then, a second acid adjustment was performed, adjusting the pH to 2.3. The temperature was then raised to 90℃ and held for 45 min. After solid-liquid separation, high-quality APV was obtained. The composition is shown in Table 2.2.

[0082] Table 2.1

[0083] Table 2.2

[0084] Precipitate AMV without diluting the purification solution. Use 200 mL of solution, adjust the pH to 9.5, and adjust the pH temperature to 40℃. After adjusting the pH, add ammonium salt at a mass ratio of TV / ammonium sulfate of 4 (38.68 g). Incubate at 30℃ for 120 min. The high-quality AMV obtained after solid-liquid separation is shown in Table 2.3.

[0085] Table 2.3

[0086] Example 3

[0087] Table 3.1

[0088] Measure 400 mL of the above vanadium sodium solution using a graduated cylinder. The composition is shown in Table 3.1. The vanadium concentration of the vanadium solution is 52 g / L. The pH of the vanadium sodium solution is 10.0 (measured at 60℃). Therefore, sodium hydroxide needs to be added to adjust the pH to 10.8. After adding sodium hydroxide, the reaction time must be 30 min. Sodium hydrosulfide is used as the reducing agent (70% effective component). The reducing agent addition coefficient Cr / S = 1 (molar ratio) is 1.97 g. The reaction pH is 10.8 (measured at 60℃), the reduction temperature is 85℃, and the reduction time is 30 min. The reducing agent is added all at once. Aluminum sulfate is used as the desiliconizing agent, with a desiliconizing agent addition coefficient Al / Si = 0.4 (molar ratio). The amount of silicon removal agent was 1.52 g, the reaction temperature was 80℃, the reaction time was 30 min, and the standing time after the reaction was 12 h. After solid-liquid separation, the residue was washed once with clean water at 20℃. The washing filtrate was added to the purification solution, and the washing water volume was 100 mL to ensure that the volume of the purification solution was approximately equal to the volume of the vanadium solution before purification. Oxidation purification was carried out using an oxidant, which was 30% hydrogen peroxide. The amount added was 2.79 mL (H2O2 / Cr = 1, molar ratio). The reaction pH was 11.4 (at 60℃), the reaction temperature was 60℃, and the reaction time was 30 min. The purified solution contained Cr = 0.002 g / L, Si = 0.01 g / L, and the vanadium loss was 2.2%.

[0089] The purified solution was used to precipitate APV. The solution was diluted to V = 30 g / L, totaling 200 mL. The pH was adjusted to 6.0 for the first time at 70℃. After the pH was adjusted, ammonium salt was added at a ratio of TV / ammonium sulfate = 1.6 (mass ratio) = 9.6 g. Then, the pH was adjusted to 2.3 for the second time. The temperature was then raised to 90℃ and held for 45 min. After solid-liquid separation, high-quality APV was obtained. The composition is shown in Table 3.2.

[0090] Table 3.2

[0091] Precipitate AMV without diluting the purification solution. Use 200 mL of solution, adjust the pH to 9.5, set the pH to 14, and the temperature to 40℃. After adjusting the pH, add ammonium salt at a mass ratio of TV / ammonium sulfate of 4 (40.68 g). Incubate at 30℃ for 120 min. The high-quality AMV obtained after solid-liquid separation is shown in Table 3.3.

[0092] Table 3.3

[0093] Example 4

[0094] Table 4.1

[0095] Measure 400 mL of the above vanadium sodium solution using a graduated cylinder. The composition is shown in Table 4.1. The vanadium concentration of the vanadium solution is 52 g / L. The pH of the vanadium sodium solution is 10.0 (measured at 60℃). Therefore, sodium hydroxide needs to be added to adjust the pH to 10.8. After adding sodium hydroxide, the reaction must proceed for 30 minutes. Sodium hydrosulfide is used as the reducing agent (70% effective component). The reducing agent addition coefficient Cr / S = 1 (molar ratio) is 1.97 g. The reducing agent is added in 5 portions, with 2-minute intervals between each addition, taking 8 minutes to complete the addition. The reaction pH is 10.8 (measured at 60℃), the reduction temperature is 85℃, and the reduction time is 30 minutes. Aluminum sulfate is used as the desiliconizing agent, with a desiliconizing agent addition coefficient Al / The Si content was 0.4 (molar ratio) and the amount of the silicon removal agent was 1.52 g. The reaction temperature was 80℃ and the reaction time was 30 min. After the reaction, the standing time was 12 h. After solid-liquid separation, the residue was washed once with clean water at 20℃. The washing filtrate was added to the purification solution, and the washing water volume was 100 mL, ensuring that the volume of the purification solution was approximately equal to the volume of the vanadium solution before purification. Oxidation purification was carried out using an oxidant, which was 30% hydrogen peroxide. The amount added was 2.79 mL of H2O2 / Cr = 1 (molar ratio). The reaction pH was 11.4 (at 60℃), the reaction temperature was 60℃, and the reaction time was 30 min. The purified solution contained Cr = 0.03 g / L, Si = 0.01 g / L, and the vanadium loss was 3.2%.

[0096] The purified solution was used to precipitate APV. The solution was diluted to V = 30 g / L, totaling 200 mL. The pH was adjusted to 6.0 for the first time at 70℃. After the pH was adjusted, ammonium salt was added at a ratio of TV / ammonium sulfate = 1.6 (mass ratio) = 9.6 g. Then, the pH was adjusted to 2.3 for the second time. The temperature was then raised to 90℃ and held for 45 min. After solid-liquid separation, high-quality APV was obtained. The composition is shown in Table 4.2.

[0097] Table 4.2

[0098] Precipitate AMV without diluting the purification solution. Use 200 mL of solution, adjust the pH to 9.5, and adjust the pH temperature to 40℃. After adjusting the pH, add ammonium salt at a mass ratio of TV / ammonium sulfate of 4 (40.68 g). Incubate at 30℃ for 120 min. The composition of the high-quality AMV after solid-liquid separation is shown in Table 4.3.

[0099] Table 4.3

[0100] Example 5

[0101] Table 5.1

[0102] 400 mL of the above vanadium sodium solution was measured using a graduated cylinder. The composition is shown in Table 5.1. The vanadium concentration of the vanadium solution was 52 g / L. The pH of the vanadium sodium solution was 10.0 (measured at 60℃). The pH of the vanadium solution was not adjusted. Sodium hydrosulfide was used as the reducing agent (70% effective component). The reducing agent addition coefficient Cr / S = 1 (molar ratio) was 1.97 g. The reaction pH was 10.0 (measured at 60℃). The reduction temperature was 85℃, and the reduction time was 30 min. The reducing agent was added all at once. Aluminum sulfate was used as the desiliconizing agent. The desiliconizing agent addition coefficient was Al / Si = 0.4 (molar ratio) and was 1.52 g. The reaction temperature was 80℃, the reaction time was 30 min, and the settling time after the reaction was 12 h. After solid-liquid separation, the residue was washed once with clean water at 20℃. The washing filtrate was added to the impurity removal solution, and the washing water volume was 100 mL, ensuring that the volume of the impurity removal solution was approximately equal to the volume of the vanadium solution before impurity removal. Oxidation purification was carried out using an oxidant, which was 30% hydrogen peroxide, with an addition amount of 2.79 mL of H2O2 / Cr = 1 (molar ratio). The reaction pH was 11.4 (at 60℃), the reaction temperature was 60℃, and the reaction time was 30 min. The purified solution contained Cr = 0.634 g / L, Si = 0.02 g / L, and the vanadium loss was 5.2%.

[0103] The purified solution was used to precipitate APV. The solution was diluted to V = 30 g / L, totaling 200 mL. The pH was adjusted to 6.0 for the first time at 70℃. After the pH was adjusted, ammonium salt was added at a ratio of TV / ammonium sulfate = 1.6 (mass ratio) = 9.6 g. Then, the pH was adjusted to 2.3 for the second time. The temperature was then raised to 90℃ and held for 45 min. After solid-liquid separation, high-quality APV was obtained. The composition is shown in Table 5.2.

[0104] Table 5.2

[0105] Precipitate AMV without diluting the purification solution. Use 200 mL of solution, adjust the pH to 9.5, and adjust the pH temperature to 40℃. After adjusting the pH, add ammonium salt at a mass ratio of TV / ammonium sulfate of 4 (40.68 g). Incubate at 30℃ for 120 min. The composition of the high-quality AMV after solid-liquid separation is shown in Table 5.3.

[0106] Table 5.3

[0107] Example 6

[0108] Table 6.1

[0109] 400 mL of the above vanadium sodium solution was measured using a graduated cylinder. The composition is shown in Table 5.1. The vanadium concentration of the vanadium solution was 52 g / L. The pH of the vanadium sodium solution was 10.0 (measured at 60℃). The pH of the vanadium solution was adjusted to 11.6 using sodium hydroxide. After adding sodium hydroxide, the reaction time was 30 min. Sodium hydrosulfide was used as the reducing agent (70% effective component). The reducing agent addition coefficient Cr / S = 1 (molar ratio) was 1.97 g. The reaction pH was 10.0 (measured at 60℃). The reduction temperature was 85℃, and the reduction time was 30 min. The reducing agent was added all at once. Aluminum sulfate was used as the desiliconizing agent. The desiliconizing agent addition coefficient was Al / Si = 0.4 (molar ratio). The molar ratio of the silicon removal agent was 1.52 g. The reaction temperature of the silicon removal agent was 80℃, the reaction time was 30 min, and the standing time after the reaction was 12 h. After solid-liquid separation, the impurity residue was washed once with clean water at 20℃. The washing filtrate was added to the impurity removal liquid, and the washing water volume was 100 mL to ensure that the volume of the impurity removal liquid was approximately equal to the volume of the vanadium liquid before impurity removal. Oxidation purification was carried out using an oxidant, which was 30% hydrogen peroxide. The amount added was 2.79 mL (H2O2 / Cr = 1, molar ratio). The reaction pH was 12.4 (at 60℃), the reaction temperature was 60℃, and the reaction time was 30 min. The purified liquid contained Cr = 0.14 g / L, Si = 0.08 g / L, and the vanadium loss was 2.6%.

[0110] The purified solution was used to precipitate APV. The solution was diluted to V = 30 g / L, totaling 200 mL. The pH was adjusted to 6.0 for the first time at 70℃. After the pH was adjusted, ammonium salt was added at a ratio of TV / ammonium sulfate = 1.6 (mass ratio) = 9.6 g. Then, the pH was adjusted to 2.3 for the second time. The temperature was then raised to 90℃ and held for 45 min. After solid-liquid separation, high-quality APV was obtained. The composition is shown in Table 6.2.

[0111] Table 6.2

[0112] Precipitate AMV without diluting the purification solution. Use 200 mL of solution, adjust the pH to 9.5, and adjust the pH temperature to 40℃. After adjusting the pH, add ammonium salt at a mass ratio of TV / ammonium sulfate of 4 (40.68 g). Incubate at 30℃ for 120 min. The high-quality AMV obtained after solid-liquid separation is shown in Table 6.3.

[0113] Table 6.3

[0114] The embodiments of this disclosure have now been described in detail. To avoid obscuring the concept of this disclosure, some details known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed herein based on the above description.

[0115] While specific embodiments of this disclosure have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of this disclosure. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner.

Claims

1. A method for selective reduction of chromium and silicon by sodium vanadium solution, characterized in that, include: Step 1: Adjust the pH value of the vanadium sodium solution so that the pH value of the system solution is 10.5-11.5 at 60℃, or 11.3-12.7 at 20℃-25℃, to obtain the pretreated vanadium sodium solution; Step 2: Add a predetermined amount of reducing agent to the pretreated vanadium sodium solution at once to carry out a reduction reaction; Step 3: At the end of the reduction reaction, add a desiliconizing agent to the reaction system to carry out the reaction and obtain the first intermediate reaction solution; Step 4: Perform solid-liquid separation on the first intermediate reaction solution, wash the solid phase with water and add it to the filtrate to obtain the purified solution; Step 5: The impurity removal solution is subjected to oxidation purification treatment to obtain a purified solution.

2. The method for selective reduction of chromium and silicon by sodium vanadium solution according to claim 1, characterized in that, Also includes: Step 6: Dilute the purified solution to a vanadium content of 25g / L-35g / L, adjust the pH to 5.0-6.0, and set the temperature to 20-70℃ before adding ammonium salt; Step 7: After adjusting the pH value to 2.0-2.3, heat to 90-100℃ and maintain the temperature for reaction, then perform solid-liquid separation to obtain APV.

3. The method for selective reduction of chromium and silicon by sodium vanadium solution according to claim 2, characterized in that, In step six, the amount of ammonium salt added is TV / ammonium sulfate = 1.2 to 2.0 by mass.

4. The method for selective reduction of chromium and silicon by sodium vanadium solution according to claim 1, characterized in that, Also includes: Step 6: Adjust the pH of the purified solution to 9.0-9.5 and the temperature to 20-40℃, then add ammonium salt; Step 7: After reacting at 10-40℃, perform solid-liquid separation to obtain AMV.

5. The method for selective reduction of chromium and silicon by sodium vanadium solution according to claim 4, characterized in that, In step six, the amount of ammonium salt added is TV / ammonium sulfate = 2.5 to 5.0 by mass.

6. The method for selective reduction of chromium and silicon by sodium vanadium solution according to claim 1, characterized in that, In step one, If the pH value of the system solution is greater than 11.5 at 60℃, sulfuric acid is added to the system solution to adjust the pH value. If the pH value of the system solution is less than 10.5 at 60℃, sodium hydroxide is added to the system solution to adjust the pH value, and the reaction must be carried out for 10 to 60 minutes after adding sodium hydroxide. Preferably, the pH value of the system solution at 60°C is 10.6 to 11.

0.

7. The method for selective reduction of chromium and silicon by sodium vanadium solution according to claim 1, characterized in that, In step two, the reducing agent is sodium hydrosulfide or sodium sulfide. The amount of reducing agent added is Cr / S = 0.75 to 1.3 by molar ratio. The pH value of the reaction system at 60℃ is 10.5 to 11.5, the reaction temperature is 60℃ to 95℃, and the reaction time is 30 min to 90 min. Preferably, in step two, the amount of reducing agent sodium hydrosulfide or sodium sulfide added is Cr / S = 0.85 to 1.0 by molar ratio, the reaction temperature is 60°C to 85°C, and the reaction time is 30 min to 60 min.

8. The method for selective reduction of chromium and silicon by sodium vanadium solution according to claim 1, characterized in that, In step three, the silicon remover is aluminum sulfate. The amount of silicon remover added is Al / Si = 0.4 to 0.8 by molar ratio. The reaction temperature is 60-95℃ and the reaction time is 30-40 min.

9. The method for selective reduction of chromium and silicon by sodium vanadium solution according to claim 1, characterized in that, In step four, the residue obtained after solid-liquid separation is washed once with clean water at 20℃~60℃. The washing filtrate is added to the residue removal liquid. The washing water volume is the same as the water volume carried away by the residue removal liquid, ensuring that the volume of the residue removal liquid is equal to the volume of the sodium vanadium solution. Preferably, in step four, the first intermediate reaction liquid obtained after the reaction is completed is subjected to solid-liquid separation without being allowed to stand.

10. The method for selective reduction of chromium and silicon by sodium vanadium solution according to claim 1, characterized in that, In step five, the oxidant used in the oxidation purification treatment is hydrogen peroxide with a mass concentration of 25% to 50%. The amount added is H2O2 / Cr = 1 to 2.5 by molar ratio. The pH value of the reaction system at 60℃ is 10.8 to 12.0, the reaction temperature is 30℃ to 95℃, and the reaction time is 10 min to 60 min. Preferably, in step five, the pH value of the reaction system at 60°C is 10.8 to 11.5, the temperature range is 60°C to 85°C, and the reaction time is 20 min to 30 min.

Images