Method for separating molybdenum and vanadium by high-efficiency membrane

Abstract

The present invention belongs to the field of metal separation technology, and specifically relates to a method for separating molybdenum and vanadium by an efficient membrane, comprising the following steps: (1) preparing a polymer coated membrane having different selectivities for molybdenum and vanadium; (2) forming a polymer coated membrane electrodialysis structure; (3) utilizing the polymer coated membrane electrodialysis structure to separate and transfer a molybdenum and vanadium mixed metal solution: pumping a feed solution, a stripping solution, and an electrode solution into corresponding chambers for circulation, wherein the feed solution enters the feed solution chamber, the stripping solution enters the stripping solution chamber, and the electrode solution enters the cathode electrode solution chamber and the anode electrode solution chamber, wherein the feed solution is mainly a molybdenum and vanadium mixed metal solution; applying an electric field in a constant current mode on both sides of the polymer coated membrane electrodialysis structure, and under the action of the electric field and the selective permeation of the polymer coated membrane, the molybdenum in the molybdenum and vanadium mixed metal solution in the feed solution chamber is transferred to the stripping solution chamber, thereby achieving a one-step separation of the molybdenum and vanadium mixed metals. The invention is simple, efficient, green and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of metal separation, and in particular relates to a method for separating molybdenum and vanadium through a high-efficiency membrane. Background Art

[0002] Molybdenum (Mo) and vanadium (V) metals, due to their unique properties such as corrosion resistance and high-temperature resistance, play a vital role in numerous high-tech fields, including aerospace and electronic communications. Due to the conflict between the ever-increasing demand for vanadium and molybdenum and resource scarcity, the separation and recovery of vanadium and molybdenum from various secondary resources, particularly spent catalysts, has become a hot topic. Hydrodesulfurization catalysts are widely used in the chemical and petroleum industries due to their unique catalytic properties. However, during the catalytic process, the catalysts are continuously contaminated and deactivated, becoming spent catalysts. Simply landfilling spent catalysts poses an environmental risk. Therefore, separating and recovering vanadium and molybdenum from spent catalysts not only addresses the environmental pollution issues associated with the disposal of spent catalysts, but also alleviates the pressure of scarce resources.

[0003] At present, the commonly used method for recycling spent catalysts is hydrometallurgical recovery, which usually uses acid leaching to treat spent catalysts to form a solution, and then uses precipitation, ion exchange, solvent extraction and other technologies to separate and recover molybdenum and vanadium in the leachate.

[0004] Chinese patent CN112899483A adds sodium carbonate and sodium sulfite in precise proportions to vanadium-molybdenum waste residue to form a reaction feedstock. This feedstock is then mixed with water in a ratio of 1:(1-2.5) kg / L and placed in a reaction tank. Stirring is performed at 25-45°C and 80-200 rpm for 2-6 hours to produce a post-reaction slurry. The post-reaction slurry is then subjected to solid-liquid separation, with the molybdenum precipitating in the reaction feedstock while the vanadium is filtered to form a leachate. 0.015-0.035 kg of ammonium chloride is added to the vanadium-containing leachate and stirred for 1-2 hours to produce ammonium metavanadate. While this technology offers good molybdenum-vanadium separation, the separation process is lengthy and complex, increasing energy consumption.

[0005] Chinese patent CN113789446A mixes spent catalyst with an alkaline solution and calcines it to form a soluble salt, which is then extracted into a solution using ultrasound. Ammonium chloride is first added to precipitate the vanadium as ammonium metavanadate using a precipitation method. Molybdenum is then recovered from the filtrate using a composite adsorption material, achieving a molybdenum recovery rate of 90.1% and a vanadium recovery rate of 95.9%. This technology consumes a large amount of chemical reagents, and the preparation of the composite adsorption material is complex, increasing process costs.

[0006] Chinese patent CN105692698A utilizes E under acidic conditions 0 Mo(VI) / Mo(V) With E 0 V(V) / V(IV)Taking advantage of the potential differences, compounds of Mo(IV) and / or Mo(V) are used as reducing agents to selectively reduce V(V) in the solution to V(IV), maximizing the differentiation of the properties of molybdenum and vanadium in the solution. Using anion exchange resins or alkaline extractants, they selectively enrich Mo(VI) in the solution but fail to adsorb V(IV), enabling deep separation of molybdenum and vanadium. While this technology is simple to operate and has a short process flow, it requires repeated pH adjustments during the separation process, consumes large amounts of acid and base, and has environmental impacts.

[0007] Chinese patent CN111118310A exploits the morphological differences between vanadium and molybdenum under acidic conditions, using pseudocations formed by the protonation of the oxyethylene units in polyoxyethylene nonionic surfactant molecules to preferentially extract and separate molybdenum. Molybdenum extraction rates exceed 90%, while vanadium extraction rates are less than 20%. This technology, which avoids the use of toxic or hazardous reagents, is a green and relatively simple process. However, its selectivity for molybdenum and vanadium is limited.

[0008] Chinese patent CN109234547A uses a nonionic surfactant as a solvent to extract a nonionic surfactant phase loaded with both vanadium and molybdenum. This phase is then stripped back to separate the vanadium and molybdenum from the precipitate and aqueous phase. The single-stage stripping efficiency for vanadium reaches over 98%, and for molybdenum over 80%. This technique is simple and easy to implement, with mild operating conditions. However, it cannot achieve a single-step separation of molybdenum and vanadium, requiring separate stripping steps. Furthermore, the single-stage stripping efficiency of molybdenum is low, which increases the process flow and consumes more chemical reagents.

[0009] In summary, the commonly used separation methods for vanadium and molybdenum, such as precipitation, adsorption, and solvent extraction, are very difficult to achieve a one-step separation of vanadium and molybdenum. Because the two metals have similar chemical properties, separation generally requires a multi-step and complex process. Among them, solvent extraction is widely used due to its simple operation and high efficiency. However, in this extraction technology, extraction and stripping need to be carried out in steps and repeated multiple times, which increases costs and process difficulty. In some extraction studies, vanadium and molybdenum are co-extracted and then separated by step-by-step stripping. However, achieving efficient stripping of molybdenum is difficult. In addition, solvent extraction technology also has the risks of flammability and explosion, and the solvent is toxic and volatile. It poses safety hazards during the production process and has irreversible impacts on the ecological environment. Therefore, seeking an efficient, green, and environmentally friendly method for separating vanadium and molybdenum is of far-reaching significance for environmental protection and effective resource utilization.

[0010] Membrane technology is considered a promising and sustainable method for metal separation due to its environmentally friendly, low energy consumption, and simple operation. Among these membrane technologies, polymer inclusion membranes (PIMs) are particularly innovative and sustainable. The most significant characteristic of PIMs, which distinguish them from other membrane processes, is that the organic carrier (extractant) is uniformly dispersed within the entangled chains of the base polymer, providing PIMs with excellent transport properties and stability. Furthermore, PIMs are expected to replace traditional solvent extraction and supported liquid membranes as an environmentally friendly alternative. Compared to solvent extraction, PIMs enable simultaneous extraction and stripping, saving extractants and being more environmentally friendly. Compared to supported liquid membranes, PIMs offer advantages such as simple preparation, strong stability, and high selectivity. Because the properties of polymer inclusion membranes are deeply influenced by the composition and ratio of the base polymer and carrier, the mechanism by which polymer inclusion membranes separate metals such as Mo(VI) and V(V) remains unclear. Therefore, a method for achieving highly selective separations of Mo(VI) and V(V) using polymer inclusion membranes is urgently needed in the metal separation field. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a method for separating molybdenum and vanadium using an efficient membrane. Based on PIMs, the method combines the high selectivity and high stability of polymer-coated membranes with the synergistic effect of the electric field on ion transport and separation in an electrodialysis (ED) configuration to achieve the separation of molybdenum and vanadium in a simple, efficient, and environmentally friendly manner.

[0012] The method for efficiently separating molybdenum and vanadium according to the present invention comprises the following steps:

[0013] (1) Preparation of polymer-coated membranes with different selectivities for molybdenum and vanadium;

[0014] (2) Establishing a polymer-coated membrane electrodialysis structure;

[0015] (3) Separation and transmission of molybdenum and vanadium mixed metal solutions using polymer-coated membrane electrodialysis structure:

[0016] The feed liquid, stripping liquid and electrode liquid are pumped into the corresponding chambers for circulation, the feed liquid enters the feed liquid chamber, the stripping liquid enters the stripping liquid chamber, and the electrode liquid enters the cathode electrode liquid chamber and the anode electrode liquid chamber, wherein the feed liquid is mainly a mixed metal solution of molybdenum and vanadium;

[0017] An electric field is applied in a constant current mode on both sides of the polymer-coated membrane electrodialysis structure, so that the molybdenum in the molybdenum and vanadium mixed metal solution in the feed liquid chamber is transferred to the stripping liquid chamber under the action of the electric field and the selective permeability of the polymer-coated membrane. However, since the polymer-coated membrane has limited transmission capacity for vanadium, most of the vanadium is retained in the feed liquid chamber, thereby realizing a one-step separation of the molybdenum and vanadium mixed metals.

[0018] The polymer-coated membrane electrodialysis structure consists of a cathode electrode liquid chamber, a feed liquid chamber, a stripping liquid chamber and an anode electrode liquid chamber; electrode plates are provided on the outside of the cathode electrode liquid chamber and the anode electrode liquid chamber, which are connected to the negative and positive poles of the power supply respectively; an anion exchange membrane is provided between the cathode electrode liquid chamber and the feed liquid chamber, a polymer-coated membrane is provided between the feed liquid chamber and the stripping liquid chamber, and a cation exchange membrane is provided between the stripping liquid chamber and the anode electrode liquid chamber.

[0019] The feed liquid contains metal ion complex NaSO4; the pH value of the feed liquid is 0.5~2.

[0020] The polymer coating film consists of a base polymer and a carrier, wherein the base polymer is polyvinylidene fluoride-hexafluoropropylene, the carrier is methyl trioctyl ammonium chloride, and the mass percentage of the base polymer in the polymer coating film is 30% to 70%.

[0021] The polymer coating is prepared by a solvent evaporation method. Specifically, the base polymer and carrier are dissolved in an organic solvent at 25-45°C, stirred for 2-4.5 hours, and then ultrasonically degassed to obtain a casting solution. The casting solution is poured into a mold, and the polymer coating is obtained after the organic solvent evaporates. The organic solvent is tetrahydrofuran.

[0022] Current density is 5~30mA / cm 2 .

[0023] The stripping solution is one or more of sulfuric acid solution, hydrochloric acid solution, nitric acid solution, sodium bisulfate solution, and magnesium sulfate solution; and the stripping solution concentration is 0.1-1.5 mol / L.

[0024] The electrode liquid is sodium sulfate solution with a concentration of 0.1~0.5mol / L.

[0025] The molybdenum and vanadium in the molybdenum-vanadium mixed metal solution are both present in the solution in the form of metal cation compounds, wherein the concentration of the metal cation compounds in the molybdenum-vanadium mixed metal solution is 50-100 mg / L.

[0026] The working process of the polymer-coated membrane electrodialysis structure described in the present invention is as follows: the cathode electrode liquid chamber and the anode electrode liquid chamber are connected in series through pipelines to realize the circulation of the same electrode liquid; the feed liquid is pumped into each chamber at a flow rate of 30L / h by a water pump to realize circulation in each chamber; an electric field is applied on both sides of the device in a constant current mode, and the current density varies with the magnitude of the applied current; under the drive of the external electric field, the charged metal ions in the solution undergo directionally movement.

[0027] The working principle of the present invention is: In the acidic feed solution, V (V) and Mo (VI) are present in the form of oxygen-containing acid radical cations. Due to the presence of HSO4 in the solution, - / SO4 2- Complex, two metal oxo cations and HSO4 - / SO4 2- Complexation forms an anionic complex. Under the action of the electric field, the two metals migrate to the surface of the polymer membrane, and the different selectivities of the polymer membrane for the two metals lead to initial separation. By adjusting the current density, stripping solution concentration, and feed solution pH, the stripping efficiency of Mo(VI) can be further improved, while V(V) is limited by its lower extraction efficiency, which continuously enhances the separation effect. This allows Mo(VI) in the feed solution to move in a directional manner under the action of the electric field and dissociate through the membrane into the stripping solution under the action of the stripping solution. A large amount of V(V) remains in the feed solution due to the selectivity of the polymer membrane and the competition between the metals. The synergistic effect of the current and stripping solution enhances the separation effect, thus achieving an efficient one-step separation of Mo(VI) and V(V), with a separation factor as high as 287.8.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The polymer coating prepared by the present invention can perform extraction and back extraction simultaneously, changing the step-by-step method of traditional extraction, simplifying the process, improving efficiency, and having the characteristics of high stability, high selectivity, and reusability;

[0030] 2. The present invention adopts a polymer-coated membrane electrodialysis structure, which improves the permeation efficiency of the polymer-coated membrane under the action of the electric field and improves the process efficiency;

[0031] 3. The polymer-coated membrane electrodialysis structure used in the present invention can achieve highly selective separation of metals with similar properties by simply adjusting process parameters such as current density, stripping solution concentration, and feed solution pH value, providing a technical idea for the separation of metals with similar chemical properties and having good industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 , a schematic diagram of the working structure of the polymer-coated membrane electrodialysis of the present invention;

[0033] Figure 2 , Mo / V mass concentration ratio and extraction rate, stripping rate, and separation coefficient in Example 9;

[0034] In the figure, 1, electrode plate; 2, anion exchange membrane; 3, polymer coating membrane; 4, cation exchange membrane. DETAILED DESCRIPTION

[0035] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments.

[0036] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0037] Example 1

[0038] The polymer coated membrane electrodialysis structure of the present invention has a structure as follows Figure 1 As shown, it consists of two outermost ruthenium-plated titanium electrode plates connected to the negative and positive poles of the power supply, and four internal chambers. The anion exchange membrane, polymer-coated membrane, and cation exchange membrane are sealed and fixed in sequence by silicone gaskets. Together with the two outermost ruthenium-plated electrode plates, they divide the internal space of the device into four equal chambers, namely the cathode electrode liquid chamber, feed liquid chamber, stripping liquid chamber, and anode electrode liquid chamber. The thickness of each chamber is 1 cm, and the effective membrane area is 20 cm 2 , that is, the volume of each chamber is about 20cm 3 .

[0039] The preparation method of the polymer coating film is as follows: polyvinylidene fluoride-hexafluoropropylene and methyl trioctyl ammonium chloride are dissolved in tetrahydrofuran at a mass ratio of 4:6 at 25°C, stirred for 4.5 hours, and then ultrasonically degassed for 15 minutes to obtain a casting liquid. The casting liquid is poured into a horizontally placed flat mold and evaporated at room temperature for 12 hours. After the tetrahydrofuran evaporates, the polymer coating film is peeled off from the mold for use.

[0040] The feed solution is mainly a mixed metal solution of molybdenum and vanadium, i.e., a mixed solution of sodium orthovanadate and sodium molybdate dihydrate, wherein the concentrations of Mo(VI) and V(V) in the sodium orthovanadate and sodium molybdate dihydrate are both 100 mg / mL; sodium sulfate is also dissolved in the feed solution as a metal ion complex, and the concentration of sodium sulfate is 0.5 mol / L; the pH value of the feed solution is adjusted to 2 with concentrated sulfuric acid;

[0041] A sulfuric acid solution with a concentration of 1 mol / L is pumped into the stripping liquid chamber as a stripping liquid, and a sodium sulfate solution with a concentration of 0.5 mol / L is pumped into the cathode electrode liquid chamber and the anode electrode liquid chamber as an electrode liquid.

[0042] Working process: using 5mA / cm 2The experiment was carried out at a current density of 100 nm. The feed liquid was pumped into each chamber through a water pump at a flow rate of 30 L / h for circulation. 1 mL of solution was taken from the feed liquid chamber and the stripping liquid chamber every 2 h to measure the concentrations of Mo (VI) and V (V) in the chamber at that moment. When the metal ion concentration remained basically unchanged, it was considered the separation endpoint.

[0043] Example 2

[0044] The difference between Example 2 and Example 1 is that the current density used during the working process is 10mA / cm 2 , other than that, it is the same as Example 1.

[0045] Example 3

[0046] The difference between Example 3 and Example 1 is that the current density used during the working process is 20mA / cm 2 , other than that, it is the same as Example 1.

[0047] Example 4

[0048] The polymer-coated membrane electrodialysis structure of the present invention is the same as that of Example 1.

[0049] The preparation method of the polymer coating film is as follows: polyvinylidene fluoride-hexafluoropropylene and methyltrioctyl ammonium chloride are dissolved in tetrahydrofuran at a mass ratio of 4:6 at 30°C, stirred for 3 hours, and then ultrasonically degassed for 15 minutes to obtain a casting liquid. The casting liquid is poured into a horizontally placed flat mold and evaporated at room temperature for 12 hours. After the tetrahydrofuran evaporates, the polymer coating film is peeled off from the mold for use.

[0050] The feed solution is mainly a mixed metal solution of molybdenum and vanadium, i.e., a mixed solution of sodium orthovanadate and sodium molybdate dihydrate, wherein the concentrations of Mo(VI) and V(V) in the sodium orthovanadate and sodium molybdate dihydrate are both 100 mg / mL; sodium sulfate is also dissolved in the feed solution as a metal ion complex, and the concentration of sodium sulfate is 0.5 mol / L; the pH value of the feed solution is adjusted to 2 with concentrated sulfuric acid;

[0051] A sulfuric acid solution with a concentration of 0.2 mol / L is pumped into the stripping liquid chamber as a stripping liquid, and a sodium sulfate solution with a concentration of 0.5 mol / L is pumped into the cathode electrode liquid chamber and the anode electrode liquid chamber as an electrode liquid.

[0052] Working process: Using 20mA / cm 2 The experiment was carried out at a current density of 100 nm. The feed liquid was pumped into each chamber through a water pump at a flow rate of 30 L / h for circulation. 1 mL of solution was taken from the feed liquid chamber and the stripping liquid chamber every 2 h to measure the concentrations of Mo (VI) and V (V) in the chamber at that moment. When the metal ion concentration remained basically unchanged, it was considered the separation endpoint.

[0053] Example 5

[0054] The difference between Example 5 and Example 4 is that a sulfuric acid solution with a concentration of 0.6 mol / L is used as the stripping solution. Other than that, the process is the same as Example 4.

[0055] Example 6

[0056] The difference between Example 6 and Example 4 is that a sulfuric acid solution with a concentration of 1.5 mol / L is used as the stripping solution. Other than that, the same as Example 4.

[0057] Example 7

[0058] The polymer-coated membrane electrodialysis structure of the present invention is the same as that of Example 1.

[0059] The preparation method of the polymer coating film is as follows: polyvinylidene fluoride-hexafluoropropylene and methyltrioctyl ammonium chloride are dissolved in tetrahydrofuran at a mass ratio of 4:6 at 45°C, stirred for 2 hours, and then ultrasonically degassed for 15 minutes to obtain a casting liquid. The casting liquid is poured into a horizontally placed flat mold and evaporated at room temperature for 12 hours. After the tetrahydrofuran evaporates, the polymer coating film is peeled off from the mold for use.

[0060] The feed solution is mainly a mixed metal solution of molybdenum and vanadium, i.e., a mixed solution of sodium orthovanadate and sodium molybdate dihydrate, wherein the concentrations of Mo(VI) and V(V) in the sodium orthovanadate and sodium molybdate dihydrate are both 100 mg / mL; the feed solution also contains a metal ion complex sodium sulfate, with a concentration of 0.5 mol / L; the pH value of the feed solution is adjusted to 1 using concentrated sulfuric acid;

[0061] A sulfuric acid solution with a concentration of 1.5 mol / L is pumped into the stripping liquid chamber as a stripping liquid, and a sodium sulfate solution with a concentration of 0.5 mol / L is pumped into the cathode electrode liquid chamber and the anode electrode liquid chamber as an electrode liquid.

[0062] Working process: Using 20mA / cm 2 The experiment was carried out at a current density of 100 nm. The feed liquid was pumped into each chamber through a water pump at a flow rate of 30 L / h for circulation. 1 mL of solution was taken from the feed liquid chamber and the stripping liquid chamber every 2 h to measure the concentrations of Mo (VI) and V (V) in the chamber at that moment. When the metal ion concentration remained basically unchanged, it was considered the separation endpoint.

[0063] Example 8

[0064] The difference between Example 8 and Example 7 is that the pH value of the mixed solution is adjusted to 0.5 with concentrated sulfuric acid. Other than that, the process is the same as Example 7.

[0065] Example 9

[0066] The polymer-coated membrane electrodialysis structure of the present invention is the same as that of Example 1.

[0067] The preparation method of the polymer coating film is as follows: polyvinylidene fluoride-hexafluoropropylene and methyltrioctyl ammonium chloride are dissolved in tetrahydrofuran at a mass ratio of 4:6 at 45°C, stirred for 2 hours, and then ultrasonically degassed for 15 minutes to obtain a casting liquid. The casting liquid is poured into a horizontally placed flat mold and evaporated at room temperature for 12 hours. After the tetrahydrofuran evaporates, the polymer coating film is peeled off from the mold for use.

[0068] The feed liquid is mainly a mixed metal solution of molybdenum and vanadium, that is, a mixed solution of sodium orthovanadate and sodium molybdate dihydrate, wherein the sum of the mass concentrations of Mo (VI) and V (V) in sodium orthovanadate and sodium molybdate dihydrate is maintained at 120 ppm, and the mixed metal solutions are prepared according to the mass concentration ratios of Mo (VI) and V (V) of 3:1, 2:1, 1:1, 1:2 and 1:3 respectively; sodium sulfate is also dissolved in the feed liquid, and the concentration of sodium sulfate is 0.5 mol / L; the pH value of the feed liquid is adjusted to 0.5 with concentrated sulfuric acid;

[0069] A sulfuric acid solution with a concentration of 1.5 mol / L is pumped into the stripping liquid chamber as a stripping liquid, and a sodium sulfate solution with a concentration of 0.5 mol / L is pumped into the cathode electrode liquid chamber and the anode electrode liquid chamber as an electrode liquid.

[0070] Working process: Using 20mA / cm 2 The experiment was carried out at a current density of 100 nm. The feed liquid was pumped into each chamber through a water pump at a flow rate of 30 L / h for circulation. 1 mL of solution was taken from the feed liquid chamber and the stripping liquid chamber every 2 h to measure the concentrations of Mo (VI) and V (V) in the chamber at that moment. When the test concentration of metal ions remained basically unchanged, it was considered the separation endpoint.

[0071] Comparative Example 1

[0072] The difference between this comparative example 1 and embodiment 1 is that the current density used in the working process is 0 mA / cm 2 , other than that, it is the same as Example 1.

[0073] Data processing:

[0074] The data of Examples 1 to 9 and Comparative Example 1 were processed, and the extraction rate, back-extraction rate and separation coefficient were calculated according to the following formulas (I), (II) and (III), respectively. The results are shown in Tables 1 and 2.

[0075] (I)

[0076] Where E% is the metal extraction efficiency at a certain moment; C0 is the initial concentration of metal ions (mg / L); C F,t: metal ion concentration in the feed solution at time t (mg / L); V: initial volume of the feed solution (mL); V F,t : feed liquid volume at time t (mL).

[0077] (II)

[0078] Where, S%: metal stripping efficiency at a certain moment; C s,t : metal ion concentration in the feed solution at time t (mg / L); V s,t : volume of stripping solution at time t (mL).

[0079] (III)

[0080] Among them, β Mo / V : Separation coefficient of two metals Mo and V; (C Mo / C V ) S,t : The ratio of the two metal concentrations in the stripping solution at time t; (C Mo / C V ) F,t : The concentration ratio of the two metals in the feed solution at time t.

[0081] Table 1 Data comparison table of Examples 1 to 8 and Comparative Example 1

[0082]

[0083] Table 2 Data comparison table of Example 9

[0084]

[0085] As shown in Table 1, through Examples 1 to 8, under the conditions of an external electric field and the feed liquid being adjusted to be acidic, the present invention can better achieve the extraction of Mo(VI) while suppressing the extraction of V(V). The extraction rate of Mo(VI) is over 93%, while the extraction rate of V(V) is below 43.8%.

[0086] It can be seen from Comparative Example 1 that when the current density is 0, the extraction rates of the two metals are both less than 50%, but the extraction rate of Mo (VI) is significantly higher than that of V (V), indicating that the polymer coating film prepared by the present invention has stronger selectivity for Mo (VI), but when the current density is 0, the stripping rate of Mo (VI) is low, which is 9.4%, and a good Mo recovery effect cannot be achieved quickly; comparing Examples 1 to 3 with Comparative Example 1, it can be seen that the introduction of the electric field significantly promotes the extraction of Mo (VI), and that with the increase of the current density, the electric field has a significant promoting effect on the transmission of Mo (VI), while the transmission effect on V (V) is limited, indicating that, in the present invention, within a certain range, the increase in current density has a stronger promoting effect on the transmission of Mo (VI), thereby enhancing the separation effect of Mo (VI) and V (V);

[0087] Comparison with Examples 4 to 6 shows that within a certain concentration range, increasing the concentration of the stripping solution can increase the extraction rate and stripping rate of Mo (VI) while reducing the extraction rate and stripping rate of V (V), thereby enhancing the separation effect of Mo (VI) and V (V);

[0088] Comparison of Examples 7 and 8 shows that under the conditions of acidic feed liquid, the stronger the acidity of the feed liquid, the enhanced separation effect of Mo (VI) and V (V);

[0089] As can be seen from Table 2, when the total mass concentration of the two metals in the raw material solution remains unchanged (120 ppm), the mass concentration ratio of Mo (VI) to V (V) changes from 3:1 to 1:3, and the Mo (VI) in the feed solution always maintains a high transmission efficiency, with more than 95% of Mo (VI) being transmitted, while the stripping rate of V (V) is less than 4.5%. The separation coefficient varies slightly with the mass concentration ratio, but is always higher than 280.3. This means that the polymer-coated membrane electrodialysis structure of the present invention can effectively separate Mo (VI) and V (V) in a wide range of mass concentration ratios. The above conclusions are from Figure 2 It can also be seen more intuitively.

[0090] In the acidic feed solution, V (V) and Mo (VI) both exist in the form of oxygen-containing acid radical cations. Due to the presence of HSO4 in the solution, - / SO4 2- Complex, two metal oxo cations and HSO4 - / SO4 2-Complexation forms an anionic complex. Under the action of the electric field, the two metals migrate to the surface of the polymer coating, and the different selectivities of the polymer coating for the two metals lead to a preliminary separation. In Examples 1-8, by adjusting the current density, stripping solution concentration, and feed solution pH, the stripping rate of Mo(VI) is continuously increased, while V(V) is limited by a lower extraction rate, resulting in a continuous strengthening of the separation effect. This allows Mo(VI) in the feed solution to move directionally under the action of the electric field and dissociate through the membrane into the stripping solution under the action of the stripping solution. A large amount of V(V) remains in the feed solution due to the selectivity of the polymer coating and the competition between the metals. The synergistic effect of the current and stripping solution enhances the separation effect, thus achieving an efficient one-step separation of Mo(VI) and V(V), with a separation factor as high as 287.8.

Claims

1. A method for efficiently separating molybdenum and vanadium, characterized in that: The following steps are involved: (1) Preparation of polymer-coated membranes with different selectivities for molybdenum and vanadium; (2) Establishing a polymer-coated membrane electrodialysis structure; (3) Separation and transmission of molybdenum and vanadium mixed metal solutions using polymer-coated membrane electrodialysis structure: The polymer-coated membrane electrodialysis structure consists of a cathode electrode liquid chamber, a feed liquid chamber, a stripping liquid chamber, and an anode electrode liquid chamber; Electrode plates are provided on the outside of the cathode electrode liquid chamber and the anode electrode liquid chamber, which are connected to the negative electrode and the positive electrode of the power supply respectively; an anion exchange membrane is provided between the cathode electrode liquid chamber and the feed liquid chamber, a polymer coating membrane is provided between the feed liquid chamber and the stripping liquid chamber, and a cation exchange membrane is provided between the stripping liquid chamber and the anode electrode liquid chamber; The feed liquid, the stripping liquid and the electrode liquid are pumped into the corresponding chambers for circulation, the feed liquid enters the feed liquid chamber, the stripping liquid enters the stripping liquid chamber, and the electrode liquid enters the cathode electrode liquid chamber and the anode electrode liquid chamber, wherein the feed liquid is mainly a mixed metal solution of molybdenum and vanadium, the molybdenum and vanadium in the mixed metal solution of molybdenum and vanadium both exist in the solution in the form of metal cation compounds, the valence of molybdenum in the feed liquid is hexavalent, and the valence of vanadium is pentavalent; An electric field is applied in a constant current mode on both sides of the polymer-coated membrane electrodialysis structure. Under the action of the electric field and the selective permeation of the polymer-coated membrane, the molybdenum in the molybdenum and vanadium mixed metal solution in the feed liquid chamber is transferred to the stripping liquid chamber, achieving a one-step separation of the molybdenum and vanadium mixed metals. The feed liquid contains a metal ion complex, sodium sulfate; the pH value of the feed liquid is 0.5-2; The polymer coating film is composed of a base polymer and a carrier, wherein the base polymer is polyvinylidene fluoride-hexafluoropropylene, the carrier is methyl trioctyl ammonium chloride, and the base polymer accounts for 30% to 70% of the mass of the polymer coating film; Current density is 5~30mA / cm 2 ; The stripping solution is one or more of sulfuric acid solution, hydrochloric acid solution, nitric acid solution, sodium bisulfate solution, and magnesium sulfate solution; and the stripping solution concentration is 0.1-1.5 mol / L.

2. The method for efficiently separating molybdenum and vanadium according to claim 1, characterized in that: The preparation method of the polymer coating film is the solvent evaporation method, and the specific steps are: dissolving the base polymer and the carrier in an organic solvent at 25~45℃, stirring for 2~4.5h, and then ultrasonically degassing to obtain a casting liquid, pouring the casting liquid into a mold, and obtaining the polymer coating film after the organic solvent evaporates.

3. The method for efficiently separating molybdenum and vanadium according to claim 2, characterized in that: The organic solvent is tetrahydrofuran.

4. The method for efficiently separating molybdenum and vanadium according to claim 1, characterized in that: The electrode liquid is sodium sulfate solution with a concentration of 0.1~0.5mol / L.

5. The method for efficiently separating molybdenum and vanadium according to claim 1, characterized in that: The concentration of the metal cation compound in the molybdenum and vanadium mixed metal solution is 50-100 mg / L.

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