A method for extracting molybdenum from lead-zinc tailings sand and an electrodialysis system

Abstract

The present invention discloses a method for extracting molybdenum from lead-zinc tailings sand and an electrodialysis system, belonging to the technical field of producing metals by electrophoresis or electrolysis. In the method of the present invention, the electric field force is utilized to promote the directional migration and separation of anions and cations in the leaching solution, and the migration of silicic acid molecules in the leaching solution is blocked by controlling the selective permeability, so as to realize the adsorption and enrichment of molybdate anions during the electrodialysis process, and at the same time inhibit the migration of molybdic acid molecules; the process is simple to operate, has high extraction efficiency and strong resistance to cation interference. The present invention also provides an electrodialysis system used in conjunction with the method. The system adopts a single-stage four-chamber structure, which can not only realize the efficient separation of silicon and molybdenum in a solution with high silicon and low molybdenum, but also realize the efficient enrichment of molybdate in the low-molybdenum solution at the same time, effectively eliminate the interference of cations such as calcium, magnesium and iron, and can effectively block the continuous migration of molybdenum entering the resin chamber to the anode chamber of the electrode, strengthening the ability of the resin chamber to enrich molybdenum.

Description

Technical Field

[0001] The present invention relates to the technical field of metal production by electrophoresis or electrolysis, and in particular to a method for extracting molybdenum from lead-zinc tailings sand and an electrodialysis system. Background Art

[0002] Molybdenum is an extremely important and scarce strategic metal, and has extensive applications in many fields such as steel, nuclear energy, petroleum processing, synthetic ammonia and other industries, environmental protection and aerospace. However, molybdenum resources are extremely scarce, and its average content in the earth's crust is only 0.001%. Therefore, extracting and recovering molybdenum from solid wastes such as minerals, catalysts, and spent fuels has important strategic significance.

[0003] Currently, the main methods for extracting molybdenum from solid waste leaching include precipitation methods (such as patents CN112662874A and CN115747530A), ion exchange adsorption methods (such as patents CN113215419A, CN114438320A, and CN111876617A), and extraction methods (such as patents CN109763003A, CN114686706A, and CN115522052A), etc. Since the precipitation method requires a sufficient amount to have a separation significance, it is usually applicable to the extraction of molybdenum in a concentrated enrichment solution. Both the ion exchange adsorption method and the extraction method can achieve the enrichment of molybdenum, but the cost of the extractant in the extraction method is relatively high. The ion exchange adsorption method has a high enrichment efficiency and is convenient and simple to operate, so it is more suitable for the enrichment of molybdenum ions with a small concentration and a high recycling rate. However, for solutions with a high acidity, a large number of heavy metal impurities, and a low molybdenum content, neither the extraction method nor the ion exchange method alone can effectively recover molybdenum (Deng Pan. Research on the extraction of molybdenum from the final solution of arsenous acid reduction containing low-concentration molybdenum [D]. Jiangxi University of Science and Technology, 2013.).

[0004] The main anions in the alkali fusion of lead-zinc tailings are silicate and carbonate, which are converted into silicic acid and carbonic acid or lost as CO2 in the air after acidification. The cation components in the acidified solution are relatively complex, and there are many types of heavy metal ions. The leached molybdate usually exists in the form of a weak acid root under weak acidic conditions. Although the application of anion exchange resin can achieve the adsorption of molybdenum, for the tailing leaching solution with a large amount of silicate, the performance of the ion exchange resin is greatly affected by silicate pollution under weak acidic conditions, which limits the direct application of the ion exchange method to enrich molybdenum. In addition, the adsorption capacity of the macroporous anion resin for molybdenum will also decrease with the decrease of pH, further limiting its application in this field.

[0005] Chinese patent document (CN110104688A) discloses a method for removing molybdenum from ammonium tungstate solution. Based on the high adsorption capacity of WDA918 resin, but its adsorption effect on low-concentration molybdenum solution is poor, while the adsorption capacity of 201×7 resin is low and it is prone to breakthrough, but its adsorption effect on low-concentration molybdenum solution is stable. Based on the above characteristics, the invention sulfides MoO4 2- to MoS4 2- , adsorbs high-concentration MoS4 with WDA918 resin 2- , and adsorbs low-concentration MoS4 with 201×7 resin 2- .

[0006] Chinese patent document (CN103866122A) discloses a method for microbial leaching of uranium-molybdenum ore and enrichment and separation of uranium and molybdenum. 201×7 resin is used to enrich uranium and molybdenum and then uranium and molybdenum are eluted step by step, and the recovery rates of uranium and molybdenum reach over 80%. It can be seen that 201×7 resin can be used to enrich molybdenum.

[0007] Electrodialysis has been widely used in the field of valuable metal recovery, but it has not been seen in the extraction of molybdenum. Although electrodialysis has good separation performance for anions and cations, it is greatly affected by the ionic composition of the sample solution. Therefore, the separation method should be reasonably designed based on the component characteristics of the leaching solution. The enrichment ability of single-stage electrodialysis is relatively low, and multi-stage extraction is often used. In addition, if molybdate anions directly migrate to the anode chamber under the action of electric field force, it will affect the reuse of the solution in the anode chamber, and the continuous increase of the acidity in the anode chamber will also affect the adsorption efficiency of molybdenum, greatly enhancing the interference of the electrolyte solution on the purity of molybdenum and increasing the complexity of the separation process. Summary of the Invention

[0008] In view of the above-mentioned defects of the prior art, in the first aspect of the present invention, a method for extracting molybdenum from lead-zinc tailings with high extraction efficiency and strong resistance to cation interference is provided, including the following steps:

[0009] Leach lead-zinc tailings to obtain a leaching solution containing silicate ions and molybdate ions; use electrodialysis to extract the leaching solution, and utilize the electric field force to promote the directional migration and separation of anions and cations in the leaching solution; block the migration of silicic acid molecules in the leaching solution by controlling the selective permeability; realize the adsorption and enrichment of molybdate anions during the electrodialysis process, and at the same time inhibit the migration of molybdic acid molecules; after the adsorption and enrichment of molybdate anions, elute and recover the eluate to complete the extraction of molybdenum.

[0010] Preferably, the method for leaching lead-zinc tailings is as follows: melt lead-zinc tailings with an alkaline substance, cool to form a eutectic mixture; acidify the eutectic mixture and separate the insoluble substances to obtain a leaching solution.

[0011] Further preferably, the mass ratio of the eutectic lead-zinc tailings to the alkaline substance is 1:0.3 to 1; the eutectic temperature is 400 to 680 °C.

[0012] Furthermore, the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, and sodium carbonate.

[0013] Further preferably, after the acidification treatment, the pH of the obtained leaching solution is 2 to 3.

[0014] Furthermore, the acidification treatment uses hydrochloric acid or sulfuric acid.

[0015] Under the preferred conditions, the concentrations of silicate ions and molybdate ions in the leaching solution obtained by leaching lead-zinc tailings are higher. On the basis of meeting the extraction of molybdenum by this method, the leaching process of lead-zinc tailings is not limited to the form of the preferred method.

[0016] Preferably, the single-stage potential difference of the electrodialysis is 5 to 20 V, the current density is 250 to 1500 A / m 2 , and the electrodialysis time is 2 to 5 h.

[0017] Preferably, the concentration of the electrolytes in the anode and cathode of the electrodialysis is 0.01 to 0.2 mol / L.

[0018] Further preferably, the electrolytes in the anode and cathode of the electrodialysis use an aqueous solution of sodium chloride or an aqueous solution of sodium sulfate.

[0019] Preferably, the adsorption and enrichment are carried out by 201×7 strongly basic type I anion exchange resin.

[0020] Further preferably, after the molybdate anions are adsorbed and enriched, they are eluted with an aqueous solution of sodium hydroxide with a concentration of 0.1 to 1 mol / L, and 1 to 6 BV of the eluate is recovered.

[0021] In the second aspect of the present invention, an electrodialysis system for extracting molybdenum from lead-zinc tailings sand is provided, which is used for the electrodialysis method for extracting molybdenum in the first aspect of the present invention:

[0022] The electrodialysis system includes an electrodialysis device, a liquid storage system, a regeneration system, and a recovery system;

[0023] The electrodialysis device is composed of single-stage or multi-stage electrodialysis units; the electrodialysis units are successively composed of an electrode anode chamber, a resin chamber, a sample chamber, and an electrode cathode chamber. In the electrodialysis units, each anode is connected in parallel and connected to the positive pole of the power supply, and each cathode is connected in parallel and connected to the negative pole of the power supply; the electrode anode chamber, the resin chamber, and the sample chamber are separated from each other by an acid- and alkali-resistant homogeneous anion exchange membrane, and the sample chamber and the electrode cathode chamber are separated by an acid- and alkali-resistant homogeneous cation exchange membrane to control the selective permeability of the electrodialysis; the resin chamber contains anion exchange resin for the adsorption of molybdenum;

[0024] The liquid storage system includes a leaching solution storage tank, a first storage tank, and a second storage tank; the leaching solution is stored in the leaching solution storage tank and is used to transport the leaching solution to the sample chamber of the first-stage electrodialysis unit; the electrolyte used for electrodialysis is stored in the first storage tank and is used to transport the electrolyte to the anodic electrode chamber and the cathodic electrode chamber; the second storage tank stores acid solution, which is used to transport acid solution to the resin chamber to keep its acidity unchanged;

[0025] The regeneration system includes a resin regeneration tank and a resin column; the anion exchange resin in the resin chamber is adsorbed and stored in the resin regeneration tank, and adding alkali solution can be used for elution to obtain eluate and regenerated anion exchange resin; the resin column contains anion exchange resin, and the low-concentration molybdenum not adsorbed by the resin chamber in the electrodialysis device is adsorbed here, and eluate and regenerated anion exchange resin can also be obtained after elution;

[0026] The recovery system includes a liquid outlet tank and a molybdenum recovery tank; the solution flowing out of the sample chamber of the electrodialysis device is stored in the liquid outlet tank and can be used for recovering silica white and iron; the eluate obtained by eluting the anion exchange resin is stored in the molybdenum recovery tank to complete the extraction of molybdenum and is used for preparing molybdenum products.

[0027] Preferably, in the resin chamber, the solid-liquid volume ratio of the anion exchange resin is 4:3 to 6:1.

[0028] Preferably, in the second storage tank, the pH of the acid solution is 1 to 2.5.

[0029] More preferably, the acid solution is sulfuric acid or hydrochloric acid.

[0030] Based on the processes and systems provided in the first and second aspects of the present invention, the design concept and extraction process of the present invention are as follows:

[0031] The present invention uses anion and cation exchange membranes in the electrodialysis method to block the migration of silicic acid molecules, uses the electric field force to promote the directional migration and separation of anions and cations, and by regulating the pH, realizes the adsorption and enrichment of condensed molybdate anions (Mo7O 24 6- or H2Mo7O 24 4- ) by 201×7 strongly basic type I anion exchange resin, while inhibiting the migration of molecules in the form of molybdic acid to the anodic electrode chamber, and promoting the migration of anions of strong acids in the resin chamber to the anodic electrode chamber, realizing the solid waste resource utilization technology of silicon-molybdenum separation and molybdenum enrichment.

[0032] During the extraction process, lead-zinc tailings are melted with alkali, acidified and separated to obtain a solution containing condensed molybdate and silicic acid, that is, the leaching solution;

[0033] The leaching solution is stored in the leaching solution storage tank. When the system is working, the solutions in the anodic chamber and cathodic chamber of the electrodes of each electrodialysis unit come from the first storage tank and circulate continuously between each anodic chamber, cathodic chamber and the first storage tank;

[0034] The solution in the first-stage sample chamber comes from the leaching solution storage tank. After electroosmosis, it flows to the next-stage sample chamber step by step. After reaching the last-stage sample chamber, it flows out to the liquid outlet tank and can be used for recovering silica white and iron;

[0035] The solution in the last-stage resin chamber comes from the second storage tank. After electroosmosis, it flows to the upper-stage resin chamber step by step. After reaching the first-stage resin chamber, it flows out to the resin column; The acid solution in the second storage tank can ensure that when the solution flows to the upper stage step by step in the resin chamber between the two anion membranes, the hydrogen ions in the solution do not migrate and the acidity remains unchanged, so that the molybdenum migrating into this chamber exists in the form of condensed ions or molybdic acid molecules. Among them, the molybdenum anions are in full contact with the resin under the stirring action and preferentially adsorbed by the resin by replacing chloride ions or sulfate radicals, while the chloride ions or sulfate radicals migrate to the anodic chamber through the anion membrane under the action of the electric field force;

[0036] When the adsorption capacity of the resin chamber is nearly saturated, the anion exchange resin is discharged from the bottom into the resin regeneration tank and eluted with an alkaline solution. The eluate is collected and stored in the molybdenum recovery tank, and the regenerated anion exchange resin is reused for adsorption;

[0037] The solution in the resin chamber flows step by step and finally reaches the resin column. The resin column is filled with the regenerated anion exchange resin. The low-concentration molybdenum not adsorbed by the resin chamber is adsorbed by the anion exchange resin here. After elution with an alkaline solution, the eluate is collected and also stored in the molybdenum recovery tank to complete the extraction of molybdenum for preparing molybdenum products.

[0038] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0039] The present invention provides a method for extracting molybdenum from lead-zinc tailings sand. The process is simple to operate, has high extraction efficiency and strong resistance to cation interference.

[0040] The present invention provides an electrodialysis system for extracting molybdenum from lead-zinc tailings sand. The system adopts a single-stage four-chamber structure and is used for the electrodialysis method. It can not only realize the efficient separation of silicon and molybdenum in a high-silicon and low-molybdenum solution (silicon-rich solution), but also realize the efficient enrichment of molybdate in the low-molybdenum solution at the same time, effectively eliminating the interference of cations such as calcium, magnesium and iron. It can effectively block the continuous migration of molybdenum entering the resin chamber to the anodic chamber of the electrode and strengthen the ability of the resin chamber to enrich molybdenum. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 XRD pattern of the lead-zinc tailings used in the examples;

[0042] Figure 2 This is the process flow diagram for extracting molybdenum from lead-zinc tailings sand in the present invention. Detailed implementation manners

[0043] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions noted in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0044] In the following examples:

[0045] The lead-zinc tailings sand comes from Jianshui City, Yunnan Province. The X-ray diffraction pattern of this raw material is as Figure 1 shown. The lead-zinc tailings sand contains substances such as silicon dioxide, calcium carbonate, and calcium magnesium carbonate.

[0046] Example 1

[0047] Study on the performance of extracting molybdenum by the electrodialysis system:

[0048] Prepare a sample solution with a molybdenum content of 959.5 mg / L and acidified with sulfuric acid using molybdenum salts such as sodium molybdate or ammonium molybdate tetrahydrate. Take 50 mL of it as the leaching solution and store it in the leaching solution storage tank for later use; use the electrodialysis system to extract molybdenum. In this example, a single-stage electrodialysis unit is used; store the 0.2 mol / L Na2SO4 aqueous solution in the first storage tank, and add sulfuric acid with a pH of 1 - 2.5 to the second storage tank; when the system conducts electrodialysis, the single-stage potential difference is 20 V, and the current density is 250 - 1500 A / m 2 , and the electrodialysis time is 2.5 h; during this process, the Na2SO4 aqueous solution in the first storage tank flows into the electrode anode chamber and the electrode cathode chamber, and continuously circulates between each electrode anode chamber, electrode cathode chamber and the first storage tank; the leaching solution in the leaching solution storage tank flows into the sample chamber, and after electrodialysis, it flows out to the liquid outlet tank; the sulfuric acid in the second storage tank flows into the resin chamber, and the solid-liquid ratio of the 201×7 strongly basic type I anion exchange resin and the liquid in the resin chamber is 1:1. After electrodialysis, the solution in the resin chamber flows out to a resin column also filled with the 201×7 strongly basic type I anion exchange resin to complete further adsorption; discharge the anion exchange resin in the resin chamber from the bottom into the resin regeneration tank, and elute it with a 1 mol / L sodium hydroxide aqueous solution, and collect 4 BV of the eluate and store it in the molybdenum recovery tank; similarly, the anion exchange resin in the resin column is eluted by the same method, and the obtained eluate is still stored in the molybdenum recovery tank to complete the extraction of molybdenum.

[0049] To detect the extraction effect of the method in this embodiment, an inductively coupled plasma optical emission spectrometer (ICP-OES) was used in the process to detect the molybdenum content of the extracts in each step. The molybdenum content of the eluate obtained by eluting the 201×7 strongly basic type I anion exchange resin in the resin chamber with 1 mol / L sodium hydroxide aqueous solution was 224.7 mg / L, and the molybdenum content of the low-concentration molybdenum eluted from the solution flowing out of the resin chamber through resin column adsorption and elution was 36.78 mg / L. The volumes of the eluates from the two sources were measured, and the extraction mass of molybdenum corresponding to the obtained after electrodialysis was calculated; at the same time, the initial mass of molybdenum in the leaching solution was calculated; the molybdenum recovery rate could be obtained through the mass ratio. In this embodiment, the total molybdenum recovery rate was 58.5%, among which the resin enrichment rate was 56.2% (from the anion exchange resin in the resin chamber), the solution enhanced enrichment rate was 2.3% (from the anion exchange resin in the resin column), and the proportion of the resin enrichment rate was 96.1%.

[0050] Example 2

[0051] Method for extracting molybdenum from lead-zinc tailings sand:

[0052] (1) Mix lead-zinc tailings and sodium hydroxide at a mass ratio of 1:0.3 - 1 and complete eutectic melting at 400 - 680 °C, and then cool to room temperature to obtain a eutectic mixture;

[0053] (2) Dissolve the eutectic mixture in sulfuric acid and acidify to pH 2 - 3, stir evenly and then centrifuge to separate the precipitate to obtain 50 mL of a leaching solution containing condensed molybdate and silicic acid, and store it in the leaching solution storage tank for later use;

[0054] (3) Use an electrodialysis system to extract molybdenum. In this embodiment, a single-stage electrodialysis unit is used; store 0.2 mol / L Na2SO4 aqueous solution in the first storage tank, and add sulfuric acid with a pH of 1 - 2.5 to the second storage tank; when the system performs electrodialysis, the single-stage potential difference is 15 V, and the current density is 250 - 1500 A / m 2, the electrodialysis time is 2.5 h; during this process, the aqueous Na2SO4 solution in the first liquid storage tank flows into the anodic electrode chamber and the cathodic electrode chamber, and continuously circulates between each anodic electrode chamber, cathodic electrode chamber and the first liquid storage tank; the leaching solution in the leaching solution storage tank flows into the sample chamber, and after electrodialysis, it flows out to the effluent tank; the sulfuric acid in the second liquid storage tank flows into the resin chamber, and the solid-liquid ratio of the 201×7 strongly basic type I anion exchange resin and the liquid in the resin chamber is 1:1. After electrodialysis, the solution in the resin chamber flows out to a resin column also filled with 201×7 strongly basic type I anion exchange resin to complete further adsorption; the anion exchange resin in the resin chamber is discharged from the bottom into the resin regeneration tank, and is eluted with 1 mol / L sodium hydroxide aqueous solution, and 1 BV of eluate is collected and stored in the molybdenum recovery tank; similarly, the anion exchange resin in the resin column is eluted by the same method, and the obtained eluate is still stored in the molybdenum recovery tank to complete the extraction of molybdenum.

[0055] To detect the extraction effect of the method in this example, an inductively coupled plasma optical emission spectrometer (ICP-OES) was used to detect the molybdenum content of the extracts in each step during the process. In step (2), the molybdenum content of the obtained leaching solution is 3.26 mg / L, and the total silicon content detected by the hydrofluoric acid conversion spectrophotometry is 2130 mg / L, and the iron content is 16.0 g / L; in step (3), the molybdenum content of the eluate obtained by eluting the 201×7 strongly basic type I anion exchange resin in the resin chamber with 1 mol / L sodium hydroxide aqueous solution is 4.04 mg / L, and the molybdenum content of the low-concentration molybdenum adsorbed and eluted by the solution flowing out of the resin chamber through the resin column is 0.071 mg / L; no silicon or iron was detected in the above eluates. The volumes of the eluates from the two sources were measured, and the extraction mass of molybdenum corresponding to the electrodialysis was calculated; at the same time, the initial mass of molybdenum in the leaching solution was calculated; the molybdenum recovery rate can be obtained by the mass ratio. In this example, the total molybdenum recovery rate is 63.3%, of which the resin enrichment rate is 62.0% (from the anion exchange resin in the resin chamber), and the solution enhanced enrichment rate is 1.3% (from the anion exchange resin in the resin column), and the resin enrichment rate accounts for 97.9%.

[0056] Example 3

[0057] Method for extracting molybdenum from lead-zinc tailings sand:

[0058] (1) Take 50 mL of the leaching solution obtained in Example 2 and store it in the leaching solution storage tank;

[0059] (2) As Figure 2As shown in the figure, an electrodialysis system is used to extract molybdenum. In this embodiment, the leaching solution is added to the sample chamber 1 of the electrodialysis device for two-stage electrodialysis; a 0.2 mol / L aqueous solution of Na2SO4 is stored in the first liquid storage tank, and sulfuric acid with a pH of 1 to 2.5 is added to the second liquid storage tank; when the system performs electrodialysis, the single-stage potential difference is 10 V, and the current density is 250 - 1500 A / m 2 , and the electrodialysis time is 3 h; during this process, the aqueous solution of Na2SO4 in the first liquid storage tank flows into the electrode anode chamber and the electrode cathode chamber of the electrodialysis unit, and continuously circulates between each electrode anode chamber, electrode cathode chamber and the first liquid storage tank; the leaching solution in the leaching solution storage tank flows into the first-stage sample chamber, and after electrodialysis, it gradually flows to the second-stage sample chamber, and flows out to the liquid outlet tank after electrodialysis; the sulfuric acid in the second liquid storage tank flows into the second-stage resin chamber, and after electrodialysis, the solution in the second-stage resin chamber flows to the first-stage resin chamber. The solid-liquid ratio of the 201×7 strongly basic type I anion exchange resin and the liquid in the above resin chambers is 1:1. After electrodialysis, the solution flows out from the first-stage resin chamber to a resin column also filled with 201×7 strongly basic type I anion exchange resin to complete further adsorption; the anion exchange resin in the resin chamber is discharged from the bottom into the resin regeneration tank and eluted with a 1 mol / L aqueous solution of sodium hydroxide. 1 BV of the eluate is collected and stored in the molybdenum recovery tank. After elution, the anion exchange resin is recovered for reuse; similarly, the anion exchange resin in the resin column is eluted by the same method, and the obtained eluate is still stored in the molybdenum recovery tank to complete the extraction of molybdenum.

[0060] In order to detect the extraction effect of the method in this embodiment, an inductively coupled plasma optical emission spectrometer (ICP-OES) is used to detect the molybdenum content of the extracts in each step during the process. The raw material source and preparation process of the leaching solution in this embodiment are the same as those in Example 1; in step (2), the molybdenum content of the eluate obtained by eluting the 201×7 strongly basic type I anion exchange resin in the resin chamber with a 1 mol / L aqueous solution of sodium hydroxide is 2.96 mg / L; after the low-concentration molybdenum adsorbed and eluted by the resin column from the solution flowing out of the resin chamber and the high-concentration molybdenum after eluting the anion exchange resin in the resin chamber are combined, the molybdenum content of the combined eluate is detected to be 1.88 mg / L, and neither silicon nor iron is detected in the eluate. By measuring the volume of the combined eluate, the total extraction mass of molybdenum is obtained, and finally the total molybdenum recovery rate in this embodiment is calculated to be 92.2%, which is higher than the recovery rate in Example 2, indicating that the process of the present invention can achieve efficient separation of silicon and molybdenum in a high-silicon and low-molybdenum solution, and can simultaneously achieve efficient enrichment of molybdate in a low-molybdenum solution, effectively eliminate the interference of cations such as calcium, magnesium and iron, and can also effectively prevent the continuous migration of molybdenum entering the resin chamber to the electrode anode chamber, strengthening the ability of the resin chamber to enrich molybdenum.

[0061] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in this technical field based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. A method for extracting molybdenum from lead-zinc tailings sand, characterized in that, It includes the following steps: Fuse lead-zinc tailings with an alkaline substance and cool to form a eutectic mixture; the mass ratio of the eutectic lead-zinc tailings to the alkaline substance is 1:0.3 - 1, the eutectic temperature is 400 - 680 °C, and the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, and sodium carbonate; the eutectic mixture is acidified and the insoluble substances are separated to obtain an extraction solution containing silicic acid and molybdate ions, and the pH of the extraction solution is 2 - 3; electro-dialysis is used to extract the said extraction solution, and the electric field force is utilized to promote the directional migration and separation of cations and anions in the extraction solution; The migration of silicic acid molecules in the extraction solution is blocked by controlling the selective permeability; During the electro-dialysis process, molybdate anions are adsorbed and enriched, and at the same time, the migration of molybdic acid molecules is inhibited; After the molybdate anions are adsorbed and enriched, they are eluted, the eluate is recovered, and the extraction of molybdenum is completed; The electro-dialysis is carried out through an electro-dialysis system, and the electro-dialysis system includes an electro-dialysis device and a liquid storage system; The electro-dialysis device is composed of single-stage or multi-stage electro-dialysis units; the electro-dialysis unit is successively composed of an anode chamber, a resin chamber, a sample chamber, and a cathode chamber; when the electro-dialysis device is single-stage, the anode in the electro-dialysis unit is connected to the positive pole of the power supply, and the cathode is connected to the negative pole of the power supply; when the electro-dialysis device is multi-stage, the anodes in the electro-dialysis unit are connected in parallel and connected to the positive pole of the power supply, and the cathodes are connected in parallel and connected to the negative pole of the power supply; the anode chamber, the resin chamber, and the sample chamber are separated from each other by an acid- and alkali-resistant homogeneous anion exchange membrane, and the sample chamber and the cathode chamber are separated by an acid- and alkali-resistant homogeneous cation exchange membrane; the resin chamber contains an anion exchange resin; The liquid storage system includes an extraction solution storage tank, a first liquid storage tank, and a second liquid storage tank; the extraction solution is stored in the extraction solution storage tank and supplies the extraction solution to the sample chamber of the first-stage electro-dialysis unit; the electrolyte used for electro-dialysis is stored in the first liquid storage tank and supplies the electrolyte to the anode chamber and the cathode chamber; the second liquid storage tank stores an acid solution with a pH of 1 - 2.5 and supplies the acid solution to the resin chamber.

2. The method according to claim 1, wherein: The single-stage potential difference of the electrodialysis is 5 to 20 V, and the current density is 250 to 1500 A / m 2 , and the electrodialysis time is 2 to 5 h.

3. The method according to claim 1, wherein: The concentration of the said electrolyte is 0.01 - 0.2 mol / L.

4. The method according to claim 1, wherein: The adsorption and enrichment are carried out by 201×7 strongly basic type I anion exchange resin.

5. The method according to claim 4, wherein: After the molybdate anions are adsorbed and enriched, they are eluted with an aqueous sodium hydroxide solution with a concentration of 0.1 - 1 mol / L, and 1 - 6 BV of the eluate is recovered.

6. The method according to claim 1, wherein: The electro-dialysis system includes a regeneration system and a recovery system; The regeneration system includes a resin regeneration tank and a resin column; the anion exchange resin in the resin chamber is stored in the resin regeneration tank after adsorption; the resin column contains an anion exchange resin, and the low-concentration molybdenum not adsorbed by the resin chamber in the electro-dialysis device is adsorbed here; The recovery system includes an effluent tank and a molybdenum recovery tank; the solution flowing out of the sample chamber of the electro-dialysis device is stored in the effluent tank; the eluate obtained by eluting the anion exchange resin is stored in the molybdenum recovery tank.

7. The method according to claim 6, wherein: In the said resin chamber, the solid-liquid volume ratio of the anion exchange resin is 4:3 - 6:1.

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