Method for extracting tellurium from sodium tellurite solution through electrodeposition

Abstract

The invention discloses a method for extracting tellurium from a sodium tellurite solution through electrodeposition, and belongs to the technical field of non-ferrous metal hydrometallurgy. The method comprises the following steps: dissolving crude tellurium dioxide in a sodium hydroxide solution at 60-90 DEG C to prepare a sodium tellurite electrolyte containing 200-240 g / L of tellurium and 90-110 g / L of sodium hydroxide; in the electrodeposition process, a composite additive composed of sodium ascorbate, pentasodium diethylenetriamine pentaacetate, sodium citrate and polyvinylpyrrolidone is synchronously added into the electrolyte. And carrying out electrodeposition for 14-15 days under the conditions that the current density is 40-60A / m, the voltage is 15-30V and the temperature is 15-30 DEG C. Through the synergistic effect of the composite additive, tellurite radicals in the anode region are remarkably inhibited from being oxidized into insoluble sodium tellurate, heavy metal impurity ions in the electrolyte are strongly complexed, and therefore the direct recovery rate of tellurium is increased to 90% or above while the better current efficiency is kept, and the purity of the obtained tellurium ingot reaches 99.95% or above.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrometallurgy of dispersed metals, in particular to a method for efficiently extracting high-purity tellurium from a sodium tellurite alkaline solution by electro-deposition, and a special composite additive used in the method. BACKGROUND

[0002] Tellurium, as an important dispersed metal element, has wide and critical applications, mainly in the following fields: In the semiconductor and electronic information industry, tellurium plays an irreplaceable role. It is the core material for manufacturing cadmium telluride thin-film solar cells, which have relatively low cost, high photoelectric conversion efficiency, and excellent performance in weak light conditions, etc., and thus occupy an important share in the photovoltaic market, providing strong support for the development of global renewable energy, and helping to reduce dependence on traditional fossil fuels and promote energy structure transformation. At the same time, tellurium also has important applications in infrared detectors, lasers, semiconductor thermoelectric materials, etc. For example, mercury cadmium telluride is a key material for making high-performance infrared detectors, widely used in military reconnaissance, environmental monitoring, medical imaging, etc., and can effectively detect and identify invisible infrared light; bismuth telluride and other tellurium-based compounds are good thermoelectric materials, which can be used to make thermoelectric modules and semiconductor coolers, and play an important role in aerospace, portable electronic device temperature control, etc., realizing the direct conversion of heat energy into electrical energy or precise temperature control.

[0003] Electrochemical extraction or refining of tellurium in alkaline medium (NaOH solution) is the mainstream process for industrial production of high-purity tellurium. In this process, tellurium usually exists in the form of tetravalent tellurite ions. However, this process has two major technical bottlenecks: (1) Anode precipitation problem: During the electro-deposition process, the main reaction at the anode is the discharge of hydroxyl ions to produce oxygen, but part of Te(IV) will be oxidized to hexavalent tellurate near the anode surface. The solubility of sodium tellurate in strong alkaline solution is limited, and it is easy to precipitate in the form of crystals or amorphous, adhering to the surface of the anode and the wall of the electrolytic cell, causing anode passivation, cell pressure rise, energy consumption increase, and frequent shutdown for cleaning.

[0004] (2) Purity problem: Anode passivation causes voltage fluctuations, affecting the stability of cathode deposition. At the same time, trace heavy metal impurity ions (such as Pb²⁺, Cu²⁺, Fe³⁺, etc.) in the electrolyte are prone to co-deposition with tellurium, reducing the purity and physical properties of the cathode tellurium.

[0005] The prior art usually adds a single complexing agent (such as ethylenediaminetetraacetic acid EDTA) to complex impurities, or adds a surfactant to improve the deposition morphology, but it is difficult to fundamentally inhibit the generation and precipitation of sodium tellurate. The introduction of some additives may even bring new side reactions or affect the quality of the cathode. Therefore, it is crucial to develop a composite additive system that can inhibit oxidation from the anode, purify the solution from the cathode, and stabilize the system as a whole, so as to improve the overall efficiency of the alkaline tellurium electrodeposition process. SUMMARY

[0006] The technical problem to be solved by the present application is to overcome the defects of serious sodium tellurate precipitation on the anode, limited purity of tellurium product on the cathode, and low metal recovery rate in the existing alkaline sodium tellurite electrodeposition process, and to provide a sodium tellurite solution electrodeposition extraction method which is stable, efficient and can directly produce high-purity tellurium. The specific technical scheme is as follows: S1. Configure electrolyte: add coarse tellurium dioxide into sodium hydroxide solution, stir and dissolve at 60-90℃ for 2-6 hours, so that tellurium enters the solution in the form of sodium tellurite. Remove the insoluble substances by filtration to obtain clear sodium tellurite electrolyte. Control the concentration of sodium hydroxide in the electrolyte to be 90-110 g / L, and the total tellurium concentration to be 200-240 g / L. This concentration range can ensure sufficient conductivity and tellurium ion concentration, which is beneficial to stable electrodeposition; S2. Electrodeposition: use stainless steel plate as the cathode and anode, and inject the electrolyte prepared in step S1 into the electrodeposition tank. During the electrodeposition process, a composite additive composed of sodium ascorbate, diethylenetriamine pentaacetic acid pentasodium, sodium citrate and polyvinylpyrrolidone is added. The concentration range of the composite additive is as follows: sodium ascorbate 0.2-1.0 g / L, diethylenetriamine pentaacetic acid pentasodium 0.1-0.5 g / L, sodium citrate 0.1-0.5 g / L, and polyvinylpyrrolidone 0.1-1.0 g / L. Control the electrodeposition process parameters as follows: cathode current density 40-60 A / m², tank voltage 15-30 V, electrolyte temperature 15-30℃, and electrodeposition cycle 14-15 days. Control the current density at 50-60 A / m² to obtain high-purity electrodeposited tellurium. During the entire electrodeposition cycle, continuously or intermittently add the consumed composite additive through a metering pump to maintain its effective concentration; S3. Post-treatment: after the electrodeposition is completed, the cathode is taken out, and the deposited black and dense tellurium sheet is peeled off. After washing with deionized water and drying, the tellurium sheet is melted and cast into an ingot under the protection of an inert atmosphere, thereby obtaining a high-purity tellurium ingot.

[0007] Further, in the electrolyte of step 1, the concentration of sodium hydroxide is 90-110 g / L, the total tellurium concentration is 200-240 g / L, Cu≤0.05 g / L, Pb≤0.05 g / L, Fe≤0.05 g / L, Bi≤0.01 g / L, and Se≤0.1 g / L. Further, the composite additive is continuously and uniformly added to the electrolyte by a metering pump during the electrodeposition process. Further, the crude tellurium dioxide in step S1 is a tellurium smelting intermediate product, and after being treated by the method, the impurity content in the obtained tellurium ingot meets: Cu≤0.005%, Pb≤0.005%, Fe≤0.003%, Bi≤0.001%, Se≤0.01%. Further, sodium ascorbate in the composite additive is used as an anode area oxidation inhibitor and an auxiliary complexing agent. Further, pentasodium diethylenetriaminepentaacetate in the composite additive is used as a strong chelating agent for heavy metal impurity ions. Further, sodium citrate in the composite additive is used as a pH stabilizing agent. Further, polyvinylpyrrolidone in the composite additive is used as a suspended matter dispersing agent and a cathode surface modifier.

[0008] The principles of the present application are as follows: The present application fundamentally improves the chemical environment of the sodium tellurite electrodeposition by introducing a multifunctional composite additive with synergistic effect, and the action mechanism is as follows: Sodium ascorbate (anode area oxidation inhibitor and auxiliary complexing agent): As a mild reducing agent, it can be slightly oxidized in the strong oxidation environment on or near the anode surface, thereby consuming part of the oxygen with strong oxidizing property, and establishing a local reducing microenvironment in the anode area. This effectively inhibits the oxidation of tellurite into insoluble sodium tellurate, and fundamentally reduces the generation of anode precipitate. Meanwhile, its oxidation product dehydroascorbic acid also has a certain complexing ability, and can assist in complexing part of the impurity ions.

[0009] Pentasodium diethylenetriaminepentaacetate (strong chelating agent): This component is a high-efficiency multidentate chelating agent that is still stable under strong alkaline conditions, has eight coordination atoms, and can form a water-soluble complex with most heavy metal ions such as Pb²⁺, Cu²⁺ and Fe³⁺, with a very high stability constant. Its core function is to strongly chelate trace impurity ions in the electrolyte to form electrochemically inert soluble complexes, thereby completely preventing the co-deposition of these impurities with tellurium at the cathode, which is the key to obtaining high-purity tellurium (99.95% or more).

[0010] Sodium citrate (pH stabilizing agent): It mainly maintains the pH of the tellurium electrodeposition solution, prevents large local pH changes in the electrodeposition process, reduces the pH of the anode due to the consumption of hydroxyl ions, and increases the pH of the cathode due to the production of hydroxyl ions, thereby enhancing the use effect of other additives.

[0011] Polyvinylpyrrolidone (dispersant and surface modifier): As a non-ionic high molecular surfactant, it can adsorb on the surface of trace suspended particles (such as extremely fine tellurite crystal nuclei that are not completely inhibited or other colloidal impurities) that may be generated in the electrolyte, preventing them from aggregating and growing and depositing on the cathode through steric hindrance effect. At the same time, it can reduce the surface tension of the electrolyte, improve the wettability of the solution to the electrode, promote ion mass transfer, and make the deposition of cathode tellurium more uniform, dense, and the physical form of the product better.

[0012] The beneficial effects of the present application are as follows: Synergistic and efficient, one dose with multiple functions: The four additives are respectively aimed at the four problems of "anodic oxidation", "impurity co-deposition", "rapid pH change" and "suspension entrainment", and synergistically form a complete electrodeposition environment optimization system, which has a qualitative leap in effect compared with single additives (such as EDTA).

[0013] Significant improvement in recovery rate: By effectively inhibiting anodic side reactions, the loss of tellurium due to the formation of sodium tellurate precipitate is significantly reduced. The direct recovery rate of tellurium can be stably improved to more than 90% from about 70% in the traditional method and about 80% in the single EDTA additive method.

[0014] High product purity: Strong chelation and dispersion ensure high cleanliness of cathode deposited tellurium. After simple washing and casting, the purity of the tellurium ingot can be stably above 99.95%, with very low impurity content.

[0015] (4) Strong process stability: Reduces anodic passivation and cell voltage fluctuation, stabilizes the electrodeposition process, prolongs the cleaning period, and improves production efficiency and continuity. DETAILED DESCRIPTION

[0016] The principles and characteristics of the present application are described below in conjunction with examples, which are used to explain the present application and not to limit the scope of the present application. Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, etc. used in the following examples can be obtained from commercial channels. EMBODIMENT

[0017] S1. Configure electrolyte: Dissolve coarse tellurium dioxide in sodium hydroxide solution at 60°C for 6h, and obtain clear sodium tellurite electrolyte after filtration; the concentration of sodium hydroxide in the electrolyte is 90g / L, the total tellurium concentration is 200g / L, the Cu concentration is 0.05g / L, the Pb concentration is 0.04g / L, the Fe concentration is 0.04g / L, the Bi concentration is 0.01g / L, and the Se concentration is 0.08g / L; S2. Electrodeposition: the electrolyte obtained in step S1 is placed in an electrodeposition tank with stainless steel plates as cathode and anode to carry out electrodeposition; the composite additive is continuously added during the electrodeposition process, and the electrodeposition control parameters are: cathode current density 40 A / m2, tank voltage 15 V, electrolyte temperature 15 ℃, electrodeposition period 15 days; The composite additive is composed of sodium ascorbate, penta-sodium diethylene triamine penta-acetic acid and polyvinyl pyrrolidone, and the concentration ranges are respectively: sodium ascorbate 0.25 g / L, penta-sodium diethylene triamine penta-acetic acid 0.12 g / L, sodium citrate 0.10 g / L, and polyvinyl pyrrolidone 0.13 g / L.

[0018] S3. Post-treatment: after the electrodeposition is completed, the tellurium pieces deposited on the cathode are collected, washed with water, dried, and cast to obtain tellurium ingots. Example

[0019] S1. Preparation of electrolyte: crude tellurium dioxide is added to a sodium hydroxide solution, dissolved at 90 ℃ for 2 h, and then filtered to obtain a clear sodium tellurite electrolyte; the concentration of sodium hydroxide in the electrolyte is 110 g / L, the total tellurium concentration is 240 g / L, the Cu concentration is 0.02 g / L, the Pb concentration is 0.04 g / L, the Fe concentration is 0.05 g / L, the Bi concentration is 0.01 g / L, and the Se concentration is 0.07 g / L; S2. Electrodeposition: the electrolyte obtained in step S1 is placed in an electrodeposition tank with stainless steel plates as cathode and anode to carry out electrodeposition; the composite additive is continuously added during the electrodeposition process, and the electrodeposition control parameters are: cathode current density 60 A / m2, tank voltage 30 V, electrolyte temperature 30 ℃, electrodeposition period 14 days; The composite additive is composed of sodium ascorbate, penta-sodium diethylene triamine penta-acetic acid and polyvinyl pyrrolidone, and the concentration ranges are respectively: sodium ascorbate 0.95 g / L, penta-sodium diethylene triamine penta-acetic acid 0.48 g / L, sodium citrate 0.49 g / L, and polyvinyl pyrrolidone 0.94 g / L.

[0020] S3. Post-treatment: after the electrodeposition is completed, the tellurium pieces deposited on the cathode are collected, washed with water, dried, and cast to obtain tellurium ingots. Example

[0021] S1. Preparation of electrolyte: crude tellurium dioxide is added to a sodium hydroxide solution, dissolved at 75 ℃ for 4 h, and then filtered to obtain a clear sodium tellurite electrolyte; the concentration of sodium hydroxide in the electrolyte is 100 g / L, the total tellurium concentration is 220 g / L, the Cu concentration is 0.02 g / L, the Pb concentration is 0.03 g / L, the Fe concentration is 0.04 g / L, the Bi concentration is 0.01 g / L, and the Se concentration is 0.09 g / L; S2. Electrodeposition: the electrolyte obtained in step S1 is placed in an electrodeposition tank with stainless steel plates as cathode and anode to carry out electrodeposition; the electrodeposition process continuously adds a composite additive, and the electrodeposition control parameters are: cathode current density 50 A / m², tank voltage 25 V, electrolyte temperature 20℃, electrodeposition period 15 days; The composite additive is composed of sodium ascorbate, penta-sodium diethylene triamine penta-acetic acid and polyvinyl pyrrolidone, and the concentration ranges are respectively: sodium ascorbate 0.6 g / L, penta-sodium diethylene triamine penta-acetic acid 0.3 g / L, sodium citrate 0.28 g / L, and polyvinyl pyrrolidone 0.16 g / L.

[0022] S3. Post-treatment: after the electrodeposition is completed, the tellurium sheet deposited on the cathode is collected, washed with water, dried, and then melted and cast to obtain a tellurium ingot.

[0023] Reference Example 1, which is different from Example 1 in that no auxiliary material is added during the electrodeposition process, and other technical features are the same as those of Example 1.

[0024] Reference Example 1, which is different from Example 1 in that the additive added during the electrodeposition process is EDTA, and other technical features are the same as those of Example 1.

[0025] The detection results of the tellurium content and main impurities in the tellurium ingots obtained in Examples 1-3 and Comparative Examples 1-2 are shown in Table 1, and the direct recovery rate of tellurium is shown in Table 2.

[0026] Among them, the main impurity elements are detected according to "Tellurium Chemical Analysis Method Part 12: Determination of Bismuth, Aluminum, Lead, Iron, Selenium, Copper, Magnesium, Sodium, Arsenic Inductively Coupled Plasma Atomic Emission Spectrometry" (YS / T 227.12-2011), and the tellurium content is calculated by the impurity reduction method.

[0027] Table 1: Content of tellurium and main impurity elements in tellurium ingot Name Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Cu (wt%) 0.003 0.004 0.003 0.12 0.09 Pb (wt%) 0.002 0.003 0.002 0.10 0.08 Fe (wt%) 0.001 0.001 0.002 0.09 0.07 Bi (wt%) 0.001 0.001 0.001 0.02 0.01 Se (wt%) 0.005 0.006 0.009 0.18 0.11 Te (wt%) 99.96 99.95 99.96 99.12 99.54 Table 2: Direct recovery rate of tellurium Name Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Te (%) 92.21 91.27 90.66 73.54 82.13 As shown in Table 1, the tellurium content of Examples 1-3 is all above 99.95%, and the tellurium content of Comparative Examples 1 and 2 is all below 99.9%; in Table 2, the direct recovery rate of tellurium of Examples 1-3 is all greater than 90%, the direct recovery rate of tellurium of Comparative Example 1 is only 73.54%, and the direct recovery rate of tellurium of Comparative Example 2 is 82.13%; it is shown that the use of the present application can effectively improve the purity of tellurium, reduce the deposition of impurity elements in the electrodeposition process, and at the same time, the direct recovery rate of tellurium is significantly improved, which is improved to more than 90%.

[0028] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for extracting tellurium by electrowinning of sodium tellurite solution, characterized in that... Includes the following steps: S1. Preparation of electrolyte: Add crude tellurium dioxide to sodium hydroxide solution and dissolve at 60-90℃ for 2-6 hours. After filtration, a clear sodium tellurite electrolyte is obtained. S2. Electrowinning: Using stainless steel plates as cathode and anode, the electrolyte obtained in step S1 is placed in an electrowinning tank for electrowinning. A composite additive is continuously added during the electrowinning process. The composite additive includes sodium ascorbate, pentasodium diethylenetriaminepentaacetate, sodium citrate, and polyvinylpyrrolidone, with concentration ranges of: sodium ascorbate 0.2-1.0 g / L, pentasodium diethylenetriaminepentaacetate 0.1-0.5 g / L, sodium citrate 0.1-0.5 g / L, and polyvinylpyrrolidone 0.1-1.0 g / L, respectively. The electrowinning control parameters are: cathode current density 40-60 A / m², tank voltage 15-30 V, electrolyte temperature 15-30 °C, and electrowinning cycle 14-15 days. S3. Post-processing: After electrodeposition, the tellurium sheets deposited at the cathode are collected, washed with water, dried, and then cast to obtain tellurium ingots.

2. The method for extracting tellurium by electrowinning of sodium tellurite solution according to claim 1, characterized in that... In the electrolyte described in step 1, the sodium hydroxide concentration is 90-110 g / L, the total tellurium concentration is 200-240 g / L, and the concentrations are Cu≤0.05 g / L, Pb≤0.05 g / L, Fe≤0.05 g / L, Bi≤0.01 g / L, and Se≤0.1 g / L.

3. The method for extracting tellurium by electrowinning of sodium tellurite solution according to claim 1 or 2, characterized in that... The composite additive is continuously and uniformly added to the electrolyte during the electrowinning process via a metering pump.

4. A method for extracting tellurium by electrowinning of sodium tellurite solution according to claim 1 or 2, characterized in that, The crude tellurium dioxide mentioned in step S1 is an intermediate product of tellurium smelting. After being processed by the method, the impurity content in the obtained tellurium ingot meets the following requirements: Cu≤0.005%, Pb≤0.005%, Fe≤0.003%, Bi≤0.001%, Se≤0.01%.

5. A method for extracting tellurium by electrowinning of sodium tellurite solution according to claim 1 or 2, characterized in that... Sodium ascorbate in the composite additive serves as an anodic oxidation inhibitor and an auxiliary complexing agent.

6. A method for extracting tellurium by electrowinning of sodium tellurite solution according to claim 1 or 2, characterized in that... In the composite additive, diethylenetriaminepentaacetic acid pentasodium acts as a powerful chelating agent for heavy metal impurity ions.

7. A method for extracting tellurium by electrowinning of sodium tellurite solution according to claim 1 or 2, characterized in that... Sodium citrate in the composite additive serves as a pH stabilizer.

8. A method for extracting tellurium by electrowinning of sodium tellurite solution according to claim 1 or 2, characterized in that... In the composite additive, polyvinylpyrrolidone serves as a suspending agent and a cathode surface modifier.