Method for recycling waste low-melting-point alloy through low-temperature molten salt electrolysis and application

Abstract

The invention relates to a method for recycling waste low-melting-point alloy through low-temperature molten salt electrolysis and application, belongs to the technical field of secondary resource recycling and electrochemical metallurgy, and solves the problems of high energy consumption, low metal product purity and serious secondary pollution caused by lengthy flow and poor metal separation selectivity in the existing pyrogenic process or wet process. The method comprises the steps that under the protective atmosphere, molten salt electrolyte is contained in an electrolytic bath provided with physical partitions, waste low-melting-point alloy containing potential difference metal is placed in an anode area to serve as an anode, and pure metal to be recycled is placed in a cathode area to serve as a cathode. According to the method, the current efficiency is high, the process is short, two metal products with the purity not lower than 99% are obtained in the single electrolysis step, the process is green, energy consumption is low, and the method is suitable for industrial production. And the method is suitable for resource utilization of the waste low-melting-point alloy of various systems.

Description

Technical Field

[0001] This invention relates to the fields of secondary resource recycling and electrochemical metallurgy, and in particular to a method and application for the low-temperature molten salt electrolysis recycling of waste low-melting-point alloys. Background Technology

[0002] Low-melting-point metals and their alloys (such as Sn-Bi, Pb-Bi, Ga-In, etc.), represented by tin (Sn), bismuth (Bi), indium (In), gallium (Ga), and lead (Pb), constitute key material systems in fields such as electronics and information, advanced manufacturing, and clean energy. They are widely used in electronic interconnects and packaging, thermistors and flexible devices, aerospace, and nuclear engineering. Bismuth, due to its low toxicity and unique electronic structure, is considered a "green metal" and shows broad application prospects in quantum devices, thermoelectric materials, and nuclear energy. Tin plays an irreplaceable role in electronic welding and photovoltaics. Indium and gallium, among others, undertake core functions in semiconductors, microelectronics, and functional devices. In recent years, ensuring a stable supply of these key metals has become a core guarantee for promoting the upgrading of high-end manufacturing and energy transformation.

[0003] However, the mining and smelting of primary minerals are facing multiple pressures, including declining resource grades, rising energy consumption, and increasingly stringent environmental constraints. Relying solely on primary resources is no longer sufficient to meet sustainable needs. To ensure supply chain security and resource recycling, the efficient utilization of secondary resources has become an inevitable path. Among these, waste low-melting-point alloys, with their high metal content and considerable reserves, are important "urban minerals." However, these alloys tend to form stable solid solutions or eutectic structures during service and solidification, and their components have similar chemical properties, limiting the efficiency of traditional physical separation. Chemical separation also suffers from insufficient selectivity, making it difficult to achieve high purity and high recovery rates.

[0004] The existing recycling processes mostly follow the pyrometallurgical or hydrometallurgical routes, and their limitations are mainly reflected in three aspects: (1) Lengthy process: Most technologies require multiple pretreatment, smelting, refining, purification and other processes, with many unit operations, high energy consumption and high cost. For example, the tin-bismuth waste recycling method reported by CN108085499A requires multiple operations such as drying, crushing, vacuum carbothermal reduction, stepwise heating and melting and vacuum sublimation, with temperatures as high as 900℃; the wet separation process reported by CN102304621A requires six processes such as roasting at 600℃, fine crushing and two-stage acid leaching, with large acid and alkali consumption and a large amount of salt and acid wastewater generated. (2) Poor separation selectivity: Pyrometallurgical treatment is prone to generating new alloy phases or dust loss, making it difficult to balance recovery rate and purity; wet methods mostly rely on strong acids, strong bases or strong oxidants for non-selective leaching, with large reagent consumption and subsequent separation difficulties. The high-tin crude bismuth refining described in patent CN102796887A relies on multi-step chemical refining and strong oxidizing / strong alkaline reagents, which is complex and generates harmful waste residue; (3) serious secondary pollution: the pyrometallurgical process is prone to generating harmful flue gas and waste residue, and the wet process inevitably generates high-salt and high-acid wastewater, which has high subsequent treatment costs and a heavy environmental burden.

[0005] In summary, existing technologies are generally constrained by drawbacks such as lengthy processes, insufficient selectivity, high energy consumption, and significant secondary pollution, making it difficult to support the industrial demands for efficient, green, and universally applicable recycling. Therefore, there is an urgent need to develop short-process, environmentally friendly separation technologies driven by selectivity. Summary of the Invention

[0006] In view of the above analysis, the present invention aims to provide a method and application for low-temperature molten salt electrolysis recycling of waste low-melting-point alloys, in order to solve at least one of the following technical problems: (1) the lack of selectivity in the existing low-melting-point alloy waste recycling technology leads to low purity of the recycled metal; (2) the existing process has high energy consumption, long process and serious secondary pollution.

[0007] The first aspect of this invention provides a method for recycling waste low-melting-point alloys by low-temperature molten salt electrolysis, comprising the following steps:

[0008] S1. In the presence of a protective gas, molten salt electrolyte is contained in an electrolytic cell. The electrolytic cell is provided with an anode area and a cathode area formed by physical separation. Waste low-melting-point alloy is placed in the anode area as the anode; and initial cathode metal is placed in the cathode area as the cathode. The waste low-melting-point alloy includes metals with low oxidation potential and metals with high oxidation potential. S2. Heat the electrolytic cell to the electrolysis temperature so that the molten salt electrolyte, the waste low-melting-point alloy and the initial cathode metal are all in a liquid state; S3. At the above-mentioned electrolysis temperature, a direct current is applied between the anode and the cathode to carry out an electrolysis reaction, thereby recovering low oxidation potential metals and high oxidation potential metals respectively.

[0009] Furthermore, the potential difference between the low oxidation potential metal and the high oxidation potential metal is ≥0.1V.

[0010] Furthermore, the waste low-melting-point alloy is selected from one of tin-based alloys, lead-based alloys, bismuth-based alloys, indium-based alloys, or gallium-based alloys.

[0011] Furthermore, the waste low-melting-point alloy is selected from Sn-Bi, In-Sn, Ga-In, Pb-Bi, In-Bi, Ga-Bi, In-Pb, Ga-Pb, and Ga-Sn.

[0012] Furthermore, the molten salt electrolyte comprises a base molten salt and an additive salt.

[0013] Furthermore, the matrix molten salt is selected from one or more of calcium chloride, aluminum chloride, sodium chloride, potassium chloride, lithium chloride, cesium chloride, gallium chloride, indium chloride, indium chloride, and zinc chloride.

[0014] Furthermore, the additive salt is a chloride salt corresponding to the metal with a lower oxidation potential in the anode.

[0015] Furthermore, based on the total mass of the molten salt electrolyte, the content of the additive salt is 2-15 wt%.

[0016] Furthermore, the electrolysis temperature is T1, and the highest melting point among the molten salt electrolyte, the waste low-melting-point alloy, and the initial cathode metal is T. max Then T1 is more than T max Temperatures can range from 20 to 80°C.

[0017] Furthermore, the conditions for the electrolysis reaction include: an electrolysis temperature of 80-500℃, and during the electrolysis process, the cathode current density and the anode current density are each independently 0.05-2 A / cm². 2 between.

[0018] Furthermore, the ratio of cathode current density to anode current density is 1-2:1.

[0019] The second aspect of this invention provides an application of the method described in the first aspect for separating and recovering valuable metals from waste low-melting-point alloys.

[0020] This invention can achieve at least one of the following beneficial effects: 1. This invention employs a low-temperature molten salt system and a fully liquid electrode scheme. It utilizes the potential difference between metals to drive electrolytic separation. Simultaneously, the liquid anode and liquid cathode are immiscible in the molten salt, forming a stable liquid / liquid interface. This not only facilitates the directional migration and redox of target metal ions but also effectively suppresses the dendrite growth problem common in solid electrodes, reduces the risk of short circuits, and minimizes inclusions of molten salt in the product. While ensuring high current efficiency, it achieves highly selective separation of two valuable metals in a single electrolysis step, simultaneously obtaining two metal products with a purity of not less than 99% at both the cathode and anode. This results in high resource utilization. Compared to traditional pyrometallurgical high-temperature smelting, this low-temperature operating condition significantly reduces energy consumption and effectively suppresses the volatilization loss and oxidation of low-melting-point metals.

[0021] 2. This invention uses a fully liquid electrolysis system to replace the complex pretreatment, leaching, purification, and electrolytic refining processes in traditional pyrometallurgical or hydrometallurgical processes. The process is significantly shortened, the operation is simple, and it is easy to achieve continuous and large-scale production. It takes into account both energy efficiency and metal purity. At the same time, the entire process of this invention is carried out in a closed molten salt system, without the need for corrosive hydrometallurgical reagents such as strong acids and strong alkalis. This avoids the generation of wastewater, waste residue and harmful gases from the source, making it a green and clean recycling technology.

[0022] 3. The method of this invention is applicable to various systems of waste low-melting-point alloys (such as Sn-based, Pb-based, Bi-based, etc.) and has strong tolerance for fluctuations in alloy composition. Furthermore, key parameters such as molten salt composition, electrolysis temperature, and current density have a wide and flexible optimization space, providing a universally applicable solution for the recycling of various low-melting-point alloys. This ensures stable separation results and product purity under different raw material conditions, improving the reliability of the technology for industrial applications.

[0023] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0024] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0025] Figure 1 The images show the XRD patterns of the waste tin-bismuth alloy, anode product, and cathode product from Example 1.

[0026] Figure 2 The images show the XRD patterns of the waste lead-bismuth alloy, anode product, and cathode product in Example 3. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, exemplary embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. For clarity and brevity, not all features of actual embodiments are described in the specification.

[0028] Existing technologies typically utilize pyrometallurgical or hydrometallurgical methods to recover metals from waste low-melting-point alloys. However, these methods require multiple pretreatment steps, resulting in high energy consumption and costs, or are complex processes that generate harmful waste residues, making it difficult to balance recovery rates and purity. To overcome these technical shortcomings, the first aspect of this invention provides a method for recovering waste low-melting-point alloys via low-temperature molten salt electrolysis, characterized by comprising the following steps: S1. In the presence of a protective gas, molten salt electrolyte is contained in an electrolytic cell. The electrolytic cell is provided with an anode area and a cathode area formed by physical separation. Waste low-melting-point alloy is placed in the anode area as the anode; and initial cathode metal is placed in the cathode area as the cathode. The waste low-melting-point alloy includes metals with low oxidation potential and metals with high oxidation potential. S2. Heat the electrolytic cell to the electrolysis temperature so that the molten salt electrolyte, the waste low-melting-point alloy and the initial cathode metal are all in a liquid state; S3. At the above-mentioned electrolysis temperature, a direct current is applied between the anode and the cathode to carry out an electrolysis reaction, thereby recovering low oxidation potential metals and high oxidation potential metals respectively.

[0029] In this invention, electrolysis is performed using a significant potential difference between the metals. The electrolysis temperature is controlled so that the waste low-melting-point alloy melts to serve as a liquid anode, and the initial cathode metal melts to serve as a liquid cathode. At the same time, the two are immiscible in the liquid molten salt electrolyte, forming a stable interface, which is conducive to the directional migration and reduction of target metal ions. While ensuring high current efficiency, metal dispersion and inclusions are significantly reduced. This achieves highly selective separation of two valuable metals in a single electrolysis step, and two metal products with a purity of not less than 99% are obtained simultaneously at the cathode and anode. The resource utilization rate is high. Compared with traditional pyrometallurgical high-temperature smelting, this low-temperature condition greatly reduces energy consumption, while effectively suppressing the volatilization loss and oxidation of low-melting-point metals (such as indium, gallium, tin, etc.).

[0030] In this invention, physical separation can be achieved by setting up physical barriers or utilizing density differences combined with the tank structure. For example, porous ceramic separators (such as those made of alumina, boron nitride, or mullite) or electrolytic cells with specific vertical separation structures (such as H-type electrolytic cells or partitioned crucibles) can be used. These separation methods allow ions in the molten salt electrolyte to pass freely to form a current loop, while effectively preventing direct contact and mixing between the anode melt and the cathode melt, thereby maintaining the physical independence of the anode and cathode regions and ensuring the selective migration of the target metal and the high-purity separation of the products during electrolysis.

[0031] In this invention, the protective gas can be nitrogen or argon.

[0032] In this invention, it should be noted that the low oxidation potential metal in the waste low melting point alloy is the same as the initial cathode metal.

[0033] In this invention, it should be noted that "low oxidation potential metal and high oxidation potential metal" refers to the comparison of the equilibrium potentials of two metals relative to the same reference electrode at the molten salt electrolyte and electrolysis temperature.

[0034] In this invention, the content of low oxidation potential metal in the waste low melting point alloy is 1%-50wt%.

[0035] It should be noted that the core working principle of the all-liquid molten salt electrolysis system constructed in this invention lies in the fact that the waste low-melting-point alloy (anode), the initial cathode metal (cathode), and the molten salt electrolyte are all in the liquid phase. The activity of the liquid metal varies with the composition of the anode alloy, unlike the approximately constant (≈1) activity characteristic of solid metal electrodes. During electrolysis, the activity difference between the target metal and the coexisting metal at the two electrodes can widen the effective separation potential window between them, thereby providing more favorable thermodynamic conditions; at the same time, the liquid system has high interfacial renewability and a large mass transfer coefficient, which can reduce polarization and improve current efficiency. Thus, thermodynamic and kinetic enhancements work synergistically, enabling the system to achieve high selectivity and deep separation of the two metals at relatively low temperatures (below 500℃).

[0036] According to some embodiments of the present invention, the waste low-melting-point alloy is selected from one of tin-based alloys, lead-based alloys, bismuth-based alloys, indium-based alloys, or gallium-based alloys.

[0037] Furthermore, in the waste low-melting-point alloy, the low-oxidation-potential metal and the high-oxidation-potential metal can form the following alloys: Sn-Bi, In-Sn, Ga-In, Pb-Bi, In-Bi, Ga-Bi, In-Pb, Ga-Pb, and Ga-Sn.

[0038] In this invention, the above alloy combination can ensure that the potential difference between the two metals is ≥0.1V, thereby selectively separating the two metals and ensuring the purity of the two metals.

[0039] According to some embodiments of the present invention, in the waste low-melting-point alloy, the potential difference between the two metals can be 0.1V, 0.2V, 0.3V, 0.5V, 0.8V, 1V, 1.2V, or 1.5V. In the present invention, if the potential difference between the two metals is <0.1V, their oxidation potentials are too close, resulting in a narrow thermodynamic separation window during electrolysis. This makes it difficult to drive the high-selectivity dissolution and deposition of a single metal. At the anode, the low-oxidation-potential metal and the high-oxidation-potential metal compete for oxidation and simultaneously enter the molten salt in ionic form. At the cathode, the various metal ions mixed in the molten salt compete for reduction, resulting in the cathode deposit being an alloy rather than a pure metal. This leads to a decrease in the purity of the cathode product and a complex composition of the anode enrichment, making it impossible to achieve efficient and highly selective separation and ensuring purity.

[0040] According to some embodiments of the present invention, the molten salt electrolyte comprises a base molten salt and an additive salt.

[0041] In this invention, the matrix molten salt is selected from one or more of calcium chloride, aluminum chloride, sodium chloride, potassium chloride, lithium chloride, cesium chloride, gallium chloride, indium chloride, and indium chloride.

[0042] In this invention, the aforementioned matrix molten salts can be compounded to form a low-melting-point eutectic system (such as LiCl-KCl eutectic point of about 352°C), which significantly reduces the electrolysis operating temperature and meets the requirements for low-temperature energy saving. Furthermore, they have high ionic conductivity in the molten state, which is beneficial for reducing ohmic polarization and improving current efficiency. At the same time, these molten salts have good dissolution and transport capabilities for target metal chlorides (such as SnCl2, InCl, etc.), ensuring the efficient migration of target metal ions in the molten salt. Moreover, they are immiscible with the liquid metal electrode and can maintain a clear phase interface.

[0043] According to a particularly preferred embodiment of the present invention, in order to achieve more efficient and stable ion conduction and metal separation in a fully liquid system, the matrix molten salt is selected from one or more of the following chloride systems and their composition range is preferably: The LiCl-KCl system has a molar ratio of LiCl to KCl of (0.4-1.5):1, for example, about 0.58:0.42.

[0044] The LiCl-KCl-AlCl3 system has a molar ratio of LiCl, KCl and AlCl3 ranging from (15-30):(25-45):(20-50).

[0045] Ternary systems containing alkaline earth metals: such as the LiCl-CaCl2-AlCl3 system, where the molar ratios of LiCl, CaCl2 and AlCl3 range from (20-30):(30-35):(50-60).

[0046] Indium-containing ternary chloride systems include LiCl-ZnCl2-InCl or KCl-ZnCl2-InCl, wherein the molar ratio of InCl to ZnCl2 is (0.5-1.2):1.

[0047] The molar ratio of alkali metal chloride (LiCl or KCl) to ZnCl2 is (0.5-0.8):1.

[0048] Gallium-containing chloride systems can be ternary systems such as LiCl-GaCl3-AlCl3, or quaternary systems such as LiCl-KCl-AlCl3-GaCl3, wherein the molar fraction of GaCl3 accounts for 10-25% of the total chloride.

[0049] The ZnCl2-InCl binary system has a molar ratio of ZnCl2 to InCl of (1.2-2.0):1, for example, 60:40.

[0050] According to some embodiments of the present invention, in order to maintain a suitable concentration of the target metal ions in the molten salt, reduce their migration activation energy and stabilize the electrolysis process, the additive salt is a chloride salt corresponding to the metal with a lower oxidation potential in the anode, such as SnCl2, PbCl2, or GaCl3.

[0051] According to some embodiments of the present invention, the content of the additive salt is 2-15 wt%, based on the total mass of the molten salt electrolyte. If the content is less than 2 wt%, the basic concentration of the target metal ions in the molten salt is insufficient, making it difficult to effectively overcome the concentration polarization during the anodic dissolution process, resulting in weak ion migration driving force and decreased current efficiency; while when the content is higher than 15 wt%, the excessive additive salt will significantly change the physicochemical properties of the matrix molten salt, and induce cathode dendrite growth or side reactions due to excessively high ion activity, while also increasing the raw material cost.

[0052] For example, the content of the additive salt can be 2wt%, 3wt%, 4wt%, 4.5wt%, 4.8wt%, 5wt%, 8wt%, 8.35wt%, 10wt%, 11wt%, or 15wt%.

[0053] According to some embodiments of the present invention, the electrolysis temperature is T1, and the highest melting point among the molten salt electrolyte, the waste low-melting-point alloy, and the initial cathode metal is T. max Then T1 is more than T max Temperatures can range from 20 to 80°C.

[0054] In this invention, T1 is more than T max A temperature of 20-50℃ can keep the molten salt electrolyte, anode alloy and cathode metal in a liquid state, ensuring that the electrolysis system is a completely liquid system and that the anode melt and cathode melt are immiscible in the molten salt. This achieves synergistic optimization of thermodynamics and kinetics, ensuring efficient and highly selective metal separation and recovery.

[0055] In this invention, it should be noted that T1 is more than T max Maintaining a temperature of 20-80℃ ensures that all components are completely melted into a liquid phase. This forms a conductive, mass-transferable liquid electrolyte and electrode, effectively preventing the anode alloy melt and cathode metal melt from miscibly dissolving or emulsifying in the molten salt due to overheating, thus maintaining a clear liquid-liquid interface. Below 20℃, the molten salt viscosity is high, which is detrimental to ion diffusion and mass transfer, and affects current efficiency. Local temperature fluctuations may also prevent the higher-melting-point components in the molten salt electrolyte, waste low-melting-point alloy, and initial cathode metal from completely melting, preventing the formation of the necessary fully liquid environment. This leads to instability at the electrode / electrolyte interface, uneven mass transfer, and severely reduced metal separation selectivity and current efficiency. Above 80℃, firstly, energy consumption increases significantly and unnecessarily; secondly, it exacerbates the volatilization loss of low-melting-point metal molten salt; and thirdly, it causes a small amount of dissolution of the originally thermodynamically immiscible anode and cathode melts in the molten salt, resulting in cross-contamination of products and a decrease in purity.

[0056] For example, T 1 to T max Temperatures are 20℃, 25℃, 30℃, 35℃, 40℃, 50℃, 60℃, 70℃, and 80℃ higher.

[0057] According to the present invention, the conditions for the electrolysis reaction include an electrolysis temperature of 100-500°C.

[0058] In this invention, the electrolysis temperature meets the aforementioned range, which matches the eutectic point characteristics of the selected chloride-based molten salt. This ensures the molten salt maintains excellent ionic conductivity and fluidity, providing a stable medium environment for all-liquid electrolysis. Secondly, this temperature range is significantly lower than traditional pyrometallurgical processes, greatly reducing heat consumption and demonstrating energy-saving advantages. More importantly, the aforementioned temperature effectively avoids the volatilization loss of low-melting-point metals and molten salt components (such as AlCl3), thereby ensuring metal recovery rate and the stability of the electrolysis system. Simultaneously, the lower temperature also helps reduce the corrosive requirements on equipment materials, extending equipment life and improving the economy and safety of the process. Therefore, controlling the electrolysis temperature within 100-500℃ is fundamental to achieving the low-temperature, green, and efficient recovery goals of this invention.

[0059] For example, the electrolysis temperature can be 100°C, 180°C, 350°C, 450°C, or 500°C.

[0060] In this invention, the melting points of the molten salt electrolyte, the waste low-melting-point alloy, and the initial cathode metal are all lower than the electrolysis temperature. For example, the melting point of the molten salt electrolyte can be 89°C, 147°C, 175°C, 245°C, 352°C, or 428°C. The melting point of the waste low-melting-point alloy can be 15.7°C, 72°C, 123°C, 138°C, 295°C, or 378°C. The melting point of the initial cathode metal can be 29.7°C, 156.5°C, 231°C, 320°C, or 327°C.

[0061] In this invention, electrolysis is performed by applying direct current between the anode and cathode at the specified electrolysis temperature. During electrolysis, metals with lower oxidation potentials in the anolyte are selectively oxidized into ions that enter the molten salt and migrate to the liquid cathode for electrochemical reduction and deposition; while metals with higher oxidation potentials remain in the anolyte due to their higher thermodynamic stability. Through this process, high-purity metals to be dissolved are ultimately obtained at the cathode, and metals with higher oxidation potentials are enriched at the anode, thereby achieving the separation and purification of the two metals.

[0062] According to some embodiments of the present invention, during electrolysis, the cathode current density and the anode current density are each independently 0.05-2 A / cm². 2 .

[0063] In this invention, the current density meets the aforementioned range, ensuring sufficient electrochemical driving force to maintain efficient mass transfer and a reasonable production rate while preventing excessive concentration polarization or impurity co-oxidation / reduction due to excessive current, thereby guaranteeing high purity and high selectivity of the metal product. The combination of the aforementioned electrolysis temperature and current density with the all-liquid system fully utilizes the renewable nature of the liquid electrode surface, achieving energy-saving, stable, and controllable electrolytic separation while maintaining high current efficiency.

[0064] According to some preferred embodiments of the present invention, the ratio of cathode current density to anode current density is 1-2:1.

[0065] In this invention, by controlling the cathode current density to be slightly higher than the anode current density (a ratio of 1-2), the driving force for the directional migration of target metal ions from the anode to the cathode can be enhanced, thus broadening the effective separation potential window from a thermodynamic and kinetic perspective. This ensures the full reduction and deposition of metals with low oxidation potentials at the cathode, while suppressing the competitive oxidation and reduction of metal ions or impurities with high oxidation potentials, thereby significantly improving the selectivity of metal separation and ensuring the purity of the target product.

[0066] For example, the ratio of the cathode current density to the anode current density is 1, 1.25, 1.43, 1.5, 1.67, 1.8, or 2, preferably 1.25-1.67.

[0067] The following examples and comparative examples further illustrate the method for recycling waste low-melting-point alloys by low-temperature molten salt electrolysis according to the present invention.

[0068] The purity of the metal was measured by ICP-OES, and the current efficiency refers to the cathode current efficiency, which was calculated by the ratio of cathode product mass to charge.

[0069] Example 1 S1. Under argon protection, an electrolytic cell is filled with a molten salt electrolyte with a melting point of 352°C (containing 495g of LiCl-KCl (molar ratio 0.58:0.42) eutectic molten salt and 55g of SnCl2), wherein SnCl2 accounts for 10wt% of the total mass of the molten salt electrolyte. The electrolytic cell is equipped with an anode area and a cathode area physically separated by a porous alumina ceramic partition. 200g of waste tin-bismuth alloy (tin content 42wt%) is added to the anode area as the anode, with a melting point of 138°C and a tin-bismuth potential difference of 0.35V. 20g of high-purity tin ingot (purity ≥99.9%) is added to the cathode area as the cathode, with a melting point of 232°C. S2. Heat the electrolytic cell to 420℃ and keep it at 420℃ for 2 hours to form a fully liquid electrolytic system; S3. Apply a direct current between the anode and cathode to carry out an electrolysis reaction, wherein the cathode current density is 0.5 A / cm². 2 Anode current density 0.35 A / cm 2 The ratio of cathode current density to anode current density is 1.43. After electrolysis, the cathode obtains metallic tin with a purity of 99.99%, the anode region is enriched with bismuth with a purity of 99.97%, and the current efficiency is 94.8%.

[0070] Figure 1 This is a comparison of XRD patterns of waste tin-bismuth alloy (Sn-Bi) processed in Example 1 of this invention. The raw material spectrum shows the simultaneous presence of diffraction peaks for both Sn and Bi, indicating their coexistence. After electrolysis, the cathode product exhibits only sharp characteristic peaks of Sn, while the anode product exhibits only characteristic peaks of Bi, with no other obvious characteristic peaks. This directly confirms that the method of this invention can achieve high selectivity and deep separation of Sn and Bi, directly obtaining tin metal with a purity of 99.99%.

[0071] Example 2 S1. Under argon protection, an electrolytic cell is filled with molten salt electrolyte (containing 550g of LiCl-KCl-AlCl3 (molar ratio of 28:42:30) and 50.1g of SnCl2) with a melting point of 297℃, wherein SnCl2 accounts for 8.35% of the total mass of the molten salt electrolyte. The electrolytic cell is equipped with an anode area and a cathode area physically separated by a porous alumina ceramic partition. 65.4g of waste tin-bismuth alloy (tin content of 5wt%) is added as the anode in the anode area, with a melting point of 258℃ and a tin-bismuth potential difference of 0.35V. 10.2g of high-purity tin ingot (purity ≥99.9%) is added as the cathode in the cathode area, with a melting point of 232℃. S2. Heat the electrolytic cell to 350℃ and keep it at that temperature for 2 hours to form a fully liquid electrolytic system; S3. Apply a direct current between the anode and cathode to carry out an electrolysis reaction, wherein the cathode current density is 0.5 A / cm². 2 Anode current density 0.4 A / cm 2 The ratio of cathode current density to anode current density is 1.25. After electrolysis, the purity of tin at the cathode is 99.95%, the purity of bismuth at the anode is 99.92%, and the current efficiency is 93.2%.

[0072] Example 3 S1. Under nitrogen protection, an electrolytic cell is filled with a molten salt electrolyte with a melting point of 334℃ (containing 600g of a mixed salt of LiCl-CaCl2-AlCl3 (molar ratio 25:31:54) and 60g of PbCl2), wherein PbCl2 accounts for 9.1% of the total mass of the molten salt electrolyte. The electrolytic cell is equipped with a partitioned crucible, physically separating an anode area and a cathode area. In the anode area, 125.1g of waste lead-bismuth alloy (lead content of 35wt%) is added as the anode, with a melting point of 145℃ and a lead-bismuth potential difference of 0.43V. In the cathode area, 12.5g of pure lead (purity ≥99.9%) is added as the cathode, with a melting point of 327.5℃. S2. Heat the electrolytic cell to 400℃ and keep it at that temperature for 2 hours to form a fully liquid electrolytic system; S3. Apply direct current between the anode and cathode to carry out an electrolysis reaction, wherein the cathode current density is 1 A / cm². 2 Anode current density 0.8 A / cm 2 The ratio of cathode current density to anode current density is 1.25. After electrolysis, the purity of lead at the cathode is 99.97%, the purity of bismuth at the anode is 99.93%, and the current efficiency is 97.2%.

[0073] Figure 2This is a comparison of XRD patterns of waste lead-bismuth alloy (Pb-Bi) processed in Example 3 of the present invention. In the original alloy, diffraction peaks of Pb and Bi coexist; after electrolysis, the cathode product shows only the characteristic peaks of Pb, and the anolyte product shows only the characteristic peaks of Bi. This result further demonstrates that the method of the present invention is universally applicable to different low-melting-point alloy systems (such as Pb-Bi), and can achieve efficient separation and high-purity recovery of the two metals in a single electrolysis step.

[0074] Example 4 S1. Under argon protection, an electrolytic cell is filled with a molten salt electrolyte with a melting point of 239°C (containing 500.4g of a mixed salt of LiCl-ZnCl2-InCl (molar ratio of 25:40:35)). The electrolytic cell is equipped with an anode zone and a cathode zone physically separated by a porous alumina ceramic partition. In the anode zone, 50.3g of waste indium-tin alloy (tin content of 60wt%) is added as the anode, with a melting point of 152°C and an indium-tin potential difference of 0.18V. In the cathode zone, 10.2g of pure indium (purity ≥99.9%) is added as the cathode, with a melting point of 156°C. S2. Heat the electrolytic cell to 260℃ and keep it at that temperature for 2 hours to form a fully liquid electrolytic system; S3. Apply a direct current between the anode and cathode to carry out an electrolysis reaction, wherein the cathode current density is 0.5 A / cm². 2 Anode current density 0.3 A / cm 2 The ratio of cathode current density to anode current density is 1.67. After electrolysis, the cathode yields metallic indium with a purity of 99.95%, the anode yields tin with a purity of 99.98%, and the current efficiency is 92.6%.

[0075] Example 5 S1. Under argon protection, an electrolytic cell is filled with molten salt electrolyte (containing 450.3g of KCl-ZnCl2-InCl (molar ratio 25:40:35), melting point 196.7℃). The electrolytic cell is equipped with an anode area and a cathode area physically separated by a porous alumina ceramic partition. In the anode area, 39.9g of waste indium-bismuth alloy (indium content 38wt%) is added as the anode, with a melting point of 149.2℃ and an indium-bismuth potential difference of 0.62V. In the cathode area, 15.2g of pure indium (purity ≥99.9%) is added as the cathode, with a melting point of 156.6℃. S2. Heat the electrolytic cell to 250℃ and keep it at that temperature for 2 hours to form a fully liquid electrolytic system; S3. Apply a direct current between the anode and cathode to carry out an electrolysis reaction, wherein the cathode current density is 0.8 A / cm². 2 Anode current density 0.5 A / cm 2The ratio of cathode current density to anode current density is 1.6. After electrolysis, the cathode obtains metallic indium with a purity of 99.95%, the anode region has a bismuth purity of 99.90%, and the current efficiency is 90.2%.

[0076] Example 6 S1. Under argon protection, an electrolytic cell is filled with molten salt electrolyte (containing 400g of LiCl-KCl-AlCl3-GaCl3 (molar ratio 38:24:23:15), melting point 236.4℃). The electrolytic cell is equipped with an anode area and a cathode area physically separated by a porous alumina ceramic partition. In the anode area, 45g of waste gallium-bismuth alloy (gallium content 21wt%) is added as the anode, with a melting point of 225.6℃ and a gallium-bismuth potential difference of 0.55V. In the cathode area, 10g of pure gallium (purity ≥99.9%) is added as the cathode, with a melting point of 29.8℃. S2. Heat the electrolytic cell to 310℃ and keep it at that temperature for 2 hours to form a fully liquid electrolytic system; S3. Apply a direct current between the anode and cathode to carry out an electrolysis reaction, wherein the cathode current density is 0.5 A / cm². 2 Anode current density 0.5 A / cm 2 The ratio of cathode current density to anode current density is 1. After electrolysis, the cathode yields gallium with a purity of 99.97%, the anode region has a bismuth purity of 99.92%, and the current efficiency is 91.3%.

[0077] Example 7 S1. Under argon protection, an electrolytic cell is filled with molten salt electrolyte (containing 400g of ZnCl2-InCl (molar ratio 60:40), melting point 172.6℃). The electrolytic cell is equipped with an anode area and a cathode area physically separated by a porous alumina ceramic partition. 75g of waste lead-indium alloy (indium content 30wt%) is added to the anode area as the anode, with a melting point of 233.6℃ and a lead-indium potential difference of 0.19V. 10g of pure indium (purity ≥99.9%) is added to the cathode area as the cathode, with a melting point of 156.6℃. S2. Heat the electrolytic cell to 300℃ and keep it at that temperature for 2 hours to form a fully liquid electrolytic system; S3. Apply a direct current between the anode and cathode to carry out an electrolysis reaction, wherein the cathode current density is 0.5 A / cm². 2 Anode current density 0.5 A / cm 2 The ratio of cathode current density to anode current density is 1. After electrolysis, the cathode obtains metallic indium with a purity of 99.91%, the lead purity in the anode region reaches 99.8%, and the current efficiency is 89.5%.

[0078] Example 8 S1. Under argon protection, an electrolytic cell is filled with molten salt electrolyte (containing 400g of LiCl-GaCl3-AlCl3 (molar ratio 35:20:45), melting point 143.5℃). The electrolytic cell is equipped with an anode area and a cathode area physically separated by a porous alumina ceramic partition. In the anode area, 101g of waste gallium-tin alloy (Ga 22wt%) is added as the anode, with a melting point of 57℃ and a gallium-tin potential difference of 0.13V. In the cathode area, 15g of pure gallium (purity ≥99.9%) is added as the cathode, with a melting point of 29.8℃. S2. Heat the electrolytic cell to 180°C and keep it at that temperature for 2 hours to form a fully liquid electrolytic system; S3. Apply a direct current between the anode and cathode to carry out an electrolytic reaction, wherein the cathode current density is 0.4 A / cm². 2 Anode current density 0.4 A / cm 2 The ratio of cathode current density to anode current density is 1. After electrolysis, the cathode yields gallium with a purity of 99.93%, the anode region has a tin purity of 99.6%, and the current efficiency is 92.6%.

[0079] Comparative Example 1 S1. Under argon protection, an electrolytic cell is filled with a molten salt electrolyte with a melting point of 352°C (containing 472.5g of LiCl-KCl (molar ratio 0.58:0.42) eutectic molten salt and 54.6g of SnCl2), wherein SnCl2 accounts for approximately 10wt% of the total mass of the molten salt electrolyte. The electrolytic cell is equipped with an anode zone and a cathode zone physically separated by a porous alumina ceramic partition. In the anode zone, 200g of waste tin-bismuth alloy (tin content 42wt%) is added as the anode, with a melting point of 138°C and a tin-bismuth potential difference of 0.35V. In the cathode zone, a graphite rod is directly used as the cathode. S2. Heat the electrolytic cell to 420℃ and keep it at 420℃ for 2 hours to form a fully liquid electrolytic system; S3. Apply a direct current between the anode and cathode to carry out an electrolysis reaction, wherein the cathode current density is 0.5 A / cm². 2 Anode current density 0.35 A / cm 2 After electrolysis, the cathode yielded metallic tin with a purity of 91.38%, the anode region enriched with bismuth with a purity of 94.46%, and the current efficiency was 81.7%.

[0080] Comparative Example 2 S1. Electrolysis was carried out at 40 °C using a mixed solution containing 10 g / L SnCl2 and 3 mol / L HCl as the electrolyte, waste tin-bismuth alloy (42 wt% tin content) as the anode plate, and tin sheet as the cathode, with the current density controlled at 0.35 A / cm².2 Electrolysis is carried out.

[0081] S3. After electrolysis begins, hydrogen gas is emitted from the cathode, and the cathode deposit is a grayish-black spongy substance. After 36 hours of reaction, anode mud is formed at the bottom of the anode in the electrolytic cell. After drying and weighing, the anode mud ratio (the ratio of dry anode mud weight to the anode electrolytic weight loss) is 58.1%. Chemical analysis shows that it contains 67.9% bismuth and 19.6% tin. The purity of the tin obtained from the cathode is 99.8%, the bismuth content is 0.013%, and the calculated current efficiency is 81.2%.

[0082] Comparative Example 3 S1. Under argon protection, an electrolytic cell is filled with molten salt electrolyte (containing 400g of LiCl-KCl-NaCl-AlCl3 (molar ratio 12:9:16:63, melting point 127.3℃) and 20g of GaCl3 is added. The electrolytic cell is equipped with an anode region and a cathode region physically separated by a porous alumina ceramic partition. In the anode region, 20.5g of waste gallium-indium alloy (gallium content 30wt%) is added as the anode, with a melting point of 89.2℃ and a gallium-indium potential difference of 0.05V. In the cathode region, 8g of pure gallium (purity ≥99.9%) is added as the cathode, with a melting point of 29.8℃. S2. Heat the electrolytic cell to 170℃ and keep it at that temperature for 2 hours to form a fully liquid electrolytic system; S3. Apply a direct current between the anode and cathode to carry out an electrolysis reaction, wherein the cathode current density is 0.6 A / cm². 2 Anode current density 0.6 A / cm 2 The ratio of cathode current density to anode current density was 1. After electrolysis, the purity of gallium at the cathode was 89.76%, the purity of indium at the anode was 82.6%, and the current efficiency was 68.4%.

[0083] The results show that this method can achieve efficient separation and purification of two valuable metals in various alloy systems such as Sn-Bi, Pb-Bi, and In-Sn. When implemented within the potential difference (≥0.1V) and electrolysis parameter range of Examples 1-8 of this invention, the purity of both cathode and anode products is not less than 99%, and the current efficiency reaches more than 90%. Among them, when the ratio of cathode current density to anode current density is within the preferred range of 1.2 to 1.8 (as in Examples 1-3), the separation selectivity, product purity, and current efficiency all reach better levels.

[0084] Comparative Example 1 used a solid cathode, which resulted in a significant decrease in product purity and current efficiency. The results of Comparative Example 3 show that when the potential difference between the metals is less than 0.1V, the separation effect deteriorates severely, and the product purity and current efficiency decrease significantly.

[0085] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recycling waste low-melting-point alloys by low-temperature molten salt electrolysis, characterized in that, Includes the following steps: S1. In the presence of a protective gas, molten salt electrolyte is contained in an electrolytic cell. The electrolytic cell is provided with an anode area and a cathode area formed by physical separation. Waste low-melting-point alloy is placed in the anode area as the anode; and initial cathode metal is placed in the cathode area as the cathode. The waste low-melting-point alloy includes metals with low oxidation potential and metals with high oxidation potential. S2. Heat the electrolytic cell to the electrolysis temperature so that the molten salt electrolyte, the waste low-melting-point alloy and the initial cathode metal are all in a liquid state; S3. At the electrolysis temperature, a direct current is applied between the anode and the cathode to carry out an electrolysis reaction, thereby recovering low oxidation potential metals and high oxidation potential metals respectively.

2. The method according to claim 1, characterized in that, The potential difference between a low oxidation potential metal and a high oxidation potential metal is ≥0.1V.

3. The method according to claim 1, characterized in that, The waste low-melting-point alloy is selected from one of tin-based alloys, lead-based alloys, bismuth-based alloys, indium-based alloys, or gallium-based alloys.

4. The method according to claim 1, characterized in that, The waste low-melting-point alloys are selected from Sn-Bi, In-Sn, Ga-In, Pb-Bi, In-Bi, Ga-Bi, In-Pb, Ga-Pb, and Ga-Sn.

5. The method according to claim 1, characterized in that, The molten salt electrolyte comprises a base molten salt and an additive salt; And / or, the matrix molten salt is selected from one or more of calcium chloride, aluminum chloride, sodium chloride, potassium chloride, lithium chloride, cesium chloride, gallium chloride, indium chloride, indium chloride, and zinc chloride.

6. The method according to claim 5, characterized in that, The additive salt is a chloride salt corresponding to the metal with a lower oxidation potential in the anode; And / or, based on the total mass of the molten salt electrolyte, the content of the additive salt is 2-15 wt%.

7. The method according to claim 1, characterized in that, The electrolysis temperature is T1, and the highest melting point among the molten salt electrolyte, the waste low-melting-point alloy, and the initial cathode metal is T. max Then T1 is more than T max Temperatures can range from 20 to 80°C.

8. The method according to claim 7, characterized in that, The conditions for the electrolysis reaction include: an electrolysis temperature of 80-500℃, and during the electrolysis process, the cathode current density and the anode current density are each independently 0.05-2 A / cm². 2 .

9. The method according to claim 8, characterized in that, The ratio of cathode current density to anode current density is 1-2:

1.

10. The application of the method according to any one of claims 1-9 in separating and recovering valuable metals from waste low-melting-point alloys.

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