Method for electrochemically recovering tin and zinc resources from electronic waste

Abstract

The application provides a method for electrochemically recycling tin and zinc resources from electronic waste, and belongs to the field of solid waste resource recycling. The method comprises the following processes: grinding electronic waste containing tin and zinc into ore powder. Disperse calcium salt, L-5-hydroxy tryptophan and ore powder in a solvent, and adjust the pH to alkaline to obtain an ore slurry. Electrolyze the ore slurry to obtain a cathode product containing tin and zinc, a liquid phase product containing tin and zinc, and a solid residue. The tin and zinc containing cathode product and the tin and zinc containing liquid phase product are post-treated to obtain tin compounds and zinc compounds. The working potential of electrolysis is 0.5 V vs. SCE-2 V vs. SCE. Through the precise coupling of the designed functional molecules and the electrochemical conditions, the selective activation, transmission and directional synthesis of the target metal at the molecular level are realized.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource recycling technology, specifically to a method for electrochemically recovering tin and zinc resources from electronic waste. Background Technology

[0002] With the rapid development of the electronics and information industry, the amount of electronic waste generated has increased dramatically. This waste contains large amounts of major non-ferrous metals such as tin (Sn) and zinc (Zn), as well as rare and precious metals such as gold (Au), silver (Ag), and palladium (Pd). How to recover valuable metals from this complex solid waste in a green and economical way has become a major challenge in the fields of resource recycling and environmental protection.

[0003] Currently, the processes for recovering metals such as tin and zinc from electronic waste are mainly divided into two categories: pyrometallurgy and hydrometallurgy. Pyrometallurgy typically involves high-temperature smelting, causing the metals to separate and concentrate in different phases while still in a molten state. This method has a large processing capacity, but it is uneconomical for low-grade materials, consumes extremely high amounts of energy, and during the high-temperature process, tin and zinc easily volatilize and enter the flue gas, causing metal loss and severe air pollution (such as the generation of toxic fumes like zinc oxide and stannous chloride). Subsequent flue gas treatment is complex and costly. Furthermore, pyrometallurgical processes struggle to achieve efficient separation of tin and zinc from coexisting precious metals (such as gold and silver), often resulting in the precious metals being dispersed in the slag or requiring complex refining.

[0004] Hydrometallurgy is currently the mainstream research and application direction, mainly including the process route of acid leaching / alkali leaching-purification-electrowinning or displacement. Traditional acid leaching: Strong inorganic acids such as hydrochloric acid, sulfuric acid, or aqua regia are commonly used as leaching agents. While this method can effectively dissolve various metals, including tin and zinc, its selectivity is extremely poor. During the leaching of the target metal, a large amount of impurity metals such as copper, iron, and nickel, as well as some precious metals, enter the solution, leading to a lengthy and complex subsequent solution purification process, high reagent consumption, and the generation of large amounts of wastewater containing heavy metals. The strong acid environment also brings serious equipment corrosion and safety risks. Alkaline leaching: Primarily for amphoteric metals (such as tin and zinc), high-concentration sodium hydroxide solutions are commonly used. Although its selectivity is better than strong acids, it still cannot effectively inhibit the co-dissolution of other metals (such as aluminum), and its leaching efficiency for tin and zinc existing in elemental or alloy forms is limited. Furthermore, high alkalinity conditions place requirements on the equipment, and the subsequent process of separating and recovering metals from the alkaline solution is relatively complex.

[0005] Therefore, electrochemical dissolution is one of the directions for improving hydrometallurgy, which promotes the anodic oxidation dissolution of the target metal by applying an external electric field. However, existing electrochemical methods still have significant shortcomings in terms of selectivity and product control. In mixed metal systems, if the applied potential is not properly controlled, it can easily lead to the co-dissolution of non-target metals (especially metals with more negative potentials), reducing product purity and increasing the difficulty of subsequent separation and purification.

[0006] In view of this, developing a new electrochemical recycling method that can achieve efficient and selective dissolution of tin and zinc, simultaneously control their dissolution forms, and is environmentally friendly and economically feasible is of great significance for the resource utilization of electronic waste. Summary of the Invention

[0007] In view of the technical problems existing in the background art, the present invention proposes a method for electrochemically recovering tin and zinc resources from electronic waste. By precisely coupling designed functional molecules with electrochemical conditions, the selective activation, transport, and directed synthesis of the target metals and the final products are achieved at the molecular level.

[0008] To achieve the above-mentioned objectives, this invention provides a method for electrochemically recovering tin and zinc resources from electronic waste, comprising:

[0009] Electronic waste containing tin and zinc is ground into mineral powder;

[0010] Calcium salt, L-5-hydroxytryptophan, and mineral powder are dispersed in a solvent, and the pH is adjusted to alkaline to obtain a mineral slurry.

[0011] Electrolysis of the slurry yields cathode products containing tin and zinc, liquid products containing tin and zinc, and solid residues.

[0012] The cathode products containing tin and zinc and the liquid-phase products containing tin and zinc were post-processed to obtain tin compounds and zinc compounds; among which,

[0013] The operating potential for electrolysis is 0.5V vs. SCE - 2V vs. SCE.

[0014] As a further improvement of the present invention, the solvent includes deionized water.

[0015] In this embodiment, deionized water has extremely high purity, effectively avoiding the interference of impurities such as metal ions and chloride ions that may be present in ordinary water on the performance of the reaction system or the final product, thereby significantly improving the purity and chemical stability of the product.

[0016] As a further improvement of the present invention, the pH of the slurry is 8-10.

[0017] In this embodiment, by controlling the pH of the slurry at 8-10, the ligands are effectively activated and can form stable soluble complexes with metal ions dissolved on the electrode surface, thereby driving the continuous transfer of tin and zinc to the liquid phase.

[0018] As a further improvement of the present invention, the mass concentration of the solvent in the slurry is 60%-90%.

[0019] In this embodiment, by keeping the solvent concentration between 60% and 90%, high purification efficiency can be ensured while maintaining good hydrodynamic state and mass transfer conditions of the reaction system, avoiding physical interference caused by excessive solid load.

[0020] As a further improvement of the present invention, the particle size of the mineral powder is less than or equal to 100 mesh.

[0021] In this embodiment, by controlling the particle size of the mineral powder to 100 mesh or less, the exposed surface area of ​​tin and zinc metals in electronic waste can be significantly increased, shortening the distance that metal ions migrate from the solid phase to the electrode interface, thereby improving the kinetic rate of the electrochemical dissolution reaction. Simultaneously, fine-grained mineral powder can be more uniformly dispersed in the slurry, reducing particle agglomeration and ensuring good suspension and flowability of the slurry, which is beneficial for the uniform distribution of current within the slurry.

[0022] As a further improvement of the present invention, the concentration of L-5-hydroxytryptophan in the slurry is 0.1 mol / L to 1 mol / L.

[0023] In this embodiment, regulating the L-5-hydroxytryptophan concentration is a key kinetic factor in the purification efficiency of tin and zinc. Within this concentration range, L-5-hydroxytryptophan can effectively complex metal ions and promote their mass transfer from the reaction interface into the solution. This concentration range ensures that the electrochemical dissolution step becomes the rate-controlled step, thereby achieving efficient and stable leaching. Sufficient L-5-hydroxytryptophan concentration guarantees the efficient migration and enrichment of tin and zinc ions from the anodic region to the cathode interface, providing a continuous source of metal ions and promoting the formation of cathode products.

[0024] As a further improvement of the present invention, the calcium ion concentration in the calcium salt in the slurry is 0.1 mol / L-0.5 mol / L.

[0025] As a further improvement of the present invention, the calcium salt includes calcium chloride.

[0026] In this embodiment, controlling the calcium ion concentration in the calcium salt is a crucial factor determining the purification rate of tin and zinc. Within this concentration range, the slurry can provide a sufficient source of calcium ions and a suitable ionic strength. Calcium chloride within this concentration range provides a stable and sufficient calcium source for the directional reaction at the cathode interface, ensuring a high purification rate while also considering process efficiency and economy.

[0027] As a further improvement of the present invention, the electrolysis working time is 2h-6h.

[0028] In this embodiment, by controlling the reaction time within the optimized range of 2h-6h, the purification rate of tin and zinc can be stably maintained at a high level. Therefore, an electrolysis working time of 2h-6h is the preferred choice for achieving a high purification rate and good process stability, ensuring the best balance between efficiency and reliability in the entire process.

[0029] As a further improvement of the present invention, the electrolysis treatment is carried out under stirring conditions.

[0030] In this embodiment, stirring can enhance the mass transfer process in the slurry, promote uniform mixing and full contact between the mineral powder particles and the solvent in the slurry, avoid the increase in local concentration gradient and mass transfer resistance caused by particle sedimentation and accumulation, thereby improving the electrochemical dissolution efficiency of tin and zinc metals.

[0031] The beneficial effects of this invention are:

[0032] By precisely coupling the designed functional molecules with electrochemical conditions, the selective activation, transport, and directional synthesis of the final product of the target metal were achieved at the molecular level.

[0033] 1) This invention utilizes L-5-hydroxytryptophan as a molecular guide and corrosion inhibitor: the amino and carboxyl groups in its molecular structure can serve as soft base sites, preferentially reacting with soft acidic Sn. 4+ and Zn 2+ It forms soluble complexes, guiding them to detach from the solid phase and enter the liquid phase; at the same time, the indole ring molecular structure fragment of L-5-hydroxytryptophan can be physically adsorbed onto the surface of copper, gold, and silver, forming a dense monolayer with strong chemisorption on the surface of precious metals such as copper, providing additional, targeted passivation protection, forming a dynamic protective film, inhibiting the oxidation and dissolution of precious metals from the molecular source, and realizing the basis for selective leaching.

[0034] 2) This invention provides a calcium source and mineralization matrix through calcium salts: Ca 2+ The ions not only provide conductivity to the slurry, but also serve as the core cations in the precipitation reaction. They combine with high-valence tin and zinc ions and hydroxyl groups generated by oxidation in the interfacial region, directly crystallizing into thermodynamically stable calcium stannate and calcium zincate.

[0035] 3) This invention uses potential as the driving force for the reaction: by precisely controlling the working potential within the specific oxidation windows of tin and zinc (e.g., 0.5V vs. SCE - 2V vs. SCE), the valence state transition of the target metal (Sn) is selectively driven energy-wise. 0 →Sn 4 + Zn 0 →Zn 2+ This avoids the oxidation of impurity metals.

[0036] 4) Under the drive of an electric field, the components of this invention form a dynamic dissolution-complexation-precipitation molecular cycle at the electrode interface. The specific mechanism is as follows: at a set potential, tin and zinc atoms lose electrons at the anode and are oxidized; the resulting ions are immediately temporarily complexed and stabilized by L-5-hydroxytryptophan molecules in the interface region; these complexes migrate in the slurry and subsequently react with Ca... 2+ And the cathode oxygen reduction reaction (O2 + 2H2O + 4e) - →4OH - The OH produced - Upon contact, a rapid ligand exchange and precipitation reaction occurs, and the released L-5-hydroxytryptophan molecules can return to the interface for further reaction. Throughout the process, the potential controls the reaction's progression, organic molecules control the reaction's selectivity and ion transport pathways, and inorganic electrolytes control the final product's form, thus achieving a precise, efficient, and green conversion from waste metals to stable calcium salts at the molecular scale.

[0037] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0039] Figure 1 This is an X-ray diffraction (XRD) analysis of the cathode product of Example 1.

[0040] Figure 2 This is the X-ray diffraction (XRD) analysis of the solid residue of Example 1. Detailed Implementation

[0041] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0043] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0044] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0045] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0046] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0047] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0048] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0049] With the rapid development of the electronics and information industry, the amount of electronic waste generated has increased dramatically. This waste contains large amounts of major non-ferrous metals such as tin (Sn) and zinc (Zn), as well as rare and precious metals such as gold (Au), silver (Ag), and palladium (Pd). How to recover valuable metals from this complex solid waste in a green and economical way has become a major challenge in the fields of resource recycling and environmental protection.

[0050] Electrochemical dissolution is one of the directions for improving hydrometallurgy, which promotes the anodic oxidation dissolution of the target metal by applying an external electric field. However, existing electrochemical methods still have significant shortcomings in terms of selectivity and product control. In mixed metal systems, if the applied potential is not properly controlled, it can easily lead to the co-dissolution of non-target metals (especially metals with more negative potentials), reducing product purity and increasing the difficulty of subsequent separation and purification.

[0051] In view of this, developing a new electrochemical recycling method that can achieve efficient and selective dissolution of tin and zinc, simultaneously control their dissolution forms, and is environmentally friendly and economically feasible is of great significance for the resource utilization of electronic waste.

[0052] To achieve the above-mentioned objective, a method for electrochemically recovering tin and zinc resources from electronic waste includes: grinding electronic waste containing tin and zinc into mineral powder; dispersing calcium salt, L-5-hydroxytryptophan, and the mineral powder in a solvent and adjusting the pH to alkaline to obtain a slurry; electrolyzing the slurry to obtain a cathode product containing tin and zinc, a liquid product containing tin and zinc, and a solid residue; and post-processing the cathode product containing tin and zinc and the liquid product containing tin and zinc to obtain tin compounds and zinc compounds; wherein the electrolysis operating potential is 0.5Vvs.SCE-2Vvs.SCE.

[0053] In the technical solution of this invention, the selective activation, transport, and directional synthesis of the final product of the target metal are achieved at the molecular level through the precise coupling of designed functional molecules and electrochemical conditions. Specifically, this invention uses L-5-hydroxytryptophan as a molecular guide and corrosion inhibitor: the amino and carboxyl groups in its molecular structure can serve as soft base sites, preferentially reacting with soft acidic Sn. 4+ and Zn 2+It forms soluble complexes, guiding them to detach from the solid phase and enter the liquid phase; at the same time, the indole ring molecular structure fragment of L-5-hydroxytryptophan can be physically adsorbed onto the surface of copper, gold, and silver, forming a dense monolayer with strong chemisorption on the surface of precious metals such as copper, providing additional, targeted passivation protection, forming a dynamic protective film, inhibiting the oxidation and dissolution of precious metals from the molecular source, and realizing the basis for selective leaching.

[0054] Furthermore, compared to existing technologies, this invention significantly improves the leaching selectivity of tin and zinc, efficiently enriches precious metals (copper, gold, and silver) in the slag, significantly improves their grade, greatly simplifies the subsequent precious metal recovery process, achieves high conversion efficiency, and significantly shortens the process flow. This invention can eliminate toxic pollution, resulting in significant environmental and safety benefits. The core advantage of this invention lies in directly stabilizing the recovered products into chemically inert calcium metastannate and calcium metazincate, fundamentally eliminating the risk of generating toxic fumes such as zinc oxide and tin dioxide during traditional pyrometallurgical processes, thus solving a major safety hazard of secondary pollution. The entire hydrometallurgical process is carried out under mild conditions, avoiding the use of highly toxic reagents such as strong acids and cyanides, and the wastewater and exhaust gas treatment pressure is low, making it a green technological path. The method of this invention is simplified and has outstanding economic benefits. The in-situ coupling mechanism of "dissolution-precipitation" eliminates the complex solution purification, separation, and metal electrolytic deposition steps in traditional hydrometallurgical processes, significantly reducing equipment investment and operating energy consumption. The obtained calcium salt products are stable, easy to store and transport, and can be used directly as safe raw materials in downstream industries, improving the economic efficiency of the entire chain. At the same time, the high selectivity at the front end creates optimal conditions for the high-value recovery of the enriched slag at the back end, resulting in significant overall resource utilization benefits.

[0055] It can be noted that electronic waste can come from various sources, including discarded circuit boards (such as computer motherboards and mobile phone motherboards) and electronic components (such as integrated circuit pins and connectors). The electrolysis operating potential of 0.5V vs. SCE - 2V vs. SCE refers to the range of potential applied to the anode in the slurry relative to the reference electrode when using a saturated calomel electrode as the reference electrode, controlled between 0.5 volts and 2 volts.

[0056] Understandably, the pH of the slurry can be adjusted to be alkaline by adding alkaline adjusters such as sodium hydroxide and potassium hydroxide. Slurry electrolysis can be carried out using a three-electrode system.

[0057] It can be explained that cathode products refer to calcium stannate and calcium zincate formed on the cathode surface through electrodeposition. Liquid products refer to soluble tin and zinc complexes that are not completely precipitated, as well as some free metal ions. These components can be further separated and recovered by adjusting the solution pH, adding precipitants, or using solvent extraction. Solid residues refer to inert components in electronic waste that did not participate in the reaction (such as plastics and glass fibers) and concentrated precious metals that are not dissolved and protected by L-5-hydroxytryptophan molecules. These can be used as secondary raw materials for precious metal recovery in subsequent processing.

[0058] It can be noted that the cathode products are poorly soluble in water. However, if the cathode products are left in the liquid phase after electrolysis, they will slowly dissolve under the action of L-5-hydroxytryptophan to form soluble complexes, which will then enter the liquid phase from the solid phase, thus obtaining a high-concentration liquid containing zinc and tin. This liquid can be used to test ion concentrations.

[0059] It can be explained that the post-processing of tin- and zinc-containing cathode products and liquid-phase products to obtain tin compounds and zinc compounds refers to the following: For the cathode products, they can be collected from the electrode surface by physical scraping or dissolution and peeling, washed with deionized water to remove residual slurry and impurities, and dried to obtain a mixed solid of calcium metastannate and calcium metazincate. For the liquid-phase products, the pH of the solution can be adjusted to a specific range to preferentially precipitate tin as calcium stannate or tin hydroxide, and zinc as zinc sulfide or zinc hydroxide, thereby obtaining zinc compounds and tin compounds.

[0060] For example, the operating potential for electrolysis can be 0.5V vs. SCE, 0.6V vs. SCE, 0.7V vs. SCE, 0.8V vs. SCE, 0.9V vs. SCE, 1.1V vs. SCE, 1.2V vs. SCE, 1.4V vs. SCE, 1.6V vs. SCE, 1.9V vs. SCE, or 2V vs. SCE.

[0061] As a further improvement of the present invention, the solvent includes deionized water.

[0062] In this embodiment, deionized water has extremely high purity, effectively avoiding the interference of impurities such as metal ions and chloride ions that may be present in ordinary water on the performance of the reaction system or the final product, thereby significantly improving the purity and chemical stability of the product.

[0063] As a further improvement of the present invention, the pH of the slurry is 8-10.

[0064] In this embodiment, by controlling the pH of the slurry at 8-10, the ligands are effectively activated and can form stable soluble complexes with metal ions dissolved on the electrode surface, thereby driving the continuous transfer of tin and zinc to the liquid phase.

[0065] For example, the pH of the slurry can be 8, 8.1, 8.4, 8.6, 8.9, 9, 9.1, 9.2, 9.5, 9.7 or 10.

[0066] As a further improvement of the present invention, the mass concentration of the solvent in the slurry is 60%-90%.

[0067] In this embodiment, by keeping the solvent concentration between 60% and 90%, high purification efficiency can be ensured while maintaining good hydrodynamic state and mass transfer conditions of the reaction system, avoiding physical interference caused by excessive solid load.

[0068] For example, the mass concentration of the solvent can be 60%, 61%, 71%, 77%, 79%, 80%, 81%, 83%, 85%, or 90%.

[0069] As a further improvement of the present invention, the particle size of the mineral powder is less than or equal to 100 mesh.

[0070] In this embodiment, by controlling the particle size of the mineral powder to 100 mesh or less, the exposed surface area of ​​tin and zinc metals in electronic waste can be significantly increased, shortening the distance that metal ions migrate from the solid phase to the electrode interface, thereby improving the kinetic rate of the electrochemical dissolution reaction. Simultaneously, fine-grained mineral powder can be more uniformly dispersed in the slurry, reducing particle agglomeration and ensuring good suspension and flowability of the slurry, which is beneficial for the uniform distribution of current within the slurry.

[0071] For example, the particle size of the mineral powder can be 1 mesh, 2 mesh, 5 mesh, 9 mesh, 16 mesh, 22 mesh, 28 mesh, 35 mesh, 37 mesh, 42 mesh, 51 mesh, 66 mesh, 79 mesh, 80 mesh, 95 mesh or 100 mesh.

[0072] As a further improvement of the present invention, the concentration of L-5-hydroxytryptophan in the slurry is 0.1 mol / L to 1 mol / L.

[0073] In this embodiment, regulating the L-5-hydroxytryptophan concentration is a key kinetic factor in the purification efficiency of tin and zinc. Within this concentration range, L-5-hydroxytryptophan can effectively complex metal ions and promote their mass transfer from the reaction interface into the solution. This concentration range ensures that the electrochemical dissolution step becomes the rate-controlled step, thereby achieving efficient and stable leaching. Sufficient L-5-hydroxytryptophan concentration guarantees the efficient migration and enrichment of tin and zinc ions from the anodic region to the cathode interface, providing a continuous source of metal ions and promoting the formation of cathode products.

[0074] For example, the concentration of L-5-hydroxytryptophan can be 0.1 mol / L, 0.12 mol / L, 0.13 mol / L, 0.25 mol / L, 0.39 mol / L, 0.44 mol / L, 0.45 mol / L, 0.51 mol / L, 0.66 mol / L, 0.73 mol / L, 0.8 mol / L, 0.9 mol / L, 0.99 mol / L, or 1 mol / L.

[0075] As a further improvement of the present invention, the calcium ion concentration in the calcium salt in the slurry is 0.1 mol / L-0.5 mol / L.

[0076] In this embodiment, controlling the calcium ion concentration in the calcium salt is a crucial factor determining the purification rate of tin and zinc. Within this concentration range, the slurry can provide a sufficient source of calcium ions and a suitable ionic strength. Calcium chloride within this concentration range provides a stable and sufficient calcium source for the directional reaction at the cathode interface, ensuring a high purification rate while also considering process efficiency and economy.

[0077] For example, in the slurry, the calcium ion concentration in the calcium salt can be 0.1 mol / L, 0.15 mol / L, 0.21 mol / L, 0.33 mol / L, 0.36 mol / L, 0.42 mol / L, 0.49 mol / L, or 0.5 mol / L.

[0078] As a further improvement of the present invention, the calcium salt includes calcium chloride.

[0079] In this embodiment, calcium chloride, as a calcium salt, is readily soluble in water and can completely dissociate in alkaline slurry, efficiently providing Ca. 2+ Ions ensure rapid binding reactions with tin, zinc, and hydroxyl ions; chloride ions (Cl...) - Calcium chloride is chemically stable under alkaline conditions and is not prone to side reactions with other components in the system, thus maintaining the stability of the ionic strength of the slurry and ensuring the smooth progress of the electrolysis process. Furthermore, calcium chloride is widely available and inexpensive, significantly reducing raw material costs and improving overall economic efficiency.

[0080] As a further improvement of the present invention, the electrolysis working time is 2h-6h.

[0081] In this embodiment, by controlling the reaction time within the optimized range of 2h-6h, the purification rate of tin and zinc can be stably maintained at a high level. Therefore, an electrolysis working time of 2h-6h is the preferred choice for achieving a high purification rate and good process stability, ensuring the best balance between efficiency and reliability in the entire process.

[0082] For example, the electrolysis working time can be 2h, 2.2h, 2.3h, 2.5h, 3.2h, 3.4h, 3.5h, 3.8h, 4h, 4.2h, 4.5h, 5.1h, 5.3h, 5.5h, 5.7h, 5.9h or 6h.

[0083] As a further improvement of the present invention, the electrolysis treatment is carried out under stirring conditions.

[0084] In this embodiment, stirring can enhance the mass transfer process in the slurry, promote uniform mixing and full contact between the mineral powder particles and the slurry, avoid the increase in local concentration gradient and mass transfer resistance caused by particle sedimentation and accumulation, thereby improving the electrochemical dissolution efficiency of tin and zinc metals.

[0085] It can be noted that stirring during the electrolysis process can be achieved through mechanical stirring devices, such as paddle stirrers, anchor stirrers, or magnetic stirrers. The stirring rate can be adjusted according to the slurry concentration and the volume of the reaction system to ensure that the slurry is in a good suspension state.

[0086] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0087] I. Preparation Method

[0088] The electronic waste used in the following examples is waste circuit boards, the main component of which includes gold (Au, 24.30 g / t). 原料 Silver (Ag, 757.60 g / t) 原料 ), copper (Cu, 13.10 g / t) 原料 Tin (Sn, 2.83 g / t) 原料 ) and zinc (Zn, 1.79 g / t) 原料 ).

[0089] Example 1

[0090] Electronic waste containing tin and zinc is ground into mineral powder with a particle size of less than 100 mesh.

[0091] Calcium salt, L-5-hydroxytryptophan, and mineral powder were dispersed in a solvent, and the pH was adjusted to alkaline to obtain a slurry. The concentration of L-5-hydroxytryptophan was 0.5 mol / L, the concentration of calcium chloride was 0.2 mol / L, the pH of the slurry was 8, and the mass concentration of the solvent was 70%.

[0092] In a 3L cylindrical electrolytic cell, 2L of mineral slurry was added. The slurry was electrolyzed using a three-electrode system. Specifically, the graphite electrode was subjected to mechanical polishing (using 400# sandpaper), ultrasonic cleaning (30 minutes each with ethanol and water), and electrochemical activation (20 cycles of cyclic voltammetry in 0.5M H₂SO₄). A titanium-based platinum-plated mesh counter electrode (150cm²) and a dual-salt bridge reference electrode constituted the three-electrode system. Mechanical stirring was maintained at 500rpm during electrolysis. The operating potential was determined to be 0.5V vs. SCE, and the operating time was 4 hours, using linear sweep voltammetry (0-30V, 100mV / s). The resulting products included cathode products containing tin and zinc, liquid products containing tin and zinc, and solid residues.

[0093] The cathode products containing tin and zinc and the liquid products containing tin and zinc are post-processed to obtain tin compounds and zinc compounds.

[0094] Example 2

[0095] The difference from Example 1 is that the pH of the slurry is 9. The rest is largely the same as Example 1 and will not be repeated here.

[0096] Example 3

[0097] The difference from Example 1 is that the pH of the slurry is 10. The rest is largely the same as Example 1 and will not be repeated here.

[0098] Example 4

[0099] The difference from Example 1 is that the pH of the slurry is 11. The rest is largely the same as Example 1 and will not be repeated here.

[0100] Example 5

[0101] The difference from Example 1 is that the pH of the slurry is 12. The rest is largely the same as in Example 1 and will not be repeated here.

[0102] Example 6

[0103] The difference from Example 1 is that the pH of the slurry is 13. The rest is largely the same as in Example 1 and will not be repeated here.

[0104] Example 7

[0105] The difference from Example 1 is that the pH of the slurry is 14. The rest is largely the same as Example 1 and will not be repeated here.

[0106] Example 8

[0107] The difference from Example 1 is that the concentration of L-5-hydroxytryptophan is 0.05 mol / L. The rest is largely the same as in Example 1 and will not be repeated here.

[0108] Example 9

[0109] The difference from Example 1 is that the concentration of L-5-hydroxytryptophan is 0.1 mol / L. The rest is largely the same as in Example 1 and will not be repeated here.

[0110] Example 10

[0111] The difference from Example 1 is that the concentration of L-5-hydroxytryptophan is 0.25 mol / L. The rest is largely the same as in Example 1 and will not be repeated here.

[0112] Example 11

[0113] The difference compared to Example 1 is that the concentration of L-5-hydroxytryptophan is 0.75 mol / L. The rest is largely the same as in Example 1 and will not be repeated here.

[0114] Example 12

[0115] The difference from Example 1 is that the concentration of L-5-hydroxytryptophan is 1.0 mol / L. The rest is largely the same as in Example 1 and will not be repeated here.

[0116] Example 13

[0117] The difference compared to Example 1 is that the concentration of L-5-hydroxytryptophan is 1.25 mol / L. The rest is largely the same as in Example 1 and will not be repeated here.

[0118] Example 14

[0119] The difference compared to Example 1 is that the calcium chloride concentration is 0.05 mol / L. The rest is largely the same as in Example 1 and will not be repeated here.

[0120] Example 15

[0121] The difference from Example 1 is that the calcium chloride concentration is 0.1 mol / L. The rest is largely the same as Example 1 and will not be repeated here.

[0122] Example 16

[0123] The difference from Example 1 is that the calcium chloride concentration is 0.3 mol / L. The rest is largely the same as Example 1 and will not be repeated here.

[0124] Example 17

[0125] The difference from Example 1 is that the calcium chloride concentration is 0.4 mol / L. The rest is largely the same as Example 1 and will not be repeated here.

[0126] Example 18

[0127] The difference from Example 1 is that the calcium chloride concentration is 0.5 mol / L. The rest is largely the same as Example 1 and will not be repeated here.

[0128] Example 19

[0129] The difference from Example 1 is that the calcium chloride concentration is 1 mol / L. The rest is largely the same as in Example 1 and will not be repeated here.

[0130] Example 20

[0131] The difference from Example 1 is that the solvent concentration is 90%. The rest is largely the same as in Example 1 and will not be repeated here.

[0132] Example 21

[0133] The difference from Example 1 is that the solvent concentration is 80%. The rest is largely the same as in Example 1 and will not be repeated here.

[0134] Example 22

[0135] The difference from Example 1 is that the solvent concentration is 60%. The rest is largely the same as in Example 1 and will not be repeated here.

[0136] Example 23

[0137] The difference from Example 1 is that the solvent concentration is 50%. The rest is largely the same as in Example 1 and will not be repeated here.

[0138] Example 24

[0139] The difference compared to Example 1 is that the electrolysis operating potential is 1V vs. SCE. The rest is largely the same as in Example 1 and will not be repeated here.

[0140] Example 25

[0141] The difference compared to Example 1 is that the electrolysis operating potential is 2V vs. SCE. The rest is largely the same as Example 1 and will not be repeated here.

[0142] Example 26

[0143] The difference compared to Example 1 is that the electrolysis time is 1 hour. The rest is largely the same as Example 1 and will not be repeated here.

[0144] Example 27

[0145] The difference compared to Example 1 is that the electrolysis time is 2 hours. The rest is largely the same as in Example 1 and will not be repeated here.

[0146] Example 28

[0147] The difference compared to Example 1 is that the electrolysis time is 6 hours. The rest is largely the same as Example 1 and will not be repeated here.

[0148] Example 29

[0149] The difference compared to Example 1 is that the electrolysis time is 6.5 hours. The rest is largely the same as Example 1 and will not be repeated here.

[0150] Comparative Example 1

[0151] The difference from Example 1 is that the pH of the slurry is 7. The rest is largely the same as Example 1 and will not be repeated here.

[0152] Comparative Example 2

[0153] The difference from Example 1 is that the concentration of L-5-hydroxytryptophan is 0 (i.e., not added). The rest is largely the same as in Example 1, and will not be repeated here.

[0154] Comparative Example 3

[0155] The difference from Example 1 is that the calcium chloride concentration is 0 (i.e., no calcium chloride is added). The rest is largely the same as in Example 1, and will not be repeated here.

[0156] Comparative Example 4

[0157] The difference compared to Example 1 is that the electrolysis operating potential is 0V vs. SCE. The rest is largely the same as Example 1 and will not be repeated here.

[0158] Comparative Example 5

[0159] The difference compared to Example 1 is that the electrolysis operating potential is 0.4V vs. SCE. The rest is largely the same as Example 1 and will not be repeated here.

[0160] Comparative Example 6

[0161] The difference compared to Example 1 is that the electrolysis operating potential is 2.5V vs. SCE. The rest is largely the same as Example 1 and will not be repeated here.

[0162] II. Testing Methods

[0163] Equipment Name: X-ray diffractometer, Model D / max2200PC. Manufacturer: Nippon Kiku Denki Co., Ltd. Testing Method: The crystal structure characteristics of each sample were determined using an X-ray diffractometer (XRD) manufactured by Nippon Kiku Denki Co., Ltd. First, the sample was placed in a 50×35×2mm... 3 The sample was placed in a quartz glass sample holder, flattened with a glass slide, and then inserted into the sample stage. The instrument operating parameters included Cu target radiation, a tube voltage of 50 kV, a tube current of 40 mA, a 2θ scan range of 5°–80°, a step size of 0.05°, and an operating temperature of 298 K. The instrument's built-in software was used for full-spectrum quantitative analysis of the sample content.

[0164] 1. Perform XRD analysis on the cathode products and conduct full-spectrum fitting quantitative analysis.

[0165] 2. Perform XRD analysis on the solid residue.

[0166] 3. The concentrations of zinc and tin in high-concentration liquids are determined by ICP-OES.

[0167] η = Vβ2 / mβ1 × 100%;

[0168] In the formula, η represents the purification rate of zinc or tin, in %; m represents the mass of the raw material, in g; β1 represents the grade of tin or zinc in the raw material, in g / t; V represents the volume of zinc or tin in the leachate, in L; and β2 represents the concentration of zinc or tin in the leachate, in g / L.

[0169] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0170] from Figure 1 It can be seen that the cathode products mainly consist of calcium stannate (CaSnO3) and calcium zincate dihydrate (CaH2ZnO4·2H2O). Quantitative analysis using full-spectrum fitting revealed that the mass fractions of these two components were 55.9% (CaSnO3) and 44.1% (CaH2ZnO4·2H2O), respectively. This result reveals the core stabilization mechanism of this invention from the product end: in alkaline slurry (containing Ca... 2 + Driven by specific electrochemical potentials, the leached Sn(IV) and Zn(II) do not exist in the form of simple ions or hydroxides, but instead undergo a directional reaction with calcium chloride added to the slurry, crystallizing in situ to form structurally stable calcium-based composite oxides.

[0171] from Figure 2It can be seen that the spectrum shows several distinct characteristic diffraction peaks at 2θ of 10.2°, 15.8°, 25.4°, and 34.0°, which do not match the standard cards for elemental copper, copper oxide, or copper hydroxide. Simultaneously, characteristic peaks not found in other XRD databases were also observed. Considering the process conditions of this system (containing L-5-hydroxytryptophan and calcium chloride), these unique diffraction peaks are attributed to a composite structure of basic copper chloride (Cu2(OH)3Cl) and an organometallic coordination layer, formed in situ under a weakly alkaline, chloride-containing, and organic ligand-containing environment. The formation mechanism of this phase is as follows: under an electrochemically controlled weak oxidation potential, a small amount of anodic dissolution occurs on the copper surface, generating Cu... 2+ Immediately with Cl in the slurry - and OH produced by the cathode reaction - The combination of these components precipitates a dense and insoluble basic salt protective layer. Simultaneously, L-5-hydroxytryptophan molecules in the solution adsorb or weakly coordinate with the surface of this precipitate through their nitrogen-containing groups, further filling and passivating the micropores of the film. This in-situ formed composite film densely covers the surface of the copper particles, effectively preventing direct contact between the slurry and the metal matrix. This significantly increases the mass transfer resistance and electrochemical overpotential of copper anodic dissolution, thus directly confirming significant passivation of the copper surface at the phase level. This provides crucial microstructural evidence to explain the extremely low copper co-solubility in the system of this invention.

[0172] Table 1: Purification rates of tin and zinc in Examples 1-29 and Comparative Examples 1-6

[0173]

[0174]

[0175] — This indicates that the level is below the ICP-OES detection limit. Considering detection errors, the purification rate of tin or zinc is almost zero.

[0176] As shown in Examples 1-7 and Comparative Example 1 in Table 1, this electrochemical leaching system is highly dependent on the pH of the slurry, exhibiting distinct performance characteristics within a specific range. At pH 7, the system is almost ineffective, with tin and zinc purification rates below the detection limit. This is mainly because the key ligand L-5-hydroxytryptophan fails to be fully deprotonated under weakly alkaline conditions, resulting in insufficient complexing activity, while the electrochemical dissolution kinetics of the target metals are weak. Within the optimal pH window of 8-10, the ligand is effectively activated, forming stable and soluble complexes with metal ions dissolved on the electrode surface, thereby driving the continuous transfer of tin and zinc to the liquid phase, achieving purification rates of over 94%. However, when the pH rises above 11, the strongly alkaline environment triggers severe competitive hydrolysis reactions, leading to Sn... 4+ and Zn 2+Hydroxide precipitates are rapidly generated; these precipitates re-attach to the surface of the raw material particles, forming a dense passivation layer. This not only blocks the electrochemical dissolution interface but also essentially "retains" the target metal in the solid phase, causing the apparent purification rate to drop sharply to below 50%. Therefore, the entire pH response curve reveals that precisely controlling the reaction environment between pH 8 and 10 is crucial to balancing and optimizing the kinetic competition among ligand activation, electrochemical dissolution, and inhibition of metal hydrolysis precipitation.

[0177] As shown in Table 1, Examples 1, 8-13, and Comparative Example 2, the concentration of L-5-hydroxytryptophan is a key kinetic factor regulating the leaching efficiency of tin and zinc. The purification rate initially increases rapidly with increasing concentration and then tends to saturate: when the concentration is below 0.25 mol / L (e.g., 0.05 mol / L in Example 8), the purification rate is significantly limited (73% for tin and 77% for zinc), indicating that the amount of ligands is insufficient to fully complex the dissolved metal ions, resulting in impaired mass transfer at the reaction interface; when the concentration rises to the range of 0.5 mol / L-1.0 mol / L (Examples 1, 11, and 12), the purification rate stabilizes at a high level of 94%-98%, indicating that the ligands are sufficiently excessive, and the electrochemical dissolution step becomes the rate-controlling step, and further increasing the concentration has limited effect on the purification rate gain (e.g., in Example 13, it is still 98% at 1.25 mol / L). Based on the formation mechanism of cathode products (calcium metastannate and calcium zincate dihydrate), sufficient ligand concentration ensures the efficient migration and enrichment of tin(IV) and zinc(II) ions from the anolyte to the cathode interface, thus providing a continuous source of metal ions for the directional precipitation and stabilization reactions occurring at the cathode interface. The results of Comparative Example 2 (L-5-hydroxytryptophan concentration of 0.00 mol / L) are crucial for comparison; its tin and zinc purification rates are below the detection limit (-), directly proving that this organic ligand is a necessary condition for the entire electrochemical leaching system. Therefore, 0.5 mol / L–1.0 mol / L is the optimized concentration range for this process, balancing leaching efficiency and economy.

[0178] As shown in Table 1, Examples 1, 14-19, and Comparative Example 3, the concentration of calcium chloride has a significant impact on the purification rate of tin and zinc. When the concentration is below 0.1 mol / L (as in Example 14), the calcium ion supply is insufficient, making it difficult to effectively drive and complete the precipitation conversion of the target metal ions into stable calcium salts, resulting in a significant drop in purification rate to below 80%. When the concentration is increased to the range of 0.2 mol / L-0.5 mol / L (Examples 1 and 16-18), sufficient calcium source and ionic strength can be provided for the continuous precipitation reaction, and the purification rate stabilizes above 90% and tends to be optimal. However, when the concentration is too high (as in Example 19, 1 mol / L), although the purification rate remains high, the excessively high electrolyte concentration will lead to increased solution viscosity, hindered ion migration, and significantly increased subsequent waste liquid treatment costs, resulting in decreased economic efficiency and operational efficiency. In particular, in a system completely free of calcium chloride (Comparative Example 3), the target calcium salt precipitate cannot be formed, the reaction pathway is blocked, and the purification process cannot proceed effectively. Therefore, controlling the calcium chloride concentration within the range of 0.1 mol / L to 0.5 mol / L can ensure a high purification rate while also taking into account the economic efficiency and operational efficiency of the process.

[0179] As shown in Table 1, Examples 1 and 20-23, the effect of solvent concentration on purification rate exhibits a wide optimization range and a clear performance inflection point. When the solvent concentration is between 60% and 90% (Examples 1 and 20-22), the purification rates of tin and zinc remain consistently high at 94% to 98%, indicating sufficient solid-liquid-electric three-phase contact within this concentration range, and the reaction mass transfer and charge transfer processes are not significantly restricted. However, when the solvent concentration decreases to 50%, the purification rate drops significantly (89% for tin and 92% for zinc). This is mainly attributed to the excessive solid content leading to too many non-conductive inert substances such as suspended plastic powder in the system. This not only severely deteriorates the rheological properties of the slurry and the effective contact area of ​​the electrode surface, but may also encapsulate the target metal particles, hindering their electrochemical dissolution and ion diffusion, thereby deteriorating the overall reaction kinetics. Therefore, considering the company's work efficiency, controlling the solvent's mass concentration within the range of 60%-90% can ensure high purification efficiency while maintaining good hydrodynamic state and mass transfer conditions of the reaction system, avoiding physical interference caused by excessive solid load.

[0180] As shown in Table 1, Examples 1, 24, 25, and Comparative Examples 4-6, the applied working potential is a key parameter for controlling the electrochemical selective oxidation process, and its value must be strictly matched to the electrochemical dissolution window of the target metal. When the potential is set between 0.5V vs. SCE and 2V vs. SCE (Examples 1, 24, and 25), the purification rates of tin and zinc are consistently maintained at a high level of 94% to 96%, indicating that this potential range is sufficient to efficiently drive the anodic oxidation dissolution of tin and zinc and successfully complete the subsequent precipitation reaction. However, when the potential is too low (such as 0V vs. SCE in Comparative Example 4 and 0.4V vs. SCE in Comparative Example 5), sufficient thermodynamic driving force cannot be provided for the oxidation of tin, resulting in an extremely low reaction rate or even failure to initiate, thus leading to low purification efficiency or ineffective detection. Conversely, when the potential is too high (such as 2.5V vs. SCE in Comparative Example 6), although the oxidation driving force for tin and zinc is further enhanced, the excessively high potential exceeds the upper limit of their selective oxidation, triggering side reactions such as moisture desorption and oxygenation, exacerbating electrode passivation, and potentially inducing non-selective dissolution of impurity metals such as copper. These competing reactions not only increase ineffective energy consumption but may also damage the purity of the precipitated products, ultimately leading to a decrease in overall purification efficiency. Therefore, precisely controlling the working potential within the range of 0.5V vs. SCE to 2V vs. SCE is the optimal electrochemical condition for achieving efficient, highly selective, and stable extraction of tin and zinc.

[0181] As shown in Table 1, Examples 1 and 26-29, reaction time is a key kinetic factor affecting the extraction and conversion process of the target metal, exhibiting a clear three-stage relationship with the purification rate: rapid increase - plateau stabilization - deterioration and decrease. When the reaction time is too short (e.g., 1 h in Example 26), the electrochemical oxidation and subsequent precipitation reactions are not fully carried out, and a large number of metal particles remain in the solid phase, resulting in purification rates of only 35% and 63% for tin and zinc, respectively, indicating a severely insufficient reaction time. Within the range of 2-6 h (Examples 1, 27, and 28), the purification rate remains stable at a high level of 93% to 97%, indicating that the reaction has basically reached dynamic equilibrium within this time period, and the conversion process of the main metals tends to be complete. However, when the reaction time is further extended to 6.5 h (Example 29), the purification rate does not continue to increase but instead shows a significant decrease (81% for tin and 79% for zinc). This may be because, under prolonged electrochemical action, the initially formed stable products such as calcium stannate and calcium zincate may undergo local redissolution or crystal transformation in the interfacial microregions, or the slowly accumulating byproducts in the system may interfere with the equilibrium of the main reaction, leading to the "redissolution" or secondary encapsulation of the converted metal, resulting in a decrease in net extraction efficiency instead of an increase. Therefore, controlling the reaction time within the range of 2-6 hours is crucial for optimizing process efficiency, ensuring complete reaction while avoiding efficiency degradation due to excessive time.

[0182] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for electrochemically recycling tin and zinc resources from electronic waste, characterized in that, The application relates to a method for recovering tin and zinc from electronic waste. The electronic waste containing tin and zinc is ground into a powder; A calcium salt, L-5-hydroxytryptophan and the powder are dispersed in a solvent, and the pH is adjusted to alkaline to obtain a slurry; The slurry is electrolyzed to obtain a cathode product containing tin and zinc, a liquid phase product containing tin and zinc and a solid residue; The cathode product containing tin and zinc and the liquid phase product containing tin and zinc are post-treated to obtain a tin compound and a zinc compound; wherein, The working potential of the electrolysis is 0.5 V vs. SCE-2 V vs. SCE; The pH of the slurry is 8-10; In the slurry, the concentration of the L-5-hydroxytryptophan is 0.1 mol / L-1 mol / L; In the slurry, the concentration of calcium ions in the calcium salt is 0.1 mol / L-0.5 mol / L; The working time of the electrolysis is 2 h-6 h.

2. The method for electrochemically recycling tin and zinc resources from electronic waste according to claim 1, characterized in that, The solvent comprises deionized water.

3. The method for electrochemically recycling tin and zinc resources from electronic waste according to claim 1, characterized in that, In the slurry, the mass concentration of the solvent is 60%-90%.

4. The method for electrochemically recycling tin and zinc resources from electronic waste according to claim 1, characterized in that, The particle size of the powder is less than or equal to 100 mesh.

5. The method for electrochemically recycling tin and zinc resources from electronic waste according to claim 1, characterized in that, The calcium salt comprises calcium chloride.

6. The method of electrochemically recycling tin and zinc resources from electronic waste according to claim 1, wherein, The electrolysis treatment is carried out under stirring.

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