Method for recovering valuable metals from electroplating sludge

Abstract

The application discloses a method for recycling valuable metals in electroplating sludge, and relates to the technical field of solid waste resource utilization, comprising the following steps: uniformly mixing the electroplating sludge with a desulfurizer, heating and stirring to obtain a solid-liquid mixture; filtering the solid-liquid mixture to obtain filtrate and filter residue; crystallizing and separating the filtrate to obtain the desulfurizer and sodium sulfate crystals, and drying the filter residue to obtain dry matter; uniformly mixing the dry matter with elemental silicon and elemental carbon, smelting under an inert atmosphere, cooling and dust collecting the high-temperature flue gas generated in the smelting process to obtain lead-zinc-containing dust, and separating the alloy ingot and slag after natural cooling at room temperature after the smelting is completed. The desulfurization rate of the application is more than 90%, and the valuable metal recovery rate is more than 95%, so that the electroplating sludge can be desulfurized at low cost and the valuable metal resources can be efficiently and comprehensively recycled, and the application has the advantages of simple operation, large processing capacity and strong adaptability.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, and in particular to a method for recovering valuable metals from electroplating sludge. Background Technology

[0002] Electroplating sludge has a complex composition, typically containing large amounts of heavy metals (Cu, Ni, Cr, Pb, Zn, etc.), and is characterized by easy migration, high water content, high ash content, and high thermal stability. If not properly disposed of, it may experience rainwater leaching and volatilization migration, posing serious harm to human health and the environment. On the other hand, the metal content in electroplating sludge is far higher than that of raw ore, thus possessing potential resource value. Currently, the main methods of disposing of electroplating sludge in my country are solidification / landfill. Every year, over 100,000 tons of valuable metals from electroplating sludge are not fully recovered and utilized, resulting in a serious waste of metal resources and increased environmental pressure. Therefore, how to achieve efficient recovery of valuable metals from electroplating sludge has become an urgent technical problem to be solved.

[0003] In existing technologies, the recovery of valuable metals from electroplating sludge mainly involves hydrometallurgy and pyrometallurgy. Hydrometallurgy dissolves valuable metals from electroplating sludge into the liquid phase through acid leaching, followed by extraction and chemical precipitation to recover the metals, as reported in patent documents CN202210240969.0, CN202111173136.9, CN202211378089.6, and CN202210757203.X. However, hydrometallurgy generates large amounts of hazardous wastewater and requires the addition of extractants and chemical reagents, limiting its large-scale application. Pyrometallurgy, due to its ability to reduce volume and efficiently recover metals, is widely used in the disposal of electroplating sludge. Patent document CN201811442392.1 also proposes a method for selectively recovering heavy metals from electroplating sludge using chlorination roasting. While this method can recover heavy metals, chlorination roasting causes significant equipment corrosion and is not suitable for widespread adoption. Patent documents CN202011171726.3 and CN201911340666.0 also propose a method for high-temperature carbothermic reduction smelting of electroplating sludge, allowing heavy metals to enter the alloy ingot and achieving comprehensive recovery of valuable metals. However, such methods require the addition of large amounts of slag-forming agents (quartz, limestone, etc.), increasing disposal costs. Furthermore, chromium in electroplating sludge is difficult to directly be carbotherm-reduced into metal, making chromium recovery impossible. Sulfur in calcium sulfate enters the alloy ingot during the smelting process, reducing alloy quality; therefore, pre-desulfurization treatment of the electroplating sludge is necessary. Currently, the mainstream desulfurization methods in existing technologies are high-temperature oxidation or high-temperature reduction desulfurization, which are not only costly but also corrode equipment. Therefore, developing a new method for comprehensive recovery of valuable metals from electroplating sludge would not only benefit the recycling of metal resources but also protect environmental safety. Summary of the Invention

[0004] The main objective of this invention is to provide a method for recovering valuable metals from electroplating sludge, aiming to achieve low-cost desulfurization of electroplating sludge and efficient comprehensive recovery of valuable metal resources.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for recovering valuable metals from electroplating sludge includes the following steps:

[0007] (1) After the electroplating sludge and desulfurizing agent are mixed evenly, the mixture is heated and stirred to obtain a solid-liquid mixture.

[0008] (2) Filter the solid-liquid mixture in step (1) to obtain filtrate and filter residue;

[0009] (3) The filtrate from step (2) is crystallized to obtain desulfurizing agent and sodium sulfate crystals, and the filter residue is dried to obtain dried product;

[0010] (4) The dried material in step (3) is mixed evenly with elemental silicon and elemental carbon and smelted under an inert atmosphere. The high-temperature flue gas generated during the smelting process is cooled and dust is collected to obtain lead-zinc flue dust. After the smelting is completed, the flue gas is naturally cooled to room temperature and then separated to obtain alloy ingots and slag.

[0011] This invention involves uniformly mixing electroplating sludge with a sodium carbonate solution at a specific mass / volume ratio, followed by heating and stirring. Calcium sulfate in the sludge reacts with sodium carbonate to form water-soluble sodium sulfate, which is then removed by filtration. The filter residue is dried and mixed uniformly with silicon-containing materials and waste carbon. The mixture is then smelted under an inert atmosphere. The oxidation of elemental silicon produces SiO2, reducing the binary basicity of the slag and thus decreasing its viscosity, promoting metal settling. Volatile metals such as lead and zinc are reduced and released into the flue gas. After cooling and dust collection, lead- and zinc-containing dust is obtained, while valuable metals such as copper, nickel, chromium, cobalt, manganese, and iron are reduced and released into alloy ingots, achieving comprehensive recovery of valuable metals.

[0012] By employing the above method, dried electroplating sludge is mixed with sodium carbonate solution and heated and stirred for desulfurization. The desulfurization filter residue is then dried and mixed evenly with silicon-containing materials and waste carbon. After heating to a set temperature, it is smelted to obtain lead-zinc dust, heavy metal alloy ingots, and harmless slag. This invention achieves a desulfurization rate of over 90% and a valuable metal recovery rate of over 95%, enabling low-cost desulfurization of electroplating sludge and efficient comprehensive recovery of valuable metal resources. It has the advantages of simple operation, large processing capacity, and strong adaptability, and is of great significance for the resource-based disposal of electroplating sludge.

[0013] Preferably, the chemical composition of the electroplating sludge includes Cu, Ni, Cr, Fe, Pb, Zn, Mn, S, Co, CaO, and SiO2.

[0014] Preferably, the desulfurizing agent in step (1) is a sodium carbonate solution, and the heating and stirring is carried out at 20-80°C for 30-120 minutes.

[0015] By employing the above method, the electroplating sludge can be desulfurized using a low-cost wet process by utilizing the solubility difference between carbonates and sulfates. The specific reaction is shown in equation (1):

[0016] CaSO 4(s) +Na2CO 3(aq) =Na2SO 4(aq) +CaCO 3(s) (1)

[0017] Wet desulfurization not only effectively removes calcium sulfate from electroplating sludge, but also enriches the metals in the sludge to a certain extent. Furthermore, the filtrate can be further separated to yield sodium sulfate and sodium carbonate, with the sodium carbonate being reusable, achieving energy conservation and emission reduction. This invention first utilizes sodium carbonate to convert calcium sulfate in electroplating sludge into highly soluble sodium sulfate for wet desulfurization, preventing sulfur from entering the alloy ingots during smelting and reducing ingot quality. It also utilizes the synergistic reduction of silicon-containing materials and waste carbon to enhance the recovery of valuable metals from the electroplating sludge. Additionally, lead- and zinc-containing flue dust can be further refined to extract lead and zinc.

[0018] The stirring method in step (1) is mechanical stirring, the stirring rate is 30 to 600 rpm, and the heating temperature is 20 to 80°C, preferably 40 to 60°C; the filtration method in step (2) is one of gravity filter, vacuum filter and pressure filter.

[0019] Preferably, the sodium carbonate solution has a mass fraction of 25-100%, and the mass-to-volume ratio of the electroplating sludge to the sodium carbonate solution is 1:(5-20)kg / L.

[0020] Preferably, the crystallization separation in step (3) involves introducing CO2 gas into the filtrate to crystallize the filtrate; the crystallization is either cooling crystallization or evaporation crystallization.

[0021] By using the above method, sodium sulfate and sodium carbonate can be easily separated by introducing CO2 gas into the filtrate.

[0022] Preferably, the mass ratio of the dried material, elemental silicon and elemental carbon in step (4) is 1:(0.05-0.30):(0.05-0.20).

[0023] To address the current limitations of carbonaceous reducing agents in directly reducing metals in electroplating sludge, this study utilizes elemental silicon and elemental carbon as reducing agents to achieve efficient reduction of valuable metals in electroplating sludge. Unlike carbonaceous reducing agents, silicon has a lower reduction reaction temperature and can also act as a slag-forming agent in the smelting process, reducing slag viscosity and promoting metal settling. Furthermore, the addition of carbon can further enhance the gas-liquid and gas-solid reduction reactions in the system, improving metal recovery. The specific reaction mechanisms are shown in equations (2) and (3):

[0024] MeO+[Si]=Me+SiO2 (2)

[0025] MeO + C = Me + CO (3)

[0026] Me refers to valuable metals such as Cu, Ni, Cr, Co, Mn, Pb, and Zn found in electroplating sludge; MeO refers to the oxides of the corresponding metals formed during the smelting process.

[0027] Elemental silicon materials can be sourced from waste monocrystalline silicon, waste polycrystalline silicon, waste crystalline silicon photovoltaic modules, industrial silicon slag, silicon alloys, and other silicon-containing materials. Elemental carbon materials can be sourced from waste activated carbon, coal tar residue, and waste cathode / anode carbon from aluminum electrolysis, achieving waste utilization. Silicon materials not only serve as reducing agents but also help adjust slag composition. Furthermore, waste carbon-containing materials such as waste cathode / anode carbon from aluminum electrolysis are the optimal materials for utilization. Waste cathode carbon contains 50-80% carbon and 10-20% fluorine, while waste anode carbon contains 20-60% carbon and 20-40% fluorine. These materials not only contain abundant elemental carbon but also fluorides, making them ideal for use. The presence of fluorides reduces slag viscosity, improving its fluidity. The recovery effect using pure carbon is slightly inferior to that using waste carbon-containing materials such as waste cathode / anode carbon from aluminum electrolysis. In addition, the oxidation of elemental silicon to form silicon dioxide can reduce the binary basicity of the slag, that is, reduce the viscosity of the slag, which facilitates the separation of pre-recovered metal precipitates.

[0028] Preferably, the particle size of both elemental silicon and elemental carbon in step (4) is less than 0.15 mm.

[0029] Preferably, the inert atmosphere in step (4) is either nitrogen or argon gas, and the gas flow rate is 0.5 to 3 L / min.

[0030] Preferably, the smelting temperature in step (4) is 1450–1550°C, and the smelting time is 30–120 min. The dust collection method is a conventional dust collection method such as gravity dust collection, bag dust collection, or electrostatic dust collection.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. This invention effectively removes sulfur from electroplating sludge through sodium carbonate solution desulfurization, preventing sulfur from entering alloy ingots and reducing their quality. The cost is far lower than current high-temperature desulfurization methods. When silicon-containing materials, waste carbon, and desulfurized electroplating sludge are smelted, the silicon-containing materials not only change the slag structure and effectively lower the slag melting point, but also enhance the reduction of valuable metals in the electroplating sludge, thereby better capturing valuable metals. Waste carbon further reduces valuable metals through gas-liquid / gas-solid reduction, achieving comprehensive and efficient recovery of valuable metals.

[0033] 2. This invention provides a low-cost desulfurization and comprehensive, green, and efficient method for recovering valuable metals from electroplating sludge. It uses a combined wet and pyrometallurgical process to efficiently, safely, and cost-effectively dispose of electroplating sludge, providing a practical and feasible technical route for the resource utilization of electroplating sludge. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0036] 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 mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0037] Example 1

[0038] This embodiment provides a method for recovering valuable metals from electroplating sludge, the preparation process of which is as follows: Figure 1 As shown, the specific steps are as follows:

[0039] (1) After drying a certain electroplating sludge (the main chemical components are shown in Table 1), it was mixed evenly with a 50% mass concentration sodium carbonate solution at a ratio of 1 kg: 15 L, and then stirred at 500 rpm for 120 min at 40℃ for desulfurization.

[0040] Table 1. Main Chemical Composition of Electroplating Sludge

[0041]

[0042] (2) After stirring, dehydration and filtration were carried out. CO2 gas was introduced into the filtrate to crystallize and separate sodium carbonate and sodium sulfate. The filter residue was dried and the chemical composition of the filter residue was tested. The results are shown in Table 2. The desulfurization rate reached 93.39%.

[0043] Table 2 Main chemical composition of filter residue after desulfurization

[0044]

[0045] (3) The dried filter residue was mixed with waste silicon wafers (Si 91.7%) and aluminum electrolysis waste anode carbon (fixed carbon 41%) at a mass ratio of 1:0.1:0.1 and then placed in an electric furnace for heating. The mixture was melted for 60 min at 1500℃ and 1 L / min nitrogen volume flow rate.

[0046] (4) After smelting, the collected flue gas was cooled and electrostatically collected to obtain lead- and zinc-containing flue gas. The slag and alloy ingots were naturally cooled to room temperature. After separating the alloy ingots and slag, the metal content in the slag was tested, and the calculated metal recovery rate is shown in Table 3. Valuable metals in electroplating sludge were recovered efficiently.

[0047] Table 3. Elemental content and recovery rate of smelting slag

[0048]

[0049] Example 2

[0050] (1) After drying a certain electroplating sludge (the main chemical components are shown in Table 1), it was mixed evenly with a 100% mass concentration sodium carbonate solution at a ratio of 1kg:20L, and desulfurized by stirring at 500 rpm for 120 min at 65℃.

[0051] (2) After stirring, dehydration and filtration were carried out. CO2 gas was introduced into the filtrate to crystallize and separate sodium carbonate and sodium sulfate. The filter residue was dried and the chemical composition of the filter residue was tested. The results are shown in Table 4. The desulfurization rate reached 95.21%.

[0052] Table 4 Main Chemical Composition of Filter Residue After Desulfurization

[0053]

[0054] (3) The dried filter residue was mixed with ferrosilicon alloy (Si 75%) and aluminum electrolysis waste cathode carbon (fixed carbon 71.4%) at a mass ratio of 1:0.15:0.05 and then placed in an electric furnace for heating. The mixture was smelted for 120 min at 1550℃ and 1 L / min nitrogen volume flow rate.

[0055] (4) After smelting, the collected flue gas was cooled and electrostatically collected to obtain lead- and zinc-containing flue gas. The slag and alloy ingots were naturally cooled to room temperature. After separating the alloy ingots and slag, the metal content in the slag was tested, and the calculated metal recovery rate is shown in Table 5. Valuable metals in electroplating sludge were recovered efficiently.

[0056] Table 5. Elemental content and recovery rate of smelting slag

[0057]

[0058] Example 3

[0059] (1) After drying a certain electroplating sludge (the main chemical components are shown in Table 1), it was mixed evenly with a 25% mass concentration sodium carbonate solution at a ratio of 1kg:5L, and the mixture was stirred at 100 rpm for 60 minutes at 20℃ for desulfurization.

[0060] (2) After stirring, dehydration and filtration were carried out. CO2 gas was introduced into the filtrate to crystallize and separate sodium carbonate and sodium sulfate. The filter residue was dried and the chemical composition of the filter residue was tested. The results are shown in Table 6. The desulfurization rate reached 82.51%.

[0061] Table 6 Main Chemical Composition of Filter Residue After Desulfurization

[0062]

[0063] (3) The dried filter residue was mixed with industrial silicon slag (Si 18.6%) and waste activated carbon (fixed carbon 76.9%) at a mass ratio of 1:0.30:0.10 and then placed in an electric furnace for heating. The mixture was melted for 30 min at 1450℃ and 0.5 L / min nitrogen volume flow rate.

[0064] (4) After smelting, the collected flue gas was cooled and electrostatically collected to obtain lead- and zinc-containing flue gas. The slag and alloy ingots were naturally cooled to room temperature. After separating the alloy ingots and slag, the metal content in the slag was tested, and the calculated metal recovery rate is shown in Table 7. Valuable metals in electroplating sludge were recovered efficiently.

[0065] Table 7. Elemental Content and Recovery Rate of Smelting Slag

[0066]

[0067] Example 4

[0068] (1) After drying a certain electroplating sludge (the main chemical components are shown in Table 8), it was mixed evenly with a 25% mass concentration sodium carbonate solution at a ratio of 1kg:10L, and the mixture was stirred at 80℃ for 30 minutes at a stirring speed of 500 rpm to carry out desulfurization.

[0069] Table 8 Main Chemical Composition of Electroplating Sludge

[0070]

[0071] (2) After stirring, dehydration and filtration were carried out. CO2 gas was introduced into the filtrate to crystallize and separate sodium carbonate and sodium sulfate. The filter residue was dried and the chemical composition of the filter residue was tested after drying. The results are shown in Table 9. The desulfurization rate reached 90.38%.

[0072] Table 9 Main Chemical Composition of Filter Residue After Desulfurization

[0073]

[0074] (3) The dried filter residue was mixed with waste polycrystalline silicon (Si 89.4%) and coal tar residue (fixed carbon 64.8%) at a mass ratio of 1:0.05:0.2 and then placed in an electric furnace for heating. The mixture was melted for 60 min at 1500℃ and 3 L / min nitrogen volume flow rate.

[0075] (4) After the smelting is completed, the collected flue gas is cooled and electrostatically collected to obtain lead and zinc flue gas. The slag and alloy ingot are naturally cooled to room temperature. After separating the alloy ingot and slag, the metal content in the slag is detected. The calculated metal recovery rate is shown in Table 10.

[0076] Table 10 Elemental Content and Recovery Rate of Smelting Slag

[0077]

[0078] In summary, this invention achieves desulfurization by mixing dried electroplating sludge with a sodium carbonate solution, heating and stirring. The desulfurization filter residue is then dried and mixed evenly with silicon-containing materials and waste carbon. After heating to a set temperature, it is smelted to obtain lead-zinc dust, heavy metal alloy ingots, and harmless slag. The desulfurization rate exceeds 90%, and the valuable metal recovery rate exceeds 95%. This invention enables low-cost desulfurization of electroplating sludge and efficient comprehensive recovery of valuable metal resources. It has the advantages of simple operation, large processing capacity, and strong adaptability, and is of great significance for the resource-based disposal of electroplating sludge.

[0079] The specific embodiments of the invention have been described in detail above, but these are merely examples, and the invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications or substitutions to the invention are also within the scope of this invention. Therefore, all equivalent transformations, modifications, and improvements made without departing from the spirit and principles of this invention should be included within the scope of this invention.

Claims

1. A method for recovering valuable metals from electroplating sludge, characterized in that, Includes the following steps: (1) After mixing the dried electroplating sludge with the desulfurizing agent evenly, heat and stir to obtain a solid-liquid mixture; (2) Filter the solid-liquid mixture from step (1) to obtain filtrate and filter residue; (3) The filtrate from step (2) is crystallized to obtain desulfurizing agent and sodium sulfate crystals, and the filter residue is dried to obtain dried product; (4) Mix the dried material in step (3) with elemental silicon and elemental carbon evenly, and smelt it under an inert atmosphere. After cooling and collecting the dust generated during the smelting process, lead-zinc dust is obtained. After the smelting is completed, the dust is separated after being naturally cooled to room temperature to obtain alloy ingots and slag. The desulfurizing agent mentioned in step (1) is a sodium carbonate solution, and the heating and stirring is to stir at 20-80°C for 30-120 minutes; The sodium carbonate solution has a mass fraction of 25-100%, and the mass-to-volume ratio of the electroplating sludge to the sodium carbonate solution is 1:(5-20)kg / L. The crystallization separation in step (3) involves introducing CO2 gas into the filtrate to crystallize the filtrate; the crystallization is either cooling crystallization or evaporation crystallization. The mass ratio of the dried material, elemental silicon and elemental carbon in step (4) is 1:(0.05-0.30):(0.05-0.20).

2. The method for recovering valuable metals from electroplating sludge according to claim 1, characterized in that, The electroplating sludge is composed of Cu, Ni, Cr, Fe, Pb, Zn, Mn, S, Co, CaO, and SiO2.

3. The method for recovering valuable metals from electroplating sludge according to claim 1, characterized in that, The particle size of elemental silicon and elemental carbon in step (4) is less than 0.15 mm.

4. The method for recovering valuable metals from electroplating sludge according to claim 1, characterized in that, The inert atmosphere mentioned in step (4) is either nitrogen or argon gas, and the gas flow rate is 0.5 to 3 L / min.

5. The method for recovering valuable metals from electroplating sludge according to claim 4, characterized in that, The melting temperature in step (4) is 1450-1550℃ and the melting time is 30-120min.

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