A method and system for recovering valuable metals from tailings

Abstract

The application provides a valuable metal recovery method and system in tailings, and relates to the technical field of metal smelting. The recovery method comprises the following steps: mixing tailings and a chlorinating agent to obtain a material mixture; performing a chlorination reaction on the material mixture to obtain high-temperature roasted material and chlorination flue gas; cooling the high-temperature roasted material, and taking hot air as secondary air; separating and purifying the chlorination flue gas to extract valuable metals, and obtaining a solution containing the chlorinating agent; and performing crystallization treatment to recover the chlorinating agent. The method adopts a burner and microwave cooperative heating, uniformly increases the temperature in the high-temperature section, and prolongs the residence time of the material, thereby preventing ring formation and greatly improving the metal extraction rate. The hot air generated by cooling is reused as secondary air to improve the heat energy utilization rate, and the chlorinating agent is crystallized and recycled to reduce the consumption and cost of the reagent, so that cost reduction and efficiency increase and energy saving and environmental protection are realized.

Description

Technical Field

[0001] This invention relates to the field of metal smelting technology, and more specifically, to a method and system for recovering valuable metals from tailings. Background Technology

[0002] In metal smelting processes, byproducts are inevitably generated, and these byproducts are typically rich in metal elements with recycling value. To achieve efficient resource extraction, chlorination roasting, a typical high-temperature chemical treatment process, is often used to extract valuable metals from raw materials. Its basic principle is to convert the target metal into a gaseous chloride complex and separate it from the bulk material, thereby achieving the separation and enrichment of the metal element from the collected flue gas.

[0003] In existing industrial applications, the chlorination roasting treatment of such materials typically relies on a multi-stage traditional process sequence, such as a process flow consisting of a series of equipment including pelletizing equipment, a chain grate machine, a rotary kiln, and a vertical cooler. After the addition of chlorination reagent, the material sequentially undergoes stages such as low-temperature drying, roasting reaction, and cooling to complete the volatilization of metal elements and subsequent collection.

[0004] However, the aforementioned traditional series process has gradually revealed its limitations during long-term operation. On the one hand, traditional heating and temperature control methods make it difficult to guarantee the effective residence time of materials in the high-temperature section of the calcining kiln, which can easily lead to insufficient internal chlorination reaction and directly affect the final metal extraction efficiency. On the other hand, the cooling and heating stages in conventional processes are often relatively independent, and the large amount of heat energy generated in the system is not properly planned in stages, resulting in low overall heat utilization efficiency. At the same time, reagents added in the process are often discharged with the fluid before fully participating in the reaction, resulting in high reagent consumption.

[0005] In summary, existing chlorination roasting technologies and systems generally suffer from technical defects such as cumbersome process flow, limited control of high-temperature reaction range, serious system heat loss, and low effective utilization rate of additives, and still need further improvement.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for recovering valuable metals from tailings. The method improves the metal extraction rate and prevents ring formation by using burner and microwave co-heating, and combines hot gas recycling and chlorination agent crystallization cycle mechanism to achieve energy-saving, cost-reducing, and environmentally friendly high-efficiency recovery.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a method for recovering valuable metals from tailings, comprising: S1, the tailings containing valuable metals are mixed with a chlorinating agent to obtain a mixture of materials; S2, the material mixture is conveyed to a chlorination roasting kiln for chlorination reaction to obtain high-temperature roasted material and chlorinated flue gas; wherein, the chlorination roasting kiln uses a combination of kiln head burners and microwave to heat the material mixture; S3, the high-temperature roasted material is fed into the cooling rotary kiln, and the high-temperature roasted material is cooled by blowing air into the cooling rotary kiln. The hot air obtained after cooling the high-temperature roasted material is introduced into the chlorination roasting kiln as the secondary air of the kiln head burner. S4, the chlorinated flue gas is separated and purified to extract valuable metals and a solution containing chlorinating agent is obtained; the solution containing chlorinating agent is crystallized to recover the chlorinating agent, and the recovered chlorinating agent is returned to step S1 for recycling.

[0009] In an optional embodiment, in step S2, the temperature of the roasting section inside the chlorination roasting kiln is controlled at 1000℃~1300℃; and / or, In step S2, the residence time of the material mixture in the high-temperature section is 20 min to 60 min.

[0010] In an optional implementation, in step S2, the microwave-assisted method is achieved by a microwave heating device; Preferably, the microwave heating device is arranged at 1 / 6 to 1 / 2 of the discharge end of the chlorination roasting kiln; Preferably, the microwave heating device includes 20 to 200 microwave tube bundles; Preferably, the microwave heating device extends from the kiln head into the interior of the chlorination roasting kiln; Preferably, the heating surface of the microwave heating device is consistent with the curvature of the refractory material of the chlorination roasting kiln.

[0011] In an optional embodiment, the chlorinating agent includes at least one selected from ammonium chloride, sodium chloride, calcium chloride, and magnesium chloride; and / or, The weight of the chlorinating agent added is 5% to 15% of the weight of the tailings to be treated.

[0012] In an optional embodiment, after mixing the tailings with the chlorinating agent in step S1, the mixture is further further subjected to a pelletizing or blistering process to obtain the material mixture.

[0013] In an optional embodiment, in step S3, a portion of the hot air is introduced into the chlorination roasting kiln as secondary air for the kiln head burner, and the remaining portion of the hot air is used as a heat source to heat and concentrate the solution containing the chlorinating agent before the crystallization treatment.

[0014] In an optional embodiment, in step S3, in addition to blowing air into the cooling rotary kiln, a jacket disposed on the outside of the cooling rotary kiln is also used for water cooling; preferably, after the high-temperature roasted material is cooled, the discharge temperature is reduced from 1000℃~1300℃ to 200℃~300℃.

[0015] In an optional embodiment, step S4, which involves separating and purifying the chlorinated flue gas to generate tail gas, further includes a step of desulfurizing and denitrifying the tail gas to achieve emission standards.

[0016] In an optional embodiment, the tailings include at least one of lead-zinc cyanide tailings, pyrite roasting slag, and gold-silver anode mud.

[0017] Secondly, the present invention provides a system for recovering valuable metals from tailings, for implementing the method for recovering valuable metals from tailings as described in any of the foregoing embodiments; the recovery system includes a mixer, a chlorination roasting kiln, a cooling rotary kiln, and a flue gas and solution treatment system; The mixer is used to mix tailings containing valuable metals with a chlorinating agent to obtain a material mixture; The chlorination roasting kiln is connected to the mixer; the chlorination roasting kiln is equipped with a kiln head burner and a microwave heating device, which are used to heat and roast the material mixture in a coordinated manner to obtain high-temperature roasted material and chlorinated flue gas; The cooling rotary kiln is connected to the discharge end of the chlorination roasting kiln; the cooling rotary kiln is equipped with a blower cooling device, and the gas outlet of the cooling rotary kiln is connected to the kiln head of the chlorination roasting kiln and the flue gas and solution treatment system through pipelines respectively, for introducing part of the hot air generated by the blower cooling device into the chlorination roasting kiln as secondary air for the kiln head burners, and introducing the other part into the flue gas and solution treatment system for heating and concentrating the solution containing chlorinating agent. The flue gas and solution treatment system is connected to the flue gas outlet of the chlorination roasting kiln and is used to separate and purify the chlorinated flue gas to extract valuable metals and to crystallize the solution containing chlorinating agent.

[0018] Compared with existing technologies, the recovery method provided by this invention highly integrates material preparation, chlorination reaction, cooling and reheating, and reagent purification, shortening the lengthy process flow of traditional treatment processes and significantly improving overall production efficiency. In the chlorination reaction stage, the use of a combined kiln head burner and microwave heating effectively compensates for the uneven heating disadvantages of a single heat source. Microwave supplementary heating can penetrate the material's interior, making the temperature distribution in the high-temperature section of the calcining kiln more uniform, substantially extending the effective residence time of the material in the high-temperature zone, promoting a more complete chlorination reaction of valuable metals, and significantly improving the volatilization and extraction efficiency of gaseous metal complexes. Simultaneously, microwave supplementary heating effectively reduces the heat load of a single burner, preventing material melting due to excessively high local temperatures, thus preventing ring formation in the rotary kiln.

[0019] During the cooling stage, air is blown into the cooling rotary kiln to exchange heat with the high-temperature roasted material. This not only achieves rapid cooling of the material but also directly returns the high-temperature hot air generated after heat exchange to the chlorination roasting kiln as secondary combustion air for the kiln head burners. This heat recycling mode fully recovers the sensible heat carried by the material, significantly reduces the overall fuel consumption of the system, and effectively alleviates the problems of heat energy waste and low utilization rate in traditional processes.

[0020] In the flue gas and solution treatment stage, the solution remaining after purifying valuable metals is crystallized, enabling the effective extraction and recycling of the internal chlorinating agent. This closed-loop recycling mechanism significantly reduces the amount of fresh chlorinating agent input at the front end, solving the problem of reagent waste caused by incomplete reaction and discharge in traditional processes. While reducing reagent consumption and production costs, it also mitigates the environmental pollution caused by discharged wastewater, improving overall environmental friendliness. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a process flow diagram of the method for recovering valuable metals from tailings provided in the embodiments of this application; Figure 2 This is a schematic diagram of the structure of the tailings valuable metal recovery system provided in the embodiments of this application.

[0023] Explanation of key component symbols: 100 - Recovery system for valuable metals in tailings; 1 - Mixer; 2 - Chlorination roasting kiln; 3 - Cooling rotary kiln; 4 - Flue gas and solution treatment system. Detailed Implementation

[0024] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0025] This application provides a method for recovering valuable metals from tailings. This method achieves efficient recycling of materials and energy by highly correlated and integrated process steps. Please refer to... Figure 1 , Figure 1 This is a process flow diagram of the method for recovering valuable metals from tailings provided in the embodiments of this application. The recovery method includes the following process flow: S1, the tailings containing valuable metals are mixed with a chlorinating agent to obtain a material mixture.

[0026] This step involves material preparation. Specifically, the tailings containing valence metals are mixed with a chlorinating agent to obtain a mixture. This mixing process ensures that the solid tailings particles are fully contacted and uniformly dispersed with the chlorinating agent, thus providing a good material basis for the subsequent chemical reaction at high temperatures. Depending on actual production needs, this mixing process can be completed using mechanical stirring equipment to ensure the uniformity of component distribution.

[0027] S2, the material mixture is transported to a chlorination roasting kiln for chlorination reaction to obtain high-temperature roasted material and chlorinated flue gas; wherein, the chlorination roasting kiln uses a combination of kiln head burners and microwave to heat the material mixture.

[0028] This step is the chlorination roasting step.

[0029] The chlorination roasting process is a high-temperature chemical purification process in which valuable metal elements in the material react with a chlorinating agent and are released from the solid phase as gaseous chlorinated complexes. This reaction process yields high-temperature roasted material with phase change separation and chlorinated flue gas rich in metal elements. During this process, the chlorination roasting kiln uses a combination of kiln head burners and microwaves to heat and control the material mixture. The penetrating heating characteristics of microwaves, combined with the surface radiation heating of the burners, effectively improve the temperature gradient of the material within the kiln. This synergistic heating mode results in more uniform heating of the material, not only extending the effective residence time of the material in the high-temperature section to promote complete chlorination, but also rationally distributing the load on the burners. This effectively prevents the material from melting due to excessively high local temperatures, thus avoiding the problem of ring formation in the rotary kiln and significantly improving the volatilization and extraction efficiency of valuable elements.

[0030] S3, the high-temperature roasted material is fed into the cooling rotary kiln, and the high-temperature roasted material is cooled by blowing air into the cooling rotary kiln. The hot air obtained after cooling the high-temperature roasted material is introduced into the chlorination roasting kiln as the secondary air for the kiln head burner.

[0031] The next step involves cooling and heat recovery. The high-temperature roasted material produced after the chlorination reaction is fed into a cooling rotary kiln. Air is continuously blown into this kiln, utilizing gas-solid heat exchange to cool the material. Simultaneously, the ambient air absorbs the sensible heat from the material and becomes hot air. This hot air, obtained after cooling the high-temperature roasted material, is then piped into the chlorination roasting kiln and used directly as secondary combustion air for the kiln head burners. This step internally recovers and reuses the heat energy that would otherwise be lost with the high-temperature material, significantly improving the system's thermal efficiency and reducing energy consumption.

[0032] S4, the chlorinated flue gas is separated and purified to extract valuable metals and a solution containing chlorinating agent is obtained; the solution containing chlorinating agent is crystallized to recover the chlorinating agent, and the recovered chlorinating agent is returned to step S1 for recycling.

[0033] Finally, a flue gas treatment and reagent recycling step is performed. The aforementioned volatilized chlorinated flue gas is separated and purified to extract valuable metals in a cascade manner. During this process, a solution containing excess or unreacted chlorinating agent is obtained. To reduce production costs and emissions, the solution containing chlorinating agent is crystallized (e.g., by evaporation crystallization) to precipitate and recover the chlorinating agent. The recovered chlorinating agent is then returned to the initial material preparation step for recycling. This closed-loop recycling mechanism significantly improves the utilization rate of the chlorinating agent, avoids waste caused by reagent discharge with the fluid, and achieves a balance between economic efficiency and environmental protection in the production process.

[0034] In summary, this method significantly improves production efficiency through a highly integrated process flow, effectively solving the technological challenges of powder ring formation and cooling difficulties in rotary kilns. Specifically, the use of kiln head burners in conjunction with microwave heating results in a more uniform temperature distribution in the high-temperature zone and extends the residence time of materials in this zone. This not only prevents material melting and ring formation caused by localized high temperatures but also promotes a more complete chlorination reaction, significantly increasing the extraction and volatilization rate of valuable metals. Simultaneously, utilizing the hot air generated by the air blown into the cooling rotary kiln as secondary air for the burners enables internal cascade recovery of heat energy, significantly improving heat utilization. Furthermore, the crystallization and recycling of the chlorinating agent solution back into the system greatly reduces the consumption of fresh reagents, saving production costs while enhancing the overall environmental friendliness of the process.

[0035] In the specific implementation process, in order to ensure the thermodynamic and kinetic conditions of the chlorination reaction and achieve efficient extraction of metal elements, the process parameters in the chlorination roasting kiln were strictly controlled in step S2.

[0036] In some embodiments, in step S2, the temperature of the roasting section inside the chlorination roasting kiln is controlled at 1000℃~1300℃.

[0037] The "roasting section" mentioned here refers to the main temperature zone inside the kiln where the materials undergo vigorous chlorination and volatilization reactions. Setting the lower temperature limit to 1000℃ provides the necessary activation energy and volatilization conditions for the valuable metals in the material (such as gold, silver, copper, zinc, etc.) to react chemically with the chlorinating agent and generate gaseous chlorinated complexes, ensuring the reaction can start and proceed rapidly. Setting the upper temperature limit to 1300℃ prevents excessively high temperatures inside the kiln from causing large-scale softening or melting of the material, thus avoiding adhesion or ring formation on the kiln wall, while also considering reasonable energy consumption and the service life of the equipment's refractory materials. In some specific production scenarios, the temperature of this roasting section can be, for example, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, etc., which can be specifically selected by technicians based on the actual physicochemical properties of the tailings.

[0038] In some embodiments, in step S2, the residence time of the material mixture in the high-temperature section is 20 min to 60 min.

[0039] The "high-temperature section" typically corresponds to the aforementioned roasting section. Due to the kinetic limitations of the chlorination reaction, a certain mass and heat transfer time is required for the reaction to penetrate from the surface of the material particles to their interior. Controlling the residence time to over 20 minutes ensures sufficient contact and reaction time between the chlorinating agent and the metal elements within the material, effectively overcoming the problems of incomplete reaction and low extraction rate caused by short residence times in conventional treatments. It also significantly reduces the sulfur and chlorine content in the final slag, optimizing its physicochemical properties. Conversely, setting the upper limit at 60 minutes ensures complete reaction while preventing excessive material retention in the kiln, thus maintaining high continuous production efficiency and throughput for the entire system. In practice, this residence time can be, for example, 20, 25, 30, 35, 40, 45, 50, 55, or 60 minutes, and can be achieved through conventional methods such as adjusting the kiln speed or tilt angle.

[0040] In some implementations, in step S2, the microwave-assisted method is achieved by a microwave heating device; The discharge end of a chlorination roasting kiln typically corresponds to the high-temperature reaction zone where the main heater is located. Precisely positioning the microwave heating device within this zone allows for secondary homogenization during the critical stage when the material reaction is most intense and is about to be discharged. This targeted heating substantially extends the effective residence time of the material in the high-temperature zone, thereby greatly promoting the chlorination volatilization rate of metal elements and helping to significantly reduce the residual sulfur and chlorine levels in the tailings.

[0041] Furthermore, the microwave heating device is arranged at 1 / 6 to 1 / 2 of the discharge end of the chlorination roasting kiln.

[0042] In actual engineering layout, the installation position can be, for example, 1 / 6, 1 / 5, 1 / 4, 3 / 10, 1 / 3, 2 / 5, 9 / 20, 1 / 2, etc. at the discharge end, and can be optimized and adjusted according to the thermal conductivity characteristics of the specific material.

[0043] Furthermore, to ensure sufficient auxiliary heating power and effective thermal matching with the main burner, the microwave heating equipment includes 20 to 200 microwave tube bundles. A reasonable number of microwave tube bundles not only effectively reduces the heat load on the main burner but also makes the temperature field distribution in the high-temperature section smoother, preventing material melting and ring formation due to excessive local heating. In different production line capacity designs, the number of microwave tube bundles can be, for example, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, etc.

[0044] Furthermore, the microwave heating device extends from the kiln head into the interior of the chlorination roasting kiln; Furthermore, the heating surface of the microwave heating device is consistent with the curvature of the refractory material of the chlorination roasting kiln.

[0045] In terms of structural installation, the microwave heating equipment is assembled by extending from the kiln head into the interior of the chlorination roasting kiln. This protruding structure effectively shortens the distance between the microwave source and the material bed, improving the transmission efficiency of electromagnetic energy. Furthermore, the heating surface of the microwave heating equipment is designed to match the curvature of the refractory material of the chlorination roasting kiln's cylinder. This contoured curved surface design not only ensures the uniformity of microwave radiation on the material surface but also minimizes physical obstruction to the normal tumbling and forward flow of materials within the kiln, ensuring a smooth production process.

[0046] In some embodiments, the chlorinating agent includes at least one selected from ammonium chloride, sodium chloride, calcium chloride, and magnesium chloride.

[0047] Under the subsequent high-temperature roasting environment, the aforementioned preferred chlorinating agent can stably decompose and release sufficient chlorine, which then undergoes a chemical complexation reaction with valuable metals such as gold, silver, copper, and zinc present in the tailings matrix. This process promotes the conversion of these metals into volatile gaseous metal chlorides, thereby achieving efficient separation from the solid matrix. Using the specific chlorides mentioned above as reaction reagents not only ensures extremely high chlorination volatilization efficiency of valuable elements, but also effectively improves and optimizes the chemical composition of the final discharged slag by allowing the reagents to remain in the roasted material after the reaction. This significantly enhances the secondary utilization properties of the tailings or their economic added value from direct sale.

[0048] In some alternative embodiments, the chlorinating agent may also include ferric chloride. Elements such as calcium, magnesium, sodium, and iron remaining in the roasted material after the reagents participate in the reaction can effectively improve and optimize the chemical composition of the final discharged slag. For example, the introduction of iron can further enhance the added value of the tailings as a raw material for ironmaking or as a component of building materials.

[0049] In some embodiments, the weight of the chlorinating agent added is 5% to 15% of the weight of the tailings to be treated.

[0050] The addition ratio range is determined based on a comprehensive consideration of chemical reaction kinetics and the economics of large-scale production. When the amount of chlorinating agent added reaches 5% or more of the tailings weight, it can provide sufficient chlorine atoms for the entire mixture system to react, effectively avoiding the problems of incomplete conversion of valuable metals and low volatilization extraction rate due to reagent shortage. Controlling the upper limit of addition to 15% ensures that the target valuable metals have fully and completely reacted, while avoiding the ineffective input of excessive reaction reagents. Excessive chlorinating agent not only increases the procurement cost of upstream consumables, but also significantly increases the operating load of subsequent washing, solution concentration, and crystallization equipment after a large amount of unreacted reagent enters the downstream circulation system with the flue gas. In actual engineering formulation, the weight ratio of the added chlorinating agent can be, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 14%, 15%, etc. Technicians can flexibly optimize the ratio according to the specific grade, occurrence state, and physical properties of the valuable metals in the tailings to be treated.

[0051] In some more preferred implementation scenarios, in order to further optimize the gas-solid reaction kinetics conditions inside the kiln and improve the hydrodynamic properties of the material, after mixing the tailings with the chlorinating agent in step S1, the mixture is further subjected to a pelletizing or blistering process to obtain the material mixture.

[0052] Typically, tailings from metal smelting are in the form of loose, fine-particle powder. If such fine powder mixtures are directly fed into a large-scale chlorination roasting kiln, they are easily blown away by the high-temperature airflow inside the kiln. This not only increases unnecessary material loss and the operating load of the downstream flue gas dust removal system, but also the poor permeability of the material bed formed by the powdery material piled up inside the kiln will severely hinder the transfer of external heat to the inside and the outward diffusion and volatilization of gaseous metal chlorides generated in the internal reaction.

[0053] By incorporating pelleting or briquetting processes, fine powder is molded into pellets or lumps with specific physical particle size and structural strength through mechanical extrusion or agglomeration. This change in physical morphology allows for the formation of abundant macroscopic voids within the material bed after the material enters the chlorination roasting kiln, significantly improving the permeability of the entire material system. This not only enables heat energy (including microwave and open flame heat radiation) to penetrate the material layer more efficiently and uniformly, providing sufficient thermodynamic conditions for the internal chlorination reaction, but also provides unobstructed diffusion channels for the smooth escape of metal chloride gases, thereby significantly improving the extraction efficiency of valuable metals. Furthermore, the regular material shape resulting from pelleting or briquetting processes is well-suited to the operating conditions of the subsequent cooling rotary kiln. This cooling equipment exhibits excellent compatibility in handling the cooling of pellets and lumpy materials, ensuring efficient connection between upstream and downstream processes and stable operation of the entire system.

[0054] In some implementations, to achieve efficient cascade recovery of internal heat energy, this method scientifically plans the route of the hot airflow generated within the system. Specifically, in the cooling and heat recovery steps, the ambient temperature air blown into the cooling rotary kiln absorbs a large amount of sensible heat carried by the high-temperature roasting material after heat exchange with it, thus transforming into high-temperature hot air.

[0055] Specifically, in step S3, a portion of the hot air is introduced into the chlorination roasting kiln as secondary air for the kiln head burner, and the remaining portion of the hot air is used as a heat source to heat and concentrate the solution containing the chlorinating agent before the crystallization process.

[0056] This process utilizes this portion of hot air in a multi-stage, diverted manner. First, a portion of the hot air is introduced into the chlorination roasting kiln via a induced draft fan and directly serves as secondary air for the kiln head burners. Since this portion of air already possesses a high preheated temperature, using it as combustion air to participate in the combustion of fuel at the kiln head significantly increases the initial enthalpy of combustion and the flame temperature. This effectively reduces the fuel consumption required to maintain the high-temperature environment inside the kiln, greatly improving the system's thermal efficiency and reducing energy consumption.

[0057] Furthermore, considering that the amount of high-temperature hot air generated by cooling under normal operating conditions is greater than the secondary air volume required by the burner, and that a large amount of heat energy is consumed in the subsequent evaporation and crystallization recovery of chloride from the solution, this process uses the remaining portion of the hot air as a heat source and directs it to the subsequent solution treatment process. Specifically, this remaining hot air is used to heat and concentrate the chlorinating agent-containing solution generated after purifying valuable metals before the crystallization process. By utilizing the system's excess waste heat for pre-evaporation and dehydration treatment of the lower-concentration chlorinating agent solution, not only is the residual calorific value of the hot air fully utilized, achieving tiered heat utilization, but the time required for the solution to reach saturation crystallization is also effectively shortened. This significantly reduces the crystallization process's dependence on external industrial steam or electricity, further improving the overall system's process integration and significantly controlling operating costs.

[0058] In more specific industrial implementation scenarios, in order to achieve efficient and stable cooling of high-temperature reaction products, a composite cooling process is adopted in the cooling and heat recovery steps.

[0059] Specifically, in step S3, in addition to blowing air into the cooling rotary kiln, a jacket located on the outside of the cooling rotary kiln is also used for water cooling.

[0060] Single-mode air cooling often requires extremely high ventilation volumes to achieve rapid cooling due to the low specific heat capacity of air. This can easily lead to severe material loss (especially powdery or fine-particle materials) within the rotary kiln. In this embodiment, a water-cooled jacket is added to the outside of the rotary kiln. Utilizing the extremely high specific heat capacity of water, the high heat transferred from the material to the kiln body is rapidly carried away. The combined effect of internal air cooling and external jacket water cooling significantly improves overall cooling efficiency and effectively controls the ventilation rate within the kiln to stabilize the material bed. Furthermore, the external jacket water cooling greatly reduces the operating temperature of the rotary kiln's metal shell, alleviating thermal stress and extending the equipment's service life.

[0061] Furthermore, after cooling, the discharge temperature of the high-temperature roasted material is reduced from 1000℃~1300℃ to 200℃~300℃.

[0062] Through the aforementioned air-water composite cooling system, the temperature of the high-temperature roasted material is rapidly and controllably reduced. In actual operation, the initial temperature of the high-temperature roasted material entering the cooling rotary kiln is typically in the high-temperature range of 1000℃ to 1300℃ (e.g., 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, etc.). After cooling, the discharge temperature of the material is effectively controlled and reduced to 200℃ to 300℃ (e.g., 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 300℃, etc.). Setting the discharge temperature within this range avoids blindly extending the size of the cooling equipment and increasing equipment investment in pursuit of ambient temperature discharge, while ensuring the stability of the material properties after cooling, fully meeting the operational safety requirements for subsequent industrial storage, short-distance transportation, or direct loading for sale.

[0063] In the subsequent exhaust emission stage, in order to ensure the environmental friendliness of the entire production system and comply with strict industrial emission standards, non-condensable exhaust gas will be separated during the separation and purification of the chlorinated flue gas to extract valuable metals in the flue gas treatment and reagent circulation steps. This embodiment also includes a step of desulfurization and denitrification treatment of the exhaust gas to ultimately achieve emission standards.

[0064] Specifically, in step S4, the process of separating and purifying the chlorinated flue gas generates tail gas, and the process also includes a step of desulfurizing and denitrifying the tail gas to achieve emission standards.

[0065] It should be noted that under actual high-temperature roasting conditions, the tailings raw material usually contains a certain amount of sulfur impurities (e.g., when processing pyrite roasting slag). These sulfur elements are easily converted into sulfur oxide gases during high-temperature reactions. Furthermore, during high-temperature combustion at the kiln head burner, nitrogen elements in the combustion system are readily oxidized to generate nitrogen oxide gases at high temperatures. After the chlorination flue gas undergoes the preceding valuable metal extraction and separation, the aforementioned acidic and polluting gases, such as sulfur oxides and nitrogen oxides, will enter the final tail gas system with the gas flow. Directly releasing this tail gas into the atmosphere will cause serious secondary environmental pollution.

[0066] Therefore, by adding desulfurization and denitrification treatment processes at the exhaust end, pollutants in the exhaust gas can be deeply removed. In specific implementation, appropriate environmental protection facilities can be configured according to the actual concentration of pollutants in the exhaust gas. For example, desulfurization can employ a wet scrubbing process using alkaline absorbents, causing sulfur oxides in the exhaust gas to undergo an acid-base neutralization reaction and be absorbed; denitrification can employ conventional technologies such as selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR) to reduce nitrogen oxides in the exhaust gas into harmless nitrogen and water. After the above-mentioned desulfurization and denitrification purification treatment, the exhaust gas, free of toxic and harmful substances, can stably meet air pollutant emission standards, thus ensuring the high environmental friendliness and social benefits of the entire process while achieving efficient refining of valuable metals and reagent recycling.

[0067] In specific industrial applications, to achieve the resource utilization of large quantities of complex metallurgical solid waste, this embodiment optimizes and defines the types of tailings fed into the plant. Specifically, the tailings include at least one of lead-zinc cyanide tailings, pyrite roasting slag, and gold- and silver-containing anode slime.

[0068] The above three types of materials are typical difficult-to-treat, high-value-added associated solid wastes in the metallurgical and chemical industries. Among them, lead-zinc cyanide tailings usually come from the waste products of conventional cyanide gold extraction processes. Due to the fine size of some precious metal particles or their dense encapsulation by gangue minerals such as sulfides and silicates, conventional processes cannot further extract them, and the associated lead and zinc elements have high recovery value. Pyrite roasting slag is a common by-product of the sulfuric acid production industry, and it often contains unreacted sulfur elements and trace amounts of non-ferrous metals such as copper, gold, and silver. Gold and silver anode mud is a by-product enriched and settled during the electrolytic refining of crude metals, and it is a secondary resource with extremely high precious metal content.

[0069] These materials share the common characteristics of complex composition and stable occurrence of valuable elements. Using them as the recovery targets in this embodiment fully leverages the advantages of this high-temperature chlorination roasting process. In the chlorination reaction system, the added chlorinating agent effectively disrupts the mineral lattice matrix of these complex tailings, transforming previously difficult-to-dissociate valuable elements such as gold, silver, copper, and zinc into volatile gaseous complexes. Treating these typical rich ore tailings, individually or in combination, as raw materials not only effectively processes and utilizes these land-consuming and environmentally hazardous industrial wastes but also allows for the deep extraction of high-value precious and non-ferrous metal resources, realizing the transformation from "difficult-to-treat solid waste" to "high-value-added products," demonstrating outstanding industrial practicality and socio-economic benefits.

[0070] To implement the aforementioned process flow, this embodiment also provides a highly integrated system for recovering valuable metals from tailings, referencing... Figure 2 , Figure 2This is a schematic diagram of the structure of the tailings valuable metal recovery system provided in the embodiments of this application. The system is used to implement the tailings valuable metal recovery method as described above. The recovery system includes a mixer, a chlorination roasting kiln, a cooling rotary kiln, and a flue gas and solution treatment system.

[0071] The mixer is used to mix tailings containing valuable metals with a chlorinating agent to obtain a material mixture.

[0072] A chlorination roasting kiln is connected to the mixing machine; the chlorination roasting kiln is equipped with a kiln head burner and a microwave heating device, which are used to heat and roast the material mixture in a coordinated manner to obtain high-temperature roasted material and chlorinated flue gas.

[0073] Furthermore, in order to ensure the long-term stable operation of the equipment and achieve precise temperature control, the chlorination roasting kiln can also be equipped with a wireless temperature measurement system to monitor the temperature field distribution inside the kiln in real time, as well as a centralized lubrication system including oil stations, pipelines and nozzles to ensure the mechanical life of the massive cylinder transmission device.

[0074] A cooling rotary kiln is connected to the discharge end of the chlorination roasting kiln. The cooling rotary kiln is equipped with a blower cooling device, and the gas outlet of the cooling rotary kiln is connected to the kiln head of the chlorination roasting kiln and the flue gas and solution treatment system through pipelines. The hot air generated by the blower cooling device is introduced into the chlorination roasting kiln as secondary air for the kiln head burners, and the other part is introduced into the flue gas and solution treatment system for heating and concentrating the solution containing chlorinating agent. A flue gas and solution treatment system is connected to the flue gas outlet of the chlorination roasting kiln and is used to separate and purify the chlorinated flue gas to extract valuable metals and to crystallize the solution containing chlorinating agent.

[0075] At the front end of the system, a mixer is installed. This mixer uses a mechanical stirring device to uniformly mix the input tailings containing valuable metals with the chlorinating agent, obtaining a material mixture with uniform texture and composition, thereby providing favorable reaction kinetic conditions for subsequent thermochemical reactions.

[0076] The discharge port of the mixer is connected to the feed port of the chlorination roasting kiln, and the mixed material is fed into the kiln by a conveying device. The chlorination roasting kiln is the core reaction equipment of this system, and its special feature is that it is equipped with both a kiln head burner and a microwave heating device. During operation, the kiln head burner provides open flame radiation heating, while the microwave heating device emits electromagnetic waves to penetrate deep into the material for volumetric heating (i.e., the material as a whole is heated synchronously from the inside out). These two devices complement each other in terms of heating mechanism, enabling the material mixture to achieve uniform and efficient heating and roasting in the kiln, effectively overcoming the problem of local melting and ring formation of materials that is easily caused by traditional single heat sources, and ultimately smoothly obtaining solid-phase high-temperature roasted material and gaseous chlorinated flue gas rich in target metals.

[0077] Downstream of the chlorination roasting kiln, the discharge end of the chlorination roasting kiln is connected to the feed end of the cooling rotary kiln, receiving high-temperature roasting materials at thousands of degrees Celsius. The cooling rotary kiln is equipped with a forced-air cooling device, which blows cold air into the rotating kiln body, causing intense heat exchange between the gas and solid phases. The air absorbs heat and transforms into high-temperature hot air. To achieve large-scale heat recovery at the system level, the gas outlet of the cooling rotary kiln is configured with a dual-loop diversion structure through a scientific pipeline layout: the gas outlet pipelines are connected to both the kiln head of the chlorination roasting kiln and the flue gas and solution treatment system. Through this pipeline system, the hot air generated by the forced-air cooling device is divided into two parts: one part of the hot air is introduced into the chlorination roasting kiln and directly used as secondary air (combustion air) for the kiln head burners, thereby improving combustion thermal efficiency and saving fresh fuel; the remaining hot air is introduced into the flue gas and solution treatment system, where its waste heat is used as a heat source to heat and concentrate the purified solution containing chlorinating agents.

[0078] At the other end of the gas path, the flue gas outlet of the chlorination roasting kiln is connected to the flue gas and solution treatment system. This system receives metal-rich chlorinated flue gas and extracts valuable metal products through internal separation and purification units such as condensation, washing, or extraction. After purifying the valuable metals, the remaining solution containing chlorinating agent in the system is pre-concentrated after absorbing the residual hot air from the aforementioned cooling rotary kiln, and further crystallized to precipitate solid chlorinating agent. This terminal treatment system not only achieves efficient monetization of metal resources but also establishes a closed-loop recycling channel for the reagents within the system, giving the entire recovery system excellent economic efficiency and environmental friendliness.

[0079] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0080] Example 1 This embodiment provides a method for recovering valuable metals from tailings, the specific steps of which are as follows: S1 Material Preparation: Lead-zinc cyanide tailings from a smelter were selected as raw materials; calcium chloride was selected as the chlorinating agent. Calcium chloride was weighed at 10% of the weight of the tailings to be treated and thoroughly mixed with the tailings in a mixer; subsequently, an appropriate amount of water was sprayed onto the mixed powder and pelletized in a disc pelletizer to obtain material mixture pellets.

[0081] S2 Chlorination Roasting: The above-mentioned material mixture pellets are conveyed to a chlorination roasting kiln equipped with microwave-assisted heating for chlorination reaction. The microwave heating equipment is located at 1 / 3 of the discharge end of the chlorination roasting kiln and includes 100 sets of microwave tubes. Its heating surface is aligned with the curvature of the refractory material in the kiln body and extends deep into the kiln head. The power of the kiln head burners and the microwave equipment is adjusted to stabilize the temperature of the roasting section within the chlorination roasting kiln at 1150℃. The residence time of the material mixture in the high-temperature section is maintained at 40 minutes by adjusting the rotary kiln speed. The reaction yields high-temperature roasted material and chlorinated flue gas rich in elements such as gold, silver, and zinc.

[0082] S3 Cooling and Heat Recovery: The high-temperature roasted material at 1150℃ is fed into the cooling rotary kiln. The jacketed water cooling system on the outside of the cooling rotary kiln is activated, and ambient temperature air is simultaneously blown into the rotary kiln to cool the material, reducing the discharge temperature to 250℃ before it is discharged and stored. The blown-in air absorbs the sensible heat of the material and becomes high-temperature hot air. Approximately 60% of this hot air is introduced into the chlorination roasting kiln as secondary air (combustion air) for the kiln head burners, and the remaining approximately 40% of the hot air is sent to the subsequent solution treatment system.

[0083] S4 Flue Gas Treatment and Reagent Recycling: The chlorinated flue gas generated in step S2 is introduced into the separation and purification system. After rapid cooling and multi-stage washing, valuable metal products such as gold, silver, and zinc are extracted, and a solution containing excess calcium chloride is obtained. The solution is heated and concentrated using the residual hot air from step S3, and then sent to an evaporator crystallizer to precipitate calcium chloride crystals. The recovered calcium chloride is returned to step S1 for recycling. Finally, the tail gas is treated with limestone-gypsum desulfurization and SCR denitrification to meet emission standards.

[0084] The specific steps in the following embodiments are basically the same as those in Embodiment 1, except that some core parameters or raw materials have been replaced: Example 2: The difference from Example 1 is that in step S2, the temperature of the roasting section in the chlorination roasting kiln is controlled at 1000℃.

[0085] Example 3: The difference from Example 1 is that in step S2, the temperature of the roasting section in the chlorination roasting kiln is controlled at 1300℃.

[0086] Example 4: The difference from Example 1 is that in step S2, the residence time of the material in the high-temperature section is controlled to be 20 minutes.

[0087] Example 5: The difference from Example 1 is that in step S2, the residence time of the material in the high-temperature section is controlled to be 60 minutes.

[0088] Example 6: The difference from Example 1 is that in step S1, the weight of calcium chloride added is 5% of the weight of the tailings to be treated.

[0089] Example 7: The difference from Example 1 is that in step S1, the weight of calcium chloride added is 15% of the weight of the tailings to be treated.

[0090] Example 8: The difference from Example 1 is that in step S1, the raw material is replaced with pyrite roasting slag, and the chlorinating agent is replaced with a mixture of equal weights of sodium chloride and magnesium chloride (the amount added is still 10%).

[0091] To further verify the technical effects achieved by synergistic heating and waste heat recovery in the technical solution of this application, the following comparative examples are set up: Comparative Example 1: The difference from Example 1 is that the microwave heating equipment was turned off, and heating was carried out solely by the kiln head burner. In order to barely maintain the reaction temperature of 1150°C inside the material, the fuel supply to the burner had to be significantly increased, and the residence time in the high-temperature zone was short.

[0092] Comparative Example 2: The difference from Example 1 is that the air pipeline connection between the cooling rotary kiln and the calcining kiln and concentration equipment is disconnected. That is, the hot air generated by the forced-air cooling is directly vented, ambient temperature air is used as secondary air for the kiln head burners, and the solution containing calcium chloride is concentrated using externally purchased industrial steam.

[0093] Comparative Example 3: The difference from Example 1 is that in step S2, the temperature of the roasting section in the chlorination roasting kiln is controlled at 850°C.

[0094] Comparative Example 4: The difference from Example 1 is that in step S2, the residence time of the material in the high-temperature section is controlled to be 10 minutes.

[0095] Performance Test Experiment and Result Analysis Table 1. Test Method Description: Sampling was performed on the tailings from the above embodiments and comparative examples. The residual gold, silver, and zinc content in the tailings was determined using aqua regia dissolution-atomic absorption spectrometry, and the volatilization rate was calculated (volatilization rate = 1 - residual amount in tailings / total content of original tailings). Simultaneously, the ring formation on the inner wall of the rotary kiln and the overall energy consumption of the system (converted to standard coal equivalent) were monitored during 168 hours of continuous operation.

[0096] Table 1. Comparison of Test Results

[0097] 2. Results and Analysis: Comparing Example 1 with Comparative Example 1, it can be seen that the combined heating of microwave and burner can achieve uniform heating of the material inside and out. This not only significantly increases the gold volatilization rate from 83.5% to 92.2%, but more importantly, it avoids the phenomenon of localized material melting and ring formation caused by overheating of a single burner.

[0098] Comparing Example 1 and Comparative Example 2, it can be seen that, with comparable extraction rates, Example 1, through its innovative hot air pipeline reuse design (secondary air combustion + solution preheating and concentration), significantly reduced the overall system energy consumption from 65 kgce to 30 kgce, achieving an extremely remarkable energy-saving effect.

[0099] Data from Examples 1-7 show that as long as the process parameters fluctuate within the range defined in the aforementioned technical solution or the numerical range used in the examples, excellent metal extraction results can be achieved. Comparative Examples 3 and 4 demonstrate that if the temperature or time is below the defined lower limit, the chlorination reaction kinetics are insufficient, and the volatilization rate will drop sharply.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recovering valuable metals from tailings, characterized in that, include: S1, the tailings containing valuable metals are mixed with a chlorinating agent to obtain a mixture of materials; S2, the material mixture is conveyed to a chlorination roasting kiln for chlorination reaction to obtain high-temperature roasted material and chlorinated flue gas; wherein, the chlorination roasting kiln uses a combination of kiln head burners and microwave to heat the material mixture; S3, the high-temperature roasted material is fed into the cooling rotary kiln, and the high-temperature roasted material is cooled by blowing air into the cooling rotary kiln. The hot air obtained after cooling the high-temperature roasted material is introduced into the chlorination roasting kiln as the secondary air of the kiln head burner. S4, the chlorinated flue gas is separated and purified to extract valuable metals and a solution containing chlorinating agent is obtained; the solution containing chlorinating agent is crystallized to recover the chlorinating agent, and the recovered chlorinating agent is returned to step S1 for recycling.

2. The method for recovering valuable metals from tailings as described in claim 1, characterized in that, In step S2, the temperature of the roasting section inside the chlorination roasting kiln is controlled at 1000℃~1300℃; and / or, In step S2, the residence time of the material mixture in the high-temperature section is 20 min to 60 min.

3. The method for recovering valuable metals from tailings as described in claim 1, characterized in that, In step S2, the microwave-assisted method is implemented using a microwave heating device; Preferably, the microwave heating device is arranged at 1 / 6 to 1 / 2 of the discharge end of the chlorination roasting kiln; Preferably, the microwave heating device includes 20 to 200 microwave tube bundles; Preferably, the microwave heating device extends from the kiln head into the interior of the chlorination roasting kiln; Preferably, the heating surface of the microwave heating device is consistent with the curvature of the refractory material of the chlorination roasting kiln.

4. The method for recovering valuable metals from tailings as described in claim 1, characterized in that, The chlorinating agent includes at least one selected from ammonium chloride, sodium chloride, calcium chloride, and magnesium chloride; and / or, The weight of the chlorinating agent added is 5% to 15% of the weight of the tailings to be treated.

5. The method for recovering valuable metals from tailings as described in claim 1, characterized in that, In step S1, after mixing the tailings with the chlorinating agent, the mixture is further subjected to pelletizing or blistering to obtain the material mixture.

6. The method for recovering valuable metals from tailings as described in claim 1, characterized in that, In step S3, a portion of the hot air is introduced into the chlorination roasting kiln as secondary air for the kiln head burner, and the remaining portion of the hot air is used as a heat source to heat and concentrate the solution containing the chlorinating agent before the crystallization process.

7. The method for recovering valuable metals from tailings as described in claim 1, characterized in that, In step S3, in addition to blowing air into the cooling rotary kiln, a jacket located on the outside of the cooling rotary kiln is also used for water cooling; preferably, after cooling, the discharge temperature of the high-temperature roasted material is reduced from 1000℃~1300℃ to 200℃~300℃.

8. The method for recovering valuable metals from tailings as described in claim 1, characterized in that, In step S4, the process of separating and purifying the chlorinated flue gas generates tail gas, and the process also includes a step of desulfurizing and denitrifying the tail gas to achieve emission standards.

9. The method for recovering valuable metals from tailings as described in claim 1, characterized in that, The tailings include at least one of lead-zinc cyanide tailings, pyrite roasting slag, and gold-silver anode mud.

10. A system for recovering valuable metals from tailings, characterized in that, A method for recovering valuable metals from tailings as described in any one of claims 1-8, the recovery system comprising a mixer, a chlorination roasting kiln, a cooling rotary kiln, and a flue gas and solution treatment system; The mixer is used to mix tailings containing valuable metals with a chlorinating agent to obtain a material mixture; The chlorination roasting kiln is connected to the mixer; the chlorination roasting kiln is equipped with a kiln head burner and a microwave heating device, which are used to heat and roast the material mixture in a coordinated manner to obtain high-temperature roasted material and chlorinated flue gas; The cooling rotary kiln is connected to the discharge end of the chlorination roasting kiln; the cooling rotary kiln is equipped with a blower cooling device, and the gas outlet of the cooling rotary kiln is connected to the kiln head of the chlorination roasting kiln and the flue gas and solution treatment system through pipelines respectively, for introducing part of the hot air generated by the blower cooling device into the chlorination roasting kiln as secondary air for the kiln head burners, and introducing the other part into the flue gas and solution treatment system for heating and concentrating the solution containing chlorinating agent. The flue gas and solution treatment system is connected to the flue gas outlet of the chlorination roasting kiln and is used to separate and purify the chlorinated flue gas to extract valuable metals and to crystallize the solution containing chlorinating agent.

Images