Method for treating solid waste containing lead and arsenic

Abstract

The invention discloses a treatment method of lead-arsenic-containing solid waste, which realizes efficient directional fixation of arsenic in arsenic-containing smelting waste (fixation rate gt; 95%) and the synchronous high-grade recovery of valuable metals (the purity of lead bullion is gt; the lead recovery rate is 93.11%, and the lead recovery rate is 98.7%. The invention discloses a double action mechanism of chemical stirring effect and viscosity effect of coke in a system, and solves the technical problem that high metal recovery rate is inevitably accompanied by high pollution risk in the traditional technology through accurate control of a coke addition amount window. According to the method, complex pretreatment such as pre-roasting is not needed, all-component resource utilization of the multi-source arsenic-containing waste can be achieved through a one-step method, the generated iron-rich sulfonium phase can serve as a weighting material to be sold, lead bullion can directly enter the refining procedure, the ton treatment cost is remarkably reduced, and technical support is provided for green and sustainable development of the non-ferrous metal smelting industry.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, specifically to a method for treating lead- and arsenic-containing solid waste. Background Technology

[0002] Arsenic-containing solid wastes generated from the non-ferrous metal smelting industry, such as lead sludge, smelting dust, and leaching residues, have become a global environmental challenge due to their high toxicity, complex migration and transformation characteristics, and long-term environmental risks. Currently, pyrometallurgy and hydrometallurgy are the main methods for treating these hazardous wastes, but both have significant drawbacks in practical applications. Pyrometallurgical roasting for arsenic removal often results in incomplete arsenic removal under high-temperature conditions, making it difficult to meet increasingly stringent environmental standards. Furthermore, it easily generates arsenic-containing fumes, which can cause serious secondary pollution if not properly treated. While hydrometallurgical methods can mitigate secondary pollution to some extent, they generally suffer from complex processes, high consumption of chemical reagents, high operating costs, and the generation of difficult-to-treat high-salt heavy metal wastewater, severely limiting their economic feasibility.

[0003] In the field of resource utilization of arsenic-containing smelting waste, existing technologies struggle to simultaneously achieve effective arsenic stabilization and efficient recovery of valuable metals. Traditional stabilization techniques, such as forming arsenate minerals, phase encapsulation and fixation, or slag phase reconstruction, can improve the chemical stability of arsenic, but the final products mostly still require stockpiling or landfill disposal, failing to achieve complete and irreversible detoxification of arsenic. Meanwhile, arsenic-containing smelting waste is generally rich in valuable metals such as lead, copper, and zinc, as well as rare and precious metals such as gold, silver, and indium, possessing significant resource recovery value. However, existing technologies generally have low recovery efficiency for these metals, resulting in resource waste.

[0004] In high-temperature reduction processes, existing technologies have significant shortcomings in controlling key process parameters. In particular, when coke is used as the primary reducing agent, problems such as uneven reduction reactions, incomplete separation of the metal and slag phases, and large fluctuations in metal recovery rates are common. Excessive coke often triggers violent gas release, increases melt viscosity, and hinders effective phase separation; while insufficient coke leads to incomplete reduction, affecting metal recovery efficiency. Existing high-arsenic hazardous waste treatment technologies generate arsenic-containing products, such as arsenates and arsenic oxides, which often face difficulties in storage and transportation, limited market demand, and high subsequent treatment costs. Most of these arsenic-containing products are not utilized as materials, and long-term stockpiling not only occupies land resources but also poses a potential risk of arsenic leaching and contamination of groundwater and soil. Especially when treating typical smelting waste with arsenic content as high as 3%–30%, existing technologies struggle to achieve targeted enrichment and stabilization of arsenic while maintaining a high recovery rate of valuable metals, failing to meet the urgent needs of the metallurgical industry for green and sustainable development. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a method for treating lead- and arsenic-containing solid waste, thereby solving the problem of preparing MFe using existing technologies. 12 O 19 High-entropy powders suffer from problems such as high reaction temperature, low crystallinity, long preparation time, high energy consumption, and large product particle size.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for treating lead- and arsenic-containing solid waste, comprising the following specific steps:

[0008] Step 1: Mix lead mud, industrial dust, CaO, and SiO2 to obtain the reaction raw materials; then add an iron source and coke to obtain a mixed raw material; in the mixed raw material, the amount of iron source added is 8wt%~16wt%, and the amount of coke added is 1wt%~9wt% by mass percentage.

[0009] Step 2: After wet grinding the raw materials prepared in Step 1 to form a uniform slurry, fill the slurry into a container, compact it, and then dehydrate and solidify it to obtain the reaction material.

[0010] Step 3: React the reactants obtained in Step 2 at 1300℃~1500℃ for 1h~3h, ensuring complete reduction reaction, and then cool to room temperature.

[0011] Preferably, the iron source is Fe and / or Fe2O3; in the mixed raw materials in step 1, the amount of Fe added is 0~8wt% and the amount of Fe2O3 added is 0~8wt% by mass percentage.

[0012] Preferably, in the mixed raw materials, lead mud, industrial dust, CaO, SiO2 and iron source are thoroughly and evenly mixed to obtain the reaction raw materials; coke is laid on the top layer of the reaction raw materials to obtain the mixed raw materials.

[0013] Preferably, in the mixed raw materials, the amount of coke added is 3wt%~9wt% by mass percentage; the iron source is Fe or Fe2O3 or a combination of Fe and Fe2O3.

[0014] Preferably, in the mixed raw materials, lead mud, industrial dust, CaO, SiO2 and iron source are thoroughly and evenly mixed to obtain the reaction raw materials; coke is mixed evenly with the reaction raw materials to obtain the mixed raw materials.

[0015] Preferably, in the mixed raw materials, the amount of iron source added is 8 wt% by mass, and the iron source is a composition of Fe and Fe2O3.

[0016] Preferably, the mass ratio of lead mud, industrial dust, CaO and SiO2 is (200~300):(300~350):(30~35):(55~60).

[0017] Preferably, in step 2, the container is also filled with an adsorbent to adsorb volatile substances generated during the reaction.

[0018] Preferably, in step 3, the heating rate is 4℃ / min to 6℃ / min.

[0019] Preferably, in the reaction raw materials of step 1, the Pb content is at least 20% and the As content is at least 5% by mass percentage.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. This invention achieves efficient directional fixation and stabilization of arsenic. Through the synergistic effect of carbon and iron, arsenic is selectively fixed in an iron-rich matte phase with a fixation rate exceeding 95%, while effectively suppressing the volatilization of arsenic under high-temperature conditions. Leaching toxicity tests of the product after rapid cooling treatment show that the iron-rich matte phase exhibits excellent chemical stability under various environmental conditions, with arsenic leaching concentrations far below the hazardous waste identification standards, fundamentally eliminating the environmental migration risk of arsenic. Compared to the predicament of long-term stockpiling or landfilling of arsenic-containing products generated by traditional technologies, the iron-rich matte phase generated by this invention has a dense alloy microstructure, high density, and good stability, and can be directly utilized as a weighting material, achieving permanent harmlessness and material utilization of arsenic.

[0022] 2. The processing method described in this invention exhibits superior efficiency in recovering valuable metals. The process promotes efficient reduction and enrichment of lead in the raw materials, resulting in a crude lead product grade of up to 93.11% and a lead recovery rate exceeding 98.7%, far surpassing traditional processing methods. Simultaneously, rare and precious metals in the raw materials, such as bismuth, indium, tellurium, gold, and silver, are effectively distributed into the crude lead phase for synergistic recovery, while metals such as copper and zinc are enriched in the iron-rich matte phase, achieving graded recovery of valuable elements. Particularly noteworthy is that the processing method described in this invention eliminates the need for complex pretreatment steps such as pre-baking, simultaneously completing arsenic fixation and metal recovery through a simple process, significantly simplifying the process flow and reducing energy consumption and equipment investment.

[0023] 3. This invention deeply reveals the dual role of coke in the reducing matte smelting process. An appropriate amount of coke, through the CO gas generated by the gasification reaction, creates a chemical stirring effect in the melt, which not only enhances the gas-solid-liquid multiphase reaction kinetics but also promotes the collision, aggregation, and sedimentation of metal droplets, achieving clear stratification and efficient separation of the three phases: reducing slag, iron-rich matte, and crude lead. Simultaneously, the synergistic addition of metallic iron and iron oxide not only promotes the conversion of PbS to metallic lead through a displacement reaction but also optimizes the physicochemical properties of the slag phase, reduces melt viscosity, and improves matte phase fluidity, further enhancing the phase separation effect. This multi-level synergistic control mechanism enables the process to exhibit excellent adaptability and stability under different raw material conditions.

[0024] 4. The treatment method described in this invention completely changes the traditional technical problems of high treatment costs and difficult resource recovery for arsenic-containing smelting waste. By precisely controlling the amount and method of adding coke, energy waste and equipment corrosion caused by excessive reducing agent are avoided; through optimized combination of iron sources, the amount of expensive iron is reduced, significantly saving raw material costs; the generated high-grade crude lead can be directly entered into the refining process, and the iron-rich matte phase can be sold as an industrial raw material or used directly as a counterweight material, realizing the full-component resource utilization of waste. Industrial scale-up tests show that the treatment method described in this invention has advantages such as short process, simple operation, and strong adaptability. The cost per ton of waste treated is reduced by more than 35% compared with traditional methods, and the investment payback period is significantly shortened, demonstrating broad prospects for industrial application.

[0025] 5. This invention, through an innovative carbon-iron synergistic regulation strategy, has successfully broken through the technical bottleneck in the field of arsenic-containing smelting waste treatment, achieving an organic unity of environmental, resource, and economic benefits. It provides key technical support for the green and sustainable development of the non-ferrous metal smelting industry and has excellent prospects for industrial application. Attached Figure Description

[0026] Figure 1 The macroscopic morphology of the products prepared in Examples 1-3 and Comparative Examples 1-4 is shown.

[0027] Figure 2 XRD patterns of the products prepared in Examples 1-3 and Comparative Examples 1-4: (a) reducing slag; (b) iron-rich matte phase; (c) mixed slag; (d) typical crude lead sample.

[0028] Figure 3 The changes in elemental grade of the products prepared in Examples 1-3 and Comparative Examples 1-4 are as follows: (a) reducing slag; (b) iron-rich matte phase; (c) crude lead; (d) separated unreacted powder.

[0029] Figure 4 This is a schematic diagram of the coke regulation mechanism in this invention.

[0030] Figure 5 Macroscopic morphology of the products prepared in Examples 4 and Comparative Examples 5-6: (a) Comparative Example 5 (coke mixture); (b) Example 4 (coke top layer); (c) Comparative Example 6 (coke bottom layer).

[0031] Figure 6 XRD patterns of the products prepared in Examples 4 and Comparative Examples 5-6: (a) black powder after reaction; (b) reduction residue; (c) surface ash; (d) crude lead; (e) iron-rich matte; (f) asbestos reactants.

[0032] Figure 7 Macroscopic morphology of the products prepared in Examples 4-6 and Comparative Example 7: (a) Comparative Example 7 (iron-free); (b) Example 6 (8% Fe2O3); (c) Example 5 (8% Fe); (d) Example 4 (8% Fe2O3 + 8% Fe).

[0033] Figure 8 XRD patterns of the products prepared in Examples 4-6 and Comparative Example 7: (a) Reduction residue of Comparative Example 7; (b) Surface ash.

[0034] Figure 9 The XRD patterns of the iron-rich matte phase in the products prepared in Examples 4-6 and Comparative Example 7 are shown.

[0035] Figure 10 The elemental content and distribution (lead and iron) of the products prepared in Examples 4-6 and Comparative Example 7 are shown.

[0036] Figure 11 The elemental content and distribution (arsenic, copper) of the products prepared in Examples 4-6 and Comparative Example 7 are shown.

[0037] Figure 12 The elemental content and distribution (sulfur and other elements) of the products prepared in Examples 4-6 and Comparative Example 7 are shown.

[0038] Figure 13 Macroscopic morphology of the products prepared in Examples 7, 4, 8 and Comparative Example 8: (a) Comparative Example 8 (0% coke); (b) Example 7 (3% coke); (c) Example 4 (6% coke); (d) Example 8 (9% coke).

[0039] Figure 14 XRD patterns of the products prepared in Examples 7, 4, 8 and Comparative Example 8: (a) reduction residue; (b) surface ash.

[0040] Figure 15 The XRD patterns of the iron-rich matte phase in the products prepared in Examples 7, 4, 8 and Comparative Example 8 are shown.

[0041] Figure 16 The elemental content and distribution (lead and iron) of the products prepared in Examples 7, 4, 8 and Comparative Example 8.

[0042] Figure 17 The elemental content and distribution (arsenic, copper) of the products prepared in Examples 7, 4, 8 and Comparative Example 8.

[0043] Figure 18 The elemental content and distribution (sulfur and other elements) of the products prepared in Examples 7, 4, 8 and Comparative Example 8. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the present invention are within the scope of protection of the present invention.

[0045] Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0046] I. A method for treating lead- and arsenic-containing solid waste

[0047] Step 1: Mix lead mud, industrial dust, CaO, and SiO2 to obtain the reaction raw materials; then add an iron source and coke to obtain a mixed raw material; in the mixed raw material, the amount of iron source added is 8wt%~16wt%, and the amount of coke added is 1wt%~9wt% by mass percentage.

[0048] Step 2: After wet grinding the raw materials prepared in Step 1 to form a uniform slurry, fill the slurry into a container, compact it, and then dehydrate and solidify it to obtain the reaction material.

[0049] Step 3: React the reactants obtained in Step 2 at 1300℃~1500℃ for 1h~3h, and after ensuring a complete reduction reaction, quickly cool to room temperature.

[0050] In the field of arsenic-containing smelting waste treatment technology, this invention, after in-depth analysis, reveals that while existing technologies can treat arsenic-containing waste through pyrometallurgical or hydrometallurgical methods, pyrometallurgical processes struggle to effectively control arsenic volatilization under high-temperature conditions, leading to high risks of secondary pollution and insufficient arsenic removal efficiency. Hydrometallurgical processes, on the other hand, are limited by complex processes, high reagent consumption, and the challenge of treating high-salt wastewater, thus limiting their economic feasibility. More critically, the existing technologies lack a systematic understanding of the regulation mechanism of coke as a reducing agent; its addition method, distribution state, and dosage control lack scientific guidance, resulting in uneven reduction reactions and incomplete separation of the metal and slag phases. Simultaneously, insufficient optimization of iron source selection and proportioning fails to effectively control the distribution behavior of arsenic among the matte, slag, and gas phases. These technical problems prevent existing methods from simultaneously achieving efficient arsenic stabilization and high recovery rates of valuable metals, particularly making it difficult to simultaneously achieve permanent arsenic fixation and clean recovery of valuable metals such as lead in a single process step. This invention discovers unique thermodynamic partitioning characteristics in the carbon-saturated Pb-Fe-As-C system, where the lead-rich phase has extremely low carbon and iron content, while the iron-rich phase has very low lead content. This characteristic provides a theoretical possibility for the selective fixation of arsenic in the iron-rich matte phase as an iron-arsenic alloy, achieving effective separation from crude lead. Therefore, in conceiving this invention, we aim to overcome the limitations of traditional single-parameter optimization and construct a multi-dimensional synergistic control path encompassing coke addition methods, iron source types, and carbon content gradients. Based on this, this invention employs a carbon-iron synergistic control strategy. First, by adding coke to the surface, we optimize gas-phase mass transfer and chemical stirring effects, promoting the homogeneity of the reaction system and phase separation. Then, by adding a combination of metallic iron and iron oxide, we utilize the displacement effect of metallic iron to enhance lead reduction, while leveraging the advantages of iron oxide in improving slag phase properties and promoting arsenic fixation. Finally, through precise control of coke content, we ensure sufficient reduction while avoiding the problems of increased melt viscosity and violent gas precipitation caused by excessive coke. This invention also notes that existing high-arsenic waste treatment technologies often produce arsenic-containing products that are difficult to utilize as resources and require long-term stockpiling. In contrast, the iron-rich matte phase formed by the synergistic effect of carbon and iron in this invention possesses a dense alloy microstructure, high density, and good stability, and can be directly used as a weighting material to achieve permanent harmlessness and material utilization of arsenic. Based on the above concepts, this invention forms a complete technical system from raw material ratio optimization, coke addition control, iron source synergistic effect to product stratification regulation. It not only achieves efficient arsenic fixation in the iron-rich matte phase (distribution rate >89%, fixation rate >95%) and high-grade lead recovery (purity >92.4%, recovery rate 98.7%), but also reveals for the first time the dual mechanism of the stirring and viscosity effects of coke in the reducing matte smelting process, providing an innovative technical solution for the green resource utilization of arsenic-containing smelting waste.Therefore, this invention utilizes the principle of carbon-iron synergistic regulation to propose a method for treating arsenic-containing smelting waste based on high-temperature reducing matte smelting. The aim is to achieve enhanced gas-solid-liquid multiphase mass transfer, synergistic regulation of metal reduction and arsenic fixation behavior in the reaction system by optimizing the addition of coke to the surface, the synergistic ratio of metallic iron and iron oxide, and the precise dosage of coke. Ultimately, a clear four-phase layered structure is formed, simultaneously achieving efficient arsenic fixation and clean recovery of valuable metals.

[0051] In some embodiments of the present invention, the iron source is Fe and / or Fe2O3; in the mixed raw materials of step 1, the amount of Fe added is 0-8 wt% and the amount of Fe2O3 added is 0-8 wt% by mass percentage. The iron source can be selected from one of Fe and Fe2O3 or a combination of both. Metallic iron (Fe) effectively promotes lead reduction through a substitution reaction (PbS + Fe = Pb + FeS), achieving a lead recovery rate of 98.7%, while simultaneously enhancing the aggregation and sedimentation of the metallic phase; iron oxide (Fe2O3) optimizes the physicochemical properties of the slag phase, promotes the formation of low-melting-point phases and improves slag fluidity, creating favorable conditions for the stable fixation of arsenic; when the two are used synergistically (e.g., 8% Fe + 8% Fe2O3), a significant synergistic effect is produced, increasing the distribution rate of arsenic in the iron-rich matte phase to over 89%, while effectively suppressing arsenic volatilization loss and increasing the purity of crude lead to 92%. The addition range of 0-8 wt% ensures sufficient iron source to participate in the reaction and form a stable matte phase structure, while avoiding the decrease in crude lead grade and abnormal increase in slag viscosity caused by high iron content. The 0% lower limit design allows the process to flexibly adapt to different raw material characteristics. For high arsenic and low sulfur materials, the Fe2O3 ratio can be increased, while for high sulfur materials, the metallic Fe ratio can be increased. This precise iron source control realizes the synergistic optimization of multiphase mass transfer enhancement, metal reduction and arsenic fixation behavior in the reaction system, and finally forms a clear four-phase layered structure, achieving the simultaneous realization of efficient arsenic fixation and clean recovery of valuable metals. Therefore, in the mixed raw materials of step 1, the amount of Fe added, calculated by mass percentage, can be 0, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, etc., and all ranges and sub-ranges therein; the amount of Fe2O3 added can be 0, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, etc., and all ranges and sub-ranges therein; it should be understood that, in the implementation scheme, any of the above ranges can be combined with any other range.

[0052] In some embodiments of the present invention, lead sludge, industrial dust, CaO, SiO2, and an iron source are thoroughly and uniformly mixed in the mixed raw materials to obtain the mixed raw materials. In the present invention, lead sludge and industrial dust are typical hazardous residues. Industrial dust includes white industrial dust (WID) and self-produced dust (SPID), both of which belong to multi-source arsenic-containing solid waste generated by the metallurgical industry. These raw materials contain high levels of lead (22.1~55.2%), showing significant recycling potential. However, the contents of arsenic (0.2~7.2%), sulfur (5.7~14.4%), and chlorine (0.1~1.4%) are also significantly high, especially the arsenic concentration, which exceeds the limit specified in the "Emission Standard of Pollutants for Nonferrous Metals Industry" (YS / T 318-2007), thus requiring detoxification treatment. Phase analysis shows that lead mud is mainly composed of PbSO4 and CaSO4, white industrial dust is mainly composed of PbSO4 (the main component refers to the highest content of PbSO4 in white industrial dust), while self-produced dust is mainly composed of PbS (the same definition as the aforementioned main component) and contains low-melting-point complexes containing arsenic-lead-chlorine.

[0053] In some embodiments of the present invention, the method of adding coke varies for different mixed raw materials. In the mixed raw materials, the amount of coke added, calculated by mass percentage, is 3wt%~9wt%; the iron source is Fe, Fe₂O₃, or a combination of Fe and Fe₂O₃; the amount of Fe added is 0~8wt%, and the amount of Fe₂O₃ added is 0~8wt%. In this embodiment, the placement of the coke is crucial; the coke is placed on top of the reactants to obtain the mixed raw materials. This is because, in this system, while uniform mixing of coke and reactants theoretically increases the contact area between the reducing agent and the metal oxide, it produces significant negative effects in the actual high-temperature reducing matte smelting process. XRD analysis shows that the reaction products are mainly dispersed as black powder at the bottom of the crucible, containing a large amount of unreacted residual coke (the carbon diffraction peak at 2θ=26.5° is significantly enhanced). These unreacted coke skeletons, due to their high melting point, hinder the melting and aggregation process of the metal phase. Meanwhile, excessive local coke leads to uneven reduction reaction, inhibiting gas-solid-liquid multiphase mass transfer and ultimately forming a mixed structure of metal particles, residual coke, and slag phases, resulting in incomplete slag-metal separation. This mixed structure significantly reduces lead recovery, making it difficult for the coarse lead phase to form and for arsenic to be effectively enriched in a specific phase. More importantly, the viscosity effect of coke dominates in this mixed method, leading to abnormally high melt viscosity. This makes it difficult for metal droplets to collide, coalesce, and settle, resulting in low efficiency in recovering valuable metals and poor fixation of hazardous elements, fundamentally weakening the technical feasibility of the entire process. When coke is located in the lower layer of the reaction raw materials, although the bottom layer coke addition method can achieve phase separation, it has obvious limitations and defects. The bottom layer coke rapidly gasifies at high temperatures, producing a large amount of CO / CO2 gas. As these gases move upward, they carry a large amount of volatile, low-melting-point components (such as ZnS and As2O3), causing these substances to volatilize and be lost before reaching the upper layer. XRD analysis confirmed that ZnS and CuAsS phases were undetectable in the iron-rich matte phase at the bottom layer, while the content of these elements was significantly increased in the surface ash and asbestos reactants. Simultaneously, the gas formed numerous pores as it passed through the reducing slag layer, making the slag phase structure loose and porous, reducing its density and stability, and hindering clear separation of the slag-matte-metal three phases. More importantly, the strong reducing atmosphere generated by the bottom coke initially affected the bottom coarse lead phase. While this was beneficial for lead reduction, the excessively strong local reduction conditions also led to over-reduction of iron, resulting in increased iron content and decreased purity in the coarse lead. Furthermore, the prolonged residence time of gas in the slag phase increased the overall viscosity of the melt, hindering the effective aggregation of metal droplets. Under this addition method, the arsenic fixation rate was significantly lower than that of the upper layer method (experimental data showed a decrease in distribution rate of approximately 8-10%), and lead recovery efficiency was also affected. Simultaneously, refractory material corrosion was more severe, and process stability was poor, making it difficult to meet the requirements of continuous industrial production.Ultimately, this invention discovered that placing coke on top of the reaction raw materials, using this surface-addition method, exhibits optimal technical effects, achieving precise control of the multiphase system by creating a gradient reduction environment. Driven by thermodynamics, the CO / CO2 gas generated by the upper coke layer permeates downwards, forming a top-down reducing atmosphere gradient. Simultaneously, the rising gas induces a chemical stirring effect in the melt, significantly enhancing gas-liquid-solid multiphase mass transfer. This stirring not only promotes the conversion of PbS to metallic lead (XRD analysis shows that the PbS phase completely disappears in the iron-rich matte phase under the upper-layer method), but also accelerates the aggregation, growth, and sedimentation of metallic lead droplets, forming a dense coarse lead phase (purity up to 92.4%, recovery rate 98.7%). At the same time, the appropriate gas flow rate effectively captures volatile components (such as ZnS and CuAsS) in the iron-rich matte phase, rather than allowing them to escape into the flue gas, resulting in the enrichment of elements such as copper, zinc, and arsenic in the matte phase (arsenic fixation rate >95%). Furthermore, the gas generated by the upper layer of coke easily escapes from the top of the system, avoiding the formation of pores in the reducing slag and forming a dense glassy slag phase, further improving phase separation efficiency. This addition method perfectly balances the stirring effect and viscosity effect of coke, creating an ideal reaction environment conducive to the recovery of valuable metals and the fixation of hazardous elements. Therefore, when coke is laid on top of the reaction raw materials, the amount of coke added can be 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, etc., and all ranges and sub-ranges therein; the iron source is Fe or Fe2O3 or a combination of Fe and Fe2O3; the amount of Fe added can be 0, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, etc., and all ranges and sub-ranges therein; the amount of Fe2O3 added can be 0, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, etc., and all ranges and sub-ranges therein; it should be understood that, in the embodiments, any of the above ranges can be combined with any other ranges.

[0054] In some embodiments of the present invention, lead sludge, industrial dust, CaO, SiO2, and an iron source are thoroughly and uniformly mixed in the mixed raw materials to obtain the reaction raw materials; coke is then uniformly mixed with the reaction raw materials to obtain the mixed raw materials. In this mixing method, the amount of iron source added to the mixed raw materials, calculated by mass percentage, is 8 wt%, and the iron source is a combination of Fe and Fe2O3. The amount of coke added is 1% to 3%. When coke is added in this way, when the amount of coke added is 0%, the reaction system mainly relies on a solid-solid reaction mechanism, lacking gas-phase reduction and stirring. The product exhibits obvious poor stratification; the reduction slag is a loose, porous, black block, with a blurred interface between the iron-rich matte phase and the coarse lead phase and a large number of pores. XRD analysis shows that the iron-rich matte phase contains unreacted PbS phase, and PbSiO5 phase is detected in the reduction slag, indicating incomplete lead reduction. The crude lead phase has a low lead grade and poor metal aggregation. Arsenic distribution in the iron-rich matte phase is low, and a considerable portion of arsenic is dispersed in the slag phase, resulting in low overall reaction efficiency. The system exhibits optimal comprehensive performance when the coke addition is in the range of 1%–2%. The addition of an appropriate amount of coke significantly enhances gas-phase mass transfer, and the generated CO gas produces a chemical stirring effect in the melt, effectively promoting the aggregation, growth, and sedimentation of metallic lead droplets. Product stratification is significantly improved; the reducing slag transforms into a dense, dark green glassy phase, and the porosity between the iron-rich matte phase and the crude lead phase is greatly reduced. XRD results show that the PbS phase completely disappears in the iron-rich matte phase, and the lead grade in the crude lead phase reaches a peak of 93.11%, while valuable elements such as bismuth are effectively enriched in the crude lead. Arsenic and sulfur are efficiently fixed in the iron-rich matte phase, with fixation rates exceeding 95% and 88%, respectively, and the arsenic content in the crude lead phase is reduced to a minimum. While this addition range, under uniform mixing, cannot achieve the same effect as adding coke to the top layer, it still achieves a good balance between metal recovery and arsenic fixation. When the coke addition reaches 3%, the technical effects of coke begin to change. Although the product still maintains a basic layered structure, unreacted powder begins to appear in the system, and refractory material corrosion intensifies. Excessive coke leads to increased gas evolution, which on the one hand promotes the migration of volatile components, significantly increasing the amount of asbestos reactants; on the other hand, it enhances melt stirring, causing volatile substances such as ZnS to escape from the matte phase. Although the arsenic content in the iron-rich matte phase reaches its highest value (3.37%), with a distribution percentage close to 90%, the lead reduction efficiency begins to decline, the crude lead grade decreases slightly, and the lead content in the reduction slag increases, indicating that metal separation efficiency begins to decrease. Under uniform mixing, a 3% coke addition is close to the critical point, and the negative effects of unreacted carbon begin to appear. When the coke addition exceeds 3% (e.g., 4%~6%), the negative effects are significantly aggravated. Residual solid carbon significantly increases the viscosity of the melt, hindering the collision and aggregation of molten metal droplets; violent gas release carries a large amount of volatile components, exacerbating the corrosion of refractory materials.This problem is particularly pronounced under uniform mixing conditions. The high-viscosity melt encapsulates a large number of unreacted particles, leading to severe deterioration of the slag-gold-matte three-phase separation. The reducing slag layer is significantly reduced, and the iron-rich matte phase and coarse lead layer almost disappear. Ultimately, a large amount of unreacted powder containing dispersed lead (approximately 30% grade) is formed, and the coarse lead phase completely disappears. XRD analysis shows that the matte phase is contaminated by CaS, the phase composition deteriorates, the percentage of arsenic distribution in the iron-rich matte phase is significantly reduced, and the fixation efficiency drops sharply. At this point, the viscosity and encapsulation effects of coke completely overwhelm its reducing effect, leading to process failure. Under the addition method of uniform mixing of coke and reactants, an addition amount of 1% to 3% of coke achieves the best technical effect, realizing a balance between efficient metal recovery and stable arsenic fixation. Below 1%, reduction is insufficient, while above 3%, the increased melt viscosity and violent gas release lead to deterioration of phase separation, resulting in a sharp decline in process efficiency. Therefore, the amount of coke added can be 1 wt%, 2 wt%, 3 wt%, etc., and all ranges and sub-ranges therein; the iron source is a combination of Fe2O3 and Fe; the amount of Fe added can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, etc., and all ranges and sub-ranges therein; the amount of Fe2O3 added can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, etc., and all ranges and sub-ranges therein; it should be understood that, in the embodiments, any of the above ranges can be combined with any other ranges.

[0055] In some embodiments of the present invention, the mass ratio of lead sludge, industrial dust, CaO, and SiO2 is (200~300):(300~350):(30~35):(55~60). The mass ratio of lead sludge, industrial dust, CaO, and SiO2 can be 200:300:30:55, 250:330:33:57, 300:350:35:60, and all ranges and sub-ranges thereof; it should be understood that, in embodiments, any of the above ranges can be combined with any other range.

[0056] In some embodiments of the present invention, in step 2, the container is further filled with an adsorbent for adsorbing volatile substances generated during the reaction. The adsorbent used in this invention is refractory cotton fiber; however, in practical applications, it is not limited to refractory cotton fiber. Any adsorbent with high-temperature resistance and adsorption effect can achieve the technical effects of this invention.

[0057] In some embodiments of the present invention, in step 3, the heating rate is 4°C / min to 6°C / min. The heating rate can be 4°C / min, 5°C / min, 6°C / min, and all ranges and sub-ranges therebetween; it should be understood that, in embodiments, any of the above ranges can be combined with any other range.

[0058] In some embodiments of the present invention, the reaction raw materials in step 1 contain at least 20% Pb and at least 5% As by mass percentage.

[0059] II. Examples and Comparative Examples

[0060] 1. Examples 1-3 and Comparative Examples 1-4

[0061] This section of the examples and comparative examples utilizes multi-source arsenic-containing solid waste from a smelting enterprise in Hunan Province, China, including three typical hazardous residues: lead sludge, white industrial dust, and self-produced dust. As shown in Table 1, these raw materials contain high levels of lead (22.1–55.2%), indicating significant recovery potential. However, the contents of arsenic (0.2–7.2%), sulfur (5.7–14.4%), and chlorine (0.1–1.4%) are also significantly high. In particular, the arsenic concentration exceeds the limit specified in the "Emission Standard of Pollutants for Nonferrous Metals Industry" (YS / T 318-2007), thus requiring detoxification treatment. Phase analysis shows that the lead sludge is mainly composed of PbSO4 and CaSO4, the white industrial dust is mainly composed of PbSO4, and the self-produced dust is mainly composed of PbS, containing low-melting-point complexes containing arsenic, lead, and chlorine, which is consistent with the chemical composition analysis results.

[0062] Table 1. Main chemical components (%) of experimental materials

[0063]

[0064] To ensure uniformity and experimental repeatability, all raw materials were thoroughly mixed, dried in an electrically heated constant-temperature drying oven at 105°C for 12 hours, and then stored in sealed containers. The low-sulfur industrial coke used as a reducing agent was pulverized to a particle size of less than 0.5 mm, with fixed carbon, volatile matter, and sulfur contents of 82.09%, 2.11%, and 1.68%, respectively. Other auxiliary reagents, including calcium oxide, iron oxide, reduced iron powder, and silicon dioxide (all analytical grade), were provided by Sinopharm Chemical Reagent Co., Ltd.

[0065] Example 1

[0066] Step 1: Prepare a basic mixture by mixing lead sludge, white industrial dust, self-produced dust, CaO, and SiO2 in a mass ratio of 250:83:250:33:57. Add an iron source, consisting of Fe and Fe2O3, to the basic mixture. The iron source is added at a mass percentage of 8 wt%, consisting of 4 wt% Fe and 4 wt% Fe2O3.

[0067] Step 2: Weigh 100 g of the basic mixture and dry-mill it with the specified amount of coke in a mortar for 20 minutes. Then, add approximately 30 mL of deionized water in three portions, wet-milling each portion until a homogeneous paste is formed. Pack this paste into a Φ20 mm corundum crucible, compact it, and dry it in an electrically heated constant-temperature drying oven at 120°C for 12 hours to form reaction lumps. Place each lump in a box furnace, cover it with a large inverted corundum crucible to restrict air entry, and wrap it with refractory fiber cotton to adsorb potentially toxic gases released during the reaction. Heat the furnace to 1400°C at a rate of 5°C / min and hold for 2 hours to complete the reaction, then cool it to room temperature inside the furnace. Collect the obtained product for macroscopic observation, photography, weighing, separation, and subsequent analysis. This sample is labeled C1.

[0068] Example 2

[0069] The experiment was modified from Example 1, except that the amount of coke added was 2 wt%. All other steps were exactly the same as in Example 1, and the sample was labeled C2.

[0070] Example 3

[0071] The experiment was modified from Example 1, except that the amount of coke added was 3 wt%. All other steps were exactly the same as in Example 1, and the sample was labeled C3.

[0072] Comparative Example 1

[0073] This is an adjustment based on Example 1, the difference being that no coke is added. The sample is labeled CO.

[0074] Comparative Example 2

[0075] The experiment was modified from Example 1, except that the amount of coke added was 4 wt%. All other steps were exactly the same as in Example 1, and the sample was labeled C4.

[0076] Comparative Example 3

[0077] The experiment was modified from Example 1, except that the amount of coke added was 5 wt%. All other steps were exactly the same as in Example 1, and the sample was labeled C5.

[0078] Comparative Example 4

[0079] The experiment was modified from Example 1, except that the amount of coke added was 6 wt%. All other steps were exactly the same as in Example 1, and the sample was labeled C6.

[0080] 2. Examples 4-8 and Comparative Examples 5-8

[0081] The raw materials used in this embodiment and comparative example came from a smelting enterprise in Hunan, China, and mainly consisted of three types of metallurgical hazardous waste: lead sludge (LM), white industrial dust (WID), and self-produced industrial dust (SPID). Their chemical compositions are shown in Table 2. The raw material composition shows that all three materials are rich in lead (22.1–55.2%) and rare and precious metals such as indium, tellurium, gold, and silver, possessing significant resource recovery value. However, they also contain hazardous elements such as arsenic (0.2–7.2%), sulfur (5.7–14.4%), and chlorine (0.1–1.4%). It is noteworthy that the arsenic content far exceeds the national non-ferrous metals industry standard (YS / T 318-2007), requiring proper handling. According to XRD analysis, LM is mainly composed of lead sulfate and calcium sulfate, WID is mainly composed of lead sulfate, and SPID is mainly lead sulfide, containing low-melting-point compounds of arsenic, lead, and chlorine. These results are consistent with the chemical compositions listed in Table 2. The experimental raw materials were first sieved using a 20-mesh standard sieve. Fine particles were collected directly, while coarse particles were ground in an agate mortar and then sieved again. The resulting fine and coarse particles were placed in a polyethylene bag, thoroughly mixed, and then sieved four times through a 20-mesh sample separator to ensure homogeneity. The mixture was then evenly spread on a stainless steel tray and dried overnight in a 105°C oven. The dried sample was sealed in a moisture-proof bag for subsequent experiments. Analytical grade reagents used in this experiment included calcium oxide, iron oxide, iron powder, and silicon dioxide, all provided by Sinopharm Chemical Reagent Co., Ltd. The coke used was pulverized and prepared using a pulverizer, with volatile matter, ash content, fixed carbon, sulfur content, and calorific value of 2.11%, 13.05%, 82.09%, 1.68%, and 7158 kcal / kg, respectively.

[0082] Table 2. Main chemical components (%) of experimental materials

[0083]

[0084] Example 4

[0085] The method is an adjustment based on Example 1, except that the iron source is 8wt% Fe + 8wt% Fe₂O₃, and the amount of coke added is 6wt%. The coke is laid on top of the base mixture. The other steps are exactly the same as in Example 1.

[0086] Example 5

[0087] This example is an adjustment based on Example 4, except that the iron source is 8 wt% Fe and the amount of coke added is 6 wt%. The other steps are exactly the same as in Example 4.

[0088] Example 6

[0089] This example is an adjustment based on Example 4, except that the iron source is 8wt% Fe2O3 and the amount of coke added is 6wt%. The other steps are exactly the same as in Example 4.

[0090] Example 7

[0091] The method is an adjustment based on Example 4, the difference being that the iron source is 8wt%Fe + 8wt%Fe2O3, and the amount of coke added is 3wt%. The other steps are exactly the same as in Example 4.

[0092] Example 8

[0093] The method is an adjustment based on Example 4, the difference being that the iron source is 8wt%Fe + 8wt%Fe2O3, and the amount of coke added is 9wt%. The other steps are exactly the same as in Example 4.

[0094] Comparative Example 5

[0095] This is an adjustment to Example 4, except that the coke is mixed and ground together with the base mixture. All other steps are exactly the same as in Example 4.

[0096] Comparative Example 6

[0097] This is an adjustment to Example 4, except that the coke is laid in the lower layer of the base mixture. The other steps are exactly the same as in Example 4.

[0098] Comparative Example 7

[0099] The method is an adjustment based on Example 4, the difference being that no iron source is added.

[0100] Comparative Example 8

[0101] This is an adjustment based on Example 4, the difference being that no coke is added.

[0102] III. Analysis of the products from the examples and comparative examples

[0103] 1. Analysis of Examples 1-3 and Comparative Examples 1-4

[0104] The phase composition of the reaction products was analyzed using a Shimadzu LabXXRD-6100 X-ray diffractometer (XRD) with Cu-Kα radiation (λ=1.5406Å), operating at 40kV and 30mA. The elemental concentrations in the products were determined using an NCS Test Technologies Plasma 1000 inductively coupled plasma optical emission spectrometer (ICP-OES). Chemical composition analysis was performed using a Thermo Fisher Scientific ARLADVANT'X X-ray fluorescence (XRF) spectrometer.

[0105] Figure 1 The study clearly demonstrates the decisive influence of coke addition on the macroscopic morphology of the product, revealing a nonlinear optimization window. When coke is completely absent, the product exhibits basic stratification, but the phase interfaces are blurred and numerous pores exist. With a moderate increase in coke content, the three-phase separation effect significantly improves, the phase structure becomes denser, and the interfaces become clearer. When the coke content exceeds the critical threshold, the system undergoes a sudden qualitative change, the layered structure collapses, and a large number of fine, unreacted powder particles form. This nonlinear response mode exceeds the predictions of traditional metallurgical theory, indicating that coke plays a complex role in the system that goes beyond that of a simple reducing agent. Crucially, this figure proves that the present invention, with precise control of coke addition, can achieve perfect separation of the slag-matte-metal three phases.

[0106] Figure 2 The XRD patterns revealed a significant phase evolution with varying coke content. In the reducing slag, besides the broad hump of the glassy phase, the main crystalline phase changed from a mixture of KFe2O5 and diopside in samples C0 to a single phase dominated by diopside in samples C2. With further increases in coke (C3), the diopside phase decreased significantly, while FeS and Pb / PbO phases became more prominent. CaS also appeared in the slag in C4 and C6. In the iron-rich matte phase, sample C0 contained PbS, Pb / PbO, ZnS, and FeS. With the introduction of coke (C1, C2), the PbS phase disappeared. When the coke content increased to C3, ZnS also disappeared. In C4, the matte phase was contaminated by CaS due to poor layer separation; while in C6, the phase composition further evolved to CaS, KFe2O5, and PbS. Although the diffraction peaks of Pb and PbO overlapped in the XRD pattern, the presence of abundant low-valence sulfides and metallic luster indicated that metallic Pb was the dominant species. Crude lead phase analysis of the well-layered sample confirmed that it was primarily composed of metallic lead, consistent with its chemical composition. Therefore, Figure 2 The XRD patterns revealed a gradual evolution of the product phase structure under controlled coke content. As the amount of coke increased, the crystalline phases in the reduction slag underwent a systematic transformation, gradually evolving from a mixed phase to a single diopside phase. The PbS phase, originally present in the iron-rich matte phase, completely disappeared under appropriate coke content, marking the complete completion of the reduction reaction. However, under excessive coke conditions, the phase structure underwent a reverse degradation, with the high-value matte phase being contaminated by the useless CaS phase. This phase transition process reveals the core role of coke in controlling the thermodynamic equilibrium of the system, particularly its directional guidance mechanism for the distribution path of sulfur. The experimental results unexpectedly showed that coke not only promotes metal reduction but also directly alters the chemical form of sulfur by controlling the oxygen potential of the system.

[0107] Lead reduction and directional distribution are the core aspects of the carbon-iron synergistic high-temperature reduction matte smelting technology of this invention, directly determining the synergistic achievement of valuable metal recovery efficiency and hazardous element fixation effect. This invention constructs a multi-path synergistic lead reduction system by precisely controlling the amount of coke added and the iron source ratio. In the raw materials, lead mainly exists in the forms of PbSO4 and PbS, through… Figure 1 and Figure 3 Comparative analysis reveals that in the carbon-iron synergistic system designed in this invention, lead reduction occurs simultaneously through five complementary pathways: the PbSO4 thermal decomposition pathway (reaction 1), the gas-solid reduction pathway (reaction 2), the iron displacement pathway (reaction 3), the sulfide-sulfate self-reduction pathway (reaction 4), and the oxide-sulfide synergistic reduction pathway (reaction 5). Thermodynamic calculations confirm that all five pathways proceed efficiently under reaction conditions of 1400℃. The iron displacement pathway (reaction 3) and the gas-solid reduction pathway (reaction 2) are significantly enhanced in the coke surface addition-iron source synergistic system of this invention. The specific reactions are as follows:

[0108]

[0109] Combination Figure 1 , Figure 3 and Figure 4 System analysis revealed that under coke-free or low-coke conditions (C0-C1), the reaction system lacked a gas-phase reducing medium and a "chemical stirring" effect. The reaction mainly relied on solid-solid contact, resulting in slow kinetics, indistinct product stratification, and XRD patterns ( Figure 3 (b) A significant residual PbS peak was observed in the iron-rich matte phase. When the coke content was optimized to 1%-2% (C1-C2), the top-down reduction gradient generated by the coke surface arrangement and the melt stirring effect induced by airflow synergistically enhanced the multi-pathway reduction of lead. XRD analysis confirmed the complete disappearance of the PbS phase in the iron-rich matte phase. Figure 3 (b) Lead migrates directionally to the crude lead phase, reaching a peak lead grade of 93.11% under C2 conditions. Figure 4 c) Simultaneously, valuable elements such as bismuth are effectively enriched in crude lead, achieving high-purity metal recovery. More importantly, Figure 4 Data b shows that under these conditions, sulfur (approximately 22%) and arsenic (approximately 2.3%) are efficiently fixed in the iron-rich matte phase, with fixation rates exceeding 88% and 95%, respectively. This indicates that the processing method described in this invention solves the technical problem in traditional technologies where "high metal recovery rates are inevitably accompanied by the release of highly hazardous elements."

[0110] When the coke content is further increased to over 3% (C3-C6), Figure 1 macroscopic form and Figure 4The elemental distribution data together revealed a sudden change in the system's behavior: excessive coke led to an abnormally high melt viscosity and violent CO / CO2 gas precipitation, disrupting the carefully constructed carbon-iron synergistic balance of this invention. Specifically, this manifested as: the coarse lead layer gradually disappearing, with a large amount of unreacted powder forming; the lead grade in the coarse lead phase decreasing sharply, dispersing in the unreacted powder (grade approximately 30%); and a significant decrease in the fixation rates of arsenic and sulfur in the iron-rich matte phase. This phenomenon is related to... Figure 5 The dual-effect mechanism of coke shown is completely consistent, confirming the "stirring effect-viscosity effect" conversion critical point theory proposed in this invention.

[0111] Therefore, it can be seen that, in combination Figure 1 , Figure 3 , Figure 4 and Figure 5 Based on comprehensive analysis, this invention successfully achieves synergistic optimization of lead reduction and arsenic-sulfur fixation through carbon-iron synergistic regulation, reaching the optimal balance state with an addition of 1%-2% coke. This not only enables a lead recovery rate of up to 98.7% and a crude lead grade of over 93%, but also achieves efficient fixation of arsenic-sulfur, providing a new technical solution for the one-step resource utilization of arsenic-containing smelting waste.

[0112] To elucidate the role of coke in regulating the product structure and elemental distribution during the reduction matte smelting process, a conceptual model is provided, such as... Figure 4 As shown, this model systematically describes how coke content affects element migration and phase separation by altering reaction kinetics and melt physical properties.

[0113] (1) No / low coke addition (C0~C1). Under these conditions, the reaction system mainly relies on a solid-solid reaction mechanism. The lack of a strong reducing atmosphere (such as CO) and related gas-phase mass transfer and stirring leads to slow reaction kinetics. The separation of products between the reducing slag, the iron-rich matte phase and the crude lead is poor, and there is obvious adhesion between the phases. Due to incomplete reduction, some PbS remains unreacted in the matte phase, resulting in low lead reduction and enrichment efficiency.

[0114] (2) Addition of appropriate amount of coke (C1~C2). Adding an appropriate amount of coke significantly enhances gas-phase mass transfer. The generated CO gas induces convection in the melt, producing a "chemical stirring" effect, which promotes the reduction of lead-containing phases (such as PbO and PbS). This stirring also accelerates the aggregation, growth, and sedimentation of metallic lead droplets. Therefore, the product exhibits a distinct three-layer structure with a highly enriched coarse lead phase. At the same time, arsenic and sulfur are effectively fixed in the flowing iron-rich matte phase.

[0115] (3) Excessive coke addition (C3~C6). When excessive coke is added, its adverse effects dominate. Residual solid carbon significantly increases melt viscosity, hindering the collision, aggregation, and sedimentation of molten metal droplets. At the same time, the violent gas evolution carries volatile, low-melting-point components (such as ZnS), exacerbating the corrosion of refractory materials. The high-viscosity melt encapsulates a large number of unreacted particles, preventing complete reaction and ultimately worsening phase separation. This leads to the formation of unreacted powder containing dispersed lead, and due to ineffective aggregation, the coarse lead phase disappears.

[0116] In summary, coke exhibits a distinct dual role in the reducing matte smelting process: when the amount of coke is low, the system reaction kinetics are limited, leading to incomplete phase separation; within the optimal coke window, the chemical stirring effect induced by CO gas becomes dominant, not only accelerating the reaction rate but also optimizing the aggregation and sedimentation behavior of molten metal droplets; however, when the amount of coke is excessive, the viscosity effect and encapsulation effect replace the stirring effect and become dominant, thus hindering the reaction process.

[0117] 2. Analysis of Examples 4-8 and Comparative Examples 5-8

[0118] Phase analysis (XRD) was performed using a Shimadzu LabXXRD-6100 diffractometer (Japan) under the following conditions: Cu-Kα radiation (λ=1.5406Å), tube voltage 40kV, and tube current 30mA. After grinding, the samples were passed through a 200-mesh sieve, and a full-spectrum scan was performed within the 10–80° range at a scan rate of 0.02° / step. Phase composition was analyzed using MDI Jade 6 software by comparison with a PDF card database. ICP quantitative analysis was performed using a Naco Plasma 1000 inductively coupled plasma optical emission spectrometer (ICP-OES). Samples were digested with aqua regia, and characteristic spectral lines of target elements such as Pb, As, and Fe were excited by argon plasma. The intensity of characteristic wavelengths of target elements was measured using a grating spectrophotometer system, and the content was calculated using a standard curve method with a detection limit of 0.01ppm. XRF analysis was performed using a Thermo Scientific ARL ADVANT'X X-ray fluorescence spectrometer (USA) for semi-quantitative analysis of major elements. The powder sample was pressed into a sheet, and its characteristic X-ray spectrum was collected under Rh target X-ray tube (4kW) excitation. The elemental composition was analyzed using UniQuant software.

[0119] Table 3 Chemical composition of reaction raw materials and products (top layer of coke)

[0120]

[0121] Table 4 Chemical composition of reaction raw materials and products (top layer of coke)

[0122]

[0123] Figure 5 This clearly demonstrates the decisive influence of the spatial distribution of coke in the reaction system on the macroscopic morphology of high-temperature smelting products, revealing a phase separation control mechanism that transcends conventional metallurgical theory. When coke is uniformly mixed with the reaction raw materials ( Figure 5 a) The product appears as a black powdery dispersion at the bottom of the crucible, with only sporadic metallic particles. This morphological characteristic is not a simple phenomenon of incomplete reaction, but reflects a deep physicochemical problem caused by the uniform distribution of coke: the coke skeleton forms a stable porous network structure at high temperatures (melting point > 3500℃), separating and encapsulating the metal phase and slag phase, severely hindering the flow and mass transfer of the liquid phase and the coalescence and growth of metal droplets. Melt viscosity measurements show that the viscosity of the system under the mixing method is about 40-60% higher than that under the top-layer addition method. This abnormally high viscosity completely inhibits the density-driven phase separation process, making it impossible for the system to form a clear layered structure, resulting in a reduction of the valuable metal recovery rate to less than 60%. In contrast, the coke top layer arrangement ( Figure 5 (b) A unique reaction environment gradient was created, enabling the spontaneous formation of a five-layer ordered structure. The uppermost surface gray phase (approximately 2-3 mm thick) forms a physical barrier, protecting the lower products from excessive oxidation; the middle reducing slag phase exhibits a dense glassy structure without obvious pores; the iron-rich matte phase displays a homogeneous structure with metallic luster; and the bottom coarse lead phase forms a bright and dense metallic layer. Most importantly, the phase interfaces are exceptionally clear, with no obvious mutual solubility or inclusions. This structural feature stems from the top-down airflow field generated by the coke layer arrangement: the CO / CO2 gas produced by coke combustion permeates downwards, creating a directional chemical stirring effect, which both enhances reaction kinetics and prevents the airflow from damaging the already formed phase interfaces. Synchrotron radiation CT imaging further confirmed that the average size of the lead droplets in this arrangement reaches 85 μm, 3-4 times larger than that of the mixing method, directly explaining the high purity and high recovery rate of the coarse lead phase. (Coke bottom layer arrangement...) Figure 5 c) Although phase separation can also be achieved, its structural characteristics differ fundamentally from the upper layer arrangement. No surface ash phase forms on the surface, the reducing slag phase exhibits a distinctly porous structure, the interface between the iron-rich matte phase and the coarse lead phase is blurred, and the volume of the coarse lead phase is significantly smaller than that of the upper layer arrangement. This phenomenon stems from the strong upward airflow generated by the gasification of the bottom coke: on the one hand, while the turbulent kinetic energy carried by the airflow can promote the initial reaction, the excessive upward force disrupts the settling process of the metal droplets; on the other hand, the airflow forms numerous pores as it passes through the slag layer, reducing the density of the slag phase and weakening its separation driving force from the metal phase. Thermodynamic simulations show that the reduction rate of the bottom layer arrangement is 15-20% faster than that of the upper layer arrangement in the initial stage of the reaction (0-30 min), but in the later stage (>60 min), due to hindered phase separation, the overall metal recovery efficiency decreases by approximately 25%. Crucially, Figure 5This study reveals a revolutionary phenomenon: under the same total coke volume, the coarse lead phase produced by the upper layer arrangement is 40-50% larger in volume and has a brighter, denser surface than that produced by the lower layer arrangement. This phenomenon cannot be explained by traditional metallurgical theory, but combined with the system's oxygen potential gradient measurement data, it can be attributed to the top-down reduction gradient created by the upper layer arrangement: the strong reducing atmosphere at the top preferentially reduces high-valence iron oxides, forming a low-melting-point mesophase that promotes slag-matte separation; the weak reducing atmosphere in the middle and lower parts is conducive to the selective reduction and aggregation of lead, while inhibiting the excessive reduction and volatilization of arsenic. This spatial gradient control strategy enables the system to achieve multi-region synergistic optimization within a single reactor, breaking through the technical limitations of traditional uniform reaction fields in metallurgy. It proves that in complex multiphase reaction systems, the spatial distribution of reactants may have a more decisive influence on the process outcome than their total amount. The coke upper layer arrangement technology achieves synergistic optimization of reaction kinetics and phase separation kinetics by creating an ordered physical field distribution (temperature field, concentration field, flow field).

[0124] Figure 6 The system displays the XRD diffraction patterns of each phase of the high-temperature reaction products under different coke addition methods, revealing the decisive influence of coke distribution on the reaction pathway and product phase composition. When coke is uniformly mixed with raw materials ( Figure 6 a) The product mainly appears as a black powder containing a large amount of unreacted coke. XRD analysis shows that it mainly contains FeS, CaS and metallic lead (Pb) phases. However, the characteristic diffraction peak of carbon (2θ=26.5°) is significantly enhanced while the characteristic peak of lead (2θ=31.3°) is weakened. This confirms the hindering effect of the coke skeleton on the aggregation of the metallic phase. Figure 6 The comparison shows that the reducing slag phase, when added to the top layer of coke, is mainly composed of silicate minerals such as diopside, exhibiting a dense glassy structure; while the slag phase with high porosity when added to the bottom layer of coke indicates that the gas evolution path has a significant impact on the physical structure of the slag phase. Figure 6 Surface ash phase analysis of c indicates that, regardless of the coke addition method, the surface ash mainly consists of Fe2O3 (2θ=33.2°), Fe3O4 (2θ=30.2°), and unreacted carbon, confirming that surface ash formation is primarily influenced by excess coke rather than the type of iron source. Crucially... Figure 6 (e) shows the XRD results of the iron-rich matte phase, which demonstrates the fundamental difference in the efficiency of hazardous element fixation due to the location of coke addition: when added to the top layer of coke, the matte phase contains various sulfide phases such as Pb, FeS, ZnS, and CuAsS, which proves that volatile elements such as arsenic and zinc are effectively captured in the matte phase; while when added to the bottom layer of coke, the matte phase is mainly composed of Pb and FeS, and the ZnS and CuAsS phases almost disappear, indicating that the upward airflow generated by the bottom coke carries these volatile components, resulting in a significant reduction in arsenic fixation rate of about 8-10%. Figure 6Further analysis revealed the influence of gas escape paths on volatile matter capture. Zinc spinel (ZnAl2O4) was formed in the asbestos reactants, confirming the migration behavior of volatile metals. Furthermore, the amount of asbestos reactants increased significantly with the coke bottom-layer addition method, indicating more severe volatilization losses of elements such as arsenic and lead. This series of phase structure differences well explains why the coke top-layer addition method can simultaneously achieve high-grade crude lead (92.4%) and efficient arsenic fixation (>95%), while mixed or bottom-layer addition methods struggle to achieve both. XRD data, at the atomic scale, revealed that the coke addition method directly determines the elemental distribution behavior between phases by regulating the gas-liquid-solid three-phase mass transfer path, providing strong microstructural evidence for the coke surface addition technology proposed in this invention. This phase structure regulation mechanism breaks through the fundamental assumption in traditional metallurgy that uniform mixing of reactants is beneficial to the reaction. The spatial distribution of coke in the reaction system has a decisive influence on the phase separation behavior and element migration paths during high-temperature reduction smelting.

[0125] Figure 5 and Figure 6 A comprehensive analysis revealed this key regulatory mechanism. When coke is uniformly mixed with the reaction raw materials ( Figure 5 a) The system exhibits complex heterogeneous reaction characteristics. XRD phase analysis ( Figure 6 a) indicates that the reaction products mainly consist of FeS, CaS, and metallic lead (Pb). However, the XRD pattern after fine powder sieving shows a significant enhancement of the characteristic diffraction peak of carbon (2θ=26.5°), while the characteristic peak of lead (2θ=31.3°) is significantly attenuated. This phenomenon reveals a deeper problem caused by the uniform mixing of coke: in areas with excessive coke, a high-melting-point (>3500℃) coke skeleton network is formed, severely hindering the melting flow and aggregation growth of the metal phase; while in areas with insufficient coke, reduction is incomplete, forming a complex mixed structure of metal particles, unreacted coke, and slag interlocking. Thermodynamic analysis shows that this non-uniform distribution disrupts the gas-liquid-solid three-phase mass transfer equilibrium of the system, making it difficult for valuable metals such as lead and zinc to migrate effectively to the metal phase under the resistance of solid-phase diffusion. The slag-metal separation efficiency is reduced to less than 65%, making it impossible to achieve efficient fixation of hazardous elements.

[0126] In contrast, the coke stratification strategy, especially the upper layer placement ( Figure 5 b) This triggered a reconfigurational change in the reaction system, forming a five-layer ordered structure based on a density gradient, with each layer possessing a unique phase composition and elemental enrichment characteristics:

[0127] (1) Formation mechanism and control of overflow phase: XRD analysis ( Figure 6f) indicates that zinc spinel (ZnAl2O4) was formed in the asbestos reactants, which is highly consistent with the 36.71% Zn content in Table 3. The top-down airflow path generated by the coke upper layer arrangement significantly altered the migration behavior of volatile components (As2O3, PbCl2, etc.). Compared to the coke lower layer arrangement, the upper layer arrangement allowed the volatiles carried by the airflow to directly enter the asbestos adsorption zone, reducing interference from the intermediate phase and achieving efficient capture of volatile substances. Thermodynamic calculations confirmed that the CO / CO2 gas generated in the upper layer of coke formed co-precipitates with volatile arsenic and sulfur compounds during its upward escape, inhibiting the release of hazardous elements.

[0128] (2) Causes and effects of the surface gray phase: This phase consists of Fe2O3 (2θ=33.2°) and Fe3O4 (2θ=30.2°) and unreacted carbon. Its formation is a combined result of surface oxidation and incomplete reaction of coke. It is worth noting that the thickness of the surface gray phase is positively correlated with the amount of coke added to the upper layer, indicating that this phase is a sign of incomplete reaction. However, its presence also protects the lower products from excessive oxidation, forming a self-regulating mechanism.

[0129] (3) Optimized formation of the reducing slag phase: The reducing slag in the upper layer of coke exhibits a dense glassy structure. XRD analysis shows that it is mainly composed of an amorphous phase of the CaO-FeO-SiO2 system, enriched with alkali metal elements such as K and Na. In contrast, the CO / CO2 gas generated in the bottom layer of coke forms a large number of pores when passing through the slag layer, resulting in a loose and porous slag phase. The gas escape path in the upper layer of coke is more direct, reducing gas retention in the slag phase and thus forming a denser physical structure. This dense structure not only improves the mechanical stability of the slag phase but also significantly reduces its permeability, providing a physical barrier for the long-term stabilization of hazardous elements.

[0130] (4) Element fixation mechanism of iron-rich matte phase: XRD analysis ( Figure 6 (e) This study revealed the profound impact of coke distribution on the matte phase composition. Multiple phases, including Pb, FeS, ZnS, and CuAsS, were detected in the upper coke sample, while the lower coke sample was dominated by Pb and FeS phases, with ZnS and CuAsS phases almost absent. This difference stems from the temperature and atmosphere gradient created by the upper coke arrangement: CO gas generated in the high-temperature reduction zone permeates downwards, creating suitable Eh-pH conditions in the middle layer, stabilizing volatile sulfides such as ZnS and CuAsS; while the rising gas flow from the lower coke arrangement carries these volatile components directly out of the system. Crucially, the presence of the CuAsS phase demonstrates that arsenic is efficiently fixed in the form of thioarsenate, rather than volatilizing as As₂O₃. This finding contradicts the traditional metallurgical understanding that "high temperatures inevitably lead to arsenic volatilization," revealing a novel approach to arsenic stabilization through precise control of the reaction atmosphere.

[0131] (5) Highly efficient enrichment of crude lead phase: The arrangement of the coke on the upper layer achieves a crude lead phase purity of 92.4% and a lead recovery rate as high as 98.7%. XRD analysis ( Figure 6 d) It was confirmed that crude lead is mainly composed of metallic lead, with rare and precious metals such as Bi and In highly enriched in the crude lead phase, while elements such as Sb, Sn, and Te are rationally distributed between the crude lead and iron-rich matte phases. This elemental distribution pattern perfectly matches the thermodynamic properties of each element: highly lead-loving elements (Bi, In) enter the crude lead phase, moderately siderophile elements (Sb, Sn) are distributed between the two phases, and highly siderophile elements (Cu, As) enter the iron-rich matte phase. The "chemical stirring effect" generated by the arrangement of coke on top significantly promotes the collision, aggregation, and sedimentation of metal droplets, achieving maximum recovery of valuable metals.

[0132] Therefore, this invention discovers that the coke top layer arrangement technology fundamentally solves the technical bottleneck in the treatment of arsenic-containing smelting waste by creating a top-down reduction gradient and optimizing the gas-solid-liquid mass transfer path: on the one hand, it eliminates the risk of environmental pollution by fixing more than 95% of arsenic and sulfur through iron matte phase; on the other hand, it achieves high-purity production of crude lead and synergistic recovery of rare and precious metals in a one-step process, providing a new technical solution for the resource-based treatment of arsenic-containing hazardous waste.

[0133] Figure 7 This clearly demonstrates the decisive influence of iron source type on the macroscopic morphology of high-temperature reaction products, revealing the fundamental differences between single and composite iron sources. Under iron-free conditions ( Figure 7 a) The reaction system exhibits an incompletely layered bilayer structure, with a blurred interface between the yellow outer solid and the black inner solid, and a relatively small volume of the coarse lead phase at the bottom. XRD analysis ( Figure 8 a) indicates that the yellow outer layer is mainly a mixture of glassy phase, CaS, and ZnS, while the black inner layer is rich in PbS, confirming that lead was not completely reduced to its metallic state. This phenomenon reveals the dual role of iron in the reaction: it is not only the driving force for lead reduction (through the substitution reaction PbS + Fe = Pb + FeS), but also a key promoter of matte phase formation. When a single iron source is added ( Figure 7 When the three-phase separation effect was significantly improved (b-7c), metallic iron and iron oxide exhibited different characteristics: the coarse lead phase in the metallic iron (8%Fe) sample was larger and denser, indicating that it had a stronger promoting effect on lead reduction; while the reduction slag in the iron oxide (8%Fe2O3) sample was dark green and had better fluidity, indicating that it optimized the physical properties of the slag phase. Figure 7 The composite iron source (8%Fe + 8%Fe2O3) exhibited by d produced a breakthrough synergistic effect, forming a perfect four-phase layered structure: a dense surface ash layer, a homogeneous glassy slag phase, a continuous iron-rich matte phase, and a large-volume coarse lead phase. XRD analysis ( Figure 9This study confirmed that under composite iron source conditions, the PbS phase completely disappeared in the iron-rich matte phase, while PbS residues remained under single iron oxide conditions. This phenomenon cannot be simply explained by an additive effect, but rather reveals an electron transfer mechanism between iron sources: metallic iron provides the reduction driving force, while iron oxide lowers the reaction activation energy by forming a low-melting-point iron oxide intermediate phase. The two form a unique electron-hole conduction network in the high-temperature melt, accelerating the lead extraction kinetics. Notably, the volume of the crude lead phase under composite iron source conditions is 35-40% larger than that under single iron source conditions, indicating that iron source synergy not only improves reduction efficiency but also optimizes the aggregation behavior of the metallic phase. This finding is completely different from the basic understanding of single reducing agent optimization in traditional metallurgy.

[0134] Figure 10-12 The elemental distribution data reveals the precise control over elemental distribution behavior by iron source type, particularly the synergistic balance between arsenic fixation and lead recovery. Under iron-free conditions, lead distribution in the crude lead phase is less than 75%, with a large amount retained in the matte and slag phases. Simultaneously, arsenic content in the overflow phase increases significantly, confirming the crucial role of iron in suppressing arsenic volatilization. Under single metallic iron conditions, lead distribution increases to 91.3%, but iron content in the matte phase is low (approximately 38%), and arsenic fixation is only 76.5%, demonstrating its limitations in arsenic fixation. Under single iron oxide conditions, iron content in the matte phase increases to 44.2%, and arsenic fixation increases to 83.7%, but lead distribution decreases to 86.4%, indicating that neither of the two single iron sources can simultaneously optimize lead recovery and arsenic fixation. Most importantly, under composite iron source (8%Fe + 8%Fe2O3) conditions… Figure 11 Lead distribution in the crude lead phase reached 98.7%, while arsenic distribution in the iron-rich matte phase exceeded 89%. This synergistic effect completely overturned the conventional wisdom that "high lead recovery inevitably comes with low arsenic fixation." Further analysis... Figure 12 Data on copper and sulfur distribution revealed that under composite iron source conditions, sulfur distribution in the matte phase reached as high as 88.3%, while copper distribution exceeded 97%, indicating that this condition simultaneously optimized the distribution behavior of multiple elements. This phenomenon stems from the unique chemical environment created by the composite iron source: metallic iron lowers the oxygen potential of the system, promoting the selective reduction of lead; iron oxide increases the sulfur capacity of the matte phase, enhancing the arsenic fixation capacity.

[0135] Figure 13 The nonlinear effect of coke addition on the macroscopic structure of the reaction products was demonstrated, revealing a precise process optimization window. Under coke-free conditions ( Figure 13 a) Although the reaction system can be stratified, the interfaces between the phases are blurred, and there are a large number of pores between the iron-rich matte phase and the coarse lead phase, resulting in a loose and porous structure in the reducing slag. XRD analysis ( Figure 14a) It was confirmed that a significant PbS characteristic peak (2θ = 28.5°) existed in the matte phase under coke-free conditions, and a PbSiO5 phase was detected in the slag phase, indicating incomplete lead reduction and severe interphase diffusion. When the coke content increased to 3% ( Figure 13 At step b), the system structure undergoes a qualitative change: the reducing slag transforms into a dense, dark green glassy phase, the porosity at the matte-lead interface significantly decreases, and the volume of the coarse lead phase increases, indicating that the CO gas generated by the gasification reaction of coke induces melt convection and enhances reaction kinetics. The coke content is further increased to 6% ( Figure 13 At time c), the four-phase separation reaches its optimal state: the surface gray phase is thin and uniform, the slag phase is dense and non-porous, the matte phase is continuous and intact, and the coarse lead phase is bright and dense, as shown in the XRD pattern ( Figure 15 The results showed that the matte phase was mainly composed of FeS and CuAsS, confirming that arsenic was stably fixed in the form of thioarsenate. However, when the coke content increased to 9% ( Figure 13 At time d), the system behavior undergoes a sudden change: the surface gray phase thickens abnormally, with characteristic peaks of Fe2O3 and Fe3O4 ( Figure 14 b) Significantly enhanced, while CaS contamination phase appears in the sulfite phase ( Figure 15 The surface of the coarse lead phase becomes rough. This phenomenon reveals a critical transition in the coke reaction mechanism: below 6%, the chemical stirring effect becomes dominant, enhancing phase separation; above 9%, viscosity and oxidation effects dominate, disrupting phase structure integrity. Particularly noteworthy is that the Zn content in the asbestos reactants reaches its peak at 3% coke. Figure 14 (a) indicates that there is an optimal matching point between the gas escape path and the volatile element capture efficiency.

[0136] Figure 16-18 The elemental distribution data system revealed a quantitative relationship between coke addition and elemental distribution efficiency, exhibiting a clear peak optimization characteristic. The distribution rate of lead in the crude lead phase showed a single-peak curve with increasing coke content, reaching a maximum of 98.7% at 6% coke. Figure 16 At this point, the crude lead grade is 92.4%. This peak phenomenon cannot be explained by simply increasing the reducing agent; rather, it reflects the comprehensive regulation of the physicochemical properties of the melt by coke: an appropriate amount of coke reduces the metal-matte interfacial tension, promoting the coalescence of lead droplets; excessive coke increases the melt viscosity, hindering the coalescence process. More importantly, Figure 17 The results show that the distribution rate of arsenic in the iron-rich matte phase reaches a peak (89.6%) at 3% coke, and then gradually decreases, dropping to 76.3% at 9% coke. This nonlinear response differs from the peak position of lead distribution, revealing the difference in sensitivity of arsenic and lead to the amount of coke added, and providing a theoretical basis for multi-element synergistic optimization. Figure 18This further demonstrates the synergistic relationship between iron and sulfur distribution. Without coke, the iron distribution rate in the matte phase is only 68.4%, with a large amount of iron entering the slag phase. With 3% coke, the iron distribution rate in the matte phase increases to 85.7%, confirming that coke promotes the selective migration of iron. At 6% coke, the optimal equilibrium is reached (distribution rate 91.2%), while the sulfur fixation rate reaches 88.3%. At 9% coke, both indicators decrease significantly. This pattern demonstrates the dual regulatory role of coke in matte phase formation: on the one hand, it promotes iron activation through reduction; on the other hand, it optimizes the fluidity of the matte phase through airflow agitation. Particularly noteworthy is... Figure 17 The results showed that, under 6% coke conditions, copper distribution in the matte phase exceeded 97%, while approximately 2.15% copper was also enriched in the coarse lead phase, achieving fractional copper recovery. This multi-element synergistic distribution model solves the technical problem of "element competitive distribution" in traditional metallurgy, providing a new approach for the precise separation of complex multi-metal waste.

[0137] 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 the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for treating lead- and arsenic-containing solid waste, characterized in that, The specific steps are as follows: Step 1: Mix lead mud, industrial dust, CaO and SiO2 to obtain reaction raw materials; then add iron source and coke to obtain mixed raw materials; in the mixed raw materials, the amount of iron source added is 8wt% to 16wt% and the amount of coke added is 1wt% to 9wt% by mass percentage. Step 2: After wet grinding the raw materials prepared in Step 1 to form a uniform slurry, fill the slurry into a container, compact it, and then dehydrate and solidify it to obtain the reaction material. Step 3: React the reactants obtained in Step 2 at 1300℃~1500℃ for 1h~3h, and after ensuring complete reduction reaction, cool to room temperature.

2. The processing method according to claim 1, characterized in that, The iron source is Fe and / or Fe2O3; in the mixed raw materials of step 1, the amount of Fe added is 0-8 wt% and the amount of Fe2O3 added is 0-8 wt% by mass percentage.

3. The processing method according to claim 2, characterized in that, In the mixed raw materials, lead mud, industrial dust, CaO, SiO2 and iron source are thoroughly mixed evenly to obtain the reaction raw materials; coke is laid on the top layer of the reaction raw materials to obtain the mixed raw materials.

4. The processing method according to claim 3, characterized in that, In the mixed raw materials, the amount of coke added is 3wt% to 9wt% by mass percentage; the iron source is Fe or Fe2O3 or a combination of Fe and Fe2O3.

5. The processing method according to claim 2, characterized in that, In the mixed raw materials, lead mud, industrial dust, CaO, SiO2 and iron source are thoroughly mixed evenly to obtain the reaction raw materials; coke is mixed evenly with the reaction raw materials to obtain the mixed raw materials.

6. The processing method according to claim 5, characterized in that, In the mixed raw materials, the amount of iron source added is 8 wt% by mass, and the iron source is a composition of Fe and Fe2O3.

7. The processing method according to claim 1, characterized in that, The mass ratio of lead mud, industrial dust, CaO and SiO2 is (200-300): (300-350): (30-35): (55-60).

8. The processing method according to claim 1, characterized in that, In step 2, the container is also filled with an adsorbent to adsorb volatile substances generated during the reaction.

9. The processing method according to claim 1, characterized in that, In step 3, the heating rate is 4℃ / min to 6℃ / min.

10. The processing method according to claim 1, characterized in that, In the reaction raw materials of step 1, the Pb content is at least 20% and the As content is at least 5% by mass percentage.

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