A method for preparing lead halide from spent lead paste by wet process

Abstract

This invention belongs to the technical field of waste lead-acid battery resource utilization and lead halide crystal preparation. It discloses a wet method for preparing lead halides from waste lead paste, comprising the following steps: S1: Desulfurizing the waste lead paste and then calcining it to obtain calcined desulfurized lead paste; S2: Leaching the calcined desulfurized lead paste in an acetic acid solution, controlling the molar ratio of acetic acid to lead in the calcined desulfurized lead paste and the equilibrium pH of the reaction system; solid-liquid separation, retaining the liquid phase solution; S3: Adding a hydrohalic acid solution for reaction, and obtaining a primary lead halide product after solid-liquid separation; S4: Dissolving the primary lead halide product in hot pure water and performing solid-liquid separation, the resulting liquid phase being cooled and recrystallized to obtain purified lead halide crystals. This invention solves the problems of low reagent utilization, high product purification difficulty, and low purity of lead halide products in existing processes. It is applicable to the preparation of lead halide materials with different halogens such as lead chloride, lead bromide, and lead iodide, and has good versatility.

Description

Technical Field

[0001] This invention belongs to the field of waste lead-acid battery resource utilization and lead halide crystal preparation technology, and more specifically, relates to a method for wet preparation of lead halide from waste lead paste. Background Technology

[0002] Lead halides (such as lead iodide, lead bromide, and lead chloride) are key precursors for the light-absorbing layer of lead-based perovskite solar cells, and their purity directly determines the photoelectric conversion efficiency and stability of photovoltaic devices. As the global photovoltaic industry moves towards the "terawatt" level, especially with all-perovskite tandem cells achieving record-breaking efficiency, the market demand for "electronic-grade" high-purity lead halides is experiencing explosive growth. Traditional commercial methods primarily rely on high-purity primary lead ingots (smelted from primary ore) through acid leaching and halogenation. This process is not only energy-intensive but also prone to secondary heavy metal pollution, and primary lead resources are becoming increasingly scarce. Meanwhile, waste lead-acid batteries, a core source of secondary lead resources, contain abundant recycled lead resources in their waste lead paste. Establishing a "closed-loop recycling" model that directly converts waste lead paste into high-purity lead halides will significantly lower the manufacturing threshold for perovskite batteries, achieving a deep integration of the circular economy and the green energy industry.

[0003] However, existing technologies still face many challenges in converting complex waste lead paste into photovoltaic-grade high-purity raw materials (lead halides such as lead iodide, lead bromide, and lead chloride, as photovoltaic-grade raw materials, often require a purity of over 99.99%; the purity of photovoltaic-grade raw materials is also the purity required for tandem solar cells). The methods disclosed in CN 201810188405.0 and CN 201810184271.5 still use lead acetate or lead nitrate derived from primary lead as raw materials, failing to address the source problem of resource recycling and resulting in extremely high acid consumption. Regarding waste lead paste recycling, CN 201911357146.0 proposes a complex process involving strong alkali desulfurization, hydrogen peroxide reduction, and methanesulfonic acid leaching. While this process achieves resource recovery, its lengthy process and failure to target and efficiently remove impurities unique to waste lead paste, such as iron (Fe), barium (Ba), antimony (Sb), and glass fiber fragments, make it difficult for the product to achieve the purity required for tandem solar cells. CN 202311159418.2 discloses a lead paste recycling process, which simplifies some steps. However, the use of oxalic acid or citric acid during the leaching process directly reacts with lead ions to form a solid precipitate, failing to remove trace metal impurities and potentially leading to significant fluctuations in precursor purity. CN 201810379427.5 discloses a method for wet recycling and impurity removal of waste lead paste to prepare high-purity lead compounds. This method uses hydrogen peroxide and acetic acid to leach desulfurized lead paste to prepare lead oxide products. However, the CO2 gas generated during the leaching process, along with the decomposition of hydrogen peroxide, causes a large number of bubbles in the solution, which is difficult to control in actual production operations. Furthermore, hydrogen peroxide is prone to self-decomposition, often requiring excessive addition. When lead halide is the target product, the excessive hydrogen peroxide reacts with hydrohalic acid, introducing halogen elements (for example, the reaction formula for hydroiodic acid is: H2O2 + 2HI = 2H2O + I2), thereby affecting product purity and overall yield.

[0004] Our research group's previous work, CN 202310804895.3, disclosed a method for recovering high-purity lead chloride from waste lead paste. However, because it uses an HCl-NaCl mixed solution as a leaching agent, the product can only be lead chloride. Another previous work, CN 202310750634.8, disclosed a method for recovering high-purity lead iodide from reduced lead paste. However, this method involves directly subjecting the waste lead paste to reduction treatment such as roasting (the Pb element in the obtained reduced lead paste mainly exists in the form of lead sulfate and PbO. The reaction formula during roasting is 2PbO2=2PbO+O2, and PbSO4 does not participate in roasting and remains in the obtained reduced roasted lead paste). Iodized salt solution is then added to desulfurize the reduced lead paste and simultaneously convert it into lead iodide to obtain a preliminary reaction solution. Then, hydroiodic acid solution is added to the preliminary reaction solution to adjust the pH value, and solid-liquid separation is performed to obtain crude lead iodide crystals. The product of this method can only be lead iodide. Because the solubility products of PbSO4, PbCl2, and PbBr2 are relatively similar, PbCl2 and PbBr2 products cannot be obtained through hydrogen halides. The two methods described above can only yield single lead halide products. However, perovskite solar cells have diverse requirements for lead halides, necessitating the simultaneous use of multiple lead halides. Therefore, if it were possible to flexibly adjust the yield to obtain lead halides corresponding to different halogens as needed, it would undoubtedly have greater practical value.

[0005] In summary, existing lead halide preparation processes generally suffer from low reagent utilization and cumbersome product purification processes. Meanwhile, recycling processes using recycled lead raw materials such as waste lead paste to prepare lead halides face challenges such as the addition of large amounts of reducing agents during the reduction process, incomplete removal of impurities from waste lead paste, and difficulty in improving product purity. Furthermore, some methods that can obtain high-purity lead halide products are limited to a specific type of halogen. Therefore, there is an urgent need to develop new wet processes for producing high-purity lead halides from waste lead paste for various halogens. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the existing technology, the purpose of this invention is to provide a method for wet preparation of lead halides from waste lead paste, which aims to solve the technical problems of low reagent utilization, high difficulty in product purification, and low purity of lead halide products in the existing process. Furthermore, the method of this invention is applicable to the preparation of lead halide materials with different halogens such as lead chloride, lead bromide, and lead iodide, and has good versatility.

[0007] To achieve the above objectives, according to the present invention, a method for wet-process preparation of lead halides from waste lead paste is provided, comprising the following steps: S1: The desulfurized lead paste obtained after desulfurization of waste lead paste is calcined at a temperature of not less than 600 °C to obtain calcined desulfurized lead paste that does not contain +4 valence Pb; wherein, the waste lead paste is waste lead paste from waste lead-acid batteries. S2: The calcined desulfurized lead paste obtained in step S1 is placed in an acetic acid solution for leaching treatment. The molar ratio of acetic acid to lead in the calcined desulfurized lead paste in the acetic acid solution is (2.1–3):1. The equilibrium pH of the reaction system is maintained between 2.0 and 5.0 by controlling the content of water solvent in the system. After the reaction is complete, the solid and liquid phases are separated, and the separated liquid phase is retained. This liquid phase is the lead acetate solution after removing impurities. S3: Add hydrohalic acid solution to the lead acetate solution after removing impurities obtained in step S2 to react and generate lead halide precipitate. After solid-liquid separation, the initial lead halide product and filtrate are obtained. S4: Dissolve the lead halide primary product obtained in step S3 in hot pure water, and adjust the pH of the system to less than 6.5 by adding hydrohalic acid solution, and then separate the solid and liquid phases; the liquid phase obtained by solid-liquid separation can be cooled and recrystallized to obtain purified lead halide crystals.

[0008] As a further preferred embodiment of the present invention, in step S2, the molar ratio of acetic acid in the acetic acid solution to lead in the calcined desulfurized lead paste is (2.3–2.5):1.

[0009] As a further preferred embodiment of the present invention, the molar ratio of acetic acid in the acetic acid solution to lead in the calcined desulfurized lead paste is 2.4:1.

[0010] As a further preferred embodiment of the present invention, in step S2, the concentration of the acetic acid solution is 0.8–1.0 mol / L.

[0011] As a further preferred embodiment of the present invention, in step S2, the equilibrium pH value of the controlled reaction system is between 2.0 and 5.0, specifically preferably between 4.0 and 5.0.

[0012] As a further preferred embodiment of the present invention, the molar ratio of halide ions in the hydrohalic acid solution used in step S3 to lead ions in the solution obtained in step S2 is 2:1. Accordingly, the filtrate obtained in step S3 is an acetic acid solution, which can be reused in step S2.

[0013] As a further preferred embodiment of the present invention, in step S1, the desulfurization is carried out by reacting waste lead paste with an alkaline desulfurizing agent. Preferably, the alkaline desulfurizing agent is at least one of Na2CO3, (NH4)2CO3, NaOH, and NH3·H2O.

[0014] As a further preferred embodiment of the present invention, in step S1, the calcination temperature is 600 °C–800 °C, and the holding time is not less than 30 minutes.

[0015] As a further preferred embodiment of the present invention, in step S3, the hydrohalic acid solution is one of HI, HBr, and HCl, and correspondingly, the lead halide primary product obtained in step S3 is one of lead iodide primary product, lead bromide primary product, and lead chloride primary product.

[0016] As a further preferred embodiment of the present invention, in step S4, the temperature of the hot pure water is 70 °C–100 °C; the addition ratio of the lead halide primary product in each liter of hot pure water is 0.5–5.0 g; The type of hydrohalic acid solution used to adjust the pH of the system is the same as that used in step S3.

[0017] Compared with the prior art, the method of this invention uses the desulfurization product of waste lead-acid battery lead paste (i.e., waste lead paste) as the starting reactant. First, it obtains roasted desulfurized lead paste (containing no +4 valence Pb, mainly composed of +2 valence Pb Pb) through roasting. Then, it leaches the roasted desulfurized lead paste with acetic acid solution. By controlling the pH value between 2.0 and 5.0, selective dissolution of lead ions is achieved in the leaching step, while retaining metallic impurities and glass fiber impurities in the solid residue. After solid-liquid separation, a low-impurity lead acetate solution (i.e., lead acetate solution after impurity removal) is obtained. Then, hydrohalic acid is added to the low-impurity lead acetate solution to react and generate lead halide precipitate. After solid-liquid separation, the primary lead halide product is obtained (the corresponding filtrate, especially the halogen ions in the hydrohalic acid solution used in the precipitation reaction can be reacted with the impurity-removed lead acetate solution). The molar ratio of lead ions in the solution is controlled at 2:1 to ensure that the filtrate is acetic acid, which can then be recycled as a leaching agent for the leaching step. Alternatively, the molar ratio of halide ions in the hydrohalic acid solution used for precipitation to lead ions in the lead acetate solution after impurity removal can also be controlled to be greater than 2:1. In this case, it does not affect the purity and yield of the final lead halide product, but only the filtrate reuse process. In addition to acetic acid, the filtrate will also contain a small amount of unreacted hydrohalic acid, which can be separated by adding lead acetate to precipitate and filter out the excess hydrohalic acid. Finally, by cooling and recrystallizing, a small amount of insoluble impurities are removed through solid-liquid separation to further improve the purity of the lead halide, thus obtaining purified lead halide crystals. (During the recrystallization process, hydrohalic acid is added to ensure that the pH of the system is less than 6.5 to avoid the formation of hydrolysis products such as Pb(OH)Cl, Pb(OH)Br, and Pb(OH)I.)

[0018] Specifically, the present invention can achieve the following beneficial effects: (1) Existing technologies for preparing lead halides from waste lead paste often involve adding large amounts of reducing agents such as H2O2, glucose, iron powder, and Na2SO3 during the reduction or leaching process. This leads to problems such as the introduction of impurity elements and high reagent consumption. When lead halides are used as the final product, the introduced unreacted reducing agents or impurity elements can affect the yield and purity of the product. This invention innovatively achieves the simultaneous decomposition of desulfurization components such as PbCO3 or Pb(OH)2 and PbO2 in desulfurized lead paste through a calcination process at 600 °C–800 °C, generating a uniform PbO phase (all of which are +2 valence Pb elements), which facilitates the subsequent leaching and impurity removal process. Furthermore, since the decomposition of PbO2 is an exothermic process, a higher reduction rate can be achieved compared to the chemical reaction with added reducing agents. This invention utilizes calcination for reduction, without adding external reducing agents or introducing new ionic impurities. This optimized precursor phase significantly improves the leaching kinetics efficiency of acetic acid in the leaching step, achieving efficient lead dissolution without the need for additional reducing agents such as hydrogen peroxide. Through the synergistic effect of the entire process, the comprehensive lead recovery rate from waste lead paste can reach over 98%, maximizing the economic value of waste secondary resources.

[0019] This invention is applicable to desulfurized lead paste obtained from various desulfurization processes. Taking Na2CO3 as an alkaline desulfurizing agent as an example, the main component of the waste lead paste desulfurization product is PbCO3, and other components include, for example, PbO2, PbO, and metallic Pb that did not participate in the desulfurization reaction. Other common alkaline desulfurizing agents, such as (NH4)2CO3, produce desulfurized lead paste with the main components of PbCO3 and / or Pb3(OH)2(CO3)2 (the main components will vary between PbCO3 and / or Pb3(OH)2(CO3)2 depending on the amount of (NH4)2CO3 used), NaOH produces desulfurized lead paste with the main component of Pb(OH)2, and NH3·H2O produces desulfurized lead paste with the main component of Pb(OH)2. In addition to the main components, these desulfurized lead pastes all include PbO2, PbO, and metallic Pb that did not participate in the desulfurization reaction. PbCO3, Pb(OH)2, and Pb3(OH)2(CO3)2 can all be completely converted into stable α-PbO and β-PbO phases at calcination temperatures of 600 °C–800 °C by extending the holding time.

[0020] The main reaction formulas of the calcination reduction process are as follows: PbCO3 = PbO + CO2(g) Pb(OH)₂ = PbO + H₂O Pb3(OH)2(CO3)2= 3PbO+H2O+2CO2(g) 2PbO₂ = 2PbO + O₂(g) Pb + PbO₂ = 2PbO The decomposition of +4 valence lead (PbO2) into PbO involves intermediate lead oxide phases with mixed valence states (such as Pb2O3 and Pb3O4). At a calcination temperature of 600 °C or higher, all lead oxide phases transform into lead oxide (PbO). The α-PbO and β-PbO phases have different thermodynamic stability and can interconvert during calcination (for example, at a calcination temperature of 700 °C or higher, α-PbO will transform into β-PbO). Furthermore, although the above reactions generate gases, they are solid-phase calcination reactions, not liquid-phase reactions; therefore, the generation of bubbles will not negatively impact the reaction.

[0021] (2) Furthermore, unlike the previous results of this research group, CN 202310804895.3 and CN 202310750634.8, which are limited to the preparation of a single lead halide compound, the process route provided by this invention has a strong ability to be flexibly controlled. It is only necessary to replace the precipitant used in the precipitation step with the corresponding hydroiodic acid HI, hydrobromic acid HBr or hydrochloric acid HCl solution. High-purity lead iodide, lead bromide or lead chloride crystals can be stably prepared using the same set of equipment and circulation system. This not only meets the diverse needs of perovskite solar cells of various systems such as single junction, wide bandgap or narrow bandgap for mixed halogen precursors, but also provides a broader industrial application prospect and extremely high commercial promotion value for this invention in the field of semiconductor material manufacturing.

[0022] (3) The existing leaching process consumes a large amount of leaching reagent, and the leached solution cannot be effectively recycled. This invention achieves acetic acid regeneration by adding hydrohalic acid and optimizing the ratio of halogen ions in the hydrohalic acid solution used in the precipitation reaction to lead ions in the lead acetate solution obtained after impurity removal from leaching to 2:1. This achieves a closed-loop cycle of the leaching agent, and the addition of hydrohalic acid does not introduce alkali metal impurities such as Na and K, which is beneficial for obtaining high-purity products with high yield. Taking hydroiodic acid as an example, the software simulation results of the phase distribution of the reaction between the leaching solution and hydrohalic acid are as follows: Figure 2 As shown, when hydrohalic acid is added to a lead acetate solution, in the acidic range of pH < 7, lead ions tend to precipitate as lead halide, while acetate ions recombine with hydrogen ions generated by the ionization of hydrohalic acid to form acetic acid.

[0023] (4) Existing aqueous solution synthesis processes for lead halide crystals suffer from problems such as long crystallization times, easy hydrolysis of lead halides in water, and difficulty in completely removing impurities due to microscopic encapsulation. This invention, after obtaining the initial lead halide product, utilizes a hot water dissolution-recrystallization method. Taking advantage of the physical property that lead halides are poorly soluble in pure water at room temperature (20°C) and that their solubility increases with temperature, impurities in the lead halide can be further removed. This invention uses hot water at a temperature higher than room temperature, and during the hot water dissolution process, the pH value is adjusted to less than 6.5 using hydrohalic acid, avoiding the formation of hydrolysis products (such as Pb(OH)I). This results in large-sized pure crystals with good crystallinity and high preferred orientation of specific crystal faces, which is more conducive to downstream photovoltaic thin film preparation.

[0024] The process of this invention has a high lead recovery rate and a product purity of ≥99.99%, realizing the high-value conversion of waste lead paste into high-purity electronic-grade lead halide.

[0025] In summary, this invention innovatively develops a four-step process of "simultaneous roasting-selective leaching-halogenation precipitation-hot water purification," successfully establishing a high-value, green, closed-loop pathway for the conversion of desulfurized lead paste into lead halides. This process overcomes the challenges of large dosages of reducing agents and residual trace metals and physical impurities in traditional processes through efficient simultaneous roasting and precise pH-targeted impurity removal technology. Simultaneously, through the synergistic transformation of the entire phase and the regeneration and recycling of the liquid solution (acetic acid system), it achieves low energy consumption and near-zero wastewater discharge while ensuring a comprehensive lead recovery rate exceeding 98%. Furthermore, this invention demonstrates excellent process flexibility, allowing for the customization of high-quality lead iodide, lead bromide, and lead chloride crystals. Therefore, this invention balances high economic efficiency, environmental friendliness, and product diversity, achieving highly efficient conversion of waste lead paste into lead halides. Attached Figure Description

[0026] Figure 1 This invention provides a process flow diagram for the wet preparation of lead halides from desulfurized lead paste.

[0027] Figure 2 The results show the phase distribution of the leaching solution reacting with hydroiodic acid, as simulated by Minteq software. The molar ratio of lead ions, acetate ions, and halide ions in the simulated system is 1:2:2.

[0028] Figure 3 The image shows the XRD pattern of the desulfurized lead paste used in Example 1.

[0029] Figure 4 The XRD pattern of the calcined desulfurized lead paste obtained in step (1) of Example 1 is shown.

[0030] Figure 5The image shows the SEM image of the acetic acid leaching solid residue obtained in step (2) of Example 1.

[0031] Figure 6 The image shows the XRD pattern of the PbI2 crystal prepared in Example 1.

[0032] Figure 7 The image shows a SEM image of the PbI2 crystal prepared in Example 1.

[0033] Figure 8 The XRD pattern of the calcined desulfurized lead paste obtained in step (1) of Comparative Example 4 is shown. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] like Figure 1 As shown, the method for preparing high-purity lead halide crystals by wet process of desulfurized lead paste of the present invention includes the following four stages in its core process flow: S1: Simultaneous roasting to achieve thermal decomposition of the desulfurized lead phase and reduction conversion of +4 valence Pb element; S2: Selective leaching with acetic acid to achieve efficient separation of lead and metal impurities by controlling the pH window of the wet process system; S3: Halogenation precipitation with hydrohalic acid to prepare lead halide primary product (the remaining acetic acid filtrate after filtration can be recycled for leaching in step S2); S4: Dissolution and recrystallization with hot pure water to obtain high-purity lead halide crystals (the temperature of the hot pure water is 20 ℃ higher than room temperature, and the corresponding cooling crystallization process can be carried out at room temperature or below room temperature).

[0036] Examples 1-6 described below are carried out according to the following steps: S1: Dismantle waste lead-acid batteries to obtain waste lead-acid battery lead paste (referred to as waste lead paste). Then, crush the waste lead paste and desulfurize it using existing technologies to obtain desulfurized lead paste. Next, simultaneously roast and transform the desulfurized lead paste into a tube furnace or muffle furnace for heat treatment (the roasting atmosphere is air; of course, nitrogen or argon can also be used). The roasting temperature is set above 600 °C (e.g., 600 °C–800 °C), and the holding time is no less than 30 minutes. At this temperature, Pb(OH)₂ and PbCO₃ undergo thermal decomposition, and PbO₂ containing +4 valence Pb undergoes simultaneous reduction. The product color changes from reddish-brown to yellowish-green, ultimately yielding roasted desulfurized lead paste composed entirely of stable α-PbO and β-PbO phases.

[0037] S2: The lead content of the calcined desulfurized lead paste is determined by titration or ICP. The dry calcined desulfurized lead paste is then immersed in an acetic acid solution. By controlling the concentration and volume of the acetic acid solution, the following conditions are achieved: i) the molar ratio of acetic acid to lead in the calcined desulfurized lead paste is (2.1–3):1; and ii) the equilibrium pH of the reaction system is between 2.0 and 5.0 (preferably 4–5). The selective dissolution of lead is achieved by utilizing the difference in solubility characteristics between lead ions and impurity ions. At this point, metallic impurities such as iron (Fe), barium (Ba), and antimony (Sb) remain in the solid phase as oxides or salts. Simultaneously, glass fiber fragments from the original waste lead paste are also retained in the solid phase. After membrane filtration, a high-purity lead acetate solution is obtained.

[0038] Of course, during the experiment, a quantitative amount of calcined desulfurized lead paste can be placed in a pure water solvent and leached by adding acetic acid solution. The final concentration of acetate in the solution system is between 0.8 and 1.0 mol / L (assuming complete dissociation of acetate), and the molar amount of acetate is controlled to be 2.1 to 3 times that of lead. By controlling the water content in the system (including the pure water solvent used before adding acetic acid solution and the solvent water in the acetic acid solution), the equilibrium pH of the system is precisely adjusted to between 2.0 and 5.0 (preferably 4 to 5), thereby obtaining a feasible concentration and volume of acetic acid solution. That is, without introducing other pH adjusters, the above i) and ii) are achieved only by controlling the amount of water in the system.

[0039] S3: Slowly add a hydrohalic acid (such as HI, HBr, or HCl) dropwise to the above high-purity lead acetate solution. Control the molar ratio of halide ions to lead ions to be 2:1, and consistent with the molar number of acetate ions participating in the leaching reaction in step S2. After the reaction is complete, perform solid-liquid separation to obtain crude lead halide solid. In addition, since the molar ratio of halide ions to lead ions in this step is 2:1, the main component of the filtrate is regenerated acetic acid solution, which can be returned to step S2 for recycling in the next batch of roasted desulfurized lead paste leaching, thus achieving closed-loop utilization of reagents.

[0040] S4: The lead halide precursor obtained in step S3 is placed in pure water at a ratio of 0.5–5.0 g (preferably 4.0 g) per liter of pure water. The lead halide is dissolved by heating the pure water, and the pH is adjusted to less than 6.5 by adding hydrohalic acid dropwise. After complete dissolution, insoluble impurities and residues are removed by solid-liquid separation. The liquid phase after solid-liquid separation is cooled to allow lead halide crystals to recrystallize. Further solid-liquid separation yields the recrystallized lead halide product. Alternatively, the liquid phase after solid-liquid separation can be recycled and reused to dissolve the lead halide precursor for recrystallization.

[0041] The following are specific examples (the hydrohalic acids used in the examples are all commercially available high-concentration solutions): Example 1 (1) Take 10 g of desulfurized lead paste after desulfurization with (NH4)2CO3 solution (XRD test results are as follows). Figure 3 As shown in the figure, its main components are PbCO3 and PbO2. It was placed in a horizontal tube furnace and calcined at 600 °C for 1 h. After cooling to room temperature, the calcined desulfurized lead paste was obtained (XRD analysis showed the results as shown in the figure). Figure 4 As shown, its main components are α-PbO and β-PbO, and its mass is 8.57 g.

[0042] (2) The calcined desulfurized lead paste was placed in a 0.8 mol / L acetic acid solution with a volume of 115 mL. The molar ratio of acetic acid to lead was 2.4:1.0, and the equilibrium pH of the solution system was 4.5. After reacting for 1 h with stirring at 400 rpm, a lead acetate solution and leaching residue were obtained through solid-liquid separation. The leaching residue was discarded (the SEM image of the leaching residue is shown in Figure 1). Figure 5 (As shown).

[0043] (3) The separated lead acetate solution was reacted with hydroiodic acid (commercially available, concentration 55wt%; the same below), with the ratio of iodide ions to lead ions being 2.0:1.0. The reaction was carried out under stirring at 400 rpm until crystallization was achieved. After solid-liquid separation and drying, the initial product of lead iodide was obtained with a product mass of 17.35 g.

[0044] (4) Dissolve the initial product in 4.2 L of pure water, adjust the pH value to acidic by adding hydroiodic acid (the pH value of the system before adjustment is 7.2–7.4), heat to 100 °C, filter the residue after complete dissolution, filter and dry after cooling and recrystallization to obtain lead iodide crystal product with a product mass of 17.40 g and a total lead yield of 97.90% (the total lead yield is calculated by first testing the actual lead content in the desulfurized lead paste by chemical titration and assuming that the product in this step is all lead iodide, the same below; in addition, considering that the solid phase on the filter paper cannot be completely collected in the actual operation, the total lead yield obtained by the process in this embodiment will be higher, and the total lead yield of the embodiments in the following text is also similar).

[0045] Depend on Figure 5 It can be seen that the solid leaching residue obtained in step (2) above is the glass fiber component in lead paste, indicating that the leaching process effectively removes physical impurities.

[0046] The lead iodide crystals obtained by recrystallization in step (4) were subjected to XRD analysis, and the results are as follows: Figure 6As shown, the final lead iodide product contains only the characteristic peak of PbI2, without any impurity phases, and the obtained lead iodide crystal has a preferred orientation of the (0 0 1) crystal plane. Furthermore, the lead iodide crystal obtained by recrystallization in step (4) was characterized by SEM, and the results are as follows: Figure 7 As shown, the product crystals exhibit a hexagonal plate-like structure, consistent with the hexagonal crystal system of lead iodide, demonstrating good crystallinity. Atomic absorption spectrometry confirmed that the purity of lead iodide in the recrystallized product reached 99.9943%.

[0047] In addition, considering that Fe, Ba, and Sb are metallic impurity elements with high content in waste lead paste, and that Cu, Zn, and Al are impurity elements that affect the performance of photovoltaic devices, the content of the above-mentioned impurities in the products of each stage of Example 1 was tested three times using ICP testing, and the average values ​​are shown in Table 1 below. Among them, the measured values ​​of Cu, Zn, and Al in recrystallized lead iodide were slightly higher than those in the initial lead iodide product, which is within the allowable range of error fluctuation (generally, it is considered that when the difference in impurity content is less than 1 mg / kg, there is no significant difference), and the Cu, Zn, and Al contents in the initial lead iodide product and recrystallized lead iodide are basically unchanged.

[0048] Table 1

[0049] Example 2 (1) Take 5 g of desulfurized lead paste after desulfurization by (NH4)2CO3 solution (the main components are PbCO3 and PbO2 as determined by XRD), place it in a muffle furnace, calcine at 600 °C for 1 h, and cool to room temperature to obtain calcined desulfurized lead paste with a mass of 4.29 g.

[0050] (2) The calcined desulfurized lead paste was placed in an acetic acid solution with a concentration of 0.8 mol / L and a solution volume of 70 mL. At this time, the molar ratio of acetate to lead was 2.8:1.0 and the equilibrium pH of the corresponding solution system was 2.6. After reacting for 1 h under stirring at 400 rpm, the lead acetate solution and leaching residue were obtained by solid-liquid separation.

[0051] (3) The separated lead acetate solution was reacted with hydroiodic acid solution, with the ratio of iodide ions to lead ions being 2.0:1.0. The reaction was carried out under stirring at 400 rpm until crystallization was achieved. After solid-liquid separation and drying, the initial product of lead iodide was obtained with a product mass of 8.88 g.

[0052] (4) The primary product was dissolved in 3.0 L of pure water, and the pH was adjusted to acidic by adding hydroiodic acid. The solution was heated to 90°C, and after complete dissolution, the residue was filtered out. After cooling and recrystallization, the solution was filtered and dried to obtain lead iodide crystals. The product mass was 8.76 g, and the total lead yield was 98.60%. Atomic absorption spectrometry confirmed that the purity of lead iodide in the recrystallized product reached 99.9917%.

[0053] Example 3 (1) Take 5 g of desulfurized lead paste after desulfurization by (NH4)2CO3 solution (the main components are PbCO3 and PbO2 as determined by XRD), place it in a muffle furnace, calcine at 700 °C for 1 h, and cool to room temperature to obtain calcined desulfurized lead paste with a mass of 4.28 g.

[0054] (2) The calcined desulfurized lead paste was placed in a 1.0 mol / L acetic acid solution with a volume of 50 mL. At this time, the molar ratio of acetic acid to lead was 2.4:1.0, and the equilibrium pH of the corresponding solution system was 4.7. After reacting for 1 h under stirring at 400 rpm, the lead acetate solution and leaching residue were obtained by solid-liquid separation.

[0055] (3) The separated lead acetate solution was reacted with hydrobromic acid (commercially available, concentration 40 wt%; the same below), with a bromide ion to lead ion ratio of 2.0:1.0. The reaction was carried out under stirring at 400 rpm until crystallization was achieved. After solid-liquid separation and drying, the initial product of lead bromide was obtained with a product mass of 7.06 g.

[0056] (4) Dissolve the initial product in 2.0 L of pure water, adjust the pH value to acidic by adding hydrobromic acid, heat to 100°C, filter the residue after complete dissolution, filter and dry after cooling and recrystallization to obtain lead bromide crystal product with a product mass of 6.82 g and a total lead yield of 96.40%.

[0057] Example 4 (1) Take 5 g of desulfurized lead paste after desulfurization by (NH4)2CO3 solution (the main components are PbCO3 and PbO2 as determined by XRD), place it in a muffle furnace, calcine at 800 °C for 1 h, and cool to room temperature to obtain calcined desulfurized lead paste with a mass of 4.28 g.

[0058] (2) The calcined desulfurized lead paste was placed in a 0.8 mol / L acetic acid solution with a volume of 60 mL. At this time, the molar ratio of acetic acid to lead was 2.4:1.0, and the equilibrium pH of the corresponding solution system was 4.6. After reacting for 1 h under stirring at 400 rpm, the lead acetate solution and leaching residue were obtained by solid-liquid separation.

[0059] (3) The separated lead acetate solution was reacted with hydroiodic acid solution, with the ratio of iodide ions to lead ions being 2.0:1.0. The reaction was carried out under stirring at 400 rpm until crystallization was achieved. After solid-liquid separation and drying, the initial product of lead iodide was obtained with a product mass of 8.87 g.

[0060] (4) The primary product was dissolved in 2.0 L of pure water, and the pH was adjusted to acidic by adding hydroiodic acid. The solution was heated to 100°C, and after complete dissolution, the residue was filtered out. After cooling and recrystallization, the solution was filtered and dried to obtain lead iodide crystals. The product mass was 8.63 g, and the total lead yield was 97.3%. Atomic absorption spectrometry confirmed that the purity of lead iodide in the recrystallized product reached 99.9926%.

[0061] Example 5 (1) Take 10 g of desulfurized lead paste after desulfurization with NaOH solution (the main components of which are Pb(OH)2 and PbO2 as determined by XRD), place it in a horizontal tube furnace, calcine it at 600 °C for 1 h, and cool it to room temperature to obtain calcined desulfurized lead paste with a mass of 9.26 g.

[0062] (2) The calcined desulfurized lead paste was placed in a 0.8 mol / L acetic acid solution with a volume of 115 mL. At this time, the molar ratio of acetic acid to lead was 2.2:1.0, and the equilibrium pH of the corresponding solution system was 4.5. After reacting for 1 h under stirring at 400 rpm, the lead acetate solution and leaching residue were obtained by solid-liquid separation.

[0063] (3) The separated lead acetate solution was reacted with hydroiodic acid solution, with the ratio of iodide ions to lead ions being 2.0:1.0. The reaction was carried out under stirring at 400 rpm until crystallization was achieved. After solid-liquid separation and drying, the initial product of lead iodide was obtained with a product mass of 19.14 g.

[0064] (4) Dissolve the primary product in 4.0 L of pure water, adjust the pH value to acidic by adding hydroiodic acid, heat to 100°C, filter the residue after complete dissolution, filter and dry after cooling and recrystallization to obtain lead iodide crystal product with a product mass of 18.45 g and a total lead yield of 96.4%.

[0065] Example 6 (1) Take 5 g of desulfurized lead paste after desulfurization with NaOH solution (the main components of which are Pb(OH)2 and PbO2 as determined by XRD), place it in a horizontal tube furnace, calcine it at 600 °C for 1 h, and cool it to room temperature to obtain calcined desulfurized lead paste with a mass of 4.63 g.

[0066] (2) The calcined desulfurized lead paste was placed in an acetic acid solution with a pH of 1.0 mol / L and a solution volume of 50 mL. At this time, the molar ratio of acetic acid to lead was 2.4:1.0, and the equilibrium pH of the corresponding solution system was 3.6. After reacting for 1 h under stirring at 400 rpm, the lead acetate solution and leaching residue were obtained by solid-liquid separation.

[0067] (3) The separated lead acetate solution was reacted with hydrochloric acid (commercially available, concentration 36–38 wt%; the same below), with a chloride ion to lead ion ratio of 2.0:1.0. The reaction was carried out under stirring at 400 rpm until crystallization was achieved. After solid-liquid separation and drying, the initial product of lead chloride was obtained with a product mass of 5.77 g.

[0068] (4) Dissolve the primary product in 2.0 L of pure water, adjust the pH value to acidic by adding hydrochloric acid, heat to 100 °C, filter the residue after complete dissolution, filter and dry after cooling and recrystallization to obtain lead chloride crystal product with a product mass of 5.61 g and a total lead yield of 97.1%.

[0069] Example 7 (1) Take 5 g of desulfurized lead paste after desulfurization by (NH4)2CO3 solution (the main components are PbCO3 and PbO2 as determined by XRD), place it in a muffle furnace, calcine at 600 °C for 1 h, and cool to room temperature to obtain calcined desulfurized lead paste with a mass of 4.27 g.

[0070] (2) The calcined desulfurized lead paste was placed in an acetic acid solution with a concentration of 0.8 mol / L and a solution volume of 60 mL. At this time, the molar ratio of acetic acid to lead was 2.4:1.0, and the equilibrium pH of the corresponding solution system was 4.3. After reacting for 1 h under stirring at 400 rpm, the lead acetate solution and leaching residue were obtained by solid-liquid separation.

[0071] (3) The separated lead acetate solution was reacted with hydroiodic acid solution, with the ratio of iodide ions to lead ions being 2.0:1.0. The reaction was carried out under stirring at 400 rpm until crystallization was achieved. After solid-liquid separation and drying, the initial product of lead iodide was obtained with a product mass of 8.86 g.

[0072] (4) The filtrate obtained in step (3) was subjected to halogen removal and evaporation concentration to obtain a reusable acetic acid solution. This solution was then reacted with 4.15 g of calcined desulfurized lead paste obtained in step (1). After reacting for 1 h with stirring at 400 rpm, solid-liquid separation was performed to obtain a lead acetate solution and leaching residue. Titration test showed that the lead concentration in the lead acetate solution was 0.305 mol / L, which is close to the maximum theoretical lead concentration (0.31 mol / L). This indicates that the leaching was complete, and the filtrate obtained in step (3) can be recycled after simple treatment.

[0073] Comparative Example 1 (1) Take 10 g of desulfurized lead paste after desulfurization by (NH4)2CO3 solution (the main components are PbCO3 and PbO2 as determined by XRD), place it in a horizontal tube furnace, calcine at 350 °C for 1 h, and cool to room temperature to obtain calcined desulfurized lead paste with a mass of 8.75 g.

[0074] (2) The calcined desulfurized lead paste was placed in a 0.8 mol / L acetic acid solution with a volume of 115 mL. At this time, the molar ratio of acetic acid to lead was 2.4:1.0, and the equilibrium pH of the corresponding solution system was 4.5. After reacting for 1 h under stirring at 400 rpm, the solid-liquid separation was performed to obtain lead acetate solution and leaching residue. The leaching residue contained unreduced PbO2 and Pb3O4.

[0075] (3) The separated lead acetate solution was reacted with hydroiodic acid solution, with the ratio of iodide ions to lead ions being 2.0:1.0. The reaction was carried out under stirring at 400 rpm until crystallization was achieved. After solid-liquid separation and drying, the initial product of lead iodide was obtained with a product mass of 13.31 g.

[0076] (4) Dissolve the primary product in 4.0 L of pure water, adjust the pH value to acidic by adding hydroiodic acid, heat to 100°C, filter the residue after complete dissolution, filter and dry after cooling and recrystallization to obtain lead iodide crystal product with a product mass of 13.25 g and a total lead yield of 73.90%.

[0077] The total lead yield of this comparative example is low, mainly due to the low roasting temperature of 350 °C in step (1), which resulted in incomplete reaction of PbO2, which remained in the solid leaching residue in step (2).

[0078] Comparative Example 2 (1) Take 10 g of desulfurized lead paste after desulfurization by (NH4)2CO3 solution (the main components are PbCO3 and PbO2 as determined by XRD), place it in a horizontal tube furnace, calcine at 600 °C for 1 h, and cool to room temperature to obtain calcined desulfurized lead paste with a mass of 8.57 g.

[0079] (2) The calcined desulfurized lead paste was placed in a 0.8 mol / L acetic acid solution with a volume of 85 mL. At this time, the molar ratio of acetic acid to lead was 1.8:1.0, and the equilibrium pH of the corresponding solution system was 6.8. After reacting for 1 h under stirring at 400 rpm, the lead acetate solution and leaching residue were obtained by solid-liquid separation.

[0080] (3) The separated lead acetate solution was reacted with hydroiodic acid solution, with the ratio of iodide ions to lead ions being 1.8:1.0. The reaction was carried out under stirring at 400 rpm until crystallization was achieved. After solid-liquid separation and drying, the initial product of lead iodide was obtained with a product mass of 7.51 g.

[0081] (4) Dissolve the primary product in 4.0 L of pure water, adjust the pH value to acidic by adding hydroiodic acid, heat to 100°C, filter the residue after complete dissolution, filter and dry after cooling and recrystallization to obtain lead iodide crystal product with a product mass of 7.51 g and a total lead yield of 43.60%.

[0082] The low overall lead yield in this comparative example is mainly due to the low molar ratio of acetic acid to lead (1.8:1.0) in step (2), the fact that the pH value did not reach the optimized range, and the lead components were not completely leached and remained in the solid leaching residue in step (2).

[0083] Comparative Example 3 (1) Take 10 g of desulfurized lead paste after desulfurization by (NH4)2CO3 solution (the main components are PbCO3 and PbO2 as determined by XRD), place it in a horizontal tube furnace, calcine at 600 °C for 1 h, and cool to room temperature to obtain calcined desulfurized lead paste with a mass of 8.55 g.

[0084] (2) The calcined desulfurized lead paste was directly reacted with hydroiodic acid solution. The ratio of iodide ions to lead element was 2.4:1.0. The reaction was carried out under stirring at 400 rpm until crystallization was achieved. After solid-liquid separation and drying, crude lead iodide crystals were obtained with a product mass of 17.12 g.

[0085] The lead iodide product obtained in this comparative example contained Fe impurities exceeding 600 mg / kg, Ba impurities exceeding 700 mg / kg, and Sb impurities exceeding 400 mg / kg. Atomic absorption spectrometry determined that the purity of the crude lead iodide crystals was only 97.1732%, which cannot meet the requirements for manufacturing perovskite solar cells and other optoelectronic applications. The main reason for this is the lack of purification processes involving acetic acid leaching and hot pure water dissolution-recrystallization.

[0086] In addition, the impurity content of the final products obtained in Examples 1-6 and Comparative Examples 1-3 was detected using ICP testing, as shown in Table 2 below: Table 2

[0087] As shown in Table 2, the Fe and Cu impurity contents of the products of each embodiment are lower than those of the comparative examples. Although the comparative examples 1 and 2 are better than some of the embodiments in terms of Ba, Sb, Zn, and Al impurity contents, the yields of each embodiment are significantly better than those of the comparative examples.

[0088] Comparative Example 4: (1) Take 5 g of desulfurized lead paste (main components of which were PbCO3 and PbO2 as determined by XRD) after desulfurization with (NH4)2CO3 solution, place it in a horizontal tube furnace, and calcine it at 500 °C for 1 h. After cooling to room temperature, calcined desulfurized lead paste with a mass of 4.46 g is obtained. The results of XRD testing are as follows: Figure 8 As shown, the main phase in the obtained roasted desulfurized lead paste is Pb3O4, and the +4 valence lead is not completely converted into +2 valence lead (this is mainly because the roasting temperature used in this comparative example is 500 °C, which is too low).

[0089] Comparative Example 5: (1) Take 10 g of desulfurized lead paste after desulfurization by (NH4)2CO3 solution (the main components are PbCO3 and PbO2 as determined by XRD), place it in a horizontal tube furnace, calcine at 600 °C for 1 h, and cool to room temperature to obtain calcined desulfurized lead paste with a mass of 8.52 g.

[0090] (2) The calcined desulfurized lead paste was placed in an acetic acid solution with a concentration of 0.7 mol / L, with a solution volume of 120 mL. At this point, the molar ratio of acetic acid to lead was 2.1:1.0, and the equilibrium pH of the corresponding solution system was 5.5, which was too high. After reacting for 1 h with stirring at 400 rpm, solid-liquid separation was performed to obtain lead acetate solution and leaching residue. When leaching was complete, the theoretical maximum lead concentration was 0.32 mol / L. However, after titration, the lead concentration in the lead acetate solution obtained in this comparative example was only 0.21 mol / L, indicating that the lead component in the calcined desulfurized lead paste was not completely leached under this pH condition, which would undoubtedly greatly affect the total lead yield.

[0091] The above embodiments are merely examples. For instance, roasting can be carried out in a roasting furnace in addition to using a tube furnace or a muffle furnace. Furthermore, besides using (NH4)2CO3 solution and NaOH solution for desulfurization, we also tried using Na2CO3 and NH3·H2O for desulfurization. The results showed that different types of desulfurizing agents and different concentrations of desulfurizing agent solutions had little effect on the content of Fe, Ba, Sb, Cu, Zn, and Al impurities in the final lead iodide product.

[0092] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for wet-process preparation of lead halide from waste lead paste, characterized in that, Includes the following steps: S1: The desulfurized lead paste obtained after desulfurization of waste lead paste is calcined at a temperature of not less than 600 °C to obtain calcined desulfurized lead paste that does not contain +4 valence Pb; wherein, the waste lead paste is waste lead paste from waste lead-acid batteries. S2: The calcined desulfurized lead paste obtained in step S1 is placed in an acetic acid solution for leaching treatment. The molar ratio of acetic acid to lead in the calcined desulfurized lead paste in the acetic acid solution is (2.1–3):

1. The equilibrium pH of the reaction system is maintained between 2.0 and 5.0 by controlling the content of water solvent in the system. After the reaction is complete, the solid and liquid phases are separated, and the separated liquid phase is retained. This liquid phase is the lead acetate solution after removing impurities. S3: Add hydrohalic acid solution to the lead acetate solution after removing impurities obtained in step S2 to react and generate lead halide precipitate. After solid-liquid separation, the initial lead halide product and filtrate are obtained. S4: Dissolve the lead halide primary product obtained in step S3 in hot pure water, and adjust the pH of the system to less than 6.5 by adding hydrohalic acid solution, and then separate the solid and liquid phases; the liquid phase obtained by solid-liquid separation can be cooled and recrystallized to obtain purified lead halide crystals.

2. The method as described in claim 1, characterized in that, In step S2, the ratio of the number of moles of acetic acid in the acetic acid solution to the number of moles of lead in the calcined desulfurized lead paste is (2.3–2.5):

1.

3. The method as described in claim 2, characterized in that, The ratio of the number of moles of acetic acid in the acetic acid solution to the number of moles of lead in the calcined desulfurized lead paste was 2.4:

1.

4. The method as described in claim 1, characterized in that, In step S2, the concentration of the acetic acid solution is 0.8–1.0 mol / L.

5. The method as described in claim 1, characterized in that, In step S2, the equilibrium pH of the controlled reaction system is between 2.0 and 5.0, specifically preferably between 4.0 and 5.

0.

6. The method as described in claim 1, characterized in that, The molar ratio of halide ions in the hydrohalic acid solution used in step S3 to lead ions in the solution obtained in step S2 is 2:

1. Accordingly, the filtrate obtained in step S3 is an acetic acid solution that can be reused in step S2.

7. The method as described in claim 1, characterized in that, In step S1, the desulfurization involves reacting waste lead paste with an alkaline desulfurizing agent. Preferably, the alkaline desulfurizing agent is at least one of Na2CO3, (NH4)2CO3, NaOH, and NH3·H2O.

8. The method as described in claim 1, characterized in that, In step S1, the roasting temperature is 600 °C–800 °C, and the holding time is not less than 30 minutes.

9. The method as described in claim 1, characterized in that, In step S3, the hydrohalic acid solution is one of HI, HBr, and HCl. Correspondingly, the lead halide primary product obtained in step S3 is one of lead iodide primary product, lead bromide primary product, and lead chloride primary product.

10. The method as described in claim 1, characterized in that, In step S4, the temperature of the hot pure water is 70 °C–100 °C; the addition ratio of the lead halide primary product in each liter of hot pure water is 0.5–5.0 g; The type of hydrohalic acid solution used to adjust the pH of the system is the same as that used in step S3.

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