A method for preparing lead iodide crystal by reducing lead paste wet process short flow

Abstract

The present application belongs to the technical field of waste lead-acid battery resource and lead iodide crystal preparation, and discloses a method for preparing lead iodide crystal by reducing lead paste through a short wet process, which comprises the following steps: S1: collecting waste lead paste from waste lead-acid batteries and reducing the waste lead paste to obtain reduced lead paste; the reduced lead paste is placed in an iodine salt solution and stirred to obtain a preliminary reaction solution; S2: adding a hydroiodic acid solution to the preliminary reaction solution, and then performing solid-liquid separation to obtain a crude crystal; S3: dissolving the crude crystal in an organic solvent, and then performing solid-liquid separation; the obtained filtrate is a lead iodide solution; S4: recrystallizing the lead iodide solution, and then performing solid-liquid separation to obtain a purified lead iodide crystal. Through the improvement of the overall design of the reaction participants and the process flow, the preparation of the lead iodide crystal can be realized through a short process, and the technical problems of long process steps, large reagent input, and low purity of the lead iodide product can be effectively solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of resource utilization of waste lead-acid batteries and preparation of lead iodide crystals, and more particularly relates to a method for preparing lead iodide crystals from reduced lead paste by a short wet process. BACKGROUND

[0002] Lead iodide is one of the most important raw materials in the preparation process of lead-based perovskite solar cells. With the increasing development of the photovoltaic industry and the gradual perfection of the large-scale industrialization of perovskite solar cells, the market demand for lead iodide, especially high-purity lead iodide, is gradually increasing. The current preparation process of commercial lead iodide raw materials uses electrolytic refined lead ingots for acid leaching and iodization, which consumes a large amount of acid reagents and energy, and the by-products of the process cannot be recycled and have low utilization value. On the other hand, with the increasing proportion of lithium batteries in the secondary battery market, a large number of waste lead-acid batteries cannot find a disposal site, and the most common pyrometallurgical recovery of lead-acid batteries produces a large amount of SO2 and lead-containing dust, which is extremely harmful to the environment. If the lead-containing components in lead-acid batteries can be recovered, purified, and further converted into lead iodide by a short wet process, it can not only provide a clean and diverse recycling path for the synthesis of lead iodide, but also provide a new application scenario for excess recycled lead resources.

[0003] CN201810188405.0 and CN201810184271.5 respectively disclose processes for preparing lead iodide crystals using lead acetate and lead nitrate. Both lead acetate and lead nitrate are lead-containing reagents obtained by acid leaching from primary lead such as lead ingots. Such reagents require the use of strong acid solutions (such as nitric acid) to react with Pb in the synthesis process, which consumes a large amount of reagents, causes serious environmental pollution, and has a long process. CN201910412336.1 discloses a process for synthesizing lead iodide from lead-zinc ore by a wet process. Lead and zinc components are separated by an ammonia-sulfamate-ammonium persulfate mixed solution, and the lead-containing components are then treated with sulfuric acid, ammonium acetate, and potassium iodide solution to obtain lead iodide solids. This method uses primary lead materials as raw materials, which should be reduced in the case of excess recycled lead resources. In addition, more than 6 reagents are added, and the process is long. CN201911357146.0 discloses a process from waste lead-acid batteries to lead iodide, which includes the steps of strong alkali desulfurization, hydrogen peroxide reduction, sulfuric acid precipitation, methyl sulfonic acid leaching, and potassium iodide precipitation. Six reagents are added, the process is long, and the lead iodide product is not purified, which may cause Fe, Ba, Sb, and other impurities in the lead-acid battery to enter the lead iodide crystal.

[0004] In summary, existing lead iodide preparation processes are all lengthy, involving steps such as desulfurization, reduction, leaching, and precipitation. Furthermore, these processes require large quantities of reagents, which cannot be recycled, resulting in significant waste. There is an urgent need to develop a new, shorter, wet process for producing high-purity lead iodide from waste lead paste. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide a short-process wet method for preparing lead iodide crystals from reduced lead paste. By improving the overall design of the reaction participants and process flow, the method achieves lead iodide crystal preparation in a short process, effectively solving the technical problems of lengthy processes, large reagent inputs, and low purity of lead iodide products in existing methods. Furthermore, the process of this invention uses small reagent dosages, has high conversion efficiency, low impurity content, and few byproducts, achieving a short-process, clean conversion from waste lead paste to high-purity lead iodide.

[0006] To achieve the above objectives, the present invention provides a method for preparing lead iodide crystals using a short wet process with reduced lead paste, characterized by comprising the following steps:

[0007] S1: Collect waste lead paste from waste lead-acid batteries and perform reduction treatment to obtain reduced lead paste that does not contain +4 valence Pb; then, place the reduced lead paste in an iodine salt solution, wherein the molar ratio of iodide ions in the iodine salt solution to lead in the reduced lead paste is 2:1-4:1; then, stir the reaction for 0.5h-2h to obtain a preliminary reaction solution.

[0008] S2: Add hydroiodic acid solution to the preliminary reaction solution obtained in step S1, adjust the pH value to 2.0-6.0, and after the reaction is complete, separate the solid and liquid; the solid obtained by this solid-liquid separation is the crude crystal.

[0009] S3: Dissolve the crude crystals obtained in step S2 in an organic solvent and then perform solid-liquid separation; the filtrate obtained from this solid-liquid separation is the lead iodide solution.

[0010] S4: After recrystallizing the lead iodide solution obtained in step S3, perform solid-liquid separation; the solid obtained from this solid-liquid separation is the purified lead iodide crystal.

[0011] As a further preferred embodiment of the present invention, in step S1, the reduced lead paste is lead paste obtained by high-temperature calcination reduction of waste lead paste from lead-acid batteries or by a reduction reaction with a reducing agent; wherein, the temperature used for high-temperature calcination reduction is 300℃-600℃, and the atmosphere used is air, N2 or an inert gas, with argon being more preferred; the reducing agent is H2O2 or sulfite, with Na2SO3 being more preferred.

[0012] As a further preferred embodiment of the present invention, the solid obtained by solid-liquid separation in step S3 can be used as reduced lead paste and reused in step S1.

[0013] The filtrate obtained from the solid-liquid separation in step S4 can be used as an organic solvent and reused in step S3.

[0014] As a further preferred embodiment of the present invention, in step S2, the reaction is specifically a stirred reaction for 10 min to 30 min;

[0015] In steps S1 and S2, the stirring speed is 300 rpm to 500 rpm.

[0016] As a further preferred embodiment of the present invention, in step S1, the ratio of the mass of the reduced lead paste to the volume of the iodized salt solution is 50 g / L-100 g / L; the stirring reaction is carried out at 0℃-80℃.

[0017] As a further preferred embodiment of the present invention, in step S1, the iodine salt solution is at least one of potassium iodide solution, sodium iodide solution, and ammonium iodide solution.

[0018] As a further preferred embodiment of the present invention, in step S3, the organic solvent is N,N-dimethylformamide (DMF), or a mixed solution formed by mixing N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) in a volume ratio of 9:1 to 6:4.

[0019] As a further preferred embodiment of the present invention, the volume fraction of the hydroiodic acid solution is 55-75%; the volume ratio of the hydroiodic acid solution to the preliminary reaction solution is 0.5 μL / mL-4 μL / mL.

[0020] As a further preferred embodiment of the present invention, in step S3, the solid-liquid separation after dissolution is carried out at a heating temperature of 50°C-80°C;

[0021] In step S4, the recrystallization is specifically a cooling recrystallization, and the temperature used is -4℃ to 20℃.

[0022] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0023] (1) This invention utilizes waste lead-acid battery lead paste as raw material and proposes a short-process technology to achieve efficient and clean conversion from waste lead paste to high-purity lead iodide. Existing waste lead paste to lead iodide conversion processes generally include at least five steps: desulfurization, reduction, acid leaching / alkaline precipitation, iodization, and purification. This invention innovatively uses the same reagent for both desulfurization and iodization, thus reducing the process to three steps (i.e., reduction, desulfurization, iodization, and purification), significantly reducing the input of chemical reagents. This achieves a combination of waste lead-acid battery resource utilization and short-process wet lead iodide preparation.

[0024] Lead iodide is an important industrial raw material; for example, it is a crucial raw material for the manufacture of perovskite solar cell modules. Traditional preparation methods involve smelting and electrolytically refining primary lead (such as lead ore) to obtain lead ingots, followed by acidic solutions (such as lead acetate or lead nitrate) to obtain lead solution, and then adding iodine-containing reagents (such as potassium iodide or hydroiodic acid) to obtain lead iodide. Wet preparation typically involves desulfurizing and reducing recycled lead (such as waste lead paste), followed by acidic leaching to obtain lead solution or alkaline precipitation (such as sodium carbonate or sodium hydroxide), then calcining to obtain lead oxide, which is then reacted with iodine-containing reagents to obtain lead iodide. Existing technologies involve the addition of multiple reagents and lengthy reaction processes. Shortening the process and reducing reagent input are the key challenges addressed in this invention.

[0025] This invention utilizes reduced lead paste, the reduction process of which can be performed according to relevant existing technologies, to reduce tetravalent lead dioxide in waste lead paste to divalent lead. For example, the reduced lead paste can be the lead paste from waste lead-acid batteries that has undergone high-temperature calcination reduction or reduction reaction with the addition of H2O2 or sulfite reducing agents. Its main components include PbSO4, PbO, metallic Pb, and Pb(OH)2. Its characteristic is that it does not contain tetravalent lead, but only divalent lead and elemental lead. In existing processes, lead sulfate requires desulfurization using alkaline reagents (such as sodium hydroxide or sodium carbonate) to facilitate the overall conversion of the lead paste into a lead-containing solution for the next reaction. This invention innovatively proposes using an iodine-containing reagent to react with the reduced lead paste, utilizing the solubility product of lead sulfate (1.6 × 10⁻⁶). -8 () is greater than lead iodide (7.47 × 10) -9 The properties of lead sulfate cause it to undergo a precipitation-transformation reaction, thus directly yielding lead iodide from lead sulfate. The method of this invention can use three common iodine salts: NaI, KI, and NH4I, as described below. Figure 2 As shown, the reaction is thermodynamically feasible; compared with the existing technology of directly reacting hydroiodic acid with Pb ions, iodine salt has better stability and is more suitable for industrial applications (hydroiodic acid is very easy to decompose, which is not conducive to industrial applications).

[0026] The method of this invention also uses hydroiodic acid solution to adjust the pH of the solution system to a value between 2.0 and 6.0, which effectively promotes the existence of Pb ions in the form of PbI2 and improves the lead conversion rate. (See below) Figure 3 As shown, Figure 3 This invention demonstrates the different forms of lead sulfate in potassium iodide solution at various pH values. Specifically, when the pH is greater than 7.0, the lead component exists as basic lead sulfate (PbO·PbSO4) and lead hydroxide (Pb(OH)2); while when the pH is less than 6, the lead component exists as lead iodide (PbI2) and a small amount of lead sulfate (PbSO4). This invention achieves pH adjustment by adding hydroiodic acid, maintaining the solution system at a pH of 2.0-6.0. Hydroiodic acid can also react with PbO and Pb(OH)2 in the reduced lead paste, thereby increasing the lead conversion rate and improving the final yield without introducing new impurity ions. The chemical reactions occurring in the above process are shown below:

[0027] PbSO4 + 2I - =SO4 2- +PbI2 (1)

[0028] PbO + 2HI = H₂O + PbI₂ (2)

[0029] Pb(OH)₂ + 2HI = 2H₂O + PbI₂ (3)

[0030] Pb + 2HI = H2 + PbI2 (4)

[0031] (2) The entire process of this invention involves only two reagent discharges. The sulfate solution generated during the desulfurization process can be recovered as a byproduct. The lead-containing solid generated during the organic solvent leaching and recrystallization process can be used as raw material for the next round of reaction, and the filtrate is recycled as an organic solvent (that is, the solid obtained in the solid-liquid separation process of step S4 of this invention is high-purity lead iodide crystals, and the obtained filtrate is an organic solvent containing a small amount of lead iodide, which can be recycled for step S3; the main component of the solid obtained in the solid-liquid separation process of step S3 is PbSO4, which is one of the main components of reduced lead paste. Therefore, the solid obtained in the solid-liquid separation process of step S3 can be used as reduced lead paste and reused in step S1. For example, the solid can be mixed with the reduced lead paste to be treated and then used for the next round of reaction). The process generates few pollutants and has minimal overall environmental pollution.

[0032] (3) This invention uses only three chemical reagents: iodized salt solution, hydroiodic acid, and organic solvent. Iodized salt provides the iodine source for lead iodide and is an essential raw material in various processes. Hydroiodic acid is used to adjust the pH value and is used in small quantities. The organic solvent, after recrystallization and filtration, contains only a small amount of dissolved lead iodide and can be used as a solvent without affecting the purity and yield of the next batch of products. Theoretically, it can be recycled without loss. This invention avoids the use of large amounts of strong acid and strong base reagents used in existing processes, thus improving the overall economic efficiency and environmental friendliness of the process.

[0033] (4) The reaction conditions in each step of the present invention are mild and the reaction efficiency is high. The reaction time of the four main steps can preferably not exceed 2 hours, which greatly increases the production efficiency. The reaction process does not use reaction conditions such as high temperature, high pressure, and high speed stirring, and the maximum reaction temperature does not exceed 80°C, making the process simple and controllable.

[0034] (5) This invention particularly utilizes the property that lead iodide is soluble in DMF (or a mixture of DMF and DMSO) organic solvents while lead sulfate is insoluble, using these organic solvents for the separation of lead iodide and lead sulfate. The lead iodide crystals obtained by this invention have high purity, and the crystal size can be controlled by adjusting the recrystallization process conditions, which is beneficial for subsequent use. The lead iodide yield of the process exceeds 95%, and the unconverted 5% lead-containing component can be recycled into the next round of reaction.

[0035] Since PbSO4 is the most abundant (generally greater than 60 wt%) and most difficult to chemically react with in waste lead paste, a desulfurization step is usually required. The most effective methods are to use alkaline reagents to convert PbSO4 into other readily reacting substances (such as Pb(OH)2, PbCO3), or to use acidic solutions (such as acetic acid) to convert PbSO4 into a lead solution. Existing research and technologies have not considered using iodine-containing reagents as desulfurizing agents. This invention innovatively uses iodine-containing reagents to directly convert PbSO4, and controls the amount of iodized salt to maintain a molar ratio of iodide ions to lead in the reduced lead paste of 2:1-4:1 (to avoid excessive iodide ions combining with lead iodide to form [PbI4]). 2- The method uses complexed ions to shorten the reaction process. However, direct use of iodized salt for desulfurization involves a precipitation transformation process, which rarely completely converts one precipitate into another; often, both precipitates coexist. This invention, through in-depth research, has determined that lead sulfate precipitate is more readily converted to lead iodide under acidic conditions (i.e., pH 2.0-6.0). Hydroiodic acid is used as a pH-adjusting reagent to increase the concentration of iodide ions while maintaining an acidic solution, thus further promoting the formation of lead iodide.

[0036] In summary, this invention innovatively combines the desulfurization step with the iodization process, using iodized salt solution as both the desulfurization and iodization reagents, thus avoiding the large-scale use of acid-base chemical reagents and achieving a short-process preparation of lead iodide crystals. The organic solvent used in this invention has no loss under ideal conditions, and the added hydroiodic acid, used as a pH adjustment reagent, is consumed in small quantities. The overall process does not utilize high temperature, high pressure, or high energy consumption conditions, and there is no discharge of lead-containing solutions or solid waste, minimizing economic consumption and environmental impact. This invention achieves a total lead yield exceeding 95%, realizing a short-process wet method for preparing high-purity lead iodide crystals. Attached Figure Description

[0037] Figure 1 This invention provides a process flow diagram for the wet short-process preparation of lead iodide crystals using reduced lead paste.

[0038] Figure 2 These are the reaction thermodynamic parameters during the reaction of NaI, KI, NH4I with lead sulfate.

[0039] Figure 3 The distribution of lead-containing components under different pH conditions was simulated using Medusa software (total concentration of lead ions in the solution was 0.5 mol / L, total concentration of sulfate ions was 0.5 mol / L, total concentration of iodide ions was 1.0 mol / L, and total concentration of potassium ions was 1.0 mol / L).

[0040] Figure 4 The image shows the XRD pattern of the coarse crystals obtained in Example 1.

[0041] Figure 5 The image shows the XRD pattern of the high-purity PbI2 crystal prepared in Example 1.

[0042] Figure 6 This is an SEM image of the high-purity PbI2 crystal prepared in Example 1. Detailed Implementation

[0043] 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.

[0044] In summary, the present invention provides a short-process wet method for preparing lead iodide crystals from reduced lead paste, comprising the following steps: S1: Desulfurizing and initially converting the reduced lead paste into lead iodide by adding iodized salt solution to obtain a preliminary reaction solution; S2: Adjusting the pH of the reaction system by adding hydroiodic acid dropwise to promote the conversion of lead sulfate, and obtaining crude lead iodide crystals after solid-liquid separation; S3: Dissolving the crude crystals with an organic solvent, and obtaining the filtrate from the solid-liquid separation as an organic solution of lead iodide (in addition, the solid after solid-liquid separation can be reused in step S2); S4: Recrystallizing the filtrate to obtain high-purity lead iodide crystals (in addition, the organic solvent after solid-liquid separation can be returned to step S3 for recycling).

[0045] Specifically, in steps S1 and S2: the iodized salt solution can be, for example, potassium iodide, sodium iodide, or ammonium iodide. The molar ratio of iodide ions in the iodized salt solution to lead in the reduced lead paste can be 2:1-4:1 (corresponding to a mass ratio of the reduced lead paste to a volume ratio of the iodized salt solution of 50 g / L-100 g / L; the specific ratio can be determined by the lead content in the reduced lead paste. When the concentration of the iodized salt solution is fixed, the higher the Pb content, the lower the solid-liquid ratio; the lead content of the reduced lead paste is generally between 68 wt% and 85 wt%, with 68 wt% corresponding to the extreme case where the reduced lead paste is entirely composed of lead sulfate). The reaction can be stirred at 0℃-80℃ for 0.5 h-2 h to obtain a preliminary reaction solution. 55-75% hydroiodic acid can be added dropwise to the preliminary reaction solution to adjust the pH to 2.0-6.0. Generally, the addition amount can be 0.5 μL / mL-4 μL / mL (i.e., 0.5 μL-4 μL of hydroiodic acid solution is added per mL of the preliminary reaction solution). The reaction solution system can be reacted for 10-30 minutes under stirring conditions of 300-500 rpm. After the reaction is complete, the solid and liquid can be separated by vacuum filtration. The solid is a coarse crystal, mainly composed of lead iodide and lead sulfate; the filtrate is mainly a sulfate solution, which can be treated to render it harmless.

[0046] In step S3: the organic solvent can be DMF, or a mixture of DMF and DMSO, as DMF can also remove impurities such as Fe, Ba, and Sb. For example, the crude crystals can be placed in an organic solvent and dissolved at a heating temperature of 50℃-80℃, followed by solid-liquid separation. The ratio of the molar amount of lead in the crystals to the volume of the organic solvent can be controlled to be 0.8 mol / L-1.4 mol / L (that is, the volume of organic solvent added can be adjusted according to the lead content in the reduced lead paste; in actual operation, it can also be assumed that the crude crystals are all lead iodide, and the volume of organic solvent added can be controlled so that the mass ratio of the crude crystals to the volume of the organic solvent is 368.8 g / L-645.4 g / L). After filtration through an organic filter membrane, the solid and liquid are separated. The solid is lead sulfate, which can be mixed with the raw materials of the reduced lead paste and enter the next round of reaction, avoiding the discharge of lead components. The solution is an organic solution of complexed lead iodide.

[0047] In step S4: recrystallization can be achieved, particularly by cooling recrystallization, where lead iodide crystals are redetermined at temperatures ranging from -4°C to 20°C. After filtration through an organic filter membrane, solid-liquid separation is achieved. The solid is lead iodide crystals. The resulting crystals contain no other components and exhibit a regular hexagonal prism shape. Correspondingly, the filtrate is DMF (or a mixed solution of DMF and DMSO), which may contain a small amount of residual lead iodide. This filtrate can be recycled for the dissolution and recrystallization of the crude crystals, and ideally, no solvent consumption occurs.

[0048] The following are specific embodiments, and each embodiment satisfies Figure 1 The process flow diagram shown.

[0049] Example 1

[0050] (1) Take 10g of reduced lead paste that has been calcined at 450℃ for 30min in air (the lead content was determined to be 0.0397mol by chemical titration) and place it in 200mL of 0.4mol / L potassium iodide solution. The solid-liquid ratio is 50g / L, and the molar ratio of iodide ions to lead ions is approximately 2:1. Stir the reaction at room temperature for 1h, filter and separate to obtain the preliminary reaction solution. The pH of the reaction solution is 7.4.

[0051] (2) Add 55% hydroiodic acid dropwise to the initial reaction solution until the pH of the solution is in the range of 2.0-6.0. In this example, the volume of hydroiodic acid added is 200 μL, and the final pH of the solution is 3.2. React for 20 min under stirring at 400 rpm, and then filter to separate the solid and liquid phases. The mass of the crude crystals obtained is 14.97 g.

[0052] (3) Place the crude crystals in 33 mL of DMF solvent, with a lead concentration of approximately 1.0 mol / L (assuming the crude crystals are entirely lead iodide; the same applies below). Heat at 60 °C for 30 min to dissolve, and then perform solid-liquid separation through an organic filter membrane.

[0053] (4) After the filtrate was cooled and recrystallized at -4℃, solid-liquid separation was performed using an organic filter membrane. The obtained solid was dried in an oven at 60℃ for 6 hours to obtain lead iodide crystals. The product mass was 14.95g and the total lead yield was 98.30% (the total lead yield was calculated by first testing the actual lead content in the reduced lead paste using chemical titration, and assuming that all the product in this step was lead iodide; the same applies below).

[0054] Furthermore, the coarse crystals obtained in step (2) of the above embodiment were subjected to XRD analysis, and the results are as follows: Figure 4 As shown. The lead iodide crystals obtained in step (4) were subjected to XRD analysis, and the results are as follows. Figure 5 As shown. (Through) Figure 4 andFigure 5 By comparison, it is not difficult to find that the main components of the crude crystal obtained in step (2) are lead iodide and lead sulfate; while in the final lead iodide crystal obtained in step (4), the PbSO4 impurity has almost completely disappeared and the crystal does not contain any other components.

[0055] In addition, the lead iodide crystals obtained in step (4) were characterized by SEM, and the results are as follows: Figure 6 As shown, it appears as regular hexagonal prisms and has good crystallinity.

[0056] Example 2

[0057] (1) Take 10g of reduced lead paste that has been calcined at 450℃ for 30min in air atmosphere (the lead content was determined to be 0.0397mol by chemical titration) and place it in 100mL of 0.8mol / L sodium iodide solution. The solid-liquid ratio is 100g / L, and the molar ratio of iodide ions to lead ions is approximately 2:1. Stir the reaction at room temperature for 1h, filter and separate to obtain the preliminary reaction solution. The pH of the reaction solution is 7.8.

[0058] (2) Add 55% hydroiodic acid dropwise to the initial reaction solution until the pH of the solution is in the range of 2.0-6.0. In this example, the volume of hydroiodic acid added is 100 μL, and the final pH of the solution is 2.8. React for 20 min under stirring at 400 rpm, and then filter to separate the solid and liquid phases. The mass of the crude crystals obtained is 14.80 g.

[0059] (3) Place the crude crystals in 30 mL of DMF solvent, with a lead concentration of approximately 1.1 mol / L. Heat at 60 °C for 30 min to dissolve, and then separate the solid and liquid phases using an organic filter membrane.

[0060] (4) After the filtrate was cooled and recrystallized at -4℃, solid-liquid separation was performed using an organic filter membrane. The obtained solid was dried in an oven at 60℃ for 6 hours to obtain lead iodide crystals. The product mass was 14.71g and the total lead yield was 96.70%.

[0061] Example 3

[0062] (1) Take 10g of reduced lead paste that has been calcined at 450℃ for 15min in air atmosphere (the lead content was determined to be 0.0374mol by chemical titration) and place it in 150mL of 0.5mol / L ammonium iodide solution. The solid-liquid ratio is 67g / L, and the molar ratio of iodide ions to lead ions is approximately 2:1. Stir the reaction at room temperature for 1.5h, filter and separate to obtain the preliminary reaction solution. The pH of the reaction solution is 7.3.

[0063] (2) Add 55% hydroiodic acid dropwise to the initial reaction solution until the pH of the solution is in the range of 2.0-6.0. In this example, the volume of hydroiodic acid added is 60 μL, and the final pH of the solution is 5.9. React for 20 min under stirring at 400 rpm, and then filter to separate the solid and liquid phases. The mass of the crude crystals obtained is 14.81 g.

[0064] (3) Place the crude crystals in 30 mL of a DMF:DMSO solvent with a volume ratio of 7:3, where the lead concentration in the solution is approximately 1.1 mol / L. Heat the solution at 60 °C for 30 min to dissolve, and then separate the solids and liquids using an organic filter membrane.

[0065] (4) After the filtrate was cooled and recrystallized at -4℃, solid-liquid separation was performed using an organic filter membrane. The obtained solid was dried in an oven at 60℃ for 6 hours to obtain lead iodide crystals. The product mass was 14.57g and the total lead yield was 96.07%.

[0066] Example 4

[0067] (1) Take 5g of reduced lead paste (with a lead content of 0.0196mol determined by chemical titration) after reacting with hydrogen peroxide solution, and place it in 100mL of 0.4mol / L potassium iodide solution. The solid-liquid ratio is 50g / L, and the molar ratio of iodide ions to lead ions is approximately 2:1. Stir the reaction at room temperature for 2h, filter and separate to obtain the preliminary reaction solution. The pH of the reaction solution is 7.3.

[0068] (2) Add 55% hydroiodic acid dropwise to the initial reaction solution until the pH of the solution is in the range of 2.0-6.0. In this example, the volume of hydroiodic acid added is 50 μL, and the final pH of the solution is 5.3. React for 10 min under stirring at 400 rpm, and then filter to separate the solid and liquid phases. The mass of the crude crystals obtained is 7.36 g.

[0069] (3) The crude crystals were placed in 12 mL of a DMF:DMSO solvent with a volume ratio of 9:1, and the lead concentration in the solution was approximately 1.37 mol / L. The solution was heated at 80 °C for 20 min to dissolve, and then separated into solid and liquid phases by passing the solution through an organic filter membrane.

[0070] (4) After the filtrate was cooled and recrystallized at -4℃, solid-liquid separation was performed using an organic filter membrane. The obtained solid was dried in an oven at 60℃ for 6 hours to obtain lead iodide crystals. The product mass was 7.34g and the total lead yield was 96.51%.

[0071] Example 5

[0072] (1) Take 20g of reduced lead paste (with a lead content of 0.0787mol determined by chemical titration) after reacting with hydrogen peroxide solution, and place it in 200mL of 0.8mol / L potassium iodide solution. The solid-liquid ratio is 100g / L, and the molar ratio of iodide ions to lead ions is approximately 2:1. Stir the reaction at room temperature for 2h, filter and separate to obtain the preliminary reaction solution. The pH of the reaction solution is 7.8.

[0073] (2) Add 55% hydroiodic acid dropwise to the initial reaction solution until the pH of the solution is in the range of 2.0-6.0. In this example, the volume of hydroiodic acid added is 200 μL, and the final pH of the solution is 3.6. React for 30 min under stirring at 500 rpm, and then filter to separate the solid and liquid phases. The mass of the crude crystals obtained is 29.48 g.

[0074] (3) Place the crude crystals in 60 mL of DMF solvent, where the lead concentration is approximately 1.1 mol / L. Heat at 60 °C for 30 min to dissolve, and then separate the solid and liquid phases using an organic filter membrane.

[0075] (4) After the filtrate was cooled and recrystallized at -4℃, solid-liquid separation was performed using an organic filter membrane. The obtained solid was dried in an oven at 60℃ for 6 hours to obtain lead iodide crystals. The product mass was 29.24g and the total lead yield was 96.11%.

[0076] Example 6

[0077] (1) Take 10g of reduced lead paste that has been calcined at 450℃ for 30min in air (the lead content was determined to be 0.0397mol by chemical titration) and place it in 200mL of 0.8mol / L potassium iodide solution. The solid-liquid ratio is 50g / L, and the molar ratio of iodide ions to lead ions is approximately 4:1. Stir the reaction at room temperature for 1h, filter and separate to obtain the preliminary reaction solution. The pH of the reaction solution is 7.9.

[0078] (2) Add 55% hydroiodic acid dropwise to the initial reaction solution until the pH of the solution is in the range of 2.0-6.0. In this example, the volume of hydroiodic acid added is 400 μL, and the final pH of the solution is 2.0. React for 20 min under stirring at 400 rpm, and then filter to separate the solid and liquid phases. The mass of the crude crystals obtained is 14.75 g.

[0079] (3) Place the crude crystals in 33 mL of DMF:DMSO = 6:4 (volume ratio) solvent, with a lead concentration of approximately 1.0 mol / L (assuming the crude crystals are entirely lead iodide; the same applies below). Heat at 60 °C for 30 min to dissolve, and then perform solid-liquid separation through an organic filter membrane.

[0080] (4) After the filtrate was cooled and recrystallized at -4℃, solid-liquid separation was performed using an organic filter membrane. The obtained solid was dried in an oven at 60℃ for 6 hours to obtain lead iodide crystals. The product mass was 14.53g and the total lead yield was 95.81%.

[0081] Table 1 Comparison of parameter conditions and total lead yield results in Examples 1-6

[0082]

[0083] Comparative Example 1

[0084] (1) Take 10g of reduced lead paste that has been calcined at 450℃ for 30min in air atmosphere (the lead content was determined to be 0.0397mol by chemical titration) and place it in 100mL of 0.8mol / L potassium iodide solution. The solid-liquid ratio is 100g / L, and the molar ratio of iodide ions to lead ions is approximately 2:1. Stir the reaction at room temperature for 1h, filter and separate to obtain the preliminary reaction solution. The pH of the reaction solution is 7.7.

[0085] (2) Without using hydroiodic acid to adjust the pH, solid-liquid separation was carried out by direct filtration, and the mass of the crude crystals obtained was 13.21g.

[0086] (3) Place the crude crystals in 30 mL of DMF solvent, where the lead concentration is approximately 0.6 mol / L. Heat at 60 °C for 30 min to dissolve, and then separate the solid and liquid phases using an organic filter membrane.

[0087] (4) After the filtrate was cooled and recrystallized at -4℃, solid-liquid separation was performed using an organic filter membrane. The obtained solid was dried in an oven at 60℃ for 6 hours to obtain lead iodide crystals. The product mass was 8.33g and the total lead yield was 63.70%.

[0088] Comparative Example 2

[0089] (1) Take 10g of reduced lead paste that has been calcined at 450℃ for 30min in air atmosphere (the lead content was determined to be 0.0397mol by chemical titration) and place it in 200mL of potassium iodide solution with a concentration of 1.4mol / L. The solid-liquid ratio is 100g / L, and the molar ratio of iodide ions to lead ions is approximately 7:1. Stir the reaction at room temperature for 1h, filter and separate to obtain the preliminary reaction solution. The pH of the reaction solution is 8.3.

[0090] (2) Add 55% hydroiodic acid dropwise to the initial reaction solution until the pH of the solution is in the range of 2.0-6.0. In this example, the volume of hydroiodic acid added is 200 μL, and the final pH of the solution is 3.7. React for 20 min under stirring at 400 rpm, and then filter to separate the solid and liquid phases. The mass of the crude crystals obtained is 13.63 g.

[0091] (3) Place the crude crystals in 30 mL of DMF solvent, where the lead concentration is approximately 0.9 mol / L. Heat at 60 °C for 30 min to dissolve, and then separate the solid and liquid phases using an organic filter membrane.

[0092] (4) After the filtrate was cooled and recrystallized at -4℃, solid-liquid separation was performed using an organic filter membrane. The obtained solid was dried in an oven at 60℃ for 6 hours to obtain lead iodide crystals. The product mass was 13.01g and the total lead yield was 87.32%.

[0093] This comparative example used an excessive amount of iodized salt solution (excess iodide ions combine with lead iodide to form [PbI4]). 2- Complex ions cause lead iodide to dissolve, resulting in a decrease in yield.

[0094] Comparative Example 3

[0095] (1) Take 10g of reduced lead paste that has been calcined at 450℃ for 30min in air atmosphere (the lead content was determined to be 0.0397mol by chemical titration) and place it in 100mL of 0.8mol / L potassium iodide solution. The solid-liquid ratio is 100g / L, and the molar ratio of iodide ions to lead ions is approximately 2:1. Stir the reaction at room temperature for 1h, filter and separate to obtain the preliminary reaction solution. The pH of the reaction solution is 7.8.

[0096] (2) Add 55% hydroiodic acid dropwise to the initial reaction solution until the pH of the solution is in the range of 2.0-6.0. In this example, the volume of hydroiodic acid added is 200 μL, and the final pH of the solution is 3.3. React for 20 min under stirring at 400 rpm, and then filter to separate the solid and liquid phases. The mass of the crude crystals obtained is 14.66 g.

[0097] (3) The product components were directly tested and found to be a mixture of lead iodide and lead sulfate, with lead iodide accounting for 95.23% and the remainder being lead sulfate impurities.

[0098] 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 producing lead iodide crystals from a lead paste by a short wet process, characterized in that, The method comprises the following steps: S1: collecting waste lead paste in a waste lead-acid battery and performing reduction treatment to obtain reduced lead paste containing no +4 valence Pb element, the main components of the reduced lead paste including PbSO4, PbO, metal Pb and Pb(OH)2; then, the reduced lead paste is placed in an iodine salt solution, the molar ratio of iodine ions in the iodine salt solution to lead elements in the reduced lead paste being 2:1-4:1; then, stirring reaction is performed for 0.5 h-2 h to obtain a primary reaction solution; S2: adding a hydriodic acid solution to the primary reaction solution obtained in step S1, adjusting the pH value to 2.0-6.0 and performing sufficient reaction, and then performing solid-liquid separation; the solid obtained by the solid-liquid separation is a crude crystal; S3: dissolving the crude crystal obtained in step S2 in an organic solvent and then performing solid-liquid separation; the filtrate obtained by the solid-liquid separation is a lead iodide solution; S4: recrystallizing the lead iodide solution obtained in step S3 and then performing solid-liquid separation; the solid obtained by the solid-liquid separation is a purified lead iodide crystal.

2. The method of claim 1, wherein, In the step S1, the reduced lead paste is obtained by high-temperature roasting reduction or reduction reaction with a reducing agent of the waste lead paste in the lead-acid battery; wherein the temperature for the high-temperature roasting reduction is 300 ℃-600 ℃, and the atmosphere used is air or N2; the reducing agent is H2O2 or a sulfite.

3. The method of claim 1, wherein, In the step S1, the reduced lead paste is obtained by high-temperature roasting reduction or reduction reaction with a reducing agent of the waste lead paste in the lead-acid battery; wherein the temperature for the high-temperature roasting reduction is 300 ℃-600 ℃, and the atmosphere used is an inert gas; the reducing agent is H2O2 or a sulfite.

4. The method of claim 3, wherein, The inert gas is argon; and the sulfite is Na2SO3.

5. The method of claim 1, wherein, The solid obtained by the solid-liquid separation in the step S3 is used as the reduced lead paste and is repeatedly used in the step S1; The filtrate obtained by the solid-liquid separation in the step S4 is used as the organic solvent and is repeatedly used in the step S3.

6. The method of claim 1, wherein, In the step S2, the reaction is specifically stirring reaction for 10 min-30 min; In the steps S1 and S2, the stirring speed is 300 rpm-500 rpm.

7. The method of claim 1, wherein, In the step S1, the ratio of the mass of the reduced lead paste to the volume of the iodine salt solution is 50 g / L-100 g / L; and the stirring reaction is performed at 0 ℃-80 ℃.

8. The method of claim 1, wherein, In the step S1, the iodine salt solution is at least one of a potassium iodide solution, a sodium iodide solution and an ammonium iodide solution.

9. The method of claim 1, wherein, In the step S3, the organic solvent is N,N-dimethylformamide or a mixed solution formed by mixing N,N-dimethylformamide and dimethyl sulfoxide at a volume ratio of 9:1-6:

4.

10. The method of claim 1, wherein, In the step S2, the volume fraction of the hydriodic acid solution is 55-75%; and the volume ratio of the hydriodic acid solution to the primary reaction solution is 0.5 μL / mL-4 μL / mL.

11. The method of claim 1, wherein, In the step S3, the solid-liquid separation after the dissolving is performed at a heating temperature of 50 ℃-80 ℃. In the step S4, the recrystallization is specifically cooling recrystallization, and the temperature used is -4 ℃-20 ℃. In the step S4, the recrystallization is specifically cooling recrystallization, and the temperature used is -4 ℃-20 ℃.

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