Method for preparing lead chloride crystal by wet short process of waste lead paste

Abstract

The present application belongs to the technical field of waste lead acid battery resource and lead chloride crystal preparation, and discloses a method for preparing lead chloride crystal from waste lead paste by a short wet process, which specifically comprises the following steps: S1: stirring and reacting the waste lead paste in a carbonate solution to obtain desulfurized lead paste; S2: using an HCl-NaCl mixed solution as a leaching agent to leach the desulfurized lead paste to obtain a leaching solution; and S3: recrystallizing to obtain lead chloride crystals. The present application improves the overall process design of the preparation method, first uses a carbonate solution to desulfurize the waste lead paste, then uses an HCl-NaCl mixed solution as a leaching agent to leach the desulfurized lead paste, and finally recrystallizes to obtain high-purity lead chloride crystals, effectively solving the technical problems of long process steps, large reagent input, and low conversion rate of lead chloride in the prior art.

Description

Technical Field

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

[0002] Lead chloride is one of the most important raw materials in the preparation of lead-based perovskite solar cells and PbS quantum dot materials. With the rapid development of photovoltaic devices, PbS quantum dot optoelectronic devices have attracted much attention due to their outstanding advantages such as high efficiency, light weight, simple fabrication process, and ability to be fabricated into large-area flexible devices. However, compared with the currently leading crystalline silicon photovoltaic devices, their manufacturing cost remains high, necessitating low-cost, high-purity lead chloride to address the issue of expensive raw materials. Currently, the commercial preparation process of lead chloride involves reacting lead carbonate, lead oxide, or lead acetate with hydrochloric acid. This process consumes large amounts of acidic reagents and energy, and the byproducts cannot be recycled and have low utilization value. On the other hand, the rapid development of lithium-ion batteries will lead to a certain degree of replacement of lead-acid batteries, resulting in a decrease in lead demand. Currently, the trend of "lead out of service and lithium in service" is obvious. Lead consumption is affected by substitution, the consumer application market is shrinking, and the recycled lead market, with lead-acid batteries as its main product, faces challenges.

[0003] Waste lead paste is the main raw material for recycled lead obtained from lead-acid batteries through crushing and screening. Its main components include PbSO4, PbO2, PbO, metallic Pb, and small amounts of metallic impurities such as Fe and Ba. Currently, traditional pyrometallurgical techniques for recycling waste lead-acid batteries easily generate emissions of acidic gases such as SO2. Furthermore, the volatilization products of lead at high temperatures are also highly harmful pollutants. While wet recycling processes significantly reduce energy consumption and lead and waste gas pollution, they still suffer from problems such as lengthy processes (often requiring sequential desulfurization, reduction, leaching, and precipitation), high energy consumption, high costs, and severe electrolyte pollution. Therefore, achieving a short-process wet recycling of high-purity lead chloride from waste lead paste would effectively promote the green and high-quality development of the recycled lead industry and provide a new target for the supply of recycled lead.

[0004] CN201710820603.X discloses a process for recycling lead paste from waste lead-acid batteries using vacuum chlorination. The process involves reducing lead dioxide in the lead paste to lead oxide through vacuum roasting, then mixing it with a chlorinating agent for vacuum chlorination. After volatilization, the mixture is condensed and crystallized to obtain crude lead chloride. This process involves high temperatures (400℃-650℃), the need for excessive addition of chlorinating agent (requiring both calcium chloride and silicon dioxide chlorination reagents, with a molar ratio of calcium chloride to lead of 12:1-30:1 and a molar ratio of silicon dioxide to lead of 12:1-60:1), and the need for further purification and optimization of the product (requiring the initial preparation of crude lead chloride, followed by purification). It also results in high energy and reagent consumption. CN202110909314.3 and CN201510935345.0 disclose a method for recovering lead chloride from lead waste residue. The method involves calcination and acid leaching to obtain a lead-containing reagent, followed by the addition of an excess chlorine-containing reagent to synthesize lead chloride. The entire process involves complex steps such as high-temperature calcination, acid leaching, and chlorination synthesis, resulting in high energy consumption and difficulty in pollution control. CN201911191909.9 and CN201010211871.X disclose a method for directly leaching waste lead paste using chloride salts. However, in this type of leaching process, the solubility product of lead chloride (2×10⁻⁶) is limited. -5 ) greater than lead sulfate (1.6 × 10 -8 Therefore, excess hydrochloric acid needs to be added to the chloride solution (for example, the weight ratio of lead paste to saturated sodium chloride solution is 1:13-15, and the weight ratio of lead paste to 37% hydrochloric acid solution is 1:2-2.5). After cooling and crystallizing to synthesize lead chloride, sulfate byproducts are present in the crystallization filtrate, which needs to be treated with calcium chloride before it can be recycled. The accumulation of unreacted calcium ions in the filtrate during this step will affect the leaching effect. In addition, a reducing agent is added during the leaching process to treat lead dioxide in waste lead paste.

[0005] In summary, existing lead chloride preparation processes all suffer from problems such as high energy consumption, large reagent dosage, unstable filtrate recycling methods, and low lead chloride conversion rates. Furthermore, there has been no clear analysis of the migration and transformation of major impurities such as Fe and Ba in waste lead paste. There is an urgent need to develop a new short-process wet process for producing high-purity lead chloride from waste lead paste. Summary of the Invention

[0006] 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 chloride crystals from waste lead paste. This method improves the overall process design by first desulfurizing the waste lead paste with a carbonate solution, then using an HCl-NaCl mixed solution as a leaching agent to leach the desulfurized lead paste, and finally recrystallizing to obtain high-purity lead chloride crystals. This effectively solves the technical problems of lengthy processes, large reagent inputs, and low lead chloride conversion rates in existing processes. The process of this invention uses small reagent dosages, achieves high conversion rates, low impurity content, and few byproducts, realizing a short-process, clean conversion from waste lead paste to high-purity lead chloride. Furthermore, the chloride-containing solution (i.e., the leaching agent) in this invention can be 100% recycled in a closed loop to the next desulfurized lead paste leaching process, resulting in high resource utilization.

[0007] To achieve the above objectives, according to the present invention, a method for preparing lead chloride crystals from waste lead paste using a short wet process is provided, characterized by comprising the following steps:

[0008] S1: Place the waste lead paste in a carbonate solution and stir for at least 1 hour, then separate the solid and liquid. The solid obtained from the solid-liquid separation is the desulfurized lead paste. The molar ratio of carbonate ions in the carbonate solution to sulfate ions in the waste lead paste is greater than or equal to 1:1.

[0009] S2: Using an HCl-NaCl mixed solution as the leaching agent, the desulfurized lead paste obtained in step S1 is placed in the leaching agent and leached at a temperature of 70℃-90℃ for at least 2 hours, followed by solid-liquid separation to obtain the filtrate; wherein the pH value of the leaching agent does not exceed 2.0;

[0010] S3: After recrystallizing the filtrate obtained in step S2, solid-liquid separation is performed. The solid obtained from this solid-liquid separation is lead chloride crystal.

[0011] As a further preferred embodiment of the present invention, in step S3, the recrystallization is specifically carried out by cooling recrystallization;

[0012] Preferably, the filtrate obtained from the solid-liquid separation can be used as a leaching agent and reused in step S2;

[0013] More preferably, the temperature used for the cooling recrystallization is -20℃ to -4℃.

[0014] As a further preferred embodiment of the present invention, in step S2, the chloride ion concentration in the leaching agent is not less than 4.32 mol / L;

[0015] Preferably, the pH value of the leaching agent is 1.0-2.0; the chloride ion concentration in the leaching agent is 4.32 mol / L-5.19 mol / L; the solid-liquid ratio of the desulfurized lead paste to the leaching agent is 30 g / L-40 g / L; more preferably, the HCl-NaCl mixed solution is obtained by adding 37-38% hydrochloric acid dropwise to a sodium chloride solution with a concentration of 250 g / L-300 g / L to adjust the pH value of the system to 1.0-2.0.

[0016] As a further preferred embodiment of the present invention, in step S1, the carbonate ion concentration in the carbonate solution is 0.36 mol / L-0.29 mol / L, and the mass ratio of the waste lead paste to the volume of the carbonate solution is 100 g / L-125 g / L.

[0017] As a further preferred embodiment of the present invention, in step S1, the molar ratio of carbonate ions in the carbonate solution to sulfate ions in the waste lead paste is greater than or equal to 1.2:1; preferably, the molar ratio of carbonate ions in the carbonate solution to sulfate ions in the waste lead paste is 1.2:1-1.4:1.

[0018] The stirring reaction is carried out at a temperature of 35°C-55°C; preferably, the temperature of 35°C-55°C is provided by water bath heating.

[0019] As a further preferred embodiment of the present invention, in step S1, the stirring speed used for the stirring reaction is 300 rpm to 500 rpm.

[0020] As a further preferred embodiment of the present invention, in step S2, the temperature condition of 70°C-90°C is provided by water bath heating.

[0021] As a further preferred embodiment of the present invention, in step S2, the leaching reaction is carried out under stirring conditions, with a stirring speed of 300 rpm to 500 rpm.

[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 chloride. Existing wet conversion processes for waste lead paste to lead chloride generally use chloride leaching directly, which has problems such as large reagent dosage, the need for filtrate treatment before recycling, and low lead chloride conversion rate (lead conversion rate is about 85%). This invention improves the process flow by first performing desulfurization pretreatment on the waste lead paste to convert lead sulfate into lead carbonate, which is more easily reacted with chloride solution, thus greatly improving the lead conversion rate (i.e., recovery rate). Furthermore, by using an HCl-NaCl mixed solution as the leaching agent, the leaching reaction is carried out with the desulfurized lead paste at a temperature of 70℃-90℃. Especially for the difficult-to-treat +4 valent lead (i.e., PbO2), simultaneous reduction and chlorination can be achieved in the HCl-NaCl solution, overcoming the technical difficulty of requiring the addition of reducing agents such as methanol and iron powder. Furthermore, using the method of this invention, impurities such as Fe and Ba in the waste lead paste are retained in the solid waste residue of the intermediate steps throughout the entire recycling process, thereby achieving the conversion of high-purity lead chloride.

[0024] Lead chloride is an important raw material for the preparation of PbS quantum dots, and lead chloride with a purity of over 99.9% is typically used, making it expensive. Traditional analytical grade lead chloride preparation methods involve reacting lead carbonate, lead oxide, or lead acetate with hydrochloric acid. Wet recovery of lead chloride usually involves reducing waste lead paste by roasting or adding an oxidant, followed by leaching with a chloride solution, cooling, and recrystallization to obtain lead chloride. Existing processes all require the addition of large amounts of hydrochloric acid to simultaneously treat lead sulfate in the waste lead paste, and additional reagents are needed to treat the filtrate for recycling. The key challenges addressed in this invention are how to reduce the amount of acidic reagents added, improve the lead chloride conversion rate, and minimize uncontrollable influences during filtrate recycling.

[0025] Waste lead paste is obtained from the crushing and dismantling of waste lead-acid batteries. Its main components include PbSO4, PbO2, PbO, metallic Pb, and a small amount of other metallic impurities. Among them, lead sulfate and tetravalent lead are more difficult to process. This invention uses carbonates to desulfurize the waste lead paste, converting the lead sulfate into lead carbonate, which is more reactive with acid. As for tetravalent lead, existing processes require high-temperature pyrolysis or the addition of reducing agents such as H2O2 and Na2SO3 for reduction. This invention achieves simultaneous reduction chlorination by first desulfurizing the waste lead paste and then using a chloride leaching reaction (as shown in reaction formulas (2) to (6) below). By first converting lead sulfate into lead carbonate, which is more reactive with hydrochloric acid, this invention can effectively reduce the amount of acid added in the entire process and improve the final yield. Furthermore, the recrystallization of lead chloride crystals can be achieved by cooling recrystallization, which eliminates the need to treat the reused filtrate before use (that is, the solid obtained after solid-liquid separation after cooling recrystallization is high-purity lead chloride crystals, and the filtrate is a chloride salt filtrate, which can be reused as a leaching agent in the method of this invention to achieve recycling; specifically, the filtrate is a mixed solvent containing NaCl, HCl and a small amount of dissolved lead chloride, NaPbCl3 and Na2PbCl4, and the pH value is basically the same as that of the leaching agent before the leaching reaction, so no further adjustment is needed, and it can be recycled for the leaching reaction; if the pH value of the leaching agent changes after multiple cycles and no longer meets the requirement of ≤2.0, the original HCl-NaCl mixed solution can be used to adjust the pH value of the leaching agent).

[0026] Taking ammonium carbonate as a desulfurization reagent as an example, the chemical reaction that occurs during the desulfurization process is shown in the following formula (1).

[0027] PbSO4+(NH4)2CO3=(NH4)2SO4+PbCO3 (1)

[0028] The ammonium carbonate content used for desulfurization can be calculated based on the lead sulfate content in the waste lead paste. The molar ratio of carbonate ions to sulfate ions in the waste lead paste needs to be greater than or equal to 1:1. To ensure sufficient desulfurization, the molar ratio of carbonate ions to sulfate ions in the waste lead paste can be further controlled to be greater than or equal to 1.2:1 (even if carbonate ions are in excess, the unreacted carbonates will still dissolve in the filtrate and will not affect the subsequent treatment of the desulfurized lead paste; of course, considering reagent costs and avoiding waste caused by a large amount of unreacted carbonates, the molar ratio of carbonate ions to sulfate ions can be controlled to 1.2:1-1.4:1). After stirring and reacting for at least 1 hour, solid and liquid separation is performed. The solid is the desulfurized lead paste, and the main component of the filtrate is ammonium sulfate solution, which can be recycled as a by-product.

[0029] The obtained desulfurized lead paste was leached with a mixed HCl-NaCl solution at a temperature of 70℃-90℃. The possible reactions are shown in equations (2) to (6). Among them, the reaction of lead dioxide, which is the most difficult to treat in the desulfurized lead paste, with hydrochloric acid (equation (3)) is also thermodynamically feasible (as described below). Figure 3 As shown, ΔG < 0, indicating that the reaction can proceed in the forward direction. Furthermore, as the temperature increases, ΔG decreases, making the reaction more likely to proceed spontaneously, thus enabling simultaneous reduction chlorination. Simulation calculations were performed to determine the speciation of lead chloride in sodium chloride solution at different pH values, as described below. Figure 4 As shown, when the pH is greater than 6.5, the lead component exists as lead hydroxide (Pb(OH)2); when the pH is greater than 4.5 and less than 6.5, the lead component exists as basic lead chloride (Pb(OH)Cl); and when the pH is less than 4.5, the lead component mainly exists as PbCl. + It exists in the form of a small amount of dissolved lead chloride (which dissolves at temperatures of 70°C-90°C). This invention allows the lead component to be transferred into the leachate by adjusting the pH of the leaching agent to no more than 2.0 (e.g., 1.0-2.0) using a small amount of hydrochloric acid solution.

[0030] PbCO3+2HCl=PbCl2+H2O+CO2↑ (2)

[0031] PbO2+4HCl=PbCl2+2H2O+Cl2↑ (3)

[0032] PbO + 2HCl = PbCl₂ + 2H₂O (4)

[0033] Pb + 2HCl = PbCl₂ + H₂↑ (5)

[0034]

[0035] After filtration and liquid-solid separation, the solid is a leaching residue containing impurities such as Fe and Ba; the solution is a complex of dissolved lead chloride, NaPbCl3 and Na2PbCl4.

[0036] The behavior of the main impurities Fe and Ba during the leaching process was analyzed. The distribution of iron in sodium chloride solutions at different pH values ​​was simulated, as shown below. Figure 5 As shown in the diagram, most of the iron remains in the leaching residue as Fe3O4, with a small portion being leached out. Even if this iron is mixed into the PbCl2 crystals during subsequent cooling and crystallization, it has little impact on the product purity and does not affect the recycling of the filtrate. The barium impurities in the desulfurized lead paste are mostly BaSO4 with a small amount of BaCO3, as described later. Figure 6As shown, almost no barium was leached out, and it remained entirely in the leaching residue. Therefore, the main components of the obtained solid leaching residue were BaFeO3 and Fe3O4, and the content of metallic impurities such as Fe and Ba in the leachate was greatly reduced.

[0037] Thus, high-purity lead chloride crystals can be obtained by simple recrystallization of the leachate, without the need for the step of first obtaining a solid crude product and then purifying it.

[0038] (2) In particular, the present invention can use a conventional cooling recrystallization method to allow lead chloride in the leaching filtrate to recrystallize in crystalline form at a cooling temperature (e.g., -20°C to -4°C), and then obtain the target lead chloride crystalline product through solid-liquid separation. As for the filtrate obtained from solid-liquid separation, the filtrate is a mixed solvent of HCl-NaCl and incompletely precipitated dissolved lead chloride, which can be recycled for hot leaching recrystallization of desulfurized lead paste with almost no solvent consumption, and will increase the lead chloride yield in the next cycle.

[0039] (3) Using the method of the present invention, the chloride ion concentration in the leaching agent can preferably be at least 4.32 mol / L before the leaching reaction. Considering the reagent cost and to avoid the waste caused by a large amount of unreacted Cl ions, the chloride ion concentration in the HCl-NaCl mixed solution can be controlled at 4.32 mol / L-5.19 mol / L (of course, even if there are unreacted Cl ions, waste can be avoided if the leaching agent is recycled). In actual operation, the present invention can adjust the pH of the system to 1.0-2.0 by adding 37-38% hydrochloric acid to a sodium chloride solution with a concentration of 250 g / L-300 g / L, thereby obtaining an HCl-NaCl mixed solution as the leaching agent. Unlike the prior art, which directly uses excess hydrochloric acid added to a saturated sodium chloride solution for leaching, the present invention reduces the concentration of sodium chloride solution, which can achieve the optimal balance between lead conversion rate and reagent cost.

[0040] (4) The existing wet process directly leaches waste lead paste and then cools and crystallizes it to obtain lead chloride. Calcium chloride needs to be added to the crystallization filtrate to treat the sulfate ions in the filtrate. Only after the sulfate ions are removed can the filtrate be recycled. This raises the issue of the amount of calcium chloride added. If too little is added, sulfate ions cannot be completely removed; if too much is added, calcium ions will accumulate in the filtrate, affecting the leaching effect in subsequent cycles. This step is cumbersome and increases the operational difficulty and uncertainty of the operational effect in actual large-scale production. However, this invention does not directly leach the waste lead paste but first performs desulfurization treatment, which can achieve at least two effects: (1) It reduces the amount of hydrochloric acid added. Lead sulfate is difficult to chlorinate and requires a large amount of hydrochloric acid and a longer leaching time. The desulfurization process converts lead sulfate into lead carbonate, which is easier to chlorinate, greatly reducing the amount of acidic reagent used and effectively reducing costs; (2) The sulfate ions are desulfurized in advance, so there is no need to treat the crystallization filtrate again. It can be directly used for the next cycle, and the leaching effect of the cycle remains unchanged.

[0041] This invention incorporates desulfurization pretreatment into the existing process of preparing lead chloride from waste lead paste, thereby converting lead sulfate to lead carbonate and obtaining recyclable sulfate byproducts. This not only avoids the problem of introducing other impurities into the process by adding additional reagents to treat the circulating filtrate, but also reduces the overall acid dosage. In this method, the amount of hydrochloric acid added can be only 3.8 mL / L-5.6 mL / L (that is, for each liter of HCl-NaCl mixed solution, only 3.8 mL-5.6 mL of 37-38% concentrated hydrochloric acid is needed to adjust the pH to no more than 2.0; of course, a high-concentration NaCl solution can also be used in combination with a low-concentration HCl solution to prepare the HCl-NaCl mixed solution, as long as the pH requirement is met). The entire process does not use 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. The total lead yield of this invention can reach 97%, and it can achieve the preparation of lead chloride crystals with a purity of up to 99.99% by a short-process wet method, with metal impurities such as Fe and Ba not exceeding 10 ppm.

[0042] (4) The entire process of this invention involves only three reagent emissions. The sulfate solution generated during desulfurization can be recovered as a byproduct. The waste residue generated during the HCl-NaCl mixed solvent leaching and recrystallization process mainly contains Fe, Ba, and Cu impurities from the waste lead paste, and the filtrate is recycled as a leaching solvent. The amount of chlorine gas generated during the leaching reaction is extremely small. For example, with a PbO2 content of 17.93 wt% in the waste lead paste, the amount of chlorine gas produced per kilogram of waste lead paste is only 0.74 mol. The process generates few pollutants, resulting in minimal overall environmental pollution.

[0043] (5) This invention uses only three chemical reagents: carbonate solution, sodium chloride solution, and hydrochloric acid. Carbonate and sodium chloride are used as the desulfurizing agent and chlorine source, respectively, in the desulfurization and chlorination processes. The amount of hydrochloric acid added is only 3.8 mL / L-5.6 mL / L. After recrystallization and filtration, the lead in the filtrate of the chloride solution exists as dissolved lead chloride and PbCl3. - and PbCl4 2- It exists in the form of [unclear] and can be directly used for the hot leaching of the next batch of desulfurized lead paste. It will not only not affect the purity of the next batch of products, but also improve the yield of the next batch of products.

[0044] (6) The reaction conditions in each step of this invention are mild and the reaction efficiency is high. The reaction time for the desulfurization reaction can be as low as 1 hour, and the reaction time for the leaching reaction can be as low as 2 hours, which greatly increases the production efficiency due to the short reaction time. The reaction process does not use reaction conditions such as high temperature, high pressure, and high-speed stirring, and the maximum reaction temperature can not exceed 90°C, making the process simple and controllable.

[0045] (7) This invention is particularly capable of directly obtaining high-purity lead chloride crystals with metal impurities such as Fe and Ba below 10 ppm. Similar to the known recrystallization process control in the prior art, the crystal size can be controlled by controlling the recrystallization process conditions (taking cooling recrystallization as an example, the crystal size of cooling crystallization is mainly affected by the cooling rate and crystallization temperature; the crystal size obtained under rapid cooling conditions is small, and the crystal size obtained under slow cooling conditions is large; the crystal size obtained at a higher crystallization temperature is large, and the crystal size obtained at a lower crystallization temperature is small), which is beneficial for subsequent use. The lead chloride yield in the process can exceed 90% (for example, up to 95%), and the 5%-10% lead-containing components that are not crystallized remain in the crystallization filtrate and can enter the next round of reaction. Attached Figure Description

[0046] Figure 1 This is a process flow diagram of the wet short-process preparation of lead chloride crystals from waste lead paste in this invention.

[0047] Figure 2 The XRD patterns of the desulfurized lead paste and waste lead paste raw materials obtained in Example 1 are shown.

[0048] Figure 3 These are the reaction thermodynamic parameters during the reaction of HCl and lead dioxide.

[0049] Figure 4 The distribution of lead-containing components under different pH conditions (the concentration of lead chloride in the solution is 0.01 mol / L, the concentration of sodium chloride is 0.1 mol / L, and the reaction temperature is set at 25℃).

[0050] Figure 5The distribution of iron impurities under different pH conditions (the concentration of iron ions in the solution is 0.01 mol / L, the concentration of sodium chloride is 0.1 mol / L, and the reaction temperature is set at 25℃).

[0051] Figure 6 The E-pH phase diagram for impurity barium is shown (the concentration of barium ions in the solution is 3 mol / kg, the concentration of carbonate ions is 1 mol / kg, the concentration of sulfate ions is 2 mol / kg, the concentration of chloride ions is 1 mol / kg, and the reaction temperature is set at 25℃).

[0052] Figure 7 The image shows the XRD pattern of the leaching impurities obtained during the process of Example 1.

[0053] Figure 8 The image shows the XRD pattern of the high-purity lead chloride crystals obtained in Example 1.

[0054] Figure 9 The image shows the SEM image of the high-purity lead chloride crystals obtained in Example 1. Detailed Implementation

[0055] 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.

[0056] The following are specific embodiments, and each embodiment satisfies Figure 1 The process flow diagram shown is shown.

[0057] Furthermore, the waste lead paste used in all embodiments came from the same batch and was obtained by crushing and dismantling waste lead-acid batteries using known methods in the prior art. Chemical titration revealed that the actual lead content in the waste lead paste was 72.79 wt%, the lead sulfate content was 72.45 wt%, and the lead dioxide content was 17.93 wt%. The impurity content test results for the waste lead paste are as follows:

[0058] Fe: 125.3ppm; Ba: 111.2ppm; Cu: 9.19ppm; Zn: 4.90ppm; Al: 1.74ppm.

[0059] Example 1

[0060] (1) Take 5g of waste lead paste and place it in 50mL of ammonium carbonate solution with a concentration of 30g / L, with a solid-liquid ratio of 100g / L. Stir and react at 35℃ for 1h, filter and separate, and dry the solid in an oven at 60℃ for 3h to obtain 4.42g of desulfurized lead paste. The filtrate obtained in this step is the sulfate filtrate.

[0061] (2) Add a small amount of 37%-38% hydrochloric acid dropwise to 111 mL of a 250 g / L sodium chloride solution to prepare a NaCl-HCl solution until the pH of the solution does not exceed 2.0. In this example, the volume of hydrochloric acid added is 600 μL, and the final pH of the solution is 1.08. Place the desulfurized lead paste obtained in the previous step into 111 mL of NaCl-HCl solution, with a solid-liquid ratio of 40 g / L. Stir and leach at a water bath temperature of 80°C for 2-3 hours, and then filter while hot to separate the solid and liquid, obtaining 113 mL of leachate. The solid residue obtained in this solid-liquid separation step is the solid leachate residue containing impurities such as Fe and Ba (these impurities mainly remain in the residue in solid form); the filtrate is the leachate mainly composed of dissolved lead chloride.

[0062] (3) The leachate was cooled to -4℃ and recrystallized for 4 hours. The solid was separated by filtration. The obtained solid was dried in an oven at 60℃ for 2 hours to obtain lead chloride crystals. The product mass was 4.67g. The purity of lead chloride in the product was tested and found to be 99.99%. The total lead yield was calculated to be 95.58%.

[0063] The total lead yield was determined by first using chemical titration to test the actual lead content in the waste lead paste, and then calculating it using the actual lead chloride yield, purity, and the mass percentage of lead in the lead chloride. The formula is as follows (subsequent examples are similar):

[0064]

[0065] Where: m 氯化铅 w1 represents the final mass of lead chloride obtained in the experiment (in g); w1 represents the final lead content of lead chloride obtained in the experiment (in %); m 废铅膏 w1 represents the mass of the waste lead paste used in the experiment (in g); w1 represents the lead content of the waste lead paste (in %).

[0066] The XRD patterns of the desulfurized lead paste and waste lead paste raw materials before and after step (1) are as follows: Figure 2 As shown, after step (1), all lead sulfate is converted into lead carbonate, and a small amount of lead dioxide remains in the desulfurized lead paste.

[0067] The solid leaching residue obtained from solid-liquid separation in step (2), such as Figure 7As shown, the main components are BaFeO3 and Fe3O4.

[0068] The solid product of step (3) is lead chloride crystals, such as... Figure 8 and Figure 9 As shown, the crystals contain no other components and are needle-shaped.

[0069] Example 2

[0070] (1) Take 5g of waste lead paste and place it in 50mL of ammonium carbonate solution with a concentration of 32g / L, with a solid-liquid ratio of 100g / L. Stir and react at 45℃ for 1h, filter and separate, and dry the solid in an oven at 60℃ for 3h to obtain 4.41g of desulfurized lead paste.

[0071] (2) Prepare a NaCl-HCl solution by adding a small amount of 37%-38% hydrochloric acid dropwise to 134 mL of a 300 g / L sodium chloride solution until the pH of the solution does not exceed 2.0. In this example, the volume of hydrochloric acid added is 750 μL, and the final pH of the solution is 1.01. Place the desulfurized lead paste obtained in the previous step into 134 mL of NaCl-HCl solution, with a solid-liquid ratio of 33 g / L. Stir and leach at a water bath temperature of 80°C for 2-3 hours, then filter to separate the solid and liquid, obtaining 137 mL of leachate.

[0072] (3) The leachate was cooled to -4℃ and recrystallized for 4 hours. The solid was separated by filtration. The obtained solid was dried in an oven at 60℃ for 2 hours to obtain lead chloride crystals. The product mass was 4.51g. The purity of lead chloride in the product was tested and found to be 99.99%, with a total lead yield of 92.31%.

[0073] Example 3

[0074] (1) Take 5g of waste lead paste and place it in 40mL of ammonium carbonate solution with a concentration of 37g / L, with a solid-liquid ratio of 125g / L. Stir and react at 55℃ for 1h, filter and separate, and dry the solid in an oven at 60℃ for 3h to obtain 4.45g of desulfurized lead paste.

[0075] (2) Prepare a NaCl-HCl solution by adding a small amount of 37%-38% hydrochloric acid dropwise to 127 mL of a 260 g / L sodium chloride solution until the pH of the solution does not exceed 2.0. In this example, the volume of hydrochloric acid added was 490 μL, and the final pH of the solution was 1.77. Place the desulfurized lead paste obtained in the previous step into 127 mL of NaCl-HCl solution, with a solid-liquid ratio of 35 g / L. Stir and leach at a water bath temperature of 80°C for 2-3 hours, then filter to separate the solid and liquid, obtaining 129 mL of leachate.

[0076] (3) The leachate was cooled to -4℃ and recrystallized for 4 hours. The solid was separated by filtration. The obtained solid was dried in an oven at 60℃ for 2 hours to obtain lead chloride crystals. The product mass was 4.58 g. The purity of lead chloride in the product was tested and found to be 99.99%, with a total lead yield of 93.74%.

[0077] Example 4

[0078] (1) Take 5g of waste lead paste and place it in 50mL of ammonium carbonate solution with a concentration of 27g / L, with a solid-liquid ratio of 100g / L. Stir and react at 55℃ for 1h, filter and separate, and dry the solid in an oven at 60℃ for 3h to obtain 4.44g of desulfurized lead paste.

[0079] (2) Prepare a NaCl-HCl solution by adding a small amount of 37%-38% hydrochloric acid dropwise to 120 mL of a 270 g / L sodium chloride solution until the pH of the solution does not exceed 2.0. In this example, the volume of hydrochloric acid added was 608 μL, and the final pH of the solution was 1.26. Place the desulfurized lead paste obtained in the previous step into 120 mL of NaCl-HCl solution, with a solid-liquid ratio of 37 g / L. Stir and leach at a water bath temperature of 80°C for 2-3 hours, then filter to separate the solid and liquid, obtaining 123 mL of leachate.

[0080] (3) The leachate was cooled to -4℃ and recrystallized for 4 hours. The solid was separated by filtration. The obtained solid was dried in an oven at 60℃ for 2 hours to obtain lead chloride crystals. The product mass was 4.65g. The purity of lead chloride in the product was tested and found to be 99.99%, with a total lead yield of 95.17%.

[0081] Example 5

[0082] (1) Take 5g of waste lead paste and place it in 40mL of ammonium carbonate solution with a concentration of 40g / L, with a solid-liquid ratio of 125g / L. Stir and react at 35℃ for 1h, filter and separate, and dry the solid in an oven at 60℃ for 3h to obtain 4.39g of desulfurized lead paste.

[0083] (2) Prepare a NaCl-HCl solution by adding a small amount of 37%-38% hydrochloric acid dropwise to 146 mL of a 280 g / L sodium chloride solution until the pH of the solution does not exceed 2.0. In this example, the volume of hydrochloric acid added was 792 μL, and the final pH of the solution was 1.13. Place the desulfurized lead paste obtained in the previous step into 146 mL of NaCl-HCl solution, with a solid-liquid ratio of 30 g / L. Stir and leach at a water bath temperature of 80°C for 2-3 hours, then filter to separate the solid and liquid, obtaining 147 mL of leachate.

[0084] (3) The leachate was cooled to -20℃ and recrystallized for 4 hours. The solid was separated by filtration. The obtained solid was dried in an oven at 60℃ for 2 hours to obtain lead chloride crystals. The product mass was 4.49 g. The purity of lead chloride in the product was tested and found to be 99.99%. The total lead yield was 91.90%.

[0085] Example 6

[0086] (1) Take 5g of waste lead paste and place it in 55mL of ammonium carbonate solution with a concentration of 20g / L, with a solid-liquid ratio of 90g / L. Stir and react at 45℃ for 1h, filter and separate, and dry the solid in an oven at 60℃ for 3h to obtain 4.91g of desulfurized lead paste (the molar ratio of carbonate ions in the carbonate solution to sulfate ions in the waste lead paste is 1:1, desulfurization is incomplete, and the sulfur content is 0.25%).

[0087] (2) Prepare a NaCl-HCl solution by adding a small amount of 37%-38% hydrochloric acid dropwise to 111 mL of a 250 g / L sodium chloride solution until the pH of the solution is in the range of 1.0-2.0. The volume of hydrochloric acid added is 600 μL, and the final pH of the solution is 1.08. Place the desulfurized lead paste obtained in the previous step into 111 mL of NaCl-HCl solution, with a solid-liquid ratio of 40 g / L. Stir and leach at a water bath temperature of 80℃ for 2-3 hours, then filter to separate the solid and liquid, obtaining 113 mL of leachate.

[0088] (3) The leachate was cooled to -4℃ and recrystallized for 4 hours. The solid was separated by filtration. The obtained solid was dried in an oven at 60℃ for 2 hours to obtain lead chloride crystals. The product mass was 4.33 g. The purity of lead chloride in the product was tested and found to be 99.74%. The total lead yield was 88.40%.

[0089] Example 7

[0090] (1) Take 5g of waste lead paste and place it in 40mL of ammonium carbonate solution with a concentration of 37g / L, with a solid-liquid ratio of 125g / L. Stir and react at 45℃ for 1h, filter and separate, and dry the solid in an oven at 60℃ for 3h to obtain 4.45g of desulfurized lead paste.

[0091] (2) Prepare a NaCl-HCl solution by adding a small amount of 37%-38% hydrochloric acid to 100 mL of a 200 g / L sodium chloride solution (chloride ion concentration of 3.44 mol / L) until the pH of the solution is in the range of 1.0-2.0. The volume of hydrochloric acid added is 400 μL, and the final pH of the solution is 1.42. Place the desulfurized lead paste obtained in the previous step into 100 mL of NaCl-HCl solution, with a solid-liquid ratio of 45 g / L. Stir and leach at a water bath temperature of 80℃ for 2-3 hours, then filter to separate the solid and liquid, obtaining 103 mL of leachate.

[0092] (3) The leachate was cooled to -4℃ and recrystallized for 4 hours. The solid was separated by filtration. The obtained solid was dried in an oven at 60℃ for 2 hours to obtain lead chloride crystals. The product mass was 4.01 g. The purity of lead chloride in the product was tested and found to be 99.99%. The total lead yield was 82.08%.

[0093] Table 1. Comparison of parameter conditions, total lead yield, and product purity results in Examples 1-7.

[0094]

[0095] The lead chloride products obtained in the above examples all have a purity of over 99%, especially the products obtained in Examples 1-5 and Example 7, which have a purity of up to 99.99%, with metal impurities such as Fe and Ba not exceeding 10 ppm (0.01% purity corresponds to 10 ppm impurity content). They have the characteristics of short process, directly obtaining high-purity products (without the need for a crude product purification step).

[0096] Furthermore, as shown in Table 1, in order to obtain a high total lead conversion rate (e.g., a total lead conversion rate of ≥90%), in the desulfurization step of the preparation method of the present invention, the molar ratio of carbonate ions in the carbonate solution to sulfate ions in the waste lead paste can be controlled to be greater than or equal to 1.2:1; and in the leaching step, the leaching agent can contain an excess concentration of chloride ions (e.g., the chloride ion concentration in the leaching agent can be controlled to be not less than 4.32 mol / L).

[0097] Example 8

[0098] The filtrate obtained from solid-liquid separation in step (3) of Example 1 is used as the leachate, and the method of the present invention is repeated. Specifically:

[0099] (1) Take 5g of waste lead paste and place it in 50mL of ammonium carbonate solution with a concentration of 30g / L, with a solid-liquid ratio of 100g / L. Stir and react at 35℃ for 1h, filter and separate, and dry the solid in an oven at 60℃ for 3h to obtain 4.42g of desulfurized lead paste.

[0100] (2) Place the desulfurized lead paste obtained in the previous step into 113 mL of filtrate (pH = 1.38) obtained by solid-liquid separation in step (3) of Example 1, stir and leach for 2-3 hours at a water bath heating temperature of 80°C, and then filter to separate solid and liquid to obtain 113 mL of leachate.

[0101] (3) The leachate was cooled to -4℃ and recrystallized for 4 hours. The solid was separated by filtration. The obtained solid was dried in an oven at 60℃ for 2 hours to obtain lead chloride crystals. The product mass was 4.77 g. The purity of lead chloride in the product was tested and found to be 99.99%, with a total lead yield of 97.63%.

[0102] Comparative Example 1

[0103] (1) Take 5g of waste lead paste and place it in 40mL of ammonium carbonate solution with a concentration of 37g / L, with a solid-liquid ratio of 125g / L. Stir and react at 45℃ for 1h, filter and separate, and dry the solid in an oven at 60℃ for 3h to obtain 4.45g of desulfurized lead paste.

[0104] (2) Prepare a NaCl-HCl solution by adding a small amount of 37%-38% hydrochloric acid dropwise to 111 mL of a 250 g / L sodium chloride solution. The volume of hydrochloric acid added is 50 μL, and the final pH of the solution is 3.47. Place the desulfurized lead paste obtained in the previous step into 111 mL of the NaCl-HCl solution, with a solid-liquid ratio of 40 g / L. Stir and leach at a water bath temperature of 80℃ for 2-3 hours, then filter to separate the solid and liquid, obtaining 113 mL of leachate.

[0105] (3) The leachate was cooled to -4℃ and recrystallized for 4 hours. The solid was separated by filtration. The obtained solid was dried in an oven at 60℃ for 2 hours to obtain lead chloride crystals. The product mass was 3.26 g. The purity of lead chloride in the product was tested and found to be 99.99%. The total lead yield was 66.73%.

[0106] The above embodiments are merely examples. For instance, in addition to ammonium carbonate, other soluble carbonates (such as sodium carbonate, potassium carbonate, and ammonium bicarbonate) can be used to achieve similar effects. The amount of carbonate solution used is specifically determined by the lead sulfate content in the waste lead paste (for example, when the concentration of the carbonate solution is fixed, the higher the lead sulfate content in the waste lead paste, the larger the volume of carbonate solution used).

[0107] 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 short-process wet method for preparing lead chloride crystals from waste lead paste, characterized in that, Includes the following steps: S1: Place the waste lead paste in a carbonate solution and stir for at least 1 hour, then separate the solid and liquid. The solid obtained from the solid-liquid separation is the desulfurized lead paste. The molar ratio of carbonate ions in the carbonate solution to sulfate ions in the waste lead paste is greater than or equal to 1:

1. S2: Using an HCl-NaCl mixed solution as the leaching agent, the desulfurized lead paste obtained in step S1 is placed in the leaching agent and leached at a temperature of 70℃-90℃ for at least 2 hours, followed by solid-liquid separation to obtain the filtrate; wherein the pH value of the leaching agent does not exceed 2.0; S3: After recrystallizing the filtrate obtained in step S2, solid-liquid separation is performed. The solid obtained from this solid-liquid separation is lead chloride crystal.

2. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 1, characterized in that, In step S3, the recrystallization specifically involves cooling recrystallization.

3. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 2, characterized in that, In step S3, the filtrate obtained from the solid-liquid separation can be used as a leaching agent and reused in step S2.

4. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 3, characterized in that, In step S3, the temperature used for cooling recrystallization is -20℃ to -4℃.

5. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 1, characterized in that, In step S2, the chloride ion concentration in the leaching agent is not less than 4.32 mol / L.

6. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 5, characterized in that, In step S2, the pH value of the leaching agent is 1.0-2.0; the chloride ion concentration in the leaching agent is 4.32 mol / L-5.19 mol / L; and the solid-liquid ratio of the desulfurized lead paste to the leaching agent is 30 g / L-40 g / L.

7. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 6, characterized in that, In step S2, the HCl-NaCl mixed solution is obtained by adding 37-38% hydrochloric acid dropwise to a sodium chloride solution with a concentration of 250 g / L-300 g / L to adjust the pH of the system to 1.0-2.

0.

8. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 1, characterized in that, In step S1, the carbonate ion concentration in the carbonate solution is 0.36 mol / L - 0.29 mol / L, and the mass ratio of the waste lead paste to the volume of the carbonate solution is 100 g / L - 125 g / L.

9. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 1, characterized in that, In step S1, the molar ratio of carbonate ions in the carbonate solution to sulfate ions in the waste lead paste is greater than or equal to 1.2:

1. The stirring reaction was carried out at a temperature of 35℃-55℃.

10. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 9, characterized in that, In step S1, the molar ratio of carbonate ions in the carbonate solution to sulfate ions in the waste lead paste is 1.2:1-1.4:

1. The temperature conditions of 35℃-55℃ are provided by water bath heating.

11. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 1, characterized in that, In step S1, the stirring speed used for the stirring reaction is 300 rpm-500 rpm.

12. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 1, characterized in that, In step S2, the temperature condition of 70 ℃-90 ℃ is provided by water bath heating.

13. The method for preparing lead chloride crystals from waste lead paste using a short wet process as described in claim 1, characterized in that, In step S2, the leaching reaction is carried out under stirring conditions, with a stirring speed of 300 rpm-500 rpm.

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