Method for preparing 4N-grade bismuth oxychloride from complex high-lead bismuth chloride solution

Abstract

The invention discloses a method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution, which comprises the following steps: hydrolyzing the high-lead bismuth chloride solution, adjusting the pH value to 0.8-3.0 to obtain crude bismuth oxychloride, washing the crude bismuth oxychloride by using an acid solution to obtain a solid substance, dissolving the solid substance by using a mixed acid solution of hydrochloric acid and sulfuric acid to obtain a dissolved solution and dissolved slag, and drying the dissolved solution and the dissolved slag to obtain the 4N-grade bismuth oxychloride. And carrying out deep lead removal on the dissolved solution, and hydrolyzing to obtain purified 4N-grade bismuth oxychloride. According to the invention, a specific mixed acid system composed of hydrochloric acid and sulfuric acid is innovatively introduced to dissolve crude bismuth oxychloride obtained by preliminary hydrolysis. According to the process, reverse mass transfer of bismuth and lead can be achieved, bismuth selectively enters the solution in the form of bismuth chloride, and lead is synchronously converted into lead sulfate sediment to be fixed in slag.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, and particularly relates to a method for preparing 4N grade bismuth oxychloride. Background Technology

[0002] Bismuth oxychloride (BiOCl) is an inorganic compound with a unique layered structure, typically appearing as white or pale yellow crystals. Due to its excellent photocatalytic properties, it shows broad application prospects in water treatment, environmental purification, and other fields. Simultaneously, its semiconductor properties and antibacterial activity also give it potential application value in electronic devices, medical and health fields.

[0003] Currently, the preparation of 4N high-purity bismuth oxychloride mostly adopts a process route using 4N bismuth ingots as raw materials. This route usually involves dissolving bismuth ingots in hydrochloric acid, followed by hydrolysis to obtain bismuth oxychloride. Although this process is mature, it has the following significant drawbacks: (1) the cost of raw material bismuth ingots is high, resulting in high overall production costs; (2) the process flow is relatively long, involving multiple steps such as metal dissolution, purification, and hydrolysis; (3) if the purity of the raw material bismuth ingots is insufficient, complex impurity removal steps are still required, further increasing the complexity and cost of the process.

[0004] In hydrometallurgical processing of bismuth concentrate, hydrochloric acid leaching directly yields a complex bismuth chloride solution. This solution often contains various impurities such as lead and iron. Traditional bismuth oxychloride production employs a hydrolysis method, where bismuth precipitates as bismuth oxychloride by increasing the solution pH. However, in this process, lead and some iron impurities in the solution readily co-precipitate, severely affecting the purity of the final product. Lead, in particular, requires effective and deep removal to meet the quality requirements of 4N-grade high-purity bismuth oxychloride.

[0005] In the prior art, most methods for lead removal from bismuth systems focus on the refining of crude bismuth metal or the preliminary purification of bismuth leachate. Chinese patent application CN112899489A discloses a method for lead removal in the bismuth refining process using a combination of high-temperature impurity remover and borax. Although this method can replace the traditional chlorine lead removal process, its process conditions are harsh and it is completely unsuitable for the deep purification of bismuth oxychloride solids or intermediate products. In the prior art, there is also a technique of adding excess barium salt and sulfate to bismuth leachate to reduce lead concentration by co-precipitating lead sulfate with barium sulfate. However, this method has obvious limitations: (1) To achieve effective co-precipitation of lead, a large excess of barium salt is required, which not only consumes a lot of reagents but also has poor effect under high lead conditions; (2) Bismuth leachate usually has the characteristics of high chloride ion and high acidity. In this complex system, the solubility of lead sulfate increases, which severely limits the depth of lead removal and makes it difficult to meet the quality requirements of 4N grade products. Summary of the Invention

[0006] To overcome the high costs caused by relying on high-purity bismuth ingots in existing technologies, and the difficulty of deep impurity removal from complex high-lead bismuth chloride solutions using traditional methods, this invention provides a method for preparing 4N-grade bismuth oxychloride from complex high-lead bismuth chloride solutions. This method has significant advantages such as high impurity removal rate, short process flow, low production cost, and environmental friendliness, and is particularly suitable for large-scale industrial production.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: This invention provides a method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution, comprising the following steps: S1. Hydrolyze the high-lead bismuth chloride solution and adjust the pH to 0.8-3.0 to obtain crude bismuth oxychloride; S2. After washing the crude bismuth oxychloride obtained in step S1 with acid, a solid substance is obtained. S3. Dissolve the solid obtained in step S2 using a mixed acid solution of hydrochloric acid and sulfuric acid to obtain a solution and a residue. S4. After deep lead removal from the solution, hydrolysis is performed to obtain purified 4N grade bismuth oxychloride.

[0008] As an optional implementation, in the method provided by the present invention, in S1, the bismuth content in the high-lead bismuth chloride solution is 50-300 g / L, the lead content is 0.1-10 g / L, and the iron content is 1-20 g / L.

[0009] As an optional implementation, in the method provided by the present invention, in S1, hydrolysis includes either dilution hydrolysis or neutralization hydrolysis.

[0010] As an optional implementation, in the method provided by the present invention, in step S2, the acid solution is 0.1 to 1.5 mol / L sulfuric acid, the liquid-solid ratio of sulfuric acid to crude bismuth oxychloride obtained in step S1 is 1:1 to 10:1, and the acid washing time is 5 to 120 min.

[0011] In this invention, the liquid-to-solid ratio refers to the ratio of the volume (ml) of sulfuric acid to the weight (g) of crude bismuth oxychloride solid.

[0012] As an optional implementation, in the method provided by the present invention, in S3, the volume ratio of hydrochloric acid to sulfuric acid in the mixed acid is 3:1 to 10:1, and the molar ratio is 2:1 to 7:1.

[0013] As an optional implementation, in the method provided by the present invention, in S3, the liquid-solid ratio of the mixed acid solution to the solid is 5:1 to 10:1, and the dissolution time is 2 to 4 hours.

[0014] In this invention, the liquid-to-solid ratio refers to the ratio of the volume (ml) of sulfuric acid to the weight (g) of crude bismuth oxychloride solid.

[0015] As an optional implementation, in the method provided by the present invention, in S4, the solution used for deep lead removal is a barium salt and a sulfate.

[0016] As an optional implementation, in the method provided by the present invention, the barium salt is selected from one or more of barium hydroxide, barium sulfate, and barium chloride.

[0017] As an optional implementation, in the method provided by the present invention, the sulfate is selected from one or more of sodium sulfate, potassium sulfate, and ammonium sulfate.

[0018] As an optional implementation, in the method provided by the present invention, in S4, the hydrolysis method after lead removal is dilution hydrolysis or neutralization hydrolysis, and the pH at the hydrolysis endpoint is 0.8 to 3.0.

[0019] As an optional implementation, in the method provided by the present invention, in step S4, sodium hydroxide is used for hydrolysis.

[0020] As an optional implementation, in the method provided by the present invention, in S4, the purified 4N grade bismuth oxychloride contains lead ≤0.0014 wt%, iron ≤0.0019 wt%, sulfur ≤0.0035 wt%, silver ≤0.0029 wt%, and calcium ≤0.0024 wt%.

[0021] The working principle of this invention is as follows: This invention achieves deep separation of bismuth and lead based on their different behaviors under specific chemical environments. First, a high-lead bismuth chloride solution is hydrolyzed. Under conditions of pH 0.8–3.0, bismuth preferentially hydrolyzes to bismuth oxychloride (BiOCl) precipitate. Iron impurities entrained in the precipitate can be removed by washing with sulfuric acid. Subsequently, a hydrochloric acid-sulfuric acid mixed acid treatment is used: bismuth oxychloride dissolves into BiCl3 in a high-chlorine environment and enters the liquid phase, while lead is converted to lead sulfate (PbSO4) solid phase precipitation, achieving efficient bismuth-lead separation. Finally, by introducing barium salt, it co-precipitates with residual lead ions to form PbSO4-BaSO4 coprecipitate, completing deep lead removal and obtaining 4N grade high-purity bismuth oxychloride. The reactions involved are as follows: Bi 3+ +Cl - +H₂O=BiOCl+2H + PbCl₂ + SO₄ 2- =PbSO4 + 2Cl - BiOCl + 2HCl = BiCl3 + H2O Ba 2+ +SO4 2- =BaSO4↓ Pb 2+ +SO4 2- =PbSO4↓.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention uses a high-lead bismuth chloride solution as raw material. First, the high-lead bismuth chloride solution is hydrolyzed, and bismuth preferentially hydrolyzes to bismuth oxychloride (BiOCl) precipitate. Iron impurities entrained in the precipitate can be removed by washing with sulfuric acid. Then, the core technology of "selective dissolution with mixed acid" is adopted. Using a mixed acid system of hydrochloric acid and sulfuric acid, bismuth enters the solution in the form of bismuth chloride, while lead is simultaneously converted into lead sulfate precipitate, thereby achieving effective separation of bismuth and lead. Then, barium salt and sulfate are combined for deep purification to remove lead, resulting in a high-purity bismuth chloride solution. Hydrolysis yields 4N bismuth oxychloride product. This invention innovatively introduces a specific mixed acid system composed of hydrochloric acid and sulfuric acid to dissolve the crude bismuth oxychloride obtained from the initial hydrolysis. This process can achieve reverse mass transfer between bismuth and lead. Bismuth selectively enters the solution in the form of bismuth chloride, while lead is simultaneously converted into lead sulfate precipitate and fixed in the residue. This strategy of transforming the solution purification problem into solid-phase selective transformation and separation is unprecedented in existing technologies.

[0023] (2) This invention innovatively transforms the challenge of deep lead removal from high-chlorine, high-acid, and high-lead solutions in traditional processes into two highly efficient steps: "selective redissolution of high-lead bismuth oxychloride" and "deep purification of low-chlorine and low-acid solutions." By shifting the lead removal process to the redissolution stage, not only is the use of toxic chlorine gas successfully eliminated, but reagent consumption is also significantly reduced. Through process route innovation, the bottleneck of lead removal is overcome.

[0024] (3) This invention relies on a two-stage lead removal mechanism consisting of “selective dissolution of mixed acid” and “synergistic precipitation of barium salt” to achieve efficient and deep separation of bismuth from lead and other impurities. It can directly and stably prepare 4N grade bismuth oxychloride with a purity of up to 99.99% from complex high-lead raw materials, solving the industry problem of difficulty in improving product purity under this system.

[0025] (4) This invention does not rely solely on traditional coprecipitation, but creatively divides the lead removal process into two distinct stages: "main body separation" and "deep purification." First, the main body of lead is separated through the above-mentioned mixed acid dissolution. Then, in the relatively pure bismuth-containing solution obtained, the synergistic effect of barium salt and sulfate is utilized to generate barium sulfate, which carries residual trace amounts of lead sulfate to form a coprecipitate, thus achieving deep purification. This functional combination and step-by-step design significantly improves the depth and reliability of lead removal.

[0026] (5) Compared to existing technologies that either rely on high-purity raw materials or involve lengthy processes and the use of toxic reagents, this invention strategically shifts the core lead removal process from the raw material solution stage to the "crude bismuth oxychloride redissolution" stage. This reconfiguration of the process route makes deep lead removal possible in a more easily handled low-chlorine, low-acid medium, thereby fundamentally avoiding the use of chlorine gas and significantly reducing reagent consumption. This method can directly process low-grade bismuth chloride solutions with complex compositions, eliminating dependence on expensive high-purity bismuth ingots, significantly reducing raw material costs, and providing an economically feasible technical path for the high-value utilization of various bismuth-containing secondary resources.

[0027] (6) The entire process of this invention avoids the use of high-risk reagents such as chlorine, the reaction conditions are mild, and the amount of waste generated is small, making it a cleaner and safer green production process. During the lead removal process, most of the lead is enriched in the slag in the form of chemically stable lead sulfate, which not only ensures the high purity of the main product, but also creates favorable conditions for the targeted recovery and resource recycling of lead. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is the process technology route of the present invention. Detailed Implementation

[0030] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0033] Example 1 A method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution, the process route is as follows: Figure 1 As shown, it includes the following steps: (1) Hydrolysis of crude bismuth oxychloride: Take 200 mL of complex high-lead bismuth chloride solution (the main elemental components are listed in Table 1), and hydrolyze the crude bismuth oxychloride by adding 6 mol / L NaOH solution to adjust the pH. The pH of the hydrolysis endpoint is 3.0, and a total of 20.12 g of crude bismuth oxychloride is obtained.

[0034] (2) Washing iron with dilute acid: The above crude bismuth oxychloride was washed with dilute sulfuric acid at a liquid-solid ratio of 2:1 to remove iron. That is, it was washed with 40 mL of 0.7 mol / L dilute sulfuric acid for 30 minutes to obtain 18.76 g of crude bismuth oxychloride after iron removal.

[0035] (3) One-time lead removal with mixed acid: Take 15g of the above-mentioned crude bismuth oxychloride for iron removal, add 80mL of mixed acid at a liquid-to-solid ratio of 6:1 and stir to dissolve for 2h until most of the bismuth oxychloride dissolves. Filter out 0.6g of insoluble matter (the main components are listed in Table 2) to obtain a bismuth chloride solution. The mixed acid ratio is hydrochloric acid:sulfuric acid volume ratio of 10:1 and molar ratio of 6:1.

[0036] (4) Deep lead removal with barium salt: Add barium chloride and ammonium sulfate to the above 80 mL bismuth chloride solution for deep lead removal. The amount of barium chloride added is 10 g / L and the amount of ammonium sulfate added is 6 g / L. Stir at room temperature for 30 min, then let stand and age for 24 h. Pour off the supernatant and filter the bottom liquid for 0.3 g of insoluble matter (the main components are listed in Table 3) to obtain bismuth chloride solution.

[0037] (5) Preparation of high-purity bismuth oxychloride by secondary hydrolysis: Add 6 mol / L NaOH solution to the above bismuth chloride solution to adjust the pH and perform secondary hydrolysis at room temperature. The pH of the hydrolysis endpoint is 2.0. After filtration, 12.15g of bismuth oxychloride product is obtained. Its main components are listed in Table 4.

[0038] Table 1. Main element content of high-lead bismuth chloride solution, g / L

[0039] Table 2. Main components of lead-insoluble matter, wt%

[0040] Table 3. Main components of insoluble matter from the filtration of the bottom liquid, wt%

[0041] Table 4. Main components of bismuth oxychloride, wt%

[0042] Example 2 A method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution, the process route is as follows: Figure 1 As shown, it includes the following steps: (1) Hydrolysis of crude bismuth oxychloride: Take 500 mL of complex high-lead bismuth chloride solution and add 4 mol / L NaOH solution to adjust the pH to hydrolyze crude bismuth oxychloride. The pH of the hydrolysis endpoint is 1.0, and a total of 50.32 g of crude bismuth oxychloride is obtained.

[0043] (2) Washing iron with dilute acid: The above crude bismuth oxychloride was washed with dilute sulfuric acid at a liquid-solid ratio of 10:1 to remove iron. That is, it was washed with 503.2 mL of 0.2 mol / L dilute sulfuric acid for 5 minutes to obtain 43.07 g of crude bismuth oxychloride after iron removal.

[0044] (3) One-time lead removal with mixed acid: Take 20g of the above-mentioned crude bismuth oxychloride after iron removal, add 200mL of mixed acid at a liquid-to-solid ratio of 10:1 and stir to dissolve for 2h until most of the bismuth oxychloride dissolves. Filter out 0.95g of insoluble matter to obtain a bismuth chloride solution. The mixed acid ratio is hydrochloric acid:sulfuric acid volume ratio of 3:1 and molar ratio of 2:1.

[0045] (4) Deep lead removal with barium salt: Add barium hydroxide and potassium sulfate to the above 100 mL bismuth chloride solution for deep lead removal. The amount of barium hydroxide added is 4 g / L and the amount of potassium sulfate added is 4 g / L. Stir at room temperature for 30 min, then let stand and age for 24 h. Pour off the supernatant and filter the bottom liquid for 0.4 g of insoluble matter to obtain bismuth chloride solution.

[0046] (5) Preparation of high-purity bismuth oxychloride by secondary hydrolysis: Add 5 mol / L NaOH solution to the above bismuth chloride solution to adjust the pH and perform secondary hydrolysis at room temperature. The pH of the hydrolysis endpoint is 0.9. After filtration, 17.54g of bismuth oxychloride product is obtained. Its main components are listed in Table 5.

[0047] Table 5. Main components of bismuth oxychloride, wt%

[0048] Example 3 A method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution, the process route is as follows: Figure 1 As shown, it includes the following steps: (1) Hydrolysis of crude bismuth oxychloride: Take 300 mL of complex high-lead bismuth chloride solution and add 8 mol / L NaOH solution to adjust the pH to hydrolyze crude bismuth oxychloride. The pH of the hydrolysis endpoint is 3.0, and a total of 30.45 g of crude bismuth oxychloride is obtained.

[0049] (2) Washing iron with dilute acid: The above crude bismuth oxychloride was washed with dilute sulfuric acid at a liquid-solid ratio of 5:1, that is, it was washed with 152.25 mL of 1.5 mol / L dilute sulfuric acid for 120 minutes to obtain 26.48 g of crude bismuth oxychloride after iron removal.

[0050] (3) One-time lead removal with mixed acid: Take 10g of the above-mentioned crude bismuth oxychloride for iron removal, add 80mL of mixed acid at a liquid-to-solid ratio of 8:1 and stir to dissolve for 2h until most of the bismuth oxychloride dissolves. Filter out 0.45g of insoluble matter to obtain a bismuth chloride solution. The mixed acid ratio is hydrochloric acid:sulfuric acid volume ratio of 10:1 and molar ratio of 7:1.

[0051] (4) Deep lead removal with barium salt: Add barium chloride and sodium sulfate to the above 50 mL bismuth chloride solution for deep lead removal. The amount of barium chloride added is 8 g / L and the amount of sodium sulfate added is 5 g / L. Stir at room temperature for 30 min, then let stand and age for 48 h. Pour off the supernatant and filter the bottom liquid for 0.29 g of insoluble matter to obtain bismuth chloride solution.

[0052] (5) Preparation of high-purity bismuth oxychloride by secondary hydrolysis: Add 8 mol / L NaOH solution to the above bismuth chloride solution to adjust the pH and perform secondary hydrolysis at room temperature. The pH of the hydrolysis endpoint is 3.0. After filtration, 8.18g of bismuth oxychloride product is obtained. Its main components are listed in Table 6.

[0053] Table 6. Main components of bismuth oxychloride, wt%

[0054] Comparative Example 1 The difference from Example 1 is that this process first removes iron and lead in the bismuth leaching solution before hydrolysis. The specific steps are as follows: (1) Iron removal by extraction: Under the condition of O / A=1.2 / 1, iron extractant was used to remove iron from the solution by 5-stage countercurrent extraction, and the iron content in the raffinate was 130 mg / L.

[0055] (2) Lead removal by double salt coprecipitation: Add 50 times the theoretical amount of barium hydroxide and 10 times the theoretical amount of sodium sulfate to the iron removal liquid. The lead removal rate is only 90%, and the lead content in the purified liquid reaches 150 mg / L.

[0056] (3) First hydrolysis: Add 5 mol / L sodium hydroxide solution to the purified solution to adjust the hydrolysis pH to 3, control the stirring speed to 500 rpm, and stir for 1 h at room temperature.

[0057] (4) Secondary resolution and hydrolysis: After dissolving the first hydrolyzed bismuth oxychloride in 6 mol / L hydrochloric acid, 5 mol / L sodium hydroxide solution is slowly added to the original solution at 500 rpm to adjust the hydrolysis pH to 2, and finally the bismuth oxychloride product is obtained. The content of the main components in the product is shown in Table 7.

[0058] Table 7: Main components of bismuth oxychloride, wt%

[0059] Compared with the process in Example 1, this process uses co-precipitation to remove lead impurities in a high-chlorine, high-acid, and high-lead solution. Due to the high lead content in the solution, reagent consumption is excessive, and the amount of barium salt added is usually more than 30 times the theoretical amount, resulting in high costs and the generation of a large amount of lead-containing barium sulfate solid waste. Furthermore, due to the interference of high concentration of chloride ions, the lead removal depth is insufficient, and the content of multiple impurities in the product exceeds the standard, with the product purity only reaching 2N5.

[0060] Comparative Example 2 The difference from Example 1 is that only hydrochloric acid was used for treatment in the mixed acid. Bismuth oxychloride product was obtained, and the content of its main components is shown in Table 8.

[0061] Table 8: Main components of bismuth oxychloride, wt%

[0062] Compared with the process in Example 1, this process uses only hydrochloric acid in the one-step lead removal step of mixed acid, which results in the lead in the crude bismuth oxychloride removed from iron not being separated in the form of lead sulfate precipitation, resulting in an excessively high lead content in the obtained product and affecting the purity of the product.

[0063] Comparative Example 3 The difference from Example 1 is that only sulfuric acid was used for treatment in the mixed acid. Bismuth oxychloride product was obtained, and the content of its main components is shown in Table 9.

[0064] Table 9: Main components of bismuth oxychloride, wt%

[0065] Compared with the process in Example 1, this process uses only sulfuric acid in the one-step lead removal step of mixed acid. However, bismuth oxychloride has low solubility in sulfuric acid solution, resulting in a low yield of bismuth oxychloride. The weight of insoluble matter exceeds 20% of the weight of crude bismuth oxychloride after iron removal, resulting in significant losses.

[0066] Comparative Example 4 The difference from Example 1 is that the endpoint pH of hydrolysis in step (1) of crude bismuth oxychloride is 4.0. Bismuth oxychloride product was obtained, and the content of the main components in the product is shown in Table 10.

[0067] Table 10: Main components of bismuth oxychloride, wt%

[0068] Compared to the process in Example 1, this process uses excessive NaOH in the hydrolysis step of crude bismuth oxychloride. This causes trace amounts of high-valence iron in the solution to simultaneously hydrolyze and release more ferric hydroxide during bismuth hydrolysis, resulting in an excessively high iron content in the product. Simultaneously, the residual NaOH in the crude bismuth oxychloride increases the amount of dilute sulfuric acid used in step (2), increasing costs.

[0069] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution, characterized in that, Includes the following steps: S1. Hydrolyze the high-lead bismuth chloride solution and adjust the pH to 0.8-3.0 to obtain crude bismuth oxychloride; S2. After washing the crude bismuth oxychloride obtained in step S1 with acid, a solid substance is obtained. S3. Dissolve the solid obtained in step S2 using a mixed acid solution of hydrochloric acid and sulfuric acid to obtain a solution and a residue. S4. After deep lead removal from the solution, hydrolysis is performed to obtain purified 4N grade bismuth oxychloride.

2. The method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution according to claim 1, characterized in that, In S1, the bismuth content in the high-lead bismuth chloride solution is 50–300 g / L, the lead content is 0.1–10 g / L, and the iron content is 1–20 g / L.

3. The method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution according to claim 1, characterized in that, In S1, hydrolysis includes either dilution hydrolysis or neutralization hydrolysis.

4. The method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution according to claim 1, characterized in that, In step S2, the acid solution is 0.1–1.5 mol / L sulfuric acid, the liquid-solid ratio of sulfuric acid to crude bismuth oxychloride obtained in step S1 is 1:1–10:1, and the acid washing time is 5–120 min.

5. The method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution according to claim 1, characterized in that, In S3, the volume ratio of hydrochloric acid to sulfuric acid in the mixed acid is 3:1 to 10:1, and the molar ratio is 2:1 to 7:

1.

6. The method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution according to claim 1, characterized in that, In S3, the liquid-to-solid ratio of the mixed acid solution to the solid is 5:1 to 10:1, and the dissolution time is 2 to 4 hours.

7. The method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution according to claim 1, characterized in that, In S4, the solution used for deep lead removal is a barium salt and a sulfate. The barium salt is selected from one or more of barium hydroxide, barium sulfate, and barium chloride, and the sulfate is selected from one or more of sodium sulfate, potassium sulfate, and ammonium sulfate.

8. The method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution according to claim 1, characterized in that, In S4, the hydrolysis method after lead removal is dilution hydrolysis or neutralization hydrolysis, and the endpoint pH of hydrolysis is 0.8 to 3.

0.

9. The method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution according to claim 1, characterized in that, In S4, sodium hydroxide is used for hydrolysis.

10. The method for preparing 4N-grade bismuth oxychloride from a complex high-lead bismuth chloride solution according to claim 1, characterized in that, In S4, the purified 4N grade bismuth oxychloride contains ≤0.0014 wt% lead, ≤0.0019 wt% iron, ≤0.0035 wt% sulfur, ≤0.0029 wt% silver, and ≤0.0024 wt% calcium.

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