Method for removing bismuth from lead fluosilicate electrolyte

Abstract

The application relates to the technical field of lead electrolytic refining, and particularly discloses a method for removing bismuth from a lead fluosilicate electrolyte, which comprises the following steps: stirring and heating the lead fluosilicate electrolyte to 35-45 DEG C, adding a mixture of polysulfur oxysalt and a reducing agent, stirring and heating to 45-65 DEG C, reacting for 1-4.5 hours, and removing the precipitate after the reaction to obtain the filtrate, which is the lead fluosilicate electrolyte from which the bismuth is removed. The method for removing bismuth from the lead fluosilicate electrolyte can effectively remove the bismuth without losing lead, the removal rate of bismuth ions reaches more than 70%, and can reach more than 99% at the highest, metal ions which affect the purity of the electrolytic lead are not introduced, the method is simple and easy to operate, and the cost is low.

Description

Technical Field

[0001] This invention relates to the field of lead electrolytic refining technology, and in particular to a method for removing bismuth from lead fluorosilicate electrolyte. Background Technology

[0002] Electrolytic refining of lead is a crucial step in modern lead smelting. Its purpose is to separate impurity elements from the main lead in the crude lead anode using electrochemical methods, thereby obtaining refined lead with a purity of over 99.99%. In this process, an anode plate cast from crude lead and a starting electrode sheet from which pure lead is deposited at the cathode are immersed together in an acidic electrolyte composed of fluorosilicic acid and lead fluorosilicate for electrolysis.

[0003] Bismuth is a common associated element in lead minerals. Because bismuth has a similar potential to lead, it readily discharges and precipitates simultaneously with lead at the cathode, whether in dissolved state or otherwise. 3+ Even suspended bismuth-containing particles can undergo reduction reactions or physical adhesion on the cathode, leading to excessive bismuth content in the cathode-deposited lead. This severely affects the quality of the final product, and electrolytic lead with high bismuth content cannot meet the purity requirements of high-standard markets (such as batteries and radiation protection). Furthermore, it easily forms floating anode mud with arsenic and antimony. In summary, this makes it the most detrimental impurity element to the quality of electrolytic lead.

[0004] Currently, traditional methods for purifying lead electrolytes in the industry mainly focus on removing negatively charged elements such as zinc, iron, and tin, and controlling antimony content through methods such as "arsenic salt removal." However, an effective and economical method for removing bismuth remains a technological bottleneck in the industry. Therefore, developing a new method for the deep removal of bismuth from lead electrolytes is urgently needed to improve the technological level of lead electrolytic refining and ensure the quality and competitiveness of high-purity lead products. Summary of the Invention

[0005] To address the above shortcomings, this invention provides a method for removing bismuth from lead fluorosilicate electrolyte, which can effectively remove bismuth from the electrolyte with minimal loss of lead. The specific technical solution is as follows: A method for removing bismuth from lead fluorosilicate electrolyte, comprising the following steps: The lead fluorosilicate electrolyte is heated to 35-45°C while stirring. A mixture of polysulfide oxyacid salt and reducing agent is added, and the temperature is raised to 45-65°C while stirring. The reaction is continued for 1-4.5 hours. After the reaction is completed, the precipitate is removed by filtration, and the filtrate is obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

[0006] Preferably, in the above-mentioned method for removing bismuth from lead fluorosilicate electrolyte, the polysulfide oxyacid salt is one or both of sodium thiosulfate and sodium dithionite.

[0007] Preferably, in the above-mentioned method for removing bismuth from lead fluorosilicate electrolyte, the reducing agent is one or more of hypophosphite and its salts, thiourea dioxide, and ascorbic acid.

[0008] Preferably, in the above-mentioned method for removing bismuth from lead fluorosilicate electrolyte, the ratio of lead fluorosilicate electrolyte to the mixture is 1L:1~4g.

[0009] Preferably, in the above-mentioned method for removing bismuth from lead fluorosilicate electrolyte, the mass ratio of the polysulfide oxyacid salt to the reducing agent is 0.8:0.2~3.2:0.8.

[0010] Preferably, in the above-mentioned method for removing bismuth from lead fluorosilicate electrolyte, the polysulfide oxyacid salt is sodium thiosulfate, and the reducing agent is thiourea dioxide.

[0011] Preferably, in the above-mentioned method for removing bismuth from lead fluorosilicate electrolyte, the stirring speed is 200-600 r / min.

[0012] Preferably, in the above-mentioned method for removing bismuth from lead fluorosilicate electrolyte, the hypophosphite and its salt are sodium hypophosphite.

[0013] Preferably, in the above-mentioned method for removing bismuth from lead fluorosilicate electrolyte, the reaction time is 2-4 hours.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. The method for removing bismuth from lead fluorosilicate electrolyte of the present invention can effectively remove bismuth without losing lead, with a bismuth ion removal rate of over 70%, and up to over 99%, without introducing metal ions that affect the purity of electrolytic lead. The method is simple to operate and has low cost.

[0015] 2. This invention utilizes sodium thiosulfate and sodium dithionite from polysulfide oxyacid salts, along with a strong reducing agent, to remove bismuth ions from lead electrolytes. Under heating conditions, thiosulfate and dithionite ions undergo a disproportionation reaction in the acidic electrolyte to generate ultrafine elemental sulfur powder. The reducing agent provides a strongly reducing environment to displace and release nascent atomic hydrogen. This nascent atomic hydrogen has high chemical reactivity and can reduce the ultrafine sulfur powder S generated by the disproportionation reaction to sulfur ions S. 2- This allows the bismuth to react with bismuth ions in the electrolyte, forming bismuth sulfide precipitate and thus removing bismuth ions. Because the solubility product and solubility of bismuth sulfide are much lower than those of lead sulfide, in acidic solutions, trace amounts or low concentrations of newly formed bismuth ions (S2) are generated. 2- It preferentially reacts with lower concentrations of bismuth ions in the solution to form bismuth sulfide precipitate.

[0016] 3. In the method of the present invention, compared with traditional sulfides, a high concentration of sulfur ions is not directly provided. On the one hand, it will not produce highly toxic and explosive hydrogen sulfide gas, and on the other hand, it will not react with the high concentration of lead ions in the electrolyte to form colloidal lead sulfide precipitate, thus avoiding lead loss.

[0017] 4. The method of the present invention is green and environmentally friendly. No metal ions that affect the purity of electrolytic lead are introduced into the environmental system, and the pH value of the system does not need to be changed. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments 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.

[0019] Figure 1 This is a photograph of the electrolyte before the reaction in Comparative Example 4 of the present invention; Figure 2 This is a photograph of the electrolyte after the reaction in Comparative Example 4 of this invention; Figure 3 This is a photograph of the electrolyte in Comparative Example 5 before the reaction in this invention; Figure 4 This is a photograph of the electrolyte after the reaction in Comparative Example 5 of this invention; Figure 5 This is a photograph of the electrolyte in Comparative Example 6 before the reaction in this invention; Figure 6 This is a photograph of the electrolyte after the reaction in Comparative Example 6 of this invention. Detailed Implementation

[0020] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0021] The sodium thiosulfate, sodium dithionite, hypophosphite, and hypophosphite used in the following examples and comparative examples were produced by Xilong Scientific, thiourea dioxide was produced by Hongye Holdings Group Co., Ltd., and ascorbic acid was produced by Guangxi Guanghua Technology Co., Ltd. The lead fluorosilicate electrolyte without bismuth removal came from a lead electrolytic production enterprise in Hunan Province, with a lead content of 70962.85 mg / L and a bismuth content of 20.448 mg / L.

[0022] Example 1 A method for removing bismuth from lead fluorosilicate electrolyte, comprising the following steps: 1L of lead fluorosilicate electrolyte was heated to 45℃ while stirring. 1g of a mixture of sodium thiosulfate and thiourea dioxide was added, with a mass ratio of sodium thiosulfate to thiourea dioxide of 0.8:0.2. The temperature was increased to 60℃ while stirring, and the reaction was carried out for 3 hours. After the reaction was completed, the precipitate was removed by filtration, and the filtrate was obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

[0023] Example 2 A method for removing bismuth from lead fluorosilicate electrolyte, comprising the following steps: 1L of lead fluorosilicate electrolyte was heated to 35℃ while stirring. 2g of a mixture of sodium thiosulfate and sodium hypophosphite was added, with a mass ratio of sodium thiosulfate to sodium hypophosphite of 1.5:0.5. The mixture was heated to 55℃ while stirring and reacted for 3.5 hours. After the reaction was completed, the precipitate was removed by filtration, and the filtrate was obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

[0024] Example 3 A method for removing bismuth from lead fluorosilicate electrolyte, comprising the following steps: 1L of lead fluorosilicate electrolyte was heated to 40℃ while stirring. 4g of a mixture of sodium thiosulfate and thiourea dioxide was added, with a mass ratio of sodium thiosulfate to thiourea dioxide of 3.2:0.8. The temperature was increased to 65℃ while stirring, and the reaction was carried out for 4 hours to remove bismuth. After the reaction was completed, the precipitate was removed by filtration, and the filtrate was obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

[0025] Example 4 A method for removing bismuth from lead fluorosilicate electrolyte, comprising the following steps: 1L of lead fluorosilicate electrolyte was heated to 45℃ while stirring. 3.5g of a mixture of sodium thiosulfate and ascorbic acid was added, with a mass ratio of sodium thiosulfate to ascorbic acid of 3:0.5. The mixture was heated to 60℃ while stirring and reacted for 2 hours to remove bismuth. After the reaction was completed, the precipitate was removed by filtration, and the filtrate was obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

[0026] Example 5 A method for removing bismuth from lead fluorosilicate electrolyte, comprising the following steps: 1 L of lead fluorosilicate electrolyte was heated to 35 °C while stirring. 2.3 g of a mixture of sodium dithionite and thiourea dioxide was added, with a mass ratio of sodium dithionite to thiourea dioxide of 2:0.3. The mixture was heated to 45 °C while stirring and reacted for 2.5 hours to remove bismuth. After the reaction was completed, the mixture was filtered to remove the precipitate, and the filtrate was obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

[0027] Example 6 A method for removing bismuth from lead fluorosilicate electrolyte, comprising the following steps: 1L of lead fluorosilicate electrolyte was heated to 40℃ while stirring. 4g of a mixture of sodium dithionite and thiourea dioxide was added, with a mass ratio of sodium dithionite to thiourea dioxide of 3.2:0.8. The temperature was increased to 65℃ while stirring, and the reaction was carried out for 4 hours to remove bismuth. After the reaction was completed, the precipitate was removed by filtration, and the filtrate was obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

[0028] Comparative Example 1 Same as Example 3, except that thiourea dioxide is not added. Specifically, 1L of lead fluorosilicate electrolyte is heated to 40°C while stirring, 4g of sodium thiosulfate is added, and the temperature is raised to 65°C while stirring. The reaction is carried out for 4 hours. After the reaction is completed, the precipitate is removed by filtration, and the filtrate is obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

[0029] Comparative Example 2 Same as Example 3, except that sodium thiosulfate is not added. Specifically, 1L of lead fluorosilicate electrolyte is heated to 40°C while stirring, 4g of thiourea dioxide is added, and the temperature is raised to 65°C while stirring. The reaction is carried out for 4 hours to remove bismuth. After the reaction is completed, the precipitate is removed by filtration, and the filtrate is obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

[0030] Comparative Example 3 Same as Example 6, except that thiourea dioxide is not added. Specifically, 1L of lead fluorosilicate electrolyte is heated to 40°C while stirring, 4g of sodium dithionite is added, and the temperature is raised to 65°C while stirring. The reaction is carried out for 4 hours to remove bismuth. After the reaction is completed, the precipitate is removed by filtration, and the filtrate is obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

[0031] Comparative Example 4 Same as Example 2, except that sodium thiosulfate was not added. Specifically, 1 L of lead fluorosilicate electrolyte was heated to 35°C while stirring, 2 g of sodium hypophosphite was added, and the temperature was raised to 55°C while stirring, and the reaction was carried out for 3.5 hours. The solution showed no change, no color change, and no precipitate was formed.

[0032] Comparative Example 5 Same as Example 3, except that sodium thiosulfate was not added. Specifically, 1L of lead fluorosilicate electrolyte was heated to 45°C while stirring, 3.5g of ascorbic acid was added, and the temperature was raised to 60°C while stirring. The reaction was carried out for 2 hours, and the solution showed no change, no color change, and no precipitation.

[0033] Comparative Example 6 1L of lead fluorosilicate electrolyte was stirred at room temperature (25℃), and 4g of a mixture of sodium thiosulfate and thiourea dioxide was added. The mass ratio of sodium thiosulfate to thiourea dioxide was 3.2:0.8. The reaction was carried out at room temperature (25℃) for 4 hours. The solution showed no change, no color change, and no precipitation.

[0034] Comparative Example 7 1 L of lead fluorosilicate electrolyte was heated to 45°C with stirring. 3 mL of 185 g / L sodium sulfide nonahydrate solution was added, and the temperature was raised to 60°C with stirring. The reaction was allowed to proceed for 2 hours. Immediately after the addition of sodium sulfide, the solution became cloudy and produced a large number of black particles. Sodium sulfide preferentially reacts with lead to form lead sulfide, resulting in lead loss.

[0035] The filtrates from the above examples and comparative examples were used to determine the bismuth and lead content in the filtrates. The bismuth content was detected according to the method in HJ694-2014, and the lead content was detected according to the method in HJ776-2015.

[0036] The bismuth removal rate and lead loss rate were calculated, and the results are shown in Table 1. As can be seen from the table, the bismuth removal rate in this embodiment of the invention is above 71%, reaching a maximum of 99.93%, while the lead loss is zero. Comparing the embodiments and Comparative Examples 1-5, it can be seen that using a single polysulfide oxyacid salt or reducing agent cannot effectively remove bismuth. Comparative Example 7 shows that directly adding sulfides causes the high concentration of lead ions in the electrolyte to react and form colloidal lead sulfide precipitates, resulting in lead loss. In summary, the method of this invention can effectively remove bismuth without loss of lead, and has the advantages of simple process and convenient operation.

[0037] Table 1. Bismuth removal rate and lead loss rate of lead fluorosilicate electrolyte in each treatment group The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for removing bismuth from lead fluorosilicate electrolyte, characterized in that, Includes the following steps: The lead fluorosilicate electrolyte is heated to 35-45°C while stirring. A mixture of polysulfide oxyacid salt and reducing agent is added, and the temperature is raised to 45-65°C while stirring. The reaction is continued for 1-4.5 hours. After the reaction is completed, the precipitate is removed by filtration, and the filtrate is obtained, which is the lead fluorosilicate electrolyte with bismuth removed.

2. The method for removing bismuth from lead fluorosilicate electrolyte according to claim 1, characterized in that, The polysulfide oxyacid salt is one or both of sodium thiosulfate and sodium dithionite.

3. The method for removing bismuth from lead fluorosilicate electrolyte according to claim 1, characterized in that, The reducing agent is one or more of hypophosphite and its salts, thiourea dioxide, and ascorbic acid.

4. The method for removing bismuth from lead fluorosilicate electrolyte according to claim 2 or 3, characterized in that, The polysulfide oxyacid salt is sodium thiosulfate, and the reducing agent is thiourea dioxide.

5. The method for removing bismuth from lead fluorosilicate electrolyte according to claim 1, characterized in that, The ratio of the lead fluorosilicate electrolyte to the mixture is 1L:1~4g.

6. The method for removing bismuth from lead fluorosilicate electrolyte according to claim 1, characterized in that, The mass ratio of the polysulfide oxyacid salt to the reducing agent is 0.8:0.2 to 3.2:0.

8.

7. The method for removing bismuth from lead fluorosilicate electrolyte according to claim 1, characterized in that, The stirring speed is 200-600 r / min.

8. The method for removing bismuth from lead fluorosilicate electrolyte according to claim 3, characterized in that, The hypophosphite and its salt are sodium hypophosphite.

9. The method for removing bismuth from lead fluorosilicate electrolyte according to claim 1, characterized in that, The reaction time is 2-4 hours.

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