A cascade process for selective extraction of arsenic and bismuth from copper electrolyte and separation of copper and nickel

Abstract

The application discloses a kind of copper electrolyte arsenic bismuth selective extraction and copper-nickel separation cascade process, after the trivalent arsenic is converted into pentavalent arsenic by pre-oxidation of feed liquid, two-stage countercurrent extraction is carried out using straight-chain trialkyl phosphine oxide organic phase containing secondary octanol modification, and efficient co-extraction of arsenic bismuth is realized;Loaded organic phase is washed by pure water two-stage countercurrent, and copper-nickel co-extracted is preferentially eluted and returned to the electrolysis system, and arsenic bismuth is retained in the organic phase;Then, arsenic bismuth is stripped out and enriched by four-stage countercurrent stripping with sodium oxalate solution, and the blank organic phase is washed and regenerated for recycling use.The application is stable below 3g / L after cascade operation of raffinate arsenic, and the bismuth extraction rate can reach 100%, the organic phase is stable in circulation, no impurity accumulation, low operation cost, suitable for industrial continuous production, significantly guaranteeing the quality of copper and operation safety.

Description

Technical Field

[0001] This invention belongs to the field of wet copper electrolysis purification and solvent extraction metallurgical technology, specifically involving a cascade process for selective extraction of arsenic and bismuth from copper electrolyte and separation of copper and nickel. Background Technology

[0002] With the continuous expansion of global copper smelting capacity, the proportion of high-arsenic complex copper concentrate in raw materials has been increasing year by year. This has led to a growing problem of arsenic accumulation in the electrolyte of copper electrolysis systems, which has become a core bottleneck restricting the production of high-purity cathode copper. When the total arsenic content in the electrolyte exceeds 3 g / L, it not only causes the cathode electrodeposited copper to blacken and increases current consumption, but also continuously generates highly toxic arsine gas during electrolysis, posing extremely high safety and environmental risks. Therefore, the industry must regularly perform open-circuit arsenic and bismuth removal treatment on the electrolyte.

[0003] Currently, the mainstream industrial processes for removing arsenic from copper electrolytes mainly include electrowinning, neutralization precipitation, and solvent extraction, but all of them have varying degrees of technical defects. (1) Electrolytic removal of arsenic: It has high energy consumption and concentrated release of arsine, which poses a great safety risk. At the same time, the toxic arsenic copper slag produced by this process is a hazardous solid waste. With increasingly stringent environmental compliance requirements and rising solid waste disposal prices year by year, enterprises face huge disposal cost pressures.

[0004] (2) Neutralization precipitation method: Arsenic iron slag is generated by adding lime, iron salt and other precipitants, but this process will introduce impurity ions such as calcium and iron into the electrolyte, causing system pollution; in addition, the amount of slag generated by this method is large, and valuable metals such as copper and nickel are lost in large quantities during the precipitation process, resulting in a decrease in copper and nickel recovery rate of 3% to 8%. In the context of continuously rising raw material costs, the economic efficiency is poor.

[0005] (3) Solvent extraction method: Traditional neutral phosphine extraction processes (such as using Cyanex 923 or TBP as extractants) are widely used, but they still have the following significant shortcomings in industrial continuous production: ① The organic phase system composed of pure extractant and kerosene is very easy to emulsify, the phase separation rate is slow, there are many interfacial flocculents, and it is difficult to achieve long-term continuous cascade production; ② This type of extractant only has the ability to extract pentavalent arsenic, and the existing process lacks a matching precise pre-oxidation process, which results in a large amount of trivalent arsenic in the raw materials not being effectively removed, and the total arsenic removal rate is usually less than 50%; ③ In the washing section, arsenic is easy to be simultaneously eluted with valuable metals such as copper and nickel, and there is a lack of effective selection. The separation method results in a large amount of valuable metals entering the back-extraction solution and being difficult to recover, leading to serious resource depletion; ④ The selectivity for bismuth is poor, and impurities such as antimony and bismuth continue to accumulate after electrolyte circulation, affecting the ductility and other quality indicators of cathode copper; ⑤ Existing processes are mostly single-stage extraction or simple multi-stage series, lacking a standardized complete cascade process design of "two-stage extraction + two-stage washing + four-stage countercurrent back-extraction". The single-stage extraction capacity is limited, making it difficult to stably reduce arsenic to below the production threshold of 3g / L; ⑥ Key parameters such as temperature and organic phase ratio lack precise range control during process operation. The extraction capacity decays significantly at high temperatures, the organic phase loss is large, and the overall operating cost is high.

[0006] In recent years, although the procurement cost of domestically produced linear trialkylphosphine oxide extractant has been reduced by more than 30% compared with that of imported Cyanex 923, and it has the potential to replace it, the existing research is still limited to the single-stage pilot stage, and the three major industrialization problems of organic phase emulsification, copper-nickel co-extraction and continuous cascade stable operation have not yet been solved.

[0007] Therefore, there is an urgent need to develop a complete cascade extraction process based on domestically produced straight-chain trialkylphosphine oxide extractant to achieve efficient removal of arsenic and bismuth from copper electrolyte and selective separation of valuable copper and nickel metals, in order to meet the industrial production requirements of low cost, high stability and recyclable organic phase. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the present invention provides a cascade process for selective extraction of arsenic and bismuth from copper electrolyte and separation of copper and nickel, which solves the problems of severe emulsification, low arsenic removal efficiency, severe entrainment in copper-nickel co-extraction, incomplete bismuth removal, and inability to operate continuously in an industrial manner in the existing copper electrolyte arsenic and bismuth removal extraction process.

[0009] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a cascade process for selective extraction of arsenic and bismuth from copper electrolyte and separation of copper and nickel, comprising the following steps: S1. Pre-oxidation of the solution: Heat the copper electrolyte containing arsenic to 45~55℃, add hydrogen peroxide and stir at a constant temperature for oxidation, and filter to obtain pentavalent arsenic oxide solution; S2. Preparation and pretreatment of modified organic phase: By volume percentage, the organic phase consists of 18-22% trialkylphosphine oxide extractant, 4-6% 2-octanol and the remainder sulfonated kerosene; after preparation, it is pretreated by washing with sodium oxalate solution and water in sequence. S3. Two-stage countercurrent extraction: The organic phase pretreated in step S2 and the pentavalent arsenic oxide feed solution in step S1 are subjected to two-stage countercurrent contact at 20~35℃ with a ratio of O / A=150:(20~40). After mixing and phase separation, the arsenic-bismuth-loaded organic phase and the raffinate electrolyte are obtained. S4. Two-stage countercurrent washing: The arsenic-bismuth-loaded organic phase in step S3 is washed with pure water at 20~35℃ in a countercurrent manner with a ratio of O / A=150:(10~20) to elute the co-extracted copper-nickel metal. The washing solution is returned to the copper electrolysis system. S5. Four-stage countercurrent back-extraction: The supported organic phase after washing in step S4 is subjected to four-stage countercurrent back-extraction at 20-35°C using a sodium oxalate solution with pH=9~11 to obtain an arsenic-bismuth-enriched back-extraction solution. S6. Organic phase regeneration and recycling: The blank organic phase after back-extraction in step S5 is regenerated by washing with water and then returned to step S2 for recycling.

[0010] Furthermore, in step S1, the arsenic-containing copper electrolyte contains 12-15 g / L of arsenic, 0.01-0.3 g / L of bismuth, 35-38 g / L of copper, 9-12 g / L of nickel, and 210-220 g / L of sulfuric acid; the concentration of hydrogen peroxide is 27.5%, and the amount added is 1 / 25 to 1 / 15 of the electrolyte volume; the constant temperature stirring oxidation time is 0.8-1.2 h.

[0011] Furthermore, the concentration of the hydrogen peroxide is 27.5%, the amount added is 1 / 20 of the electrolyte volume, and the constant temperature stirring oxidation time is 1.0 h.

[0012] Furthermore, in step S2, the volume composition of the organic phase is 20% linear trialkylphosphine oxide extractant, 5% 2-octanol and 75% sulfonated kerosene; the concentration of the sodium oxalate solution is 8 g / L.

[0013] Furthermore, in step S3, the ratio of O / A in the two-stage countercurrent extraction is 150:30, the mixing and oscillation time is 2~4 min, and the phase separation time is ≤90 s; the arsenic content of the raffinate electrolyte is ≤3 g / L.

[0014] Furthermore, in step S4, the countercurrent washing is a two-stage countercurrent washing, and compared to O / A=150:15, the single-stage washing time is 2~4 minutes.

[0015] Furthermore, in step S5, the sodium oxalate solution has a pH of 10, a concentration of 8 g / L, and a back-extraction ratio of O / A of 150:20.

[0016] Furthermore, in step S6, the back-extracted blank organic phase is washed and regenerated with pure water at a volume ratio of 1:1.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) By modifying the organic phase compound system, the problems of emulsification and phase separation difficulties of organic phase are fundamentally solved. This invention uses a specific ratio of linear trialkylphosphine oxide, 2-octanol, and sulfonated kerosene to form a modified organic phase. Among them, 2-octanol serves as a dedicated modifier, which significantly improves the interfacial tension and fluidity of the organic phase while ensuring the arsenic extraction capacity. Experiments show that this modified system completely eliminates the interfacial flocculent matter that is easily generated in traditional pure extractant systems, shortens the phase separation time to less than 90 seconds, and does not show phase separation deterioration after 72 hours of continuous operation, providing a stable physicochemical basis for industrial continuous cascade production.

[0018] (2) By coupling the pre-oxidation process with two-stage countercurrent extraction, efficient and deep removal of arsenic is achieved. In this invention, a hydrogen peroxide pre-oxidation process is set up before extraction to completely convert trivalent arsenic in the electrolyte into pentavalent arsenic, breaking through the limitation of traditional neutral phosphine extractants that can only extract pentavalent arsenic, thus greatly improving the arsenic extraction capacity; combined with the two-stage countercurrent extraction process, arsenic in high arsenic (As 12~15g / L) copper sulfate electrolyte can be stably removed to below 3g / L, with the arsenic extraction rate reaching up to 83.37%; at the same time, after two-stage countercurrent extraction, the copper-nickel entrainment rate in the arsenic-bismuth-loaded organic phase is reduced to less than 3%.

[0019] (3) By combining staged washing with alkaline back-extraction, highly selective separation of arsenic bismuth and copper-nickel and efficient recovery of valuable metals are achieved. In this invention, pure water countercurrent washing is used to preferentially wash away copper-nickel co-extracted in the loaded organic phase, so that arsenic bismuth is retained in the organic phase, which is a significant improvement over the traditional sulfuric acid washing process for valuable metal recovery. Subsequently, a sodium oxalate alkaline system is used for four-stage countercurrent back-extraction, which not only achieves complete extraction of bismuth (100% extraction rate) and simultaneous removal of antimony, but also allows the organic phase after extraction to be recycled after water washing and regeneration. It also avoids the generation of interface contaminants caused by acidic back-extraction, and does not introduce impurity ions such as calcium, iron, chloride, and fluorine into the electrolyte throughout the process, ensuring the long-term clean circulation of the electrolyte system.

[0020] (4) The process conditions are mild and highly adaptable, possessing significant industrial implementation value and economic and environmental benefits. The entire process of this invention is controlled at a temperature of 20~35℃, requiring no high-temperature heating equipment. It can be directly connected to existing open-circuit electrolyte extraction tanks in copper smelting without large-scale equipment modification. The process parameters have a wide range and are highly adaptable to fluctuations in the arsenic concentration of raw materials (12~15g / L). Compared with the electrowinning arsenic removal method, this process does not have the risk of concentrated release of arsine and avoids the problem of high energy consumption. Compared with the neutralization precipitation method, this process does not produce a large amount of arsenic-iron hazardous slag, and the back-extraction liquid can be centrally recycled to recover products such as arsenous acid and bismuth salts. At the same time, the use of domestically produced linear trialkylphosphine oxide extractant significantly reduces the cost of reagents compared with imported similar products. The washing water and reclaimed water are all internally closed-loop circulated, with no external discharge of arsenic-containing wastewater, significantly reducing the overall operating cost and environmental pressure. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0023] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0024] The technical solution of the present invention will be further described below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] In the following examples, the domestically produced trialkylphosphine oxide extractant (e.g., P113 extractant (trialkylphosphine oxide)), 2-octanol was an industrial-grade modifier, sulfonated kerosene was an industrial-grade diluent, and the concentration of industrial-grade hydrogen peroxide was 27.5% (mass fraction). Sodium oxalate, sulfuric acid, and other reagents were all analytical grade or industrial grade. The basic electrolyte composition of the raw materials in Examples 1-3 is shown in Table 1 below. Table 1

[0026] Example 1 This embodiment is a preferred embodiment of the present invention, and the basic electrolyte composition is as follows: As 12.775 g / L, Bi 0.288 g / L, Cu 37.225 g / L, Ni 9.565 g / L, Sb 0.327 g / L, and H2SO4 215 g / L.

[0027] The specific steps of the cascade process for selective extraction of arsenic and bismuth from the electrolyte and separation of copper and nickel are as follows: S1. Pre-oxidation of the feed solution: Take the above-mentioned basic electrolyte solution, heat it to 50°C, add 27.5% hydrogen peroxide at 1 / 20 of the electrolyte volume, stir and oxidize at a constant temperature for 1.0 h, filter to remove insoluble matter, and obtain pentavalent arsenic oxidation feed solution.

[0028] S2. Preparation and pretreatment of modified organic phase: By volume percentage, 20% linear trialkylphosphine oxide extractant, 5% 2-octanol and 75% sulfonated kerosene are mixed evenly to prepare a modified organic phase; after preparation, it is pretreated by washing with 8 g / L sodium oxalate solution and pure water in sequence, and then set aside.

[0029] S3. Two-stage countercurrent extraction: The organic phase pretreated in step S2 and the pentavalent arsenic oxide solution obtained in step S1 are subjected to two-stage countercurrent contact at 20°C with a ratio of O / A=150:30. The single-stage mixing and oscillation time is 3 min and the phase separation time is ≤90 s. After phase separation, the arsenic-bismuth-loaded organic phase and the raffinate electrolyte are obtained.

[0030] The analysis revealed that the As content in the residual electrolyte was 2.124 g / L, the Bi content was 0 g / L, the arsenic extraction rate was 83.37%, the bismuth extraction rate was 100%, the Cu content was 36.208 g / L, and the Ni content was 9.32 g / L.

[0031] S4. Two-stage countercurrent washing: The arsenic-bismuth-loaded organic phase obtained in step S3 is subjected to two-stage countercurrent washing with pure water, with a ratio of O / A = 150:15, a single-stage washing time of 3 min, and a temperature of 20℃; the washing solution is returned to the copper electrolysis system.

[0032] The washing solution was tested and found to contain 2.034 g / L Cu, 0.49 g / L Ni, and only 136.24 mg / L As, indicating that copper and nickel were preferentially eluted and separated, while arsenic was basically retained in the organic phase.

[0033] S5. Four-stage countercurrent back-extraction: The loaded organic phase washed in step S4 is subjected to four-stage countercurrent back-extraction at 20°C using a sodium oxalate solution with pH=10 and a concentration of 8 g / L, with a phase ratio of O / A=150:20; resulting in an arsenic-bismuth-enriched back-extraction solution.

[0034] Testing revealed that the As concentration in the back-extraction solution was 15.651 g / L and the Bi concentration was 0.401 g / L, indicating excellent arsenic-bismuth enrichment. S6. Organic phase regeneration and recycling: The blank organic phase after back-extraction in step S5 is washed and regenerated with pure water at a volume ratio of 1:1. The regenerated organic phase is then returned to step S2 for recycling. After continuous operation for 72 hours, the organic phase showed no emulsification, no white flocculent matter at the interface, and stable phase separation performance.

[0035] Example 2 In this embodiment, the basic electrolyte composition is as follows: As 12.15 g / L, Bi 0.275 g / L, Cu 36.85 g / L, Ni 9.42 g / L, Sb 0.315 g / L, and H2SO4 213 g / L.

[0036] The specific steps of the cascade process for selective extraction of arsenic and bismuth from the electrolyte and separation of copper and nickel are as follows: S1. Pre-oxidation of the feed solution: Take the basic electrolyte of the raw material, heat it to 45℃, add 27.5% hydrogen peroxide at 1 / 25 of the electrolyte volume, stir and oxidize at a constant temperature for 1.2h, and filter to obtain the pentavalent arsenic oxide feed solution.

[0037] S2. Preparation and pretreatment of modified organic phase: By volume percentage, 18% linear trialkylphosphine oxide extractant, 4% 2-octanol and 78% sulfonated kerosene are mixed evenly; after preparation, the mixture is pretreated by washing with 8 g / L sodium oxalate solution and pure water in sequence, and then set aside.

[0038] S3. Two-stage countercurrent extraction: The organic phase pretreated in step S2 and the oxidized feed solution obtained in step S1 are subjected to two-stage countercurrent contact at 20°C with a ratio of O / A=150:40. The single-stage mixing and shaking time is 4 min, and the phase separation time is ≤90 s. After phase separation, the arsenic-bismuth-loaded organic phase and the raffinate electrolyte are obtained.

[0039] The analysis revealed that the As content in the residual electrolyte was 2.68 g / L, the Bi content was below the detection limit, the arsenic extraction rate was 77.9%, and the bismuth extraction rate was 100%; the Cu content was 36.113 g / L, and the Ni content was 9.18 g / L.

[0040] S4. Two-stage countercurrent washing: The arsenic-bismuth-loaded organic phase obtained in step S3 is subjected to two-stage countercurrent washing with pure water, with a ratio of O / A = 150:20, a single-stage washing time of 4 min, and a temperature of 20℃; the washing solution is returned to the copper electrolysis system.

[0041] The washing solution was tested and found to contain 1.48 g / L of Cu, 0.48 g / L of Ni, and only 142.15 mg / L of As, indicating a good preferential elution and separation effect of copper and nickel.

[0042] S5. Four-stage countercurrent back-extraction: The loaded organic phase washed in step S4 is subjected to four-stage countercurrent back-extraction at 20°C using a sodium oxalate solution with pH=9 and a concentration of 8 g / L, with a phase ratio of O / A=150:20; resulting in an arsenic-bismuth-enriched back-extraction solution.

[0043] The analysis revealed that the concentration of As in the back-extraction solution was 18.09 g / L and the concentration of Bi was 0.47 g / L.

[0044] S6. Organic phase regeneration and recycling: The blank organic phase after back-extraction in step S5 is washed and regenerated with pure water at a volume ratio of 1:1. The regenerated organic phase is then returned to step S2 for recycling. After continuous operation for 72 hours, the organic phase showed no emulsification, no flocculent matter at the interface, and stable phase separation performance.

[0045] Example 3 In this embodiment, As 14.86 g / L, Bi 0.295 g / L, Cu 37.58 g / L, Ni 9.71 g / L, Sb 0.338 g / L, and H2SO4 218 g / L.

[0046] The specific steps of the cascade process for selective extraction of arsenic and bismuth from the electrolyte and separation of copper and nickel are as follows: S1. Pre-oxidation of the feed solution: Take the basic electrolyte of the raw material, heat it to 55℃, add 27.5% hydrogen peroxide at 1 / 15 of the electrolyte volume, stir and oxidize at a constant temperature for 0.8h, and filter to obtain the pentavalent arsenic oxide feed solution.

[0047] S2. Preparation and pretreatment of modified organic phase: By volume percentage, 22% linear trialkylphosphine oxide extractant, 6% 2-octanol and 72% sulfonated kerosene are mixed evenly; after preparation, the mixture is pretreated by washing with 8 g / L sodium oxalate solution and pure water in sequence, and then set aside.

[0048] S3. Two-stage countercurrent extraction: The organic phase pretreated in step S2 and the oxidized feed solution obtained in step S1 are subjected to two-stage countercurrent contact at 35°C with a ratio of O / A=150:20. The single-stage mixing and shaking time is 2 min, and the phase separation time is ≤90 s. After phase separation, the arsenic-bismuth-loaded organic phase and the raffinate electrolyte are obtained.

[0049] The test results showed that the As content in the raffinate electrolyte was 2.91 g / L, the Bi content was below the detection limit, the arsenic extraction rate was 80.4%, and the bismuth extraction rate was 100%; the Cu content was 36.79 g / L, and the Ni content was 9.49 g / L.

[0050] S4. Two-stage countercurrent washing: The arsenic-bismuth-loaded organic phase obtained in step S3 is subjected to two-stage countercurrent washing with pure water, with a ratio of O / A = 150:10, a single-stage washing time of 2 min, and a temperature of 35℃; the washing solution is returned to the copper electrolysis system.

[0051] The washing solution was tested and found to contain 1.582 g / L of Cu, 0.44 g / L of Ni, and only 115.26 mg / L of As, indicating a good preferential elution and separation effect of copper and nickel.

[0052] S5. Four-stage countercurrent back-extraction: The loaded organic phase washed in step S4 is subjected to four-stage countercurrent back-extraction at 35°C using a sodium oxalate solution with pH=11 and a concentration of 8 g / L, with a phase ratio of O / A=150:20; resulting in an arsenic-bismuth-enriched back-extraction solution.

[0053] The analysis revealed that the concentration of As in the back-extraction solution was 10.48 g / L and the concentration of Bi was 0.26 g / L.

[0054] S6. Organic phase regeneration and recycling: The blank organic phase after back-extraction in step S5 is washed and regenerated with pure water at a volume ratio of 1:1. The regenerated organic phase is then returned to step S2 for recycling. After continuous operation for 72 hours, the organic phase showed no emulsification, no flocculent matter at the interface, and stable phase separation performance.

[0055] The detection results of Examples 1 to 3 above are summarized and analyzed, as shown in Table 2 below.

[0056] Table 2

[0057] As shown in Table 2 above, Example 1 achieved a maximum arsenic extraction rate of 83.37% under optimal process parameters, with an arsenic content in the raffinate as low as 2.124 g / L, significantly better than the production limit of 3 g / L. Examples 2 and 3 were operated at the lower and upper limits of the raw material arsenic concentration fluctuation range, respectively, achieving arsenic extraction rates of 77.9% and 80.4%, respectively, with the arsenic content in the raffinate consistently controlled below 3 g / L. Furthermore, after two-stage countercurrent extraction in Examples 1-3, the copper-nickel entrainment rate in the arsenic-bismuth-loaded organic phase was reduced to below 3%. The arsenic concentration in the washing liquid of all three examples was below 150 mg / L, and the organic phase showed no emulsification or interfacial flocculent matter throughout the process. This indicates that the present invention has strong adaptability to raw material arsenic concentration fluctuations of 12-15 g / L, and can stably achieve the technical objectives of deep arsenic removal, complete bismuth extraction, and selective separation of copper and nickel within this parameter range, demonstrating good reproducibility and industrial applicability.

[0058] Comparative Example 1 This embodiment is used to compare the effects of different washing systems on the separation of copper, nickel and arsenic; except for the washing section in step S4, the operating parameters and raw material electrolyte composition of the remaining S1, S2, S3, S5 and S6 are exactly the same as those in Example 1.

[0059] S4. Two-stage countercurrent washing: The arsenic-bismuth-loaded organic phase obtained in step S3 is washed in a two-stage countercurrent process using 4 mol / L sulfuric acid solution instead of pure water, with an O / A ratio of 150:15. The single-stage washing time is 3 min and the temperature is 20℃. The washing solution is returned to the copper electrolysis system.

[0060] The results showed that the As content in the residual electrolyte was 2.124 g / L, and the arsenic extraction rate was 83.37%, which was the same as in Example 1; however, the As concentration in the washing solution was as high as 8.363 g / L, the Cu concentration was 2.134 g / L, and the Ni concentration was 0.52 g / L.

[0061] The results show that under sulfuric acid washing conditions, arsenic and copper-nickel undergo simultaneous and massive elution, making selective separation impossible and subsequent recovery difficult. These results demonstrate that pure water washing is a key technical feature for achieving efficient and selective separation of copper-nickel from arsenic and bismuth.

[0062] Comparative Example 2 In this comparative example, the extraction system remained unchanged, and the washing process used a sodium oxalate solution with a pH of 4. Except for the washing step S4, all other operating parameters and the composition of the basic electrolyte were exactly the same as in Example 1.

[0063] S4. Staged cross-flow washing: The arsenic-bismuth-loaded organic phase obtained in step S3 is washed in two stages using sodium oxalate solution with pH=4 instead of pure water. The ratio of O / A is 150:15, the single-stage washing time is 3 min, and the temperature is 20℃. The washing solution is returned to the copper electrolysis system.

[0064] The analysis revealed that the As content in the residual electrolyte was 2.372 g / L, with an arsenic extraction rate of 81.43%; the Cu concentration in the washing solution was 2.036 g / L, the Ni concentration was 0.51 g / L, and the As concentration was 5.89 g / L.

[0065] The results showed that although washing with weakly acidic sodium oxalate improved the arsenic concentration compared to washing with sulfuric acid, the arsenic concentration in the washing solution was significantly higher than that of copper and nickel, making selective separation impossible and subsequent recovery difficult. Overall, the separation efficiency and economics were inferior to the pure water washing scheme in Example 1.

[0066] Comparative Example 3 This comparative example is used to verify the necessity of 2-octanol as a specific modifier; except for the organic phase composition in step S2, the other operating parameters and the composition of the basic electrolyte are the same as in Example 1.

[0067] S2. Preparation and pretreatment of modified organic phase: By volume percentage, 20% linear trialkylphosphine oxide extractant and 80% sulfonated kerosene were mixed evenly without the addition of 2-octanol; after preparation, the mixture was pretreated by washing with 8 g / L sodium oxalate solution and pure water in sequence, and then set aside.

[0068] S3. Two-stage countercurrent extraction: The organic phase pretreated in step S2 and the oxidized feed solution obtained in step S1 are subjected to two-stage countercurrent contact at 20°C with a ratio of O / A = 150:30 and a single-stage mixing and shaking time of 3 min.

[0069] The results showed that the organic phase and the feed solution were severely emulsified after mixing, with a phase separation time >10 min and a large amount of white flocculent material generated at the interface, making stable and continuous extraction impossible; the process completely failed. These results demonstrate that 2-octanol is a necessary component for solving the emulsification problem of the extractant system and ensuring continuous industrial operation.

[0070] Comparative Example 4 This comparative example is used to verify the decisive role of the pre-oxidation process in the removal of trivalent arsenic. Except for the omission of step S1 pre-oxidation, all other operating parameters and raw material electrolyte composition are the same as in Example 1.

[0071] S3. Two-stage countercurrent extraction: The unoxidized raw material electrolyte (containing a large amount of trivalent arsenic) is directly used and the organic phase after pretreatment in step S2 is subjected to two-stage countercurrent contact at 20°C with a ratio of O / A=150:30. The single-stage mixing and shaking time is 3 min and the phase separation time is ≤90 s.

[0072] Testing revealed that the linear trialkylphosphine oxide extractant had extremely weak extraction ability for trivalent arsenic, resulting in an As content as high as 7.65 g / L in the raffinate after two-stage extraction, far exceeding the mandatory production limit of 3 g / L, indicating that the arsenic removal process was completely substandard.

[0073] The results demonstrate that the pre-oxidation process is a prerequisite for converting trivalent arsenic into extractable pentavalent arsenic and achieving deep arsenic removal.

[0074] The foregoing has provided a detailed description of a cascade process for selective extraction of arsenic and bismuth from a copper electrolyte and separation of copper and nickel, as disclosed in this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of these embodiments are merely illustrative of the method and its core ideas. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims of this invention.

Claims

1. A cascade process for selective extraction of arsenic and bismuth from copper electrolyte and separation of copper and nickel, characterized in that, Includes the following steps: S1. Pre-oxidation of the solution: Heat the copper electrolyte containing arsenic to 45~55℃, add hydrogen peroxide and stir at a constant temperature for oxidation, and filter to obtain pentavalent arsenic oxide solution; S2. Preparation and pretreatment of modified organic phase: By volume percentage, the organic phase consists of 18-22% trialkylphosphine oxide extractant, 4-6% 2-octanol and the remainder sulfonated kerosene; after preparation, it is pretreated by washing with sodium oxalate solution and water in sequence. S3. Two-stage countercurrent extraction: The organic phase pretreated in step S2 and the pentavalent arsenic oxide feed solution in step S1 are subjected to two-stage countercurrent contact at 20~35℃ with a ratio of O / A=150:(20~40). After mixing and phase separation, the arsenic-bismuth-loaded organic phase and the raffinate electrolyte are obtained. S4. Two-stage countercurrent washing: The arsenic-bismuth-loaded organic phase from step S3 is washed countercurrently with pure water at 20~35℃, with a ratio of O / A=150:(10~20), to elute the co-extracted copper-nickel metal. The washing solution is returned to the copper electrolysis system. S5. Four-stage countercurrent back-extraction: The loaded organic phase washed in step S4 is subjected to four-stage countercurrent back-extraction at 20-35°C using a sodium oxalate solution with pH=9~11 to obtain an arsenic-bismuth-enriched back-extraction solution. S6. Organic phase regeneration and recycling: The blank organic phase after back-extraction in step S5 is regenerated by washing with water and then returned to step S2 for recycling.

2. The cascade process according to claim 1, characterized in that, In step S1, the arsenic-containing copper electrolyte contains 12-15 g / L of arsenic, 0.01-0.3 g / L of bismuth, 35-38 g / L of copper, 9-12 g / L of nickel, and 210-220 g / L of sulfuric acid; the concentration of hydrogen peroxide is 27.5%, and the amount added is 1 / 25 to 1 / 15 of the electrolyte volume; the constant temperature stirring oxidation time is 0.8-1.2 h.

3. The cascade process according to claim 2, characterized in that, The arsenic-containing copper electrolyte contains 12.775 g / L of arsenic, 0.288 g / L of bismuth, 37.225 g / L of copper, 9.565 g / L of nickel, and 215 g / L of sulfuric acid.

4. The cascade process according to claim 2, characterized in that, The concentration of hydrogen peroxide is 27.5%, and the amount added is 1 / 20 of the electrolyte volume. The constant temperature stirring oxidation time is 1.0 h.

5. The cascade process according to claim 1, characterized in that, In step S2, the volume composition of the organic phase is 20% linear trialkylphosphine oxide extractant, 5% 2-octanol and 75% sulfonated kerosene; the concentration of the sodium oxalate solution is 8 g / L.

6. The cascade process according to claim 1, characterized in that, In step S3, the ratio O / A of the two-stage countercurrent extraction is 150:30, the mixing and oscillation time is 2~4 min, and the phase separation time is ≤90 s; the arsenic content of the raffinate electrolyte is ≤3 g / L.

7. The cascade process according to claim 1, characterized in that, In step S4, the countercurrent washing is a two-stage countercurrent washing, and compared to O / A=150:15, the single-stage washing time is 2~4 minutes.

8. The cascade process according to claim 1, characterized in that, In step S5, the sodium oxalate solution has a pH of 10, a concentration of 8 g / L, and a back-extraction ratio of O / A of 150:

20.

9. The cascade process according to claim 1, characterized in that, In step S6, the back-extracted blank organic phase is washed and regenerated with pure water at a volume ratio of 1:1.

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