Treatment method for contaminated acid in copper smelting

Abstract

The present application provides a method for treating contaminated acid in copper smelting, which relates to the technical field of contaminated acid treatment. In this method, hydrogen sulfide gas is first prepared by reacting dilute sulfuric acid with an aqueous solution of sodium hydrosulfide, and after single-step enhanced sulfidation treatment of the contaminated acid in the form of dispersed bubbles through aeration, a contaminated acid treatment solution is obtained by filtration. Then, the pH value of the contaminated acid treatment solution is adjusted to 11-12 with lime milk, filtered, and then the pH is adjusted back to 8-9 with concentrated sulfuric acid and filtered to complete the treatment of the contaminated acid. The method provided by the present application effectively avoids the phenomenon of cadmium exceeding the standard caused by cadmium redissolution through two-step neutralization. By adjusting the pH to 11-12 for the first time, heavy metal precipitates mainly composed of Fe(OH)3, Zn(OH)2, Cr(OH)3, and Cd(OH)2 in the contaminated acid are removed. By adjusting the pH back to 8-9 for the second time, the Cd(OH)2 redissolved during the first pH adjustment process is redeposited and removed, and at the same time, CdS dissolved in the contaminated acid treatment solution during the enhanced sulfidation treatment is removed. The present application rationally designs the process flow, improves the treatment efficiency, reduces the treatment cost, and enhances the economic benefits of the overall process.

Description

Technical Field

[0001] This application relates to the technical field of waste acid treatment, and particularly to a method for treating waste acid in copper smelting. Background Art

[0002] During the process of copper smelting, a large amount of waste acid is often generated. The waste acid contains heavy metals mainly composed of arsenic, copper, and cadmium, as well as other acidic substances. If not properly treated before discharge, the adverse impact on the environment is immeasurable. Currently, the sulfidation-neutralization method is relatively common in waste acid treatment.

[0003] In the prior art, the patent with the publication number CN117401847A discloses a method for synthesizing hydrogen sulfide and removing arsenic from waste acid in the copper smelting industry. This method uses concentrated sulfuric acid to react with ferrous sulfide to prepare hydrogen sulfide. After the reaction ends, nitrogen is used for aeration, and then hydrogen sulfide is introduced into a sulfidation reaction tank containing waste acid. The sulfidation reaction is carried out through cyclic spraying, and then arsenic sulfide slag precipitate and sulfided liquid are obtained by filtration. This invention reduces the concentration of hydrogen sulfide through nitrogen aeration and reduces the loss during the process of removing arsenic from waste acid.

[0004] In the prior art, the patent with the publication number CN117776447A discloses a method for treating waste acid from lead-zinc smelting. This method uses one of hydrogen sulfide, sodium sulfide, and sodium bisulfide as a sulfiding agent, including four steps: primary sulfidation, secondary sulfidation, neutralization to a pH value of 3-5, and tertiary desulfurization. In the three sulfidation steps, the addition amount of the sulfiding agent is controlled by the ORP (oxidation-reduction potential) difference respectively, realizing the staged removal of arsenic thallium, cadmium lead, and zinc, and realizing the recycling of cadmium and zinc.

[0005] However, for enterprises, using sodium sulfide or sodium bisulfide for waste acid treatment in the prior art will introduce a large amount of sodium salts, resulting in the continuous enrichment of the salt content in the system and poor usability of the recycled water; and the sulfide or hydroxide precipitate of cadmium is prone to redissolution. In many sulfidation-neutralization processes, in order to fully remove cadmium metal, the waste acid is subjected to multiple enhanced sulfidation treatments, with a cumbersome process, high cost, and a large amount of by-products generated, causing new pressure on the environment.

[0006] In view of this, it is necessary to design an improved method for treating waste acid in copper smelting to solve the above problems. Summary of the Invention

[0007] The purpose of this application is to provide a method for treating contaminated acid in copper smelting. This method uses hydrogen sulfide to strengthen the sulfidation of contaminated acid, avoiding the introduction of sodium ions, solving the problem of system salt crystallization existing in the prior art, and the by-product sodium sulfate produced meets the requirements of Class I Grade A products specified in GB / T 6009-2014, having commercial value; this method can make the arsenic concentration lower than 0.2 g / L and the copper concentration lower than 0.04 g / L through one-time strengthened sulfidation, improving the efficiency of contaminated acid treatment; this method uses a two-step method to neutralize the treated liquid after sulfidation, effectively avoiding the re-dissolution of cadmium.

[0008] To achieve the above-mentioned invention purpose, this application provides a method for treating contaminated acid in copper smelting, including the following steps:

[0009] S1, Drop dilute sulfuric acid into an aqueous solution of sodium hydrosulfide, react under normal temperature, stirring, and aeration conditions to obtain hydrogen sulfide gas and a sodium sulfate solution; Pass the hydrogen sulfide gas into the contaminated acid in the form of dispersed bubbles through an aeration device to carry out strengthened sulfidation treatment on the contaminated acid, control the end point of the sulfidation reaction by monitoring the oxidation-reduction potential value of the contaminated acid, and filter after the reaction ends to remove the sulfide slag to obtain a contaminated acid treatment liquid;

[0010] S2, First, adjust the pH value of the contaminated acid treatment liquid obtained in step S1 to 11-12 with lime milk to generate heavy metal precipitates mainly composed of iron hydroxide, zinc hydroxide, chromium hydroxide, and cadmium hydroxide, filter to remove the precipitates, and then use concentrated sulfuric acid to adjust the pH value of the filtrate back to 8-9 to make the cadmium re-dissolved into the contaminated acid precipitate again in the form of cadmium hydroxide or cadmium sulfide, and finally filter to remove the precipitates to complete the treatment of the contaminated acid.

[0011] As a further improvement of this application, the method for treating contaminated acid in copper smelting also includes recovering sodium sulfate. The specific steps are to remove impurities in the sodium sulfate solution obtained in step S1 by a multi-effect evaporation process and filter to obtain a sodium sulfate product.

[0012] As a further improvement of this application, the sodium sulfate product meets the requirements of Class I Grade A indicators specified in GB / T 6009-2014.

[0013] As a further improvement of this application, in step S1, the dosage of the hydrogen sulfide gas is 16-19 g / L.

[0014] As a further improvement of this application, in step S1, the temperature of the strengthened sulfidation reaction is 20-40 °C, and the reaction time is 1.5-2 h.

[0015] As a further improvement of this application, in step S1, the end point of the strengthened sulfidation reaction is when the oxidation-reduction potential value is lower than 18 mV.

[0016] As a further improvement of the present application, in step S1, the dosage of the dilute sulfuric acid is 65 - 70 mL / L, and the dosage of the sodium hydrosulfide aqueous solution is 75 - 85 mL / L.

[0017] As a further improvement of the present application, in step S1, the concentration of the dilute sulfuric acid is 18 - 22%, and the concentration of the sodium hydrosulfide aqueous solution is 30 - 34%.

[0018] As a further improvement of the present application, in step S2, the dosage of the lime milk is 200 - 400 mL / L, and the dosage of the concentrated sulfuric acid is 0.5 - 2 g / L.

[0019] As a further improvement of the present application, in step S2, the concentration of the lime milk is 10 - 30%, and the concentration of the concentrated sulfuric acid is 98%.

[0020] The beneficial effects of the present application are as follows:

[0021] The present application provides a method for treating contaminated acid in copper smelting. This method uses hydrogen sulfide to perform primary enhanced sulfidation on the contaminated acid and uses a two-step method to neutralize the sulfidated contaminated acid treatment liquid, solving the problem of system salt crystallization existing in the prior art, improving the efficiency of contaminated acid treatment. The treatment process flow is short, environmentally friendly, and low in cost, and the recovered sodium sulfate has commercial value and has good application prospects.

[0022] (1) The present application uses hydrogen sulfide to perform enhanced sulfidation on the contaminated acid. Only one enhanced sulfidation process is required, and no sodium ions are introduced during the treatment process, which can effectively reduce the salt crystallization phenomenon in the system, improve the stability and operation efficiency of the production system. At the same time, by adding an aeration device to the reaction system of dilute sulfuric acid and sodium hydrosulfide aqueous solution, the reaction efficiency of dilute sulfuric acid and sodium hydrosulfide is improved. The hydrogen sulfide gas is introduced into the contaminated acid in the form of dispersed bubbles through the aeration device, improving the enhanced sulfidation reaction efficiency of hydrogen sulfide and the contaminated acid and increasing the utilization rate of hydrogen sulfide. During the enhanced sulfidation process in step S1, impurities such as arsenic and copper and most of the cadmium are converted into sulfide precipitates and removed in the filtration step.

[0023] (2) In step S2 of this application, a two-step neutralization method is adopted to treat the sulfided waste acid treatment liquid. The purpose is to fully remove cadmium ions in the waste acid in a more concise treatment method, so that the treated waste acid meets the effluent water quality requirements. In the two-step neutralization method, the pH value of the waste acid treatment liquid is adjusted to 11-12, aiming to generate heavy metal precipitates mainly composed of iron hydroxide [Fe(OH)3], zinc hydroxide [Zn(OH)2], chromium hydroxide [Cr(OH)3], and cadmium hydroxide [Cd(OH)2]; the pH is then adjusted back to 8-9, aiming to re-precipitate and remove Cd(OH)2 that has redissolved into the waste acid during the first pH adjustment process. At the same time, cadmium sulfide (CdS) that has dissolved in the waste acid treatment liquid during the sulfidation treatment will also re-precipitate and be removed in this step of adjusting the pH back. With such a setting, the phenomenon of cadmium exceeding the standard caused by cadmium redissolution can be effectively avoided.

[0024] In a high pH environment, Cd 2+ will react with OH - to form Cd(OH)2 precipitate. However, as the reaction continues, part of the Cd(OH)2 will continue to react with the excess OH - to form soluble cadmate (such as Cd(OH)4 2- ), resulting in cadmium redissolution. In the two-step neutralization method adopted in this application, the pH is first adjusted to 11-12 in the first step to precipitate most of the heavy metals in the treatment liquid, such as generating precipitates of Fe(OH)3, Zn(OH)2, Cr(OH)3, and Cd(OH)2, etc. These precipitates are all removed in the first filtration step; in the second step, the pH is adjusted back to 8-9, which not only prevents Cd(OH)2 from continuing to react with the excess OH - to form cadmate, but also causes a small amount of the dissolved Cd(OH)2 to re-precipitate in the form of Cd(OH)2 or CdS and be removed in the subsequent second filtration step, thereby reducing the cadmium concentration in the final treatment liquid. In addition, there may still be some dissolved CdS remaining in the waste acid treatment liquid obtained in step S1, and these cadmium ions will also re-precipitate in the form of Cd(OH)2 or CdS in the two-step neutralization method and be removed in the second filtration step of step S2.

[0025] (3) The treatment method of waste acid in copper smelting provided by this application avoids the waste of chemical agents by reasonably designing the process flow and optimizing the reaction conditions, effectively shortens the process steps and duration, and the by-product sodium sulfate meets the requirements of Class I Grade A products specified in GB / T 6009-2014 after being treated by the multi-effect evaporation process, with commercial value, which improves the economic benefits of the overall process and brings a better sustainable development prospect for the enterprise. Description of the Drawings

[0026] Figure 1Flow chart of the method for treating waste acid in copper smelting in Example 1;

[0027] Figure 2 Schematic diagram of the influence of the dosage of sodium hydrosulfide on the arsenic and copper removal effects in Comparative Examples 3-7;

[0028] Figure 3 Schematic diagram of the influence of reaction temperature on the arsenic removal effect in Examples 2-3 and Comparative Examples 9-11;

[0029] Figure 4 Schematic diagram of the influence of reaction time on the arsenic removal effect in Example 4 and Comparative Examples 12-15. Detailed implementation manners

[0030] In order to make the objectives, technical solutions and advantages of this application clearer, the following describes this application in detail with reference to the accompanying drawings and specific embodiments.

[0031] Here, it should also be noted that in order to avoid obscuring this application due to unnecessary details, only the structures and / or processing steps closely related to the solution of this application are shown in the drawings, while other details less related to this application are omitted.

[0032] In addition, it should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0033] Please refer to Figure 1 As shown, this application provides a method for treating waste acid in copper smelting, which specifically includes the following steps:

[0034] S1. Set up an atmospheric pressure sulfidation reaction device, and use a constant pressure dropping funnel to drop dilute sulfuric acid (20% w / w) into an aqueous solution of sodium hydrosulfide (32% w / w), and react under normal temperature (25°C), stirring and aeration conditions to prepare hydrogen sulfide gas and sodium sulfate solution; pass the hydrogen sulfide gas into the waste acid in the form of dispersed bubbles through an aeration device to perform enhanced sulfidation treatment on the waste acid, and monitor the oxidation-reduction potential (ORP) value of the waste acid to control the end point of the sulfidation reaction. After the reaction is completed, filter to remove the sulfide slag to obtain the waste acid treatment solution;

[0035] Specifically, the concentration of dilute sulfuric acid is 20%, and the dosage is 65 - 70 mL / L; the concentration of sodium hydrosulfide aqueous solution is 32%, and the dosage is 75 - 85 mL / L, and the dosage of hydrogen sulfide gas is 16 - 19 g / L; the temperature for enhancing the sulfidation reaction is 20 - 40 °C, and the reaction time is 1.5 - 2 h; the end point of the enhancing sulfidation reaction is when the ORP value is lower than 18 mV. An alkali solution is also provided in the atmospheric pressure sulfidation reaction device to absorb the residual hydrogen sulfide gas that is not completely reacted in the enhancing sulfidation reaction.

[0036] In this application, hydrogen sulfide is used to enhance the sulfidation of waste acid. Only one enhancing sulfidation process is required, and no sodium ions are introduced during the treatment process, which can effectively reduce the salt crystallization phenomenon in the system, improve the stability and operation efficiency of the production system. At the same time, by adding an aeration device to the reaction system of dilute sulfuric acid and sodium hydrosulfide aqueous solution, the reaction efficiency of dilute sulfuric acid and sodium hydrosulfide is improved. The hydrogen sulfide gas is introduced into the waste acid in the form of dispersed bubbles through the aeration device, which improves the enhancing sulfidation reaction efficiency of hydrogen sulfide and the waste acid, and improves the utilization rate of hydrogen sulfide. During the enhancing sulfidation process of step S1, impurities such as arsenic and copper and most of the cadmium are converted into sulfide precipitates and removed in the filtration step.

[0037] The chemical equation for the reaction of sulfuric acid and sodium hydrosulfide is: 2NaHS+H2SO4=2H2S↑+Na2SO4.

[0038] In the enhancing sulfidation reaction, the hydrogen sulfide dissolved in the solution ionizes S 2- ,S 2- reacts with As, Cu, Pb and other heavy metal ions M n+ to form precipitates. Taking divalent metal ions as an example, the reaction formula is M 2+ +S 2- =MS↓. By calculating the ionization equilibrium constant, it can be known that the equilibrium concentration of metal ions in the solution decreases with the increase of pH value and also decreases with the increase of the total sulfur concentration [S] T . Generally, the higher the pH value of the solution, the higher the arsenic removal rate, but too high pH will cause the re-dissolution of arsenic. Therefore, most of the arsenic is removed under acidic conditions, that is, in the enhancing sulfidation reaction of step S1. In order to shift the reaction equilibrium towards the direction of generating precipitates (such as MS↓), the sulfur concentration [S] T in the solution can be appropriately increased to reduce the concentration of metal ions in the solution.

[0039] S2. First, adjust the pH value of the waste acid treatment liquid obtained in step S1 to 11 - 12 with a certain amount of lime milk, filter to remove the precipitate, and then adjust the pH value of the filtrate back to 8 - 9 with concentrated sulfuric acid, and filter to remove the precipitate to complete the treatment of the waste acid.

[0040] Specifically, the concentration of lime milk is 10 - 30%, and the dosage is 200 - 400 mL / L; the concentration of concentrated sulfuric acid is 98%, and the dosage is 0.5 - 2 g / L.

[0041] In step S2 of this application, a two-step neutralization method is adopted to treat the sulfided waste acid treatment liquid. The purpose is to fully remove cadmium ions in the waste acid in a more concise treatment method, so that the treated waste acid meets the effluent water quality requirements. In the two-step neutralization method, the pH value of the waste acid treatment liquid is adjusted to 11 - 12, aiming to generate heavy metal precipitates mainly composed of Fe(OH)3, Zn(OH)2, Cr(OH)3, and Cd(OH)2; the pH is then adjusted back to 8 - 9, aiming to redeposit and remove cadmium hydroxide [Cd(OH)2] that redissolved into the waste acid during the first pH adjustment process. At the same time, cadmium sulfide (CdS) that had dissolved in the waste acid treatment liquid during the sulfidation treatment will also redeposit and be removed in this step of adjusting the pH back. With such settings, the phenomenon of cadmium exceeding the standard caused by cadmium redissolution can be effectively avoided.

[0042] In a high pH environment, Cd 2+ will react with OH - to form Cd(OH)2 precipitate. However, as the reaction continues, part of the Cd(OH)2 will continue to react with the excessive OH - to form soluble cadmate (such as Cd(OH)4 2- ), resulting in cadmium redissolution. In the two-step neutralization method adopted in this application, the pH is first adjusted to 11 - 12 in the first step to precipitate most of the heavy metals in the treatment liquid, such as forming precipitates of Fe(OH)3, Zn(OH)2, Cr(OH)3, and Cd(OH)2, etc. These precipitates are all removed in the first filtration step; in the second step, the pH is adjusted back to 8 - 9, which not only prevents Cd(OH)2 from continuing to react with the excessive OH - to form cadmate, but also redeposits a small amount of the dissolved Cd(OH)2 in the form of Cd(OH)2 or CdS and removes it in the subsequent second filtration step, thereby reducing the concentration of cadmium in the final treatment liquid. In addition, there may still be some dissolved CdS remaining in the waste acid treatment liquid obtained in step S1, and these cadmium ions will also redeposit in the form of Cd(OH)2 or CdS in the two-step neutralization method and be removed in the second filtration step of step S2.

[0043] The method for treating waste acid in copper smelting proposed in this application also includes recovering sodium sulfate. The specific steps are as follows: impurities in the sodium sulfate solution obtained in step S1 are removed by a multi-effect evaporation process, and then filtered to obtain a sodium sulfate product that meets the requirements of Class I first-grade products specified in GB / T 6009 - 2014. This product has commercial value, can improve the economic benefits of the overall process, and reduce the treatment cost.

[0044] The following describes the method for treating contaminated acid in copper smelting provided by this application in combination with specific embodiments. The contaminated acid used in the embodiments contains 17100 mg / L of arsenic, 879 mg / L of copper, 642 mg / L of cadmium, and the pH value of the contaminated acid is 0.7.

[0045] Example 1

[0046] This example proposes a method for treating contaminated acid in copper smelting. The specific steps are as follows:

[0047] S1, Set up an atmospheric pressure sulfidation reaction device. Drop dilute sulfuric acid (20% w / w) into an aqueous sodium hydrosulfide solution (32% w / w) using a constant pressure dropping funnel. React under normal temperature (25°C), stirring, and aeration conditions to prepare hydrogen sulfide gas and sodium sulfate solution. Directly introduce the hydrogen sulfide gas into 250 mL of contaminated acid, and carry out an enhanced sulfidation reaction at 40°C. Monitor the change in the ORP value of the contaminated acid. When the ORP value is below 18 mV, it is determined as the end point of the sulfidation reaction. Then, filter the contaminated acid after enhanced sulfidation treatment to separate the sulfide slag and obtain the contaminated acid treatment solution.

[0048] S2, Carry out two-step neutralization treatment on the contaminated acid treatment solution obtained in step S1. First, adjust the pH of the contaminated acid treatment solution to 11 - 12 with 75 mL of lime milk (20% w / w) to generate metal hydroxide precipitates, and filter to obtain the filtrate. Then, use 0.267 g of concentrated sulfuric acid (98% w / w) to adjust the pH of the filtrate back to 8 - 9, and filter again to remove the newly formed precipitates to complete the treatment of the contaminated acid;

[0049] In the enhanced sulfidation reaction of step S1, the sulfidation reaction time is 1.5 h, the amount of hydrogen sulfide gas used is 4.48 g, and a total of 19.1 mL of sodium hydrosulfide and 16.3 mL of sulfuric acid are consumed to prepare the hydrogen sulfide gas. The change trends of the ORP value and arsenic concentration in the contaminated acid during the reaction are shown in the following table.

[0050]

[0051] Referring to the above table, it can be seen that as the oxidation-reduction potential decreases, the residual concentration of arsenic in the contaminated acid gradually decreases. When the ORP drops below 18 mV, the residual concentration of arsenic is below 0.2 mg / L, meeting the effluent water quality requirements. This indicates that monitoring the oxidation-reduction potential of the contaminated acid can effectively judge the end point of the enhanced sulfidation reaction, and the subsequent automatic adjustment of the treatment process can be realized through systematic monitoring and feedback.

[0052] Remove impurities from the sodium sulfate solution remaining after the reaction of dilute sulfuric acid and sodium hydrosulfide in step S1 through a multi-effect evaporation process, and filter to obtain sodium sulfate products. After testing, the recovered sodium sulfate products meet the requirements of Class I first-class product indicators specified in GB / T 6009-2014 in terms of purity, impurity content, particle size, etc. See the following table for details.

[0053]

[0054] Comparative Example 1-2

[0055] The difference between Comparative Example 1-2 and Example 1 is that in step S1, the dosage of sodium hydrosulfide is set to 4 times the theoretical value (50 mL), and the generation amount of hydrogen sulfide gas is controlled by adjusting the dosage of dilute sulfuric acid. The specific steps are as follows: Drop different volumes of dilute sulfuric acid (20% w / w) into 50 mL of sodium hydrosulfide aqueous solution (32% w / w), react to prepare hydrogen sulfide gas under normal temperature (25 °C), stirring, and aeration conditions, and introduce it into 250 mL of waste acid, and carry out enhanced sulfidation treatment at 40 °C for 1.5 h. The ORP value of the waste acid is monitored to be lower than 18 mV. Then, filter the waste acid after enhanced sulfidation treatment to separate the sulfide residue to obtain a waste acid treatment solution. The other contents are roughly the same as those in Example 1 and will not be elaborated here.

[0056] Test the residual concentrations of arsenic and copper in the waste acid treatment solutions obtained in Example 1 and Comparative Example 1-2. The results are shown in the following table.

[0057]

[0058] Please refer to the above table. As the dosage of hydrogen sulfide increases, the residual concentrations of arsenic and copper in the waste acid treatment solution both decrease significantly. When the dosage of hydrogen sulfide is 4.478 g, the concentration of arsenic in the waste acid treatment solution is less than 0.2 mg / L, and the concentration of copper is less than 0.04 mg / L, meeting the requirements of the reclaimed water effluent quality (<0.5 mg / L). At this time, the optimal dosage of hydrogen sulfide is 1.54 times the theoretical value.

[0059] This is because the reaction of hydrogen sulfide with heavy metals such as arsenic and copper is a gas-liquid heterogeneous reaction. During the reaction process, hydrogen sulfide gas first dissolves in the liquid phase and then reacts with the heavy metals in the liquid phase. Eventually, the amount of hydrogen sulfide gas participating in the reaction is not only related to the dosage of concentrated sulfuric acid and sodium hydrosulfide, but also related to the yield of hydrogen sulfide, its dissolution and diffusion in the waste acid, and the reaction efficiency of hydrogen sulfide with heavy metals. Therefore, appropriately increasing the dosage of hydrogen sulfide can offset its losses during processes such as reaction, dissolution, and diffusion, provide sufficient reactants for the reaction system, and thus obtain better treatment effects. However, it should be noted that excessive dosage of hydrogen sulfide will increase the treatment cost and pose safety hazards. Therefore, the optimal dosage of hydrogen sulfide is 17.9 g / L, that is, 17.9 g of hydrogen sulfide is consumed for every 1 L of waste acid treated. From the fact that 19.1 mL of sodium hydrosulfide aqueous solution was used to prepare hydrogen sulfide gas in Example 1, the optimal dosage of sodium hydrosulfide aqueous solution is 76.4 mL / L.

[0060] Comparative Examples 3-7

[0061] In Comparative Examples 3-7, sodium hydrosulfide aqueous solution (32% w / w) was directly added to the original waste acid solution for sulfidation reaction, and the dosages were set to 35 mL / L, 45 mL / L, 55 mL / L, 65 mL / L, and 75 mL / L respectively. The specific steps were as follows: Measure 5 groups of 200 mL of waste acid, and add 7 mL, 9 mL, 11 mL, 13 mL, and 15 mL of sodium hydrosulfide aqueous solution respectively. Stir and react at 40 °C for 0.5 h, and test the residual concentrations of arsenic and copper in the reaction solution. The test conditions and results are shown in Figure 2 and the following table.

[0062]

[0063] Refer to Figure 2 and the above table. It can be seen that at the same temperature, with the increase in the dosage of sodium hydrosulfide aqueous solution, the residual concentrations of arsenic and copper in the treated solution both continuously decrease, and the amount of slag produced is positively correlated with the treatment effect. The best dosage of sodium hydrosulfide aqueous solution is 75 mL / L. At this time, the residual concentration of arsenic in the treated solution is lower than 0.2 mg / L, and the residual concentration of copper is lower than 0.04 mg / L, which can achieve the expected treatment target. According to Comparative Examples 1-2, the optimal dosage of sodium hydrosulfide aqueous solution in the treatment method provided in this application is 76.4 mL / L. By comparison, the optimal dosages of sodium hydrosulfide in the two treatment methods are very close, indicating that the enhanced sulfidation treatment method provided in this application will not cause an increase in the dosage of sodium hydrosulfide. Moreover, the by-product sodium sulfate produced by the preparation of hydrogen sulfide meets the requirements of Class I first-class product indicators specified in GB / T 6009-2014 and has commercial value, which can offset part of the treatment cost and reduce the overall cost.

[0064] Comparative Example 8

[0065] The difference between Comparative Example 8 and Example 1 lies in that in Step 2, the pH of the waste acid treatment liquid is directly neutralized to 8-9. The specific steps are as follows: Use an aqueous sodium hydroxide solution (10% w / w) to adjust the pH of the waste acid treatment liquid obtained in Step S1 to 8-9, filter, and complete the treatment of the waste acid. The other contents are substantially the same as those in Example 1 and will not be elaborated here.

[0066] The residual concentrations of arsenic, copper, sodium, cadmium, lead, zinc, and mercury in the solution after sulfidation treatment and neutralization treatment were respectively tested, and the results are shown in the following table.

[0067]

[0068] Referring to the above table, it can be seen that after sulfidation treatment, the contents of arsenic, copper, sodium, lead, and mercury in the waste acid have reached the effluent water quality requirements, but the cadmium exceeds the standard by 54,400 times and the zinc exceeds the standard by 58 times. Therefore, it is necessary to further neutralize the waste acid treatment liquid. Comparative Example 8 uses a one-step method for neutralization, and the cadmium still exceeds the standard by 424 times, while Example 1 uses a two-step method for neutralization, and the cadmium concentration is less than 0.01, meeting the standard requirements. This is because the Ksp of Cd(OH)2 is relatively large, and a higher concentration of hydroxide ions is required to form Cd(OH)2. In Comparative Example 8, the pH value is directly adjusted to 8-9, which may cause the cadmium ions in the solution to not be completely converted into Cd(OH)2 precipitates, resulting in cadmium exceeding the standard; in the two-step neutralization method, first use lime milk to adjust the pH of the waste acid treatment liquid to 11-12. In a high-pH environment, Cd 2+ reacts with OH - to form Cd(OH)2 precipitates, filter out Cd(OH)2, and then use concentrated sulfuric acid to adjust the pH of the solution back to 8-9. This not only avoids the continuous reaction of Cd(OH)2 with excessive OH - to form cadmiumates, but also causes a small amount of dissolved Cd(OH)2 to precipitate again in the form of Cd(OH)2 or CdS and be removed through subsequent filtration steps. The two-step neutralization method provided by the present application not only improves the cadmium removal rate but also reduces the generation of by-products such as cadmiumates (such as Cd(OH)4 2- ), making the finally obtained treatment liquid meet the intermediate effluent water quality requirements.

[0069] In addition, there may still be some dissolved CdS remaining in the waste acid treatment liquid obtained in Step S1, and these cadmium ions will also precipitate again in the form of Cd(OH)2 or CdS in the two-step neutralization method and be removed in the filtration step.

[0070] Examples 2-3 and Comparative Examples 9-11

[0071] Examples 2-3 and Comparative Examples 9-11 are different from Example 1 in that the temperatures for enhancing the vulcanization reaction are set at 20°C, 30°C, 40°C, 50°C, 60°C, and 70°C respectively, and other contents are substantially the same as those in Example 1, which will not be elaborated here.

[0072] The residual concentration of arsenic in the waste acid treatment solution prepared in Test Step 1 is shown in Figure 3 and the following table.

[0073]

[0074] Please refer to Figure 3 and the above table. It can be seen that when the reaction temperature is lower than or equal to 40°C, the residual concentration of arsenic is lower than 0.5 mg / L, and the arsenic removal rate reaches 99.999%. However, between 50-70°C, as the reaction temperature increases, the arsenic removal rate gradually decreases. This is because when the temperature of the reaction system is lower than or equal to 40°C, sufficient sulfide ions can be ensured in the solution, and within this range, the higher the temperature, the faster the reaction rate, thus presenting a better arsenic removal effect. Therefore, the optimal temperature for enhancing the vulcanization reaction is 40°C.

[0075] Example 4 and Comparative Examples 12-15

[0076] Example 4 and Comparative Examples 12-15 are different from Example 1 in that the times for enhancing the vulcanization reaction are set at 0.25, 0.5, 1.0, 2.0, and 2.5 h respectively, and other contents are substantially the same as those in Example 1, which will not be elaborated here.

[0077] The residual concentration of arsenic in the waste acid treatment solution prepared in Test Step 1 is shown in Figure 4 and the following table.

[0078]

[0079] Referring to Figure 4 and the above table, it can be known that within a certain reaction time, the residual concentration of arsenic decreases as the reaction time increases. When the reaction time is 2.5 h, the residual concentration of arsenic slightly increases. This is because the arsenic removal process is basically completed at 1.5 h of reaction, and continuing to extend the reaction time leads to the phenomenon of partial arsenic redissolution. Therefore, the reaction time for enhancing vulcanization should be controlled at 1.5-2 h. Considering saving time and avoiding arsenic redissolution, the optimal reaction time is 1.5 h, and at this time, the ORP value of the waste acid is lower than 18 mV. In subsequent industrial applications, both the reaction time and the ORP value can be used to judge the end point of the vulcanization reaction.

[0080] In summary, in the present application, hydrogen sulfide is prepared by using sodium hydrosulfide and sulfuric acid, which avoids the introduction of new sodium ion impurities into the waste acid. By reasonably designing the process flow and optimizing the reaction conditions, the process is effectively shortened, the waste of chemical agents is reduced, and the treatment cost is lowered. Finally, the produced sodium sulfate product meets the requirements of Class I first-class products in the national recommended standard (GB / T 6009-2014), has commercial value, and the concentrations of As, Cu, Na, Cd, Pb, Zn, and Hg in the treated waste acid can all meet the enterprise's intermediate water discharge quality standard.

[0081] In the method for treating waste acid in copper smelting provided by the present application, the dosage of sodium hydrosulfide is 76.4 g / L, the dosage of hydrogen sulfide gas is 17.91 g / L, the enhanced sulfidation reaction is carried out at 40 °C for 1.5 h, and the best treatment effect can be achieved when the redox potential is 20 mV.

[0082] The above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for treating polluted acid in copper smelting, characterized in that: The following steps are involved: S1, adding dilute sulfuric acid dropwise to a sodium hydrosulfide aqueous solution, reacting under normal temperature, stirring and aeration conditions to obtain hydrogen sulfide gas and sodium sulfate solution; passing the hydrogen sulfide gas into the waste acid in the form of diffuse bubbles through an aeration device to perform enhanced sulfidation treatment on the waste acid, regulating the end point of the sulfidation reaction by monitoring the redox potential value of the waste acid, filtering after the reaction is completed to remove the sulfided slag, and obtaining a waste acid treatment liquid; S2, first adjusting the pH value of the waste acid treatment liquid obtained in step S1 to 11-12 with lime milk to generate a heavy metal precipitate with iron hydroxide, zinc hydroxide, chromium hydroxide and cadmium hydroxide as main components, filtering out the precipitate, and then adjusting the pH value of the filtrate to 8-9 with concentrated sulfuric acid, so that the cadmium dissolved back into the waste acid during the treatment is re-precipitated in the form of cadmium hydroxide or cadmium sulfide, and finally filtering out the precipitate to complete the waste acid treatment; the concentration of the lime milk is 10-30%, and the concentration of the concentrated sulfuric acid is 98%; the amount of the lime milk is 200-400mL / L, and the amount of the concentrated sulfuric acid is 0.5-2g / L.

2. The method for treating polluted acid in copper smelting according to claim 1, characterized in that: The method for treating the waste acid in copper smelting also includes recovering sodium sulfate, and the specific steps are: using a multi-effect evaporation process to remove impurities in the sodium sulfate solution obtained in step S1, filtering, and obtaining a sodium sulfate product.

3. The method for treating polluted acid in copper smelting according to claim 2, characterized in that: The sodium sulfate product meets the index requirements of Class I first-class products specified in GB / T 6009-2014.

4. The method for treating polluted acid in copper smelting according to claim 1, characterized in that: In step S1, the amount of hydrogen sulfide gas used is 16-19 g / L.

5. The method for treating polluted acid in copper smelting according to claim 4, characterized in that: In step S1, the temperature of the enhanced vulcanization reaction is 20-40°C, and the reaction time is 1.5-2h.

6. The method for treating polluted acid in copper smelting according to claim 5, characterized in that: In step S1, the end point of the enhanced sulfurization reaction is when the redox potential value is lower than 18 mV.

7. The method for treating polluted acid in copper smelting according to claim 6, characterized in that: In step S1, the amount of the dilute sulfuric acid is 65-70 mL / L, and the amount of the sodium hydrosulfide aqueous solution is 75-85 mL / L.

8. The method for treating polluted acid in copper smelting according to claim 7, characterized in that: In step S1, the concentration of the dilute sulfuric acid is 18-22%, and the concentration of the sodium hydrosulfide aqueous solution is 30-34%.

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