Treatment method of waste acid in copper smelting

Abstract

The invention provides a treatment method for waste acid in copper smelting, and relates to the technical field of waste acid treatment. The method comprises the following steps: reacting dilute sulphuric acid with a sodium hydrosulfide aqueous solution to prepare hydrogen sulfide gas, performing single-time enhanced sulfuration treatment on the waste acid in a dispersed bubble form through aeration, and filtering to obtain a waste acid treatment solution; and adjusting the pH value of the waste acid treatment liquid to 11-12 by using lime milk, filtering, adjusting the pH value back to 8-9 by using concentrated sulfuric acid, and filtering to complete waste acid treatment. According to the method provided by the invention, the phenomenon that cadmium exceeds the standard due to redissolution of cadmium is effectively avoided through two-step neutralization, heavy metal precipitates mainly comprising Fe (OH) 3, Zn (OH) 2, Cr (OH) 3 and Cd (OH) 2 in the waste acid are removed by adjusting the pH value to 11-12 for the first time, and the Cd (OH) 2 redissolved in the process of adjusting the pH value for the first time is re-precipitated and removed by adjusting the pH value to 8-9 for the second time, so that the heavy metal precipitates in the waste acid are removed. Meanwhile, the CdS dissolved in the waste acid treatment liquid during the enhanced vulcanization treatment is removed. The process flow is reasonably designed, the treatment efficiency is improved, the treatment cost is reduced, and the economic benefit of the whole process is improved.

Description

Technical Field

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

[0002] The copper smelting process is often accompanied by the production of a large amount of waste acid, which contains a large number of heavy metals, mainly arsenic, copper, and cadmium, as well as other acidic substances. If it is not properly treated before discharge, the adverse impact on the environment is difficult to estimate. At present, the sulfidation-neutralization method is more common in the treatment of waste acid.

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

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

[0005] However, for enterprises, the existing technology of using sodium sulfide or sodium hydrosulfide to treat waste acid will bring in a large amount of sodium salt, resulting in continuous enrichment of the salt content in the system and poor return water availability; and the sulfide or hydroxide precipitation of cadmium is prone to re-dissolution. In order to fully remove the cadmium metal, many sulfide-neutralization processes require multiple enhanced sulfidation treatments of the waste acid. The process is cumbersome and costly, and a large amount of by-products will be produced, which puts new pressure on the environment.

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

[0007] The purpose of the present application is to provide a method for treating waste acid in copper smelting. The method uses hydrogen sulfide to perform enhanced sulfidation on the waste acid, avoids the introduction of sodium ions, solves the problem of system salt crystallization in the prior art, and the produced by-product sodium sulfate meets the requirements of Class I first-class products specified in GB / T 6009-2014 and has commercial value; the method can reduce the arsenic concentration to less than 0.2g / L and the copper concentration to less than 0.04g / L through one enhanced sulfidation, thereby improving the efficiency of waste acid treatment; the method uses a two-step method to neutralize the treatment solution after sulfidation, effectively avoiding the re-dissolution of cadmium.

[0008] To achieve the above-mentioned purpose of the invention, the present application provides a method for treating contaminated acid in copper smelting, comprising the following steps: 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, firstly adjusting the pH value of the waste acid treatment liquid obtained in step S1 to 11-12 with lime milk to generate heavy metal precipitates with iron hydroxide, zinc hydroxide, chromium hydroxide and cadmium hydroxide as main components, filtering out the precipitates, 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 precipitates to complete the waste acid treatment.

[0009] As a further improvement of the present application, the method for treating waste acid in copper smelting also includes recovering sodium sulfate. 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.

[0010] As a further improvement of the present application, the sodium sulfate product meets the index requirements of Class I first-class products specified in GB / T 6009-2014.

[0011] As a further improvement of the present application, in step S1, the amount of hydrogen sulfide gas used is 16-19 g / L.

[0012] As a further improvement of the present application, in step S1, the temperature of the enhanced vulcanization reaction is 20-40°C, and the reaction time is 1.5-2h.

[0013] As a further improvement of the present application, in step S1, the reaction endpoint of the enhanced sulfurization reaction is when the redox potential value is lower than 18 mV.

[0014] As a further improvement of the present application, 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.

[0015] 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%.

[0016] As a further improvement of the present application, in step S2, the amount of the lime milk is 200-400 mL / L, and the amount of the concentrated sulfuric acid is 0.5-2 g / L.

[0017] 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%.

[0018] The beneficial effects of this application are: The present application provides a method for treating waste acid in copper smelting. The method uses hydrogen sulfide to perform a primary enhanced sulfidation on the waste acid, and adopts a two-step method to neutralize the waste acid treatment liquid after sulfidation, thereby solving the system salt crystallization problem existing in the prior art and improving the waste acid treatment efficiency. The treatment process is short, environmentally friendly, and low in cost, and the recovered sodium sulfate has commercial value and good application prospects.

[0019] (1) The present application uses hydrogen sulfide to perform enhanced sulfidation on the waste acid, which only requires one enhanced sulfidation process, and no sodium ions are introduced during the treatment process, which can effectively reduce the salt crystallization phenomenon in the system and improve the stability and operation efficiency of the production system. At the same time, by adding an aeration device to the system of the reaction of dilute sulfuric acid and sodium hydrosulfide aqueous solution, the reaction efficiency of dilute sulfuric acid and sodium hydrosulfide is improved, and hydrogen sulfide gas is introduced into the waste acid in the form of diffuse bubbles through the aeration device, thereby improving the enhanced sulfidation reaction efficiency of hydrogen sulfide and waste acid, and improving the utilization rate of hydrogen sulfide. In the enhanced 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.

[0020] (2) In step S2, the present application adopts a two-step neutralization method to treat the waste acid treatment liquid after sulfidation, the purpose of which is to fully remove the cadmium ions in the waste acid in a more brief 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, the purpose of which is 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 adjusted back to 8-9, the purpose of which is to re-precipitate and remove the Cd(OH)2 that has been dissolved in the waste acid during the first pH adjustment process, and at the same time, the cadmium sulfide (CdS) that has been dissolved in the waste acid treatment liquid during the enhanced sulfidation treatment will also be re-precipitated and removed in the pH adjustment step. This setting can effectively avoid the phenomenon of cadmium exceeding the standard caused by cadmium re-dissolution.

[0021] Under high pH conditions, Cd 2+ Will be with OH - The reaction generates Cd(OH)2 precipitate, but as the reaction continues, part of the Cd(OH)2 will continue to react with the excess OH - The reaction produces soluble cadmium salts (such as Cd(OH)4 2- ), causing cadmium to dissolve back. In the two-step neutralization method adopted in the present application, the pH is adjusted to 11-12 for the first time to precipitate most of the heavy metals in the treatment solution, such as Fe(OH)3, Zn(OH)2, Cr(OH)3 and Cd(OH)2 precipitation, which are all removed in the first filtration step; the pH is adjusted back to 8-9 for the second time, which not only prevents Cd(OH)2 from continuing to react with excessive OH - The reaction generates cadmates, and a small amount of dissolved Cd(OH)2 is precipitated again in the form of Cd(OH)2 or CdS, and removed in the subsequent second filtering step, thereby reducing the concentration of cadmium in the final treatment solution. In addition, there may be some dissolved CdS remaining in the dirty acid treatment solution obtained in step S1, and these cadmium ions will also be precipitated again in the form of Cd(OH)2 or CdS in the two-step neutralization method, and removed in the second filtering step of step S2.

[0022] (3) The method for treating waste acid in copper smelting provided in this application avoids the waste of chemical agents by rationally designing the process flow and optimizing the reaction conditions, effectively shortening the process steps and duration, and the by-product sodium sulfate meets the requirements of Class I first-class products specified in GB / T 6009-2014 after being treated by a multi-effect evaporation process, and has commercial value, thereby improving the economic benefits of the overall process and bringing better sustainable development prospects to the enterprise. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1The flowchart of the method for treating the waste acid in copper smelting in Example 1 is as follows; Figure 2 It is a schematic diagram showing the effect of sodium hydrosulfide dosage on arsenic removal and copper removal in Comparative Examples 3-7; Figure 3 Schematic diagram showing the effect of reaction temperature on arsenic removal in Examples 2-3 and Comparative Examples 9-11; Figure 4 Schematic diagram showing the effect of reaction time on arsenic removal in Example 4 and Comparative Examples 12-15. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] It should also be noted here that in order to avoid obscuring the present application due to unnecessary details, only the structures and / or processing steps closely related to the scheme of the present application are shown in the accompanying drawings, while other details that are not very relevant to the present application are omitted.

[0026] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0027] See also Figure 1 As shown, the present application provides a method for treating contaminated acid in copper smelting, which specifically comprises the following steps: S1, build a normal pressure sulfidation reaction device, use a constant pressure dropping funnel to add dilute sulfuric acid (20% w / w) to a sodium hydrosulfide aqueous solution (32% w / w), react at room 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 diffuse bubbles through the aeration device to perform enhanced sulfidation treatment on the waste acid, and monitor the oxidation-reduction potential (ORP) value of the waste acid to regulate the end point of the sulfidation reaction, filter after the reaction is completed, remove the sulfidation slag, and obtain a waste acid treatment liquid; Specifically, the concentration of dilute sulfuric acid is 20%, and the dosage is 65-70mL / L; the concentration of sodium hydrosulfide aqueous solution is 32%, and the dosage is 75-85mL / L; the dosage of hydrogen sulfide gas is 16-19g / L; the temperature of the enhanced sulfidation reaction is 20-40°C, and the reaction time is 1.5-2h; the reaction end point of the enhanced sulfidation reaction is when the ORP value is lower than 18mV. Alkali solution is also provided in the atmospheric pressure sulfidation reaction device to absorb the residual hydrogen sulfide gas that has not reacted completely in the enhanced sulfidation reaction.

[0028] The present application uses hydrogen sulfide to perform enhanced sulfidation on the waste acid, which only requires one enhanced sulfidation process, and no sodium ions are introduced during the treatment process, which can effectively reduce the salt crystallization phenomenon in the system and improve the stability and operation efficiency of the production system. At the same time, by adding an aeration device to the system of the reaction of dilute sulfuric acid and sodium hydrosulfide aqueous solution, the reaction efficiency of dilute sulfuric acid and sodium hydrosulfide is improved, and hydrogen sulfide gas is introduced into the waste acid in the form of diffuse bubbles through the aeration device, thereby improving the enhanced sulfidation reaction efficiency of hydrogen sulfide and waste acid, and improving the utilization rate of hydrogen sulfide. In the enhanced 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.

[0029] The equation for the reaction of sulfuric acid and sodium hydrosulfide is: 2NaHS + H2SO4 = 2H2S↑ + Na2SO4.

[0030] In the enhanced sulfidation reaction, hydrogen sulfide dissolved in the solution ionizes to produce S 2- , S 2- With As, Cu, Pb and other heavy metal ions M n+ The reaction generates a precipitate. Taking divalent metal ions as an example, the reaction formula is M 2+ +S 2- =MS↓, the equilibrium concentration of metal ions in the solution decreases with increasing pH value and increases with the total sulfur concentration [S]. T Generally, the higher the pH value of the solution, the higher the arsenic removal rate, but too high a pH value will cause arsenic to dissolve back, so most of the arsenic is removed under acidic conditions, that is, in the enhanced sulfurization reaction of step S1. In order to shift the reaction equilibrium toward the direction of precipitation (such as MS↓), the sulfur concentration in the solution [S] can be appropriately increased. T , which reduces the concentration of metal ions in the solution.

[0031] S2, firstly 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, then adjust the pH value of the filtrate to 8-9 with concentrated sulfuric acid, filter to remove the precipitate, and complete the waste acid treatment.

[0032] 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.

[0033] In step S2, the present application adopts a two-step neutralization method to treat the waste acid treatment liquid after sulfidation, the purpose of which is to fully remove the 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, the purpose is to generate heavy metal precipitates with Fe(OH)3, Zn(OH)2, Cr(OH)3 and Cd(OH)2 as the main components; the pH is adjusted back to 8-9, the purpose is to re-precipitate and remove the cadmium hydroxide [Cd(OH)2] that is dissolved in the waste acid during the first pH adjustment process, and at the same time, the cadmium sulfide (CdS) that has been dissolved in the waste acid treatment liquid during the enhanced sulfidation treatment will also be re-precipitated and removed in the pH adjustment step. Such a setting can effectively avoid the phenomenon of cadmium exceeding the standard caused by cadmium re-dissolution.

[0034] Under high pH conditions, Cd 2+ Will be with OH - The reaction generates Cd(OH)2 precipitate, but as the reaction continues, part of the Cd(OH)2 will continue to react with the excess OH - The reaction produces soluble cadmium salts (such as Cd(OH)4 2- ), causing cadmium to dissolve back. In the two-step neutralization method adopted in the present application, the pH is adjusted to 11-12 for the first time to precipitate most of the heavy metals in the treatment solution, such as Fe(OH)3, Zn(OH)2, Cr(OH)3 and Cd(OH)2 precipitation, which are all removed in the first filtration step; the pH is adjusted back to 8-9 for the second time, which not only prevents Cd(OH)2 from continuing to react with excessive OH - The reaction generates cadmates, and a small amount of dissolved Cd(OH)2 is precipitated again in the form of Cd(OH)2 or CdS, and removed in the subsequent second filtering step, thereby reducing the concentration of cadmium in the final treatment solution. In addition, there may be some dissolved CdS remaining in the dirty acid treatment solution obtained in step S1, and these cadmium ions will also be precipitated again in the form of Cd(OH)2 or CdS in the two-step neutralization method, and removed in the second filtering step of step S2.

[0035] The method for treating the contaminated acid in copper smelting proposed in the present application also includes recovering sodium sulfate. 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. The product meets the requirements of Class I first-class products specified in GB / T 6009-2014, has commercial value, can improve the economic benefits of the overall process, and reduce processing costs.

[0036] The following is an explanation of the method for treating the waste acid in copper smelting provided by the present application in conjunction with specific examples. The waste acid used in the examples contains 17100 mg / L of arsenic, 879 mg / L of copper, and 642 mg / L of cadmium, and the pH value of the waste acid is 0.7.

[0037] Example 1 This embodiment proposes a method for treating polluted acid in copper smelting, and the specific steps are as follows: S1, build a normal pressure sulfidation reaction device, use a constant pressure dropping funnel to add dilute sulfuric acid (20% w / w) to a sodium hydrosulfide aqueous solution (32% w / w), react at room temperature (25°C), stirring, and aeration conditions to prepare hydrogen sulfide gas and sodium sulfate solution, directly pass hydrogen sulfide gas into 250mL of waste acid, perform enhanced sulfidation reaction at 40°C, and monitor the change in the ORP value of the waste acid. When the ORP value is below 18mV, it is determined as the end point of the sulfidation reaction. Then, filter the waste acid after enhanced sulfidation treatment, separate the sulfided slag, and obtain the waste acid treatment liquid.

[0038] S2, performing a two-step neutralization treatment on the waste acid treatment liquid obtained in step S1, firstly adjusting the pH of the waste acid treatment liquid to 11-12 with 75 mL of lime milk (20% w / w) to generate a metal hydroxide precipitate, filtering to obtain a filtrate, and then adjusting the pH of the filtrate to 8-9 with 0.267 g of concentrated sulfuric acid (98% w / w), filtering again to remove the newly generated precipitate, and completing the waste acid treatment; In the enhanced sulfidation reaction of step S1, the sulfidation reaction time is 1.5 hours, 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 hydrogen sulfide gas. The ORP value and arsenic concentration change trend of the waste acid in the reaction are shown in the table below.

[0039] Refer to the table above, and you can see that as the redox potential decreases, the residual concentration of arsenic in the waste acid gradually decreases. When the ORP drops below 18 mV, the residual concentration of arsenic is less than 0.2 mg / L, meeting the effluent water quality requirements. This shows that monitoring the redox potential of waste acid can effectively determine the end point of the enhanced sulfidation reaction, and the automatic adjustment of the treatment process can be achieved through system monitoring and feedback in the future.

[0040] The sodium sulfate solution remaining from the reaction of dilute sulfuric acid and sodium hydrosulfide in step S1 is subjected to a multiple-effect evaporation process to remove impurities and filtered to obtain a sodium sulfate product. The recovered sodium sulfate product is tested to meet the requirements of Class I first-class product indicators specified in GB / T 6009-2014 in terms of purity, impurity content and particle size, as shown in the following table.

[0041] Comparative Example 1-2 The difference between Comparative Example 1-2 and Example 1 is that in step S1, the amount of sodium hydrosulfide is set to 4 times the theoretical value (50 mL), and the amount of hydrogen sulfide gas generated is controlled by adjusting the amount of dilute sulfuric acid. The specific steps are: different volumes of dilute sulfuric acid (20% w / w) are added dropwise to 50 mL of sodium hydrosulfide aqueous solution (32% w / w), reacting to prepare hydrogen sulfide gas under normal temperature (25°C), stirring, and aeration conditions, and passing it into 250 mL of waste acid, and strengthening the sulfurization treatment at 40°C for 1.5 hours, and the ORP value of the waste acid is monitored to be lower than 18mV. Then, the waste acid after the strengthening sulfurization treatment is filtered, the sulfurized slag is separated, and the waste acid treatment liquid is obtained. The other contents are roughly the same as those in Example 1, and will not be repeated here.

[0042] The residual concentrations of arsenic and copper in the waste acid treatment solutions obtained in Example 1 and Comparative Examples 1-2 were tested, and the results are shown in the table below.

[0043] Please refer to the table above. As the amount of hydrogen sulfide increases, the residual concentrations of arsenic and copper in the waste acid treatment liquid are significantly reduced. When the amount of hydrogen sulfide is 4.478g, the concentration of arsenic in the waste acid treatment liquid is less than 0.2 mg / L, and the concentration of copper is less than 0.04 mg / L, which meets the water quality requirements of the reclaimed water (<0.5 mg / L). At this time, the optimal amount of hydrogen sulfide is 1.54 times the theoretical value.

[0044] This is because the reaction of hydrogen sulfide with heavy metals such as arsenic and copper belongs to gas-liquid heterogeneous reaction. During the reaction process, hydrogen sulfide gas is first dissolved in the liquid phase, and then reacts with the heavy metals in the liquid phase. The amount of hydrogen sulfide gas finally involved in the reaction is not only related to the dosage of concentrated sulfuric acid and sodium hydrosulfide, but also to the yield of hydrogen sulfide, its dissolution and diffusion in dirty acid, and the efficiency of hydrogen sulfide and heavy metal reaction. Therefore, appropriately increasing the amount of hydrogen sulfide can offset its loss in the process of reaction, dissolution, diffusion, etc., provide sufficient reactants for the reaction system, and then obtain better treatment effect. However, it should be noted that excessive hydrogen sulfide consumption will increase the processing cost and also bring potential safety hazards. Therefore, the optimal amount of hydrogen sulfide is 17.9g / L, that is, 17.9g hydrogen sulfide needs to be consumed for each treatment of 1L dirty acid. It can be seen from the use of 19.1mL sodium hydrosulfide aqueous solution in the preparation of hydrogen sulfide gas in Example 1 that the optimal amount of sodium hydrosulfide aqueous solution is 76.4mL / L.

[0045] Comparative Examples 3-7 Comparative Example 3-7: Sodium hydrosulfide aqueous solution (32% w / w) was directly added to the waste acid stock solution for sulfidation reaction, and the dosage was set to 35 mL / L, 45 mL / L, 55 mL / L, 65 mL / L and 75 mL / L, respectively. The specific steps were: 5 groups of 200 mL of waste acid were measured, and 7 mL, 9 mL, 11 mL, 13 mL and 15 mL of sodium hydrosulfide aqueous solution were added, respectively, and the reaction was stirred at 40 ° C for 0.5 h, and the residual concentrations of arsenic and copper in the reaction solution were tested. The test conditions and test results are detailed in Figure 2 and the table below.

[0046] See also Figure 2 As can be seen from the table above, at the same temperature, as the amount of sodium hydrosulfide aqueous solution increases, the residual concentrations of arsenic and copper in the treatment solution continue to decrease, and the slag production is positively correlated with the treatment effect. The best amount of sodium hydrosulfide aqueous solution is 75 mL / L, at which time the residual concentration of arsenic in the treatment solution is less than 0.2 mg / L, and the residual concentration of copper is less than 0.04 mg / L, and the expected treatment target can be achieved. According to Comparative Examples 1-2, the optimal amount of sodium hydrosulfide aqueous solution in the treatment method provided by the present application is 76.4 mL / L. By comparison, the optimal amount of sodium hydrosulfide in the two treatment methods is very similar, indicating that the enhanced sulfidation treatment method provided by the present application will not increase the amount of sodium hydrosulfide, and the sodium sulfate byproduct produced by the preparation of hydrogen sulfide meets the requirements of Class I first-class product indicators specified in GB / T 6009-2014 after treatment, and has commercial value, which can offset part of the treatment cost and reduce the overall cost.

[0047] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that in step 2, the pH of the waste acid treatment liquid is directly neutralized to 8-9. The specific steps are: using sodium hydroxide aqueous solution (10% w / w) to adjust the pH of the waste acid treatment liquid obtained in step S1 to 8-9, filtering, and completing the waste acid treatment. The other contents are roughly the same as Example 1 and will not be repeated here.

[0048] The residual concentrations of arsenic, copper, sodium, cadmium, lead, zinc and mercury in the solutions after sulfidation treatment and neutralization treatment were tested respectively. The results are shown in the table below.

[0049] Please refer to the table above, and you can see 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, so 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 the hydroxide concentration required to form Cd(OH)2 is relatively high. Comparative Example 8 directly adjusts the pH value to 8-9, which may result in the inability to convert all cadmium ions in the solution into Cd(OH)2 precipitation, resulting in cadmium exceeding the standard; while in the two-step neutralization method, lime milk is first used to adjust the pH of the waste acid treatment liquid to 11-12. In a high pH environment, Cd 2+ With OH - Cd(OH)2 precipitate is generated, filtered to remove Cd(OH)2, and then the pH of the solution is adjusted back to 8-9 with concentrated sulfuric acid, which not only prevents Cd(OH)2 from continuing to react with excess OH - The reaction generates cadmium salts and also causes a small amount of dissolved Cd(OH)2 to precipitate again in the form of Cd(OH)2 or CdS, which is removed by subsequent filtration steps. The two-step neutralization method provided in this application not only improves the cadmium removal rate, but also reduces the cadmium salts (such as Cd(OH)4 2- )The production of such by-products ensures that the final treated liquid meets the water quality requirements for reclaimed water.

[0050] In addition, some dissolved CdS may remain in the waste acid treatment liquid obtained in step S1. These cadmium ions will also be re-precipitated in the form of Cd(OH)2 or CdS in the two-step neutralization method and removed in the filtration step.

[0051] Examples 2-3 and Comparative Examples 9-11 The difference between Examples 2-3 and Comparative Examples 9-11 and Example 1 is that the temperature of the enhanced vulcanization reaction is set to 20°C, 30°C, 40°C, 50°C, 60°C, and 70°C, respectively. The other contents are substantially the same as those in Example 1 and will not be repeated here.

[0052] The residual concentration of arsenic in the waste acid treatment solution prepared in step 1 is tested. Figure 3 and as shown in the table below.

[0053] See also Figure 3From the table above, we can see 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%. Between 50-70°C, as the reaction temperature increases, the arsenic removal rate gradually decreases. This is because when the reaction system temperature is lower than or equal to 40°C, it can ensure that there are enough sulfur ions in the solution, and the higher the temperature within this range, the faster the reaction rate, thus showing a better arsenic removal effect. Therefore, the optimal temperature for strengthening the sulfidation reaction is 40°C.

[0054] Example 4 and Comparative Examples 12-15 The difference between Example 4 and Comparative Examples 12-15 and Example 1 is that the time for the enhanced vulcanization reaction is set to 0.25, 0.5, 1.0, 2.0, and 2.5 h, respectively. The other contents are substantially the same as those in Example 1 and will not be repeated here.

[0055] The residual concentration of arsenic in the waste acid treatment solution prepared in step 1 is tested. Figure 4 and as shown in the table below.

[0056] See also Figure 4 As can be seen from the table above, within a certain reaction time, the residual concentration of arsenic decreases as the reaction time increases. When the reaction time is 2.5h, the residual concentration of arsenic increases slightly. This is because the dearsenicization process is basically completed after 1.5h of reaction. Further extension of the reaction time causes some arsenic to dissolve back. Therefore, the reaction time of enhanced sulfidation should be controlled to 1.5-2h. From the perspective of saving time and avoiding arsenic dissolution, the optimal reaction time is 1.5h, at which time the ORP value of the dirty acid is lower than 18mV. In subsequent industrial applications, the reaction time and ORP value can be used to determine the end point of the sulfidation reaction.

[0057] In summary, the present application adopts sodium hydrosulfide and sulfuric acid to prepare hydrogen sulfide, thereby avoiding the introduction of new sodium ion impurities into the waste acid, and effectively shortening the process by reasonably designing the process flow and optimizing the reaction conditions, reducing the waste of chemical agents, and reducing the treatment cost. The sodium sulfate product finally produced meets the requirements of Class I first-class products in the national recommended standard (GB / T 6009-2014) and has commercial value. The concentrations of As, Cu, Na, Cd, Pb, Zn, and Hg in the treated waste acid can meet the water quality standards of the enterprise's reclaimed water effluent.

[0058] In the method for treating waste acid in copper smelting provided in 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 1.5 hours at 40°C, and the best treatment effect can be achieved when the redox potential is 20 mV.

[0059] The above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the preferred embodiments, a person skilled in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution 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, firstly adjusting the pH value of the waste acid treatment liquid obtained in step S1 to 11-12 with lime milk to generate heavy metal precipitates with iron hydroxide, zinc hydroxide, chromium hydroxide and cadmium hydroxide as main components, filtering out the precipitates, 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 precipitates to complete the waste acid treatment.

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%.

9. The method for treating polluted acid in copper smelting according to claim 1, characterized in that: In step S2, the amount of lime milk used is 200-400 mL / L, and the amount of concentrated sulfuric acid used is 0.5-2 g / L.

10. The method for treating polluted acid in copper smelting according to claim 2, characterized in that: In step S2, the concentration of the lime milk is 10-30%, and the concentration of the concentrated sulfuric acid is 98%.

Images