A process for clean and efficient removal of arsenic from polluted acid and its comprehensive utilization

Abstract

The present invention relates to a process for cleanly and efficiently removing arsenic from waste acid and its comprehensive utilization, wherein a certain amount of FeS is added under suitable conditions to precipitate arsenic in the waste acid in the form of arsenic sulfide. The present invention comprehensively utilizes sulfuric acid therein, and the whole process does not generate hydrogen sulfide gas, does not adjust the pH value, and does not discharge wastewater, generate worthless hazardous waste, or generate waste gas such as hydrogen sulfide in the whole production process, so that no secondary environmental pollution will be caused.

Description

Technical Field

[0001] The present invention relates to a process for cleanly and efficiently removing arsenic from polluted acid and comprehensively utilizing it. The arsenic in the polluted acid generated in the process of acid production by pyrometallurgical smelting of sulfide concentrate is cleanly and efficiently removed, and the sulfuric acid therein is comprehensively utilized. The entire process does not generate industrial waste water, does not generate hazardous waste that needs to be landfilled, and does not generate waste gas that causes environmental pollution. The process belongs to the field of water pollution control technology. Background Art

[0002] In the pyrometallurgical smelting process of sulfide concentrates such as lead, copper, and zinc, sulfuric acid is usually prepared using sulfur dioxide flue gas as raw material, and the harmful element arsenic in the sulfide concentrate will also volatilize into the sulfur dioxide flue gas. Therefore, the waste acid produced in the sulfuric acid preparation process contains heavy metal arsenic. However, in the current waste acid treatment process, although arsenic can be effectively removed and the sulfuric acid liquid may be comprehensively utilized, a large amount of waste slag, wastewater, and waste gas will be generated in the process of arsenic removal and sulfuric acid application, causing secondary pollution to the environment.

[0003] On May 11, 2021, China Invention Patent Application Announcement No. CN112777789A disclosed a method for treating waste acid, which is to directly add zinc oxide soot or siderite to the waste acid, adjust the pH of the waste acid to 1.5-4.5, introduce air into the slurry or add hydrogen peroxide or pyrolusite or zinc powder to the Fe in the slurry. 2+ Oxidized to Fe 3+ , so that arsenic and iron are co-precipitated. Although this method makes comprehensive utilization of sulfuric acid in the waste acid, the co-precipitation of arsenic and iron will produce a large amount of arsenic and iron hazardous wastes. The harmless disposal of these hazardous wastes will not only increase the huge disposal cost but also bring huge risks and hidden dangers to the secondary pollution of the environment.

[0004] On September 21, 2016, China's invention patent application announcement number CN105950874A disclosed a method for the combined treatment of copper smelting ash and dirty acid, which uses dirty acid as a leaching agent to leach arsenic, copper, zinc and other metals in copper ash, precipitates copper in it with sodium sulfide, precipitates arsenic in it with reduction crystallization, and uses alkali liquor to synthesize the wastewater after arsenic precipitation. Although this process makes comprehensive use of sulfuric acid in dirty acid, after leaching arsenic, copper, zinc and other metals in copper ash, due to the low solubility of hydrogen sulfide in dirty acid, when hydrogen sulfide is passed into dirty acid, more hydrogen sulfide will overflow from dirty acid before reacting with arsenic, enter the atmosphere, and cause serious air pollution. On the other hand, the entire treatment process adds a variety of inorganic salts such as sodium sulfide and alkali liquor, so that the wastewater produced is high-concentration salt wastewater, and it is also necessary to carry out wastewater terminal treatment, which not only requires high wastewater treatment costs, but also requires solid waste harmless disposal of inorganic salt waste residues. Summary of the invention

[0005] In view of some problems existing in the prior art, the present invention proposes a process for cleanly and efficiently removing arsenic from waste acid and its comprehensive utilization. Under suitable conditions, a certain amount of FeS is added to precipitate the arsenic in the waste acid in the form of arsenic sulfide. The whole process does not generate hydrogen sulfide gas, does not adjust the pH value, and in the whole production process, no wastewater is discharged, no worthless hazardous waste is generated, and no waste gas such as hydrogen sulfide is generated.

[0006] The technical solution of the present invention is: a process for cleanly and efficiently removing arsenic from polluted acid and comprehensive utilization, which adopts the following steps:

[0007] (1) Removal of arsenic from waste acid: adding ferrous sulfide to the waste acid, the reaction temperature is 85-95°C, the reaction time is 40min-60min, and the amount of FeS added is 0.3-0.5 times or 3-6 times the mass of arsenic in the waste acid; after the reaction is complete, a primary precipitate residue and a arsenic-removed liquid are obtained; the primary precipitate residue is mainly composed of arsenic sulfide, and the arsenic product is recovered from the arsenic sulfide using conventional processes;

[0008] (2) Leaching of zinc oxide ash: continuously add zinc oxide ash to the arsenic removal solution, stir, and monitor the pH value of the arsenic removal solution while adding; when the pH is adjusted to 1-2.5, stop adding zinc oxide ash; during the leaching reaction, control the leaching temperature to 85-95°C and the reaction time to 2-3h; obtain zinc-containing leaching solution and lead mud, and send the lead mud to the lead smelting recovery system to collect lead;

[0009] (3) H2O2 purification: Add hydrogen peroxide directly to the zinc-containing leaching solution at room temperature. The amount of hydrogen peroxide added is 0.4-0.6 times the mass of iron in the solution. After reacting for 1-2.5 hours, filter. Obtain H2O2 purified solution and Fe 2+ and arsenic coprecipitation residue;

[0010] (4) Zinc powder purification: Add zinc powder to the H2O2 purified solution, the amount of zinc powder added is 1.2-1.5 times the total content of copper and cadmium in the solution, stir and react for 0.5h and then filter to obtain a pure zinc-containing solution and purified slag; recover copper and cadmium from the purified slag using conventional processes;

[0011] (5) Preparation of zinc sulfate heptahydrate: The pure zinc-containing solution is evaporated and concentrated to obtain zinc sulfate heptahydrate and a crystallization mother liquor; the crystallization mother liquor is a pure H2SO4-ZnSO4 solution, which is directly returned to the leaching step of zinc oxide ash as the arsenic-removed liquid;

[0012] The main chemical reaction equation of the process is as follows:

[0013] 3FeS+6H + +2HAsO2=3Fe 2++As2S3+4H2O

[0014] 2H3AsO3+8FeSO4+4H2O2+H2O=(Fe2O3)4·As2O3+8H2SO4.

[0015] When the amount of FeS added is 3-6 times the mass of arsenic in the waste acid, the precipitated residue obtained after the reaction can be used for multiple times to remove arsenic from the waste acid.

[0016] The invention can produce arsenic in the waste acid in the form of high-content arsenic sulfide precipitation without generating hydrogen sulfide gas by controlling the amount of ferrous sulfide added, temperature, time and other factors, and can also convert the waste acid into a pure H2SO4-FeSO4 solution, which can be used together with zinc oxide ash to prepare zinc sulfate heptahydrate, thereby saving the cost of H2SO4-FeSO4 that should be generated in the process of preparing sulfuric acid heptahydrate from zinc oxide ash.

[0017] The key technologies of the present invention are:

[0018] (1) During the entire process of waste acid treatment, no industrial wastewater is discharged, no hazardous waste that needs to be disposed of is generated, and no harmful gases such as hydrogen sulfide are generated;

[0019] (2) In the process of FeS removing arsenic from waste acid, the entire reaction process is regulated by strictly controlling the reaction temperature, reaction time, and the mass ratio of FeS to arsenic in the waste acid, so that the arsenic can be completely removed and FeS can prevent the formation of hydrogen sulfide gas with sulfuric acid in the waste acid;

[0020] (3) Although FeS reacts with waste acid to produce Fe 2+ However, since a small amount of arsenic is contained in the zinc oxide ash and will enter the leaching solution, and since there is iron in the leaching solution, a small amount of arsenic in the solution can be precipitated by directly adding hydrogen peroxide, and since the arsenic-iron precipitate also contains about 10% zinc, the arsenic-iron precipitate residue can be directly put into the rotary kiln to recover zinc, and there is no hazardous waste that needs to be disposed of. At the same time, it also saves the cost of sulfuric acid and iron flocculants that should be added in the process of preparing zinc sulfate heptahydrate from conventional zinc oxide ash;

[0021] (4) Since the entire process system only uses cheap reagents such as iron sulfide and hydrogen peroxide, the process is relatively simple and the production cost of the entire system is low. While easily treating the waste acid, it does not produce other worthless hazardous wastes and will not cause secondary environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Attached Figure 1 This is the process flow of this method. DETAILED DESCRIPTION

[0023] Example 1

[0024] (1) Take 1L of waste acid, which contains 4.12g / L arsenic and 260g / L sulfuric acid;

[0025] (2) 16 g of ferrous sulfide was added to the waste acid, and the reaction was carried out at a leaching temperature of 85°C for 40 min. After the reaction was complete, 26.37 g of primary precipitate was obtained. 980 mL of arsenic-free solution was obtained, and the arsenic concentration in the arsenic-free solution was 0.1 mg / L.

[0026] (3) The primary precipitate residue was placed in a beaker, and 1L of waste acid was added to react at a leaching temperature of 85°C for 45 minutes. After the reaction was complete, 29.10g of secondary precipitate residue was obtained; 975mL of arsenic-free liquid was obtained, and the arsenic concentration in the arsenic-free liquid was 0.2mg / L;

[0027] (4) The secondary precipitate residue was placed in a beaker, and 0.9 L of waste acid was added to react at a leaching temperature of 90 °C for 50 min. After the reaction was complete, 32.99 g of the tertiary precipitate residue was obtained; 870 mL of arsenic-free liquid was obtained, and the arsenic concentration in the arsenic-free liquid was 0.1 mg / L;

[0028] (5) The tertiary precipitate residue was placed in a beaker, and 0.74 L of waste acid was added to react at a leaching temperature of 90 °C for 55 min. After the reaction was complete, 35.16 g of the tertiary precipitate residue was obtained; 730 mL of arsenic-free liquid was obtained, and the arsenic concentration in the arsenic-free liquid was 0.1 mg / L;

[0029] (6) The four-time precipitate residue was placed in a beaker, and 0.6L of waste acid was added to react at a leaching temperature of 95°C for 60 minutes. After the reaction was complete, 37.30g of the five-time precipitate residue was obtained; 580mL of arsenic-free liquid was obtained, and the arsenic concentration in the arsenic-free liquid was 0.1mg / L;

[0030] (7) The five-time precipitate residue was placed in a beaker, and 0.48L of waste acid was added to react at a leaching temperature of 95°C for 60 minutes. After the reaction was complete, 39.47g of the six-time precipitate residue was obtained; 458mL of arsenic-free liquid was obtained, and the arsenic concentration in the arsenic-free liquid was 0.1mg / L;

[0031] (8) The slag from the sixth precipitation was placed in a beaker, and 0.41 L of waste acid was added to react at a leaching temperature of 95 °C for 60 min. After the reaction was complete, 40.91 g of slag from the seventh precipitation was obtained; 393 mL of arsenic-free liquid was obtained, and the arsenic concentration in the arsenic-free liquid was 0.1 mg / L;

[0032] (9) The slag from the seventh precipitation was placed in a beaker, and 0.34 L of waste acid was added to react at a leaching temperature of 95 °C for 60 min. After the reaction was complete, 43.06 g of slag from the eighth precipitation was obtained; 300 mL of arsenic-free liquid was obtained, and the arsenic concentration in the arsenic-free liquid was 0.1 mg / L, and the iron concentration was 1.72 g / L;

[0033] (10) The eight-time precipitate residue was placed in a beaker, and 0.27L of waste acid was added to react at a leaching temperature of 95°C for 60 min. After the reaction was complete, 44.16g of the nine-time precipitate residue was obtained, which contained 5.24% iron and 53.51% arsenic. 250mL of arsenic-free liquid was obtained, and the arsenic concentration in the arsenic-free liquid was 0.05mg / L.

[0034] (11) The arsenic-free solution (5.536 L) obtained in the above step was placed in a large beaker, and zinc oxide ash was continuously added to adjust the pH of the solution to 1.5. The reaction temperature was controlled to 85°C, and the reaction was carried out for 2.5 hours before filtering to obtain a zinc-containing solution and lead mud (sent to the lead smelting recovery system);

[0035] (12) Add 5 g of hydrogen peroxide to the zinc-containing solution, react for 1.5 h, filter, add 2 g of zinc powder to the filtrate, react for 0.5 h, and filter to obtain a pure zinc-containing solution;

[0036] (13) The pure zinc-containing solution is subjected to three-effect crystallization to obtain industrial-grade zinc sulfate heptahydrate and crystallization mother liquor (0.52 L). The crystallization mother liquor can be directly returned to the secondary zinc oxide ash leaching process, and there is no wastewater discharge in the entire system;

[0037] The above-mentioned three-effect crystallization is a three-effect crystallization system composed of three evaporators connected in series. The heating steam of 100°C is introduced into the first effect to heat the pure zinc-containing solution, so that the zinc-containing solution produces almost the same amount of evaporation at a temperature lower than that of the steam; the generated steam is introduced into the second effect as heating steam, so that the zinc-containing solution in the second effect evaporates at a temperature lower than that of the first effect; the generated steam is introduced into the third effect as heating steam, so that the zinc-containing solution in the third effect evaporates at a temperature lower than that of the second effect; the condensate of the first effect returns to the heat source, and the condensate of other effects is collected and output as distilled water. One portion of steam input can evaporate multiple times of water; at the same time, the pure zinc-containing solution is concentrated from the first effect to the last effect in sequence, and the zinc sulfate in the concentrated zinc-containing solution in the last effect reaches supersaturation and crystallizes as zinc sulfate heptahydrate to precipitate; thereby, the solid-liquid separation of the pure zinc-containing solution is achieved; the crystallized zinc sulfate heptahydrate is processed and packaged as a product; the H2SO4-ZnSO4 solution that cannot be crystallized is directly returned to the leaching step of zinc oxide ash as arsenic removal liquid.

[0038] Example 2

[0039] (1) Take 1L of waste acid, which contains 3.82g / L arsenic and 240g / L sulfuric acid;

[0040] (2) Add 1.91 g of ferrous sulfide to the waste acid and react for 40 min at a leaching temperature of 85 °C. The arsenic concentration in the solution is 2.74 g / L.

[0041] (3) 1.37 g of ferrous sulfide was added to the waste acid and the reaction was carried out at a leaching temperature of 85 °C for 40 min. The arsenic concentration in the solution was 1.94 g / L.

[0042] (4) Continue to add 0.97 g of ferrous sulfide to the waste acid and react for 40 min at a leaching temperature of 85 °C. The arsenic concentration in the solution is 1.38 g / L.

[0043] (5) Continue to add 0.69 g of ferrous sulfide to the waste acid, react for 40 min at a leaching temperature of 85 °C, and the arsenic concentration in the solution is 0.98 g / L;

[0044] (6) Continue to add 0.49 g of ferrous sulfide to the waste acid and react for 40 min at a leaching temperature of 85 °C. The arsenic concentration in the solution is 0.70 g / L.

[0045] (7) Continue to add 0.35 g of ferrous sulfide to the waste acid and react for 40 min at a leaching temperature of 85 °C. The arsenic concentration in the solution is 0.50 g / L.

[0046] (8) Continue to add 1.5 g of ferrous sulfide to the waste acid, react at a leaching temperature of 95 °C for 55 min, filter, and obtain 7.17 g of arsenic sulfide precipitate, which contains 53.26% arsenic and 10.73% iron; obtain 950 mL of arsenic-free solution, the arsenic concentration of which is 0.08 mg / L;

[0047] (10) The arsenic-free solution (0.95 L) obtained in the above step was placed in a large beaker, and zinc oxide ash was continuously added to adjust the pH of the solution to 1.5. The reaction temperature was controlled to be 85°C. After reacting for 1.5 hours, the solution was filtered to obtain a zinc-containing solution and lead mud (sent to the lead smelting recovery system);

[0048] (11) Add 1.12 g of hydrogen peroxide to the zinc-containing solution, react for 1.5 h, filter, add 0.3 g of zinc powder to the filtrate, react for 0.5 h, and filter to obtain a pure zinc-containing solution;

[0049] (12) The pure zinc-containing solution is subjected to triple crystallization to obtain industrial-grade zinc sulfate heptahydrate and crystallization mother liquor (0.05 L). The crystallization mother liquor can be directly returned to the secondary zinc oxide ash leaching process, and the entire system has no wastewater discharge.

[0050] Comparative case 1:

[0051] On December 1, 2020, China Invention Patent Application Announcement No. CN112010390A disclosed a method for removing arsenic from waste acid by ultrasonic self-cleaning. The process uses an ultrasonic device and ultrasonic enhanced treatment to remove As from the waste acid. However, the concentration of arsenic in the solution after arsenic removal in the patent implementation case is above 0.37 mg / L, which does not meet the special emission limit of water pollutants in the "Lead and Zinc Industrial Pollutant Emission Standard" (As≤0.1 mg / L). At the same time, the arsenic composition in the arsenic-containing filter residue produced is complex, which is not conducive to the next step of arsenic disposal and recovery. This patent can not only make the As in the solution after arsenic removal less than 0.1 mg / L, but also turn the waste acid after arsenic removal into a pure H2SO4-FeSO4 solution. At the same time, the arsenic in the waste acid is precipitated in the form of arsenic sulfide, and the precipitate is an arsenic series product.

Claims

1. A process for cleanly and efficiently removing arsenic from polluted acid and its comprehensive utilization, characterized in that: The process steps are as follows: (1) Removal of arsenic from waste acid: adding ferrous sulfide to the waste acid, the reaction temperature is 85-95°C, the reaction time is 40min-60min, the amount of FeS added is 0.3-0.5 times or 3-6 times the mass of arsenic in the waste acid, and the reaction does not produce hydrogen sulfide gas; after the reaction is complete, a primary precipitate residue and a arsenic-removed liquid are obtained; the primary precipitate residue is mainly composed of arsenic sulfide, and the arsenic product is recovered from the arsenic sulfide; (2) Leaching of zinc oxide ash: continuously add zinc oxide ash to the arsenic removal solution, stir, and monitor the pH value of the arsenic removal solution while adding; when the pH is adjusted to 1-2.5, stop adding zinc oxide ash; during the leaching reaction, control the leaching temperature to 85-95°C and the reaction time to 2-3h; obtain zinc-containing leaching solution and lead mud, and send the lead mud to the lead smelting recovery system to collect lead; (3) H2O2 purification: Add hydrogen peroxide directly to the zinc-containing leaching solution at room temperature. The amount of hydrogen peroxide added is 0.4-0.6 times the mass of iron in the solution. After reacting for 1-2.5 hours, filter. Obtain H2O2 purified solution and Fe 3+ and arsenic coprecipitation residue; (4) Zinc powder purification: Add zinc powder to the H2O2 purified solution, the amount of zinc powder added is 1.2-1.5 times the total content of copper and cadmium in the solution, stir and react for 0.5h and then filter to obtain a pure zinc-containing solution and purified slag; recover copper and cadmium from the purified slag; (5) Preparation of zinc sulfate heptahydrate: The pure zinc-containing solution is evaporated and concentrated to obtain zinc sulfate heptahydrate and a crystallization mother liquor; the crystallization mother liquor is a pure H2SO4-ZnSO4 solution, which is directly returned to the leaching step of zinc oxide ash as the arsenic-removed liquid.

2. The process for cleanly and efficiently removing arsenic from polluted acid and its comprehensive utilization according to claim 1 is further characterized by: When the amount of FeS added is 3-6 times the mass of arsenic in the waste acid, the precipitated slag obtained after the reaction can be used for arsenic removal from the waste acid many times.

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