Method for removing trivalent arsenic in wastewater by seed-induced enhanced removal

Abstract

The application discloses a method for removing trivalent arsenic in wastewater by seed induction intensification, and belongs to the technical field of wastewater treatment. 3+ ∶As 3+ ∶SO4 2‑ The molar ratio of Fe 3+ ∶As 3+ ∶SO4 2‑ is 1.5:1:0.25, and the pH is kept unchanged during the sampling process; the stirring and heating are continued until the temperature reaches 25-65 DEG C, and then the reaction is ended; the obtained precipitate is separated; and the hydrobasoalite seed is added into the bottom liquid. The application promotes the nucleation and growth by using the hydrobasoalite seed, reduces the sludge amount, and the removal rate of trivalent arsenic reaches 95%; the obtained hydrobasoalite has low leaching toxicity, and the leaching toxicity is below 5 mg / L; the process is simple, and has wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial wastewater pollution prevention and control, and particularly relates to a method for seed-induced enhanced removal of trivalent arsenic in wastewater. BACKGROUND

[0002] Non-ferrous metal industry is a pillar industry of China's national economy and social development. Arsenic is mostly present in non-ferrous metal deposits. With the continuous development of non-ferrous metal mining and smelting in China, arsenic pollution is becoming increasingly serious. Arsenic mainly exists in the environment in the form of inorganic arsenic oxide and methylation. The toxicity of inorganic arsenic is much greater than that of organic arsenic, and the toxicity of trivalent arsenic is 25-60 times that of pentavalent arsenic. In addition, As(III) has greater solubility and mobility than As(V), and mainly exists in the form of non-ionic arsenite at pH < 9.2, so it is more difficult to remove. Common methods effective for As(V) removal, such as chemical precipitation, adsorption, ion exchange, etc., are not effective for As(III) removal.

[0003] Goslarite is the only arsenic sulfate iron mineral found so far. The stability of artificially synthesized goslarite has not yet met the standards. Whether chemically synthesized or biologically synthesized, the leaching toxicity test results are all greater than 10 mg / L, which does not meet the emission standards of Hazardous Waste Leaching Toxicity Identification Standard (GB 5085.3-2007). In addition, the amount of slag produced by the current artificial synthesis of goslarite is large. After being synthesized by the traditional method, the sludge settles for 30 minutes, and the sludge settling ratio exceeds 0.5. Therefore, the performance of goslarite in sludge reduction and arsenic stabilization needs to be improved.

[0004] Chinese patent CN110451598A discloses a method for enhanced removal of trivalent arsenic in acidic wastewater by humic acid. The stability of goslarite is enhanced by humic acid. Although the arsenic removal rate after the reaction is more than 90%, the arsenic leaching toxicity of the obtained product goslarite is all greater than 10 mg / L. Chinese patent CN11578440A discloses a method for enhancing the stability of goslarite by adding carboxyl-containing organic matter. The stability of goslarite is improved, but the arsenic leaching toxicity needs to be improved, and the sludge settling property is not good.

[0005] Therefore, further improving the removal rate of arsenic and the stability of the obtained product goslarite are the keys to efficiently treating wastewater containing arsenic and stabilizing arsenic in the wastewater at the same time. SUMMARY

[0006] In view of the problems in the prior art, the present application aims to provide a method for seed-induced enhanced removal of trivalent arsenic in wastewater. By adding seed to induce trivalent arsenic in wastewater to form goslarite, the removal rate of arsenic is improved, the leaching toxicity of arsenic is reduced, and sludge reduction is achieved.

[0007] To achieve the above objectives, this invention provides a method for seed-induced enhanced removal of trivalent arsenic from wastewater, comprising: adding an appropriate concentration of sulfate solution to arsenic(III)-containing wastewater to form a base solution, adjusting the pH to <3, and then adding a trivalent ferric salt solution, wherein Fe... 3+ ∶As 3+ SO4 2- The molar ratio is 1.5:1:0.25, and the pH is kept constant during the injection process; the mixture is heated and stirred until the temperature reaches 25-65℃. After the reaction is complete, the precipitate is separated. This also includes:

[0008] Add water-soluble hydroxyarsenic iron alum seed crystals to the base solution.

[0009] In the above technical solution, the method for preparing the aqueous hydroxyarsenic iron alum seed crystals is as follows: deionized water and sulfate solution are added to a trivalent arsenic solution to form a base solution, and then a solution containing trivalent iron salt is injected, wherein Fe... 3+ ∶As 3+ SO4 2- The molar ratio was 1.5:1:0.25, the pH was kept constant at 2.4 during the injection process, the reaction temperature was 25℃, and the stirring rate was 450 rpm. Fe 3+ The solution was introduced into the system at a rate of 1500 μL / min using a peristaltic pump, and the reaction time was 3 days. After the reaction was completed, the precipitate was separated, dried, and ground to obtain the final product.

[0010] In a preferred embodiment, the size of the water-soluble hydroxyarsenic iron alum seed crystals is 40-65 μm, preferably 60 μm.

[0011] Furthermore, the amount of water-soluble hydroxyarsenic iron alum seed crystals added is 0.1-2 g / L, preferably 0.5 g / L.

[0012] In a preferred embodiment, the water-soluble hydroxyarsenic iron alum seed crystals are added at a time of 0-15 minutes after the start of the reaction, preferably 10 minutes.

[0013] In a preferred embodiment, the trivalent ferric salt is any one of ferric sulfate, ferric chloride, and ferric nitrate nonahydrate.

[0014] More preferably, the trivalent iron salt solution is ferric nitrate nonahydrate solution.

[0015] In a preferred embodiment, the temperature is 45°C.

[0016] In a preferred embodiment, the reaction time is 6-72 hours, preferably 12-24 hours, and more preferably 18 hours.

[0017] In a preferred embodiment, the pH is 2-2.8, preferably 2.6.

[0018] In a preferred embodiment, the stirring rate in the reaction solution is 300-700 rpm, preferably 600 rpm.

[0019] In a preferred embodiment, the rate of the injected ferric iron salt solution is 1000-2500 μl / min, preferably 1500 μl / min.

[0020] Principle of the present application:

[0021] The addition of the seed crystal can shorten the mineral nucleation process and reduce the reaction energy barrier. The dissolution-recrystallization process after the addition of the seed crystal can promote the aggregation of iron and arsenic elements, and make the mineral structure growth more stable. Through the optimization of the reaction conditions, the proportion of amorphous arsenic is reduced, and the proportion of crystalline state is increased, so that the mineral is more stable, and the leaching toxicity of arsenic is reduced. On this basis, the addition of the seed crystal also increases the size of the sludge and improves the compaction, and improves the settling performance of the hydroxyarsenite iron sludge.

[0022] Advantages of the present application:

[0023] After the method provided by the present application is used, the removal rate of arsenic in the wastewater is more than 90%. After the seed crystal is added, the sludge settling ratio is reduced by 30%. The leaching toxicity of the obtained product hydroxyarsenite iron sludge is 4.38 mg / L, which is reduced by 49.5% compared with the case without adding the seed crystal, and the stability of the obtained mineral is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0025] Figure 1 is the removal rate of As(III) in acid wastewater and the leaching toxicity of the obtained product hydroxyarsenite iron sludge under different reaction temperatures in Example 1;

[0026] Figure 2 is the sludge settling ratio of the product hydroxyarsenite iron sludge obtained by strengthening the removal of As(III) in acid wastewater under different reaction temperatures in Example 1;

[0027] Figure 3 is the removal rate of As(III) in acid wastewater and the leaching toxicity of the obtained product hydroxyarsenite iron sludge under different reaction pH values in Example 2;

[0028] Figure 4 is the sludge settling ratio of the product diagram water ferrihydrite arsenate obtained by strengthening the removal of As(III) in acidic wastewater in Example 2 under different reaction pH values;

[0029] Figure 5 is the leaching toxicity of the product diagram water ferrihydrite arsenate obtained by strengthening the removal of As(III) in acidic wastewater in Example 3 under different seed addition amounts;

[0030] Figure 6 is the sludge settling ratio of the product diagram water ferrihydrite arsenate obtained by strengthening the removal of As(III) in acidic wastewater in Example 3 under different seed addition amounts;

[0031] Figure 7 is the leaching toxicity of the product diagram water ferrihydrite arsenate obtained by strengthening the removal of As(III) in acidic wastewater in Example 4 under different reaction stirring speeds;

[0032] Figure 8 is the sludge settling ratio of the product diagram water ferrihydrite arsenate obtained by strengthening the removal of As(III) in acidic wastewater in Example 4 under different reaction stirring speeds;

[0033] Figure 9 is the leaching toxicity of the product diagram water ferrihydrite arsenate obtained by strengthening the removal of As(III) in acidic wastewater in Example 5 under different reaction times;

[0034] Figure 10 is the sludge settling ratio of the product diagram water ferrihydrite arsenate obtained by strengthening the removal of As(III) in acidic wastewater in Example 5 under different reaction times;

[0035] Figure 11 is the leaching toxicity of the product diagram water ferrihydrite arsenate obtained by removing As(III) in acidic wastewater in Example 2 and Comparative Example 1 after 18h of reaction and without adding seeds, and the leaching toxicity of the product diagram water ferrihydrite arsenate obtained by removing As(III) in acidic wastewater without adding seeds after 18h and 24h of reaction;

[0036] Figure 12 is the sludge settling ratio of the product diagram water ferrihydrite arsenate obtained by removing As(III) in acidic wastewater in Example 2 and Comparative Example 1 after 18h of reaction with or without adding seeds;

[0037] Figure 13 is the proportion of each form in the arsenic speciation sequential extraction of the product diagram water ferrihydrite arsenate obtained by removing As(III) in acidic wastewater in Example 2 and Comparative Example 1 after 18h of reaction with or without adding seeds;

[0038] Figure 14The XRD pattern of the product obtained after 0-24 h of removing As(III) from acidic wastewater in Comparative Example 1 without seed crystals is shown.

[0039] Figure 15 The image shows the XRD pattern of the product obtained after adding seed crystals to remove As(III) from acidic wastewater in Example 2, after a reaction of 0-18 hours. Detailed Implementation

[0040] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] In this application, the method for preparing the aqueous hydroxyarsenic iron alum seed crystals is as follows: deionized water and sulfate solution are added to a trivalent arsenic solution to form a base solution, and then a solution containing trivalent iron salt is injected, wherein Fe... 3+ ∶As 3+ SO4 2- The molar ratio was 1.5:1:0.25, the pH was kept constant at 2.4 during the injection process, the reaction temperature was 25℃, and the stirring rate was 450 rpm. Fe 3+ The solution was introduced into the system at a rate of 1500 μL / min using a peristaltic pump, and the reaction time was 3 days. After the reaction was completed, the precipitate was separated, dried, and ground to obtain the final product.

[0042] Example 1: This example compares the effects of different reaction temperatures on seed-induced removal of As(III) from acidic wastewater. The specific process is as follows: 30 mg / L of 0.1 mol / L As(III) solution and 30 ml of 0.025 mol / L Na₂SO₄ solution were mixed with 30 ml of deionized water to form a base solution. The pH was adjusted to 2.4 with dilute nitric acid or sodium hydroxide. 0.15 mol / L of 30 ml of Fe(III) solution was added to the base solution at a rate of 1500 μl / min using a peristaltic pump. At the beginning of the reaction, 0.1 g / L of hydroxyarsenic alum seed crystals were added to the solution. The pH was kept constant during the reaction. The stir bar speed was 500 rpm. After the sample injection, the reaction was carried out at 25℃, 35℃, 45℃, 55℃, and 65℃ for three days. After the reaction, the supernatant was taken to detect the arsenic concentration. Simultaneously, the sample was vacuum filtered through a 0.22 μm filter membrane and vacuum dried at 60℃. The leaching toxicity of the arsenic in the solid sample was determined.

[0043] Example 2: This example compares the effect of different reaction pH values on seed-induced removal of As(III) from acidic wastewater. The specific process is as follows: 30 mg / L of 0.1 mol / L As(III) solution and 30 ml of 0.025 mol / L Na2SO4 solution are mixed to form a base solution, and dilute nitric acid or sodium hydroxide is used to adjust the pH to 2.2, 2.4, 2.6, 2.8, and 3.0. 0.15 mol / L of 30 ml Fe(III) is added to the base solution at a speed of 1500 μl / min using a peristaltic pump. At the beginning of the reaction, 0.1 g / L of hydroxyarsenatoferrite seed crystals are added to the solution, and the pH is maintained constant during the process. The stirring speed in the reaction is 500 rpm. After the sample is added, the reaction is carried out at 45°C for three days. After the reaction is completed, the supernatant is detected for arsenic concentration, and the solid sample is vacuum filtered using a 0.22 μm filter membrane and dried at 60°C under vacuum. The leaching toxicity of arsenic in the solid sample is determined.

[0044] Example 3: This example compares the effect of different seed crystal addition amounts on seed-induced removal of As(III) from acidic wastewater. The specific process is as follows: 30 mg / L of 0.1 mol / L As(III) solution and 30 ml of 0.025 mol / L Na2SO4 solution are mixed to form a base solution, and dilute nitric acid or sodium hydroxide is used to adjust the pH to 2.6. 0.15 mol / L of 30 ml Fe(III) is added to the base solution at a speed of 1500 μl / min using a peristaltic pump. At the beginning of the reaction, 0.1 g / L, 0.25 g / L, 0.5 g / L, 0.75 g / L, and 1 g / L of hydroxyarsenatoferrite seed crystals are added to the solution, and the pH is maintained constant during the process. The stirring speed in the reaction is 500 rpm. After the sample is added, the reaction is carried out at 45°C for three days. After the reaction is completed, the supernatant is detected for arsenic concentration, and the solid sample is vacuum filtered using a 0.22 μm filter membrane and dried at 60°C under vacuum. The leaching toxicity of arsenic in the solid sample is determined.

[0045] Example 4: This example compares the effect of different stirring speeds on the removal of As(III) from acidic wastewater induced by seed crystals. Specifically, 30 mg / L of 0.1 mol / L As(III) solution and 30 ml of 0.025 mol / L Na2SO4 solution were mixed with 30 ml of deionized water to form a base solution. The pH was adjusted to 2.6 using dilute nitric acid or sodium hydroxide. 0.15 mol / L 30 ml Fe(III) was added to the base solution at a speed of 1500 μl / min using a peristaltic pump. At the beginning of the reaction, 0.5 g / L of hydroxyarsenatoferrite seed crystals were added to the solution. The pH was maintained constant during the process. The stirring speed of the reaction was 300 rpm, 400 rpm, 500 rpm, 600 rpm, and 700 rpm. After the sample was added, the reaction was carried out at 45°C for 18 h. After the reaction was completed, the supernatant was collected to determine the concentration of arsenic. The solid sample was vacuum filtered using a 0.22 μm filter membrane and vacuum dried at 60°C. The leaching toxicity of arsenic in the solid sample was determined.

[0046] Example 5: This example compares the effect of different reaction times on the removal of As(III) from acidic wastewater induced by seed crystals. Specifically, 30 mg / L of 0.1 mol / L As(III) solution and 30 ml of 0.025 mol / L Na2SO4 solution were mixed with 30 ml of deionized water to form a base solution. The pH was adjusted to 2.6 using dilute nitric acid or sodium hydroxide. 0.15 mol / L 30 ml Fe(III) was added to the base solution at a speed of 1500 μl / min using a peristaltic pump. At the beginning of the reaction, 0.5 g / L of hydroxyarsenatoferrite seed crystals were added to the solution. The pH was maintained constant during the process. The stirring speed of the reaction was 500 rpm. After the sample was added, the reaction was carried out at 45°C for 12 h, 18 h, 24 h, 30 h, and 36 h. After the reaction was completed, the supernatant was collected to determine the concentration of arsenic. The solid sample was vacuum filtered using a 0.22 μm filter membrane and vacuum dried at 60°C. The leaching toxicity of arsenic in the solid sample was determined.

[0047] Comparative Example 1: 30 mg / L of 0.1 mol / L As(III) solution and 30 ml of 0.025 mol / L Na2SO4 solution were mixed with 30 ml of deionized water to form a base solution. The pH was adjusted to 2.6 using dilute nitric acid or sodium hydroxide. 0.15 mol / L 30 ml Fe(III) was added to the base solution at a speed of 1500 μl / min using a peristaltic pump. The pH was maintained constant during the process. The stirring speed of the reaction was 600 rpm. After the sample was added, the reaction was carried out at 45°C for 12 h, 18 h, 24 h, 30 h, and 36 h. After the reaction was completed, the supernatant was collected to determine the concentration of arsenic. The solid sample was vacuum filtered using a 0.22 μm filter membrane and vacuum dried at 60°C. The leaching toxicity of arsenic in the solid sample was determined.

[0048] Figure 1 is the removal rate of As(III) in the acidic wastewater and the leaching toxicity of the product schwertmannite obtained under the reaction temperature of 25-65°C in Example 1, Figure 2 is the sludge settling ratio of the product schwertmannite obtained under the reaction temperature of 25-65°C in Example 1. As can be seen from the figure, with the change of the reaction temperature, the arsenic removal rate is mostly kept at about 90%, the arsenic removal rate is lower when the reaction temperature is 25°C, the arsenic removal rate is slightly higher when the reaction temperature is 35°C, and the arsenic removal rates are 82% and 93.5% respectively. In terms of leaching toxicity, when the reaction temperature is 35°C, the leaching toxicity is lower, which is 6.1 mg / L, but combined with Figure 2 the sludge settling ratio, the sludge settling ratio of the product obtained at the reaction temperature of 35°C is greater than that of the product obtained at the reaction temperature of 45°C, so it can be considered that when the reaction temperature is 45°C, it is most beneficial to obtain the stable product schwertmannite and reduce the amount of sludge.

[0049] Figure 3 is the removal rate of As(III) in the acidic wastewater and the leaching toxicity of the product schwertmannite obtained under the reaction pH value of 2.2-3.0 in Example 2, Figure 4 is the sludge settling ratio of the product schwertmannite obtained under the reaction pH value of 2.2-3.0 in Example 2. As can be seen from the figure, with the change of the reaction pH value, the arsenic removal rate is kept at about 92% without too much change, and the arsenic removal rate is lower when the pH is 2.8. In terms of leaching toxicity, when the reaction pH value is 2.2 and 2.6, the leaching toxicity is lower, which is 7.1 and 14.2 mg / L respectively, but combined with Figure 4 the sludge settling ratio, the sludge settling ratio of the product obtained at the reaction pH of 2.2 is much greater than that of the product obtained at the reaction pH of 2.6, so it can be considered that when the reaction pH is 2.6, it is most beneficial to obtain the stable product schwertmannite and reduce the amount of sludge.

[0050] Figure 5 is the removal rate of As(III) in the acidic wastewater and the leaching toxicity of the product schwertmannite obtained under the seed addition amount of 0.1-1 g / L in Example 3, Figure 6 is the sludge settling ratio of the product schwertmannite obtained under the seed addition amount of 0.1-1 g / L in Example 3. As can be seen from the figure, with the change of the seed addition amount, the arsenic removal rate is kept at about 92% without too much change. In terms of leaching toxicity, when the seed addition amount is 0.5 g / L, the leaching toxicity is lower, which is 11.21 mg / L. From Figure 6It can be seen that with the change of seed addition amount, the sludge settling ratio fluctuates around 0.4, and when the seed addition amount is 0.5 g / L, the sludge settling ratio is lower, which is 0.385. Combined with the leaching toxicity, it can be considered that when the seed addition amount is 0.5 g / L, it is most beneficial to obtain the stability of the product graphic water hydroxy arsenic iron and the reduction of sludge amount.

[0051] Figure 7 is the removal rate of As(III) in acid wastewater and the leaching toxicity of the product graphic water hydroxy arsenic iron obtained by strengthening the removal of As(III) in acid wastewater under the reaction stirring rate of 300-700 rpm in Example 4, Figure 8 is the sludge settling ratio of the product graphic water hydroxy arsenic iron obtained by strengthening the removal of As(III) in acid wastewater under the reaction stirring rate of 300-700 rpm in Example 4. It can be seen from the figure that with the change of the reaction stirring rate, the arsenic removal rate remains around 90%. In terms of leaching toxicity, when the reaction stirring rate is 600 rpm, the leaching toxicity is the lowest, which is 4.5 mg / L. It can be seen from the figure that when the reaction stirring rate is 600 rpm, the sludge settling ratio of the product is the lowest, so it can be considered that when the reaction stirring rate is 600 rpm, it is most beneficial to obtain the stability of the product graphic water hydroxy arsenic iron and the reduction of sludge amount. Figure 8

[0052] Figure 9 is the removal rate of As(III) in acid wastewater and the leaching toxicity of the product graphic water hydroxy arsenic iron obtained by strengthening the removal of As(III) in acid wastewater under the reaction time of 12-36 h in Example 5, Figure 10 is the sludge settling ratio of the product graphic water hydroxy arsenic iron obtained by strengthening the removal of As(III) in acid wastewater under the reaction time of 12-36 h in Example 5. It can be seen from the figure that with the change of the reaction time, the arsenic removal rate gradually rises, and when the reaction time is 18 h, an inflection point appears, and the arsenic removal rate is 92.4%, and then the arsenic removal rate rises slowly with the increase of the reaction time. In terms of leaching toxicity, when the reaction time is 18 h, the leaching toxicity is the lowest, which is 4 mg / L. It can be seen from the figure that when the reaction time is 18 h, the sludge settling ratio of the product is the lowest, so it can be considered that when the reaction time is 18 h, it is most beneficial to obtain the stability of the product graphic water hydroxy arsenic iron and the reduction of sludge amount. Figure 10

[0053] Figure 11 is the removal rate of As(III) in acid wastewater and the leaching toxicity of the product graphic water hydroxy arsenic iron obtained by strengthening the removal of As(III) in acid wastewater under the reaction stirring rate of 300-700 rpm in Example 4, Figure 12 ​​is the sludge sedimentation ratio of the product obtained after 18 hours of reaction of removing As(III) in acidic wastewater in Example 2 and Comparative Example 1 without adding crystal seeds. In the case of not adding crystal seeds, the arsenic removal rate after 18 hours of reaction is 91.5%, the leaching toxicity of the product is 8.67 mg / L, and the sludge sedimentation ratio is 0.33; the arsenic removal rate after 24 hours of reaction is 92.4%, and the leaching toxicity of the product is 9.87 mg / L; in the case of adding 0.06 g of crystal seeds, the arsenic removal rate after 18 hours of reaction is 95.3%, the leaching toxicity of the product obtained is 4.38 mg / L, and the sludge sedimentation ratio is 0.23; under the action of crystal seeds, the arsenic removal rate is improved, the leaching toxicity is reduced by 49.5%, and the sludge sedimentation ratio is reduced by 30.3%, which effectively improves the stability of the mineral and reduces the amount of sludge.

[0054] Figure 13 is the figure of the proportion of each form in the sequential extraction of arsenic form in the product obtained after 18 hours of reaction of removing As(III) in acidic wastewater in Example 2 and Comparative Example 1 with or without adding crystal seeds; the proportion of the crystal iron oxide state and the residue state of arsenic in the mineral in the crystal seed induction system is 67.56%, and the proportion of the two in the non-crystal seed induction system is 47.55%, the proportion of the two in the crystal seed induction system is increased by 20%, more arsenic is fixed in the crystal lattice, and the stability of the mineral is enhanced.

[0055] Figure 14 is the XRD figure of the product obtained after 0-24 hours of reaction of removing As(III) in acidic wastewater in Comparative Example 1 without adding crystal seeds. Figure 15 is the XRD figure of the product obtained after 0-18 hours of reaction of removing As(III) in acidic wastewater in Example 2 with adding crystal seeds. In the case of not adding crystal seeds, the characteristic peaks of the product appear 10-12 hours after the start of the reaction, while in the case of adding crystal seeds, the characteristic peaks of the product appear 6 hours after the start of the reaction, and the intensity of the characteristic peaks after the reaction is larger, which indicates that the crystallinity is better. The XRD image peak intensity of the product obtained by not adding crystal seeds for 24 hours is similar to that of the product obtained by adding crystal seeds for 18 hours, and the crystallinity is also similar, but the leaching toxicity of the product obtained by not adding crystal seeds for 24 hours is more than twice that of the product obtained by adding crystal seeds for 18 hours, so the introduction of crystal seeds not only accelerates the reaction rate, but also improves the stability of arsenic. Figure 11

[0056] The above examples are only preferred embodiments of the present application, and the protection scope of the present application is not limited to the above examples. Any technical solutions falling within the concept of the present application shall fall within the protection scope of the present application. It should be pointed out that improvements and refinements made by ordinary technical personnel in the technical field without departing from the principles of the present application shall also be regarded as the protection scope of the present application.​

Claims

1. A method for seed-induced enhanced removal of trivalent arsenic from wastewater, characterized in that, include: An appropriate concentration of sulfate solution was added to the arsenic (III)-containing wastewater to form a base solution, and the pH was adjusted to <3. Then, a ferric salt solution was added, wherein Fe... 3+ ∶As 3+ SO4 2- The molar ratio is 1.5:1:0.25, and the pH is kept constant during the injection process; the mixture is heated and stirred until the temperature reaches 25-65℃, with a stirring rate of 300-700 rpm. After the reaction is complete, the precipitate is separated. This also includes: Add water-soluble hydroxyarsenic alum seed crystals to the base solution. The preparation method of the water-soluble hydroxyarsenic alum seed crystals is as follows: add deionized water and sulfate solution to a trivalent arsenic solution to form a base solution, and then inject a solution containing trivalent ferric salt, wherein Fe... 3+ :As 3+ :SO4 2- The molar ratio was 1.5:1:0.25, the pH was kept constant at 2.4 during the injection process, the reaction temperature was 25℃, and the stirring rate was 450 rpm. Fe 3+ The solution was introduced into the system at a rate of 1500 μL / min using a peristaltic pump, and the reaction time was 3 days. After the reaction was completed, the precipitate was separated, dried, and ground to obtain the final product.

2. The method according to claim 1, characterized in that, The size of the water-soluble hydroxyarsenic iron alum seed crystals is 40-65 μm.

3. The method according to claim 1, characterized in that, The amount of hydroxyarsenic alum seed crystals added to the figure is 0.1-2 g / L.

4. The method according to claim 1, characterized in that, The water-soluble hydroxyarsenic iron alum seed crystals are added 0-15 minutes after the reaction begins.

5. The method according to claim 1, characterized in that, The ferric salt is any one of ferric sulfate, ferric chloride, and ferric nitrate nonahydrate.

6. The method according to claim 1, characterized in that, The reaction time is 6-72 hours.

7. The method according to claim 1, characterized in that, The pH is 2-2.

8.

8. The method according to claim 1, characterized in that, The rate at which the ferric salt solution is added is 1000-2500 μl / min.

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