Composite flocculant, preparation process and application thereof

Abstract

This invention provides a composite flocculant, its preparation process, and its application. The invention relates to the field of waste acid treatment technology. It comprises 35%–55% wt of an amide flocculant (containing a strong anionic monomer with a sulfonic acid group), a compound capable of generating high-valence metal ions, and 0.2%–1.5% wt of water-soluble silicate. The composite flocculant of this invention not only contains highly polar hydrophilic groups such as sulfonic acid and carboxyl groups, but also a certain amount of high-valence metal ions, equivalent to cross-linking between metal ions and the amide polymer. This mainly overcomes the difficulty of hydrolyzing polyacrylamide flocculants under acidic or dilute acid conditions, thereby achieving the neutralization of surface charges and destabilization of fine particles suspended in solution under acidic or dilute acid conditions. Using the above-mentioned composite flocculant can flocculate dust in waste sulfuric acid, reducing the area of ​​the waste sulfuric acid sedimentation tank and shortening the sedimentation time.

Description

Technical Field

[0001] This invention relates to the field of waste acid treatment technology, and in particular to a composite flocculant, a composite flocculant preparation process, and its application. Background Technology

[0002] Currently, most of the washing circulating acid in pyrite or smelting flue gas sulfuric acid production systems is treated using settling tanks, sedimentation ponds, or filters. Due to factors such as the high concentration of waste sulfuric acid (approximately 10%–15% wt) and temperatures reaching 56°C, conventional coagulants or flocculants cannot be used to enhance sedimentation.

[0003] Therefore, the dust content in the waste sulfuric acid after precipitation treatment easily exceeds the production control requirements (150 mg / L), sometimes reaching 1 g / L, causing production problems such as blockage of the furnace gas scrubbing tower and filter. To alleviate this phenomenon, the only solution is to increase the amount of waste acid discharged and the amount of makeup water for flue gas scrubbing. The adverse effects are: a decrease in the concentration of circulating acid in the scrubbing process (2%–5% wt) and a sharp increase in the load on the waste acid treatment.

[0004] Since the sulfuric acid concentration in the SO2 flue gas scrubbing circulating acid is approximately 2%–15% wt, practical experience has shown that commercially available flocculants, coagulants, or coagulant aids cannot effectively flocculate the dust in waste sulfuric acid. To achieve the return of waste sulfuric acid from bypass sedimentation to the production system, the area of ​​the waste sulfuric acid sedimentation tank must be increased by nearly tenfold, and the sedimentation time extended. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a composite flocculant, a composite flocculant preparation process, and its application. This invention aims to solve the problem of high dust content in SO2 flue gas scrubbing circulating acid during recycling, by enhancing dust precipitation (or settling) in waste sulfuric acid and improving the stability of the production system.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] A composite flocculant comprises 35%–55% wt of an amide flocculant (containing a strong anionic monomer with a sulfonic acid group), a compound capable of generating high-valence metal ions, and 0.2%–1.5% wt of a water-soluble silicate.

[0008] Preferably, the compound capable of generating high-valence metal ions is polyaluminum chloride, with a mass fraction of 2% to 10% wt.

[0009] A process for preparing a composite flocculant, used to prepare the composite flocculant according to claim 1 or 2, includes the following steps: S1, preparing an amide flocculant, a polyaluminum chloride solution, and a water-soluble silicate; S2, first placing the amide flocculant in a production reaction stirred tank, maintaining a predetermined reaction temperature while continuously stirring, then adding the polyaluminum chloride solution dropwise, and after a predetermined time, stopping the addition of the polyaluminum chloride solution when the solution pH = 3.5 to 4.5;

[0010] S3. After the polyaluminum chloride has been added, add water-soluble silicate solution to the reactor. After a predetermined time, when the pH of the solution is 4.8 to 5.2, stop adding the water-soluble silicate solution.

[0011] S4. Increase the operating temperature of the reactor to heat and concentrate the composite flocculant to obtain the finished composite flocculant (gel-like).

[0012] Preferably, the polyaluminum chloride solution has a mass fraction of about 13% and a water-soluble silicate mass fraction of about 38%.

[0013] Preferably, in step S4, the operating temperature in the reactor is raised to 85-95°C, and the concentration of amide flocculant in the product is controlled to be 35%-55%wt.

[0014] Preferably, the production reaction stirred tank includes a stirring device and a circulating pumping device. The stirring device controls the thorough mixing of solutions at different horizontal positions, and the circulating pumping device controls the thorough mixing of solutions at different height positions.

[0015] An application of a composite flocculant, which involves precipitating dust and particulate matter in waste acid, includes the following steps: First, the prepared composite flocculant product is dissolved in natural water by stirring to prepare a composite flocculant solution; Second, a certain concentration of waste sulfuric acid is extracted, wherein the concentration of sulfuric acid in the waste sulfuric acid is 2.63% to 8.95% and the concentration of dust (or suspended matter) is 12.86 g / L to 38.25 g / L; 400 mL of waste sulfuric acid is poured into a beaker and stirred; Third, the flocculant solution to be used is added to the waste sulfuric acid, wherein the flocculant solution is 2 mL to 12 mL, and after stirring for a predetermined time (5 s), the stirring speed is adjusted to 50 rpm and stirred for about 10 min, then stirring is stopped and the mixture is allowed to stand for 2 h.

[0016] Preferably, the concentration of the flocculant solution in the first step is 0.25‰ to 0.5‰.

[0017] Preferably, the stirring speed in the second step is 350 rpm.

[0018] The beneficial effects of this invention are as follows:

[0019] Compared with existing technologies, the composite flocculant of this invention not only contains highly polar hydrophilic groups such as sulfonic acid groups and carboxyl groups, but also contains a certain amount of metal ions with higher valence states, which is equivalent to the cross-linking of metal ions with amide polymers. This mainly overcomes the characteristic that polyacrylamide flocculants are difficult to hydrolyze under acidic or dilute acid conditions, thereby achieving the neutralization of the surface charge of suspended particles and the destabilization of fine particles in the solution under acidic or dilute acid conditions. Using the above-mentioned composite flocculant can produce a flocculation effect on dust in waste sulfuric acid, reduce the area of ​​waste sulfuric acid sedimentation tank, and shorten the sedimentation time. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments.

[0021] The furnace gas from pyrite or smelting flue gas sulfuric acid production systems (generally, the furnace gas temperature is controlled at the dew point +20 to 30°C) enters the wet purification process and is first washed and dusted by circulating acid (sulfuric acid concentration ≤20%, also known as waste sulfuric acid), and the furnace gas temperature is reduced to below 60°C. Dust in the circulating acid gradually accumulates during the washing process.

[0022] To control the dust content of circulating acid within specified limits (generally below 30 mg / L), bypass sedimentation treatment of the circulating acid is required. The clarified dilute sulfuric acid after treatment is returned to the production system, while another portion is sent to a waste acid treatment plant for further processing. Whether the dilute sulfuric acid is returned to the production system or sent to the waste acid treatment plant, the precipitation treatment of waste sulfuric acid not only effectively recovers dust but also reduces the amount of solid waste generated.

[0023] Currently, the circulating acid used in pyrite or smelting flue gas sulfuric acid production systems is mostly treated using settling tanks, sedimentation ponds, or filters. However, due to the high concentration of waste sulfuric acid (approximately 10%–15% wt) and temperatures reaching 56°C, conventional coagulants or flocculants cannot be used to enhance sedimentation. Therefore, the dust content in the waste sulfuric acid after sedimentation treatment easily exceeds production control requirements (150 mg / L), sometimes reaching 1 g / L, causing production problems such as blockage of the furnace gas scrubbing tower and filters. To alleviate this, the only solution is to increase the amount of waste acid discharged and the amount of makeup water for flue gas scrubbing. The adverse effects are: a decrease in the concentration of circulating acid (2%–5% wt) and a sharp increase in the load on waste acid treatment.

[0024] Since the sulfuric acid concentration in the SO2 flue gas scrubbing circulating acid is approximately 2%–15% wt, practical experience has shown that commercially available flocculants, coagulants, or coagulant aids cannot effectively flocculate the dust in waste sulfuric acid. To achieve the return of waste sulfuric acid from bypass sedimentation to the production system, the area of ​​the waste sulfuric acid sedimentation tank must be increased by nearly tenfold, and the sedimentation time extended.

[0025] To address the aforementioned problems, this invention discloses a composite flocculant. The flocculant is formulated from an amide flocculant (containing a strong anionic monomer with a sulfonic acid group), polyaluminum chloride, and water-soluble silicate. The amide flocculant is synthesized using fatty acids, alkanolamine organic compounds, acid anhydrides, and sulfonating agents through amidation, esterification, and sulfonation processes to obtain an amide flocculant containing polar groups such as sulfonic acid and carboxyl groups. The composite flocculant of this invention is used to precipitate dust (or suspended solids) in waste sulfuric acid. The concentration and dosage of the composite flocculant are adjusted according to the different concentrations of dust and sulfuric acid in the waste sulfuric acid to be treated, thereby achieving a better dust (or suspended solids) precipitation effect.

[0026] A composite flocculant consists of 35%–55% wt amide flocculant (containing a strong anionic monomer with a sulfonic acid group), 2%–10% wt polyaluminum chloride, and 0.2%–1.5% wt water-soluble silicate.

[0027] The aforementioned composite flocculant can reduce the dust content in waste sulfuric acid to 20 mg / L.

[0028] It should be noted that the polyaluminum chloride mentioned above can also be selected from other metal compounds, as long as they can generate crosslinking between high-valence metal ions and amide polymers; those skilled in the art can select aluminum sulfate (Al2(SO4)3), ferric sulfate (Fe2(SO4)3), etc., according to actual needs.

[0029] The composite flocculant of this invention not only contains hydrophilic groups such as highly polar sulfonic acid groups and carboxyl groups, but also contains a certain amount of metal ions with high valence, which is equivalent to the cross-linking of metal ions with amide polymers. This mainly overcomes the characteristic that polyacrylamide flocculants are difficult to hydrolyze under acidic or dilute acid conditions, thereby achieving the neutralization of the surface charge of suspended particles and the destabilization of fine particles in the solution under acidic or dilute acid conditions.

[0030] Using the above-mentioned composite flocculant can flocculate the dust in waste sulfuric acid, reduce the area of ​​the waste sulfuric acid sedimentation tank, and shorten the sedimentation time.

[0031] When this composite flocculant solution is added to waste sulfuric acid, it undergoes several complex intermediate reactions. The entire reaction process can be roughly described by the hydrolysis of the composite flocculant monomers as follows:

[0032]

[0033] Equation (1) can represent the hydrolysis products of the composite flocculant, which can neutralize the negative charge of dust in waste sulfuric acid, adsorb and condense into larger particles, and the anions close to the surface of the colloidal particles can neutralize the positive charge of the flocculant and become unstable. The introduction of silicates increases the settling speed of the colloidal particles.

[0034] The dosage of the composite flocculant of this invention can be adjusted according to the different concentrations of dust and sulfuric acid in the waste sulfuric acid to be treated, so as to achieve a better dust precipitation effect.

[0035] The preparation process of the composite flocculant will be further explained below.

[0036] A composite flocculant preparation process is disclosed. The method for preparing amide flocculants involves using fatty acids, organic alcohol amines, acid anhydrides, sulfonating agents, etc., and following the synthesis reaction steps. Fatty acids, organic alcohol amines, acid anhydrides, and sulfonating agents are added sequentially to a reaction vessel, and an appropriate amount of catalyst is added. After amidation, esterification, and sulfonation processes, an amide flocculant containing polar groups such as sulfonic acid groups and carboxyl groups is synthesized.

[0037] In the production reactor, the concentration of the synthesized amide flocculant is controlled at 20%–35% wt, the reaction temperature is maintained at 40–60℃, and the stirring speed is 30–75 rpm. Then, a polyaluminum chloride solution with a mass fraction of approximately 13% is added dropwise over a time of 90–120 min. The addition of the polyaluminum chloride solution is stopped when the solution pH is 3.5–4.5. After the polyaluminum chloride is added, a water-soluble silicate solution with a mass fraction of approximately 38% is added dropwise over a time of 30–60 min. The addition of the water-soluble silicate solution is stopped when the solution pH is 4.8–5.2. Finally, the operating temperature of the reactor is raised to 85–95℃ to heat and concentrate the composite flocculant, controlling the concentration of the amide flocculant in the product to be 35%–55% wt, thus obtaining the finished composite flocculant (gel-like).

[0038] In order to improve the mixing effect of polyaluminum chloride solution dropwise, the production reaction vessel here includes a stirring device and a circulation pumping device. The stirring device can control the solution in the production reaction vessel to rotate directionally around the vertical axis, and control the solution at different horizontal positions to be fully mixed.

[0039] The circulating pumping device includes a circulating pumping pipeline and a circulating pump. The circulating pumping pipeline is connected to the upper and lower ends of the production reaction stirring vessel, which can pump the solution at the bottom of the production reaction stirring vessel to the top for stirring and mixing. It can control the solution at different heights to be fully mixed, which greatly improves the overall solution mixing effect, improves the uniformity of solution preparation after dripping, greatly shortens the dripping and stirring time, and improves the quality of the final product composite flocculant.

[0040] The invention will be further explained below in conjunction with the application of composite flocculants.

[0041] The application of the above-mentioned composite flocculant to precipitate dust and particulate matter in waste acid includes the following steps.

[0042] The first step is to dissolve the prepared composite flocculant product with natural water to prepare a composite flocculant solution, wherein the concentration of the flocculant solution is 0.25‰ to 0.5‰.

[0043] The second step is to extract waste sulfuric acid of a certain concentration, wherein the concentration of sulfuric acid in the waste sulfuric acid is 2.63% to 8.95%; the concentration of dust (or suspended matter) is 12.86 g / L to 38.25 g / L; take 400 mL of waste sulfuric acid and pour it into a beaker, and stir the waste sulfuric acid at a stirring speed of 350 rpm.

[0044] The third step is to add the flocculant solution to the waste sulfuric acid. The flocculant solution is 2mL to 12mL. After stirring for a predetermined time (5s), adjust the stirring speed to 50rpm and stir for about 10min. Then stop stirring and let it stand for 2h.

[0045] After standing, the supernatant was taken to determine the dust concentration, and the dust content in the waste sulfuric acid was measured to be reduced to the level of 25 mg / L.

[0046] Example 1

[0047] Take 0.1g of the prepared composite flocculant (concentration of 50%), add 200g of tap water and stir to dissolve, and use it as a flocculant solution (concentration of 0.5‰) for later use.

[0048] A waste sulfuric acid sample was taken from the production system for precipitation testing. The sulfuric acid concentration of the waste sulfuric acid was 5.47%, and the dust (or suspended solids) concentration was 12.86 g / L. Under room temperature conditions (ambient temperature approximately 30°C), 400 mL of waste sulfuric acid was poured into a beaker, and stirring was started at 350 rpm. 2 mL of the flocculant solution to be used was added to the waste sulfuric acid, and stirring was carried out for about 5 seconds. Then, the stirring speed was adjusted to 50 rpm and stirred for about 10 minutes. After stirring was stopped, the mixture was allowed to stand for nearly 2 hours. The height of the sludge layer was approximately 15% (based on the height of the beaker). The dust concentration of the supernatant was measured, and the result was 22.5 mg / L.

[0049] Example 2

[0050] Take 0.1g of the prepared composite flocculant (concentration of 50%), add 300g of tap water and stir to dissolve, and use it as a flocculant solution (concentration of about 0.3‰) for later use.

[0051] A waste sulfuric acid sample was taken from the production system for precipitation testing. The sulfuric acid concentration of the waste sulfuric acid was 8.95%, and the dust (or suspended solids) concentration was 38.25 g / L. 400 mL of waste sulfuric acid was poured into a beaker, and stirring was started in a water bath at 350 rpm. 10 mL of the flocculant solution to be used was added to the waste sulfuric acid, and stirring was continued for about 5 seconds. The stirring speed was then increased to 50 rpm and stirred for about 10 minutes. Stirring was then stopped, and the mixture was allowed to stand for nearly 2 hours. The height of the sludge layer was approximately 12% (based on the height of the beaker). The dust concentration of the supernatant was measured, and the result was 27.8 mg / L.

[0052] Example 3

[0053] Take 0.1g of the prepared composite flocculant (concentration of 50%), add 400g of tap water and stir to dissolve, and use it as a flocculant solution (concentration of 0.25‰) for later use.

[0054] A waste sulfuric acid sample was taken from the production system for precipitation testing. The sulfuric acid concentration of the waste sulfuric acid was 2.63%, and the dust (or suspended solids) concentration was 15.72 g / L. 400 mL of waste sulfuric acid was poured into a beaker, and stirring was started in a water bath at 350 rpm. 12 mL of the flocculant solution to be used was added to the waste sulfuric acid, and stirring was continued for about 5 seconds. The stirring speed was then increased to 50 rpm and stirred for about 10 minutes. Stirring was then stopped, and the mixture was allowed to stand for nearly 2 hours. The height of the sludge layer was approximately 12% (based on the height of the beaker). The dust concentration of the supernatant was measured, and the result was 17.5 mg / L.

[0055] Comparative Example 1

[0056] A test was conducted on the precipitation of dust from waste acid using polyacrylamide prepared for waste acid neutralization treatment. The concentration of the flocculant was approximately 1.5‰.

[0057] A waste sulfuric acid sample was taken from the production system for precipitation testing. The sulfuric acid concentration was 3.68%, and the dust (or suspended solids) concentration was 22.46 g / L. 400 mL of waste sulfuric acid was poured into a beaker, and stirring was started in a water bath at 350 rpm. 12 mL of the planned flocculant solution was added, and the mixture was stirred for about 5 seconds. The stirring speed was then increased to 50 rpm and stirred for about 10 minutes. Stirring was then stopped, and the mixture was allowed to stand for nearly 2 hours. The water and sludge separation was not obvious, and the liquid at the top of the beaker remained a dark reddish-brown color. The dust concentration of the supernatant was measured, and the result was 12.36 g / L, which is insufficient to meet the requirements for reuse in production.

[0058] Comparative Example 2

[0059] A test was conducted on the precipitation of dust from waste acid using polyacrylamide prepared for waste acid neutralization treatment. The concentration of the flocculant was approximately 4.5‰.

[0060] A waste sulfuric acid sample was taken from the production system for precipitation testing. The sulfuric acid concentration was 2.85%, and the dust (or suspended solids) concentration was 10.15 g / L. 400 mL of waste sulfuric acid was poured into a beaker, and stirring was started in a water bath at 350 rpm. 10 mL of the flocculant solution to be used was added to the waste sulfuric acid, and stirring was continued for about 5 seconds. The stirring speed was then increased to 50 rpm and stirred for about 10 minutes. Stirring was then stopped, and the mixture was allowed to stand for nearly 2 hours. The separation of water and sludge was not obvious, and the liquid at the top of the beaker remained pale red. The dust concentration of the supernatant was measured, and the result was 0.98 g / L, which is insufficient to meet the requirements for reuse in production.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An application of a composite flocculant, characterized in that, A composite flocculant is applied to waste acid to precipitate dust and particulate matter. The composite flocculant comprises 35%–55% wt of an amide flocculant, wherein the amide flocculant contains a strong anionic monomer with a sulfonic acid group, and further includes a compound capable of generating high-valence metal ions and 0.2%–1.5% wt of water-soluble silicate. The process includes the following steps: The first step is to dissolve the prepared composite flocculant product with natural water to prepare a composite flocculant solution. The second step is to extract waste sulfuric acid of a certain concentration, wherein the concentration of sulfuric acid in the waste sulfuric acid is 2.63%~8.95%; the concentration of dust or suspended matter is 12.86 g / L~38.25 g / L; take 400 mL of waste sulfuric acid and pour it into a beaker, and stir the waste sulfuric acid. The third step is to add the flocculant solution to the waste sulfuric acid. The flocculant solution is 2 mL to 12 mL. After stirring for the predetermined time, adjust the stirring speed to 50 rpm and stir for about 10 minutes. Then stop stirring and let it stand for 2 hours.

2. The application of the composite flocculant according to claim 1, characterized in that, In the first step, the concentration of the flocculant solution is 0.25‰~0.5‰.

3. The application of the composite flocculant according to claim 1, characterized in that, In the second step, the stirring speed is 350 rpm.

4. The application of the composite flocculant according to claim 1, characterized in that, Among them, the compound that can produce high-valence metal ions is polyaluminum chloride, with a mass fraction of 2% to 10% wt.

5. The application of the composite flocculant according to claim 4, characterized in that, The preparation of the composite flocculant includes the following steps: S1. Prepare amide flocculants, polyaluminum chloride solution, and water-soluble silicates; S2. First, place the amide flocculant in the production reaction stirred tank, maintain the predetermined reaction temperature while stirring continuously, and then add polyaluminum chloride solution dropwise. After the predetermined time, when the solution pH=3.5~4.5, stop adding polyaluminum chloride solution. S3. After the polyaluminum chloride has been added, add water-soluble silicate solution to the reaction vessel. After a predetermined time, when the pH of the solution is 4.8 to 5.2, stop adding the water-soluble silicate solution. S4. Increase the operating temperature of the reactor to heat and concentrate the composite flocculant to obtain the finished gel-like composite flocculant.

6. The application of the composite flocculant according to claim 5, characterized in that, The polyaluminum chloride solution has a mass fraction of approximately 13%, and the water-soluble silicate has a mass fraction of approximately 38%.

7. The application of the composite flocculant according to claim 5, characterized in that, In step S4, the operating temperature in the reactor is raised to 85-95°C, and the concentration of amide flocculant in the product is controlled to be 35%-55%wt.

8. The application of the composite flocculant according to claim 5, characterized in that, The production reaction vessel includes a stirring device and a circulating pumping device. The stirring device controls the thorough mixing of solutions at different horizontal levels, and the circulating pumping device controls the thorough mixing of solutions at different height levels.

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