Polyaluminum chloride sulfate for pulp and papermaking wastewater and its preparation method

Abstract

The application provides polymeric aluminum sulfate chlorides for pulp and papermaking wastewater and a preparation method thereof, which comprises the following steps: mixing dilute sulfuric acid, aluminum hydroxide, hydrochloric acid and water, stirring, transferring to a reaction kettle, opening a steam warming valve of the reaction kettle, performing steam warming reaction, stopping the steam warming, continuing the reaction of sulfuric acid, hydrochloric acid and aluminum hydroxide until the reaction is completed to obtain a reaction liquid; cooling the reaction liquid, stirring, adding calcium aluminate slurry, adding the calcium aluminate slurry, performing steam warming reaction, keeping warm, completing the reaction to obtain a reaction material; cooling the reaction material, filtering, taking the filtrate and obtaining a target product. The polymeric aluminum sulfate chlorides provided by the application have obvious effects on pulp and papermaking wastewater treatment, can effectively reduce the total soluble solid content and chemical oxygen demand of pulp and papermaking wastewater, and have better treatment effects on pulp and papermaking wastewater and lower costs compared with traditional PAC.

Description

Technical Field

[0001] This invention relates to the field of chemical product technology, and in particular to a polyaluminum chloride sulfate for pulp and paper wastewater and its preparation method. Background Technology

[0002] Pulp and paper wastewater has a complex composition, depending not only on the pulp production method but also on factors such as the type of product and raw materials. Suspended solids in the wastewater mainly originate from fibers and fillers lost during various pulping and papermaking processes. Its main characteristics include complex composition, high pollutant concentration, a high content of recalcitrant organic matter, and poor biodegradability.

[0003] Currently, polyaluminium chloride (PAC) is the commonly used flocculant in pulp and paper manufacturing processes. In water, PAC undergoes physicochemical processes such as charge neutralization, adsorption bridging, and netting / sweeping, resulting in good flocculation. The flocculation ability of PAC is closely related to its basicity; generally, the basicity of PAC in water treatment agents must be greater than 60%. However, high alkalinity significantly reduces the stability of PAC, easily leading to large amounts of precipitation during storage. Conversely, low PAC basicity causes a significant drop in the pH of the water after adding the flocculant, requiring the addition of alkaline substances to adjust the pH. Furthermore, using PAC alone to treat pulp and paper wastewater also has drawbacks, including slow flocculation speed, poor flocculation effect, easy exceedance of water-insoluble matter and heavy metals, and high production costs. Summary of the Invention

[0004] In view of this, the present invention addresses the shortcomings of current polyaluminum chloride flocculants by providing a polyaluminum chloride sulfate for pulp and paper wastewater and its preparation method. This polyaluminum chloride sulfate can be used in wastewater treatment, drinking water purification, and industrial wastewater treatment, with particularly significant effects in pulp and paper wastewater treatment. The polyaluminum chloride sulfate is produced by adding SO4 during the production process. 2- Polyaluminum chloride molecules are linked together through hydrogen bonds to increase its degree of polymerization. Polyaluminum chloride sulfate is a multi-carboxyl complex with varying forms, composed of aluminum ions, chloride ions, sulfate ions, calcium ions, and iron ions. It has advantages such as rapid flocculation and sedimentation, a wide applicable pH range, and non-corrosiveness to pipes and equipment. Its water purification effect is significant, effectively removing color, suspended particles, heavy metal ions, colloidal substances, and organic matter from water.

[0005] The technical solution of this invention is implemented as follows:

[0006] A method for preparing polyaluminum chloride sulfate for pulp and paper wastewater includes the following steps:

[0007] S1 mixes dilute sulfuric acid, aluminum hydroxide, hydrochloric acid, and water, and stirs to obtain a mixture;

[0008] S2 transfers the mixture to the reactor, opens the steam heating valve of the reactor, and begins the steam heating reaction. First, the steam heating valve is opened to 8-12%. After 10-15 minutes, the opening is increased to 18-22%. As the temperature rises, the opening is increased to 28-32%, and this 28-32% opening is maintained until the temperature reaches 75-85°C. Steam heating is then stopped. By gradually adjusting the opening of the steam heating valve, the preheating time can be controlled, and the temperature can rise steadily, allowing the reaction to proceed fully and orderly.

[0009] After the steam heating of S3 is stopped, sulfuric acid, hydrochloric acid and aluminum hydroxide continue to react. Once the reaction is complete, the reaction solution is obtained.

[0010] S4 Cool the reaction solution and add calcium aluminate slurry while stirring. After adding the calcium aluminate slurry, steam heating reaction is carried out at 120-130℃ for 2-2.5 hours. The temperature is maintained until the reaction is completed, and the reaction material is obtained.

[0011] S5 cools the reaction mixture, filters it, collects the filtrate, and obtains the target product.

[0012] Furthermore, by weight, the dilute sulfuric acid comprises 22-30 parts, aluminum hydroxide 6-8 parts, hydrochloric acid 15-20 parts, calcium aluminate slurry 48-52 parts, and water 5-20 parts.

[0013] Furthermore, the calcium aluminate slurry is obtained by adding calcium aluminate powder to water and stirring at a mass ratio of 18-20:5-7.

[0014] Furthermore, in step S1, the stirring rate is 80-100 r / min, and the stirring time is 10-20 min.

[0015] Furthermore, in step S2, the steam heating valve is first opened to 9-11%, and after 10 minutes, the steam heating valve is opened to 19-21%. When the temperature rises, the steam heating valve is opened to 29-31%, and the opening is maintained at 29-31% until the temperature rises to 78-82°C, at which point the steam heating is stopped.

[0016] Furthermore, in step S3, sulfuric acid, hydrochloric acid, and aluminum hydroxide continue to react until the temperature rises to 115–125°C, and the reaction continues for 2–2.5 hours to obtain a reaction solution.

[0017] Furthermore, in step S4, the reaction solution is cooled to 85-95°C for 25-35 minutes; in step S4, the time for adding calcium aluminate slurry to the reaction solution is 15-20 minutes; and the heat preservation time is 1-1.5 hours.

[0018] Furthermore, in step S5, the reaction solution is cooled to 75-85°C.

[0019] On the other hand, the present invention provides polyaluminum chloride sulfate prepared by the above-mentioned preparation method. The polyaluminum chloride sulfate has a significant water purification effect and can effectively remove color, suspended particles, heavy metal ions, colloidal substances and organic matter from water. Compared with traditional PAC, it has a better treatment effect on pulp and paper wastewater and a lower cost.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] The polyaluminum chloride sulfate provided by this invention has a significant effect on the treatment of pulp and paper wastewater. It can effectively reduce the total soluble solids content and chemical oxygen demand of pulp and paper wastewater. Compared with traditional PAC, the polyaluminum chloride sulfate of this invention has a better treatment effect on pulp and paper wastewater and is also cheaper.

[0022] This invention appropriately introduces low-concentration waste sulfuric acid, a byproduct of caustic soda plants, and through scientific adjustment of raw material ratios, reduces the content of Al2O3 and hydrochloric acid in the product without affecting the wastewater treatment effect of polyaluminum chloride, resulting in a cost advantage.

[0023] This invention ensures the basicity of polyaluminum chloride sulfate by using appropriate reaction temperature, time, and pressure, while reducing the occurrence of crystallization and precipitation during storage, thus guaranteeing stability.

[0024] This invention achieves better regulation of the aluminum content and basicity of polyaluminum sulfate by uniformly controlling various parameters during the production process, effectively controlling the reaction, and finding the optimal ratio of polyaluminum sulfate for treating pulp and paper wastewater, resulting in good wastewater treatment effect. Attached Figure Description

[0025] Figure 1 This is a diagram illustrating the production process of polyaluminum chloride sulfate according to the present invention. Detailed Implementation

[0026] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0027] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0028] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0029] Example 1

[0030] The preparation method of polyaluminum chloride sulfate includes the following steps:

[0031] (1) Add 30 parts dilute sulfuric acid, 8 parts aluminum hydroxide, 20 parts hydrochloric acid and 5 parts water to the mixing tank according to the weight, start the stirring paddle, adjust the stirring speed to 90 rpm, stir for 15 minutes, and stir thoroughly until uniform.

[0032] (2) Use a slurry transfer pump to transfer the slurry into the reactor. Open the steam heating valve of the reactor to start heating. First, open the valve to 10%, and after 10 minutes, open it to 20% and 30% to control the temperature to rise steadily. After 1 hour, when the temperature rises to 80°C, stop steam heating.

[0033] (3) After heating is stopped, sulfuric acid, hydrochloric acid and aluminum hydroxide will continue to react. The temperature rises to 120°C. After 2 hours of reaction, the reaction is complete and the reaction solution becomes a transparent liquid.

[0034] (4) Slowly add cooling water to lower the temperature, control the temperature to drop slowly, and take 30 minutes to lower the temperature to 90℃.

[0035] (5) Add 36 parts of water to the calcium aluminate mixing tank, start the stirring paddle, slowly add 14 parts of calcium aluminate powder, and stir thoroughly to form calcium aluminate slurry.

[0036] (6) Transfer the calcium aluminate slurry into the reactor using a slurry transfer pump to start the polymerization reaction. Control the transfer speed and the transfer time to 15 to 20 minutes. During this process, the reactor agitator must not be stopped.

[0037] (7) After the calcium aluminate slurry is transferred, the heating operation is carried out. The steam heating valve is opened and the temperature is slowly raised to 120-130℃. After reacting for 2 hours under this temperature condition, the steam heating valve is closed and the temperature is maintained for 1 hour. The reaction is then complete.

[0038] (8) Start the reaction material cooling operation. After cooling to 80°C, put the material into the clarification tank and use a filter pump to extract the clarified liquid for filtration to obtain the filtrate, which is the product polyaluminum chloride sulfate.

[0039] This product is named #1 Polyaluminum Chloride Sulfate.

[0040] Example 2

[0041] The preparation method of polyaluminum chloride sulfate includes the following steps:

[0042] (1) Add 22 parts dilute sulfuric acid, 6 parts aluminum hydroxide, 15 parts hydrochloric acid and 20 parts water to the mixing tank according to the weight, start the stirring paddle, adjust the stirring speed to 90 rpm, stir for 15 minutes, and stir thoroughly until uniform.

[0043] (2) Use a slurry transfer pump to transfer the slurry into the reactor. Open the steam heating valve of the reactor to start heating. First, open the valve to 10%, and after 10 minutes, open it to 20% and 30% to control the temperature to rise steadily. After 1 hour, when the temperature rises to 80°C, stop steam heating.

[0044] (3) After heating is stopped, sulfuric acid, hydrochloric acid and aluminum hydroxide will continue to react. The temperature rises to 120°C. After 2 hours of reaction, the reaction is complete and the reaction solution becomes a transparent liquid.

[0045] (4) Slowly add cooling water to lower the temperature, control the temperature to drop slowly, and take 30 minutes to lower the temperature to 90℃.

[0046] (5) Add 40 parts of water to the calcium aluminate mixing tank, start the stirring paddle, slowly add 10 parts of calcium aluminate powder, and stir thoroughly to form calcium aluminate slurry.

[0047] (6) Transfer the calcium aluminate slurry into the reactor using a slurry transfer pump to start the polymerization reaction. Control the transfer speed and the transfer time to 15 to 20 minutes. During this process, the reactor agitator must not be stopped.

[0048] (7) After the calcium aluminate slurry is transferred, the heating operation is carried out. The steam heating valve is opened and the temperature is slowly raised to 120-130℃. After reacting for 2 hours under this temperature condition, the steam heating valve is closed and the temperature is maintained for 1 hour. The reaction is then complete.

[0049] (8) Start the reaction material cooling operation. After cooling to 80°C, put the material into the clarification tank and use a filter pump to extract the clarified liquid for filtration to obtain the filtrate, which is the product polyaluminum chloride sulfate.

[0050] This product is named No. 2 Polyaluminum Chloride Sulfate.

[0051] Comparative Example 1

[0052] (1) According to Al(OH)3:HCl:H2O = 800KG:4.5m3:0.6m 3 In the specified proportions, aluminum hydroxide, hydrochloric acid, and water are added sequentially to the mixing vessel and stirred for 10 minutes.

[0053] (2) Use a slurry transfer pump to transfer the slurry into the reactor. Open the steam heating valve of the reactor to start heating. First, open the valve to 25%, then open it to 50% after 10 minutes, then to 75% after 5 minutes, and finally to 100% after 5 minutes. When the temperature rises to 80°C, close the steam heating valve and let the reaction continue. When Al(OH)3 is completely dissolved and the turbid liquid becomes a transparent liquid, the reaction is complete.

[0054] (3) Slowly increase the cooling water to lower the temperature, and control the temperature to drop slowly to 110℃;

[0055] (4) Add 3500 kg of water to the calcium aluminate mixing tank, start the stirring paddle, slowly add 1500 kg of calcium aluminate powder, and stir thoroughly to form a calcium aluminate slurry.

[0056] (5) Transfer the calcium aluminate slurry into the reactor using a slurry transfer pump to start the polymerization reaction. Control the transfer speed and the transfer time to 15 to 20 minutes. During this process, the reactor agitator must not be stopped.

[0057] (6) Open the steam heating valve of the reactor to start heating. First, open the valve to 25%, then open it to 50% after 10 minutes, then to 75% after 5 minutes, and finally to 100% after 5 minutes. When the temperature rises to 110℃, close the steam heating valve and start heat preservation. The heat preservation time is 60 minutes. During the heat preservation process, maintain the temperature between 115-125℃ and the pressure at 0.2MPa.

[0058] (7) When the temperature drops to 90°C, the material is discharged into the clarification tank and the clarified liquid is extracted by a filter pump for filtration to obtain the filtrate, which is the product polyaluminum chloride.

[0059] This product is named Traditional PAC.

[0060] Experimental Example 1

[0061] A comparative experiment was conducted between the polyaluminum chloride sulfate obtained in Examples 1-3 and polyaluminum chloride, and the results are as follows:

[0062] Table 1

[0063]

[0064]

[0065] The data on the new product's application in pulp and paper wastewater, compared with traditional PAC (dosage of 120 ppm), show the following results for total soluble solids (TSS) and chemical oxygen demand (COD):

[0066] Table 2

[0067]

[0068] As shown in Tables 1 and 2 above, after comparative testing and analysis using the new product and the traditional PAC, the effect of No. 1 polyaluminum chloride is significantly better than that of the original PAC, and the wastewater treatment effect of No. 3 polyaluminum chloride is better than that of PAC. Moreover, the material cost is only 68% of that of PAC, which has a significant advantage.

[0069] Comparative Example 2

[0070] Compared with Example 1, the preparation method of polyaluminum chloride sulfate in this comparative example is different. The specific steps are as follows:

[0071] (1) Add 30 parts dilute sulfuric acid, 8 parts aluminum hydroxide, 20 parts hydrochloric acid and 5 parts water to the mixing vessel according to the weight, start the stirring paddle, adjust the stirring speed to 90 rpm, stir for 15 minutes, and react for 3 hours at 0.5 MPa and 140℃ to obtain the reaction solution.

[0072] (2) Add 36 parts of water to the calcium aluminate mixing tank, start the stirring paddle, slowly add 14 parts of calcium aluminate powder, and stir thoroughly to form calcium aluminate slurry.

[0073] (3) Add 0.05 parts of sodium aluminate to 10 parts of aluminum sulfate solution (containing 8% aluminum oxide), and react at 80°C under normal pressure for 3 hours to obtain aluminum sulfate reaction solution;

[0074] (4) Add calcium aluminate slurry to the reaction solution and control the transfer time to 15 to 20 minutes. During this process, the stirring paddle of the reactor should not be stopped. After reacting at 100°C under normal pressure for 1 hour, add aluminum sulfate reaction solution and react at 80°C under normal pressure for 2 hours to obtain the reaction product.

[0075] (5) Filter the reaction product to obtain polyaluminum chloride sulfate.

[0076] In Comparative Example 2, the removal efficiency of polyaluminum sulfate in pulp and paper wastewater was as follows: TSS removal efficiency was 760 mg / L before dosing and 155 mg / L after dosing; COD removal efficiency was 1542 mg / L before dosing and 1105 mg / L after dosing.

[0077] Comparative Example 3

[0078] Compared with Example 1, the preparation conditions of polyaluminum chloride sulfate in this comparative example have been adjusted. The specific steps are as follows:

[0079] (1) Add 30 parts dilute sulfuric acid, 8 parts aluminum hydroxide, 20 parts hydrochloric acid and 5 parts water to the mixing tank according to the weight, start the stirring paddle, adjust the stirring speed to 90 rpm, stir for 15 minutes, and stir thoroughly until uniform.

[0080] (2) Use a slurry transfer pump to transfer the slurry into the reactor. Open the steam heating valve of the reactor to start heating. First, open the valve to 20%, and after 20 minutes, open it to 30%. Control the temperature to rise steadily at 40% opening until the temperature reaches 100℃, then stop steam heating.

[0081] (3) After heating is stopped, sulfuric acid, hydrochloric acid and aluminum hydroxide will continue to react. The temperature rises to 140°C. After 2 hours of reaction, the reaction is complete and the reaction solution becomes a transparent liquid.

[0082] (4) Slowly add cooling water to lower the temperature, control the temperature to drop slowly, and take 30 minutes to lower the temperature to 90℃.

[0083] (5) Add 36 parts of water to the calcium aluminate mixing tank, start the stirring paddle, slowly add 14 parts of calcium aluminate powder, and stir thoroughly to form calcium aluminate slurry.

[0084] (6) Transfer the calcium aluminate slurry into the reactor using a slurry transfer pump to start the polymerization reaction. Control the transfer speed and the transfer time to 15 to 20 minutes. During this process, the reactor agitator must not be stopped.

[0085] (7) After the calcium aluminate slurry is transferred, the heating operation is carried out. The steam heating valve is opened and the temperature is slowly raised to 120-130℃. After reacting for 2 hours under this temperature condition, the steam heating valve is closed and the temperature is maintained for 1 hour. The reaction is then complete.

[0086] (8) Start the reaction material cooling operation. After cooling to 80°C, put the material into the clarification tank and use a filter pump to extract the clarified liquid for filtration to obtain the filtrate, which is the product polyaluminum chloride sulfate.

[0087] In Comparative Example 3, the removal efficiency of polyaluminum sulfate in pulp and paper wastewater was as follows: TSS removal efficiency: 760 mg / L before dosing and 170 mg / L after dosing; COD removal efficiency: 1542 mg / L before dosing and 1212 mg / L after dosing.

[0088] 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. A method for preparing polyaluminum chloride for pulp and papermaking wastewater, characterized by, Includes the following steps: S1. Mix dilute sulfuric acid, aluminum hydroxide, hydrochloric acid and water, and stir to obtain a mixture; by weight, the dilute sulfuric acid is 22-30 parts, aluminum hydroxide is 6-8 parts, hydrochloric acid is 15-20 parts, calcium aluminate slurry is 48-52 parts and water is 5-20 parts. S2. Transfer the mixture to the reactor, open the steam heating valve of the reactor, and carry out steam heating reaction. First, open the steam heating valve to 8~12%, and after 10~15 minutes, open the steam heating valve to 18~22%. When the temperature rises, open the steam heating valve to 28~32%, and maintain the 28~32% opening until the temperature rises to 75~85℃, then stop steam heating. After S3 stops steam heating, sulfuric acid, hydrochloric acid and aluminum hydroxide continue to react until the temperature rises to 115~125℃. After the reaction is completed in 2~2.5 hours, the reaction solution is obtained. S4. Cool the reaction solution to 85~95℃ for 25~35 min, add calcium aluminate slurry while stirring, and add the calcium aluminate slurry in 15~20 min. Then, heat the reaction with steam at 120~130℃ for 2~2.5 h, keep warm for 1~1.5 h, and the reaction is complete to obtain the reaction material. S5 cools the reaction mixture, filters it, collects the filtrate, and obtains the target product.

2. A method for preparing polyaluminum chloride for pulp and paper mill effluent according to claim 1, characterized by, The calcium aluminate slurry is obtained by adding calcium aluminate powder to water and stirring at a mass ratio of 18~20:5~7.

3. The method for preparing polyaluminum chloride sulfate for pulp and paper wastewater according to claim 1, characterized in that, In step S1, the stirring rate is 80~100 r / min, and the stirring time is 10~20 min.

4. The method for preparing polyaluminum chloride sulfate for pulp and paper wastewater according to claim 1, characterized in that, In step S2, first open the steam heating valve to 9-11%, and after 10 minutes, open the steam heating valve to 19-21%. When the temperature rises, open the steam heating valve to 29-31% and maintain the 29-31% opening until the temperature rises to 78-82℃, then stop steam heating.

5. The method for preparing polyaluminum chloride sulfate for pulp and paper wastewater according to claim 1, characterized in that, In step S5, the reaction solution is cooled to 75~85℃.

6. Polyaluminum chloride sulfate prepared by the method according to any one of claims 1 to 5.

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