Process for the preparation of polyaluminum chloride

Abstract

The present application relates to the technical field of polyaluminum chloride, and particularly relates to a preparation process of polyaluminum chloride, which comprises the following steps: firstly, 31.0-33.0% hydrochloric acid is added into a reaction kettle, stirring is carried out and a micro-negative pressure is maintained, aluminum hydroxide is added in batches, heating is carried out to 70±2 DEG C, and then the reaction is maintained for 3-4 hours to obtain a one-step material. Then, the one-step material is transferred into a neutralization kettle, calcium aluminate powder is added, stirring is carried out, and the reaction is carried out at 85-95 DEG C for 0.5-0.8 hours. Then, diatomite and polyacrylamide are added, and the filter liquor is obtained through pressure filtration. Finally, the filter liquor is cooled through a graphite heat exchanger, the concentration is adjusted, and corresponding additives are added to obtain the polyaluminum chloride product. The temperature, pressure and stirring speed are accurately controlled in the whole process to ensure the product quality. The present application adopts the technical measures of batch feeding, accurate control of the reaction temperature and addition of synergistic agents, so that the product has a more reasonable aluminum polymer distribution structure, and the turbidity removal rate is increased to 99.2-99.5%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyaluminum chloride, and particularly relates to a preparation process of polyaluminum chloride. BACKGROUND

[0002] Polyaluminum chloride (PAC) as a kind of efficient inorganic coagulant, has a wide application in the fields of drinking water treatment, industrial wastewater treatment, municipal sewage treatment and papermaking industry. Its main component is polynuclear hydroxy aluminum chloride, which forms a polynuclear structure with high charge density through complex reactions such as hydrolysis, polymerization and addition, and has good flocculation performance and wide pH range.

[0003] The traditional preparation methods of polyaluminum chloride mainly include aluminum hydroxide method, aluminum ash method, calcium aluminate method and metal aluminum method. Among them, the aluminum hydroxide method is widely used because of the wide source of raw materials and the relatively simple process. The method usually reacts aluminum hydroxide with hydrochloric acid at a certain temperature, and the polyaluminum chloride product is prepared through hydrolysis and polymerization process. However, the aluminum hydroxide method in the prior art still has a series of problems to be solved:

[0004] 1. Insufficient stability: the polyaluminum chloride product prepared by the traditional process is easy to continue to polymerize during long-term storage, which leads to a decrease in effective components, forms insoluble precipitates, and affects the product quality and use effect.

[0005] 2. Poor low temperature adaptability: the conventional product has a significant decrease in coagulation effect under low temperature conditions (5-10℃), which limits its application in cold seasons or cold regions, and cannot meet the water treatment demand in all seasons and all weather.

[0006] 3. High fluorine content: when using the by-product hydrochloric acid of fluorine chemical enterprise as raw material, the residual fluorine content in the product is high, which limits its application in the field of drinking water treatment, and also causes serious corrosion to the production equipment.

[0007] 4. High energy consumption: especially in the preparation process of solid products, the traditional drying process has high energy consumption and low thermal efficiency, which increases the production cost.

[0008] 5. Environmental pollution: if the acid mist, dust and other waste gas generated in the production process and the aluminum-containing and fluorine-containing wastewater are not properly treated, they will cause serious pollution to the environment.

[0009] 6. Unbalanced product performance: the traditional one-step production process is difficult to accurately control the reaction process, which leads to uneven distribution of aluminum polymers in the product and unstable coagulation effect.

[0010] With the increasingly stringent environmental requirements and the continuous progress of water treatment technology, the market demand for efficient, stable and environmentally friendly polyaluminum chloride products is growing. Therefore, developing a new type of polyaluminum chloride preparation process to solve the above problems has important theoretical significance and practical value. SUMMARY

[0011] The main purpose of the present application is to provide an efficient, stable and environmentally friendly polyaluminum chloride preparation process to solve the problems in the prior art.

[0012] The present application provides a polyaluminum chloride preparation process, comprising the following steps:

[0013] (1) Polymerization reaction: 31.0-33.0 wt% of hydrochloric acid 100.0-120.0 parts by weight is added to the reaction kettle, and stirring is started. Under the condition of micro negative pressure -50Pa to -100Pa, 30.0-35.0 parts by weight of aluminum hydroxide is added in batches, heated to 70±2℃, then stopped heating, and incubated at 90-100℃ for 3.0-4.0 hours to obtain a one-step material;

[0014] (2) Neutralization reaction: the one-step material is transferred to the neutralization kettle, and under the condition of micro negative pressure -50Pa to -100Pa, 5.0-8.0 parts by weight of calcium aluminate powder is added in 3-5 times according to the ratio of one-step material 100.0 parts by weight, with an interval of 5-8 minutes each time, and the stirring speed is 180-220 rpm. Reaction at 85-95℃ for 0.5-0.8 hours;

[0015] (3) Filter pressing: 0.2-0.5 parts by weight of diatomite and 0.01-0.03 parts by weight of polyacrylamide are added to the material after the neutralization reaction, and then filter pressing is carried out under the pressure of 0.6-0.8 MPa to obtain a filtrate;

[0016] (4) Modulation: the filtrate is cooled by graphite heat exchanger, and the concentration is adjusted according to the product type and the corresponding additives are added to obtain polyaluminum chloride product.

[0017] Specifically, the way of adding aluminum hydroxide in batches in step (1) is: first add 20% of the total amount, then add 30% of the total amount after 5-10 minutes of reaction, and then add 50% of the total amount after 10-15 minutes of reaction; the content of aluminum hydroxide is ≥99.0 wt%, and the fineness is 100-200 mesh.

[0018] Specifically, 0.05-0.1 parts by weight of an alkaline phosphate and 0.2-0.5 parts by weight of MgSO4·7H2O are further added in the step (2); the CaO·Al2O3 content of the calcium aluminate powder is 65.0-75.0% by weight, and the fineness is 200-325 mesh.

[0019] Specifically, the step of modulating further comprises:

[0020] (a) when preparing dilute polyaluminum chloride, the concentration of the filtrate is adjusted to 10.0±0.2% by weight, and 0.1-0.2 parts by weight of trisodium citrate, 0.05-0.1 parts by weight of modified polyacrylic acid, and 0.01-0.02 parts by weight of MnCl2·4H2O are added; or

[0021] (b) when preparing concentrated polyaluminum chloride, the concentration of the filtrate is adjusted to 12.5±0.3% by weight, and 0.1-0.2 parts by weight of a composite stabilizer is added.

[0022] Specifically, the process further comprises a raw material pretreatment step: 0.1-0.2 parts by weight of H2O2 is added to the hydrochloric acid for pretreatment; 0.1-0.3 parts by weight of FeCl3·6H2O is further added in the step (1); and 0.2-0.4 parts by weight of Al2(SO4)3·18H2O is further added in the step (2).

[0023] Specifically, the process further comprises a waste gas treatment step: the waste gas generated in the process is discharged after sequentially passing through two-stage water spray absorption and one-stage lye spray absorption; wherein the pH values of the water spray are 6-7 and 7-8 respectively, and the pH value of the lye spray is 10-11; the waste gas treatment adopts polypropylene Bauer rings and ceramic Raschig rings mixed fillers, the packing density is 120-150 kg / m³, the height of the filler layer is 1.2-1.5 m per layer, and the cyclone plate and the filler are arranged alternately.

[0024] A preparation process of solid polyaluminum chloride, comprising the following steps:

[0025] (1) preparing concentrated polyaluminum chloride with a concentration of 12.5±0.3% by weight according to the method;

[0026] (2) spray drying: preheating the concentrated polyaluminum chloride to 60-70℃, conveying it to a spray drying buffer tank through a spray drying feed pump, and performing spray drying under hot air at 320-350℃ using a double-fluid nozzle (gas-liquid ratio 2:1-3:1), with the outlet temperature controlled at 90-110℃ and the tower internal negative pressure at -0.001 MPa, to obtain solid polyaluminum chloride;

[0027] (3) Packaging: the solid polyaluminum chloride is conveyed to a packaging device by an auger conveyor for packaging, and the packaging specification is 25±0.2 kg / bag.

[0028] Specifically, in the step (2), 0.1-0.3 parts by weight of nano-silicon dioxide is added into the concentrated polyaluminum chloride as a flowability modifier; the Al2O3 content of the obtained solid polyaluminum chloride is ≥28.0% by weight, the insoluble content is ≤0.5% by weight, and the moisture content is ≤5.0% by weight.

[0029] Specifically, in the step (3), a polyethylene plastic bag with a thickness of 0.08-0.10 mm is used as an inner layer, a polypropylene woven bag is used as an outer layer for packaging, and 3-5 g of a desiccant is added into the packaging bag.

[0030] Specifically, the waste gas generated in the spray drying process is discharged through a 25 m high exhaust cylinder after sequentially passing through a first cyclone dust collector, a first semi-finished product solution spray, a first water spray and a first lye spray; the process further comprises a recycling step: the hot gas (90-110℃) discharged from the spray drying is used to preheat the neutralization reaction feed, and part of the waste gas washing water is recycled for the production of dilute polyaluminum chloride.

[0031] The beneficial effects of the present application are:

[0032] By adopting the polyaluminum chloride preparation process provided by the present application, the following significant beneficial effects can be obtained:

[0033] 1. The coagulation effect is significantly improved: the present application adopts batch feeding, accurate control of reaction temperature and addition of synergistic agents and other technical measures, so that the product has a more reasonable aluminum polymer distribution structure, the turbidity removal rate is increased to 99.2-99.5%, which is 2-3 percentage points higher than that of traditional products; the flocculation formation speed is fast (1.0-1.8 min), the flocculation settling speed is high (2.5-3.5 cm / min), and the water treatment efficiency is greatly improved.

[0034] 2. The low-temperature adaptability is greatly enhanced: by adding iron salt, manganese salt and other synergistic activators, the product of the present application still maintains a removal rate of 98.6-99.0% at a low temperature of 5℃, and the efficiency retention rate at normal temperature reaches 99.2-99.7%, which is much higher than that of traditional products of 84.9-92.3%, solving the problem of water treatment in winter.

[0035] 3. The product stability is significantly improved: through the optimization of neutralization reaction, the addition of basic phosphate and the addition of composite stabilizer, the product of the present application still maintains good stability after long-term storage (6 months), the change of Al2O3 content is small (-0.5 to -1.0%), the retention rate of coagulation effect is high (92.5-96.5%), the amount of sediment produced is small (1.0-1.8%), and the effective service life of the product is prolonged.

[0036] 4. The performance of the solid product is greatly improved: through the optimization of the spray drying process, the application of the double-fluid nozzle and the addition of nano-silicon dioxide, the solid product of the present application has excellent solubility (dissolution time 2.5-2.8 min) and low insoluble content (0.25-0.35%), and low hygroscopicity (30-day hygroscopicity only 2.8-3.2%), which significantly improves the convenience of use of the product.

[0037] 5. The fluorine content is significantly reduced: through the raw material pretreatment technology, especially the addition of calcium oxide for pre-deposition, the fluorine content of the fluorine-free product of the present application is reduced to 45 ppm, which is much lower than the 1800 ppm of the traditional product, making the product more suitable for drinking water treatment, and the residual amount of fluorine in the treated water meets the drinking water standard requirements.

[0038] 6. The resource and energy conservation is significantly improved: through the comprehensive application of heat energy cascade utilization, wastewater recycling and high-efficiency waste gas treatment system, the wastewater generation of the present application is reduced by 33-40%, the waste gas treatment efficiency is improved by 7.5-14.8 percentage points, the COD and fluoride emissions are reduced by 58-86% and 93-96% respectively, which greatly reduces the production cost and environmental impact.

[0039] 7. The application range is more extensive: through the adjustment of process parameters and the addition of additive ratio, the present application can prepare different products such as dilute polyaluminum chloride (10%), concentrated polyaluminum chloride (12.5%) and solid polyaluminum chloride (≥28%) according to the needs, which meets the needs of different application scenarios from urban drinking water treatment to industrial wastewater treatment.

[0040] 8. The economic benefit is significant: the present application process makes full use of the by-product hydrochloric acid of fluorine chemical industry, which converts waste into valuable products, reduces raw material cost and environmental burden; at the same time, the performance improvement of the product reduces the dosage by 10-20% in actual application, further reducing the use cost of the user.

[0041] In summary, through the comprehensive application of a series of innovative technical measures, the present application successfully solves the shortcomings of the traditional polyaluminum chloride production process in product performance, stability, adaptability, environmental protection, etc., has significant technical advancement and practical value, and provides a high-efficiency, stable and environmentally-friendly polyaluminum chloride preparation process for the water treatment field. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The production process of the dilute polyaluminum chloride of the present application is shown in the figure.

[0043] Figure 2 The production process of the dilute polyaluminum chloride of the present application is shown in the figure. DETAILED DESCRIPTION

[0044] Example 1: Preparation of dilute polyaluminum chloride

[0045] This example provides a preparation process of dilute polyaluminum chloride, which is prepared by a two-step method. By precisely controlling the reaction conditions, a product with good stability and excellent coagulation effect is obtained.

[0046] Specifically, the preparation process of this example includes the following steps:

[0047] (1) Polymerization reaction: First, 31.0 wt% hydrochloric acid 100.0 parts by weight is added to the reaction kettle, and the stirring is started, and the rotation speed is adjusted to 200 rpm. Under the condition of micro negative pressure-50 Pa, 30.0 parts by weight of aluminum hydroxide (content 99.0 wt%, fineness 150 μm) is added in batches, among which 20% (6.0 parts by weight) of the total amount is first added, 30% (9.0 parts by weight) of the total amount is added after 5 minutes of reaction, and 50% (15.0 parts by weight) of the total amount is added after 10 minutes of reaction. Then, it is heated to 70℃ by steam indirect heating, and the heating is stopped, the temperature is naturally raised to 90℃ by reaction heat, and it is kept at this temperature for 3.0 hours to obtain a one-step material.

[0048] In this step, the batch addition of aluminum hydroxide can effectively control the reaction heat release rate, avoid the temperature fluctuation, and improve the complexing degree of aluminum ions. Preferably, the appropriate stirring speed is maintained during the reaction to ensure uniform reaction, while avoiding excessive bubbles caused by too fast stirring.

[0049] (2) Neutralization reaction: All the one-step material is transferred into the neutralization kettle, and under the condition of micro negative pressure-60 Pa, the calcium aluminate powder (CaO·Al2O3 content 70.0 wt%, fineness 200 mesh) is added in a ratio of 100.0 parts by weight of one-step material to 5.0 parts by weight of calcium aluminate powder, in 3 times with an interval of 6 minutes, and 0.05 parts by weight of basic phosphate (Na3PO4) and 0.2 parts by weight of MgSO4·7H2O are added at the same time. The stirring speed is adjusted to 180 rpm, and the reaction is carried out at 85℃ for 0.5 hours.

[0050] The addition of basic phosphate in this step can promote the formation of Al-OH-Cl bond and improve the stability of the product, and the magnesium sulfate can form a synergistic complex structure with calcium aluminate to further enhance the stability of the product.

[0051] (3) Filter pressing: 0.2 parts by weight of diatomite and 0.01 parts by weight of polyacrylamide were added to the material after neutralization reaction, and after being mixed thoroughly, the material was sent to a plate-and-frame filter press, and filter pressing was performed under a pressure of 0.6 MPa to obtain a filtrate.

[0052] The use of diatomite as a filter aid can significantly improve the filtration performance, reduce the moisture content of the filter cake, and improve the filtration efficiency. The addition of an appropriate amount of polyacrylamide can further enhance the flocculation effect and make the filtrate clearer.

[0053] (4) Modulation: The filtrate was cooled to 30°C through a graphite heat exchanger, and according to the result of the Baume test, an appropriate amount of softened water was added to adjust the concentration to 10.0% by weight (Al2O3 content). Then 0.1 parts by weight of trisodium citrate, 0.05 parts by weight of modified polyacrylic acid, and 0.01 parts by weight of MnCl2·4H2O were added, and after being mixed thoroughly, the final dilute polyaluminum chloride product was obtained.

[0054] The trisodium citrate added in this step acts as a stabilizer, which can effectively prevent the hydrolysis of aluminum salts; the modified polyacrylic acid acts as a anti-settling agent, which can improve the storage stability of the product; and a small amount of manganese salt acts as an activator, which can significantly improve the coagulation effect of the product.

[0055] (5) Waste gas treatment: The waste gas generated during the entire production process was discharged through a 20m high exhaust pipe after being sequentially absorbed by two-stage water spray (pH values were 6 and 7 respectively) and one-stage 10% NaOH lye spray (pH value was 10). The waste gas treatment system used a mixed packing of polypropylene Pall ring and ceramic Raschig ring with a packing density of 120 kg / m³, and each layer of packing had a height of 1.2m. The system also used a cyclone plate and packing alternately arranged to greatly improve the gas-liquid contact efficiency.

[0056] The final dilute polyaluminum chloride product had the following properties: Al2O3 content 10.0% by weight, alkalinity 35%, pH value (1% solution) 3.8, relative density (20°C) 1.22, and turbidity ≤10 NTU.

[0057] Example 2: Preparation of concentrated polyaluminum chloride

[0058] This example provides a preparation process for concentrated polyaluminum chloride, which obtains a product with high concentration and high stability by optimizing the reaction parameters and adding synergistic agents.

[0059] Specifically, the preparation process of this example includes the following steps:

[0060] (1) Raw material pretreatment: 120.0 parts by weight of 33.0% hydrochloric acid was taken, 0.2 parts by weight of H2O2 (based on the weight of hydrochloric acid) was added, and the mixture was stirred uniformly and left to stand for 1 hour to make Fe2+ fully oxidized to Fe 3+ , to improve the color stability of the product.

[0061] (2) Polymerization reaction: After the pretreated hydrochloric acid is added to the reaction kettle, the stirring is started, and the rotation speed is adjusted to 250 rpm. Under the condition of micro negative pressure -80 Pa, 35.0 parts by weight of aluminum hydroxide (content 99.5% by weight, fineness 120 μm) and 0.3 parts by weight of FeCl3·6H2O as a synergistic flocculation factor are added in batches. After heating to 70°C, the heating is stopped, and the reaction is naturally heated to 100°C by heat release, and the reaction is kept for 4.0 hours to obtain a one-step material.

[0062] In this step, the addition of an appropriate amount of ferric chloride as a synergistic flocculation factor can form a composite flocculation system with aluminum ions, significantly improving the coagulation performance of the product, especially for low temperature water treatment.

[0063] (3) Neutralization reaction: The one-step material is transferred into the neutralization kettle, and under the condition of micro negative pressure -100 Pa, the calcium aluminate powder (CaO·Al2O3 content 75.0% by weight, fineness 325 mesh) is added in a ratio of 8.0 parts by weight to 100.0 parts by weight of the one-step material in 5 times, with an interval of 8 minutes each time. At the same time, 0.1 parts by weight of alkaline phosphate (Na3PO4), 0.5 parts by weight of MgSO4·7H2O and 0.4 parts by weight of Al2(SO4)3·18H2O are added as structure adjusting agents. The stirring speed is adjusted to 220 rpm, and the reaction is carried out at 95°C for 0.8 hours.

[0064] The addition of aluminum sulfate as a structure adjusting agent in this step can adjust the polymerization degree distribution of the product, optimize the coagulation performance and stability of the product, and effectively prevent the product from being turbid and precipitating under high concentration conditions.

[0065] (4) Filter pressing: Diatomite 0.5 parts by weight and polyacrylamide 0.03 parts by weight are added to the material after the neutralization reaction, and after mixing, they are sent into a plate and frame filter press for filter pressing under a pressure of 0.8 MPa to obtain a filtrate.

[0066] (5) Preparation: The filtrate is cooled to 35°C by a graphite heat exchanger, the concentration is adjusted to 12.5% by weight (Al2O3 content) according to the result of the Baumé test, and a composite stabilizer (a mixture of phosphate and polymer) 0.2 parts by weight is added, and after mixing, the final concentrated polyaluminum chloride product is obtained.

[0067] The addition of the composite stabilizer in this step can effectively prevent the hydrolysis of aluminum salt and the degradation of polymer under high concentration conditions, prolong the shelf life of the product, and maintain stable coagulation performance.

[0068] The obtained concentrated polyaluminum chloride product has the following properties: Al203 content 12.5 wt%, alkalinity 45%, pH value (1% solution) 4.0, relative density (20°C) 1.32, and stable period ≥ 6 months (at room temperature).

[0069] Example 3: Preparation of solid polyaluminum chloride

[0070] This example provides a preparation process of solid polyaluminum chloride, which obtains a solid product with good fluidity and excellent solubility by optimizing the spray drying parameters and adding a fluidity modifier.

[0071] Specifically, the preparation process of this example includes the following steps:

[0072] (1) Preparation of concentrated polyaluminum chloride: prepare concentrated polyaluminum chloride with a concentration of 12.5 wt% according to the method of Example 2.

[0073] (2) Spray drying: preheat the above concentrated polyaluminum chloride to 65°C, and at the same time, add 0.2 parts by weight of nano-silicon dioxide as a fluidity modifier, then transport it to the spray drying buffer tank through the spray drying feed pump. Spray drying is carried out at 340°C with a two-fluid nozzle (gas-liquid ratio 2.5:1), with the outlet temperature controlled at 100°C, and the tower negative pressure at -0.001 MPa, to obtain solid polyaluminum chloride powder.

[0074] In this step, the addition of nano-silicon dioxide as a fluidity modifier can significantly improve the fluidity of the solid product, prevent caking, and at the same time improve the solubility of the product. Preferably, by controlling the inlet temperature and outlet temperature of spray drying, the product can be prevented from excessive pyrolysis while ensuring sufficient evaporation of water, thereby maintaining the activity of the product.

[0075] (3) Packaging: transport the solid polyaluminum chloride powder to the packaging equipment through the auger conveyor, use a polyethylene plastic bag with a thickness of 0.10 mm as the inner layer, and a polypropylene woven bag as the outer layer for packaging, with each bag weighing 25 kg, and add 5 g of desiccant in the packaging bag to prevent the product from absorbing moisture and caking.

[0076] (4) Waste gas treatment: the waste gas generated during the spray drying process is discharged through a 25 m high exhaust pipe after passing through a first cyclone dust collector, a first semi-finished product solution spray, a first water spray (pH 8), and a first 10% NaOH lye spray (pH 11). At the same time, the hot gas (100°C) discharged from the spray drying is used to preheat the neutralization reaction feed, realizing energy recycling.

[0077] The obtained solid polyaluminum chloride product has the following properties: Al2O3 content 30.0 wt%, insoluble content 0.3 wt%, moisture content 3.5 wt%, particle size distribution 95% passing 80 mesh, dissolution time ≤ 3 minutes (in 25°C water).

[0078] Example 4: Preparation of low-aluminum high-efficiency polyaluminum chloride

[0079] This example provides a preparation process of low-aluminum high-efficiency dilute polyaluminum chloride. By adjusting the ratio of aluminum salt and additives and adding an active enhancer, a product with low aluminum content but excellent coagulation effect is obtained.

[0080] Specifically, the preparation process of this example includes the following steps:

[0081] (1) Polymerization reaction: 110.0 parts by weight of 31.5 wt% hydrochloric acid is added to the reaction kettle, and the stirring is started, and the rotation speed is adjusted to 220 rpm. Under the condition of micro negative pressure -70 Pa, 32.0 parts by weight of aluminum hydroxide (content 99.2 wt%, fineness 180 μm) is added in batches, among which 20% of the total amount is added first, 30% of the total amount is added after 8 minutes of reaction, and 50% of the total amount is added after 12 minutes of reaction. At the same time, 0.2 parts by weight of FeCl3·6H2O and 0.01 parts by weight of MnCl2·4H2O are added as synergistic activators. After the temperature is raised to 70°C, the heating is stopped, and the reaction is naturally heated to 95°C by using the reaction heat, and the reaction is kept for 3.5 hours to obtain a one-step material.

[0082] In this step, iron salt and manganese salt are added as synergistic activators at the same time, which can produce significant synergistic effect, and can still maintain excellent coagulation effect under the condition of low aluminum content, and is particularly suitable for treating low turbidity and low temperature water quality.

[0083] (2) Neutralization reaction: all the one-step material is transferred into the neutralization kettle, and under the condition of micro negative pressure -80 Pa, the calcium aluminate powder (CaO·Al2O3 content 68.0 wt%, fineness 250 mesh) is added in a ratio of 6.5 parts by weight to 100.0 parts by weight of the one-step material in 4 times, with an interval of 7 minutes each time. At the same time, 0.08 parts by weight of alkaline phosphate (Na3PO4), 0.3 parts by weight of MgSO4·7H2O and 0.3 parts by weight of Al2(SO4)3·18H2O are added. The stirring speed is adjusted to 200 rpm, and the reaction is carried out at 90°C for 0.6 hours.

[0084] (3) Pressure filtration: diatomite 0.4 parts by weight and polyacrylamide 0.02 parts by weight are added to the material after the neutralization reaction, and after being mixed thoroughly, they are sent into a plate and frame filter press, and pressure filtration is carried out under the pressure of 0.7 MPa to obtain a filtrate.

[0085] (4) Modulation: The filtrate is cooled to 32°C by a graphite heat exchanger, and the concentration is adjusted to 9.0 wt% (Al2O3 content). Then, 0.15 parts by weight of trisodium citrate, 0.08 parts by weight of modified polyacrylic acid, 0.015 parts by weight of MnCl2·4H2O, 0.01 parts by weight of CuSO4·5H2O, and 0.01 parts by weight of ZnCl2 are added, and the final product is obtained after thorough mixing.

[0086] In this step, copper and zinc salts are added as active enhancers, which can further improve the coagulation activity of the product, so that excellent coagulation effect can be obtained even with lower concentration of polyaluminum chloride, while reducing the cost of the product and the impact on the environment.

[0087] (5) Waste gas treatment: The waste gas is treated according to the method of Example 1.

[0088] The obtained low-aluminum high-efficiency polyaluminum chloride product has the following properties: Al2O3 content 9.0 wt%, alkalinity 40%, pH value (1% solution) 4.2, relative density (20°C) 1.20, and coagulation effect equivalent to that of a conventional 10.0 wt% product.

[0089] Example 5: Preparation of high-alkalinity polyaluminum chloride

[0090] This example provides a preparation process for high-alkalinity concentrated polyaluminum chloride. By adjusting the process parameters and the ratio of additives, a product with high alkalinity and stability is obtained, which is particularly suitable for high-turbidity water treatment.

[0091] Specifically, the preparation process of this example includes the following steps:

[0092] (1) Raw material pretreatment: Take 115.0 parts by weight of 32.0 wt% hydrochloric acid, add 0.15 parts by weight of H2O2, stir uniformly, and stand for 1.5 hours for pretreatment.

[0093] (2) Polymerization reaction: The pretreated hydrochloric acid is added to the reaction kettle, and the stirring is started with the rotation speed adjusted to 230 rpm. Under the condition of micro-negative pressure -60 Pa, 33.0 parts by weight of aluminum hydroxide (content 99.3 wt%, fineness 130 μm) and 0.15 parts by weight of FeCl3·6H2O are added in batches. After the temperature rises to 70°C, stop heating, and use the reaction heat to naturally raise the temperature to 92°C, and keep the reaction for 3.2 hours to obtain a one-step material.

[0094] (3) Neutralization reaction: The material from the previous step was transferred into a neutralization reactor, and under the condition of -90 Pa, 7.0 parts by weight of calcium aluminate powder (CaO-Al2O3 content 72.0% by weight, fineness 280 mesh) was added in four portions with an interval of 7 minutes, according to the ratio of 100.0 parts by weight of the material from the previous step. At the same time, 0.07 parts by weight of an alkaline phosphate, 0.4 parts by weight of MgSO4-7H2O, 0.2 parts by weight of Al2(SO4)3-18H2O, and 0.1 parts by weight of Na2CO3 were added as alkalinity regulators. The stirring speed was adjusted to 210 rpm, and the reaction was carried out at 92°C for 0.7 hours.

[0095] In this step, a small amount of sodium carbonate was added as an alkalinity regulator, which could improve the alkalinity of the product, strengthen the treatment effect on high turbidity water quality, and maintain the stability of the product.

[0096] (4) Pressure filtration: Diatomite 0.3 parts by weight and polyacrylamide 0.025 parts by weight were added to the material after the neutralization reaction, and after thorough mixing, the material was fed into a plate-and-frame filter press and pressure filtration was carried out at a pressure of 0.75 MPa to obtain a filtrate.

[0097] (5) Modulation: The filtrate was cooled to 33°C by a graphite heat exchanger, the concentration was adjusted to 11.0% by weight (Al2O3 content), and a composite stabilizer 0.15 parts by weight was added, and after thorough mixing, the final product was obtained.

[0098] The high-alkalinity polyaluminum chloride product of the present embodiment has the following properties: Al2O3 content 11.0% by weight, alkalinity 65%, pH value (1% solution) 4.5, relative density (20°C) 1.26, and is particularly suitable for treating raw water with high turbidity and high organic matter content.

[0099] Example 6: Preparation of fluorine-free solid polyaluminum chloride

[0100] The present embodiment provides a preparation process for fluorine-free solid polyaluminum chloride, which optimizes the spray drying process for deep treatment of fluorine-containing hydrochloric acid, and obtains a solid product with extremely low fluorine content.

[0101] Specifically, the preparation process of the present embodiment includes the following steps:

[0102] (1) Deep treatment of raw materials: 120.0 parts by weight of 33.0% by weight of hydrochloric acid (fluorine content 2500 ppm) was taken, 0.2 parts by weight of H2O and 1.0 parts by weight of CaO were added, and after stirring for 2 hours, it was allowed to stand for 12 hours. The supernatant was filtered through filter cloth to obtain pretreated hydrochloric acid, and the fluorine content was reduced to below 200 ppm.

[0103] In this step, the addition of calcium oxide can react with fluoride ions in hydrochloric acid to form insoluble CaF2 precipitate, significantly reducing the fluoride content in hydrochloric acid, and laying the foundation for the preparation of fluoride-free products.

[0104] (2) Polymerization reaction: After pretreatment, the hydrochloric acid is added to the reaction kettle, and the stirring is started. The speed is adjusted to 240 rpm. Under the condition of micro negative pressure-75 Pa, 34.0 parts by weight of aluminum hydroxide and 0.25 parts by weight of FeCl3·6H2O are added in batches. After the temperature rises to 70°C, stop heating, and use the reaction heat to naturally heat to 98°C, and keep the reaction for 3.8 hours to obtain a one-step material.

[0105] (3) Neutralization reaction: All the one-step material is transferred to the neutralization kettle. Under the condition of micro negative pressure-95 Pa, according to the ratio of one-step material 100.0 parts by weight, calcium aluminate powder 7.5 parts by weight, the calcium aluminate powder is added in 5 times, and each time interval is 6 minutes. At the same time, 0.09 parts by weight of basic phosphate, 0.45 parts by weight of MgSO4·7H2O and 0.35 parts by weight of Al2(SO4)3·18H2O are added. The stirring speed is adjusted to 215 rpm, and the reaction is carried out at 93°C for 0.75 hours.

[0106] (4) Filter pressing: Add 0.45 parts by weight of diatomite and 0.025 parts by weight of polyacrylamide to the material after the neutralization reaction, mix thoroughly, and then send it to the plate and frame filter press for filter pressing under the pressure of 0.75 MPa to obtain the filtrate.

[0107] (5) Spray drying: After adjusting the concentration of the filtrate to 12.5% by weight, preheat it to 68°C, add 0.25 parts by weight of nano silicon dioxide, and then transport it to the spray drying buffer tank through the spray feed pump. Spray drying is carried out at 335°C with hot air, using a double-fluid nozzle (gas-liquid ratio 3:1), the outlet temperature is controlled at 105°C, and the tower negative pressure is-0.001 MPa, to obtain solid polyaluminum chloride powder.

[0108] In this step, higher gas-liquid ratio and appropriate outlet temperature are used to obtain products with uniform particle size, low moisture content and good solubility, while minimizing residual fluoride in the products.

[0109] (6) Packaging: The solid polyaluminum chloride powder is transported to the packaging equipment by the auger conveyor, and the thickness of the polyethylene plastic bag is 0.09 mm, which is used as the inner layer, and the polypropylene woven bag is used as the outer layer for packaging, with a net weight of 25 kg per bag, and 4 g of desiccant is added in the packaging bag.

[0110] (7) Waste gas treatment and energy recovery: The method of Example 3 is used for waste gas treatment and energy recovery.

[0111] The obtained fluorine-free solid polyaluminum chloride product has the following properties: Al2O3 content 29.5 wt%, fluorine content ≤50 ppm, insoluble content 0.4 wt%, and moisture content 4.0 wt%, and is particularly suitable for drinking water treatment and food industry water treatment.

[0112] Through the detailed description of the above examples, various embodiments of the polyaluminum chloride preparation process of the present application are fully demonstrated, covering preparation methods of different types of products and optimized combinations of various process parameters. The technical solution of the present application solves the problems of poor stability, unsatisfactory coagulation effect, and narrow environmental adaptability of traditional polyaluminum chloride products by precisely controlling the reaction conditions, adding various synergistic additives, and optimizing the process flow, etc., and a series of products with excellent performance and wide application range are obtained.

[0113] Comparative Example 1: Preparation of dilute polyaluminum chloride by traditional single-step method

[0114] The comparative example uses the traditional single-step method to prepare dilute polyaluminum chloride, without using the stepwise feeding, synergistic additive, etc. technical measures of the present application.

[0115] Specifically, the preparation process of Comparative Example 1 includes the following steps:

[0116] (1) Reaction: 31.0 wt% hydrochloric acid 100.0 wt parts was added to the reaction kettle, and the stirring was started, and the rotation speed was adjusted to 150 rpm. Under normal pressure, 30.0 wt parts of aluminum hydroxide was added at one time, and then heated to 90℃, and reacted for 4.0 hours to obtain a reaction product.

[0117] (2) Pressure filtration: the reaction product was directly sent to a plate and frame filter press for pressure filtration under a pressure of 0.5 MPa to obtain a filtrate.

[0118] (3) Preparation: the filtrate was cooled to room temperature, and the concentration was adjusted to 10.0 wt% (Al2O3 content) to obtain the final product.

[0119] The obtained polyaluminum chloride product has the following properties: Al2O3 content 10.0 wt%, alkalinity 25%, pH value (1% solution) 3.2, relative density (20℃) 1.22, and turbidity 15 NTU.

[0120] Compared with Example 1, the product prepared in Comparative Example 1 has poorer coagulation effect, especially the coagulation efficiency decreases by more than 50% under low temperature conditions; the product has poor stability, and obvious precipitation occurs after storage for more than 3 months; more dosage is required during use to achieve the same treatment effect, increasing the use cost.

[0121] Comparative Example 2: Preparation of concentrated polyaluminum chloride without neutralization step

[0122] The comparative example omits the neutralization reaction step, directly from the polymerization reaction to the filter pressing preparation, without adding calcium aluminate powder, basic phosphate and other synergists.

[0123] Specifically, the preparation process of Comparative Example 2 includes the following steps:

[0124] (1) Polymerization reaction: 33.0 wt% hydrochloric acid 120.0 parts by weight was added to the reaction kettle, the stirring was started, and the rotation speed was adjusted to 200 rpm. 35.0 parts by weight of aluminum hydroxide was added in two portions under normal pressure. The temperature was raised to 100℃, and the reaction was kept for 5.0 hours to obtain the reactant.

[0125] (2) Filter pressing: the reactant was directly sent to a plate and frame filter press for filter pressing under a pressure of 0.6 MPa to obtain a filtrate.

[0126] (3) Preparation: the filtrate was cooled to room temperature, and the concentration was adjusted to 12.5 wt% (Al2O3 content) to obtain the final product.

[0127] The obtained concentrated polyaluminum chloride product has the following properties: Al2O3 content 12.5 wt%, alkalinity 20%, pH value (1% solution) 2.8, relative density (20℃) 1.32, and stable period about 2 months (at room temperature).

[0128] Compared with Example 2, the product prepared by Comparative Example 2 has low alkalinity, poor coagulation effect, especially unsatisfactory treatment effect on high turbidity water; the product has poor stability, and delamination and crystallization phenomenon will occur during long-term storage; the product has strong acidity and greater corrosion to equipment.

[0129] Comparative Example 3: preparation of solid polyaluminum chloride by conventional hot air drying

[0130] The comparative example uses conventional hot air drying instead of spray drying to prepare solid polyaluminum chloride, and does not use a flowability modifier and precise temperature control.

[0131] Specifically, the preparation process of Comparative Example 3 includes the following steps:

[0132] (1) Preparation of concentrated polyaluminum chloride: the concentrated polyaluminum chloride with a concentration of 12.5 wt% was prepared according to the method of Comparative Example 2.

[0133] (2) Hot air drying: the above concentrated polyaluminum chloride was directly poured into a drying tray and placed in a hot air circulating oven at 150℃ for drying for 24 hours to obtain a solid product.

[0134] (3) Crushing and packaging: the blocky product after drying was crushed with a crusher, and then packaged after screening.

[0135] The obtained solid polyaluminum chloride product has the following properties: Al2O3 content 28.0 wt%, insoluble content 1.2 wt%, moisture content 8.5 wt%, and dissolution time about 10 minutes (in 25°C water).

[0136] Compared with Example 3, the product prepared in Comparative Example 3 has uneven particle size, poor solubility, and is prone to caking and insoluble matter during use; the product has strong hygroscopicity and is prone to caking during storage; the solution after dissolution is turbid and contains a large amount of insoluble matter, affecting the use effect.

[0137] Comparative Example 4: Preparation of low-aluminum polyaluminum chloride without synergistic activator

[0138] In this comparative example, no synergistic activator such as iron salt or manganese salt is added during the preparation of low-aluminum polyaluminum chloride.

[0139] Specifically, the preparation process of Comparative Example 4 includes the following steps:

[0140] (1) Polymerization reaction: 110.0 parts by weight of 31.5 wt% hydrochloric acid is added to a reaction kettle, and stirring is started with a rotation speed of 200 rpm. 32.0 parts by weight of aluminum hydroxide is added at one time. The temperature is raised to 95°C, and the reaction is kept for 4.0 hours to obtain a reaction product.

[0141] (2) Neutralization reaction: the reaction product is transferred to a neutralization kettle, and 6.5 parts by weight of calcium aluminate powder is added. The reaction is carried out at 90°C for 1.0 hour.

[0142] (3) Pressure filtration: the material after the neutralization reaction is sent to a plate-and-frame filter press, and pressure filtration is carried out at a pressure of 0.6 MPa to obtain a filtrate.

[0143] (4) Modulation: the filtrate is cooled to room temperature, and the concentration is adjusted to 9.0 wt% (Al2O3 content) to obtain a final product.

[0144] The obtained low-aluminum polyaluminum chloride product has the following properties: Al2O3 content 9.0 wt%, alkalinity 35%, pH value (1% solution) 4.0, and relative density (20°C) 1.20.

[0145] Compared with Example 4, the product prepared in Comparative Example 4 has a significantly poorer coagulation effect, and the treatment efficiency under the same conditions is only 60-70% of that of Example 4; the coagulation activity of the product is greatly reduced under low-temperature conditions; and the product has poor treatment effect on water bodies with high color and high organic matter content.

[0146] Comparative Example 5: Preparation of solid polyaluminum chloride without fluorine pretreatment

[0147] In this comparative example, fluorine-containing hydrochloric acid is not pretreated and is directly used for the preparation of solid polyaluminum chloride.

[0148] Specifically, the preparation process of Comparative Example 5 includes the following steps:

[0149] (1) Polymerization reaction: 33.0 wt% of fluorine-containing hydrochloric acid (fluorine content 2500 ppm) 120.0 parts by weight was directly added into the reaction kettle, the stirring was started, and the rotation speed was adjusted to 200 rpm. 34.0 parts by weight of aluminum hydroxide was added in two times. The temperature was raised to 95℃, and the reaction was kept for 4.0 hours to obtain the reactant.

[0150] (2) Neutralization reaction: the reactant was transferred into the neutralization kettle, 7.5 parts by weight of calcium aluminate powder was added, and the reaction was kept at 90℃ for 1.0 hour.

[0151] (3) Pressure filtration: the material after the neutralization reaction was sent into the plate and frame filter press for pressure filtration to obtain the filtrate.

[0152] (4) Spray drying: the filtrate was directly subjected to spray drying after adjusting the concentration to obtain the solid product.

[0153] (5) Packaging: the solid product was simply packaged.

[0154] The obtained solid polyaluminum chloride product has the following properties: Al2O3 content 29.0 wt%, fluorine content about 1800 ppm, insoluble content 0.8 wt%, and moisture content 5.5 wt%.

[0155] Compared with Example 6, the product prepared by Comparative Example 5 has high fluorine content, which does not meet the requirements for drinking water treatment; fluorine volatilization occurs during storage of the product, which causes secondary pollution to the environment; white precipitate occurs after the product is dissolved, which affects the use effect; and the existence of fluorine ions also affects the coagulation performance and stability of the product.

[0156] Through the comparison between the above comparative example and the examples of the present application, it can be seen that the technical measures such as step-by-step feeding, synergistic additive, neutralization reaction optimization, waste gas treatment and heat energy recovery adopted by the present application make the product have significant performance advantages, including better coagulation effect, higher stability, wider use range and better environmental performance, which fully proves the creativity and practicality of the technical scheme of the present application.

[0157] In order to fully evaluate the advantages of the preparation process of the present application, the products of the examples and comparative examples were subjected to systematic performance test and analysis. The test methods and result analysis are described in detail below.

[0158] I. Test method

[0159] 1. Coagulation effect test

[0160] Test method: Jar-test method

[0161] Instrumentation: Six-unions electric stirrer (ZR4-6, Shanghai Meiying Experimental Instrument Co., Ltd.), standard 2L beaker

[0162] Test water sample: High turbidity water sample (turbidity 500±20 NTU, pH 7.5±0.2, water temperature 25±1℃), prepared by kaolin

[0163] Operation steps:

[0164] Take 1000 mL water sample in a beaker;

[0165] Add the measured polyaluminum chloride product (10 mg / L in terms of Al2O3);

[0166] Fast stirring (200 rpm) for 1 minute;

[0167] Slow stirring (40 rpm) for 10 minutes;

[0168] Stand for 30 minutes;

[0169] Take the supernatant to measure turbidity (use HACH 2100Q turbidimeter);

[0170] Calculation method: removal rate (%) = (original turbidity - turbidity after treatment) / original turbidity × 100%

[0171] 2. Low temperature adaptability test

[0172] Test method: the same as coagulation effect test, but the water sample temperature is controlled at 5±1℃;

[0173] 3. Product stability test

[0174] Test method:

[0175] Liquid product: place the product in an opaque sealed container, store at room temperature (25±2℃), and regularly (0, 1, 3, 6 months) take samples to measure Al2O3 content, pH value and coagulation effect;

[0176] Solid product: place the product in a closed environment (relative humidity 60±5%), and measure the moisture absorption rate and solubility changes at different times (0, 7, 15, 30 days);

[0177] 4. Product solubility test (solid product)

[0178] Test method:

[0179] Take 100 mL 25℃ deionized water in a 500 mL beaker;

[0180] Add 1.0 g of solid product;

[0181] Time required for complete dissolution of product was recorded under stirring condition of 300 rpm;

[0182] After dissolution, turbidity and insoluble content of the solution were determined;

[0183] 5. Fluorine content test;

[0184] Test method: Ion selective electrode method (GB / T 7484-1987)

[0185] Instrument and equipment: Fluoride ion selective electrode, pH / ion meter (METTLER TOLEDO Seven Compact S220);

[0186] Operation steps:

[0187] Prepare total ionic strength adjusting buffer (TISAB);

[0188] Prepare fluoride ion standard solution (0.1-10 mg / L) to draw calibration curve;

[0189] Sample pretreatment: Solid samples need to be dissolved and pH adjusted to 5-6;

[0190] Take 10 mL sample, add 10 mL TISAB solution and mix well;

[0191] Dip into fluoride ion electrode to determine content;

[0192] 6. Resource consumption and environmental impact assessment

[0193] Test method:

[0194] Energy consumption determination: Record the energy consumption of each process unit output, such as electric energy, steam, etc;

[0195] Wastewater generation: Determine the wastewater generation and main pollutant indicators of each process unit output;

[0196] Efficiency of waste gas treatment: Determine the acid mist and dust concentration before and after treatment, and calculate the removal rate.

[0197] II. Test results

[0198] Table 1: Comparison of coagulation effect (at room temperature 25℃)

[0199] Sample No. Dosing amount (mg / L Al203) Initial turbidity (NTU) Turbidity after treatment (NTU) Removal rate (%) Flocculation time (min) Flocculation sedimentation velocity (cm / min) Example 1 10 500±20 3.2 99.36 1.5 2.8 Example 2 10 500±20 2.5 99.5 1.2 3.2 Example 3 10 500±20 2.3 99.54 1 3.5 Example 4 10 500±20 3.8 99.24 1.8 2.5 Example 6 10 500±20 2.4 99.52 1.1 3.3 Comparative Example 1 10 500±20 12.5 97.5 3.5 1.2 Comparative Example 2 10 500±20 10.2 97.96 2.8 1.5 Comparative Example 3 10 500±20 15.4 96.92 3.8 1 Comparative Example 4 10 500±20 18.2 96.36 4.2 0.8 Comparative Example 5 10 500±20 8.6 98.28 2.5 1.8

[0200] Table 2: Comparison of low temperature adaptability (at 5℃)

[0201] Sample No. Dosing amount (mg / L AI2O3) Initial turbidity (NTU) Turbidity after treatment (NTU) Removal rate (%) Flocculation time (min) Efficiency ratio at normal temperature (%) Example 1 10 500±20 6.8 98.64 3.2 99.27 Example 2 10 500±20 5.3 98.94 2.8 99.44 Example 3 10 500±20 4.8 99.04 2.5 99.5 Example 4 10 500±20 5.2 98.96 3 99.71 Example 6 10 500±20 5 99 2.6 99.48 Comparative Example 1 10 500±20 52.3 89.54 8.5 91.84 Comparative Example 2 10 500±20 38.6 92.28 7.2 94.2 Comparative Example 3 10 500±20 68.4 86.32 9.6 89.06 Comparative Example 4 10 500±20 75.2 84.96 10.3 88.17 Comparative Example 5 10 500±20 42.5 91.5 7.8 93.1

[0202] Note: Normal temperature efficiency ratio = Low temperature removal rate / Normal temperature removal rate × 100%

[0203] Table 3: Product stability comparison (liquid product)

[0204] Sample No. Storage time (month) Al2O3 content change (%) pH value change Coagulation effect retention rate (%) Sediment amount (%) Example 1 0 0 0 100 0 1 -0.2 -0.1 98.5 0.3 3 -0.5 -0.2 96.2 0.8 6 -0.8 -0.3 94 1.5 Example 2 0 0 0 100 0 1 -0.1 -0.1 99.2 0.2 3 -0.3 -0.1 97.8 0.5 6 -0.5 -0.2 96.5 1 Example 4 0 0 0 100 0 1 -0.2 -0.1 97.8 0.4 3 -0.6 -0.2 95.3 1 6 -1 -0.3 92.5 1.8 Comparative Example 1 0 0 0 100 0 1 -0.8 -0.4 85.6 2.5 3 -2.3 -0.8 72.4 8.6 6 -4.2 -1.5 58.2 15.4 Comparative Example 2 0 0 0 100 0 1 -1.2 -0.6 82.3 3.8 3 -3.1 -1.2 65.8 12.5 6 -5.8 -1.8 45.2 22.6 Comparative Example 4 0 0 0 100 0 1 -1 -0.5 84.2 3.2 3 -2.8 -1 68.5 10.8 6 -4.5 -1.6 52.6 18.5

[0205] Note: Coagulation effect retention rate = removal rate after a certain period of storage / initial removal rate x 100%

[0206] Table 4: Performance comparison of solid products

[0207] Sample No. Dissolution time (min) Insoluble content (%) 15-day moisture absorption rate (%) 30-day moisture absorption rate (%) Solution turbidity (NTU) Example 3 2.5 0.25 1.2 2.8 5.2 Example 6 2.8 0.35 1.5 3.2 6 Comparative Example 3 9.8 1.15 8.6 15.4 38.5 Comparative Example 5 7.5 0.85 6.2 12.8 28.6

[0208] Table 5: Fluorine content comparison and drinking water application evaluation

[0209] Sample No. Fluorine content (ppm) Fluorine residue in treated water (mg / L) Drinking water standard compliance Equipment corrosion rating Example 1 320 0.32 Compliant Low Example 3 180 0.1 Compliant Extremely low Example 6 45 0.02 Compliant Extremely low Comparative Example 1 1250 0.85 Not compliant Medium Comparative Example 3 950 0.62 Basically compliant Medium Comparative Example 5 1800 1.25 Not compliant High

[0210] Note: Drinking water standards refer to GB 5749-2006 "Drinking Water Health Standards", and the limit of fluoride is 1.0 mg / L

[0211] Table 6: Comparison of resource consumption and environmental impact (per ton of product produced)

[0212] Process scheme Energy consumption (kWh) Steam consumption (kg) Waste water production (m³) Waste gas treatment efficiency (%) COD emission (kg) Fluoride emission (g) Example 1-2 120 350 0.8 99.5 0.5 12 Example 3, 6 180 580 1.2 99.8 0.8 8 Comparative Example 1-2 150 420 1.5 92 1.2 65 Comparative Example 3, 5 240 780 2 85 1.8 120

[0213] III. Analysis of test results

[0214] 1. Coagulation effect analysis

[0215] As shown in Table 1, the coagulation effect of the product of the present application is significantly better than that of the comparative product. The turbidity removal rate of the product of the example is all above 99.2%, while the removal rate of the comparative product is between 96-98%. It is especially noteworthy that the flocculation formation speed of the product of the example is faster (1.0-1.8 min), and the flocculation settling speed is higher (2.5-3.5 cm / min), which is of great significance to the filter load and effluent water quality in actual water treatment projects.

[0216] Example 3 (solid product) and Example 2 (concentrated polyaluminum chloride) exhibit the best coagulation effect, which is mainly due to the comprehensive effect of the batch feeding technology, neutralization reaction optimization and addition of synergist of the present application, making the product have a more reasonable aluminum polymer distribution structure.

[0217] 2. Low temperature adaptability analysis

[0218] Table 2 data show that the product of the present application still maintains a high treatment efficiency under low temperature conditions, with a removal rate of 98.6-99.0%, and a retention rate of 99.2-99.7% compared with the efficiency under normal temperature conditions. The treatment efficiency of the comparative product significantly decreases under low temperature conditions, with a removal rate of only 84.9-92.3%, and a decrease of 6.8-11.9 percentage points compared with normal temperature.

[0219] Example 4 (low-aluminum high-efficiency product) exhibits the best low-temperature adaptability (normal-temperature efficiency retention rate of 99.7%), which is mainly due to the synergistic effect of the activators such as iron salt, manganese salt and copper salt added therein, which still maintain a high hydrolysis activity under low temperature conditions, making up for the insufficient hydrolysis rate of aluminum ions under low temperature.

[0220] 3. Product stability analysis

[0221] As can be seen from Table 3, the liquid product of the present application still maintains good stability after long-term storage (6 months), with a small change in Al2O3 content (-0.5 to -1.0%), a high retention rate of coagulation effect (92.5-96.5%) and a small amount of sediment (1.0-1.8%). In contrast, the Al2O3 content of the comparative product significantly decreases (-4.2 to -5.8%) after storage for the same period, the coagulation effect is greatly reduced (the retention rate is only 45.2-58.2%), and a large amount of sediment is produced (15.4-22.6%).

[0222] Example 2 (concentrated polyaluminum chloride) exhibits the best storage stability, which is due to the addition of the composite stabilizer and the structure regulator in the present application, which can effectively prevent the further polymerization and precipitation of aluminum polymers, and maintain the long-term stability of the product.

[0223] 4. Performance analysis of solid product

[0224] The data in Table 4 show that the solid product of the present application has excellent solubility (dissolution time of 2.5-2.8 min) and low insoluble content (0.25-0.35%), and low hygroscopicity (hygroscopicity rate of only 2.8-3.2% in 30 days). The dissolution time of the solid product of the comparative product is long (7.5-9.8 min), the insoluble content is high (0.85-1.15%), and the hygroscopicity is strong (hygroscopicity rate of 12.8-15.4% in 30 days).

[0225] The solid product of Example 3 performs best, which is mainly due to the comprehensive effect of the optimization of the spray drying process, the application of the double-fluid nozzle and the addition of nano-silicon dioxide as a flowability modifier in the present application, which makes the product have a more uniform particle size distribution and better physical properties.

[0226] 5. Fluorine content and drinking water application evaluation

[0227] Table 5 shows that the fluorine content of the product of the embodiment of the present application is significantly lower than that of the comparative product, especially the fluorine content of Example 6 (fluorine-free product) is only 45 ppm, which is much lower than 1800 ppm of Comparative Example 5. This makes the product of the present application more suitable for drinking water treatment, and the residual amount of fluorine in the treated water can meet the drinking water standard requirements.

[0228] Example 6 performs best, which benefits from the deep pretreatment technology of the raw materials of the present application, and the fluorine content in hydrochloric acid is significantly reduced by adding calcium oxide for pre-precipitation, thereby obtaining a high-quality product suitable for drinking water treatment.

[0229] 6. Resource consumption and environmental impact analysis

[0230] Table 6 data shows that compared with the process of the comparative example, the process of the embodiment of the present application has significant advantages in wastewater generation, waste gas treatment efficiency and pollutant emissions, although there are slight differences in energy consumption and steam consumption. The wastewater generation of the process of the embodiment is reduced by 33-40%, the waste gas treatment efficiency is increased by 7.5-14.8 percentage points, and the COD and fluoride emissions are reduced by 58-86% and 93-96%, respectively.

[0231] This is mainly due to the comprehensive application of the heat energy cascade utilization, wastewater recycling and efficient waste gas treatment system of the present application, which not only improves the resource utilization efficiency, but also significantly reduces the environmental impact.

[0232] Four, comprehensive conclusion

[0233] Through the above system test and analysis, it is fully proved that the polyaluminum chloride preparation process of the present application has the following significant advantages compared with the traditional process:

[0234] Excellent coagulation effect: high turbidity removal rate, fast flocculation formation, fast settling speed, and treatment efficiency increased by 2-3 percentage points;

[0235] Strong low temperature adaptability: still maintains more than 97% normal temperature efficiency at 5℃ low temperature, which is 10-15 percentage points higher than traditional products;

[0236] Good product stability: high performance retention rate after long-term storage, less sediment, and long service life;

[0237] Solid product performance is outstanding: fast dissolution speed, less insoluble matter, low hygroscopicity, and convenient to use;

[0238] Excellent environmental indicators: low fluorine content, treated water quality meets drinking water standards, and equipment corrosion is small;

[0239] Significant resource saving: wastewater generation is reduced, waste gas treatment efficiency is high, and pollutant emissions are significantly reduced.

[0240] The test results fully prove that the process of the present application successfully solves the deficiencies of traditional polyaluminum chloride products in coagulation effect, stability, adaptability and environmental protection through the comprehensive application of a series of innovative technical measures, has significant technical advancement and practical value, and provides a high-efficiency, stable and environmentally-friendly polyaluminum chloride preparation process for the water treatment field.

[0241] It should be noted that the above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing polyaluminum chloride, characterized by, The method comprises the following steps: (1) polymerization reaction: 31.0-33.0 wt% of hydrochloric acid 100.0-120.0 parts by weight is added to the reaction kettle, and stirring is started. Under the condition of micro negative pressure -50 Pa to -100 Pa, 30.0-35.0 parts by weight of aluminum hydroxide is added in batches, heated to 70±2℃, and then stopped heating. After keeping the reaction at 90-100℃ for 3.0-4.0 hours, a step product is obtained; (2) neutralization reaction: the step product is transferred to the neutralization kettle, and under the condition of micro negative pressure -50 Pa to -100 Pa, the calcium aluminate powder is added in a ratio of 100.0 parts by weight of the step product to 5.0-8.0 parts by weight of the calcium aluminate powder, in 3-5 times, with an interval of 5-8 minutes each time, and the stirring speed is 180-220 rpm. The reaction is carried out at 85-95℃ for 0.5-0.8 hours; (3) filter pressing: 0.2-0.5 parts by weight of diatomite and 0.01-0.03 parts by weight of polyacrylamide are added to the material after the neutralization reaction, and then filter pressing is carried out under a pressure of 0.6-0.8 MPa to obtain a filtrate; (4) preparation: the filtrate is cooled by a graphite heat exchanger, and the concentration is adjusted and the corresponding additives are added according to the type of product to obtain a polyaluminum chloride product.

2. The production method according to claim 1, characterized by, In step (1), the aluminum hydroxide is added in batches as follows: first, 20% of the total amount is added, then after 5-10 minutes of reaction, 30% of the total amount is added, and then after 10-15 minutes of reaction, 50% of the total amount is added. The content of aluminum hydroxide is ≥99.0 wt%, and the fineness is 100-200 mesh.

3. The preparation method according to claim 1, characterized in that, In step (2), 0.05-0.1 parts by weight of alkaline phosphate and 0.2-0.5 parts by weight of MgSO4·7H2O are also added. The CaO·Al2O3 content of the calcium aluminate powder is 65.0-75.0 wt%, and the fineness is 200-325 mesh.

4. The method of claim 1, wherein, The preparation step further comprises: (a) when preparing dilute polyaluminum chloride, the concentration of the filtrate is adjusted to 10.0±0.2 wt%, and 0.1-0.2 parts by weight of trisodium citrate, 0.05-0.1 parts by weight of modified polyacrylic acid, and 0.01-0.02 parts by weight of MnCl2·4H2O are added; or (b) when preparing concentrated polyaluminum chloride, the concentration of the filtrate is adjusted to 12.5±0.3 wt%, and 0.1-0.2 parts by weight of a composite stabilizer is added.

5. The method of claim 1, wherein, The preparation method further comprises a raw material pretreatment step: 0.1-0.2 parts by weight of H2O2 is added to the hydrochloric acid for pretreatment; 0.1-0.3 parts by weight of FeCl3·6H2O is also added in step (1); and 0.2-0.4 parts by weight of Al2(SO4)3·18H2O is also added in step (2).

6. The method of claim 1, wherein, The preparation method further comprises a waste gas treatment step: the waste gas generated in the preparation process is discharged after sequentially passing through two-stage water spray absorption and one-stage lye spray absorption; wherein the pH values of the water spray are 6-7 and 7-8 respectively, and the pH value of the lye spray is 10-11; the waste gas treatment adopts polypropylene Bauer rings and ceramic Raschig rings mixed fillers, the filling density is 120-150 kg / m3, the filler layer height is 1.2-1.5 m per layer, and the cyclone plate and the filler are arranged alternately.

7. A method for producing a solid polyaluminum chloride, characterized by, The method comprises the following steps: (1) preparing concentrated polyaluminum chloride with a concentration of 12.5±0.3% by weight according to the method of any one of claims 1 to 6; (2) spray drying: preheating the concentrated polyaluminum chloride to 60-70℃, conveying it to a spray drying buffer tank through a spray drying feed pump, and performing spray drying under hot air at 320-350℃ using a two-fluid nozzle with a gas-liquid ratio of 2:1-3:1, controlling the outlet temperature at 90-110℃, and controlling the tower negative pressure at -0.001 MPa, to obtain solid polyaluminum chloride; (3) packaging: conveying the solid polyaluminum chloride to a packaging device through an auger conveyor for packaging, and the packaging specification is 25±0.2 kg / bag.

8. The preparation method according to claim 7, characterized in that, In the step (2), 0.1-0.3 parts by weight of nano-silicon dioxide is added to the concentrated polyaluminum chloride as a flowability improver; the Al2O3 content of the obtained solid polyaluminum chloride is ≥28.0% by weight, the insoluble content is ≤0.5% by weight, and the moisture content is ≤5.0% by weight.

9. The preparation method according to claim 7, characterized in that, In the step (3), a polyethylene plastic bag with a thickness of 0.08-0.10 mm is used as the inner layer, a polypropylene woven bag is used as the outer layer for packaging, and 3-5 g of desiccant is added in the packaging bag.

10. The preparation method according to claim 7, characterized in that, The waste gas generated in the spray drying process is discharged through a 25 m high exhaust pipe after sequentially passing through one-stage cyclone dust removal, one-stage semi-finished product solution spray, one-stage water spray and one-stage lye spray; the preparation method further comprises a recycling step: using the 90-110℃ hot gas discharged from the spray drying to preheat the neutralization reaction feed, and recycling part of the waste gas washing water for dilute polyaluminum chloride production.

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