Method for synthesizing high-purity polyaluminum chloride

Abstract

The invention relates to the technical field of preparation of polyaluminum chloride, in particular to a method for synthesizing high-purity polyaluminum chloride. The method comprises the following steps: carrying out first neutralization reaction on carbonate and an aluminum chloride solution containing hydrogen ions to obtain a mixed solution containing a large amount of hydroxyl ions; and carrying out polymerization reaction on the mixed solution containing a large amount of hydroxyl ions to obtain high-purity polyaluminum chloride. According to the method, the ionization balance of the aluminum chloride solution is broken through the first neutralization reaction of carbonate and the aluminum chloride solution, and the concentration of free hydroxyl ions is increased. The hydroxyl ions fully replace chloride ions around aluminum ions in the subsequent polymerization reaction to form a polymeric chain with an Al-OH-Al bridging structure, so that the polycondensation reaction of an aluminum hydroxyl complex is promoted, and a polyaluminum chloride product is generated. The method is carried out under the normal pressure condition, and the adsorption effect of the polyaluminum chloride product can be effectively improved.

Description

Technical Field

[0001] This application relates to the technical field of polyaluminum chloride preparation, and particularly relates to a method for synthesizing high-purity polyaluminum chloride. Background Art

[0002] High-purity polyaluminum chloride is a white or milky white milk powder-like fine powder. High-purity polyaluminum chloride has the characteristics of high chlorine content, low insoluble matter content, no other heavy metals except Al 3+ , low iron content, and easy solubility at low temperature. In recent years, high-purity polyaluminum chloride has replaced aluminum sulfate as a neutral sizing precipitant in the paper industry; in addition, with the continuous use of polyaluminum chloride in water purifying agents, it is expected that the production demand for high-purity polyaluminum chloride will continue to increase in the future.

[0003] However, at present, the production method of high-purity polyaluminum chloride is basically carried out in a closed reaction kettle by the high-temperature and high-pressure method (generally with a pressure of 0.3 MPa to 0.5 MPa and a temperature ≥ 150 °C), which makes this production method generally have the defects of high energy consumption, high equipment damage rate, high safety risk, and high production cost. And because it is difficult to effectively remove hydrogen ions under high temperature and high pressure, the adsorption effect of the polyaluminum chloride product is poor. Summary of the Invention

[0004] This application provides a method for synthesizing high-purity polyaluminum chloride to solve the following technical problem: how to improve the adsorption effect of the polyaluminum chloride product.

[0005] In a first aspect, an embodiment of this application provides a method for synthesizing high-purity polyaluminum chloride, and the method includes:

[0006] Performing a first neutralization reaction on a carbonate and an aluminum chloride solution containing hydrogen ions to obtain a mixed solution containing a large amount of hydroxide ions;

[0007] Performing a polymerization reaction on the mixed solution containing a large amount of hydroxide ions to obtain high-purity polyaluminum chloride.

[0008] Optionally, the mass m1 of the carbonate and the mass m2 of the aluminum chloride solution satisfy the relationship: m1:m2 ≥ 10:100.

[0009] Optionally, the carbonate includes sodium carbonate and / or calcium carbonate.

[0010] Optionally, the addition time of the carbonate ≥ 30 min.

[0011] Optionally, the temperature of the first neutralization reaction is 70 °C to 80 °C.

[0012] Optionally, the temperature of the polymerization reaction ≥ 70 °C, and the time of the polymerization reaction ≥ 1 h.

[0013] Optionally, the method for preparing the aluminum chloride solution includes:

[0014] Performing a second neutralization reaction on hydrochloric acid and aluminum hydroxide to obtain an aluminum chloride solution containing hydrogen ions.

[0015] Optionally, the temperature of the second neutralization reaction is 95°C to 100°C, and the time of the second neutralization reaction is ≥1 h.

[0016] Optionally, the mass m3 of the hydrochloric acid and the mass m4 of the aluminum hydroxide satisfy the relationship: m3:m4 = (3.5 - 4.0):1.

[0017] Optionally, performing a polymerization reaction on the mixed solution containing a large amount of hydroxide ions to obtain high-purity polyaluminum chloride includes the steps of:

[0018] Performing a polymerization reaction on the mixed solution containing a large amount of hydroxide ions to obtain a polymerization product;

[0019] Filtering the polymerization product to obtain high-purity polyaluminum chloride.

[0020] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0021] A method for synthesizing high-purity polyaluminum chloride provided by an embodiment of the present application first uses a carbonate and an aluminum chloride solution to perform a first neutralization reaction. By consuming the hydrogen ions in the aluminum chloride solution with the carbonate, the ionization equilibrium of the aluminum chloride solution can be broken under normal pressure conditions to increase the concentration of free hydroxide ions in the aluminum chloride solution. These hydroxide ions can fully replace the chloride ions coordinated around the aluminum ions in the aluminum chloride solution during the subsequent polymerization reaction stage to form a polymerization chain with an Al-OH-Al bridging structure. These polymerization chains can promote the polycondensation reaction of aluminum hydroxy complexes, so that aluminum chloride can form a polyaluminum chloride product. In addition, the hydrogen ion content of these polymerization chains is low, and it has a good adsorption effect during the use stage of the polyaluminum chloride product. Description of the Drawings

[0022] The accompanying drawings here are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other accompanying drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 Schematic diagram of the process for a method of synthesizing high-purity polyaluminum chloride provided by an embodiment of the present application;

[0025] Figure 2 Detailed schematic diagram of the process for a method of synthesizing high-purity polyaluminum chloride provided by an embodiment of the present application;

[0026] Figure 3 Comparison chart of the results of the floc formation speed in the flocculation experiment provided by the present application;

[0027] Figure 4 Comparison chart of the results of the sedimentation speed in the flocculation test provided by the present application;

[0028] Figure 5 Comparison chart of the results of the decontamination ability in the flocculation test provided by the present application;

[0029] Among them, A1, A2, and A3 are polyaluminum chloride products of Example 1, B1, B2, and B3 are yellow materials, and C1, C2, and C3 are polyaluminum chloride products of Comparative Example 1. Detailed implementation manners

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0031] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the description of the range has specifically disclosed all possible sub-ranges and individual values within that range; for example, it should be considered that the description of the range from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0032] In this text, terms such as "including" mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects and indicates that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "multiple" means two or more; "at least one kind", "at least one of the following items" or similar expressions refer to any combination of these items, including any combination of single items or plural items; for example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both represent: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. "Part representation methods" such as weight parts and mass parts represent the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0033] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in this text can be obtained through market purchases or can be prepared by existing methods.

[0034] It should be noted that the essence of aluminum chloride polymerization is that OH - replaces Cl of aluminum chloride - to form a polymerization chain. At present, mainly by increasing conditions such as the pressure and temperature of the polymerization reaction, the dissolution of aluminum hydroxide is increased to consume H + in quantity, thereby increasing the content of OH - in the solution to promote the polymerization of aluminum chloride.

[0035] Figure 1 Exemplarily shows a schematic process diagram of a method for synthesizing high-purity polyaluminum chloride provided by an embodiment of the present application;

[0036] In the embodiments of the present application, by introducing carbonate to regulate the hydrolysis and polycondensation paths of aluminum chloride in stages, the controllable synthesis of polyaluminum chloride (PAC) with a high degree of polymerization is achieved under normal pressure. As Figure 1As shown in the figure, a method for synthesizing high-purity polyaluminum chloride provided by an embodiment of the present application includes:

[0037] S1. Perform a first neutralization reaction on a carbonate and an aluminum chloride solution containing hydrogen ions to obtain a mixed solution containing a large amount of hydroxide ions;

[0038] S2. Perform a polymerization reaction on the mixed solution containing a large amount of hydroxide ions to obtain high-purity polyaluminum chloride.

[0039] When neutralizing AlCl3 with a traditional direct addition of alkali (such as NaOH), H + is rapidly consumed, resulting in the instant supersaturation hydrolysis of Al 3 + and the formation of Al(OH)3 precipitate instead of active intermediates. In the embodiment of the present application, a carbonate (such as Na2CO3) reacts with H + to generate CO2, and the pH is gradually increased through the slow release of CO2 (instead of reaching the target value in one step), maintaining the dynamic balance of free OH - in the solution. Al 3 + preferentially generates hydroxy complexes {Al(OH) 2+ , Al6(OH) 12 6+ etc.} under mild hydrolysis conditions, rather than directly precipitating, providing active precursors for subsequent polycondensation.

[0040] In the polymerization stage, OH- gradually replaces the Cl 3+ coordinated with Al - to form an Al-OH-Al oxygen bridge bond. This process is accelerated under heating (such as 60°C to 80°C) and stirring, promoting the conversion of oligomers {such as Al2(OH)2Cl4} to polymers {such as Al 13 O4(OH) 24 Cl7}. The Al-OH-Al bridging network has a high charge density and an open pore structure, and can efficiently capture pollutants through electrostatic adsorption and bridging effects.

[0041] Neutralization thoroughness: The staged neutralization of carbonate ensures that H + is fully consumed, and the residual H + in the final product is extremely low (pH is close to neutral). Adsorption enhancement: The low H + concentration avoids competing with pollutants (such as negatively charged colloids) for adsorption sites, improving the charge neutralization ability of PAC.

[0042] It should be noted that the aluminum chloride solution is generally acidic to ensure the stable existence of aluminum chloride.

[0043] It should be noted that both the first neutralization reaction and the polymerization reaction are carried out under the condition of a constant stirring speed.

[0044] It should be noted that a method for synthesizing high-purity polyaluminum chloride provided by an embodiment of the present application breaks the ionization equilibrium of an aluminum chloride solution through a first neutralization reaction between a carbonate and the aluminum chloride solution, thereby increasing the concentration of free hydroxide ions. These hydroxide ions fully replace the chloride ions around aluminum ions during subsequent polymerization reactions, forming a polymerization chain with an Al-OH-Al bridging structure, which further promotes the polycondensation reaction of aluminum hydroxy complexes to produce a polyaluminum chloride product. This method is carried out under atmospheric pressure conditions, which can effectively improve the adsorption effect of the polyaluminum chloride product. Specifically:

[0045] The core of this method lies in using a carbonate to carry out the first-stage neutralization reaction with the aluminum chloride solution. During this process, the carbonate consumes the hydrogen ions in the aluminum chloride solution, thereby breaking its ionization equilibrium and causing the concentration of free hydroxide ions in the solution to rise.

[0046] Subsequently, in the second-stage polymerization reaction, these increased hydroxide ions fully combine with aluminum ions to form a polymerization chain with an Al-OH-Al bridging structure. These polymerization chains further promote the polycondensation reaction of aluminum hydroxy complexes, ultimately producing a high-purity polyaluminum chloride product; in addition, the hydrogen ion content of these polymerization chains is relatively low, which can expose sufficient adsorption sites and improve the adsorption performance of the polyaluminum chloride product.

[0047] Compared with traditional high-temperature and high-pressure polymerization methods, this method is carried out under atmospheric pressure conditions, which not only reduces energy consumption, but also effectively reduces the consumption of raw materials, while improving the adsorption performance of the product.

[0048] In some alternative embodiments, the mass m1 of the carbonate and the mass m2 of the aluminum chloride solution satisfy the relationship: m1:m2 ≥ 10:100.

[0049] In these embodiments, the mass m1 of the carbonate and the mass m2 of the aluminum chloride solution satisfy the relationship: m1:m2 ≥ 10:100, such that there is a sufficient amount of carbonate in the first neutralization reaction. The sufficient amount of carbonate can fully consume the hydrogen ions in the aluminum chloride solution, break the ionization equilibrium of the aluminum chloride solution under atmospheric pressure conditions, increase the concentration of free hydroxide ions in the aluminum chloride solution, and these hydroxide ions can form a polymerization chain with an Al-OH-Al bridging structure, enabling the aluminum chloride to fully form a polyaluminum chloride product and providing sufficient adsorption sites, thereby improving the adsorption performance of the polyaluminum chloride product.

[0050] The value of the mass m1 of the carbonate can be 13, 14, 15, 16, 17, 18, 19, or 20.

[0051] In some alternative embodiments, the carbonate includes sodium carbonate and / or calcium carbonate.

[0052] In these embodiments, the carbonate may include sodium carbonate and / or calcium carbonate, covering most common carbonates, so that the carbonate can sufficiently consume the hydrogen ions in the aluminum chloride solution, thereby increasing the concentration of free hydroxide ions in the aluminum chloride solution under atmospheric pressure, enabling the aluminum chloride to fully form polyaluminum chloride products and providing sufficient adsorption sites, thus improving the adsorption performance of the polyaluminum chloride products.

[0053] It should be noted that a mixture of calcium carbonate and sodium carbonate can be used as the carbonate. By replacing part of the sodium carbonate with calcium carbonate, the amount of sodium carbonate added can be further reduced, thereby further reducing the preparation cost of this method.

[0054] It should be noted that when the carbonate includes a mixture of sodium carbonate and calcium carbonate, the mass ratio of sodium carbonate to calcium carbonate ≥ 4:3.

[0055] In some alternative embodiments, the addition time of the carbonate ≥ 30 min.

[0056] In these embodiments, the addition time of the carbonate can be ≥ 30 min, so that the carbonate is uniformly added to the aluminum chloride solution, enabling the carbonate to sufficiently consume the hydrogen ions in the aluminum chloride solution, breaking the ionization equilibrium of the aluminum chloride solution under atmospheric pressure to increase the concentration of free hydroxide ions in the aluminum chloride solution; additionally, based on the large amount of aluminum ions in the aluminum chloride solution, this way of uniformly adding the carbonate to the aluminum chloride solution can prevent the precipitation of aluminum hydroxide solid phase due to excessive local hydroxide ion concentration in the aluminum chloride solution, thus obtaining a mixed solution with uniform distribution of hydroxide ions.

[0057] The addition time of the carbonate can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0058] In some alternative embodiments, the temperature of the first neutralization reaction is 70 °C to 80 °C.

[0059] In these embodiments, the temperature of the first neutralization reaction can be 70 °C to 80 °C. Based on the characteristic that the first neutralization reaction is an exothermic reaction, by controlling the temperature of the first neutralization reaction, the reaction rate of the first neutralization reaction can be accelerated, enabling the carbonate to sufficiently consume the hydrogen ions in the aluminum chloride solution without causing violent boiling of the aluminum chloride solution under atmospheric pressure, thereby increasing the concentration of free hydroxide ions in the aluminum chloride solution and enabling the aluminum chloride to fully form polyaluminum chloride products.

[0060] The temperature of the first neutralization reaction can be 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C or 80 °C.

[0061] In some alternative embodiments, the temperature of the polymerization reaction is ≥70 °C, and the time of the polymerization reaction is ≥1 h.

[0062] In these embodiments, the temperature of the polymerization reaction can be ≥70 °C, and the time of the polymerization reaction can be ≥1 h, so that the hydroxide ions in the mixed solution can fully replace the chloride ions coordinated around the aluminum ions in the aluminum chloride solution to form a polymerization chain with an Al-OH-Al bridging structure. These polymerization chains can promote the polycondensation reaction of the aluminum hydroxy complex, so that aluminum chloride can form a polyaluminum chloride product.

[0063] The temperature of the polymerization reaction can be 70 °C, 71 °C, 72 °C, 73 °C, 74 °C or 75 °C.

[0064] The time of the polymerization reaction can be 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2 h.

[0065] Figure 2 Exemplarily shown is a detailed process schematic diagram of a method for synthesizing high-purity polyaluminum chloride provided by an embodiment of the present application;

[0066] In some alternative embodiments, as Figure 2 shown, the method for preparing the aluminum chloride solution includes:

[0067] S101. Perform a second neutralization reaction on hydrochloric acid and aluminum hydroxide to obtain an aluminum chloride solution containing hydrogen ions.

[0068] In these embodiments, hydrochloric acid and aluminum hydroxide are subjected to a second neutralization reaction so that aluminum hydroxide is fully converted into an aluminum chloride solution, thereby facilitating the subsequent first neutralization reaction of the carbonate.

[0069] In some alternative embodiments, the temperature of the second neutralization reaction is 95 °C to 100 °C, and the time of the second neutralization reaction is ≥1 h.

[0070] In these embodiments, the temperature of the second neutralization reaction can be 95 °C to 100 °C, and the time of the second neutralization reaction can be ≥1 h, so that the second neutralization reaction between hydrochloric acid and aluminum hydroxide is fully carried out, so that aluminum hydroxide is fully converted into an aluminum chloride solution, thereby facilitating the subsequent first neutralization reaction of the carbonate.

[0071] The temperature of the second neutralization reaction can be 95 °C, 96 °C, 97 °C, 98 °C, 99 °C or 100 °C.

[0072] The time of the second neutralization reaction can be 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2 h.

[0073] In some alternative embodiments, the mass m3 of the hydrochloric acid and the mass m4 of the aluminum hydroxide satisfy the relationship: m3:m4 = (3.5 - 4.0):1.

[0074] In these embodiments, the mass m3 of the hydrochloric acid and the mass m4 of the aluminum hydroxide can satisfy the relationship: m3:m4 = (3.5 - 4.0):1, such that the hydrochloric acid can fully undergo the second neutralization reaction with the aluminum hydroxide, thereby obtaining an aluminum chloride solution with a large amount of hydrogen ions.

[0075] The value of the mass m3 of the hydrochloric acid can be 3.5, 3.6, 3.7, 3.8, 3.9 or 4.0.

[0076] In some alternative embodiments, polymerizing the mixed solution containing a large amount of hydroxide ions to obtain high-purity polyaluminum chloride includes the steps of:

[0077] S201. Polymerize the mixed solution containing a large amount of hydroxide ions to obtain a polymerization product;

[0078] S202. Filter the polymerization product to obtain high-purity polyaluminum chloride.

[0079] In these embodiments, filtering the polymerization product after polymerizing the mixed solution can fully separate the liquid phase component of the polymerization product from the solid phase to obtain a liquid polyaluminum chloride product with an alumina content of 7% or more.

[0080] This filtration can be carried out using a plate and frame filter press.

[0081] The following further elaborates on this application in conjunction with specific examples. For the experimental methods without specific conditions indicated in the following examples, they are usually determined in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out in accordance with general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0082] Example 1

[0083] As Figure 2 shown, a method for synthesizing high-purity polyaluminum chloride includes:

[0084] S101. Perform a second neutralization reaction on hydrochloric acid and aluminum hydroxide to obtain an aluminum chloride solution containing hydrogen ions;

[0085] S1. Perform a first neutralization reaction on the carbonate and the aluminum chloride solution containing hydrogen ions to obtain a mixed solution containing a large amount of hydroxide ions;

[0086] S201. Perform a polymerization reaction on the mixed solution containing a large amount of hydroxide ions to obtain a polymerization product;

[0087] S202. Filter the polymerization product to obtain high-purity polyaluminum chloride.

[0088] The mass m1 of the carbonate and the mass m2 of the aluminum chloride solution satisfy the relationship: m1:m2 = 10:100.

[0089] The carbonate is sodium carbonate.

[0090] The addition time of the carbonate is 30 min.

[0091] The temperature of the first neutralization reaction is 70 °C.

[0092] The temperature of the polymerization reaction is 70 °C, and the time of the polymerization reaction is 1 h.

[0093] The temperature of the second neutralization reaction is 100 °C, and the time of the second neutralization reaction is 1 h.

[0094] The mass m3 of hydrochloric acid and the mass m4 of aluminum hydroxide satisfy the relationship: m3:m4 = 3.9:1.

[0095] Example 2

[0096] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0097] The carbonate is calcium carbonate.

[0098] The mass m1 of the carbonate and the mass m2 of the aluminum chloride solution satisfy the relationship: m1:m2 = 10:100.

[0099] The temperature of the first neutralization reaction is 80 °C.

[0100] The temperature of the second neutralization reaction is 95 °C, and the time of the second neutralization reaction is 1 h.

[0101] The mass m3 of hydrochloric acid and the mass m4 of aluminum hydroxide satisfy the relationship: m3:m4 = 3.5:1.

[0102] Example 3

[0103] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0104] The carbonate includes a mixture of sodium carbonate and calcium carbonate, and the mass ratio of sodium carbonate to calcium carbonate ≥ 4:3.

[0105] The mass m1 of the carbonate and the mass m2 of the aluminum chloride solution satisfy the relationship: m1:m2 = 12:100.

[0106] The temperature of the first neutralization reaction is 75 °C.

[0107] The temperature of the second neutralization reaction is 98 °C, and the time of the second neutralization reaction is 1.5 h.

[0108] The mass m3 of hydrochloric acid and the mass m4 of aluminum hydroxide satisfy the relationship: m3:m4 = 4.0:1.

[0109] Comparative Example 1

[0110] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0111] Based on the traditional high-temperature and high-pressure method, the aluminum chloride solution is subjected to a polymerization reaction. At this time, the pressure of the polymerization reaction is 0.4 Mpa, and the temperature of the polymerization reaction is 150 °C.

[0112] Comparative Example 2

[0113] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0114] Use polyaluminum chloride with a mass concentration of 17% to replace the carbonate.

[0115] Comparative Example 3

[0116] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0117] The mass m1 of the carbonate and the mass m2 of the aluminum chloride solution satisfy the relationship: m1:m2 = 8:100.

[0118] Comparative Example 4

[0119] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0120] The addition time of the carbonate is 5 min.

[0121] Comparative Example 5

[0122] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0123] The temperature of the first neutralization reaction is 60 °C.

[0124] Comparative Example 6

[0125] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0126] The temperature of the first neutralization reaction is 90 °C.

[0127] Relevant experimental and effect data:

[0128] 1. Taking 100 g of aluminum chloride solution as the experimental object, the parameters of the mixed solutions of Example 1, Example 2, and Example 3 were respectively counted, as shown in Table 1 specifically.

[0129] Table 1 Distribution of parameters of mixed solutions in each example and comparative example

[0130]

[0131] It can be seen from Table 1 that by using sodium carbonate and calcium carbonate to carry out the first neutralization reaction with aluminum chloride solution respectively, the basicity of the obtained mixed solution can be increased to more than 40%, which indicates that the polymerization reaction has initially occurred in the mixed solution; however, the alumina content of the mixed solution of sodium carbonate and calcium carbonate is relatively low, which shows that the addition of carbonate may dilute the alumina content of the mixed solution.

[0132] 2. Using the polyaluminum chloride of Example 1 and Comparative Example 1 as flocculants respectively, and using the yellow liquor (ordinary polyaluminum chloride solution produced by the reaction of aluminum chloride solution and calcium aluminate) as a control, then taking the sewage selected at the same location and the same time as the experimental object, and conducting 3 flocculation experiments with the formation rate of flocs, sedimentation rate, and decontamination ability as the three indicators. The results are as Figure 3 , Figure 4 and Figure 5 shown. The results show that the polyaluminum chloride obtained in Example 1 is optimal in terms of the formation rate of flocs, sedimentation rate, and decontamination ability.

[0133] 3. Conducting flocculation tests on the products produced in each example and comparative example respectively, and the results are shown in Table 3.

[0134] Table 3 Dosage of polyaluminum chloride products in each example and comparative example

[0135]

[0136]

[0137] The data in the above table is the dosage of polyaluminum chloride products required to reduce the raw water from 500 NTU to 5 NTU.

[0138] As can be seen from Table 3, a method for synthesizing high-purity polyaluminum chloride provided by an embodiment of the present application breaks the ionization equilibrium of the aluminum chloride solution through the first neutralization reaction of carbonate and aluminum chloride solution, and increases the concentration of free hydroxide ions. These hydroxide ions fully replace the chloride ions around the aluminum ions in the subsequent polymerization reaction to form a polymerization chain with an Al-OH-Al bridging structure, thereby promoting the polycondensation reaction of aluminum hydroxy complexes to produce a polyaluminum chloride product. This method is carried out under normal pressure conditions and can effectively improve the adsorption effect of the polyaluminum chloride product.

[0139] In addition, a method for synthesizing high-purity polyaluminum chloride provided by an embodiment of the present application uses the primary polyaluminum chloride solution as a raw material, and quantitatively and at a constant speed adds a carbonate auxiliary agent thereto, which can effectively consume the hydrogen ions in the primary polyaluminum chloride solution, and at the same time provide a large amount of hydroxide ions to replace the chloride ions of aluminum chloride, so that the polymerization reaction of aluminum chloride moves forward, and thus a polyaluminum chloride product with a large number of adsorption sites can be obtained.

[0140] In summary, a method for synthesizing high-purity polyaluminum chloride provided by an embodiment of the present application has the following advantages:

[0141] 1. Advantage comparison:

[0142]

[0143] 2. Reaction path innovation: By replacing the "one-step neutralization" of strong alkali with the "step-by-step slow-release neutralization" of carbonate, the traditional process of "hydrolysis → precipitation → re-dissolution" is optimized to "controlled hydrolysis → directional polycondensation", significantly improving the product polymerization degree.

[0144] 3. Structure design innovation: Utilize the gradual replacement of Cl- by OH- to construct an Al-OH-Al bridging structure to form PAC with a hierarchical pore structure and a high specific surface area (>200m 2 / g), and its adsorption capacity is more than 1.5 times higher than that of traditional products.

[0145] 4. Impurity control innovation: The carbonate reaction by-products (such as NaCl) are removed by centrifugation or membrane separation during the polymerization stage, and the salt residue in the final product is <0.5%, avoiding the blockage of PAC active sites by impurities.

[0146] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A method for synthesizing high-purity polyaluminum chloride, the method comprising: Performing a first neutralization reaction on a carbonate and an aluminum chloride solution containing hydrogen ions to obtain a mixed solution containing a large amount of hydroxide ions; Performing a polymerization reaction on the mixed solution containing a large amount of hydroxide ions to obtain high-purity polyaluminum chloride.

2. The method according to claim 1, wherein the mass m1 of the carbonate and the mass m2 of the aluminum chloride solution satisfy the relationship: m1:m2 ≥ 10:

100.

3. The method according to claim 1 or 2, wherein the carbonate comprises sodium carbonate and / or calcium carbonate.

4. The method according to claim 1, wherein the addition time of the carbonate is ≥ 30 min.

5. The method according to claim 1, wherein the temperature of the first neutralization reaction is 70°C to 80°C.

6. The method according to claim 1, wherein the temperature of the polymerization reaction is ≥ 70°C and the time of the polymerization reaction is ≥ 1 h.

7. The method according to claim 1, wherein the preparation method of the aluminum chloride solution comprises: Performing a second neutralization reaction on hydrochloric acid and aluminum hydroxide to obtain an aluminum chloride solution containing hydrogen ions.

8. The method according to claim 7, wherein the temperature of the second neutralization reaction is 95°C to 100°C and the time of the second neutralization reaction is ≥ 1 h.

9. The method according to claim 7, wherein the mass m3 of the hydrochloric acid and the mass m4 of the aluminum hydroxide satisfy the relationship: m3:m4 = (3.5 - 4.0):

1.

10. The method according to claim 1, wherein the step of performing a polymerization reaction on the mixed solution containing a large amount of hydroxide ions to obtain high-purity polyaluminum chloride comprises: Performing a polymerization reaction on the mixed solution containing a large amount of hydroxide ions to obtain a polymerization product; Filtering the polymerization product to obtain high-purity polyaluminum chloride.

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