Preparation method of soluble aluminum hydroxide with low sodium oxide content

Abstract

The invention relates to the technical field of aluminum hydroxide preparation, in particular to a preparation method of soluble aluminum hydroxide with low sodium oxide content. The preparation method comprises the following steps: under a temperature condition of first gradient cooling, carrying out first decomposition reaction on a partial decomposition stock solution with a preset caustic ratio by using an aluminum hydroxide seed crystal to obtain a first aluminum hydroxide solid phase with a relatively compact crystal form and a complete structure; and under the temperature condition of second gradient cooling, performing multiple rounds of second decomposition reaction on the residual decomposition stock solution by using the first aluminum hydroxide solid phase and the aluminum hydroxide seed crystal to obtain a second aluminum hydroxide solid phase which is relatively compact in crystal form and complete in structure. According to the preparation method, through multiple decomposition reactions, the decomposition stock solution forms aluminum hydroxide crystals which are more compact in crystal form and higher in structural integrity, so that the weight content of sodium oxide of the soluble aluminum hydroxide is reduced.

Description

Technical Field

[0001] This application relates to the technical field of aluminum hydroxide preparation, and particularly relates to a method for preparing easily soluble aluminum hydroxide with a low sodium oxide content. Background Art

[0002] At present, as an environmentally friendly flame retardant with non-toxic and smoke-suppressing characteristics, aluminum hydroxide can be widely used in industries such as building decoration materials, electronics, chemical engineering, glass, and papermaking. The quality of these environmentally friendly flame retardants and the quality of their appearance effects are closely related to the quality of aluminum hydroxide used as a filler. Currently, the production methods of aluminum hydroxide fine powder mainly include physical methods and chemical methods. Compared with physical methods, chemical methods have disadvantages such as high energy consumption, high cost, complex operation, and environmental pollution. Therefore, physical methods have huge application scenarios. Physical methods generally require mechanical grinding, that is, using equipment such as ball mills or jet mills to grind large-particle-size aluminum hydroxide into finer particle sizes. Therefore, the grinding difficulty of aluminum hydroxide will directly affect the quality of aluminum hydroxide fine powder. Among many aluminum hydroxide fine powders, easily soluble aluminum hydroxide not only has excellent dissolution performance due to its unique crystal structure, but also is easily ground into powder. Therefore, using easily soluble aluminum hydroxide instead of ordinary aluminum hydroxide as a raw material to grind and produce aluminum hydroxide fine powder will greatly reduce the energy consumption of grinding and save the production cost of aluminum hydroxide fine powder.

[0003] However, the weight content of sodium oxide in easily soluble aluminum hydroxide is 0.6% - 1.2%. This high weight content of sodium oxide limits the application of easily soluble aluminum hydroxide in many aspects. For example, when the sodium oxide content in aluminum hydroxide is relatively high, the color of the product will turn yellow, and the heat resistance of sanitary ware prepared with this aluminum hydroxide filler is relatively poor; in addition, a high content of sodium oxide will also affect the compatibility between the aluminum hydroxide filler and the resin, reduce the firmness of resin bonding, cause the bonding interface between the aluminum hydroxide filler and the resin to peel off, and thus reduce the transparency of resin products. At present, organic acids can be used to reduce the acidity and alkalinity of aluminum hydroxide to improve the compatibility between the aluminum hydroxide filler and the resin. However, this method cannot reduce the sodium element content of the aluminum hydroxide filler, but instead introduces new organic acid impurities and reduces the quality of aluminum hydroxide products. Summary of the Invention

[0004] This application provides a method for preparing easily soluble aluminum hydroxide with a low sodium oxide content to solve the following technical problem: how to reduce the weight content of sodium oxide in easily soluble aluminum hydroxide.

[0005] In a first aspect, an embodiment of this application provides a method for preparing easily soluble aluminum hydroxide with a low sodium oxide content. The preparation method includes:

[0006] Under the temperature condition of the first gradient cooling, using aluminum hydroxide seeds to carry out a first decomposition reaction on a part of the decomposed stock solution with a preset caustic ratio to obtain a first aluminum hydroxide solid phase with relatively dense crystal form and complete structure;

[0007] Under the temperature condition of the second gradient cooling, using the first aluminum hydroxide solid phase and the aluminum hydroxide seeds to carry out multiple rounds of second decomposition reactions on the remaining decomposed stock solution to obtain a second aluminum hydroxide solid phase with relatively dense crystal form and complete structure.

[0008] Optionally, the end temperatures of the first decomposition reaction and the second decomposition reaction are 70°C to 80°C respectively, and the cooling ranges of the first gradient cooling and the second gradient cooling are both 1°C to 3°C.

[0009] Optionally, the times of the first decomposition reaction and the second decomposition reaction are 20h to 40h respectively.

[0010] Optionally, the mass m1 of aluminum hydroxide in the aluminum hydroxide seeds and the mass m2 of aluminum hydroxide in the decomposed stock solution satisfy the relational expression: m1:m2 = (4 - 12):1000.

[0011] Optionally, the mass m3 of the first aluminum hydroxide solid phase and the volume V1 of the decomposed stock solution satisfy the relational expression: m3:V1 = (195 - 205):1. If the unit of m3 is g, then the unit of V1 is L.

[0012] Optionally, the mass m2 of aluminum hydroxide in the decomposed stock solution and the volume V1 of the decomposed stock solution satisfy the relational expression: m2:V1 = (140 - 170):1. If the unit of m2 is g, then the unit of V1 is L.

[0013] Optionally, before using aluminum hydroxide seeds to carry out a first decomposition reaction on a part of the decomposed stock solution with a preset caustic ratio under the temperature condition of the first gradient cooling to obtain a first aluminum hydroxide solid phase with relatively dense crystal form and complete structure, it includes:

[0014] Mixing Bayer process semen and a washing liquid containing alumina to obtain a decomposed stock solution with a preset caustic ratio.

[0015] Optionally, the preset caustic ratio is 1.45 to 1.65.

[0016] Optionally, the median particle size of the aluminum hydroxide seeds is 3μm to 5μm.

[0017] Optionally, the median particle size of the readily soluble aluminum hydroxide product is 70μm to 110μm; and / or

[0018] The acid dissolution rate of the readily soluble aluminum hydroxide product > 90%; and / or

[0019] The mass m4 of sodium oxide in the soluble aluminum hydroxide product is 0.20% - 0.27% of the mass of the soluble aluminum hydroxide product.

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

[0021] A preparation method of soluble aluminum hydroxide with low sodium oxide content provided by an embodiment of the present application. In this preparation method, first, a part of the partially decomposed mother liquor undergoes a first decomposition reaction under the action of aluminum hydroxide seeds, and the first decomposition reaction is carried out in a gradient cooling manner. By gradient cooling, the growth rate of aluminum hydroxide crystals in the partially decomposed mother liquor is inhibited. The aluminum hydroxide crystals with a low growth rate can form aluminum hydroxide crystals with a relatively dense crystal form and a complete structure, making the aluminum hydroxide crystals form a porous and less dense structure with smaller voids. The aluminum hydroxide crystals with a structure with smaller voids can reduce the content of sodium oxide retained in the aluminum hydroxide crystals, thereby reducing the weight content of sodium oxide in the aluminum hydroxide crystals. Then, the obtained first aluminum hydroxide solid phase is used as seeds and combined with aluminum hydroxide seeds to carry out a second decomposition reaction on the remaining decomposed mother liquor, which can provide a large number of seeds for the second decomposition reaction. And the second decomposition reaction is carried out in a gradient cooling manner. By gradient cooling, the growth rate of aluminum hydroxide crystals in the remaining decomposed mother liquor can be inhibited, so that the aluminum hydroxide in the remaining decomposed mother liquor can form aluminum hydroxide crystals with a denser crystal form and higher structural integrity during the crystal nucleation and secondary nucleation stages, which can further reduce the weight content of sodium oxide in the aluminum hydroxide crystals, making the weight content of sodium oxide in the soluble aluminum hydroxide at a relatively low level. Therefore, through multiple decomposition reactions, this preparation method enables the decomposed mother liquor to form aluminum hydroxide crystals with a denser crystal form and higher structural integrity, so as to reduce the weight content of sodium oxide in the soluble aluminum hydroxide. Description of the Drawings

[0022] The drawings here are incorporated into the specification and form a part of this specification, showing embodiments in line 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 drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a schematic flow chart of a preparation method of soluble aluminum hydroxide with low sodium oxide content provided by an embodiment of the present application;

[0025] Figure 2Schematic diagram of the detailed process for preparing a sodium oxide content-reduced and easily soluble aluminum hydroxide provided by an embodiment of the present application;

[0026] Figure 3 SEM image of the easily soluble aluminum hydroxide obtained by the method for preparing a sodium oxide content-reduced and easily soluble aluminum hydroxide provided by Embodiment 1 of the present application at a scale of 80 μm;

[0027] Figure 4 SEM image of the easily soluble aluminum hydroxide obtained by the method for preparing a sodium oxide content-reduced and easily soluble aluminum hydroxide provided by Embodiment 1 of the present application at a scale of 30 μm. Detailed implementation manners

[0028] 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, rather than 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.

[0029] 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 described range description has specifically disclosed all possible sub-ranges and single values within that range; for example, it should be considered that the range description 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 single 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.

[0030] In this text, terms including "comprising" and the like 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 such actual relationship or order between these entities or operations. "And / or", describing the association relationship of associated objects, indicates that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, or B exists alone; where A and B can be singular or plural. "At least one" means one or more, "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 item or plural items; for example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both mean: 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.

[0031] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, equipment, etc. used in this text can be obtained through market purchase or can be prepared by existing methods.

[0032] Figure 1 Exemplarily, a schematic flow diagram of a preparation method of easily soluble aluminum hydroxide with a low sodium oxide content provided by an embodiment of the present application is shown;

[0033] As Figure 1 shown, an embodiment of the present application provides a preparation method of easily soluble aluminum hydroxide with a low sodium oxide content, and the preparation method includes:

[0034] S1. Under the temperature condition of the first gradient cooling, using aluminum hydroxide seeds to perform a first decomposition reaction on a part of the decomposition stock solution with a preset caustic ratio to obtain a first aluminum hydroxide solid phase with relatively dense crystal form and complete structure;

[0035] S2. Under the temperature condition of the second gradient cooling, using the first aluminum hydroxide solid phase and the aluminum hydroxide seeds to perform multiple rounds of second decomposition reactions on the remaining decomposition stock solution to obtain a second aluminum hydroxide solid phase with relatively dense crystal form and complete structure.

[0036] It should be noted that the aluminum hydroxide seed crystals are added to the decomposition stock solution in the form of aluminum hydroxide fine powders, and the particle size of these aluminum hydroxide fine powders is generally 3 μm to 5 μm.

[0037] It should be noted that there is a solid-liquid separation step after the first decomposition reaction and the second decomposition reaction to separate the liquid phase remaining in the reaction stage.

[0038] It should be noted that the second aluminum hydroxide solid phase can be dried to obtain a soluble aluminum hydroxide product.

[0039] It should be noted that, since the crystal form of readily soluble aluminum hydroxide is generally a loose radial crystal form, the second aluminum hydroxide solid phase prepared by this method is still a radial crystal form, but the crystal form of the second aluminum hydroxide solid phase is denser than the traditional readily soluble aluminum hydroxide crystal form.

[0040] It should be noted that the present application embodiment provides a method for preparing soluble aluminum hydroxide with low sodium oxide content. The core of the preparation method is to optimize the growth process of aluminum hydroxide crystals through multiple decomposition reactions combined with gradient cooling technology, thereby reducing the sodium oxide content in the product. The specific steps are as follows:

[0041] (1) First, a portion of the decomposed stock solution is subjected to a first decomposition reaction under the action of aluminum hydroxide seed crystals. The key to this step is to use a gradient cooling method, that is, gradually lowering the decomposition temperature to inhibit the excessive growth of aluminum hydroxide crystals; in this way, aluminum hydroxide crystals with relatively dense crystal form and complete structure can be formed. These crystals have a dispersed structure with small gaps, which helps to reduce the retention of sodium oxide in the crystals, thereby reducing the sodium oxide content of the aluminum hydroxide crystals.

[0042] (2) Next, the first aluminum hydroxide solid phase obtained from the first decomposition reaction is used as a seed crystal, together with the aluminum hydroxide seed crystal, for the second decomposition reaction of the remaining decomposition stock solution. This step not only provides a large number of seed crystals for the second decomposition reaction, but also uses a gradient cooling method again. By suppressing the growth rate of aluminum hydroxide crystals in the remaining decomposition stock solution, aluminum hydroxide crystals with a relatively denser crystal form and higher structural integrity can be formed during the nucleus formation and secondary nucleation stages. This process further reduces the sodium oxide content in the aluminum hydroxide crystals, so that the final soluble aluminum hydroxide product has a lower sodium oxide weight content.

[0043] The readily soluble aluminum hydroxide product prepared by this method not only has a low sodium oxide content, but also has a relatively dense crystal form and a complete structure, and has excellent physical and chemical properties. This method is not only applicable to the preparation of ordinary aluminum hydroxide, but also can meet special application fields with strict requirements for the sodium oxide content, such as 5G ceramic raw materials, etc.

[0044] In summary, the embodiment of the present application provides a method for preparing readily soluble aluminum hydroxide with a low sodium oxide content. This preparation method successfully reduces the sodium oxide content of readily soluble aluminum hydroxide through multiple decomposition reactions and gradient cooling techniques, while ensuring the unique radial crystal form of the readily soluble aluminum hydroxide product, and the obtained readily soluble aluminum hydroxide has a relatively dense crystal structure, providing a new technical approach for the preparation and application of aluminum hydroxide.

[0045] In some optional embodiments, the end temperatures of the first decomposition reaction and the second decomposition reaction are 70°C to 80°C respectively, and the temperature reduction ranges of the first gradient cooling and the second gradient cooling are both 1°C to 3°C.

[0046] In these embodiments, the end temperatures of the first decomposition reaction and the second decomposition reaction can be 70°C to 80°C respectively, so that the temperatures of the first decomposition reaction and the second decomposition reaction are at a relatively low level. The first decomposition reaction and the second decomposition reaction at a relatively low temperature level can inhibit the growth rate of aluminum hydroxide crystals in the decomposition stock solution. In addition, the temperature reduction ranges of the first gradient cooling and the second gradient cooling can both be 1°C to 3°C, so that the temperature fluctuations of the first decomposition reaction and the second decomposition reaction are in a relatively gentle state, which can further inhibit the growth rate of aluminum hydroxide crystals in the decomposition stock solution, enabling the aluminum hydroxide in the decomposition stock solution to form aluminum hydroxide crystals with a relatively denser crystal form and higher structural integrity during the crystal nucleus formation and secondary nucleation stages, and can further reduce the weight content of sodium oxide in the aluminum hydroxide crystals, making the weight content of sodium oxide in the readily soluble aluminum hydroxide at a relatively low level.

[0047] The end temperatures of the first decomposition reaction and the second decomposition 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 respectively.

[0048] The temperature reduction ranges of the first gradient cooling and the second gradient cooling can both be 1°C, 1.5°C, 2.0°C, 2.5°C or 3.0°C.

[0049] In some optional embodiments, the times of the first decomposition reaction and the second decomposition reaction are 20h to 40h respectively.

[0050] In these embodiments, the times of the first decomposition reaction and the second decomposition reaction can be 20 h to 40 h respectively, such that the first decomposition reaction and the second decomposition reaction have sufficient decomposition times. The first decomposition reaction and the second decomposition reaction with sufficient decomposition times can enable the aluminum hydroxide in the decomposition stock solution to form aluminum hydroxide crystals with relatively denser crystal forms and higher structural integrity during the crystal nucleus formation and secondary nucleation stages, which can reduce the weight content of sodium oxide in the aluminum hydroxide crystals, thereby enabling the weight content of sodium oxide in the readily soluble aluminum hydroxide to be at a relatively low level.

[0051] The times of the first decomposition reaction and the second decomposition reaction can be 20 h, 22 h, 24 h, 26 h, 28 h, 30 h, 32 h, 34 h, 36 h, 38 h or 40 h respectively.

[0052] In some alternative embodiments, the mass m1 of aluminum hydroxide in the aluminum hydroxide seed crystal and the mass m2 of aluminum hydroxide in the decomposition stock solution satisfy the relationship: m1:m2 = (4 - 12):1000.

[0053] In these embodiments, the mass m1 of aluminum hydroxide in the aluminum hydroxide seed crystal and the mass m2 of aluminum hydroxide in the decomposition stock solution can satisfy the relationship: m1:m2 = (4 - 12):1000, such that the decomposition stock solution has a sufficient amount of aluminum hydroxide seed crystals. The sufficient amount of aluminum hydroxide seed crystals can prompt the aluminum hydroxide in the decomposition stock solution to form aluminum hydroxide crystals with relatively denser crystal forms and higher structural integrity during the crystal nucleus formation and secondary nucleation stages, so as to reduce the weight content of sodium oxide in the aluminum hydroxide crystals, thereby enabling the weight content of sodium oxide in the readily soluble aluminum hydroxide to be at a relatively low level.

[0054] The value of the mass m1 of aluminum hydroxide in the aluminum hydroxide seed crystal can be 4, 5, 6, 7, 8, 9, 10, 11 or 12.

[0055] It should be noted that the ratio of the mass m1 of aluminum hydroxide in the aluminum hydroxide seed crystal to the mass m2 of aluminum hydroxide in the decomposition stock solution is generally referred to as the "seed ratio".

[0056] In some alternative embodiments, the mass m3 of the first aluminum hydroxide solid phase and the volume V1 of the decomposition stock solution satisfy the relationship: m3:V1 = (195 - 205):1. If the unit of m3 is g, then the unit of V1 is L.

[0057] In these embodiments, the mass m3 of the first aluminum hydroxide solid phase and the volume V1 of the decomposition stock solution may satisfy the relationship: m3:V1 = (195 - 205):1, such that the remaining decomposition stock solution has sufficient aluminum hydroxide crystal seeds, which can promote the formation of aluminum hydroxide crystals with a relatively denser crystal form and higher structural integrity in the remaining decomposition stock solution, so as to reduce the weight content of sodium oxide in the aluminum hydroxide crystals, thereby enabling the weight content of sodium oxide in the readily soluble aluminum hydroxide to be at a relatively low level.

[0058] The value of the mass m3 of the first aluminum hydroxide solid phase may be 195, 196, 197, 198, 199, 200, 201, 202, 203, 204 or 205.

[0059] In some alternative embodiments, the mass m2 of aluminum hydroxide in the decomposition stock solution and the volume V1 of the decomposition stock solution satisfy the relationship: m2:V1 = (140 - 170):1. If the unit of m2 is g, then the unit of V1 is L.

[0060] In these embodiments, the mass m2 of aluminum hydroxide in the decomposition stock solution and the volume V1 of the decomposition stock solution may satisfy the relationship: m2:V1 = (140 - 170):1, such that the decomposition stock solution has sufficient aluminum hydroxide grains. A sufficient amount of aluminum hydroxide grains can form aluminum hydroxide crystals with a relatively denser crystal form and higher structural integrity in the first decomposition reaction or the second decomposition reaction stage, so as to reduce the weight content of sodium oxide in the aluminum hydroxide crystals, thereby enabling the weight content of sodium oxide in the readily soluble aluminum hydroxide to be at a relatively low level.

[0061] The value of the mass m2 of aluminum hydroxide in the decomposition stock solution may be 140, 145, 150, 155, 160, 165 or 170.

[0062] Figure 2 Exemplarily shown is a detailed process schematic diagram of a method for preparing readily soluble aluminum hydroxide with a low sodium oxide content provided by an embodiment of the present application;

[0063] In some alternative embodiments, as Figure 2 shown, before carrying out the first decomposition reaction on a part of the decomposition stock solution with a preset caustic ratio using aluminum hydroxide crystal seeds under the temperature condition of the first gradient cooling to obtain a first aluminum hydroxide solid phase with a relatively dense crystal form and complete structure, it includes:

[0064] S101. Mix the Bayer process liquor and the washing liquid containing alumina to obtain a decomposition stock solution with a preset caustic ratio.

[0065] In these embodiments, the Bayer process semen and the washing liquid containing alumina are mixed. The washing liquid containing alumina can be used to dilute the aluminum hydroxide in the Bayer process semen to a decomposition stock solution with a preset caustic ratio, which is convenient for the subsequent decomposition stock solution to form aluminum hydroxide crystals with a relatively denser crystal form and higher structural integrity through the first decomposition reaction and the second decomposition reaction, so as to reduce the weight content of sodium oxide in the aluminum hydroxide crystals, thereby enabling the weight content of sodium oxide in the readily soluble aluminum hydroxide to be at a relatively low level.

[0066] It should be noted that the washing liquid containing alumina can be the waste liquid from the washing of the flat plate filter in the alumina production stage.

[0067] In some alternative embodiments, the preset caustic ratio is 1.45 - 1.65.

[0068] In these embodiments, the preset caustic ratio can be 1.45 - 1.65, so that the decomposition stock solution has sufficient alumina and a relatively low sodium oxide content, and can form aluminum hydroxide crystals with a relatively denser crystal form and higher structural integrity during the first decomposition reaction and the second decomposition reaction stages, so as to reduce the weight content of sodium oxide in the aluminum hydroxide crystals, thereby enabling the weight content of sodium oxide in the readily soluble aluminum hydroxide to be at a relatively low level.

[0069] The preset caustic ratio can be 1.45, 1.46, 1.47, 1.48, 1.49, 1.50, 1.51, 1.52, 1.53, 1.54, 1.55, 1.60 or 1.65.

[0070] It should be noted that the preset caustic ratio refers to the molar concentration ratio of sodium oxide to alumina in the sodium aluminate solution. Therefore, controlling the preset caustic ratio within a relatively low range can make the decomposition stock solution have a relatively low sodium oxide content, and thus ultimately obtain readily soluble aluminum hydroxide with a relatively low weight content of sodium oxide.

[0071] In some alternative embodiments, the median particle size of the aluminum hydroxide seed crystal is 3 μm - 5 μm.

[0072] In these embodiments, the median particle size of the aluminum hydroxide seed crystal can be 3 μm - 5 μm, so that the aluminum hydroxide seed crystal is within a relatively fine particle size range. The relatively fine particle size aluminum hydroxide seed crystal can form aluminum hydroxide crystals with a relatively denser crystal form and higher structural integrity during the first decomposition reaction and the second decomposition reaction stages, so as to reduce the weight content of sodium oxide in the aluminum hydroxide crystals, thereby enabling the weight content of sodium oxide in the readily soluble aluminum hydroxide to be at a relatively low level.

[0073] The median particle size of the aluminum hydroxide seed crystal can be 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm.

[0074] In some alternative embodiments, the median particle size of the readily soluble aluminum hydroxide product is 70 μm to 110 μm; and / or

[0075] the acid dissolution rate of the readily soluble aluminum hydroxide product > 90%; and / or

[0076] the mass m4 of sodium oxide in the readily soluble aluminum hydroxide product is 0.20% to 0.27% of the mass of the readily soluble aluminum hydroxide product.

[0077] In these embodiments, the median particle size of the readily soluble aluminum hydroxide product can be 70 μm to 110 μm, and the acid dissolution rate of the readily soluble aluminum hydroxide product > 90%, and the mass m4 of sodium oxide in the readily soluble aluminum hydroxide product can be 0.20% to 0.27% of the mass of the readily soluble aluminum hydroxide product, which indicates that the readily soluble aluminum hydroxide product is easy to grind and has a low sodium oxide content.

[0078] The median particle size of the readily soluble aluminum hydroxide product can be 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm or 110 μm.

[0079] The acid dissolution rate of the readily soluble aluminum hydroxide product can be 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%.

[0080] The mass m4 of sodium oxide in the readily soluble aluminum hydroxide product can be 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26% or 0.27% of the mass of the readily soluble aluminum hydroxide product.

[0081] It should be noted that the acid dissolution rate of the readily soluble aluminum hydroxide product is closely related to the crystal morphology and crystal form of the aluminum hydroxide in the readily soluble aluminum hydroxide product. When the crystal morphology of the aluminum hydroxide is good and the crystal structure is loose, the higher the parameter of the acid dissolution rate, and the aluminum hydroxide crystal with good morphology and loose crystal structure can reduce the grinding difficulty. Therefore, the acid dissolution rate of the readily soluble aluminum hydroxide product can be used to characterize the grinding difficulty of the readily soluble aluminum hydroxide product.

[0082] The following further elaborates on this application in conjunction with specific examples. For the experimental methods without specific conditions noted in the following examples, they are generally determined according to national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out according to general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0083] Example 1

[0084] As shown Figure 2 below, a method for preparing easily soluble aluminum hydroxide with a low sodium oxide content includes:

[0085] S101. Mix Bayer process semen and a washing solution containing alumina to obtain a mother liquor for decomposition with a preset caustic ratio;

[0086] S1. Under the temperature condition of the first gradient cooling, use aluminum hydroxide seeds to carry out a first decomposition reaction on a part of the mother liquor for decomposition with a preset caustic ratio to obtain a first aluminum hydroxide solid phase with relatively dense crystal form and complete structure;

[0087] S2. Under the temperature condition of the second gradient cooling, use the first aluminum hydroxide solid phase and aluminum hydroxide seeds to carry out multiple rounds of second decomposition reactions on the remaining mother liquor for decomposition to obtain a second aluminum hydroxide solid phase with relatively dense crystal form and complete structure.

[0088] The initial temperatures of the first decomposition reaction and the second decomposition reaction are 85°C respectively, the end temperatures of the first decomposition reaction and the second decomposition reaction are 79°C respectively, and the temperature reduction ranges of the first gradient cooling and the second gradient cooling are both 2°C.

[0089] The times of the first decomposition reaction and the second decomposition reaction are both 21h.

[0090] The mass m1 of aluminum hydroxide in the aluminum hydroxide seeds and the mass m2 of aluminum hydroxide in the mother liquor for decomposition satisfy the relationship: m1:m2 = 8:1000.

[0091] The mass m3 of the first aluminum hydroxide solid phase and the volume V1 of the mother liquor for decomposition satisfy the relationship: m3:V1 = 200g:1L.

[0092] The mass m2 of aluminum hydroxide in the mother liquor for decomposition and the volume V1 of the mother liquor for decomposition satisfy the relationship: m2:V1 = 150g:1L.

[0093] The preset caustic ratio is 1.50.

[0094] The particle size of the aluminum hydroxide seeds is 3μm to 5μm.

[0095] Example 2

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

[0097] The preset caustic ratio is 1.51.

[0098] The temperature reduction ranges of the first gradient cooling and the second gradient cooling are both 1°C.

[0099] Example 3

[0100] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0101] The preset caustic ratio is 1.47.

[0102] The temperature drop amplitudes of the first gradient cooling and the second gradient cooling are both 3°C.

[0103] Example 4

[0104] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0105] The times of the first decomposition reaction and the second decomposition reaction are 40 h respectively.

[0106] The mass m1 of aluminum hydroxide in the aluminum hydroxide seed crystal and the mass m2 of aluminum hydroxide in the decomposition mother liquor satisfy the relationship: m1:m2 = 4:1000.

[0107] The mass m3 of the first aluminum hydroxide solid phase and the volume V1 of the decomposition mother liquor satisfy the relationship: m3:V1 = 195 g:1 L.

[0108] The mass m2 of aluminum hydroxide in the decomposition mother liquor and the volume V1 of the decomposition mother liquor satisfy the relationship: m2:V1 = 140 g:1 L.

[0109] The particle size of the aluminum hydroxide seed crystal is 3 μm to 5 μm.

[0110] Example 5

[0111] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0112] The times of the first decomposition reaction and the second decomposition reaction are 20 h respectively.

[0113] The mass m1 of aluminum hydroxide in the aluminum hydroxide seed crystal and the mass m2 of aluminum hydroxide in the decomposition mother liquor satisfy the relationship: m1:m2 = 12:1000.

[0114] The mass m3 of the first aluminum hydroxide solid phase and the volume V1 of the decomposition mother liquor satisfy the relationship: m3:V1 = 205 g:1 L. If the unit of m3 is g, then the unit of V1 is L.

[0115] The mass m2 of aluminum hydroxide in the decomposition mother liquor and the volume V1 of the decomposition mother liquor satisfy the relationship: m2:V1 = 170 g:1 L.

[0116] The particle size of the aluminum hydroxide seed crystal is 3 μm to 5 μm.

[0117] Comparative Example 1

[0118] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0119] The preset caustic ratio is 1.38.

[0120] The mass m1 of aluminum hydroxide in the aluminum hydroxide seed and the mass m2 of aluminum hydroxide in the mother liquor for decomposition satisfy the relationship: m1:m2 = 2:1000.

[0121] The temperatures of the first decomposition reaction and the second decomposition reaction are 79 °C, and the temperature drop amplitude of the gradient temperature drop is 0 °C. That is, the first decomposition reaction and the second decomposition reaction are carried out under isothermal conditions.

[0122] Comparative Example 2

[0123] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0124] The preset caustic ratio is 1.48.

[0125] The temperatures of the first decomposition reaction and the second decomposition reaction are 79 °C, and the temperature drop amplitude of the gradient temperature drop is 0 °C. That is, the first decomposition reaction and the second decomposition reaction are carried out under isothermal conditions.

[0126] Comparative Example 3

[0127] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0128] The preset caustic ratio is 1.54.

[0129] Comparative Example 4

[0130] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0131] Comparative Example 5

[0132] On the basis of the content disclosed in Example 1, the following further modifications are made:

[0133] The preset caustic ratio is 1.50.

[0134] The mass m1 of aluminum hydroxide in the aluminum hydroxide seed and the mass m2 of aluminum hydroxide in the mother liquor for decomposition satisfy the relationship: m1:m2 = 20:1000.

[0135] Relevant experiments and effect data:

[0136] Figure 3 Exemplarily shown is a scanning electron micrograph of the easily soluble aluminum hydroxide obtained by the method for preparing easily soluble aluminum hydroxide with low sodium oxide content provided in Example 1 of the present application at a scale of 80 μm;

[0137] Figure 4An SEM image of the readily soluble aluminum hydroxide obtained by the preparation method of readily soluble aluminum hydroxide with low sodium oxide content provided in Embodiment 1 of the present application is exemplarily shown at a scale of 30 μm;

[0138] 1. The readily soluble aluminum hydroxide product obtained in Embodiment 1 was observed by SEM, and the results are as Figure 3 and Figure 4 shown. The morphology of the aluminum hydroxide crystals is good, and its crystal structure is loose.

[0139] 2. The median particle size D50, acid dissolution rate, and weight content of sodium oxide of the readily soluble aluminum hydroxide products of each embodiment and comparative example were respectively counted, and the results are shown in Table 1.

[0140] Table 1 Characteristic results of readily soluble aluminum hydroxide products of each embodiment and comparative example

[0141]

[0142]

[0143] As can be seen from Table 1, for the preparation method of readily soluble aluminum hydroxide with low sodium oxide content provided in the embodiments of the present application, through multiple decomposition reactions and gradient cooling techniques, the sodium oxide content of the readily soluble aluminum hydroxide was successfully reduced to the range of 0.20% - 0.27%. In addition, the median particle size of the readily soluble aluminum hydroxide is in the range of 70 μm - 110 μm, and the acid dissolution rate of the readily soluble aluminum hydroxide product is above 90%, which indicates the relative denseness and structural integrity of the crystal form of the readily soluble aluminum hydroxide product.

[0144] In addition, for the preparation method of readily soluble aluminum hydroxide with low sodium oxide content provided in the embodiments of the present application, the aluminum hydroxide product prepared by this preparation method can replace ordinary aluminum hydroxide in the ground aluminum hydroxide filler. Moreover, this aluminum hydroxide product can not only meet the requirement of low weight content of sodium oxide in the aluminum hydroxide filler, but also reduce the production energy consumption of the aluminum hydroxide filler and save the production cost of the aluminum hydroxide filler, having broad market application prospects.

[0145] 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 broadest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A method for preparing a soluble aluminum hydroxide with a low sodium oxide content, the preparation method comprising: Under the temperature condition of the first gradient temperature drop, a partially decomposed stock solution having a preset caustic ratio is subjected to a first decomposition reaction using aluminum hydroxide seed crystals to obtain a first aluminum hydroxide solid phase with a relatively dense crystal form and a complete structure; Under the second gradient temperature condition, the remaining decomposition stock solution is subjected to multiple rounds of second decomposition reaction using the first aluminum hydroxide solid phase and the aluminum hydroxide seed crystals to obtain a second aluminum hydroxide solid phase with relatively dense crystal form and complete structure.

2. The preparation method according to claim 1, wherein the terminal temperatures of the first decomposition reaction and the second decomposition reaction are 70°C to 80°C respectively, and the cooling ranges of the first gradient cooling and the second gradient cooling are both 1°C to 3°C.

3. The preparation method according to claim 1, wherein the time for the first decomposition reaction and the second decomposition reaction is 20 hours to 40 hours respectively.

4. The preparation method according to claim 1, wherein the mass m1 of the aluminum hydroxide in the aluminum hydroxide seed crystal and the mass m2 of the aluminum hydroxide in the decomposition stock solution satisfy the relationship: m1:m2=(4-12):1000.

5. According to the preparation method of claim 1, the mass m3 of the first aluminum hydroxide solid phase and the volume V1 of the decomposition solution satisfy the relationship: m3:V1=(195~205):1, if the unit of m3 is g, the unit of V1 is L.

6. According to the preparation method of claim 1, the mass m2 of the aluminum hydroxide in the decomposition stock solution and the volume V1 of the decomposition stock solution satisfy the relationship: m2:V1=(140-170):1, if the unit of m2 is g, the unit of V1 is L.

7. The preparation method according to claim 1, wherein under the first gradient temperature condition, the partially decomposed stock solution with a preset caustic ratio is subjected to a first decomposition reaction using aluminum hydroxide seeds to obtain a first aluminum hydroxide solid phase with a relatively dense crystal form and a complete structure, which comprises: The Bayer process concentrate and the washing liquid containing aluminum oxide are mixed to obtain a decomposition stock solution with a preset caustic ratio.

8. The preparation method according to claim 1 or 7, wherein the preset causticity ratio is 1.45 to 1.

65.

9. The preparation method according to claim 1, wherein the median particle size of the aluminum hydroxide seed crystals is 3 μm to 5 μm.

10. The preparation method according to claim 1, wherein the median particle size of the readily soluble aluminum hydroxide product is 70 μm to 110 μm; and / or The acid solubility of the readily soluble aluminum hydroxide product is greater than 90%; and / or The mass m4 of the sodium oxide in the readily soluble aluminum hydroxide product is 0.20% to 0.27% of the mass of the readily soluble aluminum hydroxide product.

Images