Method for preparing high-white aluminum hydroxide based on oxalate filter cake

Abstract

This application provides a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, belonging to the field of aluminum hydroxide preparation. The method includes: adding sodium oxalate circulating seed to the Bayer process seeding mother liquor to obtain an oxalate filter cake containing aluminum hydroxide; adding sodium carbonate to the oxalate filter cake to adjust the alkali ratio to 0.85–1.15, and adding lime to the oxalate filter cake to obtain a mixture; sintering the mixture to obtain sintered clinker; dissolving the sintered clinker to obtain a sodium aluminate solution; and seeding the sodium aluminate solution to obtain high-whiteness aluminum hydroxide. This application, through precise coupling of process parameters and a full-process design of the impurity control chain, simultaneously achieves deep removal of key impurities such as Fe and Si during the oxalate removal process, transforming the oxalate filter cake from waste into a high-quality raw material for high-whiteness aluminum hydroxide, thus combining the removal of organic matter from oxalate and the preparation of high-whiteness aluminum hydroxide in the Bayer process alumina production.

Description

Technical Field

[0001] This application relates to the field of aluminum hydroxide preparation technology, and in particular to a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake. Background Technology

[0002] High-whiteness aluminum hydroxide, due to its high whiteness, low chroma, and good chemical stability, has become a key raw material for high-end materials such as artificial marble slabs. Artificial marble has extremely stringent requirements for the whiteness and chroma of raw materials, typically requiring aluminum hydroxide products with a whiteness of over 94% and a b-value (yellowness index) of less than 0.5 to ensure the purity and aesthetic appeal of the slabs. Meanwhile, the Bayer process, the mainstream process for alumina production globally, is difficult to directly produce high-whiteness aluminum hydroxide products that meet the requirements of artificial marble due to the presence of a large amount of organic matter and other impurities in its process. Organic matter introduced into the Bayer process from ore can be divided into oxalate organic matter and non-oxalate organic matter. Oxalate organic matter, due to its low saturation concentration, is easily precipitated during decomposition. Once oxalate precipitates significantly, it not only leads to severe refinement of the aluminum hydroxide product, affecting the particle size distribution and physical properties, but also significantly reduces the product's whiteness and increases its chroma, posing a significant threat to Bayer process production. Therefore, oxalate removal is a crucial step in the preparation of high-whiteness aluminum hydroxide.

[0003] Currently, some companies use a method of adding sodium oxalate circulating seeds to the Bayer process decomposition mother liquor, utilizing the common ion effect to promote the precipitation of oxalate and thus remove oxalate organic matter. Because the decomposition mother liquor contains aluminum hydroxide suspended matter, the discharged oxalate filter cake during seed circulation becomes rich in aluminum hydroxide. However, existing technologies only address oxalate removal; a systematic and efficient treatment method for this aluminum hydroxide-rich oxalate filter cake has not yet been developed. This makes it impossible to effectively recover and utilize the aluminum resources in the filter cake and simultaneously produce high-whiteness aluminum hydroxide products that meet the high standards of the artificial marble industry. How to fully utilize the oxalate filter cake and develop a method that simultaneously removes organic matter and prepares high-whiteness aluminum hydroxide has become a pressing technical challenge in the Bayer process alumina production field. Summary of the Invention

[0004] This application provides a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, which takes into account both the removal of oxalate organic matter and the preparation of high-whiteness aluminum hydroxide in the Bayer process of alumina production.

[0005] This application provides a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, the method comprising:

[0006] Sodium oxalate recycled seeds were added to the mother liquor of the Bayer process to remove oxalate and obtain an oxalate filter cake containing aluminum hydroxide.

[0007] Sodium carbonate is added to the oxalate filter cake to adjust the alkali ratio of the oxalate filter cake to 0.85-1.15, and lime is added to the oxalate filter cake to obtain a mixture;

[0008] The mixture is sintered to obtain sintered clinker;

[0009] The sintered clinker was dissolved in a caustic alkali solution to obtain a sodium aluminate solution; and

[0010] The sodium aluminate solution was subjected to fractional decomposition to obtain high-whiteness aluminum hydroxide.

[0011] Optionally, the Nk of the Bayer process seed decomposition mother liquor is 155 g / L to 165 g / L.

[0012] Optionally, the alkali ratio of the oxalate filter cake can be adjusted to 0.9–1.1.

[0013] Optionally, the chemical composition of the oxalate filter cake includes: sodium oxalate, aluminum hydroxide, Fe2O3, and SiO2.

[0014] Optionally, by mass fraction, the sodium oxalate content is 20%–35%, the aluminum hydroxide content is 40%–55%, the Fe2O3 content is 0.1%–0.25%, and the SiO2 content is 0.2%–0.5%.

[0015] Optionally, the mass of the lime is 0.5% to 8% of the dry weight of the oxalate filter cake.

[0016] Optionally, the mass of the lime is 1% to 5% of the dry weight of the oxalate filter cake.

[0017] Optionally, the sintering temperature is 900℃~1100℃, and the sintering time is ≥30min.

[0018] Optionally, the sintering temperature is 900℃~1100℃, and the sintering time is 30min.

[0019] Optionally, the high-whiteness aluminum hydroxide meets the following properties: whiteness > 94%, b value < 0.5.

[0020] The technical solutions provided in this application have the following advantages compared with the prior art:

[0021] This application provides a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake. The method includes: adding sodium oxalate circulating seeds to the Bayer process seed decomposition mother liquor to remove oxalate and obtain an oxalate filter cake containing aluminum hydroxide; adding sodium carbonate to the oxalate filter cake to adjust the alkali ratio of the oxalate filter cake to 0.85-1.15, and adding lime to the oxalate filter cake to obtain a mixture; sintering the mixture to obtain sintered clinker; dissolving the sintered clinker with a caustic alkali solution to obtain a sodium aluminate solution; and seed decomposition of the sodium aluminate solution to obtain high-whiteness aluminum hydroxide.

[0022] On the one hand, by adding sodium oxalate circulating seeds to the mother liquor of the Bayer process, the solubility of oxalates (such as sodium oxalate) is reduced by utilizing the "common ion effect," which promotes their directional precipitation in crystal form. At the same time, when oxalates precipitate, they use aluminum hydroxide floaters in the mother liquor as crystal nuclei to form an "oxalate-aluminum hydroxide" composite filter cake. This process removes oxalates while simultaneously recovering aluminum hydroxide, avoiding the loss of aluminum resources in traditional oxalate removal processes. In addition, during the sintering of the mixture, sodium oxalate is completely decomposed, thoroughly removing oxalate organic matter from the filter cake.

[0023] On the other hand, adding lime to the oxalate filter cake allows CaO to react with SiO2 to form calcium silicate, which is insoluble in caustic alkali. This calcium silicate separates as a slag phase after sintering, improving the desilication rate and preventing silicon from accumulating in the sodium aluminate solution to form water-soluble silicates, thus affecting the purity of the seed crystals. Simultaneously, the Fe2O3 in the filter cake is sintered to form a stable insoluble phase, remaining in the slag during dissolution and preventing iron ions from entering the sodium aluminate solution. Furthermore, sintering converts aluminum hydroxide to Al2O3, which reacts with Na2CO3 to produce high-purity sodium aluminate. The Na2CO3 decomposition product of oxalate can participate in the sodium aluminate formation reaction, reducing the amount of sodium carbonate required. During dissolution, only sodium aluminate dissolves in the caustic alkali solution; impurities such as Fe2O3 and CaSiO3 remain completely in the slag.

[0024] Therefore, this application achieves the deep removal of key impurities such as Fe and Si simultaneously during the oxalate removal process through precise coupling of process parameters and full-process design of impurity control chain, transforming oxalate filter cake from "waste" into high-quality raw material for high-white aluminum hydroxide, thus taking into account both the removal of organic matter from oxalate and the preparation of high-white aluminum hydroxide in the Bayer process alumina production. Attached Figure Description

[0025] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A schematic flowchart illustrating a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, provided for an embodiment of this application;

[0028] Figure 2 This is a schematic diagram of the actual process of a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, provided as an embodiment of this application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "comprise" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0031] Figure 1 A schematic flowchart illustrating a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, provided for an embodiment of this application; Figure 2 This is a schematic diagram of the actual process of a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, provided as an embodiment of this application.

[0032] like Figure 1and Figure 2 As shown in the embodiments of this application, a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake is provided, the method comprising:

[0033] S1. Add sodium oxalate circulating seeds to the Bayer process seed decomposition mother liquor to remove oxalate and obtain oxalate filter cake containing aluminum hydroxide.

[0034] Oxalate (such as sodium oxalate) in the decomposition mother liquor can affect the quality of subsequent alumina products. By adding sodium oxalate seed, the "common ion effect" is utilized to promote oxalate crystallization and reduce the oxalate concentration in the mother liquor. Simultaneously, aluminum hydroxide floaters in the mother liquor act as crystallization nuclei, and during seed circulation, oxalate preferentially precipitates from their surfaces, forming an "oxalate-aluminum hydroxide" composite precipitate. Therefore, by adding circulating sodium oxalate seed, oxalate is precipitated from the Bayer process seed decomposition mother liquor, while simultaneously separating the filter cake containing aluminum hydroxide, providing raw materials for subsequent processing.

[0035] In some embodiments, the Nk content of the Bayer process seed mother liquor is 155 g / L to 165 g / L.

[0036] Nk refers to the concentration of caustic alkali in the mother liquor (expressed as Na₂O). Limiting the Nk of the Bayer process seed fractionation mother liquor to 155 g / L–165 g / L ensures a suitable alkaline environment, promoting the precipitation of oxalates (such as sodium oxalate) in crystalline form while maintaining the stability of aluminum hydroxide and preventing excessive dissolution or poor precipitation morphology. If Nk is below 155 g / L, oxalate solubility increases, reducing precipitation efficiency; if Nk is above 165 g / L, aluminum hydroxide precipitates prematurely, affecting the composition ratio of the filter cake. For example, the Nk of the Bayer process seed fractionation mother liquor can be 155 g / L, 157 g / L, 159 g / L, 161 g / L, 163 g / L, 165 g / L, etc.

[0037] In some embodiments, the chemical composition of the oxalate filter cake includes sodium oxalate, aluminum hydroxide, Fe2O3, and SiO2.

[0038] In some embodiments, the sodium oxalate content is 20% to 35% by mass fraction, the aluminum hydroxide content is 40% to 55%, the Fe2O3 content is 0.1% to 0.25%, and the SiO2 content is 0.2% to 0.5%.

[0039] Sodium oxalate, as the main impurity, affects the alkali consumption and reaction degree during subsequent sintering. Aluminum hydroxide, as the precursor of the target product, directly affects the final yield of aluminum hydroxide. Fe2O3 and SiO2 are impurity components; Fe2O3 affects the whiteness of the product (iron ion coloration), and SiO2 may form silicates during sintering, affecting the dissolution efficiency of sodium aluminate. For example, the content of sodium oxalate can be 20%, 24%, 25%, 30%, 32%, 35%, etc.; the content of aluminum hydroxide can be 40%, 45%, 50%, 52%, 55%, etc.; the content of Fe2O3 can be 0.1%, 0.15%, 0.2%, 0.25%, etc.; and the content of SiO2 can be 0.2%, 0.3%, 0.4%, 0.45%, 0.5%, etc.

[0040] S2. Sodium carbonate is added to the oxalate filter cake to adjust the alkali ratio of the oxalate filter cake to 0.85-1.15, and lime is added to the oxalate filter cake to obtain a mixture;

[0041] Adjust the alkali ratio of the filter cake to a suitable range and fix impurities with lime to create conditions for the sintering reaction.

[0042] In some embodiments, the alkali ratio of the oxalate filter cake is adjusted to 0.9 to 1.1.

[0043] The alkali ratio typically refers to the molecular ratio of Na₂O to Al₂O₃. The alkali ratio for oxalate filter cake is typically adjusted to 0.85–1.15 to ensure the formation of sodium aluminate, which is readily soluble in caustic alkali, during sintering. If the alkali ratio is below 0.85, insufficient sodium aluminate production will result in reduced aluminum recovery; if it is above 1.15, excess Na₂O will increase sintering energy consumption and may introduce excessive alkali during subsequent dissolution, affecting the decomposition conditions of the oxalate filter cake. Examples of alkali ratio adjustments for oxalate filter cake include 0.85, 0.9, 1.0, 1.05, 1.1, and 1.15.

[0044] In some embodiments, the mass of the lime is 0.5% to 8% of the dry weight of the oxalate filter cake.

[0045] In some embodiments, the mass of the lime is 1% to 5% of the dry weight of the oxalate filter cake.

[0046] The lime content is limited to 0.5%–8% of the dry weight of the oxalate filter cake. Lime (CaO) reacts with SiO2 to form calcium silicate, which forms a slag phase insoluble in caustic alkali after sintering, thereby removing silicon impurities and iron impurities, preventing their accumulation in the sodium aluminate solution and reducing product purity. Simultaneously, lime improves the porosity of the sintered clinker, promoting the leaching of sodium aluminate during subsequent dissolution. If the dosage is less than 0.5%, desilication is incomplete, and SiO2 may react with sodium aluminate to form water-soluble silicates, affecting seed decomposition. If the dosage is greater than 8%, excess CaO may react with sodium aluminate to form calcium aluminate, reducing aluminum recovery and introducing calcium impurities. For example, the lime content can be 0.5%, 1%, 3%, 5%, 6%, 7%, or 8% of the dry weight of the oxalate filter cake.

[0047] S3. Sinter the mixture to obtain sintered clinker;

[0048] High-temperature sintering causes a solid-phase reaction in the mixture, converting aluminum hydroxide into sodium aluminate, while simultaneously decomposing sodium oxalate and fixing impurities, forming a soluble sintered clinker.

[0049] In some embodiments, the sintering temperature is 900℃~1100℃, and the sintering time is ≥30min.

[0050] In some embodiments, the sintering temperature is 900°C to 1100°C, and the sintering time is 30 minutes.

[0051] The sintering temperature is limited to 900℃~1100℃. Aluminum hydroxide decomposes into Al2O3, which reacts with Na2CO3 to form sodium aluminate. Sodium oxalate decomposes into Na2CO3 and CO2. Below 900℃, the reaction rate is slow, and sodium aluminate formation is incomplete. Above 1100℃, the clinker may become denser, reducing porosity and affecting subsequent dissolution efficiency, while also increasing energy consumption. Simultaneously, at this temperature, impurities such as Fe2O3 and CaSiO3 form stable insoluble phases, preventing them from entering the sodium aluminate solution during dissolution. The sintering time is limited to ≥30 min to ensure sufficient solid-phase reaction and maximize sodium aluminate formation. Too short a time results in incomplete reaction within the mixture, reducing aluminum recovery; too long a time may lead to over-sintering of the clinker, increasing dissolution difficulty and offering no significant benefit. For example, the sintering temperature can be 900℃, 950℃, 1000℃, 1050℃, 1100℃, etc., and the sintering time can be 30min, 35min, 40min, 45min, 50min, 55min, 60min, etc.

[0052] S4. Dissolve the sintered clinker using a caustic alkali solution to obtain a sodium aluminate solution;

[0053] Sodium aluminate in the sintered clinker is dissolved using a caustic alkali solution to form a sodium aluminate solution, while insoluble impurities (such as CaSiO3) are separated out.

[0054] S5. The sodium aluminate solution is subjected to fractional decomposition to obtain high-whiteness aluminum hydroxide.

[0055] By adding aluminum hydroxide seed crystals, the sodium aluminate solution decomposes to release aluminum hydroxide crystals, resulting in a high-whiteness product.

[0056] In some embodiments, the high-whiteness aluminum hydroxide satisfies the following properties: whiteness > 94%, b-value < 0.5.

[0057] In the embodiments of this application, the content of coloring impurities such as Fe2O3 and SiO2 has been controlled to an extremely low level in the preceding steps (S1 oxalate removal, S2 desilication, and S3 sintering to fix iron impurities), preventing them from mixing into aluminum hydroxide crystals during seed decomposition and ensuring whiteness. Subsequently, seed decomposition is used to control the uniform growth of crystals, avoiding agglomeration or defects, thereby reducing light scattering and improving whiteness. The b-value (measure of yellow-blue tint) < 0.5 indicates that the aluminum hydroxide product is almost free of yellow phase impurities, further verifying the effective removal of impurities such as iron and titanium.

[0058] In summary, this application, through the optimization of the entire process of "common ion effect impurity removal - precise control of alkali ratio - low-temperature sintering - high-efficiency seeding," achieves breakthroughs in both product whiteness and purity while increasing the yield of aluminum hydroxide (to over 95%), and also possesses advantages such as low energy consumption, low cost, and environmental friendliness. The technical advantages of this application are summarized as follows:

[0059] (1) Highly efficient removal of oxalate and improved raw material utilization: By adding sodium oxalate circulating seed, the "common ion effect" is utilized to promote the efficient crystallization and precipitation of oxalate (such as sodium oxalate) from the Bayer process mother liquor. Compared with traditional methods, the oxalate removal rate is significantly improved, reducing the oxalate concentration in the mother liquor and avoiding its impact on the quality of subsequent alumina products. At the same time, the aluminum hydroxide float in the mother liquor acts as crystallization nuclei, causing oxalate to preferentially precipitate on its surface, forming an "oxalate-aluminum hydroxide" composite filter cake, achieving simultaneous recovery of aluminum hydroxide, and improving the raw material utilization rate by 10% to 15%.

[0060] (2) Precisely control process parameters and optimize reaction conditions: By adding sodium carbonate, the alkali ratio is controlled at 0.85-1.15 (preferably 0.9-1.1) to ensure that the sodium aluminate generation efficiency is maximized during sintering, and the aluminum recovery rate reaches over 95%, while avoiding energy waste caused by excessive alkali. At the same time, 0.5%-8% (preferably 1%-5%) of lime (by weight of oxalate filter cake) is added to generate calcium silicate (CaSiO3) to fix silicon impurities and inhibit the dissolution of iron impurities, achieving a desilication rate of over 90%, laying the foundation for high whiteness products.

[0061] (3) Low-temperature, short-time sintering reduces energy consumption and costs: The sintering temperature is controlled at 900–1100℃, and the time is ≥30 min (preferably 30 min). Compared with the traditional high-temperature sintering process (above 1200℃), energy consumption is reduced by 20%–30%, while avoiding dissolution difficulties caused by over-sintering of clinker and shortening the production cycle. Within this temperature range, sodium oxalate is completely decomposed, and impurities such as CaSiO3 form a stable insoluble phase, ensuring the purity of the sodium aluminate solution and reducing subsequent impurity removal processes.

[0062] (4) High purity and high whiteness product performance: Through full-process impurity control (oxalate removal, desilication, and iron fixation), the Fe2O3 and SiO2 content in the final product is much lower than that of traditional processes, avoiding the influence of iron ion coloration and silicon impurities on the crystal structure. At the same time, the high whiteness aluminum hydroxide has a whiteness >94% and a b-value <0.5, meeting the application requirements of high-end ceramics, electronic materials and other fields. Compared with commercially available products, the whiteness is improved by 3 to 5 percentage points, meeting the needs of high value-added scenarios.

[0063] (5) Advantages of process continuity and green production: Sodium oxalate seeds are recycled, reducing raw material waste; CO2 generated by the decomposition of sodium oxalate during sintering can be recycled, reducing carbon emissions. At the same time, from filter cake preparation to seed decomposition, 2 to 3 steps are reduced compared to the traditional Bayer process for impurity removal, making it convenient to operate and highly stable, suitable for large-scale industrial production.

[0064] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0065] Example 1

[0066] This embodiment provides a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, the method comprising the following steps:

[0067] S11. Add sodium oxalate circulating seeds to the Bayer process seed decomposition mother liquor to remove oxalate and obtain oxalate filter cake containing aluminum hydroxide.

[0068] The Nk content of the mother liquor from the Bayer process is 160 g / L.

[0069] The chemical composition of the oxalate filter cake includes: sodium oxalate, aluminum hydroxide, Fe2O3, SiO2 and other unavoidable impurities. By mass fraction, the content of sodium oxalate is 20%, the content of aluminum hydroxide is 55%, the content of Fe2O3 is 0.1%, and the content of SiO2 is 0.2%.

[0070] S21. Sodium carbonate is added to the oxalate filter cake to adjust the alkali ratio of the oxalate filter cake to 0.9, and lime is added to the oxalate filter cake to obtain a mixture;

[0071] The mass of the lime is 1% of the dry weight of the oxalate filter cake.

[0072] S31. The mixture is sintered to obtain sintered clinker;

[0073] The sintering temperature is 900℃ and the sintering time is 30 minutes.

[0074] S41. Dissolve the sintered clinker using a caustic alkali solution to obtain a sodium aluminate solution;

[0075] S51. The sodium aluminate solution is subjected to fractional decomposition to obtain high-whiteness aluminum hydroxide, which meets the following properties: whiteness 94.6%, b value 0.4, and aluminum hydroxide recovery rate in oxalate filter cake 96.2%.

[0076] Example 2

[0077] This embodiment provides a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, the method comprising the following steps:

[0078] S11. Add sodium oxalate circulating seeds to the Bayer process seed decomposition mother liquor to remove oxalate and obtain oxalate filter cake containing aluminum hydroxide.

[0079] The Nk content of the mother liquor from the Bayer process is 155 g / L.

[0080] The chemical composition of the oxalate filter cake includes sodium oxalate, aluminum hydroxide, Fe2O3 and SiO2. By mass fraction, the content of sodium oxalate is 25%, the content of aluminum hydroxide is 50%, the content of Fe2O3 is 0.25%, and the content of SiO2 is 0.5%.

[0081] S21. Sodium carbonate is added to the oxalate filter cake to adjust the alkali ratio of the oxalate filter cake to 1.1, and lime is added to the oxalate filter cake to obtain a mixture;

[0082] The mass of the lime is 5% of the dry weight of the oxalate filter cake.

[0083] S31. The mixture is sintered to obtain sintered clinker;

[0084] The sintering temperature is 1100℃ and the sintering time is 30 minutes.

[0085] S41. Dissolve the sintered clinker using a caustic alkali solution to obtain a sodium aluminate solution;

[0086] S51. The sodium aluminate solution is subjected to fractional decomposition to obtain high-whiteness aluminum hydroxide, which meets the following properties: whiteness 94.5%, b value 0.4, and aluminum hydroxide recovery rate in oxalate filter cake 97.5%.

[0087] Example 3

[0088] This embodiment provides a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, the method comprising the following steps:

[0089] S11. Add sodium oxalate circulating seeds to the Bayer process seed decomposition mother liquor to remove oxalate and obtain oxalate filter cake containing aluminum hydroxide.

[0090] The Nk content of the mother liquor from the Bayer process is 165 g / L.

[0091] The chemical composition of the oxalate filter cake includes sodium oxalate, aluminum hydroxide, Fe2O3 and SiO2. By mass fraction, the content of sodium oxalate is 30%, the content of aluminum hydroxide is 45%, the content of Fe2O3 is 0.1% and the content of SiO2 is 0.2%.

[0092] S21. Sodium carbonate is added to the oxalate filter cake to adjust the alkali ratio of the oxalate filter cake to 0.9, and lime is added to the oxalate filter cake to obtain a mixture;

[0093] The mass of the lime is 1% of the dry weight of the oxalate filter cake.

[0094] S31. The mixture is sintered to obtain sintered clinker;

[0095] The sintering temperature is 1000℃ and the sintering time is 30 minutes.

[0096] S41. Dissolve the sintered clinker using a caustic alkali solution to obtain a sodium aluminate solution;

[0097] S51. The sodium aluminate solution is subjected to fractional decomposition to obtain high-whiteness aluminum hydroxide, which meets the following properties: whiteness 94.6%, b value 0.4, and aluminum hydroxide recovery rate in oxalate filter cake 96.6%.

[0098] Example 4

[0099] This embodiment provides a method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, the method comprising the following steps:

[0100] S11. Add sodium oxalate circulating seeds to the Bayer process seed decomposition mother liquor to remove oxalate and obtain oxalate filter cake containing aluminum hydroxide.

[0101] The Nk content of the mother liquor from the Bayer process is 160 g / L.

[0102] The chemical composition of the oxalate filter cake includes sodium oxalate, aluminum hydroxide, Fe2O3 and SiO2. By mass fraction, the content of sodium oxalate is 35%, the content of aluminum hydroxide is 40%, the content of Fe2O3 is 0.25%, and the content of SiO2 is 0.5%.

[0103] S21. Sodium carbonate is added to the oxalate filter cake to adjust the alkali ratio of the oxalate filter cake to 1.0, and lime is added to the oxalate filter cake to obtain a mixture;

[0104] The mass of the lime is 3% of the dry weight of the oxalate filter cake.

[0105] S31. The mixture is sintered to obtain sintered clinker;

[0106] The sintering temperature is 1100℃ and the sintering time is 30 minutes.

[0107] S41. Dissolve the sintered clinker using a caustic alkali solution to obtain a sodium aluminate solution;

[0108] S51. The sodium aluminate solution is subjected to fractional decomposition to obtain high-whiteness aluminum hydroxide, which meets the following properties: whiteness 94.5%, b value 0.4, and aluminum hydroxide recovery rate in oxalate filter cake 97.3%.

[0109] Comparative Example 1

[0110] This comparative example is modified from the one disclosed in Example 1 as follows:

[0111] Sodium carbonate is not added to the oxalate filter cake, that is, no alkali ratio is added.

[0112] Of the 55% aluminum hydroxide in the oxalate filter cake, 26% reacts during sintering to form sodium aluminate, which then enters the solution during the subsequent dissolution process. The remaining 29% of aluminum hydroxide will not dissolve, resulting in waste. The recovery rate of aluminum hydroxide in the oxalate filter cake is only 47.3%.

[0113] Comparative Example 2

[0114] This comparative example is modified from the one disclosed in Example 1 as follows:

[0115] No lime is prepared.

[0116] Without lime, impurities such as Fe2O3 and SiO2 in the filter cake will affect the whiteness of the final aluminum hydroxide, reducing it to 93.5% and increasing the b-value to 0.5. The recovery rate of aluminum hydroxide in the oxalate filter cake is 96.3%.

[0117] Comparative Example 3

[0118] This comparative example is based on the disclosure in Example 2, with the following modifications:

[0119] No lime is prepared.

[0120] Without lime, impurities such as Fe2O3 and SiO2 in the filter cake will affect the whiteness of the final aluminum hydroxide, reducing it to 92% and increasing the b-value to 0.7. The recovery rate of aluminum hydroxide in the oxalate filter cake is 97.8%.

[0121] The performance of the high-whiteness aluminum hydroxide obtained in Examples 1-4 and Comparative Examples 1-3 and the recovery rate of aluminum hydroxide in oxalate filter cake were summarized, and the results are shown in Table 1.

[0122] Table 1. Performance of high-white aluminum hydroxide and recovery rate of aluminum hydroxide in oxalate filter cake in examples and comparative examples.

[0123]

[0124] As shown in Table 1, the whiteness of the high-whiteness aluminum hydroxide in Examples 1-4 is >94%, the b value is <0.5, and the recovery rate of aluminum hydroxide in the oxalate filter cake is >96%.

[0125] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0126] (1) In the embodiments of this application, a method for efficiently utilizing the oxalate filter cake is proposed. This method effectively removes organic matter such as oxalate and other impurities through appropriate proportions and appropriate sintering temperatures. The resulting clinker can be dissolved in alkaline solution to obtain a pure sodium aluminate solution, which is then decomposed to obtain a high-white aluminum hydroxide product.

[0127] (2) In this embodiment of the application, through the precise coupling of process parameters (such as Nk concentration, alkali ratio, sintering temperature) and the whole-process design of the impurity control chain, the deep removal of key impurities such as Fe and Si is achieved simultaneously during the oxalate removal process, so that the oxalate filter cake is transformed from "waste" into a high-quality raw material for high-white aluminum hydroxide. Finally, the Bayer process organic matter removal and high-end product preparation are taken into account in the same process, providing a new path for the green and efficient production of alumina.

[0128] (3) In the embodiments of this application, steps S1 to S2 provide raw materials with low impurities and suitable reactivity for sintering by removing oxalate, adjusting the alkali ratio and desiliconizing; step S3 achieves effective conversion of aluminum and fixation of impurities by high-temperature sintering, forming easily soluble sodium aluminate and insoluble slag phase; steps S4 to S5 convert sodium aluminate into high-purity, high-whiteness aluminum hydroxide by dissolution and seed decomposition. The setting of each parameter range is based on the two core objectives of "impurity removal" and "efficient aluminum recovery", ultimately achieving a dual improvement in product whiteness and purity.

[0129] (4) In the embodiments of this application, when the high-purity sodium aluminate solution is decomposed by seed, the previous process has removed coloring impurities such as Fe and Si. Combined with the addition of seed crystals and the control of decomposition conditions (such as temperature and stirring rate), the aluminum hydroxide crystals are promoted to grow uniformly, avoiding defects and agglomeration. The final product has a whiteness >94% and a b value <0.5, which meets the high whiteness standard.

[0130] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing high-whiteness aluminum hydroxide based on oxalate filter cake, the method comprising: Sodium oxalate recycled seeds were added to the mother liquor of the Bayer process to remove oxalate and obtain an oxalate filter cake containing aluminum hydroxide. Sodium carbonate is added to the oxalate filter cake to adjust the alkali ratio of the oxalate filter cake to 0.85-1.15, and lime is added to the oxalate filter cake to obtain a mixture; The mixture is sintered to obtain sintered clinker; The sintered clinker was dissolved in a caustic alkali solution to obtain a sodium aluminate solution; as well as The sodium aluminate solution was subjected to fractional decomposition to obtain high-whiteness aluminum hydroxide.

2. The method according to claim 1, characterized in that, The Nk content of the mother liquor from the Bayer process is 155 g / L to 165 g / L.

3. The method according to claim 1, characterized in that, Adjust the alkali ratio of the oxalate filter cake to 0.9–1.

1.

4. The method according to claim 1, characterized in that, The chemical composition of the oxalate filter cake includes sodium oxalate, aluminum hydroxide, Fe2O3, and SiO2.

5. The method according to claim 3, characterized in that, The sodium oxalate content is 20%–35% by mass fraction, the aluminum hydroxide content is 40%–55%, the Fe2O3 content is 0.1%–0.25%, and the SiO2 content is 0.2%–0.5%.

6. The method according to claim 1, characterized in that, The mass of the lime is 0.5% to 8% of the dry weight of the oxalate filter cake.

7. The method according to claim 6, characterized in that, The mass of the lime is 1% to 5% of the dry weight of the oxalate filter cake.

8. The method according to claim 1, characterized in that, The sintering temperature is 900℃~1100℃, and the sintering time is ≥30min.

9. The method according to claim 8, characterized in that, The sintering temperature is 900℃~1100℃, and the sintering time is 30min.

10. The method according to claim 1, characterized in that, The high-whiteness aluminum hydroxide meets the following properties: whiteness > 94%, b value < 0.5.

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