Calcium balance control method and system for producing aluminum oxide by low-temperature Bayer process

Abstract

The invention provides a calcium balance control method and system for producing aluminum oxide through a low-temperature Bayer process, and belongs to the field of aluminum oxide metallurgy. The method comprises the following steps: mixing bauxite with a blending solution, and then carrying out pre-desiliconization dissolution to obtain pre-desiliconization slurry; carrying out high-temperature dissolution on the pre-desiliconized slurry, and then carrying out settling separation to obtain a decomposed stock solution; mixing part of the decomposed stock solution with lime milk for reaction to obtain an activating solution; adding the activation solution into the rest of the decomposition stock solution, filtering, and dynamically adjusting the addition amount of the activation solution to obtain a refined decomposition stock solution with the Ca < 2 + > concentration of less than or equal to 15 ppm; and judging whether the calcium content in first-tank aluminum hydroxide obtained after seed decomposition of the refined decomposition stock solution is not greater than 180ppm or not, and if so, continuing seed decomposition of the refined decomposition stock solution to obtain low-calcium aluminum hydroxide. Therefore, the technical problem that the calcium content in the aluminum oxide product subjected to pre-desilicication by using guinea ore is increased is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alumina metallurgy, and in particular to a calcium balance control method and system for producing alumina by low-temperature Bayer process. BACKGROUND

[0002] Alumina is an important basic raw material for the development of national economy, and is widely used in metallurgy, chemical industry, building materials and other fields. In the production process of alumina, the Bayer process has become the mainstream process due to its simple process and high efficiency, and the low-temperature Bayer process has been widely adopted due to its low energy consumption and light equipment corrosion. Domestic low-temperature Bayer process has long relied on imported bauxite as raw material, and early bauxite from Indonesia and Australia was mainly used. However, with the continuous expansion of domestic alumina production capacity, the import of bauxite from Indonesia and Australia has gradually decreased, and the supply of raw materials is facing tension. Under this background, the bauxite from Guinea with rich reserves is gradually introduced into the low-temperature Bayer process production system as a substitute raw material, becoming an important choice to alleviate the shortage of raw materials.

[0003] However, the bauxite from Guinea has significant ore characteristic defects: first, the active silicon content in the ore is low, which increases the difficulty of controlling the sodium aluminate solution aluminum-silicon ratio (A / S); second, the red mud has poor settling performance, directly causing problems such as high content of red mud separation floating matter in the production process and low leaf filter material passing efficiency, which seriously affects the continuity of production. To solve the above problems, the existing technology increases the pre-desiliconization process to improve the activity of silicon and increase the solution aluminum-silicon ratio, and adds lime milk as a filter aid to improve the filtering performance of the leaf filter. Although these measures have alleviated the filtering problem to some extent, they have caused the abnormal increase of calcium content in alumina. After using the bauxite from Guinea, the calcium content in the decomposition stock solution can reach up to 25 ppm, finally causing the CaO content in the product alumina to increase from 0.025% to 0.05%, exceeding the industry standard of 0.03%, which seriously affects the purity of alumina and the quality of the product. At the same time, in the existing low-temperature Bayer process technical system, there is a lack of calcium balance integrated control scheme for the characteristics of the bauxite from Guinea, which cannot effectively solve the problem of excessive calcium content in alumina caused by the accumulation of calcium ions in the pre-desiliconization and filtration processes, becoming the core technical bottleneck restricting the efficient application of the bauxite from Guinea in the low-temperature Bayer process. SUMMARY

[0004] The present application provides a calcium balance control method and system for producing alumina by low-temperature Bayer process, to solve the technical problem of the increase of calcium content in alumina after pre-desiliconization of the bauxite from Guinea.

[0005] In a first aspect, the embodiments of the present application provide a calcium balance control method for producing alumina by low-temperature Bayer process, which comprises:

[0006] Mixing bauxite with a preparation solution, and then pre-desiliconization and dissolution to obtain a pre-desiliconization slurry;

[0007] subjecting the pre-desilication slurry to high-temperature dissolution, and then to sedimentation separation to obtain a decomposition stock solution;

[0008] mixing part of the decomposition stock solution with lime milk to obtain an activated solution containing filter aid crystals;

[0009] adding the activated solution into the remaining part of the decomposition stock solution for filtration, and dynamically adjusting the amount of the activated solution added according to the real-time monitoring value of the Ca 2+ concentration in the filtrate of the filtration to obtain a refined decomposition stock solution with a Ca 2+ concentration of ≤15 ppm;

[0010] judging whether the calcium content in the first tank aluminum hydroxide obtained after seed fraction decomposition of the refined decomposition stock solution satisfies not more than 180 ppm, if yes, continuing the seed fraction decomposition of the refined decomposition stock solution to obtain low-calcium aluminum hydroxide; if no, subjecting the refined decomposition stock solution to decomposition purification to enrich and remove Ca 2+ in the refined decomposition stock solution to obtain high-calcium aluminum hydroxide and a decomposition purification stock solution, and then subjecting the decomposition purification stock solution to the seed fraction decomposition to obtain low-calcium aluminum hydroxide;

[0011] subjecting the low-calcium aluminum hydroxide to calcination to obtain low-calcium aluminum oxide product;

[0012] The pre-desilication dissolution includes the following parameters: temperature ≥85℃, solid content ≥400g / L, and dissolution time ≥12h.

[0013] Optionally, the pre-desilication dissolution includes the following parameters: temperature 85℃, solid content ≥400g / L, and dissolution time 12h.

[0014] The temperature of the high-temperature dissolution is 140℃-150℃.

[0015] Optionally, the mixing reaction time is ≥1h.

[0016] The mass ratio of part of the decomposition stock solution to the lime milk is (1.5-2.5):1.

[0017] Optionally, the NK of the decomposition stock solution is 140g / L-150g / L, and the ak is 1.40-1.43.

[0018] The effective calcium of the lime milk is ≥180g / L, and the solid content is ≥280g / L.

[0019] Optionally, the filter cloth material of the filtration is polypropylene with a gas permeation rate ≥200L / m 2 ·s, and the top pressure of the leaf filter of the filtration is ≤200kpa.

[0020] Optionally, the volume of the activation solution accounts for a proportion of ≤3.5‰ of the volume of the remaining portion of the decomposition stock solution.

[0021] Optionally, the decomposition purification comprises the following parameters: a decomposition solid content of 100 g / L-400 g / L, a decomposition initial temperature of 75°C-85°C, and a decomposition time of 10 h-20 h.

[0022] Optionally, the seed decomposition comprises the following parameters: a decomposition solid content of 600 g / L-700 g / L, a decomposition initial temperature of 70°C-75°C, a decomposition final temperature of 50°C-55°C, and a decomposition time of 40 h-60 h.

[0023] Optionally, the low-calcium alumina product has a calcium content of ≤0.03%.

[0024] In a second aspect, the embodiments of the present application provide a calcium balance control system for producing alumina by a low-temperature Bayer process, which is suitable for the method of any one of the embodiments of the first aspect, and the system comprises:

[0025] A pre-desilication dissolution unit, configured to mix bauxite with a conditioning solution, and then perform pre-desilication dissolution to obtain a pre-desilication slurry;

[0026] A decomposition stock solution preparation unit, an inlet of the decomposition stock solution preparation unit being in communication with an outlet of the pre-desilication dissolution unit, and configured to perform high-temperature dissolution on the pre-desilication slurry, and then perform sedimentation separation to obtain a decomposition stock solution;

[0027] A high-efficiency filter aid preparation unit, the high-efficiency filter aid preparation unit being in communication with the decomposition stock solution preparation unit, and configured to mix part of the decomposition stock solution with lime milk to obtain an activation solution containing filter aid crystals;

[0028] A leaf filter, an inlet of the leaf filter being in communication with an outlet of the decomposition stock solution preparation unit and an outlet of the high-efficiency filter aid preparation unit, respectively, and configured to filter a mixed solution of the activation solution and the decomposition stock solution to obtain a Ca 2+ concentration of ≤15 ppm refined decomposition stock solution;

[0029] An online Ca 2+ concentration monitoring unit, the online Ca 2+ concentration monitoring unit being in communication with a liquid outlet of the leaf filter, and configured to monitor the Ca 2+ concentration in the filtered filtrate in real time;

[0030] A decomposition purification unit, the decomposition purification unit being in communication with the liquid outlet of the leaf filter, and configured to perform decomposition purification on the refined decomposition stock solution to obtain high-calcium aluminum hydroxide and a decomposition purification stock solution;

[0031] a seed fraction decomposition unit, which is in communication with the liquid outlet of the leaf filter and the liquid outlet of the decomposition purification unit respectively, and is used for carrying out seed fraction decomposition on the refined decomposition stock solution and the decomposition purification stock solution to obtain low calcium aluminum hydroxide;

[0032] a calcination unit, which is in communication with the solid outlet of the seed fraction decomposition unit, and is used for carrying out calcination on the low calcium aluminum hydroxide to obtain low calcium aluminum oxide product.

[0033] Compared with the prior art, the above technical solution provided by the embodiments of the present application has the following advantages:

[0034] The embodiments of the present application provide a calcium balance control method for producing aluminum oxide by low-temperature Bayer process, which comprises the following steps: mixing bauxite with a preparation solution, and then carrying out pre-desilication dissolution to obtain a pre-desilication slurry; carrying out high-temperature dissolution on the pre-desilication slurry, and then carrying out sedimentation separation to obtain a decomposition stock solution; mixing part of the decomposition stock solution with lime milk to obtain an activated solution containing filter aid crystals; adding the activated solution into the remaining part of the decomposition stock solution for filtration, and dynamically adjusting the addition amount of the activated solution according to the real-time monitoring value of Ca 2+ concentration in the filtrate of the filtration, so as to obtain a refined decomposition stock solution with Ca 2+ concentration ≤ 15 ppm; judging whether the calcium content in the first tank aluminum hydroxide obtained after the seed fraction decomposition of the refined decomposition stock solution meets the condition of not more than 180 ppm, if yes, continuing to carry out the seed fraction decomposition on the refined decomposition stock solution to obtain low calcium aluminum hydroxide; if no, carrying out decomposition purification on the refined decomposition stock solution to enrich and remove Ca 2+ in the refined decomposition stock solution, to obtain high calcium aluminum hydroxide and a decomposition purification stock solution, and then carrying out the seed fraction decomposition on the decomposition purification stock solution to obtain low calcium aluminum hydroxide; carrying out calcination on the low calcium aluminum hydroxide to obtain low calcium aluminum oxide product; wherein the pre-desilication dissolution comprises the following parameters: temperature ≥ 85℃, solid content ≥ 400 g / L, and dissolution time ≥ 12 h.

[0035] Firstly, in the pre-desilication dissolution link, according to the characteristics of Guinea bauxite, the temperature is increased to ≥ 85℃, the solid content is controlled to be ≥ 400 g / L, and the dissolution time is prolonged to ≥ 12 h, so as to enhance the stability of calcium-silicon residue and reduce the release of calcium ions from the solid phase to the solution, thereby reducing the risk of calcium pollution from the beginning of raw material treatment and reducing the pressure of calcium control in the subsequent process;

[0036] Secondly, through the decomposition of the mixed reaction of the stock solution and lime milk, the two are fully reacted to form high-efficiency filter aid crystals (such as tricalcium aluminate TCA) with complete crystal form. TCA has a loose and porous "bridge" structure, which can effectively improve the filtration performance, without relying on excess lime milk, thereby avoiding excess lime milk in the reaction process, reducing free Ca 2+ ;

[0037] Thirdly, by introducing online Ca 2+ concentration monitoring, dynamically adjusting the lime milk dosage, and ensuring that the calcium ion content in the decomposition stock solution is less than 15 ppm;

[0038] Finally, increase the decomposition purification, optimize the decomposition system, carry out the main and auxiliary double-feeding decomposition process, control the decomposition conditions of the decomposition purification auxiliary process, so that the impurity calcium is enriched, and the calcium ion in the main process is reduced;

[0039] Therefore, through the preparation of high-efficiency filter aid process, while increasing the online calcium ion detection system to dynamically adjust the high-efficiency filter aid lime milk dosage, optimizing the pre-desilication dissolution conditions, and increasing the decomposition purification unit, the technical problem of the increase of calcium content in the alumina product after pre-desilication of Guinea ore is solved. BRIEF DESCRIPTION OF DRAWINGS

[0040] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the specification, serve to explain the principles of the application.

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor.

[0042] Figure 1 A flowchart of a calcium balance control method for producing alumina by low-temperature Bayer process provided by the embodiments of the present application;

[0043] Figure 2 A structure diagram of a calcium balance control system for producing alumina by low-temperature Bayer process provided by the embodiments of the present application;

[0044] Figure 3 A structure diagram of a high-efficiency filter aid preparation unit provided by the embodiments of the present application;

[0045] Reference signs:

[0046] 1 - pre-desilication dissolution unit, 2 - decomposition stock solution preparation unit, 3 - high-efficiency filter aid preparation unit, 4 - leaf filter, 5 - online Ca 2+Concentration monitoring unit, 6 - decomposition purification unit, 7 - kind of decomposition unit, 8 - calcination unit. DETAILED DESCRIPTION

[0047] To make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0048] The range descriptions described herein, such as numerical range, ratio range, etc., all include all possible sub-ranges within the range and single values, for example, the range description of "1 to 6" or "1 ~ 6" covers 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 "include", "contain" and the like used herein mean "include but not limited to"; the relationship terms "first", "second" and the like are only used to distinguish different entities or operations, and do not imply actual sequence or relationship; "and / or" means that multiple cases can exist independently or simultaneously; "at least one", "multiple", "at least one" and the like refer to any combination of the corresponding objects, including single or multiple combinations of objects. The proportional relationship involved herein, such as mass ratio, molar ratio, etc., should be understood as the corresponding relationship between the front and the rear in the proportional form according to the sequence of description. The raw materials, reagents, instruments and equipment used herein can be purchased or prepared by existing methods.

[0049] The ore reserves of Boffa mine in Guinea are large, but the ore also has the disadvantages of low active silicon and poor red mud settling performance, which can easily cause high red mud separation and plankton in the process of use. The applicant of the present application increases pre-desiliconization to improve the activity of silicon and increase the solution aluminum-silicon ratio (A / S), and adds lime milk to improve the filtration performance of the leaf filter, but the problem of abnormal increase of calcium content in alumina occurs. Through a series of research and analysis, it is found that it is mainly caused by the following five aspects:

[0050] (1) Excessive addition of lime milk: Lime milk as a filter aid is mainly due to the formation of a "bridging" structure of tricalcium aluminate (TCA) or activated garnet with uniform and loose porous crystals between lime milk and sodium aluminate solution. If the activation is not complete, the lime milk will cover the filter cloth, resulting in poor leaf filter material. Since there is no effective monitoring means in the addition process, it is easy to cause excessive addition of lime milk (Ca(OH)2), resulting in free Ca 2-The concentration is increased. According to statistics, the addition amount of lime milk reaches 6 ‰ at most, which not only increases the consumption of lime milk, but also causes the calcium content in the process to exceed the standard.

[0051] (2) Low-temperature calcium salt dissolution characteristics: under the low-temperature conditions of the pre-desilication process, the calcium-silicon residue (such as Ca3SiO5) has poor stability, and the solubility of CaSO4 abnormally increases, which aggravates the residual calcium ions.

[0052] (3) Aluminum ion complexation effect: in the high A / S solution, Al(OH)4 - forms a soluble complex with Ca 2+ , inhibiting the precipitation of calcium salt.

[0053] (4) Defects of the leaf filter system: due to improper selection of filter cloth used in the leaf filter and improper process operation, free calcium penetrates the filter cloth, causing the calcium ion and suspended matter to exceed the standard. According to statistics, the average content of suspended matter in the pregnant liquor reaches more than 0.04 g / L. In terms of material, the performance of different materials of filter cloth is obviously different. For example, the polypropylene filter cloth has good air permeability, which can ensure the smooth progress of the filtration process; while the air permeability of the polypropylene fiber filter cloth is relatively poor, which is easy to cause blockage; and the air permeability of the filter cloth directly affects the content of suspended matter and calcium ions in the filtrate. In order to prevent calcium ions from penetrating, filter cloth with small pore size, high porosity and good pressure resistance should be selected.

[0054] (5) The impurity-free purification process leads to continuous enrichment of calcium ions in the process, causing the calcium content in the product to exceed the standard. The calcium-containing mother liquor that is not discharged in time gradually accumulates in the circulation. According to statistics, due to the above reasons, the calcium content in the decomposition pregnant liquor process using Guinea ore reaches 25 ppm at most, the Ca content in the first tank is more than 250 ppm, and finally the CaO content in the product alumina increases from 0.025% to 0.05%.

[0055] Therefore, based on the above five problems, the application solves the technical problem of the increase of calcium content in the alumina product after the pre-desilication of Guinea ore by preparing a high-efficiency filter aid process, simultaneously increasing an online calcium ion detection system to dynamically adjust the addition amount of high-efficiency filter aid lime milk, optimizing the pre-desilication dissolution conditions, and increasing the decomposition and purification unit. The specific technical scheme of the application is as follows:

[0056] Figure 1 A flowchart of a calcium balance control method for producing alumina by a low-temperature Bayer process is provided in the embodiments of the application.

[0057] As shown in Figure 1 , the embodiments of the application provide a calcium balance control method for producing alumina by a low-temperature Bayer process, which comprises:

[0058] S1, mixing bauxite with a conditioning solution, and then performing pre-desilication dissolution to obtain a pre-desilication slurry;

[0059] In some embodiments, the pre-desilication leaching includes the following parameters: temperature ≥ 85℃, solid content ≥ 400g / L, and leaching time ≥ 12h.

[0060] The embodiments of the present application enhance the stability of calcium-silicon residue by optimizing the pre-desilication process, reduce the release of calcium ions from the solid phase to the solution, and reduce the risk of calcium pollution from the source. The calcium-silicon residue has poor stability at low temperature and is easily decomposed, resulting in residual calcium ions. Raising the temperature to ≥ 85℃ can promote the formation of stable crystal structure of calcium-silicon residue (such as Ca3SiO5 is more difficult to dissolve at high temperature), inhibit its decomposition in the subsequent process, and reduce the release of calcium ions to the solution. At the same time, limiting the pre-desilication solid content to ≥ 400g / L, high solid content (≥ 400g / L) can increase the concentration of solid phase particles in the ore slurry, increase the contact efficiency of bauxite and the adjusting solution, promote the combination of silicon (especially the silicon in Guinea ore with low active silicon) and calcium to form calcium-silicon residue, reduce the residual free silicon in the solution, and indirectly reduce the abnormal reaction of calcium and silicon in the subsequent process (such as the problem of increased solubility of CaSO4 at low temperature). In addition, the active silicon in Guinea ore is low, and it is difficult to remove silicon. Extending the leaching time to ≥ 12h can ensure that silicon is fully reacted with calcium to form calcium-silicon residue, avoid the formation of unstable compounds (such as CaSO4) between unreacted silicon and calcium in the subsequent process, and further reduce the residual calcium ions. For example, the temperature of pre-desilication leaching can be 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, etc., the solid content can be 400g / L, 410g / L, 420g / L, 430g / L, 440g / L, 450g / L, etc., and the leaching time can be 12h, 12.1h, 12.2h, 12.3h, 12.4h, 12.5h, 13h, etc.

[0061] In some embodiments, the pre-desilication leaching includes the following parameters: temperature is 85℃, solid content ≥ 400g / L, and leaching time is 12h.

[0062] S2, the pre-desilication slurry is subjected to high-temperature leaching, and then subjected to sedimentation separation to obtain a decomposition stock solution;

[0063] In some embodiments, the temperature of the high-temperature leaching is 140℃-150℃.

[0064] S3, part of the decomposition stock solution is mixed with lime milk to obtain an activated solution containing filter aid crystals;

[0065] The embodiments of the present application prepare efficient filter aid crystals (such as tricalcium aluminate TCA) to ensure the filtration performance while avoiding excessive lime milk to cause free Ca 2+ to increase.

[0066] In some embodiments, the mixing reaction time is ≥ 1h.

[0067] The mass ratio of the decomposition solution to the lime milk is (1.5-2.5):1.

[0068] Excessive lime slurry is a key factor leading to excessive calcium levels. Limiting the mass ratio of the decomposition solution to lime slurry to (1.5–2.5):1 ensures sufficient reaction between the lime slurry and the sodium aluminate solution in the decomposition solution to form TCA or activated garnet (filter aid crystals). This avoids both insufficient lime slurry leading to incomplete bridging (poor filtration) and excessive lime slurry causing free calcium. 2+ Increased concentration (Ca in the leaching solution) 2+ (Exceeding the standard). For example, the mass ratio of the decomposition stock solution to lime milk can be 1.5:1, 1.7:1, 1.9:1, 2.0:1, 2.1:1, 2.3:1, 2.5:1, etc.

[0069] Limiting the mixing reaction time to ≥1 hour ensures that the lime slurry and sodium aluminate solution react fully, forming a loose, porous "bridging" structure with complete crystal structure and uniform distribution. This ensures the filtration effect while reducing the residue of unreacted lime slurry. For example, the mixing reaction time can be 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, etc.

[0070] In some embodiments, the NK of the decomposition stock solution is 140 g / L to 150 g / L, and the ak is 1.40 to 1.43;

[0071] The lime slurry has an effective calcium content ≥180g / L and a solid content ≥280g / L.

[0072] Excessive NK (caustic soda concentration) can lead to supersaturation of the solution, affecting crystal formation; controlling ak (sodium aluminate solution molecular ratio) between 1.40 and 1.43 can ensure the concentration of Al(OH)₄ in the solution. - A moderate concentration is beneficial for reacting with Ca. 2+ It forms stable TCA crystals (filter aid) while avoiding high ak levels in Al(OH)4. - With Ca 2+ This forms a soluble complex, reducing calcium ion residue. For example, the NK of the decomposition solution can be 140 g / L, 142 g / L, 144 g / L, 146 g / L, 148 g / L, 150 g / L, etc., and the ak can be 1.40, 1.41, 1.42, 1.425, 1.43, etc.

[0073] Available calcium and solid content are essential for ensuring the calcium content of lime milk. 2+ Concentration is key to ensuring sufficient Ca in the reaction system. 2+ Participate in the formation of filter aid crystals, avoiding the formation of Ca 2+Inadequate activation. For example, the effective calcium of the lime milk can be 180 g / L, 182 g / L, 185 g / L, 190 g / L, 195 g / L, 200 g / L, etc., and the solid content can be 280 g / L, 285 g / L, 290 g / L, 295 g / L, 300 g / L, etc.

[0074] S4, adding the activation liquid to the remaining part of the decomposition stock solution to perform filtration, and dynamically adjusting the addition amount of the activation liquid according to the Ca 2+ concentration of the filtrate of the filtration, so as to obtain a refined decomposition stock solution with a Ca 2+ concentration of ≤15 ppm.

[0075] The present application optimizes the filtration conditions and the addition amount of the activation liquid, reduces the penetration of calcium ions into the filter cloth into the filtrate, and avoids the excessive introduction of calcium caused by excessive activation liquid.

[0076] In some embodiments, the filtration filter cloth material is polypropylene with a gas permeability of ≥200 L / m 2 ·s, and the top pressure of the leaf filter is ≤200 kpa.

[0077] Polypropylene filter cloth is easy to block due to poor air permeability, while polypropylene filter cloth has good air permeability, high porosity, and strong pressure resistance. High air permeability (≥200 L / m 2 ·s) can ensure smooth filtration and avoid pressure rise caused by blockage; its small pore size structure can effectively intercept free Ca 2+ and calcium-containing floating objects, reducing the penetration of calcium ions into the second decomposition stock solution. For example, the air permeability of the polypropylene filter cloth can be 200 L / m 2 ·s, 202 L / m 2 ·s, 205 L / m 2 ·s, 210 L / m 2 ·s, 215 L / m 2 ·s, 220 L / m 2 ·s, etc.

[0078] Excessive pressure can cause the filter cloth to deform and break, allowing unintercepted free Ca 2+ to directly penetrate the filter cloth. Controlling the pressure to be ≤200 kpa can protect the integrity of the filter cloth structure, ensure the filtration precision, and reduce the calcium ion content in the filtrate. For example, the top pressure of the leaf filter can be 199 kpa, 195 kpa, 190 kpa, 185 kpa, 180 kpa, 170 kpa, etc.

[0079] In some embodiments, the volume of the activation liquid accounts for ≤3.5 ‰ of the volume of the remaining part of the decomposition stock solution.

[0080] The activation solution is one of the main sources of calcium ions, and an excessively high proportion can lead to total Ca 2+ Excessive introduction. Limiting the proportion to ≤3.5‰ can control calcium input from the source, combined with online Ca 2+ Concentration monitoring dynamically adjusts the dosage, realizes "on-demand dosing", balances the filter aid effect and calcium content control. Thus, through online Ca 2+ Concentration monitoring dynamically adjusts the dosage of lime milk, ensuring that the calcium ion content in the decomposed stock solution is less than 15 ppm. For example, the volume of the activation solution can account for 3.4‰, 3.3‰, 3.2‰, 3.1‰, 3.0‰, 2.9‰, 2.8‰, 2.7‰, etc. of the volume of the remaining portion of the decomposed stock solution.

[0081] Thus, the embodiments of the present application implement an efficient filter aid preparation technology, increase the reaction tank and the reserve tank, ensure sufficient time and temperature to prepare efficient filter aids with uniform crystal morphology, monitor the preparation effect through electron microscopy and qualitative phase analysis, optimize the dosing system to ensure the filter aid effect, and reduce the use of lime milk and excessive calcium ions. At the same time, the leaf filter system is optimized, the filter cloth is optimized, the filter cloth performance is increased, and calcium ion penetration is avoided; the leaf filter system process control is refined to avoid short circuit of the leaf filter system.

[0082] S5, determining whether the calcium content in the first tank aluminum hydroxide obtained after the seed separation of the refined decomposed stock solution meets not more than 180 ppm, if yes, continuing the seed separation of the refined decomposed stock solution to obtain low calcium aluminum hydroxide; if no, decomposing and purifying the refined decomposed stock solution to enrich and remove Ca 2+ in the refined decomposed stock solution, obtaining high calcium aluminum hydroxide and a decomposed and purified stock solution, and then performing the seed separation of the decomposed and purified stock solution to obtain low calcium aluminum hydroxide;

[0083] The present application enriches and removes excessive calcium ions through hierarchical processing (direct seed separation if meeting the standard, decomposing and purifying if not meeting the standard), ensures that the calcium content in the first tank aluminum hydroxide is ≤180 ppm. Thus, the present application increases the decomposing and purifying unit, optimizes the decomposition system, develops a main and auxiliary double-feeding decomposition process, controls the decomposition conditions of the auxiliary process of decomposing and purifying, enriches impurity calcium, and reduces calcium ions in the main process.

[0084] In some embodiments, the decomposing and purifying includes the following parameters: the decomposed solid content is 100 g / L-400 g / L, the initial decomposing temperature is 75°C-85°C, and the decomposing time is 10 h-20 h.

[0085] When Ca 2+When the content exceeds the standard, the following mechanisms are used to enrich and remove calcium: low solid content (100 g / L-400 g / L) can reduce the viscosity of the solution, promote the migration of calcium ions to the solid phase (aluminum hydroxide), and temperature 75-85°C can balance the precipitation of calcium salt and the decomposition of complex; extending the time to 10-20h can ensure that the calcium ions are fully enriched in high-calcium aluminum hydroxide, so that the calcium content of the decomposition mother liquor after purification is reduced to ≤15ppm and the calcium content of the first tank is ≤180ppm.

[0086] In some embodiments, the seed decomposition includes the following parameters: decomposition solid content is 600 g / L-700 g / L, initial decomposition temperature is 70-75°C, final decomposition temperature is 50-55°C, and decomposition time is 40-60h.

[0087] High solid content (600 g / L-700 g / L) is suitable for the growth of aluminum hydroxide crystals in low-calcium solution, reducing the embedding of calcium ions into the crystal lattice; temperature is the initial temperature 70-75°C and the final temperature 50-55°C, which can inhibit the Ca 2+ and Al(OH)4 - form a soluble complex; long time (40h) ensures complete decomposition and generates high-purity low-calcium aluminum hydroxide.

[0088] S6, calcining the low-calcium aluminum hydroxide to obtain a low-calcium aluminum oxide product;

[0089] In some embodiments, the calcium content of the low-calcium aluminum oxide product is ≤0.03%.

[0090] The present application effectively removes process calcium ions, effectively controls the calcium in the sodium aluminate solution process through pre-desiliconization process control, increases the preparation process of high-efficiency filter aid, and decomposes and purifies the unit, and the Ca 2+ concentration in the seed decomposition solution is below 15ppm, the calcium content in the first tank is ≤180ppm, and the calcium content of the aluminum oxide product is ≤0.03%.

[0091] Based on a general inventive concept, the embodiments of the present application provide a calcium balance control system for producing aluminum oxide by low-temperature Bayer process, which is suitable for the method of any one of the above embodiments, and the system comprises:

[0092] A pre-desiliconization dissolution unit is used to mix bauxite with a conditioning solution, and then pre-desiliconization dissolution is performed to obtain a pre-desiliconization slurry;

[0093] A decomposition mother liquor preparation unit, the inlet of which is in communication with the outlet of the pre-desiliconization dissolution unit, is used to perform high-temperature dissolution on the pre-desiliconization slurry, and then perform sedimentation separation to obtain a decomposition mother liquor;

[0094] An efficient filter aid preparation unit, which is in communication with the decomposition stock preparation unit, is used for mixing reaction of part of the decomposition stock with lime milk to obtain an activated liquid containing filter aid crystals;

[0095] A leaf filter, an inlet of which is in communication with outlets of the decomposition stock preparation unit and the efficient filter aid preparation unit respectively, is used for filtering the mixed liquid of the activated liquid and the decomposition stock to obtain Ca 2+ A refined decomposition stock with a Ca

[0096] An online Ca 2+ Concentration monitoring unit, which is in communication with the liquid outlet of the leaf filter, is used for real-time monitoring of the Ca 2+ Concentration in the filtered filtrate. 2+ Concentration;

[0097] A decomposition purification unit, which is in communication with the liquid outlet of the leaf filter, is used for impurity purification of the refined decomposition stock to obtain high-calcium aluminum hydroxide and a decomposition purification stock.

[0098] A seed fraction decomposition unit, which is in communication with liquid outlets of the leaf filter and the decomposition purification unit respectively, is used for seed fraction decomposition of the refined decomposition stock and the decomposition purification stock to obtain low-calcium aluminum hydroxide.

[0099] A calcination unit, which is in communication with the solid outlet of the seed fraction decomposition unit, is used for calcination of the low-calcium aluminum hydroxide to obtain a low-calcium aluminum oxide product.

[0100] It should be noted that the online Ca 2+ Concentration monitoring unit includes an alkali corrosion-resistant calcium ion selective electrode integrated with a temperature and pH sensor. By periodically sending samples for ICP detection of calcium content comparison, a process calcium ion monitoring account is established to effectively monitor the calcium ions in the decomposition stock.

[0101] Figure 3 The structure diagram of the efficient filter aid preparation unit provided by the embodiment of the application is shown.

[0102] As Figure 3 shown, in some embodiments, the efficient filter aid preparation unit includes an activated liquid preparation tank and a storage tank.

[0103] In this system, the specific operation process of the efficient filter aid preparation unit is as follows:

[0104] Semen concentrate (decomposition stock solution) is drawn from the semen heating pump pipeline into the activation solution preparation tank. Simultaneously, lime slurry is also transported from the lime slurry tank through the lime slurry co-preparation tank and the lime slurry reaction tank to the activation solution preparation tank. The decomposition stock solution (semen) and lime slurry are mixed and reacted in a specific ratio for a reaction time of ≥1 hour.

[0105] After the reaction in the activation solution preparation tank is completed, the prepared activation solution (containing filter aid crystals) is pumped into the activation solution storage tank. The activation solution remains in the storage tank to ensure sufficient reaction time, further guaranteeing the stability and activity of the filter aid crystals. Subsequently, the activation solution is pumped from the storage tank to the stock solution tank via an activation solution addition process, where it is mixed with the decomposition stock solution before entering the subsequent filtration stage. Through this series of operations in the reaction tank and storage tank, a highly efficient filter aid is prepared, providing excellent filtration performance for subsequent filtration processes while controlling the amount of calcium ions introduced.

[0106] The calcium balance control scheme for low-temperature Bayer process alumina production provided in this application has several advantages:

[0107] (1) Source control: In the pre-desiliconization leaching process, in view of the characteristics of Guinea Bohemia ore, the stability of calcium silicate slag is enhanced by increasing the temperature to ≥85℃, controlling the solid content to ≥400g / L, and extending the leaching time to ≥12h. This reduces the release of calcium ions from the solid phase into the solution, thereby reducing the risk of calcium pollution from the initial stage of raw material processing and alleviating the pressure of calcium control in subsequent processes.

[0108] (2) Precise preparation of filter aid: During the mixed reaction, the mass ratio of the decomposition stock solution to lime slurry is precisely limited to (1.5~2.5):1, the reaction time is ≥1h, and the NK of the decomposition stock solution is 140~150g / L, ak is 1.40~1.43, the effective calcium of the lime slurry is ≥180g / L, and the solid content is ≥280g / L. This series of parameter controls ensures the formation of a highly efficient filter aid with complete crystal structure and uniform distribution (such as tricalcium aluminate TCA), which not only meets the filtration performance requirements but also prevents excessive lime slurry from causing free Ca. 2+ Increase the concentration to achieve a balance between filtration and calcium content control.

[0109] (3) Fine control of the filtration process: Select an air permeability of 200L / m 2 The polypropylene filter cloth is used, and the pressure at the top of the leaf filter is controlled to be ≤200 kPa. Simultaneously, the ratio of the activation liquid volume to the original decomposition liquid volume is limited to ≤3.5‰, and online Ca2+ is used. 2+ Concentration monitoring dynamically adjusts the dosage. These measures ensure smooth filtration while effectively preventing calcium ions from penetrating the filter cloth, avoiding excessive calcium introduction by the activation solution, and achieving precise control of calcium content during the filtration process.

[0110] (4) Graded calcium removal to ensure purity: Based on the Ca content in the first batch of aluminum hydroxide...2+ Concentration was graded. The Ca in the first tank of hydrogen-aluminum was... 2+ When the concentration is greater than 180 ppm, the excess calcium ions are enriched and removed through a decomposition and purification unit (decomposition solids content 100 g / L~400 g / L, initial decomposition temperature 75℃~85℃, decomposition time 10h~20h). Then, the decomposition and purification stock solution is further decomposed (decomposition solids content 700 g / L, initial decomposition temperature 70℃~75℃, final decomposition temperature 50℃~55℃, decomposition time 40h~60h). This staged treatment method ensures that the calcium content of the stock solution entering the seed solution meets the standard, reduces the calcium content in aluminum hydroxide, and improves the purity of alumina.

[0111] (5) Product quality meets standards: Through effective control of calcium ions throughout the entire process, including the synergistic effect of pre-desiliconization process optimization, high-efficiency filter aid preparation, filtration and decomposition purification, the calcium content in the first tank of hydrogen aluminum is reduced to below 180ppm, and the calcium content of the final alumina product is ≤0.03%, meeting the high quality requirements.

[0112] 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.

[0113] Example 1

[0114] This embodiment provides a method for controlling calcium balance in low-temperature Bayer process alumina production, the method comprising:

[0115] S11. Guinean bauxite is mixed and ground with a blending solution, and then pre-desiliconized and dissolved to obtain a pre-desiliconized slurry.

[0116] The concentrations of the prepared solution are ak 2.92, NK 195 g / L, AO 110 g / L, and NT 239 g / L;

[0117] The pre-desilicon leaching process includes the following parameters: temperature of 85℃, solid content of 400g / L, and leaching time of 12h;

[0118] S21. The pre-desiliconized slurry is leached at 140°C. The leached slurry is then separated by sedimentation to obtain the decomposition original solution.

[0119] S31. Part of the decomposition stock solution and lime milk are mixed and reacted in a newly built activation tank to obtain an activation solution containing filter aid crystals; electron microscopy analysis shows that the filter aid crystals are loose and porous with complete crystal form and morphology.

[0120] The mixing reaction time is 1h;

[0121] The mass ratio of the decomposition stock solution to the lime milk is 2:1;

[0122] The NK of the decomposition stock solution is 150g / L, and the ak is 1.41; the effective calcium of the lime milk is 180g / L, and the solid content is 280g / L;

[0123] S41, the activation solution is added to the remaining part of the decomposition stock solution for filtration, and the Ca 2+ The concentration real-time monitoring value is dynamically adjusted to obtain a refined decomposition stock solution;

[0124] The filter cloth material of the filtration has a gas permeation amount of 200L / m 2 s of polypropylene, and the top pressure of the leaf filter of the filtration is 190kpa;

[0125] The volume of the activation solution accounts for 3.2‰ of the volume of the decomposition stock solution;

[0126] S51, the Ca 2+ The concentration of the refined decomposition stock solution is 10ppm, the refined decomposition stock solution is subjected to seed decomposition, the calcium content in the first tank of aluminum hydroxide is 150ppm, and low-calcium aluminum hydroxide is obtained;

[0127] The seed decomposition includes the following parameters: decomposition solid content is 700g / L, initial decomposition temperature is 70℃, final decomposition temperature is 50℃, and decomposition time is 40h;

[0128] S61, the low-calcium aluminum hydroxide is calcined to obtain low-calcium aluminum oxide product with a CaO percentage content of 0.024%.

[0129] Example 2

[0130] The embodiment provides a calcium balance control method for producing aluminum oxide by a low-temperature Bayer process, and the method comprises the following steps:

[0131] S11, Guinea bauxite is mixed and ground with a preparation solution, and then pre-desilication dissolution is performed to obtain a pre-desilication slurry;

[0132] The concentration of the preparation solution is ak 2.92, NK 195g / L, AO 110g / L, and NT 239g / L;

[0133] The pre-desilication dissolution includes the following parameters: temperature is 85℃, solid content is 400g / L, and dissolution time is 12h;

[0134] S21, the pre-desilication slurry is subjected to high-temperature leaching at 150 DEG C, and the leached slurry is subjected to sedimentation separation to obtain a decomposition stock solution;

[0135] S31, part of the decomposition stock solution is mixed with lime milk in a newly-built activation tank to obtain an activated solution containing filter aid crystals; electron microscope analysis shows that the filter aid crystals are loose and porous, and the crystal type and morphology are complete;

[0136] The mixing reaction time is 1 h;

[0137] The mass ratio of the decomposition stock solution to the lime milk is 2:1;

[0138] The NK of the decomposition stock solution is 140 g / L, and the ak is 1.40; the effective calcium of the lime milk is 200 g / L, and the solid content is 300 g / L;

[0139] S41, the activated solution is added to the remaining part of the decomposition stock solution for filtration, and the addition amount of the activated solution is dynamically adjusted according to the real-time monitoring value of the Ca 2+ concentration in the filtrate of the filtration to obtain a refined decomposition stock solution;

[0140] The filtration filter cloth material is a polypropylene fiber with a gas permeability of 220 L / m 2 ·s, and the top pressure of the leaf filter for filtration is 180 kpa;

[0141] The volume ratio of the activated solution to the decomposition stock solution is 3.5‰;

[0142] S51, the Ca 2+ concentration of the refined decomposition stock solution is measured to be 17 ppm, and the calcium content in the first tank hydrogen aluminate is measured to be 175 ppm, the refined decomposition stock solution is subjected to decomposition purification to enrich and remove the Ca 2+ in the refined decomposition stock solution, to obtain high-calcium aluminum hydroxide and a decomposition purification stock solution, and then the decomposition purification stock solution is subjected to seed decomposition to obtain low-calcium aluminum hydroxide;

[0143] The decomposition purification includes the following parameters: decomposition solid content is 300 g / L, decomposition initial temperature is 85 DEG C, and decomposition time is 18 h;

[0144] The seed decomposition includes the following parameters: decomposition solid content is 700 g / L, decomposition temperature initial temperature is 70 DEG C, final temperature is 50 DEG C, and decomposition time is 40 h;

[0145] S61, the low-calcium aluminum hydroxide is calcined to obtain a low-calcium aluminum oxide product with a CaO percentage content of 0.0260%.

[0146] Example 3

[0147] The embodiment provides a calcium balance control method for producing alumina by a low-temperature Bayer process, and the method comprises the following steps:

[0148] S11, Guinea bauxite is mixed and ground with a preparation liquid, and then pre-desilication dissolution is performed to obtain a pre-desilication slurry;

[0149] The concentration of the preparation liquid is ak 2.92, NK 195 g / L, AO 110 g / L and NT 239 g / L.

[0150] The pre-desilication dissolution comprises the following parameters: the temperature is 85 DEG C, the solid content is 440 g / L, and the dissolution time is 12 h.

[0151] S21, the pre-desilication slurry is subjected to high-temperature dissolution at 145 DEG C, and the slurry after dissolution is subjected to sedimentation separation to obtain a decomposition stock solution;

[0152] S31, part of the decomposition stock solution is mixed with lime milk in a newly-built activation tank to obtain an activated liquid containing filter aid crystals; electron microscope analysis shows that the filter aid crystals are loose and porous, and the crystal type and morphology are complete.

[0153] The mixing reaction time is 1.5 h.

[0154] The mass ratio of the decomposition stock solution to the lime milk is 2:1.

[0155] The NK of the decomposition stock solution is 130 g / L, and the ak is 1.43; the effective calcium of the lime milk is 210 g / L, and the solid content is 295 g / L.

[0156] S41, the activated liquid is added to the remaining part of the decomposition stock solution to perform filtration, and the addition amount of the activated liquid is dynamically adjusted according to the real-time monitoring value of the Ca 2+ concentration in the filtrate of the filtration, to obtain a refined decomposition stock solution.

[0157] The filter cloth material of the filtration is polypropylene with a gas permeation amount of 230 L / m 2 ·s, and the top pressure of the leaf filter of the filtration is 190 kpa.

[0158] The volume ratio of the activated liquid to the decomposition stock solution is 2.5 ‰.

[0159] S51, the Ca 2+ concentration of the refined decomposition stock solution is measured as 20 ppm, and the calcium content in the first tank hydrogen aluminum is measured as 195 ppm. The refined decomposition stock solution is subjected to decomposition purification to enrich and remove the Ca 2+, to obtain high calcium aluminum hydroxide and decomposition and purification of the original solution, and then the decomposition and purification of the original solution is carried out by seed decomposition, to obtain low calcium aluminum hydroxide;

[0160] Among them, the decomposition and purification includes the following parameters: the decomposition solid content is 250g / L, the initial decomposition temperature is 78℃, and the decomposition time is 16h;

[0161] The seed decomposition includes the following parameters: the decomposition solid content is 650g / L, the initial decomposition temperature is 75℃, the final decomposition temperature is 52℃, and the decomposition time is 40h;

[0162] S61, the low calcium aluminum hydroxide is calcined to obtain a low calcium aluminum oxide product with a CaO content of 0.0288%.

[0163] Comparative Example 1

[0164] The present comparative example provides a calcium balance control method for producing aluminum oxide by low temperature Bayer process, which comprises:

[0165] S11, Guinea bauxite is mixed and ground with a preparation solution, and then pre-desilication dissolution is carried out to obtain a pre-desilication slurry;

[0166] Among them, the concentration of the preparation solution is ak 2.92, NK 195g / L, AO 110g / L, NT 239g / L;

[0167] The pre-desilication dissolution includes the following parameters: the temperature is 80℃, the solid content is 300g / L, and the dissolution time is 12h;

[0168] S21, the pre-desilication slurry is subjected to high temperature dissolution at 150℃, and the slurry after dissolution is subjected to sedimentation separation to obtain a decomposition original solution;

[0169] S31, lime milk is added to the decomposition original solution for filtration to obtain a refined decomposition original solution;

[0170] Among them, the effective calcium of the lime milk is 180g / L, and the solid content is 280g / L;

[0171] The filter cloth material of the filtration has a gas permeability of 300L / m 2 ·s of polypropylene, the top pressure of the leaf filter of the filtration is 300kpa;

[0172] The volume of the lime milk accounts for 6‰ of the volume of the decomposition original solution;

[0173] S31, the Ca 2+ Concentration of the refined decomposition original solution is measured to be 25ppm, and the refined decomposition original solution is subjected to seed decomposition to obtain aluminum hydroxide with a calcium content of 240ppm;

[0174] The decomposition of the seed solution includes the following parameters: decomposition solid content 700 g / L, initial temperature 75°C, final temperature 52°C, and decomposition time 50 h.

[0175] S51, roasting the aluminum hydroxide to obtain an alumina product with a CaO content of 0.040%.

[0176] The CaO content of the low-calcium alumina products of Examples 1-3 and Comparative Example 1 was determined, and the results are shown in Table 1.

[0177] Table 1 CaO content (wt.%) of the alumina products of Examples 1-3 and Comparative Example 1

[0178]

[0179]

[0180] In Comparative Example 1, there was no online Ca 2+ The concentration monitoring system was generally reported after 2 days. Lime milk was directly added to the original solution tank, and the filter had poor performance.

[0181] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0182] In the embodiments of the present application, the efficient filter aid preparation process is prepared, the online calcium ion detection system is added to dynamically adjust the lime milk dosage of the efficient filter aid, the pre-desiliconization dissolution conditions are optimized, and the decomposition purification unit is added to solve the technical problem of increased calcium content in aluminum hydride after pre-desiliconization of Guinea ore.

[0183] In the embodiments of the present application, the calcium content in the alumina process refining decomposition original solution is less than 15 ppm, the alumina content is less than 0.03%, the lime milk dosage is reduced by 20%, and the process is suitable for industrial production of alumina using Guinea ore low-temperature Bayer process.

[0184] In the embodiments of the present application, the Ca 2+ The removal rate is ≥50%.

[0185] In the embodiments of the present application, a calcium ion full-process detection system is formed, and the calcium content in the process is effectively monitored through online detection and ICP, and the process calcium content is timely warned when it exceeds the standard.

[0186] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications and changes can be made to these embodiments without departing from the spirit and scope of the application. It is intended that the scope of the application should not be limited by the particular representative embodiments described above.

Claims

1. A method for controlling calcium balance in low-temperature Bayer process alumina production, the method comprising: Bauxite is mixed with a blending solution, and then pre-desiliconized and dissolved to obtain a pre-desiliconized slurry. The pre-desiliconized slurry is dissolved at high temperature and then separated by sedimentation to obtain the decomposition stock solution; A portion of the decomposition solution was mixed with lime slurry to obtain an activated solution containing filter aid crystals; The activating solution is added to the remaining portion of the decomposition stock solution for filtration, and the Ca content in the filtrate is determined accordingly. 2+ The concentration is monitored in real time, and the amount of activation solution added is dynamically adjusted to obtain Ca. 2+ Refined decomposition stock solution with a concentration ≤15ppm; Determine whether the calcium content in the first tank of aluminum hydroxide obtained after the seed decomposition of the refined decomposition stock solution meets the requirement of not more than 180 ppm. If it does, the refined decomposition stock solution is further subjected to the seed decomposition to obtain low-calcium aluminum hydroxide. If the conditions are not met, the refined decomposition solution is further decomposed and purified to enrich and remove Ca from the refined decomposition solution. 2+ High-calcium aluminum hydroxide and decomposition and purification stock solution were obtained. Then, the decomposition and purification stock solution was subjected to the above-mentioned fractional decomposition to obtain low-calcium aluminum hydroxide. The low-calcium aluminum hydroxide is calcined to obtain a low-calcium aluminum oxide product. The pre-desilicon leaching process includes the following parameters: temperature ≥ 85℃, solid content ≥ 400 g / L, and leaching time ≥ 12 h.

2. The method according to claim 1, characterized in that, The pre-desilicon leaching process includes the following parameters: temperature of 85℃, solid content ≥400g / L, and leaching time of 12h; The high-temperature leaching temperature is 140℃~150℃.

3. The method according to claim 1, characterized in that, The mixing reaction time is ≥1 hour; The mass ratio of the decomposition solution to the lime milk is (1.5-2.5):

1.

4. The method according to claim 3, characterized in that, The NK concentration of the decomposition stock solution is 140 g / L to 150 g / L, and the ak concentration is 1.40 to 1.

43. The lime slurry has an effective calcium content ≥180g / L and a solid content ≥280g / L.

5. The method according to claim 1, characterized in that, The filter cloth material used for filtration has an air permeability of ≥200L / m². 2 The polypropylene fiber used in the filter is ·s, and the top pressure of the filter leaf is ≤200kPa.

6. The method according to claim 1, characterized in that, The volume of the activation solution is ≤3.5‰ of the volume of the remaining decomposition original solution.

7. The method according to claim 1, characterized in that, The decomposition and purification process includes the following parameters: solid content of 100g / L to 400g / L, initial decomposition temperature of 75℃ to 85℃, and decomposition time of 10h to 20h.

8. The method according to claim 1, characterized in that, The seed decomposition includes the following parameters: decomposition solid content of 600 g / L to 700 g / L, initial decomposition temperature of 70℃ to 75℃, final decomposition temperature of 50℃ to 55℃, and decomposition time of 40 h to 60 h.

9. The method according to claim 1, characterized in that, The calcium content of the low-calcium alumina product is ≤0.03%.

10. A calcium balance control system for low-temperature Bayer process alumina production, the system being adapted to the method described in any one of claims 1 to 9, the system comprising: The pre-desilicon leaching unit is used to mix bauxite with the blending solution, and then perform pre-desilicon leaching to obtain a pre-desilicon slurry; The decomposition stock solution preparation unit has its inlet connected to the outlet of the pre-desilicon leaching unit, and is used to leach the pre-desilicon slurry at high temperature, followed by sedimentation and separation to obtain the decomposition stock solution. A high-efficiency filter aid preparation unit is connected to the decomposition stock solution preparation unit and is used to mix and react a portion of the decomposition stock solution with lime milk to obtain an activated solution containing filter aid crystals. A leaf filter, the inlet of which is connected to the outlet of the decomposition solution preparation unit and the outlet of the high-efficiency filter aid preparation unit, is used to filter the mixture of the activation solution and the decomposition solution to obtain Ca. 2+ Refined decomposition stock solution with a concentration ≤15ppm; Online Ca 2+ Concentration monitoring unit, the online Ca 2+ The concentration monitoring unit is connected to the liquid outlet of the leaf filter and is used to monitor the Ca concentration in the filtered filtrate in real time. 2+ concentration; The decomposition and purification unit is connected to the liquid outlet of the leaf filter and is used to decompose and purify the refined decomposition raw liquid to obtain high-calcium aluminum hydroxide and decomposition and purification raw liquid. The seed decomposition unit is connected to the liquid outlet of the leaf filter and the liquid outlet of the decomposition and purification unit, respectively, and is used to decompose the refined decomposition raw liquid and the decomposition and purification raw liquid to obtain low-calcium aluminum hydroxide. The roasting unit is connected to the solid outlet of the seed decomposition unit and is used to roast the low-calcium aluminum hydroxide to obtain a low-calcium aluminum oxide product.

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