A method for improving the economics of bayer process production of alumina

Abstract

The application relates to a method for improving the economy of bayer process for producing alumina and belongs to the technical field of alumina production. The method comprises the following steps: adding a first adjusting solution and a sodium aluminate solution into bauxite, then performing crushing and wet grinding in sequence to perform first-stage dissolution to obtain a dissolved slurry; diluting the dissolved slurry with a red mud washing solution to obtain a diluted slurry; performing first solid-liquid separation on the diluted slurry to obtain a refined solution and first-stage red mud; decomposing the refined solution through a crystal seed to crystallize and precipitate aluminum hydroxide; adding a second adjusting solution into the first-stage red mud, then performing second-stage dissolution and second solid-liquid separation in sequence to obtain second-stage dissolution liquid and second-stage red mud, the second-stage dissolution liquid is a high-concentration sodium aluminate solution and is recycled to the first-stage dissolution step; and washing the second-stage red mud to obtain solid red mud and the red mud washing solution. Through the design of the segmented dissolution process, the contradiction between the alumina dissolution rate and the crystal seed decomposition rate can be balanced, the aluminum loss of the system is reduced, and the economy of the bayer process for producing alumina is improved as a whole.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alumina production, in particular to a method for improving the economy of producing alumina by the Bayer process. BACKGROUND

[0002] In the pipeline digestion process of the Bayer process, there is a difference between the initial digestion rate of alumina in bauxite and the theoretical digestion rate, that is, the relative digestion rate cannot reach 100% (the relative digestion rate = the initial digestion rate / the theoretical digestion rate x 100%), which indicates that gibbsite is not dissolved. XRD characterization of gibbsite-type digestion red mud of Malaysia mine, Ghana mine, Indonesia mine, Australia mine, Guinea mine and Brazil mine shows that the digestion red mud of each foreign mine contains 1% to 7% of gibbsite.

[0003] At present, in the production of alumina by the Bayer process, there is a difference of 1% to 3% between the initial digestion rate of alumina and the net digestion rate, which indicates that there is a systematic hydrolysis loss of alumina in the process of separating and washing the red mud, resulting in a decrease in the net digestion rate, that is, a loss of alumina.

[0004] The above two points cause the alumina in bauxite to be unable to be fully recovered, and the reason is that the pipeline digestion process of bauxite needs to balance multiple indexes such as the digestion rate of alumina and the decomposition rate of sodium aluminate solution seed. On the one hand, the digestion rate of alumina in bauxite increases with the increase of the digestion caustic ratio, and on the other hand, the decomposition rate of the seed decreases with the increase of the digestion caustic ratio.

[0005] In order to ensure a certain digestion rate of alumina and decomposition rate of seed, under the condition that other conditions remain unchanged, the digestion caustic ratio is usually controlled between 1.35 and 1.45, under which the relative digestion rate of alumina is around 95%, and the decomposition rate of the seed is around 50%. Under this condition, gibbsite in the ore cannot be fully dissolved, and there is also a hydrolysis loss of about 2% of alumina. SUMMARY

[0006] The present application provides a method for improving the economy of producing alumina by the Bayer process, to solve the technical problem of how to improve the economy of producing alumina by the Bayer process.

[0007] The present application provides a method for improving the economy of producing alumina by the Bayer process, which comprises:

[0008] After adding a first adjusting solution and a sodium aluminate solution to the bauxite, crushing and wet grinding are sequentially performed to carry out a first digestion, to obtain a digestion slurry;

[0009] In the Bayer process for producing alumina, the particle size of bauxite is reduced by crushing, followed by wet grinding to further refine the particle size. This process significantly increases the specific surface area of the mineral particles, allowing the pregnant liquor to contact the aluminum minerals more fully in the digestion reaction, improving the digestion efficiency of gibbsite (Al(OH)3). The small mineral particles shorten the distance of OH - diffusion into the interior of the mineral, reducing the mass transfer resistance and thus increasing the digestion reaction rate, which means that under the same digestion conditions, bauxite that has been crushed and wet ground can achieve a higher alumina digestion rate more quickly. In addition, during the wet grinding process, the pregnant liquor is fully mixed with the bauxite to form a uniform slurry. This uniform slurry has good fluidity, which facilitates subsequent transportation and processing. Good fluidity helps to reduce plugging and sedimentation during transportation, improving the operating efficiency of production equipment.

[0010] The digestion slurry is diluted with a red mud wash solution to obtain a diluted slurry;

[0011] The red mud wash solution is a solution containing a certain concentration of caustic soda and alumina produced in the two-stage red mud washing process. By recycling it to dilute the first-stage digestion slurry, the closed-loop circulation of caustic soda and alumina in the system can be achieved, reducing the consumption of new lye and thus reducing production costs. Through the dilution effect of the red mud wash solution, the alumina concentration can be reduced to a suitable concentration for seed decomposition, and due to the high caustic ratio of the red mud wash solution, hydrolysis loss during the dilution process is avoided. This helps to create more favorable conditions for the subsequent seed decomposition process, improving the crystallization efficiency of aluminum hydroxide, and thus increasing the seed decomposition rate.

[0012] The diluted slurry is subjected to first solid-liquid separation to obtain a pregnant liquor and a first-stage red mud;

[0013] Through solid-liquid separation and purification, a sodium aluminate pregnant liquor is obtained, which is directly used as raw material for seed decomposition. The low caustic ratio in the pregnant liquor is beneficial to improving the crystallization efficiency of aluminum hydroxide in the subsequent process. The first-stage red mud is further extracted by the second-stage digestion to extract the residual alumina, so that the overall recovery rate of alumina in bauxite is increased to > 87%.

[0014] The pregnant liquor is subjected to seed decomposition to crystallize and precipitate aluminum hydroxide;

[0015] Seed decomposition introduces aluminum hydroxide seeds as growth cores, which can promote the decomposition of sodium aluminate solution in the pregnant liquor and crystallize and precipitate aluminum hydroxide. This process helps to remove impurities in the pregnant liquor, improve the purity of alumina products, and meet the demand for high-quality alumina in high-end application fields. The low caustic ratio of the pregnant liquor increases the supersaturation of the solution, which increases the driving force for decomposition, and ultimately achieves a seed decomposition rate of > 55%.

[0016] The second-stage preparation liquid is added to the first-stage red mud, and second-stage dissolution and second-stage solid-liquid separation are sequentially performed to obtain a second-stage dissolution liquid and second-stage red mud, the second-stage dissolution liquid being a high-concentration sodium aluminate solution and being returned to the first-stage dissolution step for recycling;

[0017] The first-stage red mud obtained after the solid-liquid separation still contains a certain amount of undissolved aluminum oxide, mainly the difficultly soluble minerals such as diaspore and a small amount of residual gibbsite, and this red mud is used as raw material for subsequent second-stage dissolution to further extract the aluminum oxide therein through high caustic ratio dissolution, thereby improving the overall recovery rate of aluminum oxide.

[0018] The second-stage red mud is washed to obtain solid red mud and the red mud washing liquid;

[0019] The second-stage red mud washing liquid carries the following effective components recovered from the second-stage red mud: undissolved aluminum oxide (Al2O3), unreacted caustic soda (Na2O), and other soluble mineral components, and these components are recycled (for diluting the dissolution slurry obtained through the first-stage dissolution) to improve the overall recovery rate of aluminum oxide to > 87%.

[0020] The caustic ratio of the first-stage dissolution is 1.20-1.25, and the caustic ratio of the second-stage dissolution is 2.15-2.25.

[0021] In the Bayer process for producing aluminum oxide, the caustic ratio refers to the molar ratio of caustic soda (Na2O) to aluminum oxide (Al2O3) in the dissolution system, which is used to represent the caustic strength of the solution. The low caustic ratio (αk = 1.20-1.25) of the first-stage dissolution is conducive to preparing a low caustic ratio liquor, and the low caustic ratio of the liquor is conducive to improving the crystallization efficiency of aluminum hydroxide (Al(OH)3) in the seed decomposition process. The low caustic ratio of the liquor increases the supersaturation of the solution, providing a stronger driving force for seed decomposition, thereby improving the seed decomposition rate, which has a significant effect on improving the yield and quality of aluminum oxide. At the same time, although the aluminum oxide dissolution rate may be lower at a low caustic ratio (αk = 1.20-1.25), the high caustic ratio treatment of the red mud in the second stage can make up for this, improving the overall recovery rate.

[0022] The caustic ratio of the second-stage dissolution needs to be controlled at 2.15-2.25, which is significantly higher than the caustic ratio (1.20-1.25) of the first-stage dissolution, thereby enhancing the dissolution driving force, so that the difficultly soluble aluminum oxide (such as diaspore) in the first-stage red mud and a small amount of gibbsite that is not dissolved due to insufficient dissolution driving force can be more fully dissolved, which helps to reduce the content of undissolved aluminum oxide in the red mud and improve the dissolution efficiency. The second-stage dissolution liquid, as a high-concentration sodium aluminate solution, can be returned to the first-stage dissolution system for recycling, reducing the consumption of fresh lye, which not only reduces production costs but also meets the concept of green production and sustainable development.

[0023] Optionally, the temperature of the first-stage dissolution is 135-145°C, and the time of the first-stage dissolution is 30-60 minutes.

[0024] The temperature of the first-stage dissolution (135-145°C) belongs to the medium temperature range, which can meet the dissolution kinetics requirement of gibbsite (Al(OH)3). When the temperature of the first-stage dissolution is lower than 135°C, the reaction rate significantly decreases, and the dissolution time needs to be prolonged. When the temperature of the first-stage dissolution is higher than 145°C, the steam consumption increases. The dissolution time of 30-60 minutes can meet the dissolution kinetics requirement of gibbsite (Al(OH)3), and realize the efficient dissolution of active alumina. When the dissolution time is longer than 60 minutes, the structure of red mud particles is easily reorganized, which leads to the increase of the difficulty of alumina extraction in the subsequent second-stage dissolution. The temperature and time range of the first-stage dissolution, in combination with the setting of low caustic ratio (αk = 1.20-1.25), can ensure the dissolution efficiency of gibbsite while avoiding the negative impact of high caustic ratio on the decomposition rate of crystal seeds.

[0025] Optionally, the temperature of the second-stage dissolution is 140-270°C, and the time of the second-stage dissolution is 10-30 minutes.

[0026] In the second-stage dissolution process of the Bayer process for producing alumina, the temperature of dissolution is determined according to the mineral composition of the ore. When the content of diaspore is very low, a low temperature range is basically selected. When the ore contains diaspore (AlOOH), the temperature of the second-stage dissolution needs to be increased to about 240°C (one water soft alumina) or 260°C (one water hard alumina). This is because high temperature can break through the lattice energy barrier of diaspore, and the residual insoluble alumina in the first-stage red mud is extracted again, so that the net dissolution rate is increased. The selection of temperature also needs to consider the content of goethite. In addition, the second-stage dissolution adopts short-time high temperature (dissolution temperature is 140-270°C, and dissolution time is 10-30 minutes), which can ensure the reaction rate and avoid excessive energy consumption through time control.

[0027] After the first-stage dissolution, the red mud is subjected to the second-stage high caustic ratio (2.15-2.25) dissolution, which can enhance the dissolution dynamics and make the residual gibbsite be fully dissolved. This process can reduce the content of undissolved Al2O3 in the red mud, and avoid the loss caused by the hydrolysis of residual sodium aluminate solution in the subsequent red mud washing process. The process design of staged dissolution can balance the contradiction between the dissolution rate of alumina and the decomposition rate of crystal seeds, and reduce the aluminum loss of the system.

[0028] Optionally, the volume ratio of the first-stage adjusting solution to the second-stage adjusting solution is (0.97-1.18):1.

[0029] The first-stage dissolution stage is used for diluting the first-stage dissolution slurry, and low-ak (1.20-1.25) conditions are used to preferentially dissolve gibbsite in the ore, and at the same time, low-ak liquor is provided for seed decomposition, so that the decomposition rate is improved. In the second-stage dissolution stage, the first-stage dissolution liquor is mixed with the second-stage dissolution overflow liquor, and high-ak (2.15-2.25) conditions are used for secondary dissolution of residual alumina in the red mud, so that the net dissolution rate is improved, and the hydrolysis loss in the washing process is reduced. The volume ratio of the first-stage dissolution liquor to the second-stage dissolution liquor is 0.97-1.18, which is suitable for bauxite with a mass fraction of gibbsite of 55% or more and an effective A / S of 7 or more, and can fully utilize the dissolution potential of high-activity gibbsite in the ore, while inhibiting the silicon pollution of low-activity diaspore (1.5% or more).

[0030] Optionally, the first-stage dissolution liquor and the second-stage dissolution liquor both satisfy: NT is 210 g / L-230 g / L, AO is 100 g / L-110 g / L, and NK is 195 g / L-210 g / L.

[0031] NT (total sodium concentration) is the total content of sodium ions in the liquor, and the unit is g / L. In the embodiments of the present application, NT is set to 210 g / L-230 g / L, which can ensure that the dissolution system has sufficient sodium ion concentration, ensure that the sodium aluminate solution remains chemically stable in the dissolution reaction, and inhibit the hydrolysis of alumina (Al2O3).

[0032] AO specifically refers to the concentration index of alumina (Al2O3) in the field of alumina production, specifically the mass concentration of Al2O3 in the liquor, and the unit is g / L. In the embodiments of the present application, the AO (alumina concentration) in the first-stage and second-stage dissolution liquors is controlled to be 100 g / L-110 g / L, which not only provides a basic concentration gradient for subsequent seed decomposition, but also avoids the decline in decomposition efficiency caused by solution supersaturation.

[0033] NK (caustic alkali concentration) specifically refers to the concentration index of caustic soda (Na2O) in the dissolution system in the Bayer process for producing alumina, and the unit is g / L. In the embodiments of the present application, the caustic alkali concentration is directly related to the dissolution ak (caustic ratio), and the difference between the first-stage dissolution ak (1.20-1.25) and the second-stage dissolution ak (2.15-2.25) is realized by the NK concentration of the liquor and the dissolution temperature. NT (total sodium concentration) and AO (alumina concentration) and NK (caustic alkali concentration) together constitute the basic parameters of the liquor, which are suitable for bauxite with a mass fraction of gibbsite of 55% or more and an effective A / S of 7 or more, and can meet the needs of the staged dissolution process (low-ak in the first stage and high-ak in the second stage) to improve the recovery rate of alumina.

[0034] Optionally, in the bauxite, the mass fraction of gibbsite is 55% or more, and the mass fraction of diaspore is 1.5% or more.

[0035] Gibbsite is one of the main forms of alumina in bauxite, and it is relatively easy to dissolve in the Bayer process. Therefore, a gibbsite content of ≥55% helps to improve the dissolution efficiency of alumina and increase the concentration of alumina in the dissolved slurry. As another form of alumina, boehmite is generally more difficult to dissolve. In the embodiments of the present application, through the staged dissolution process, gibbsite can be preferentially dissolved in the first stage, and boehmite can be selectively dissolved in the second stage by using high temperature. At the same time, the high caustic ratio in the second stage can dissolve the residual gibbsite in the first stage and the aluminum hydroxide produced by hydrolysis in the dilution process in the first stage, thereby optimizing the overall dissolution process and improving the recovery rate of alumina.

[0036] Optionally, the effective A / S in the bauxite is ≥7.

[0037] In the field of alumina production, A / S refers to the alumina to silica ratio, i.e., the mass ratio of Al2O3 to SiO2 in bauxite. The higher the ratio, the higher the content of effective component Al2O3 and the lower the content of impurity SiO2 in bauxite. In the embodiments of the present application, the effective A / S in bauxite is ≥7, which is the threshold value for the technical solution of the present application to be applicable, and is used to screen gibbsite-type bauxite suitable for the staged dissolution process. An effective A / S in bauxite of ≥7 means that the alumina in the ore is relatively enriched, and a relatively high alumina dissolution rate can be achieved under a relatively low caustic ratio, which helps to reduce the consumption of caustic alkali in the dissolution process, reduce production costs, and is beneficial to the subsequent seed decomposition process, because the low caustic ratio of the pregnant liquor is more conducive to the crystallization and precipitation of aluminum hydroxide. In addition, when A / S ≥7, it means that less silicon minerals enter the solution during dissolution and subsequent processing, which helps to reduce the impact of silicon pollution on the quality of alumina products and improve the purity and quality of the products. At the same time, more Al2O3 can be extracted per ton of bauxite, and the consumption of caustic alkali (NaOH) and Al2O3 required for the removal of SiO2 is reduced, directly improving production efficiency.

[0038] Optionally, the solid content of the first-stage red mud is ≥700 g / L.

[0039] The first-stage red mud with a solid content of ≥700 g / L can more effectively reduce the loss caused by the liquid attached to the red mud in the first solid-liquid separation process, and reduce the ineffective circulation of the first-stage dissolution liquor, thereby improving the utilization rate of resources. At the same time, the first-stage red mud, with a solid content of ≥700 g / L, provides a suitable reaction concentration for the second-stage dissolution, which helps to better control the reaction conditions in the second-stage dissolution process and improve the dissolution efficiency of alumina.

[0040] Optionally, the seed decomposition time is 40-45 h.

[0041] Seed decomposition is a gradual crystallization process, which needs a certain time to ensure the complete growth of aluminum hydroxide crystals. Controlling the seed decomposition time in 40h-45h can ensure that the aluminum hydroxide crystals have sufficient time to crystallize, form crystals with complete structure and uniform particle size, thereby improving the quality and stability of the product. If the seed decomposition time is less than 40h, it may lead to incomplete crystallization of aluminum hydroxide, affecting the purity and crystallinity of the product; and if the time is longer than 45h, it may cause secondary nucleation or decrease in seed activity, increasing energy consumption. Controlling the time in 40h-45h can balance the decomposition efficiency while avoiding unnecessary increase in energy consumption, achieving a balance between energy consumption and efficiency. In addition, the seed decomposition time of 40h-45h helps to optimize the overall production cycle. If the decomposition time is less than 40h, it may lead to substandard product quality, requiring additional processing procedures; and if the time is longer than 45h, it will prolong the production cycle and reduce the production efficiency. The time range of 40h-45h ensures product quality while taking into account production efficiency, which helps to optimize the production cycle.

[0042] The seed decomposition time is 40-45 hours, which balances the decomposition efficiency and energy consumption cost. If the seed decomposition time is less than 40h, it may lead to incomplete decomposition; and if the time is longer than 45h, it may affect the product particle size distribution.

[0043] Optionally, the method can achieve: the recovery rate of alumina > 87%, the seed decomposition rate > 55%, and the yield of solid red mud < 37%.

[0044] The αk of the first-stage dissolution is controlled in 1.20-1.25, which can directly reduce the caustic ratio of the concentrate and create favorable conditions for seed decomposition. The low caustic ratio concentrate can increase the supersaturation of Al(OH)3 and promote the driving force of the decomposition reaction, thereby increasing the decomposition rate to more than 55%. The AO concentration in the first-stage preparation solution is controlled at 100g / L, which not only provides sufficient Al2O3 raw material for seed decomposition, but also avoids spontaneous nucleation (competing with seed growth) caused by over-saturation of the solution, thereby ensuring the stability of the decomposition rate. The first-stage dissolution temperature (135-145℃) and time (30-60min) ensure high decomposition rate of the concentrate under low caustic ratio, while dissolving as much gibbsite as possible. The mass fraction of gibbsite in bauxite is ≥55%, and the effective A / S is ≥7, which ensures high purity of alumina in the dissolution solution, reduces the toxic effect of impurities (such as SiO2) on the active sites on the seed surface, and indirectly increases the decomposition rate.

[0045] In the first stage of dissolution, the gibbsite (Al(OH)3) in bauxite is preferentially dissolved by reducing the caustic ratio of the first stage liquor, and a low caustic ratio liquor is provided for seed decomposition. By controlling the temperature (135-145℃) and time (30-60min) of the first stage of dissolution, the reaction rate and energy consumption are balanced to avoid the compactification of red mud structure at high temperature, which hinders the secondary dissolution. The second stage of dissolution of the first stage red mud is carried out at a higher caustic ratio to enhance the dissolution efficiency of diaspore (AlOOH). The high caustic ratio environment of the second stage of dissolution can make up for the possible dissolution deficiency of alumina in the first stage. The second stage of dissolution uses short-time high-temperature treatment (140-270℃, 10-30min) to break through the dissolution energy barrier of diaspore, thereby increasing the net dissolution rate. Through the above process combination, the recovery rate of alumina can be > 87%.

[0046] The overflow after the second stage of dissolution (second stage of dissolution liquor) is returned to the first stage of dissolution system, and the red mud washing liquor is used to dilute the first stage of dissolution slurry. This closed loop design reduces the loss of free caustic in the solution, maintains the stability of the dissolution system, and avoids the hydrolysis of alumina caused by fluctuations in the composition of the solution.

[0047] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0048] The embodiments of the present application provide a method for improving the economic efficiency of bauxite production, which comprises: adding a first stage liquor and a sodium aluminate solution to bauxite, and then sequentially crushing and wet grinding to perform a first stage of dissolution to obtain a dissolution slurry; diluting the dissolution slurry with a red mud washing liquor to obtain a diluted slurry; performing a first solid-liquid separation on the diluted slurry to obtain a liquor and a first stage of red mud; the liquor is subjected to seed decomposition to crystallize and precipitate aluminum hydroxide; adding a second stage liquor to the first stage of red mud, and then sequentially performing a second stage of dissolution and a second solid-liquid separation to obtain a second stage of dissolution liquor and a second stage of red mud; washing the second stage of red mud to obtain solid red mud and the red mud washing liquor, and the second stage of dissolution liquor is a high-concentration sodium aluminate solution, which is returned to the first stage of dissolution step for recycling. The first stage of dissolution uses a low caustic ratio to dissolve as much gibbsite as possible in the bauxite while reducing the caustic ratio of the liquor, thereby improving the seed decomposition rate. After the first stage of dissolution, a second stage of high caustic ratio dissolution is performed on the red mud to enhance the dissolution power, so that the residual gibbsite and the difficultly soluble diaspore are fully dissolved, which can reduce the content of undissolved alumina in the red mud. At the same time, due to the increase of the caustic ratio, the loss caused by the hydrolysis of sodium aluminate solution in the subsequent red mud washing process can be avoided. Through the above process design, the contradiction between the dissolution rate of alumina and the seed decomposition rate can be balanced, and the system aluminum loss can be reduced, thereby improving the economic efficiency of bauxite production by the Bayer process as a whole. BRIEF DESCRIPTION OF DRAWINGS

[0049] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate preferred embodiments of the present application and, together with the description, serve to explain the principles of the application.

[0050] 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, those skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0051] Figure 1 A flowchart of a method for improving the economy of producing alumina by the Bayer process is provided in the embodiments of the present application. DETAILED DESCRIPTION

[0052] In order to make the objects, 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 in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a 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 those skilled in the art without any creative effort fall within the scope of protection of the present application.

[0053] The range descriptions described herein, such as numerical range, ratio range, etc., include all possible sub-ranges and single values within the range, 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 values (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 the objects. The ratio relationship described herein, such as mass ratio, molar ratio, etc., should be understood as the corresponding relationship between the front and rear terms in the ratio. The raw materials, reagents, instruments and equipment used herein can be purchased or prepared by existing methods.

[0054] Figure 1 A flowchart of a method for improving the economy of producing alumina by the Bayer process is provided in the embodiments of the present application.

[0055] Please refer to Figure 1 The embodiments of the present application provide a method for improving the economy of producing alumina by the Bayer process, which comprises:

[0056] S1, a first preparation solution and a sodium aluminate solution are added to the bauxite, and then crushing and wet grinding are sequentially performed to perform a first leaching to obtain a leached slurry;

[0057] In some embodiments, the mass fraction of gibbsite in the bauxite is ≥55%, and the mass fraction of diaspore is ≥1.5%.

[0058] In some embodiments, the effective A / S in the bauxite is ≥7.

[0059] In some embodiments, the caustic ratio of the first leaching is 1.20-1.25.

[0060] In some embodiments, the temperature of the first leaching is 135-145°C, and the time of the first leaching is 30-60 minutes.

[0061] S2, the leached slurry is diluted with a red mud washing solution to obtain a diluted slurry;

[0062] S3, the diluted slurry is subjected to a first solid-liquid separation to obtain a pregnant solution and a first red mud;

[0063] In some embodiments, the solid content of the first red mud is ≥700g / L.

[0064] S4, the pregnant solution is subjected to seed decomposition to crystallize and precipitate aluminum hydroxide;

[0065] In some embodiments, the time of seed decomposition is 40-45 hours.

[0066] S5, a second preparation solution is added to the first red mud, and then a second leaching and a second solid-liquid separation are sequentially performed to obtain a second leaching solution and a second red mud;

[0067] In some embodiments, the caustic ratio of the second leaching is 2.15-2.25.

[0068] In some embodiments, the temperature of the second leaching is 140-270°C, and the time of the second leaching is 10-30 minutes.

[0069] In some embodiments, the volume ratio of the first preparation solution to the second preparation solution is (0.97-1.18):1.

[0070] S6, the second red mud is washed to obtain a solid red mud and the red mud washing solution;

[0071] In some embodiments, the method can achieve: an aluminum oxide recovery rate > 87%, a seed decomposition rate > 55%, and a yield of the solid red mud < 37%.

[0072] The present application is further described below in connection with specific examples. The experimental methods in the following examples, unless otherwise specified, are generally determined according to national / industry standards; if there is no corresponding national / industry standard, it is determined according to the general international standards, conventional conditions or according to the conditions recommended by the manufacturer.

[0073] The chemical composition (wt %) and mineral composition (wt %) of the bauxite are shown in Table 1.

[0074] Table 1 Chemical composition (wt %) and mineral composition (wt %) of bauxite

[0075]

[0076] Example 1

[0077] First-stage dissolution control: dissolution αk1.25, dissolution temperature 138℃, dissolution time 60min; the first-stage dissolution slurry is diluted with the second-stage red mud washing solution, settled, separated, refined, and then seed decomposition, seed decomposition time 45h. The solid content of the underflow (first-stage red mud) is 700g / L. The second-stage red mud washing solution is diluted according to Al2O3165g / L control.

[0078] Second-stage dissolution control: dissolution αk2.20, dissolution temperature 140℃, dissolution time 30min; after the second-stage dissolution, solid-liquid separation is performed, the overflow (second-stage dissolution solution) is returned to the first stage to continue to dissolve the ore with the adjusting solution; the red mud washing solution is returned to the first stage to dilute the dissolution slurry.

[0079] Example 2

[0080] First-stage dissolution control: dissolution αk1.22, dissolution temperature 140℃, dissolution time 40min; the first-stage dissolution slurry is diluted with the second-stage red mud washing solution, settled, separated, refined, and then seed decomposition, seed decomposition time 45h. The solid content of the underflow (first-stage red mud) is 715g / L. The second-stage red mud washing solution is diluted according to Al2O3165g / L control.

[0081] Second-stage dissolution control: dissolution αk2.18, dissolution temperature 260℃, dissolution time 15min; after the second-stage dissolution, solid-liquid separation is performed, the overflow (second-stage dissolution solution) is returned to the first stage to continue to dissolve the ore with the adjusting solution; the red mud washing solution is returned to the first stage to dilute the dissolution slurry.

[0082] Example 3

[0083] Stage 1 dissolution control: dissolution αk1.25, dissolution temperature 140℃, dissolution time 40min; the stage 1 dissolution slurry is diluted with the stage 2 red mud wash, settled, separated, refined, and then seed decomposition, seed decomposition time 45h. The underflow (stage 1 red mud) solid content is 720g / L. The stage 2 red mud wash is diluted according to Al2O3 165g / L control.

[0084] Stage 2 dissolution control: dissolution αk2.20, dissolution temperature 260℃, dissolution time 20min; after stage 2 dissolution, solid-liquid separation is performed, the overflow (stage 2 dissolution liquid) is returned to the stage 1 and combined with the preparation liquid to continue to dissolve the ore; the red mud wash is returned to dilute the stage 1 slurry.

[0085] Comparative Example 1

[0086] According to the existing Bayer process dissolution process control, namely: dissolution αk1.37, dissolution temperature 142℃, dissolution time 60min. The dissolution slurry is diluted with the red mud wash, separated, the crude liquid is refined, and then seed decomposition, seed decomposition time 45h. The red mud is discharged after washing or utilized. The red mud wash is diluted according to Al2O3 165g / L control.

[0087] Table 2: Solution composition

[0088]

[0089] Table 3: Solid red mud composition (wt %)

[0090]

[0091] Table 4: Index comparison

[0092]

[0093] From Tables 1-4, it can be seen that the example utilizes the staged dissolution technology, stage 1 low αk dissolution of bauxite, preparing low αk refined liquid, improving the seed decomposition rate; stage 1 red mud is subjected to stage 2 high αk dissolution, which effectively reduces or even avoids the hydrolysis loss of alumina in the red mud washing process, thereby improving the recovery rate of ore alumina, reducing the consumption of ore, and reducing the output rate of red mud.

[0094] The one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0095] Overall, the staged dissolution process design of the embodiments of the present application balances the contradiction between the alumina dissolution rate and the seed decomposition rate, reduces the system aluminum loss, reduces the ore consumption and chemical loss, thereby improving the economic efficiency of the Bayer process for producing alumina.

[0096] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications to the description will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other implementations without departing from the spirit or scope of the application. Accordingly, the application is not intended to be limited to the implementations described herein but is to be accorded the widest scope consistent with the principles and novel features to the application.

Claims

1. A method for improving the economic efficiency of alumina production via the Bayer process, characterized in that, The method includes: After adding a first-stage conditioning solution and sodium aluminate solution to bauxite, crushing and wet milling are carried out in sequence to perform a first-stage leaching to obtain a leached slurry. The temperature of the first-stage leaching is 135℃~145℃ and the time of the first-stage leaching is 30min~60min. The dissolved slurry was diluted with red mud washing solution to obtain a diluted slurry; The diluted slurry was subjected to a first solid-liquid separation to obtain a concentrate and a first-stage red mud, wherein the solid content of the first-stage red mud was ≥700g / L; The semen was decomposed by seed crystals, and aluminum hydroxide was crystallized out. A second-stage preparation solution is added to the first-stage red mud, and the second-stage dissolution and second solid-liquid separation are carried out sequentially to obtain the second-stage dissolution solution and the second-stage red mud. The second-stage dissolution solution is a high-concentration sodium aluminate solution, which is returned to the first-stage dissolution step for recycling. The temperature of the second-stage dissolution is 260℃~270℃, and the time of the second-stage dissolution is 10min~20min. The two sections of red mud are washed to obtain solid red mud and the red mud washing solution; The caustic ratio of the first stage of leaching is 1.20 to 1.25, and the caustic ratio of the second stage of leaching is 2.15 to 2.

25. The bauxite contains ≥55% gibbsite by mass, ≥1.5% monohydrate by mass, and an effective A / S ratio ≥7. The method achieves an alumina recovery rate of >87%, a seed crystal decomposition rate of >55%, and a solid red mud yield of <37%. Both the first-stage and second-stage preparation solutions meet the following requirements: NT is 210 g / L to 230 g / L, AO is 100 g / L to 110 g / L, and NK is 195 g / L to 210 g / L.

2. The method according to claim 1, characterized in that, The volume ratio of the first-stage preparation solution to the second-stage preparation solution is (0.97–1.18):

1.

3. The method according to claim 1, characterized in that, The seed crystal decomposition time is 40h to 45h.

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