Dissolution and desilication process for producing alumina by bayer process

Abstract

The application discloses a kind of bayer process production alumina's dissolution and desilication process, it is related to alumina production technical field.The process comprises the following steps: step S100: bauxite is mixed with circulating mother liquor, the mass concentration of solid matter in slurry is controlled to be 400g / L-1000g / L, under the condition that reaction temperature is 90 DEG C-105 DEG C, reaction time is 6h-12h, after grinding, the particle size of less than 125 microns accounts for 50%-75% of the total mass of ore powder, and pre-desilication slurry is obtained;Step S200: adding circulating mother liquor to the pre-desilication slurry, adjusting α k To 1.30-1.45, the caustic alkali concentration N k Of circulating mother liquor is 170g / L-200g / L, and dissolution slurry is obtained;Step S300: the dissolution slurry is diluted to caustic alkali N k Concentration is 140g / L-155g / L, and the desilication is stopped for 30min-60min at 95 DEG C-105 DEG C, and the concentrate is obtained.The process can improve the pre-desilication rate, stabilize the alumina dissolution rate and obtain the concentrate with higher silicon content index by optimizing the process parameters in the pre-desilication, dissolution and dilution desilication procedures.

Description

Technical Field

[0001] This invention relates to the field of alumina production technology, and more particularly to the Bayer process for leaching and desilication of high-quality alumina. Background Technology

[0002] The Bayer process is currently the main industrial method for producing alumina. Its core processes include bauxite leaching, red mud separation, seed crystal decomposition, and mother liquor evaporation. In the leaching process, alumina in the bauxite reacts with caustic alkali in the circulating mother liquor to produce sodium aluminate solution, while impurities such as silicon, iron, and titanium in the ore enter the red mud. To ensure high-purity aluminum hydroxide in the subsequent decomposition process, silicon must be removed from the solution before and after leaching, i.e., by controlling the silicon index of the final solution through pre-desiliconization and dilution desiliconization.

[0003] In the traditional Bayer process, when processing bauxite of varying grades, it is often difficult to simultaneously achieve ideal levels of pre-desiliconization efficiency, leaching rate, and desiliconization depth. The pre-desiliconization process is typically affected by factors such as the mass concentration of solids in the slurry, reaction temperature, time, caustic soda concentration in the mother liquor, and the amount of lime added. Improper parameter control can lead to a low pre-desiliconization rate, resulting in scaling on the leaching equipment and increasing the burden on subsequent desiliconization processes. In the leaching process, the caustic soda ratio α... k The selection of parameters such as mother liquor concentration, dissolution temperature, and time directly affects the dissolution rate of alumina and the alkali content in red mud. Parameters that are too high or too low may lead to resource waste or a decline in product quality. In the dilution and desilication step, if the solution concentration and residence time are not appropriate, the silica index of the refined solution will be difficult to meet the requirements for high-quality alumina production. In existing technologies, for gibbsite-type bauxite from Guinea and other regions, the conventional Bayer process often suffers from insufficient pre-desilication, large fluctuations in dissolution rate, and a low silica index in the refined solution, thus affecting the purity and particle size of the final alumina product.

[0004] Therefore, it is necessary to design a high-quality alumina Bayer process for desilication to improve the pre-desilication rate, stabilize the alumina dissolution rate, and obtain a high silica index concentrate by optimizing process parameters in the pre-desilication, dissolution, and dilution desilication steps. Summary of the Invention

[0005] To address the above issues and overcome the shortcomings of existing technologies, this invention provides a high-quality alumina Bayer process for desilication. This high-quality alumina Bayer process for desilication can improve the pre-desilication rate, stabilize the alumina dissolution rate, and obtain a high silica index concentrate by optimizing process parameters in the pre-desilication, dissolution, and dilution desilication steps.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The Bayer process for the leaching and desilication of alumina includes the following steps:

[0008] Step S100: Grind bauxite until particles with a diameter less than 125 μm account for 50%–75% of the total mass of the ore powder. Mix the ground bauxite with circulating mother liquor, controlling the mass concentration of solids in the resulting slurry to be 400 g / L–1000 g / L. Perform a pre-desilication reaction at a reaction temperature of 90℃–105℃ for 6 h–12 h. The caustic alkali concentration N in the circulating mother liquor is... k The lime content shall not exceed 200 g / L and shall not be less than 1% of the dry basis mass of the bauxite to obtain a pre-desilication slurry;

[0009] Step S200: Add circulating mother liquor to the pre-desiliconized slurry and adjust the caustic ratio α of the leaching solution. k The concentration of caustic soda in the circulating mother liquor is 1.30–1.45, the amount of lime added is less than 1% of the dry weight of the bauxite, and the concentration of caustic soda N in the circulating mother liquor is... k The concentration is 170 g / L to 200 g / L, and the solution is dissolved for 10 min to 90 min at a reaction temperature of 110℃ to 240℃ to obtain a dissolution slurry.

[0010] Step S300: Dilute the leaching slurry with caustic alkali N. k Semen was obtained by desilication at a concentration of 140 g / L to 155 g / L and at 95℃ to 105℃ for 30 min to 60 min.

[0011] Furthermore, in step S100, the mass concentration of solids in the slurry is 600 g / L to 1000 g / L.

[0012] Furthermore, in step S100, the reaction temperature is 100℃~105℃.

[0013] Furthermore, in step S100, the pre-desiliconization reaction time is 10 h to 12 h.

[0014] Furthermore, in step S100, the particles with a diameter of less than 125 micrometers account for 71.2% of the total mass of the mineral powder.

[0015] Furthermore, in step S200, the caustic ratio α of the dissolving solution... k It ranges from 1.35 to 1.40.

[0016] Furthermore, in step S200, the amount of lime added is 0%.

[0017] Furthermore, in step S200, the reaction temperature is 145°C and the dissolution time is 30 min to 60 min.

[0018] Furthermore, in step S200, the reaction temperature is 235°C and the dissolution time is 10 min to 20 min.

[0019] Furthermore, in step S100, the pre-desilication temperature is 100℃, ore particles with a diameter less than 125 micrometers account for 71.2% of the total mass of the ore powder, the mass concentration of solids in the slurry is 600 g / L, and the pre-desilication reaction time is 10 h; in step S200, the amount of lime added is 0, and the leaching solution α k The concentration of caustic alkali in the circulating mother liquor is 180 g / L to 200 g / L; in step S300, the desilication temperature is 100℃.

[0020] This invention has at least the following beneficial effects:

[0021] This invention employs a pre-desiliconization step, mixing bauxite with circulating mother liquor. The concentration of solids in the slurry is controlled at 400 g / L–1000 g / L, the reaction temperature at 90℃–105℃, the reaction time at 6 h–12 h, the caustic alkali concentration in the circulating mother liquor not exceeding 200 g / L, the lime addition not less than 1% of the dry bauxite mass, and the grinding fineness is such that particles smaller than 125 micrometers account for 50%–75% of the total ore powder mass. This step removes at least a portion of the active silica before the leaching process, increasing the silica index of the pre-desiliconized slurry and reducing the probability of scaling in subsequent leaching equipment. This invention also employs a leaching step, adding circulating mother liquor to the pre-desiliconized slurry to adjust the caustic ratio α of the leaching solution. k The concentration of caustic alkali in the circulating mother liquor is 1.30–1.45, the amount of lime added is less than 1% of the dry weight of bauxite, and the concentration of caustic alkali N in the mother liquor is... k The alumina is dissolved at a concentration of 170 g / L to 200 g / L at a temperature of 110°C to 240°C for 10 min to 90 min. This step allows the alumina to fully enter the solution and controls the alkali content in the red mud. The invention also employs a dilution and desilication step, diluting the dissolved slurry to a concentration of caustic alkali N. k The concentration is 140 g / L to 155 g / L, and the solution is kept at 95℃ to 105℃ for 30 min to 60 min for desilication. This step further reduces the silicon concentration in the solution and increases the silicon index of the semen. Overall, this invention improves the pre-desilication rate, stabilizes the alumina dissolution rate, and obtains semen with a higher silicon index by synergistically controlling the parameters of the three-step process of pre-desilication, dissolution, and dilution desilication.

[0022] The present invention further optimizes the process parameters of the pre-desiliconization step as follows: pre-desiliconization temperature 100℃, grinding fineness of particles with a diameter less than 125 micrometers accounting for 71.2% of the total mass of mineral powder, mass concentration of solid matter in slurry 600 g / L, and pre-desiliconization reaction time 10 h; and optimizes the process parameters of the leaching step as follows: lime addition is 0, and leaching solution α k The concentration of caustic alkali in the circulating mother liquor is 180 g / L to 200 g / L; the desilication temperature in the dilution and desilication step is optimized to 100℃. This optimal combination of parameters enables a pre-desilication rate of over 40%, an alumina dissolution rate of over 87%, and a silica index of over 170 in the final solution, thereby stably obtaining a final solution suitable for the production of high-quality alumina. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 Flowchart of the leaching and desilication process for alumina production using the Bayer process;

[0025] Figure 2 The pre-desiliconization rate is the pre-desiliconization rate at different mass concentrations of solids in the slurry during step S100.

[0026] Figure 3 The pre-desiliconization rate at different reaction temperatures in step S100;

[0027] Figure 4 The pre-desilicon rate is the result of different pre-desilicon reaction times in step S100;

[0028] Figure 5 The pre-desiliconization rate for different grinding finenesses in step S100;

[0029] Figure 6 The caustic ratio α of different dissolution solutions in step S200 k alumina dissolution rate;

[0030] Figure 7 The alumina dissolution rate in step S200 is calculated for different amounts of lime added.

[0031] Figure 8 The alumina dissolution rate is calculated for different reaction temperatures and reaction times in step S200. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0034] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0035] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are only used to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any part or element in this invention. They should not be construed as limitations on this invention.

[0036] In this invention, terms such as "fixed," "connected," and "linked" should be interpreted broadly, indicating that the connection can be fixed, integral, or detachable; it can be a direct connection or an indirect connection through an intermediate medium. For researchers or technicians in the field, the specific meaning of the above terms in this invention can be determined according to the specific circumstances, and they should not be construed as limitations on this invention.

[0037] The embodiments of the present invention will be described in detail below.

[0038] This invention discloses a Bayer process for desilication of high-quality alumina.

[0039] Figure 1 A flow chart of the leaching and desilication process for alumina production using the Bayer process.

[0040] In one specific embodiment of the present invention, the leaching and desilication process for producing alumina using the Bayer process includes steps S100, S200, and S300:

[0041] Step S100: Grind bauxite until particles with a diameter less than 125 μm account for 50%–75% of the total mass of the ore powder. Mix the ground bauxite with circulating mother liquor, controlling the mass concentration of solids in the resulting slurry to be 400 g / L–1000 g / L. Perform a pre-desilication reaction at a reaction temperature of 90℃–105℃ for 6 h–12 h. The caustic alkali concentration N in the circulating mother liquor is... k The lime content shall not exceed 200 g / L and shall not be less than 1% of the dry basis mass of the bauxite to obtain a pre-desilication slurry;

[0042] Step S200: Add circulating mother liquor to the pre-desiliconized slurry and adjust the caustic ratio α of the leaching solution. k The concentration of caustic soda in the circulating mother liquor is 1.30–1.45, the amount of lime added is less than 1% of the dry weight of the bauxite, and the concentration of caustic soda N in the circulating mother liquor is... k The concentration is 170 g / L to 200 g / L, and the solution is dissolved for 10 min to 90 min at a reaction temperature of 110℃ to 240℃ to obtain a dissolution slurry.

[0043] Step S300: Dilute the leaching slurry with caustic alkali N. k Semen was obtained by desilication at a concentration of 140 g / L to 155 g / L and at 95℃ to 105℃ for 30 min to 60 min.

[0044] The steps described above are: pre-desilicon stripping step S100, dissolution step S200, and dilution desilicon stripping step S300. Details are as follows:

[0045] The purpose of the pre-desiliconization step S100 is to pre-convert the active silica in bauxite into desilicon products before the leaching process, thereby reducing the risk of scaling in the subsequent leaching equipment and creating favorable conditions for the subsequent purification process. Specifically, bauxite is mixed with circulating mother liquor to form a slurry.

[0046] In this embodiment, the mass concentration of solids in the slurry is controlled at 400 g / L to 1000 g / L; in other embodiments, the mass concentration may also be selected as 500 g / L, 700 g / L or 900 g / L depending on the ore characteristics and equipment capacity, but 400 g / L to 1000 g / L is the basic operating range.

[0047] To investigate the pre-desiliconization rate under different solid concentrations in the slurry during step S100, the effects of solid concentrations of 300 g / L, 400 g / L, 600 g / L, 800 g / L, and 1000 g / L on the pre-desiliconization effect were examined under the conditions of a pre-desiliconization temperature of 105℃, a caustic soda concentration of 200 g / L in the mother liquor, a pre-desiliconization time of 12 h, and no lime addition. The experimental results are listed in Table 1, and the corresponding trends in pre-desiliconization rate are as follows: Figure 2 As shown.

[0048] Table 1 shows the pre-desiliconization rate at different mass concentrations of solids in the slurry during step S100. Figure 2 The pre-desiliconization rate is the pre-desiliconization rate at different mass concentrations of solids in the slurry during step S100.

[0049] From Table 1 and Figure 2 It can be seen that under the above pre-desiliconization conditions, when the mass concentration of solids in the slurry increases from 300 g / L to 1000 g / L, the pre-desiliconization rate increases from 28.42% to 44.33%. Among them, when the mass concentration of solids increases from 300 g / L to 400 g / L, the pre-desiliconization rate increases by 8.61 percentage points; with further increases in the mass concentration of solids, the increase in the pre-desiliconization rate tends to level off.

[0050] Meanwhile, as the mass concentration of solids in the slurry increased, the mass concentration of silicon dioxide (SiO2) in the leaching solution decreased from 2.06 g / L to 1.13 g / L. Correspondingly, the silicon content index (defined as the ratio of the mass concentration of alumina (Al2O3) to the mass concentration of silicon dioxide (SiO2) in the solution, i.e., the silicon content index value is ρ(Al2O3) / ρ(SiO2)) increased from 95 to 138.

[0051] The above results indicate that the mass concentration of solids in the slurry has a significant impact on the pre-desiliconization effect. This is because increasing the mass concentration of solids increases the amount of SiO2 dissolved from the solid phase into the liquid phase per unit volume of slurry, leading to a higher SiO2 concentration in the solution, which in turn promotes the desiliconization reaction to proceed to the right.

[0052] Table 1. Pre-desiliconization rate at different mass concentrations of solids in the slurry during step S100.

[0053]

[0054] Therefore, in the pre-desiliconization step S100, the mass concentration of solids in the slurry is preferably 600 g / L to 1000 g / L. In this embodiment, using a solids mass concentration of 1000 g / L ensures sufficient desiliconization while maintaining the fluidity of the slurry.

[0055] To investigate the pre-desiliconization rate at different reaction temperatures in step S100, the effects of pre-desiliconization temperatures of 90℃, 95℃, 100℃, and 105℃ on the pre-desiliconization effect were examined under the conditions of a circulating mother liquor caustic alkali concentration of 200 g / L, a pre-desiliconization time of 12 h, a slurry solid content of 400 g / L, and no lime addition. The experimental results are listed in Table 2, and the corresponding trends in pre-desiliconization rate are as follows: Figure 3 As shown.

[0056] Table 2 shows the pre-desiliconization rate at different reaction temperatures in step S100; Figure 3 The pre-desiliconization rate is the pre-desiliconization rate at different reaction temperatures in step S100.

[0057] From Table 2 and Figure 3 It can be seen that under the above conditions, when the pre-desiliconization temperature increases from 90℃ to 105℃, the pre-desiliconization rate increases from 31.79% to 37.03%. Simultaneously, the SiO2 concentration in the leaching solution decreases from 2.29 g / L to 1.61 g / L, and the silicon content index (i.e., the mass concentration ratio of Al2O3 to SiO2) increases from 76 to 115. These results indicate that increasing the pre-desiliconization temperature helps the desiliconization reaction proceed more fully, thereby increasing the pre-desiliconization rate.

[0058] Table 2 Pre-desiliconization rate at different reaction temperatures in step S100

[0059]

[0060] Therefore, in step S100, the reaction temperature is further limited to 100℃~105℃. This temperature range allows the desiliconization reaction rate to be moderate, avoiding both excessively slow reaction at low temperatures and unnecessary energy consumption caused by excessively high temperatures.

[0061] To investigate the pre-desiliconization rate of different pre-desiliconization reaction times in step S100, the effect of pre-desiliconization time on the pre-desiliconization rate was examined under the conditions of a pre-desiliconization temperature of 105℃, a caustic soda concentration of 200 g / L in the circulating mother liquor, a slurry solid content of 400 g / L, and no lime addition. The experimental results are listed in Table 3, and the corresponding trends in pre-desiliconization rate are as follows: Figure 4 As shown.

[0062] Table 3 shows the pre-desilicon rates for different pre-desilicon reaction times in step S100; Figure 4 The pre-desilicon rate is the result of different pre-desilicon reaction times in step S100.

[0063] From Table 3 and Figure 4It can be seen that under the above conditions, when the pre-desilicon removal time is extended from 6 h to 12 h, the pre-desilicon removal rate increases from 34.03% to 37.03%. Specifically, when the pre-desilicon removal time is extended from 8 h to 10 h, the pre-desilicon removal rate increases by 2.19 percentage points; while when the time is extended from 10 h to 12 h, the pre-desilicon removal rate only increases by 0.11 percentage points, and the increase is significantly smaller.

[0064] Meanwhile, with the extension of the pre-desiliconization time, the SiO2 concentration in the leaching solution decreased from 2.70 g / L to 1.61 g / L, and the silicon content index (defined as the ratio of Al2O3 to SiO2 mass concentrations) increased from 75 to 115. These results indicate that extending the pre-desiliconization time allows for a more complete desiliconization reaction, thereby increasing the pre-desiliconization rate and reducing the SiO2 concentration in the solution. However, after the pre-desiliconization time exceeds 10 h, further extension has limited effect on improving the pre-desiliconization rate.

[0065] Table 3. Pre-desiliconization rate at different pre-desiliconization reaction times in step S100

[0066]

[0067] Therefore, in step S100, the pre-desilicon reaction time is further limited to 10 h to 12 h. Within this time range, the desilicon reaction tends to be complete, and the increase in pre-desilicon rate tends to be gradual.

[0068] To investigate the pre-desiliconization rate of different grinding finenesses in step S100, under the conditions of a circulating mother liquor caustic soda concentration of 200 g / L, a pre-desiliconization time of 12 h, a pre-desiliconization temperature of 105℃, and no lime addition, the pre-desiliconization effects of two grinding finenesses (i.e., particles smaller than 125 μm accounting for 41.3% and 71.2% of the total mass of mineral powder, respectively) under different slurry solid contents were compared. The experimental results are listed in Table 4, and the corresponding trends in pre-desiliconization rate are as follows: Figure 5 As shown.

[0069] Table 4 shows the pre-desiliconization rate for different grinding finenesses in step S100; Figure 5 The pre-desiliconization rate is the result of different grinding finenesses in step S100.

[0070] From Table 4 and Figure 5It can be seen that under the above conditions, when the ore grinding fineness is such that particles with a diameter less than 125 μm account for 41.3% and 71.2% of the total mass of ore powder, respectively, the pre-desiliconization rate increases as the slurry solid content increases from 300 g / L to 600 g / L, and the solution silica index also increases accordingly. Under the same solid content conditions, increasing the grinding fineness from 41.3% to 71.2% of the total mass of ore powder with a diameter less than 125 μm results in an increase in the pre-desiliconization rate. Taking a solid content of 600 g / L as an example, the pre-desiliconization rate increases from 41.43% to 48.12%. The above results indicate that increasing the slurry fineness is beneficial for a more complete desiliconization reaction, thereby improving the pre-desiliconization rate.

[0071] Table 4. Pre-desiliconization rate at different grinding finenesses in step S100

[0072]

[0073] Therefore, in step S100, the grinding fineness is further limited to particles with a diameter of less than 125 micrometers accounting for 71.2% of the total mass of the mineral powder. Under this fineness condition, the specific surface area of ​​the ore is large, which is conducive to the contact between the alkali solution and the mineral surface, thereby improving the desilication and leaching efficiency.

[0074] In summary, in step S100, the slurry undergoes a pre-desilication reaction at a reaction temperature of 90℃~105℃ for 6 h~12 h. In this embodiment, the preferred reaction temperature is 100℃~105℃ and the preferred reaction time is 10 h~12 h. The caustic soda concentration (calculated as Na2O) of the circulating mother liquor does not exceed 200 g / L. The amount of lime added is not less than 1% of the dry weight of bauxite. The role of lime addition is to promote the desilication reaction to generate hydrated garnet and further reduce the silica concentration in the solution. In this embodiment, the amount of lime added can be 1%, 1.5%, or 2%. After grinding, particles with a diameter less than 125 micrometers are required to account for 50%~75% of the total mass of the ore powder. In this embodiment, the preferred proportion is 71.2%, which balances reaction efficiency and grinding energy consumption.

[0075] Through the above pre-desiliconization steps, a pre-desiliconized slurry is obtained. The silicon index (i.e., the mass concentration ratio of Al2O3 to SiO2) of this pre-desiliconized slurry can reach over 130, and the pre-desiliconization rate can reach over 40%.

[0076] The purpose of the leaching step S200 is to dissolve the alumina in the pre-desiliconized slurry into the solution as fully as possible, while controlling the alkali content in the red mud.

[0077] Specifically, circulating mother liquor is added to the pre-desiliconized slurry to adjust the caustic ratio α of the leaching solution. k (i.e., Na2O) kThe molar ratio of α to Al2O3 is 1.30 to 1.45. In this embodiment, α is preferred. k It ranges from 1.35 to 1.40.

[0078] The amount of lime added is less than 1% of the dry weight of bauxite. In this embodiment, it is preferable that the amount of lime added is 0%, that is, no lime is added, in order to avoid alumina loss and additional solid impurities caused by lime.

[0079] caustic alkali concentration N in circulating mother liquor k The concentration is 170 g / L to 200 g / L. In this embodiment, N is preferred. k The concentration is 180 g / L to 200 g / L.

[0080] The reaction temperature is 110℃~240℃, and the dissolution time is 10 min~90 min. In this embodiment, for gibbsite-type bauxite, the preferred reaction temperature is 145℃ and the dissolution time is 30 min~60 min. This low-temperature dissolution condition can achieve an alumina dissolution rate of over 87% with low energy consumption. In other embodiments, for bauxite containing boehmite or sparingly soluble minerals, high-temperature short-time conditions can also be used, such as a reaction temperature of 235℃ and a dissolution time of 10 min~20 min, to achieve a higher dissolution rate.

[0081] To investigate the caustic ratio α of different dissolving solutions in step S200 k The alumina leaching rate was determined using a ore sample with a grinding fineness of 71.2% of the total ore powder having particles smaller than 125 μm. The leaching was conducted at a leaching temperature of 145℃, a circulating mother liquor caustic soda concentration of 200 g / L, without lime addition, and a leaching time of 60 min. The α-alumina leaching rate of the leaching solution was investigated. k The effect on alumina dissolution rate. The experimental results are listed in Table 5, and the corresponding dissolution rate trends are as follows: Figure 6 As shown.

[0082] Table 5 shows the caustic ratio α of different dissolution solutions in step S200. k alumina dissolution rate; Figure 6 The caustic ratio α of different dissolution solutions in step S200 k The alumina dissolution rate.

[0083] From Table 5 and Figure 6 It can be seen that, under the above experimental conditions, as the caustic ratio α of the dissolution solution increases... k With the increase of [amount], the alumina dissolution rate initially rises and then levels off. The mechanism lies in the caustic ratio α of the dissolution solution. k Increasing the caustic alkali content in the solution leads to a corresponding increase in the amount of soluble alumina, reducing the amount of residual alumina in the solid phase and thus improving the dissolution rate. When the caustic alkali ratio α of the dissolution solution increases...k After reaching a certain value, the dissolution rate basically tends to reach equilibrium.

[0084] Specifically, when the caustic ratio α of the dissolution solution k When the caustic ratio is 1.25, the alumina dissolution rate is 82.79%; the caustic ratio of the leaching solution is... k When the concentration was increased to 1.35, the dissolution rate was 87.11%, compared to α. k =1.25, an increase of 4.32 percentage points; caustic ratio α of the dissolution solution k When the concentration was increased further to 1.40, the dissolution rate was 87.49%, an increase of only 0.38 percentage points; the caustic ratio α of the dissolution solution... k When the caustic ratio α of the dissolution solution was further increased to 1.43, the dissolution rate was 87.51%, an increase of only 0.02 percentage points. These results indicate that when the caustic ratio α of the dissolution solution is further increased... k Once the value exceeds 1.35, continue to increase the caustic ratio α of the leachate. k The effect on improving the dissolution rate is limited.

[0085] Table 5. Caustic ratio α of different dissolution solutions in step S200 k alumina dissolution rate

[0086]

[0087] Therefore, in step S200, the caustic ratio αk of the leaching solution is further limited to 1.35 to 1.40. This range can ensure a high alumina dissolution rate while avoiding excessive alkali consumption and evaporation energy consumption.

[0088] To investigate the alumina leaching rate in step S200 with different lime addition amounts, the effects of 0%, 1%, and 2% lime addition (based on dry bauxite mass) on the leaching effect of Guinean bauxite were examined under the conditions of a leaching temperature of 145℃, a caustic soda concentration of 200 g / L in the circulating mother liquor, and a leaching time of 60 min. The experimental results are listed in Table 6, and the corresponding trends in alumina leaching rate are shown below. Figure 7 As shown.

[0089] Table 6 shows the alumina dissolution rate in step S200 with different lime addition amounts; Figure 7 The alumina dissolution rate is the value of different lime addition amounts in step S200.

[0090] From Table 6 and Figure 7It can be seen that under the above conditions, as the amount of lime added increases from 0% to 2%, the alumina dissolution rate decreases from 87.11% to 85.65%, a decrease of 1.46 percentage points; simultaneously, the N / S ratio (mass ratio of Na2O to SiO2) of the red mud decreases from 0.30 to 0.23, a decrease of 0.07. Furthermore, the silica index of the solution (the ratio of the mass concentration of Al2O3 to SiO2) increases slightly with the increase of lime added, from 86 to 91, an increase of 5.

[0091] Table 6. Alumina dissolution rate with different lime addition amounts in step S200

[0092]

[0093] Therefore, in step S200, the amount of lime added is further limited to 0%, that is, no lime is added, thereby simplifying the operation and reducing the cost of auxiliary materials.

[0094] To investigate the alumina dissolution rate at different reaction temperatures and times in step S200, the effects of different dissolution temperatures and times on bauxite dissolution were examined under the condition that the caustic soda concentration in the circulating mother liquor was 200 g / L and no lime was added. Since the dissolution reaction is more complete under high-temperature conditions, the experiment was designed as follows: at dissolution temperatures of 110℃ and 145℃, dissolution times were set to 30 min, 45 min, 60 min, and 90 min, respectively; at a dissolution temperature of 235℃, dissolution times were set to 10 min, 20 min, and 30 min, respectively. The experimental results are listed in Table 7, and the corresponding alumina dissolution rates are as follows: Figure 8 As shown.

[0095] Table 7 shows the alumina dissolution rate at different reaction temperatures and times in step S200; Figure 8 The alumina dissolution rate is the result of different reaction temperatures and reaction times in step S200.

[0096] From Table 7 and Figure 8It can be seen that at a dissolution temperature of 110℃, as the dissolution time increased from 30 min to 90 min, the alumina dissolution rate increased from 80.47% to 81.56%, an increase of 1.09 percentage points. At a dissolution temperature of 145℃, as the dissolution time increased from 30 min to 90 min, the alumina dissolution rate decreased from 87.62% to 86.38%, a decrease of 1.24 percentage points. At a dissolution temperature of 235℃, as the dissolution time increased from 10 min to 30 min, the alumina dissolution rate decreased from 91.07% to 90.65%, a decrease of 0.42 percentage points. Overall, the alumina dissolution rate significantly increased when the dissolution temperature increased from 110℃ to 235℃; at 110℃, extending the dissolution time slightly increased the dissolution rate; while at 145℃ and 235℃, extending the dissolution time actually led to a slight decrease in the dissolution rate.

[0097] Table 7 shows that, at the same leaching temperature, the N / S ratio (mass ratio of Na₂O to SiO₂) of red mud increases with prolonged leaching time, indicating that some silicon-containing minerals react with the alkaline solution after extending the reaction time. Specifically, at a leaching temperature of 110℃, the N / S ratio of red mud increases from 0.12 to 0.16; at a leaching temperature of 145℃, it increases from 0.21 to 0.35; and at a leaching temperature of 235℃, it increases from 0.61 to 0.71. Furthermore, under the same leaching time conditions, the N / S ratio of red mud increases significantly when the leaching temperature increases from 110℃ to 235℃. This phenomenon is consistent with the fact that even relatively stable quartz under high-temperature conditions can react with alkaline solution.

[0098] Table 7. Alumina dissolution rate at different reaction temperatures and times in step S200.

[0099]

[0100] Therefore, in step S200, the reaction temperature is further limited to 145°C, and the dissolution time is further limited to 30 min to 60 min, which is suitable for low-temperature dissolution of gibbsite-type bauxite. Alternatively, the reaction temperature is further limited to 235°C, and the dissolution time is further limited to 10 min to 20 min, which is suitable for high-temperature short-time dissolution of diaspore or sparingly soluble minerals.

[0101] The leaching slurry is obtained through the above-described leaching step S200. The alumina leaching rate in the slurry can reach over 87%, and the N / S ratio (mass ratio of Na2O to SiO2) of the red mud can be controlled at around 0.30 to 0.35.

[0102] The purpose of the dilution and desilication step S300 is to further remove silicon from the solution by utilizing the principle that the equilibrium solubility of silicon dioxide decreases after the solution concentration is reduced, thereby increasing the silicon content index of the semen.

[0103] Specifically, the leaching slurry is diluted with caustic alkali N. k The concentration is 140 g / L to 155 g / L. In this embodiment, it is preferred to dilute N. k The concentration is 140 g / L to 145 g / L; in other embodiments, it can also be adjusted to 150 g / L or 155 g / L depending on the concentration of the red mud washing solution, but usually not exceeding 155 g / L to ensure the desilication effect.

[0104] The solution is desilication at 95℃ to 105℃ for 30 to 60 minutes. In this embodiment, the preferred desilication temperature is 100℃ and the residence time is 30 to 60 minutes. In other embodiments, if the silicon content of the solution is high, the residence time can be extended to 90 minutes or 120 minutes, but usually 30 to 60 minutes is sufficient to obtain a satisfactory silicon index.

[0105] Semen is obtained through step S300. The silica index of this semen can reach 161-180, which meets the requirements for high-quality alumina production.

[0106] In a preferred embodiment, the pre-desiliconization step S100 uses the following parameters: pre-desiliconization temperature 100℃, ore particles smaller than 125 micrometers accounting for 71.2% of the total mass of the ore powder, the mass concentration of solids in the slurry is 600 g / L, and the pre-desiliconization reaction time is 10 h; the leaching step S200 uses: lime addition is 0, and the leaching solution α... k The concentration of caustic alkali in the circulating mother liquor is 180 g / L to 200 g / L; the dilution and desilication step S300 uses a desilication temperature of 100℃. This optimal combination of parameters results in a pre-desilication rate of over 40%, an alumina dissolution rate of over 87%, and a silica index of over 170 in the final solution, thereby stably obtaining a final solution suitable for the production of high-quality alumina.

[0107] To further illustrate the technical effects of the present invention, comparative experimental data with existing technologies are provided below (the existing technologies are conventional Bayer processes, i.e., without controlling pre-desilicon parameters and without optimizing α-dissolution). kAnd dilution and desilication conditions). The same batch of gibbsite-type bauxite (Al2O3 content 42.43%, SiO2 content 2.28%, A / S 18.61) was used, and the ore was ground according to the preferred embodiment of the present invention (pre-desilication temperature 100℃, solid matter mass concentration 600 g / L, time 10 h, ore grinding fineness of particles smaller than 125 μm accounting for 71.2% of the total ore powder mass; leaching temperature 145℃, time 45 min, α... k =1.38, without lime; diluted desilication N k =145 g / L, temperature 100℃, time 45 min) and conventional process (no pre-desiliconization, dissolution temperature 145℃, time 60 min, α k =1.45, Mother liquor N k =200 g / L, diluted desilicon N k A comparison was made using a concentration of 160 g / L, a temperature of 95℃, and a time of 30 min.

[0108] The results show that the pre-desiliconization rate of the embodiment of the present invention reached 42.3%, the alumina dissolution rate was 87.5%, and the silica index of the final solution was 175; while the alumina dissolution rate of the conventional process was 85.2%, and the silica index of the final solution was only 92. It is evident that the present invention, through the synergistic use of parameters in the pre-desiliconization, dissolution, and dilution desiliconization steps, can improve the alumina dissolution rate to a certain extent and significantly increase the silica index of the final solution.

[0109] The working principle of this invention is roughly as follows:

[0110] First, bauxite is mixed with circulating mother liquor. Under controlled conditions of solid mass concentration, temperature, time, caustic alkali concentration in the mother liquor, lime addition, and grinding fineness, a pre-desiliconization reaction is carried out. This causes the active silica in the ore to react with the alkali to form sodium silicate slag or hydrated garnet precipitate, thereby removing most of the silica before leaching and increasing the silica index of the slurry. Then, circulating mother liquor is added to the pre-desiliconized slurry to adjust the α-coefficient of the leaching solution. k The solution is brought to a suitable range and subjected to a leaching reaction at a specific temperature and time to dissolve the alumina in the bauxite, forming a sodium aluminate solution, while simultaneously controlling the alkali content in the red mud. Finally, the leaching slurry is diluted to a lower N2 level. k Concentration: Taking advantage of the characteristic that silicon's solubility decreases at low concentrations, silicon-containing precipitates are further precipitated during the residence process to obtain a high silicon content index concentrate, providing pure raw materials for subsequent seed crystal decomposition processes.

[0111] In summary, this application achieves its goals through the synergistic effect of the pre-desiliconization step S100, the leaching step S200, and the dilution desiliconization step S300, and by precisely controlling the key process parameters in each step (including the mass concentration of solids in the slurry, reaction temperature, reaction time, caustic soda concentration in the mother liquor, lime addition, grinding fineness, and α-coated leaching solution). k This process (including methods such as [list of methods]) can improve the pre-desiliconization rate, stabilize the alumina leaching rate, and obtain a concentrate with a higher silica index. When processing gibbsite-type bauxite, this process helps reduce scaling in leaching equipment, lowers alkali and energy consumption, and improves concentrate purity, thus providing reliable technical support for the production of high-quality alumina.

[0112] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. The leaching and desilication process for alumina production using the Bayer process, characterized in that, Includes the following steps: Step S100: Grind bauxite until particles with a diameter less than 125 μm account for 50%–75% of the total mass of the ore powder. Mix the ground bauxite with circulating mother liquor, controlling the mass concentration of solids in the resulting slurry to be 400 g / L–1000 g / L. Perform a pre-desilication reaction at a reaction temperature of 90℃–105℃ for 6 h–12 h. The caustic alkali concentration N in the circulating mother liquor is... k The lime content shall not exceed 200 g / L and shall not be less than 1% of the dry basis mass of the bauxite to obtain a pre-desilication slurry; Step S200: Add circulating mother liquor to the pre-desiliconized slurry and adjust the caustic ratio α of the leaching solution. k The concentration of caustic soda in the circulating mother liquor is 1.30–1.45, the amount of lime added is less than 1% of the dry weight of the bauxite, and the concentration of caustic soda N in the circulating mother liquor is... k The concentration is 170 g / L to 200 g / L, and the solution is dissolved for 10 min to 90 min at a reaction temperature of 110℃ to 240℃ to obtain a dissolution slurry. Step S300: Dilute the leaching slurry with caustic alkali N. k Semen was obtained by desilication at a concentration of 140 g / L to 155 g / L and at 95℃ to 105℃ for 30 min to 60 min.

2. The leaching and desilication process for alumina production using the Bayer process according to claim 1, characterized in that, In step S100, the mass concentration of solids in the slurry is 600 g / L to 1000 g / L.

3. The leaching and desilication process for alumina production using the Bayer process according to claim 1, characterized in that, In step S100, the reaction temperature is 100℃~105℃.

4. The leaching and desilication process for alumina production using the Bayer process according to claim 1, characterized in that, In step S100, the pre-desiliconization reaction time is 10 h to 12 h.

5. The leaching and desilication process for alumina production using the Bayer process according to claim 1, characterized in that, In step S100, particles with a diameter of less than 125 micrometers account for 71.2% of the total mass of the mineral powder.

6. The leaching and desilication process for alumina production using the Bayer process according to claim 1, characterized in that, In step S200, the caustic ratio α of the dissolution solution k It ranges from 1.35 to 1.

40.

7. The leaching and desilication process for alumina production using the Bayer process according to claim 1, characterized in that, In step S200, the amount of lime added is 0%.

8. The leaching and desilication process for alumina production using the Bayer process according to claim 1, characterized in that, In step S200, the reaction temperature is 145°C and the dissolution time is 30 min to 60 min.

9. The leaching and desilication process for alumina production using the Bayer process according to claim 1, characterized in that, In step S200, the reaction temperature is 235°C and the dissolution time is 10 min to 20 min.

10. The leaching and desilication process for alumina production using the Bayer process according to any one of claims 1 to 9, characterized in that: In step S100, the pre-desiliconization temperature is 100℃, the ore particles with a diameter of less than 125 micrometers account for 71.2% of the total mass of the ore powder, the mass concentration of solid matter in the slurry is 600 g / L, and the pre-desiliconization reaction time is 10 h. In step S200, the amount of lime added is 0, and the amount of leaching solution α is... k The value is 1.40, and the concentration of caustic alkali in the circulating mother liquor is 180 g / L to 200 g / L; In step S300, the desiliconization temperature is 100°C.

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