A method for removing iron and improving quality by magnetic separation after high-iron bauxite mother liquor grinding

Abstract

The application provides a method for removing iron from high-iron bauxite mother liquor after grinding and magnetic separation, and belongs to the field of mineral processing. The method comprises the following steps: grinding and treating mixed ore slurry of high-iron bauxite and circulating mother liquor to obtain alkaline ore slurry; the circulating mother liquor is a caustic alkali circulating liquid generated in an alumina dissolution process; using the circulating mother liquor as ore unloading water, the alkaline ore slurry is subjected to magnetic separation to remove iron to obtain iron-removed ore slurry and iron-rich ore slurry; the iron-removed ore slurry is sent to the alumina dissolution process; and the iron-rich ore slurry is subjected to separation treatment to obtain the circulating mother liquor and iron concentrate. In the application, iron minerals are efficiently removed under the premise of not introducing additional moisture, after the bauxite minerals are fully dissociated and before entering the dissolution process, so as to reduce alkali consumption, reduce the amount of red mud, and realize the resource utilization of iron minerals.

Description

Technical Field

[0001] This application relates to the field of mineral processing technology, and in particular to a method for iron removal and upgrading of high-iron bauxite mother liquor by magnetic separation after grinding. Background Technology

[0002] Bauxite is the main raw material for alumina production, and its quality directly affects the energy consumption, alkali consumption, and economic benefits of the Bayer process. High-iron bauxite has abundant reserves both domestically and internationally, with a high aluminum-silicon ratio, but its iron (Fe2O3) content is generally high (15%–35%), which severely impacts alumina production efficiency. Iron minerals do not participate in the reaction during the Bayer process and instead enter the red mud. On the one hand, some iron minerals encapsulate gibbsite as fine particles, hindering its dissolution and leading to a decrease in alumina recovery. On the other hand, it increases red mud production, increases processing difficulty, and exacerbates the loss of alkali and alumina in the liquid.

[0003] Currently, the most commonly used iron removal technology for bauxite in the Bayer process of alumina production is magnetic separation. Existing technologies generally place the magnetic separation process before the grinding process; that is, the crushed coarse-grained bauxite is first magnetically separated, and then the magnetically separated ore is mixed with circulating mother liquor for grinding before being sent to the leaching process. This process has the following core problems: Insufficient iron mineral liberation and low iron removal efficiency: The bauxite is crushed to a coarse particle size, and the aluminum and iron minerals in the coarse-grained ore are not completely liberated. During magnetic separation, it is difficult to effectively separate encapsulated iron minerals, resulting in a low iron removal rate of only 60%–70%, with some iron minerals still entering the leaching process; High steam consumption in the leaching process: Magnetic separation before grinding often uses wet magnetic separation processes, and the aluminum concentrate will have attached water (8%–12% moisture content). Introducing the water into the subsequent grinding and leaching systems requires additional steam to evaporate external moisture in order to maintain the necessary alkali concentration and temperature for leaching, leading to increased steam consumption in the leaching process and increased production costs. The process flow is also inefficient: the concentrate after magnetic separation before grinding needs to be remixed with the circulating mother liquor to prepare the slurry, making the process cumbersome. Furthermore, fluctuations in the particle size, concentration, and temperature of the slurry can affect the stability of subsequent leaching reactions. Red mud iron recovery: after the Bayer process leaches and separates red mud, magnetic separation is used to recover iron from the red mud. This method is a downstream resource utilization method; although it can recover some iron minerals, it cannot solve the interference of iron minerals on the upstream leaching process, nor can it improve the alumina leaching rate or reduce alkali consumption. Moreover, the red mud being processed is already extremely fine, making separation difficult and costly. Therefore, how to efficiently remove iron minerals without introducing additional moisture, after the bauxite minerals have been fully liberated and before entering the leaching process, has become a key technical challenge for optimizing the Bayer process for high-iron bauxite production and improving economic efficiency. Summary of the Invention

[0004] This application provides a method for removing iron and upgrading high-iron bauxite mother liquor by magnetic separation after grinding, in order to solve the following technical problem: how to efficiently remove iron minerals after the bauxite minerals have been fully liberated and before entering the leaching process without introducing additional water, thereby improving leaching efficiency, reducing alkali consumption, reducing red mud, and realizing the resource utilization of iron minerals.

[0005] This application provides a method for iron removal and upgrading of high-iron bauxite mother liquor by magnetic separation after grinding. The method includes: The mixed slurry of high-iron bauxite and circulating mother liquor is ground to obtain an alkaline slurry; the circulating mother liquor is a caustic alkali circulating liquid produced in the alumina leaching process. Using the circulating mother liquor as the unloading medium, the alkaline slurry is subjected to magnetic separation to remove iron, resulting in iron-removed slurry and iron-rich slurry. The iron-removed slurry is then fed into the alumina leaching process. The iron ore slurry is separated to obtain the circulating mother liquor and iron concentrate.

[0006] Optionally, in the high-iron bauxite, the Fe2O3 content is 25%–35% and the Al2O3 content is 38%–45% by mass fraction.

[0007] Optionally, the solids content of the alkaline slurry is 300 g / L to 400 g / L, and the grinding fineness of the alkaline slurry is -200 mesh, accounting for 75% to 90%.

[0008] Optionally, the temperature of the circulating mother liquor is 50℃~70℃, and the alkaline concentration of the circulating mother liquor, calculated as NaOH, is 180g / L~250g / L.

[0009] Optionally, the magnetic separation equipment for removing iron is a vertical ring high gradient magnetic separator or a pulsed high gradient magnetic separator, and the magnetic field strength for removing iron is 0.8T to 1.8T.

[0010] Optionally, the components of the magnetic separator that come into contact with the slurry or circulating mother liquor are made of alkali-resistant, high-temperature-resistant, and corrosion-resistant materials, which are selected from titanium and titanium alloys, super austenitic stainless steel, or special ceramics.

[0011] Optionally, the amount of the circulating mother liquor used as unloading water is 10% to 15% of the amount of ore processed by magnetic separation for iron removal.

[0012] Optionally, the temperature difference between the circulating mother liquor used as unloading water and the alkaline slurry is ≤5°C.

[0013] Optionally, in the concentrate product corresponding to the concentrate slurry, the content of Al2O3 is 47% to 55% and the content of Fe2O3 is 15% to 24% by mass fraction.

[0014] Optionally, the Fe2O3 content in the iron concentrate is >65% by mass fraction.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for iron removal and upgrading of high-iron bauxite mother liquor by magnetic separation after grinding. Through four closely linked steps, the method achieves efficient separation of iron minerals at the critical node between the full dissociation of bauxite minerals and the entry into the leaching process without introducing additional moisture. This achieves multiple objectives, including improving leaching efficiency, reducing alkali consumption, reducing red mud, and resource utilization of iron minerals.

[0016] First, the slurry of high-iron bauxite and circulating mother liquor is ground, a step that achieves complete liberation of the aluminum and iron minerals. The grinding process separates the previously intertwined or linked aluminum and iron minerals, creating the necessary conditions for subsequent selective separation based on differences in physical properties. Simultaneously, the use of caustic alkali circulating mother liquor from the alumina leaching process as the grinding medium ensures that the entire slurry system is fully integrated into the Bayer process's original media circulation from the initial stage, preventing the introduction of external moisture and ensuring a high degree of matching between the slurry's temperature and alkalinity and subsequent processes.

[0017] Secondly, using recycled mother liquor as unloading water, the dissociated alkaline slurry is subjected to magnetic separation for iron removal, which is the core step in achieving efficient separation. Utilizing the significant difference in magnetic response characteristics between iron and aluminum minerals, the magnetic separator captures the strongly magnetic iron minerals to form an iron-rich slurry, while the non-magnetic portion of the main aluminum-containing minerals flows away with the slurry, becoming the iron-removed slurry. The key to this step is using recycled mother liquor instead of conventional clean water as unloading water. This design fundamentally avoids the entry of external water into the production system, eliminating the additional steam consumption required to evaporate this water. Simultaneously, because the minerals in the slurry to be separated have been fully dissociated, the magnetic separation operation can efficiently capture iron minerals, ensuring effective iron removal.

[0018] Subsequently, the iron-removed slurry is directly fed into the alumina leaching process, achieving seamless integration between the upgraded slurry and the main process. Because this slurry uses circulating mother liquor as a medium, its key parameters such as temperature and alkali concentration are completely consistent with the requirements of the leaching process, and no external moisture is introduced. Therefore, it can be directly subjected to high-temperature and high-pressure leaching without any intermediate treatment or adjustment. The amount of iron minerals entering the leaching system is significantly reduced due to the preceding magnetic separation. This means that: on the one hand, iron minerals that might have coated bauxite or interfered with the leaching reaction are removed, improving the alumina leaching efficiency; on the other hand, due to the reduction in the amount of iron minerals that do not participate in the reaction, the total amount of red mud generated is significantly reduced, and the amount of alkali and alumina attached to and discharged with the red mud is also reduced, thereby effectively reducing alkali consumption and the loss of useful components.

[0019] Finally, the rich iron ore slurry undergoes separation treatment, achieving media recovery and iron resource utilization. Through sedimentation concentration or filtration washing, the high-value recycled mother liquor entrained in the rich iron ore slurry is fully recovered and returned to the production system, ensuring a closed-loop media circulation. The solid phase obtained after separation is high-grade iron concentrate, which can be used as a raw material for iron smelting or for preparing iron-based pigments. This step transforms iron minerals that would otherwise become red mud waste into economically valuable products, achieving comprehensive resource utilization while further reducing solid waste emissions. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic flowchart of a method for iron removal and upgrading of high-iron bauxite mother liquor after grinding, provided for an embodiment of this application; Figure 2 A schematic diagram of the process principle of a method for removing iron and upgrading high-iron bauxite mother liquor by magnetic separation after grinding, provided in an embodiment of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0025] Figure 1 A schematic flowchart of a method for iron removal and upgrading of high-iron bauxite mother liquor after grinding, provided for an embodiment of this application; Figure 2 A schematic diagram of the process principle of a method for removing iron and upgrading high-iron bauxite mother liquor by magnetic separation after grinding, provided in an embodiment of this application.

[0026] like Figure 1 and Figure 2 As shown in the embodiment of this application, a method for iron removal and upgrading of high-iron bauxite mother liquor by magnetic separation after grinding is provided. The method includes: S1. Grind the mixed slurry of high-iron bauxite and circulating mother liquor to obtain an alkaline slurry; the circulating mother liquor is a caustic alkali circulating liquid produced in the alumina leaching process. S2. Using the circulating mother liquor as the unloading medium, the alkaline slurry is subjected to magnetic separation to remove iron, resulting in iron-removed slurry and iron-rich slurry. S3. The iron-removed slurry is sent to the alumina leaching process. S4. The iron ore slurry is separated to obtain the circulating mother liquor and iron concentrate.

[0027] It should be noted that step S1 serves to create the necessary physical and chemical conditions for subsequent magnetic separation to remove iron. The high-iron bauxite is mixed with the circulating mother liquor and then ground. This process first reduces the particle size of the minerals, allowing for the complete dissociation of aluminum and iron minerals from their intergrowth state, which is fundamental to achieving efficient separation. Simultaneously, using the caustic alkali circulating mother liquor generated from the alumina leaching process as the grinding medium not only preheats the slurry, matching its temperature to subsequent processes, but also ensures the stability of the chemical composition of the entire slurry system, providing homogeneous material for separation under alkaline conditions.

[0028] Step S2 is crucial for the physical separation of aluminum and iron minerals and is the core upgrading step in the entire process. This step uses recycled mother liquor as the unloading water to magnetically separate the fully dissociated alkaline slurry. Utilizing the magnetic difference between iron and aluminum minerals, the strongly magnetic iron minerals are captured under the influence of a magnetic field, forming an iron-rich slurry. The non-magnetic portion of the main aluminum-bearing minerals flows away with the slurry, resulting in a de-ironized slurry. The key to this step is using recycled mother liquor instead of conventional clean water as the unloading water. This design avoids introducing external moisture into the production system, thus eliminating the additional steam consumption required for evaporating this moisture.

[0029] Step S3 seamlessly integrates the upgraded main material into the Bayer process's main production flow. The iron-removed slurry obtained after magnetic separation is directly fed into the alumina leaching process, achieving a tight connection between the processes. Since the slurry's key parameters, such as temperature, alkali concentration, and solids content, are completely consistent with the requirements of the leaching process, and no external moisture is introduced, high-temperature, high-pressure leaching can be performed directly without any adjustments, ensuring the stability and continuity of the production process. Simultaneously, the reduced iron content improves alumina leaching efficiency and reduces red mud formation.

[0030] Step S4 involves the resource recovery and media recovery of the separated iron-containing by-products. The iron-rich ore slurry obtained from magnetic separation undergoes sedimentation concentration or filtration and washing treatment. The purpose is to fully recover the high-value alkaline circulating mother liquor entrained within and return it to the Bayer process for recycling, achieving zero discharge of the alkaline solution. The solid phase obtained after washing and separation is high-grade iron concentrate, which can be used as a raw material for iron smelting or to prepare iron-based pigments. This achieves efficient and comprehensive utilization of associated iron resources in high-iron bauxite, reducing solid waste emissions.

[0031] In some embodiments, the high-iron bauxite contains 25%–35% Fe2O3 and 38%–45% Al2O3 by mass fraction.

[0032] In some embodiments, the solids content of the alkaline slurry is 300 g / L to 400 g / L, and the grinding fineness of the alkaline slurry is -200 mesh, accounting for 75% to 90%.

[0033] The solid content of the slurry is a key process parameter in the leaching process, which directly affects magnetic separation efficiency, process economy, process efficiency, and process stability. If the solids content of the alkaline slurry is higher than 400 g / L, the slurry viscosity is too high, causing non-magnetic minerals (such as aluminum-containing minerals) to be mechanically carried into the magnetic product, increasing bauxite loss. At the same time, the excessive density of solid particles hinders the full diffusion and circulation of alkaline solution between particles during subsequent leaching, resulting in uneven local reactions. Some ores may not react completely due to insufficient contact, reducing the leaching rate. If the solids content of the alkaline slurry is lower than 300 g / L, the concentration of magnetic iron mineral particles in the slurry is low, reducing the probability of collision between iron minerals and the magnetic field of the magnetic separator per unit volume. The slurry flow rate is too fast, and some fine iron mineral particles flow away quickly with the slurry, failing to be captured by the magnetic field, resulting in decreased magnetic separation efficiency, reduced ore processing capacity of the equipment, and a significant increase in energy consumption per unit capacity, leading to a significant increase in production costs. In addition, the excessive liquid phase during subsequent leaching makes the system's heat and material buffer too large, resulting in a sluggish response to precise control of process parameters and affecting the leaching rate index.

[0034] Grinding particle size affects the degree of liberation of iron and aluminum minerals in ore, thus impacting magnetic separation and leaching efficiency. If the grinding fineness of the alkaline slurry is less than 75% (-200 mesh), the main impact on magnetic separation is that a large amount of iron minerals are encapsulated by aluminum minerals, making it difficult for the magnetic separator to effectively capture them, resulting in a decrease in iron removal rate. This iron then enters the alumina process. If unliberated iron-alumina intergrowths are adsorbed by the magnetic field, it will cause Al2O3 loss. The impact on the leaching process is that a high proportion of coarse bauxite particles leads to insufficient contact with the mother liquor, reducing the Al2O3 leaching rate and alumina recovery rate. Coarse particles easily settle to the bottom of the leaching tank, increasing the load on the agitator and even causing a "sinking" failure, preventing the leaching process from proceeding normally. If the grinding fineness of the alkaline slurry is higher than 90% (-200 mesh), the impact on magnetic separation is as follows: The increase in fine particles means that the magnetic attraction of these fine particles is much less than the fluid resistance, making them unrecoverable for the leaching process and increasing subsequent processing volume. The impact on leaching is that the reaction rate between mineral particles and the mother liquor is too fast, easily leading to a localized over-alkaline environment. This results in the leaching of large amounts of impurities such as SiO2 and TiO2, increasing the difficulty of subsequent red mud separation. Furthermore, the caustic ratio of the leaching solution fluctuates greatly, affecting the quality of alumina products. For example, the solids content of the alkaline slurry may be 300, 320, 340, 360, 380, or 400 g / L; the fineness of the slurry after grinding may be 75%, 80%, 85%, or 90% (-200 mesh).

[0035] In some embodiments, the temperature of the circulating mother liquor is 50°C to 70°C, and the alkaline concentration of the circulating mother liquor, calculated as NaOH, is 180 g / L to 250 g / L.

[0036] The parameters of a circulating mother liquor temperature of 50℃~70℃ and an alkali concentration of 180g / L~250g / L jointly ensure the stability of the grinding and magnetic separation processes and their compatibility with subsequent leaching processes. This temperature range ensures suitable slurry fluidity, avoiding both excessively low temperatures that increase viscosity and affect separation efficiency, and excessively high temperatures that cause unnecessary heat loss. Simultaneously, this temperature is close to the mother liquor temperature in the leaching process, eliminating thermal shock when the slurry enters the leaching system. The alkali concentration range ensures the chemical stability of the slurry system, preventing changes in mineral surface properties due to concentration fluctuations from interfering with magnetic separation. More importantly, this concentration is completely consistent with the process requirements of the Bayer process leaching, allowing the slurry after iron removal to directly enter the leaching process without adjustment.

[0037] In some embodiments, the magnetic separation equipment for removing iron is a vertical ring high gradient magnetic separator or a pulsed high gradient magnetic separator, and the magnetic field strength for removing iron is 0.8T to 1.8T.

[0038] Different types of magnetic separators are selected based on the different forms and particle size distributions of iron minerals in alkaline slurries. If the iron minerals are weakly magnetic and have a high proportion of intergrowths with aluminum minerals, the weak magnetic particles have weak adsorption to the magnetic medium and are easily washed away by the slurry under a static magnetic field. Pulsating disturbances allow the intergrowths to pass through the magnetic medium multiple times, increasing the probability of iron mineral liberation and capture while reducing the entrainment of non-magnetic intergrowths. In this case, a pulsating magnetic separator is preferred. If the iron minerals are relatively strongly magnetic and the magnetic particles have sufficient adsorption to the magnetic medium, a static magnetic field can achieve a high recovery rate. In this case, a vertical ring magnetic separator has a more significant advantage in throughput and lower experimental costs, making a vertical ring magnetic separator the preferred choice.

[0039] The reason for controlling the magnetic separation intensity is that magnetic separation is a method of separating minerals based on differences in their magnetic properties. The magnetic separation intensity directly determines the types of minerals that the magnetic separator can capture, their particle size, and the separation efficiency. If the magnetic separation intensity is below 0.8T, the magnetic field gradient force of weakly magnetic iron minerals is insufficient to overcome the fluid resistance of the slurry. The dissociated iron mineral particles are lost with the slurry, resulting in a decrease in iron removal rate, separation efficiency, and throughput. If the magnetic field strength is above 1.8T, the excessively strong magnetic field force will adsorb non-magnetic bauxite particles (especially ultrafine bauxite), leading to Al2O3 loss. Simultaneously, the energy consumption of the excitation system increases with the magnetic field strength, resulting in increased equipment wear and energy consumption. Examples of magnetic separation field strengths include 0.8T, 1.0T, 1.2T, 1.4T, 1.6T, and 1.8T.

[0040] In some embodiments, the components of the magnetic separator that come into contact with the slurry or circulating mother liquor are made of alkali-resistant, high-temperature-resistant, and corrosion-resistant materials, selected from titanium and titanium alloys, super austenitic stainless steel, or special ceramics.

[0041] In some embodiments, the amount of the circulating mother liquor used as unloading water is 10% to 15% of the amount of ore processed by the magnetic separation for iron removal.

[0042] The reason for controlling the amount of circulating mother liquor used in unloading is that the unloading water during magnetic separation is to ensure the effective removal of magnetic iron minerals from the magnetic media (steel wool / steel mesh) while maintaining a stable slurry concentration. If the amount of circulating mother liquor used in unloading is too low, the water flow impact force is insufficient, and the magnetic iron minerals adsorbed on the surface of the magnetic media cannot be completely washed off. The residual iron minerals will gradually clog the gaps in the magnetic media, causing a decrease in the magnetic field gradient and reducing the subsequent iron mineral capture efficiency. If the amount of circulating mother liquor used in unloading is too high, it will lead to an increase in the amount of circulating mother liquor used, increasing costs, and also increasing the amount of iron concentrate settling and pressure filtration required. For example, the amount of circulating mother liquor used is 10%, 11%, 12%, 13%, 14%, 15% of the ore processed by the magnetic separator, etc.

[0043] In some embodiments, the temperature difference between the circulating mother liquor, which serves as unloading water, and the alkaline slurry is ≤5°C.

[0044] The reason for controlling the temperature difference to ≤5℃ is to avoid excessive temperature difference from causing abrupt changes in the physical properties of the slurry system, damage to chemical stability, and disorder of the process flow, thereby ensuring the stability of the entire grinding-magnetic separation-leaching process and preventing a decrease in separation efficiency.

[0045] In some embodiments, the magnetic separation iron removal process is performed after the grinding process and before the leaching process.

[0046] The process described in this application fully utilizes the grinding process to achieve the dissociation of aluminum and iron minerals. The current grinding → magnetic separation → leaching process uses the logic of dissociation followed by separation to remove iron minerals in a single grinding operation, while simultaneously meeting the particle size requirements of the leaching process. This avoids the cumbersome process of conventional processes involving crushing and grinding to remove iron, sedimentation and filtration of the concentrate, and further grinding before entering the alumina process. It also reduces the amount of moisture carried into the alumina process by the concentrate, achieving a triple improvement in magnetic separation efficiency, leaching effect, and resource utilization.

[0047] In some embodiments, the concentrate product corresponding to the concentrate slurry contains, by mass fraction, 47%–55% Al2O3 and 15%–24% Fe2O3.

[0048] The mass fraction range of Al2O3 content (47%–55%) and Fe2O3 content (15%–24%) in the concentrate product characterizes the upgrading effect of this method on high-iron bauxite. The results show that after grinding and magnetic separation to remove iron, aluminum minerals are effectively enriched, and the alumina content is significantly increased compared to the original ore. Simultaneously, the iron content is controlled within the range of 15% to 24%, significantly reducing the amount of iron minerals entering the leaching system. This grade of concentrate, when entering the leaching process, will effectively reduce the amount of red mud generated, reduce the loss of alumina and alkali in the leaching solution, thereby improving alumina leaching efficiency and reducing production costs.

[0049] In some embodiments, the Fe2O3 content in the iron concentrate is >65% by mass fraction.

[0050] The Fe2O3 content exceeding 65% in the iron concentrate defines the quality grade of the by-product recovered by this method. This grade indicates that the iron concentrate obtained after separation of rich iron ore slurry meets the entry-level standard for industrial ironmaking raw materials and can be directly sold to steel companies or used to prepare iron-based pigments. This parameter not only verifies the high-efficiency separation capability of the magnetic separation process but also demonstrates the value of this method in realizing the high-value utilization of associated iron resources in bauxite, transforming waste into marketable products, significantly improving the overall economic benefits of the process, and reducing red mud emissions.

[0051] The present application provides a method for magnetic separation and iron removal after grinding of high-iron bauxite mother liquor, which can effectively separate aluminum and iron minerals in bauxite, reduce production costs, improve ore grade, and achieve efficient utilization of high-iron bauxite resources, resulting in significant social and economic benefits. In summary, the present application provides a method for magnetic separation and iron removal after grinding of high-iron bauxite mother liquor, which has the following advantages: (1) Reduce moisture introduction and lower production costs: In conventional magnetic separation processes, the magnetic separation is mainly carried out in aqueous slurry. The resulting aluminum concentrate is filtered after sedimentation and pressure filtration, with a moisture content of 15-20%. This external moisture will enter the subsequent regrinding and leaching processes with the aluminum concentrate, increasing evaporation energy consumption. This invention moves the magnetic separation process to after grinding and before leaching, and carries out magnetic separation in the circulating mother liquor slurry, avoiding the introduction of moisture and reducing production costs.

[0052] (2) Reduce grinding costs and decrease energy and material consumption: Conventional processes require two grinding operations: the first is coarse grinding of the raw ore (to prepare for magnetic separation) + the second is regrinding of the concentrate (to dissociate residual iron minerals). The total energy consumption of grinding is relatively high. At the same time, the aluminum minerals have been partially dissociated during the regrinding of the concentrate. Over-grinding will produce a large amount of ultrafine bauxite, which will lead to colloidalization and difficulty in sedimentation during leaching. This application only requires one grinding operation to achieve full dissociation of iron minerals, while meeting the leaching particle size requirements, reducing grinding energy consumption and steel ball / liner consumption.

[0053] (3) Simplify the process flow and reduce equipment investment and maintenance costs: Conventional iron removal processes require additional processes such as concentrate settling, filter pressing, and transportation, which increases equipment maintenance costs. The present invention has a compact connection between the grinding, magnetic separation, and leaching processes, without the need for additional auxiliary processes, and the process flow is smooth.

[0054] (4) More efficient iron resource recovery and reduced solid waste emissions: In conventional processes, the iron concentrate captured by magnetic separation is not fully liberated, has a low grade, and contains a large amount of bauxite, making it unusable directly; the residual solution of the liberated iron minerals after re-grinding increases red mud emissions and increases solid waste treatment costs. In this application, the fully liberated iron minerals after grinding are captured by magnetic separation, resulting in high-grade iron concentrate that can be directly used as raw material for ironmaking or iron-based pigments, while reducing red mud emissions, thus improving resource utilization and reducing environmental costs.

[0055] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0056] Example 1 High-iron bauxite was mixed with circulating mother liquor to form a slurry, which was then fed into a grinding mill to obtain an alkaline slurry. The high-iron bauxite contained 40.21% Al2O3 and 30.10% Fe2O3 by mass. The circulating mother liquor temperature was 55℃, the alkaline concentration was 180 g / L, the slurry solids content was 320 g / L, and the proportion of -200 mesh particles in the slurry was 75.21%. A vertical ring high-gradient magnetic separator was used for magnetic separation to remove iron. The magnetic field strength was 1.0T, and the unloading medium was the circulating mother liquor, used at a rate of 10% of the ore weight. After magnetic separation, the alumina content in the concentrate slurry was 47.69%. The magnetic product (iron-rich tailings) was subjected to sedimentation and pressure filtration to obtain an iron concentrate with a Fe2O3 grade of 68.0%. The filtrate was recycled.

[0057] Example 2 High-iron bauxite was mixed with circulating mother liquor to form a slurry, which was then fed into a grinding mill to obtain an alkaline slurry. The high-iron bauxite contained 44.87% Al2O3 and 25.32% Fe2O3 by mass. The circulating mother liquor temperature was 65℃, the alkaline concentration was 220 g / L, the slurry solids content was 360 g / L, and the proportion of -200 mesh particles in the slurry was 84.86%. A vertical ring high-gradient magnetic separator was used for magnetic separation to remove iron. The magnetic field strength was 0.8T, and the unloading medium was the circulating mother liquor, which accounted for 13% of the ore weight. After magnetic separation, the alumina content in the concentrate slurry was 54.34%. The magnetic product (iron-rich tailings) was subjected to sedimentation and pressure filtration to obtain an iron concentrate with a Fe2O3 grade of 67.15%. The filtrate was recycled.

[0058] Example 3 High-iron bauxite was mixed with circulating mother liquor to form a slurry, which was then fed into a grinding mill to obtain an alkaline slurry. The high-iron bauxite contained 42.11% Al2O3 and 28.54% Fe2O3 by mass. The circulating mother liquor temperature was 70℃, the alkaline concentration was 200 g / L, the slurry solids content was 380 g / L, and the proportion of -200 mesh particles in the slurry was 80.12%. A pulsed high-gradient magnetic separator was used for magnetic separation to remove iron. The magnetic field strength was 1.2T, and the unloading medium was the circulating mother liquor, used at 11% of the ore weight. After magnetic separation, the alumina content in the concentrate slurry was 51.73%. The magnetic product (iron-rich tailings) was subjected to sedimentation and pressure filtration to obtain an iron concentrate with a Fe2O3 grade of 70.24%. The filtrate was recycled.

[0059] Example 4 High-iron bauxite was mixed with circulating mother liquor to form a slurry, which was then fed into a grinding mill to obtain an alkaline slurry. The high-iron bauxite contained 38.16% Al2O3 and 34.79% Fe2O3 by mass. The circulating mother liquor temperature was 60℃, the alkaline concentration was 250 g / L, the slurry solids content was 300 g / L, and the proportion of -200 mesh in the slurry was 89.37%. A vertical ring high-gradient magnetic separator was used for magnetic separation to remove iron. The magnetic field strength was 1.8T, and the unloading medium was the circulating mother liquor, which accounted for 12% of the ore weight. After magnetic separation, the alumina content in the concentrate slurry was 47.02%. The magnetic product (iron-rich tailings) was subjected to sedimentation and pressure filtration to obtain an iron concentrate with a Fe2O3 grade of 69.82%. The filtrate was recycled.

[0060] Example 5 High-iron bauxite was mixed with circulating mother liquor to form a slurry, which was then fed into a grinding mill to obtain an alkaline slurry. The high-iron bauxite contained 41.53% Al2O3 and 32.16% Fe2O3 by mass. The circulating mother liquor temperature was 50℃, the alkaline concentration was 250 g / L, the slurry solids content was 400 g / L, and the proportion of -200 mesh in the slurry was 82.04%. A periodic high-gradient magnetic separator was used for magnetic separation to remove iron. The magnetic field strength was 1.6T, and the unloading medium was the circulating mother liquor, used at 15% of the ore weight. After magnetic separation, the alumina content in the concentrate slurry was 51.56%. The magnetic product (iron-rich tailings) was subjected to sedimentation and pressure filtration to obtain an iron concentrate with a Fe2O3 grade of 73.24%. The filtrate was recycled.

[0061] Comparative Example 1 Using the high-iron bauxite raw material from Example 1, the upgrading process parameters remained consistent, but the medium was replaced with clean water instead of circulating mother liquor. After upgrading, the alumina content in the concentrate slurry was 47.31%, and the moisture content of the concentrate after filtration was 20.13%. The magnetic product (iron-rich tailings) was subjected to sedimentation and pressure filtration to obtain an iron concentrate with a Fe2O3 grade of 65.02%.

[0062] Comparative Example 2 Using the high-iron bauxite raw material from Example 2, the upgrading process parameters remained consistent, but the medium was replaced with clean water instead of circulating mother liquor. After upgrading, the alumina content in the concentrate slurry was 53.92%, and the moisture content of the concentrate after filtration was 19.24%. The magnetic product (iron-rich tailings) was subjected to sedimentation and pressure filtration to obtain an iron concentrate with a Fe2O3 grade of 64.35%.

[0063] Comparative Example 3 Using the high-iron bauxite raw material from Example 3, the upgrading process parameters remained consistent, but the medium was replaced with clean water instead of circulating mother liquor. After upgrading, the alumina content in the concentrate slurry was 51.22%, and the moisture content of the concentrate after filtration was 22.54%. The magnetic product (iron-rich tailings) was subjected to sedimentation and pressure filtration to obtain an iron concentrate with a Fe2O3 grade of 67.21%.

[0064] Comparative Example 4 Using the high-iron bauxite raw material from Example 4, the upgrading process parameters remained consistent, but the medium was replaced with clean water instead of circulating mother liquor. After upgrading, the alumina content in the concentrate slurry was 46.87%, and the moisture content of the concentrate after filtration was 20.27%. The magnetic product (iron-rich tailings) was subjected to sedimentation and pressure filtration to obtain an iron concentrate with a Fe2O3 grade of 67.36%.

[0065] Comparative Example 5 Using the high-iron bauxite raw material from Example 5, the upgrading process parameters remained consistent, but the medium was replaced with clean water instead of circulating mother liquor. After upgrading, the alumina content in the concentrate slurry was 50.69%, and the moisture content of the concentrate after filtration was 21.09%. The magnetic product (iron-rich tailings) was subjected to sedimentation and pressure filtration to obtain an iron concentrate with a Fe2O3 grade of 70.63%.

[0066] The experimental results of a method for removing iron and upgrading high-iron bauxite mother liquor by magnetic separation after grinding provided in Examples 1-5 and Comparative Examples 1-5 are shown in Table 1 below.

[0067] Table 1. Experimental results of magnetic separation for iron removal and upgrading after grinding of high-iron bauxite mother liquor

[0068] As shown in Table 1, there is a significant difference in the upgrading effect of using recycled mother liquor as the magnetic separation medium versus using clean water as the magnetic separation medium on high-iron bauxite.

[0069] Regarding the moisture content of the concentrate, the experimental results of Comparative Examples 1 to 5 show that when using clean water as the magnetic separation medium, the resulting concentrate slurry must undergo pressure filtration, and the moisture content of the concentrate after pressure filtration is as high as 19.24% to 22.54%. This external moisture, existing in the form of clean water, will enter the alumina leaching process along with the concentrate, inevitably increasing the steam consumption of the evaporation process during production. In contrast, Examples 1 to 5 use circulating mother liquor as the grinding medium and magnetic separation unloading water throughout the process. The resulting slurry after iron removal is an alkaline slurry that meets the temperature and alkalinity requirements of the leaching process, eliminating the need for pressure filtration and dewatering, and can be directly sent to the alumina leaching process, completely avoiding the introduction of external moisture.

[0070] Secondly, in terms of sorting efficiency and product indicators, the data from Examples 1 to 5 are all superior to those of the comparative examples. The concentrate yields obtained in the examples range from 75.37% to 81.13%, the alumina content in the concentrate increases to 47.02% to 54.34%, and the Fe2O3 grade in the iron concentrate reaches 67.15% to 73.24%. In contrast, under the same raw materials and process parameters, the comparative examples, simply by changing the medium to water, showed a slight decrease in concentrate yield and alumina content, and the iron concentrate grade was generally lower than that of the corresponding examples. For example, the iron concentrate grade in Example 1 was 68.00%, while that in Comparative Example 1 was 65.02%.

[0071] Regarding the tailings products, the tailings obtained in the examples (i.e., iron concentrate) had a higher Fe2O3 grade and a lower Al2O3 content. This indicates that when using recycled mother liquor as the medium, the magnetic separation process has better selectivity, more thorough recovery of iron minerals, and less loss of aluminum minerals in the tailings.

[0072] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: (1) High iron removal efficiency and significant quality improvement: The magnetic separation process is located after grinding. At this time, aluminum and iron minerals have been fully liberated, and iron minerals are liberated from the encapsulated intergrowths. This avoids the problem of low iron removal efficiency caused by insufficient iron mineral liberation in conventional magnetic separation before grinding. The iron removal rate can reach 75% to 85%, and the iron concentrate grade can reach 50% to 60%. The aluminum-silicon ratio of the pulp after iron removal is further improved, which directly improves the "grade" of the ore.

[0073] (2) Outstanding energy-saving effect, directly reducing production costs: The core advantage of this invention is that it completely avoids the introduction of external water (clean water). The circulating mother liquor with matching temperature and alkali concentration in the system is used as the unloading solution, which does not disturb the water balance and heat balance of the main process. It eliminates the problem of external water (including water vapor) introduced by conventional wet magnetic separation before grinding, and there is no need to consume additional steam to evaporate external water. Compared with conventional processes, the steam consumption of the leaching process is significantly reduced, resulting in significant economic benefits. (3) Smooth process integration, improving technical and economic indicators: After grinding, the slurry is buffered and homogenized before entering the magnetic separation process, ensuring stable slurry particle size, concentration, and temperature. The non-magnetic concentrate slurry after magnetic separation can be directly sent to the leaching process without additional adjustment of slurry parameters, seamlessly connecting with the preceding and following processes. At the same time, the reduced iron content entering the leaching system means a reduction in the amount of red mud generated, which correspondingly reduces the loss of alkali and alumina, and also alleviates the environmental pressure on the red mud dump.

[0074] (4) Green and environmentally friendly, and recyclable: After the magnetic tailings are processed, the washing liquid is returned to the system for recycling, and the solid phase can be discharged as an iron-containing by-product or used for ironmaking, realizing the recovery of iron resources and the recycling of alkali liquid, reducing waste emissions, and conforming to the concept of green production.

[0075] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for iron removal and upgrading of high-iron bauxite mother liquor by magnetic separation after grinding, characterized in that, The method includes: The mixed slurry of high-iron bauxite and circulating mother liquor is ground to obtain an alkaline slurry; the circulating mother liquor is a caustic alkali circulating liquid produced in the alumina leaching process. Using the circulating mother liquor as the unloading medium, the alkaline slurry is subjected to magnetic separation to remove iron, resulting in iron-removed slurry and iron-rich slurry. The iron-removed slurry is then fed into the alumina leaching process. The iron ore slurry is separated to obtain the circulating mother liquor and iron concentrate.

2. The method according to claim 1, characterized in that, In the aforementioned high-iron bauxite, the Fe2O3 content is 25%–35% and the Al2O3 content is 38%–45% by mass fraction.

3. The method according to claim 1, characterized in that, The alkaline slurry has a solids content of 300 g / L to 400 g / L, and the grinding fineness of the alkaline slurry is -200 mesh, accounting for 75% to 90%.

4. The method according to claim 1, characterized in that, The temperature of the circulating mother liquor is 50℃~70℃, and the alkaline concentration of the circulating mother liquor, calculated as NaOH, is 180g / L~250g / L.

5. The method according to claim 1, characterized in that, The magnetic separation equipment for iron removal is a vertical ring high gradient magnetic separator or a pulsed high gradient magnetic separator, and the magnetic field strength for iron removal is 0.8T to 1.8T.

6. The method according to claim 5, characterized in that, The components of the magnetic separation equipment that come into contact with the slurry or circulating mother liquor are made of alkali-resistant, high-temperature-resistant, and corrosion-resistant materials, selected from titanium and titanium alloys, super austenitic stainless steel, or special ceramics.

7. The method according to claim 1, characterized in that, The amount of the circulating mother liquor used as unloading water is 10% to 15% of the amount of ore processed by magnetic separation for iron removal.

8. The method according to claim 7, characterized in that, The temperature difference between the circulating mother liquor used as unloading water and the alkaline slurry is ≤5℃.

9. The method according to claim 1, characterized in that, In the concentrate product corresponding to the concentrate slurry, the content of Al2O3 is 47% to 55% by mass fraction, and the content of Fe2O3 is 15% to 24%.

10. The method according to claim 1, characterized in that, In the iron concentrate, the Fe2O3 content is >65% by mass fraction.

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