Bauxite hydrogen reduction dissolution method

Abstract

The invention belongs to the technical field of metallurgy, and discloses a hydrogen reduction dissolution method for bauxite. Comprising the following steps: mixing bauxite and circulating mother liquor to form raw ore pulp, adding a reducing agent, and performing Bayer process reduction dissolution; the reducing agent is hydrogen. According to the method, impurity-free and low-energy-consumption efficient dissolution is realized by introducing the gas-phase reducing agent hydrogen, red mud discharge is reduced from the source, and the recovery rate of valuable components is increased.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a Bayer process for leaching bauxite and a leaching system. More specifically, it relates to a hydrogen reduction leaching method and leaching system for bauxite. Background Technology

[0002] In the Bayer process for alumina production from bauxite, titanium minerals in the bauxite often hinder the leaching of refractory aluminum-containing minerals such as gibbsite and goethite. To eliminate this leaching hindrance, the traditional Bayer process requires the addition of large amounts of lime, leading to a series of problems including large quantities of red mud, complex red mud composition, and difficulties in recovering valuable components. Currently, my country's accumulated red mud stockpiles exceed 1 billion tons, while the comprehensive utilization rate is only about 10%. To address the drawbacks of traditional lime-dependent processes, existing non-lime leaching technologies have attempted to use metal or organic additives, but both have significant shortcomings.

[0003] Patent CN201310005597.4 discloses a method for reducing iron compounds in iron-containing materials. This method uses organic additives to reduce and leach iron polymetallic ores or iron-containing metallurgical waste in an alkaline solution, followed by hydrothermal treatment at 90–350°C for 20–600 min. The leached residue is then magnetically separated. The total iron (TFe) content and iron recovery rate of the iron concentrate are 56.30% and 48.74%, respectively. In contrast, the total iron (TFe) content and iron recovery rate of the magnetically separated concentrate without the reducing agent are 30.52% and 17.37%, respectively. However, the organic additives and their decomposition products accumulate in the Bayer process recycling system, which has a serious adverse impact on the Bayer process alumina production system.

[0004] Patent CN201210529200.7 describes a method using iron powder or ether-based cellulose additives to prepare a raw ore slurry from monohydrate gibbsite-type bauxite, recycled mother liquor, and additives. This slurry is then subjected to high-pressure leaching to obtain a leachate and red mud. The leachate is used to produce alumina. While this method avoids the addition of lime, it has several drawbacks: Iron powder and other metal additives exhibit high reactivity under the high-temperature, alkaline conditions of the Bayer process, easily reacting with the alkaline solution in the low-temperature preheating stage of the slurry. This makes it difficult to precisely control their reaction to reach the high-temperature stage where titanium and iron minerals readily react, resulting in large quantities of metal additives and high costs. Furthermore, the decomposition products of ether-based cellulose may accumulate in the mother liquor, affecting the purity of the alumina.

[0005] In Zhou Guotao's research, aluminum plates were used as additives to react with alkaline solutions to generate hydrogen. After hydrothermal hydrogen reduction at 270℃ with an H2 / red mud ratio of 0.085 mol / 20g for 60 min, the relative recovery rate of alumina reached 95.40%, and the iron content in the residue could be enriched to 55.85%. However, this method requires concentrated acid pretreatment to remove the oxide film when using aluminum plates. The acid residue and the reaction between the aluminum plates and alkaline solutions consume the alkali content in the mother liquor, which is not conducive to the dissolution process. Furthermore, the amount of hydrogen generated is difficult to control, depending on the reaction between the aluminum plates and alkaline solutions. It also suffers from problems such as large additive dosage and high cost.

[0006] Hydrogen, as a commonly used reducing agent in the metallurgical industry, has significant characteristics: the reaction product is only water, without introducing metal ions or organic residues, thus avoiding contamination of the mother liquor; its high-temperature selective activation characteristics ensure that the reaction occurs precisely within the temperature range where titanium and iron minerals are highly effective, overcoming the shortcomings of existing metal additives that react prematurely at low temperatures.

[0007] Therefore, developing an efficient leaching method for bauxite based on hydrogen reduction is of great significance for overcoming the technological bottleneck of red mud emission reduction and realizing the green utilization of resources. Summary of the Invention

[0008] The purpose of this invention is to provide a method for hydrogen reduction leaching of bauxite to solve at least one technical problem existing in the background art.

[0009] To achieve the objectives of this invention, the following technical solution is provided: A method for hydrogen reduction leaching of bauxite includes the following steps: mixing bauxite with circulating mother liquor to form a raw ore slurry, adding a reducing agent, and then performing Bayer reduction leaching; wherein the reducing agent is hydrogen.

[0010] Furthermore, Bayer reduction dissolution is carried out in a Bayer dissolution system, wherein the Bayer dissolution system is a reaction vessel, a tubular dissolution reactor, or a combination of a tubular dissolution reactor and a reaction vessel system.

[0011] More preferably, when the Bayer process leaching system includes a reaction vessel, the hydrogen gas is injected into the reaction vessel in the form of a high-pressure gas, and the hydrogen pressure inside the reaction vessel is 0.3~6 MPa.

[0012] More preferably, when the Bayer leaching system includes a tubular leaching reactor, the hydrogen is injected into the tubular leaching reactor in the form of a high-pressure gas; the hydrogen flow rate is 2 to 10% of the leaching slurry flow rate, where the flow rate unit is volumetric flow rate.

[0013] Furthermore, the hydrogen gas is injected into the Bayer process bauxite leaching system at a high pressure of 0.5~6 MPa.

[0014] Furthermore, the alkali concentration of the circulating mother liquor, calculated as Na2O, is 170–320 g / L, and the caustic ratio is 2.5–4.0.

[0015] Furthermore, the raw ore slurry has a molecular ratio of 1.3 to 1.5, and the circulating mother liquor is at least one of sodium hydroxide solution and sodium aluminate solution.

[0016] Furthermore, the reaction temperature for the Bayer process reduction dissolution is 240–280°C.

[0017] Furthermore, the reaction time for the Bayer process reduction dissolution is 20–120 min.

[0018] Furthermore, the hydrogen gas is added after the slurry has been preheated.

[0019] Furthermore, at least one of the following: monohydrate gibbsite bauxite, trihydrate gibbsite bauxite containing aluminum goethite, and mixed ore.

[0020] Furthermore, the bauxite Bayer process leaching system is equipped with a slurry pipeline, on which a preheating device and a heating device are sequentially installed, and a hydrogen inlet is provided between the preheating device and the heating device.

[0021] Furthermore, the tubular leaching reactor includes multiple reaction vessels connected in series, with the reaction vessels being fed in from the bottom and discharged from the top.

[0022] Furthermore, the tubular leaching reactor includes multiple reaction tanks connected in series, and a non-condensable gas venting device is provided between adjacent reaction tanks to ensure that gas does not accumulate in the reaction tanks and cause a decrease in the tank filling rate; the venting device includes a gas venting pipe, which is inserted into the slurry pipeline between the insulated tanks to enhance the mixing of gas and slurry.

[0023] The structure of the reaction vessel in this application avoids the large accumulation of non-condensable gases such as hydrogen in the leaching system, and the gas connection pipe is inserted into the slurry pipeline between the insulated tanks to enhance the mixing of gas and slurry.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention introduces hydrogen as a gaseous reducing agent and utilizes its high-temperature selective reaction characteristics to achieve efficient dissolution with no impurities and low energy consumption, thereby reducing red mud emissions from the source and improving the recovery rate of valuable components.

[0025] (2) During the leaching process, hydrogen promotes the reduction of some iron minerals to highly magnetic magnetite, significantly improving the magnetic separation efficiency of iron minerals in red mud and creating conditions for subsequent recovery. At the same time, the low-valent iron species generated by reduction interact with titanium minerals, eliminating their leaching hindrance to sparingly soluble aluminum minerals (such as gibbsite). High-efficiency leaching can be achieved with little or no lime, reducing red mud generation from the source. In addition, due to the reduced lime addition, the composition of red mud is simplified, and the decomposition degree of valuable components such as iron is increased, further promoting the recovery and reduction of valuable components in red mud. (3) As a gaseous reducing agent, hydrogen only produces water after reaction and does not introduce metal ions (such as Fe). 2+ This process avoids contamination of the mother liquor by traditional additives, as well as organic residues. Its high-temperature selective activation characteristics (240~280℃) ensure that the reaction occurs precisely within the temperature range where titanium / iron minerals are most effective, overcoming the problems of high alkali consumption and large dosage caused by premature reaction of existing metal additives at low temperatures, significantly reducing reducing agent consumption and cost. Furthermore, hydrogen does not react directly with the alkali solution, eliminating the need for pretreatment of additives (such as concentrated acid treatment of aluminum plates), avoiding fluctuations in mother liquor composition, and ensuring the stability and continuity of the production system. (4) Under the premise of ensuring the alumina leaching rate, a low-energy leaching process is achieved, which significantly reduces energy and material consumption compared with traditional processes and existing technologies. By reducing red mud emissions at the source and improving the recovery rate of valuable components such as iron, the environmental pressure of red mud stockpiling is solved, and the resource utilization efficiency is improved. It has the dual advantages of reducing red mud volume and resource utilization, as well as reducing production costs and enhancing process economy, providing an innovative solution for the green and efficient utilization of bauxite. Detailed Implementation

[0026] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0027] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0029] Example 1 Chemical composition (wt%) of Guangxi monohydrate gibbsite type bauxite: Al2O350.81%, SiO25.51%, Fe2O322.31%, TiO23.16%.

[0030] The circulating mother liquor is a sodium aluminate solution with a caustic soda concentration of Na₂O. k 240g / L, caustic molecule ratio 3.1.

[0031] The Bayer process for leaching with added hydrogen was carried out in a stirred reactor. The conditions for Bayer process leaching were: a molecular weight ratio of 1.40, a leaching temperature of 270℃, and a high-temperature leaching time of 70 min. The volume of the slurry in the stirred reactor was approximately 40% of the reactor's volume. Before heating the stirred reactor, high-pressure hydrogen was introduced into the reactor until the hydrogen pressure inside the stirred reactor reached 3.5 MPa. After the leaching reaction, the stirred reactor was cooled, and the leached slurry underwent liquid-solid separation and red mud washing to obtain leaching solution and red mud.

[0032] Analysis and testing showed that the relative leaching rate of alumina during the leaching process was 98.1%, the red mud slag rate (mass ratio of red mud to bauxite, the same below) was 44.5%, the Fe2O3 content in the red mud was 49.5%, and the red mud was magnetically separated to obtain iron concentrate with an iron grade of 55.2%, and the iron recovery rate of the concentrate was 72.3%.

[0033] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that hydrogen gas is not introduced into the stirred reactor.

[0034] After the leaching reaction, analysis showed that the relative leaching rate of alumina was 21.20%, and the red mud residue rate was 91.40%. This comparative example demonstrates that introducing reducing hydrogen gas during the Bayer process can significantly improve the leaching rate of alumina.

[0035] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that hydrogen is not introduced into the stirred reactor, but lime of 8% by weight of bauxite is added to the slurry in the reactor.

[0036] After the leaching reaction, analysis showed that the relative leaching rate of alumina was 94.96%, and the red mud residue rate was 56.98%. The Fe2O3 content in the red mud was 39.08%. After magnetic separation, the red mud was used to obtain iron concentrate with an iron grade of 52.7%, and the iron recovery rate of the concentrate was 45.7%.

[0037] Comparative Example 2 shows that, compared with the traditional Bayer process for bauxite leaching with added lime, the technical solution of the present invention can improve the alumina leaching rate, significantly reduce the amount of red mud, and improve the sorting performance of iron minerals in red mud.

[0038] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that hydrogen is not introduced into the stirred reactor during the dissolution process, but 1 wt.% of glycerol in the dry ore of the slurry is added to the slurry of the reactor as a reducing additive.

[0039] After the leaching reaction, analysis showed that the relative leaching rate of alumina was 95.6%, and the red mud residue rate was 47.8%. The concentrations of total organic carbon and sodium oxalate in the leaching solution increased by 1.1 g / L and 2.5 g / L, respectively, compared to the previous example. The increase in sodium oxalate concentration in the leaching solution was significantly higher than the controllable levels required for current Bayer process alumina production systems (generally <2 g / L).

[0040] Comparative Example 3 shows that the solution of the present invention can overcome the problems of rapid accumulation of organic carbon and oxalate concentration in the production system caused by organic additives and their harm to subsequent production.

[0041] Example 2 Chemical composition (wt%) of Guangxi monohydrate gibbsite type bauxite: Al2O350.81%, SiO25.51%, Fe2O322.31%, TiO23.16%.

[0042] The circulating mother liquor is a sodium aluminate solution with a caustic soda concentration of Na₂O. k 240g / L, caustic molecule ratio 3.1.

[0043] The Bayer process for leaching with added hydrogen was carried out in a stirred reactor. The conditions for Bayer process leaching were: a molecular weight ratio of 1.40, a leaching temperature of 270℃, and a high-temperature leaching time of 70 min. The volume of the slurry in the stirred reactor was approximately 40% of the reactor's volume. Before heating the stirred reactor, high-pressure hydrogen was introduced into the reactor until the hydrogen pressure inside the stirred reactor reached 1.0 MPa. After the leaching reaction, the stirred reactor was cooled, and the leached slurry underwent liquid-solid separation and red mud washing to obtain leaching solution and red mud.

[0044] Analysis and testing showed that the relative dissolution rate of alumina during the leaching process was 94.5%.

[0045] Example 3 Chemical composition (wt%) of Guangxi monohydrate gibbsite type bauxite: Al2O350.81%, SiO25.51%, Fe2O322.31%, TiO23.16%.

[0046] The circulating mother liquor is a sodium aluminate solution with a caustic soda concentration of Na₂O. k 240g / L, caustic molecule ratio 3.1.

[0047] The Bayer process for leaching with added hydrogen was carried out in a stirred reactor. The conditions for Bayer process leaching were: a molecular weight ratio of 1.40, a leaching temperature of 260℃, and a high-temperature leaching time of 80 min. The volume of the slurry in the reactor was approximately 40% of the volume of the stirred reactor. Before heating the stirred reactor, high-pressure hydrogen was introduced into the reactor until the hydrogen pressure inside the stirred reactor reached 3.0 MPa. After the leaching reaction, the stirred reactor was cooled, and the leached slurry underwent liquid-solid separation and red mud washing to obtain leaching solution and red mud.

[0048] Analysis and testing showed that the relative dissolution rate of alumina during the leaching process was 93.8%.

[0049] Example 4 The chemical composition (wt%) of a certain imported gibbsite-type bauxite is as follows: Al2O3 42.50%, SiO2 2.32%, Fe2O3 24.32%, TiO2 2.32%. The main aluminum-bearing mineral in the bauxite is gibbsite, with a small amount of boehmite and goethite.

[0050] The circulating mother liquor is a sodium aluminate solution with a caustic soda concentration of Na₂O. k 170g / L, caustic molecule ratio 3.2.

[0051] The Bayer process for leaching with added hydrogen was carried out in a stirred reactor. The conditions for Bayer process leaching were: a molecular weight ratio of 1.40, a leaching temperature of 260℃, and a high-temperature leaching time of 60 min. The volume of the slurry in the stirred reactor was approximately 60% of the reactor's volume. Before heating the stirred reactor, high-pressure hydrogen was introduced into the reactor until the hydrogen pressure inside the reactor reached 3.0 MPa. After the leaching reaction, the stirred reactor was cooled, and the leached slurry underwent liquid-solid separation and red mud washing to obtain leaching solution and red mud.

[0052] Analysis and testing showed that the actual alumina leaching rate during the leaching process was 95.5%, and the red mud residue rate was 31.2%; the Fe2O3 content in the red mud was 76.3%.

[0053] Comparative Example 4 Comparative Example 4 is basically the same as Example 4, except that hydrogen gas is not introduced into the stirred reactor.

[0054] After the leaching reaction, analysis and testing showed that the actual leaching rate of alumina was 91.1%, the red mud residue rate was 36.3%, and the Fe2O3 content in the red mud was 67.1%.

[0055] Example 5 Chemical composition (wt%) of Guangxi monohydrate gibbsite type bauxite: Al2O3 47.60%, SiO2 5.41%, Fe2O3 27.68%, TiO2 3.34%.

[0056] The circulating mother liquor is a sodium aluminate solution with a caustic soda concentration of Na₂O. k 250g / L, caustic molecule ratio 3.05.

[0057] The Bayer process leaching system is a tubular leaching reactor employing a pipelined preheating / heating system and residence tanks for hydrogen-added Bayer process leaching. The tubular leaching reactor includes slurry pipelines, a 10-stage pipelined preheater, a 3-stage pipelined heater, and 8 leaching residence tanks. The preheaters, heaters, and leaching residence tanks are connected in series, with adjacent residence tanks connected by slurry pipelines. A non-condensable gas vent pipe is installed above the residence tanks and connects to the inter-tank slurry pipelines. A hydrogen inlet is located in the slurry pipeline at the final stage of the pipelined preheater.

[0058] The leaching conditions were: a molecular weight ratio of 1.40, a leaching temperature of 272℃ (outlet temperature of the pipeline heater), and a high-temperature leaching time of 70 min (total average residence time in 8 leaching residence tanks). High-pressure hydrogen was introduced through the hydrogen inlet at the final-stage pipeline preheater, where the slurry preheating temperature was approximately 230℃. The hydrogen flow rate was 5% of the leaching slurry flow rate (volume flow rate at the leaching system inlet). After the leaching reaction, the leaching slurry underwent liquid-solid separation and red mud washing to obtain leaching solution and red mud.

[0059] Analysis showed that the relative alumina leaching rate during the leaching process was 97.5%, the Fe2O3 content in the red mud was 55.3%, and the red mud was subjected to magnetic separation to obtain iron concentrate with an iron grade of 56.1% TFe, and the iron recovery rate of the concentrate was 63.5%.

[0060] Example 6 Chemical composition (wt%) of Guangxi monohydrate gibbsite type bauxite: Al2O3 47.60%, SiO2 5.41%, Fe2O3 27.68%, TiO2 3.34%.

[0061] The circulating mother liquor is a sodium aluminate solution with a caustic soda concentration of Na₂O. k 250g / L, caustic molecule ratio 3.05.

[0062] The Bayer process leaching system is a tubular leaching reactor employing a pipelined preheating / heating system and residence tanks for hydrogen-added Bayer process leaching. The tubular leaching reactor includes slurry pipelines, a 10-stage pipelined preheater, a 3-stage pipelined heater, and 8 leaching residence tanks. The preheaters, heaters, and leaching residence tanks are connected in series, with adjacent residence tanks connected by slurry pipelines. A non-condensable gas vent pipe is installed above the residence tanks and connects to the inter-tank slurry pipelines. Each residence tank is connected to a hydrogen inlet in the slurry pipeline at the final stage of the pipelined preheater.

[0063] The leaching conditions were as follows: a molecular weight ratio of 1.40, a lime addition of 1.5% of the ore weight, a leaching temperature of 272℃ (outlet temperature of the pipeline heater), and a high-temperature leaching time of 70 min (total average residence time in 8 leaching residence tanks). High-pressure hydrogen was introduced through the hydrogen inlet at the final-stage pipeline preheater, where the slurry preheating temperature was approximately 230℃. The hydrogen flow rate was 5% of the leaching slurry flow rate (volume flow rate at the leaching system inlet).

[0064] After the leaching reaction, the leached slurry underwent liquid-solid separation and red mud washing to obtain leaching solution and red mud. Analysis showed that the relative leaching rate of alumina during the leaching process was 99.1%, and the Fe2O3 content in the red mud was 53.7%. Magnetic separation of the red mud yielded an iron concentrate with an iron content of 55.6% TFe, and an iron recovery rate of 61.2%.

[0065] Example 7 Example 7 is basically the same as Example 6, except that the hydrogen flow rate is reduced to 2% of the leaching slurry flow rate.

[0066] After the leaching reaction, analysis and testing showed that the relative leaching rate of alumina was 97.1%.

[0067] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the present invention.

Claims

1. A method for hydrogen reduction leaching of bauxite, characterized in that, Bauxite is mixed with circulating mother liquor to form a raw ore slurry. After adding a reducing agent, the ore is reduced and leached using the Bayer process. The reducing agent is hydrogen gas.

2. The method as described in claim 1, characterized in that, Bayer process reduction dissolution is carried out in a Bayer process dissolution system, wherein the Bayer process dissolution system is a reaction vessel, a tubular dissolution reactor, or a combination of a tubular dissolution reactor and a reaction vessel system.

3. The method as described in claim 2, characterized in that, When the Bayer process leaching system includes a reaction vessel, the hydrogen gas is injected into the reaction vessel in the form of a high-pressure gas, and the hydrogen pressure inside the reaction vessel is 0.3~6MPa.

4. The method as described in claim 2, characterized in that, When the Bayer process leaching system includes a tubular leaching reactor, the hydrogen is forced into the tubular leaching reactor in the form of a high-pressure gas; the hydrogen flow rate is 2 to 10% of the leaching slurry flow rate.

5. The method according to any one of claims 1 to 4, characterized in that, The reaction temperature for the Bayer process reduction dissolution is 240–280 °C, and the reaction time is 20–120 min.

6. The method according to any one of claims 1 to 4, characterized in that, The hydrogen gas is added after the slurry is preheated.

7. The method according to any one of claims 1 to 4, characterized in that, The bauxite is at least one of the following: monohydrate gibbsite bauxite, trihydrate gibbsite bauxite containing aluminum goethite, or mixed ore.

8. The method according to any one of claims 1 to 4, characterized in that, The molecular ratio of the raw ore slurry is 1.3 to 1.5; The circulating mother liquor is at least one of sodium hydroxide solution and sodium aluminate solution; The alkali concentration of the circulating mother liquor, calculated as Na2O, is 170–320 g / L, and the caustic ratio is 2.5–4.

0.

9. The method according to any one of claims 1 to 4, characterized in that, The bauxite Bayer process leaching system is equipped with a slurry pipeline, a preheating device and a heating device on the slurry pipeline, and a hydrogen inlet on the slurry pipeline between the preheating device and the heating device.

10. The method as described in claim 9, characterized in that, The tubular dissolution reactor comprises multiple reaction vessels connected in series; The reaction tank is fed and discharged from the bottom up. Alternatively, a non-condensable gas venting device may be installed between adjacent reaction tanks; the venting device includes a gas venting pipe, which is inserted into the slurry pipeline between the insulated tanks.