Method for strengthening bayer process dissolution of high-iron gibbsite-type bauxite by a reducing agent

Abstract

The present application belongs to the technical field of nonferrous metallurgy, and particularly relates to a method for strengthening bayer process dissolution of high-iron gibbsite-type bauxite by a reducing agent. The method comprises the following steps: (1) preparing a mixed ore slurry by mixing high-iron gibbsite-type bauxite, sodium aluminate circulating mother liquor and an organic acid reducing agent containing an alpha-hydroxy acid structure; (2) heating the mixed ore slurry to 210-250 DEG C to perform a dissolution reaction, obtaining a dissolution slurry and a dissolution residue, and washing the dissolution residue with hot water to obtain an iron concentrate. The method can realize conversion of aluminum goethite at a lower temperature in the bayer process dissolution process, improve the dissolution rate of aluminum, directly produce red mud with high iron grade and low aluminum content for iron resource recovery, shorten the process flow and reduce the process energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metallurgical technology, specifically relating to a method for strengthening the Bayer process leaching of high-iron trihydrate gibbsite bauxite with reducing agents. Background Technology

[0002] In high-speed iron gibbsite bauxite, gibbsite is easily dissolved under low-temperature Bayer process conditions. However, iron minerals, especially goethite, contain a certain amount of structurally dissolved aluminum, which is difficult to release under normal conditions. This results in insufficient aluminum extraction, low iron grade in red mud, and high alumina content, which is not conducive to the full extraction of aluminum resources, nor to the subsequent recycling of iron and titanium resources in red mud.

[0003] Therefore, if in-situ release of structural aluminum from goethite can be achieved during the Bayer process in high-iron gibbsite bauxite, not only can the aluminum resources in the ore be fully extracted, but high-iron grade, low-aluminum red mud suitable as a raw material for ironmaking can also be produced simultaneously. This can alleviate the environmental risks and disposal pressures posed by red mud, while maximizing the utilization rate of resources in bauxite, which is of great significance for promoting the development of the alumina industry towards high efficiency, low consumption, and low emissions.

[0004] To address the difficulty in effectively converting goethite in gibbsite under both low-temperature (110~150℃) and high-temperature (240~260℃) Bayer leaching conditions, patent document CN115608982A discloses a Bayer leaching process for gibbsite-type bauxite using activated iron powder as a reducing agent. This method involves adding pre-treated activated iron powder to the slurry for high-temperature leaching, promoting the conversion of goethite to increase the relative alumina leaching rate and reduce red mud emissions. The red mud can be recycled by pyrometallurgical treatment to recover the iron powder. However, this method requires an optimal processing temperature of 240~280℃, resulting in high energy consumption, a complex process, and a heavy equipment load. Patent document CN121553969A discloses a hydrogen reduction leaching method for bauxite, which uses hydrogen as a reducing agent for high-temperature Bayer leaching of various ores, including gibbsite-type bauxite. Hydrogen is a relatively clean reducing agent, but it relies on high-pressure gas supply and specialized ventilation, sealing, and continuous exhaust structures, placing high demands on equipment and operating conditions, and requiring a processing temperature of 240-280℃. Patent document CN120483203A discloses a high-temperature Bayer process for treating high-iron trihydrate gibbsite bauxite using calcium oxide or calcium carbonate as additives. The calcium additive, combined with high temperature, can promote the conversion of goethite to hematite and reduce sodium entering the red mud. However, the addition of calcium additives will carry away some aluminum from the solution into the red mud, and excessively high aluminum content in iron ore is detrimental to the blast furnace ironmaking process. Regarding other reducing additives, CN102976377A, CN120308993A, and CN120210543A disclose a variety of organic reducing agents, but they are all used for the Bayer process leaching of gibbsite-type or boehmite-type bauxite. These include alcohols, sugars, organic bases, carboxylic acids, amino acids, chitin, or cellulose biomass. Their mechanism of action is mainly to promote the dispersion and dissociation of silica mineral impurities in gibbsite-type bauxite. They have limited effect on promoting the transformation of goethite and the release of aluminum in gibbsite-type bauxite, and the optimal processing temperature is generally limited to above 260℃.

[0005] In summary, there is an urgent need to develop new reducing agents for high-speed gibbsite-type bauxite, which can achieve the conversion of goethite in the Bayer process at lower temperatures, improve the alumina leaching rate, and directly produce red mud with high iron grade and low aluminum content for iron resource recovery, thereby shortening the process flow and reducing process energy consumption. Summary of the Invention

[0006] To achieve low-temperature and efficient leaching of high-iron trihydrate gibbsite bauxite using the Bayer process, the present invention aims to provide a method for enhancing the leaching of high-iron trihydrate gibbsite bauxite using the Bayer process with a reducing agent.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for enhancing the Bayer process leaching of high-iron trihydrate gibbsite bauxite using a reducing agent includes the following steps:

[0009] (1) Prepare a mixed slurry by mixing high-speed iron trihydrate gibbsite type bauxite, sodium aluminate circulating mother liquor and organic acid reducing agent containing α-hydroxy acid structure;

[0010] (2) The mixed slurry is heated to 210~250℃ to carry out a leaching reaction to obtain leaching slurry and leaching residue. The leaching residue is washed with hot water to obtain iron concentrate.

[0011] Furthermore, the high-speed iron gibbsite type bauxite mentioned in step (1) refers to bauxite whose main component is gibbsite, iron mineral content >15% (calculated as mass percentage in the form of Fe2O3), and iron mineral is mainly goethite (goethite accounts for more than 50% of the total iron mineral content).

[0012] Furthermore, the Na2O in the sodium aluminate circulating mother liquor mentioned in step (1) k The concentration is 130~260 g / L, and the Al2O3 concentration is 71~143 g / L.

[0013] Furthermore, the mass ratio of the added high-speed iron trihydrate gibbsite type bauxite in step (1) to the mass-volume ratio of the sodium aluminate circulating mother liquor is 142~251 g / L.

[0014] Further, the organic acid reducing agent containing an α-hydroxy acid structure mentioned in step (1) is preferably at least one of glycolic acid, lactic acid, and gluconic acid. Glycolic acid is more preferred.

[0015] This invention utilizes an organic acid reducing agent containing a specific α-hydroxy acid structure, which can exert strong reducing activity at lower reaction temperatures and efficiently promote the transformation of goethite in bauxite and release aluminum into the solution, thereby achieving full extraction of aluminum from bauxite.

[0016] Furthermore, the amount of the organic acid reducing agent containing the α-hydroxy acid structure added is 2 to 10 wt% of the mass of high-iron gibbsite bauxite, more preferably 4 to 8 wt%.

[0017] Furthermore, the dissolution reaction time in step (2) is 60~120 min.

[0018] Furthermore, the hot water washing in step (2) is performed using hot water at 80~100℃.

[0019] Further, the slurry in step (2) is first diluted and finely filtered, and then aluminum hydroxide is added to the obtained filtrate as a seed crystal to induce the dissolved aluminum in the solution to precipitate as aluminum hydroxide. After filtration, aluminum hydroxide and filtrate are obtained. The aluminum hydroxide is further calcined to obtain alumina product. The filtrate is concentrated by evaporation and the alkali content is replenished before it is used as a circulating mother liquor for sodium aluminate.

[0020] The principle of this invention lies in the addition of α-hydroxy acid additives to promote the transformation of the iron-bearing phase and the release of structural aluminum during the Bayer process leaching of ferrous gibbsite-type bauxite, thereby increasing the alumina leaching rate and improving the quality of the leaching residue. α-hydroxy acid structural additives can endow reducing agents with stronger interfacial interaction capabilities, reducing activity, and a more direct reaction pathway during the Bayer process leaching of ferrous gibbsite-type bauxite.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] (1) Compared with the conventional Bayer process at low or even high temperatures, this method can significantly improve the aluminum leaching rate. The resulting leaching residue has the characteristics of high iron content and low aluminum content, and has the potential to be used as an iron-containing raw material for further recovery of Fe and Ti resources.

[0023] (2) Compared with lime, active iron powder, hydrogen and macromolecular organic reducing agents that rely on higher temperatures, this method can efficiently convert the aluminum goethite phase into the magnetic mineral phase at a lower temperature, achieving a higher aluminum leaching rate and leaching residue quality.

[0024] (3) This method can directly use existing Bayer process equipment, the process is simple, and the low-alumina and iron-rich red mud produced can be used for disposal in the steel industry, achieving near-zero emissions of solid waste. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0026] Example 1

[0027] A method for enhancing the Bayer process leaching of high-iron trihydrate gibbsite bauxite using a reducing agent includes the following steps:

[0028] (1) A mixed slurry was prepared by combining high-speed gibbsite-type bauxite (mineral composition mainly includes: Al2O3 53.76%, Fe2O3 18.10%, TiO2 2.75%, SiO2 0.22% by mass), 100 mL of circulating mother liquor, and the additive glycolic acid. For the circulating mother liquor, Na2O... kThe concentration was 230 g / L, and the Al2O3 concentration was 126 g / L. The ratio of bauxite added mass to circulating mother liquor volume was 251 g / L, and the amount of glycolic acid additive added was 6 wt% of the bauxite added mass.

[0029] (2) After the mixed slurry is prepared, the reaction is carried out. The temperature is raised to 220℃ and the reaction is carried out for 100 min. After the reaction is completed, the temperature of the slurry is lowered to room temperature. The slurry is taken out and solid-liquid separation is performed. The separated solid is washed three times with hot water at 80~100℃ to obtain leaching slurry and leaching residue. The total iron (calculated as Fe2O3) content of the leaching residue is 84.64%, the aluminum (calculated as Al2O3) content is 4.08%, and the titanium (calculated as TiO2) content is 11.02%. The direct leaching rate of alumina was 98.38% (direct leaching rate of alumina = ((aluminum-iron ratio of bauxite - aluminum-iron ratio of leaching residue) / aluminum-iron ratio of bauxite × 100%). For the leaching slurry, it was first diluted and finely filtered. Then, aluminum hydroxide was added to the filtrate as a seed crystal to induce the dissolved aluminum in the solution to precipitate as aluminum hydroxide. After filtration, aluminum hydroxide and filtrate were obtained. The aluminum hydroxide was further calcined to obtain the alumina product. The obtained alumina product conformed to GB / T 24487-2022 standard. The filtrate was concentrated by evaporation, and after replenishing the alkali content, it was reused as a mother liquor for sodium aluminate recycling.

[0030] Example 2

[0031] In Example 2, the additive glycolic acid was replaced with an equal amount of lactic acid, while the other dissolution conditions remained the same compared to Example 1.

[0032] Comparative Example 1

[0033] Compared to Example 1, Comparative Example 1 did not include the additive glycolic acid, but all other dissolution conditions were the same.

[0034] Comparative Example 2

[0035] Compared with Example 1, Comparative Example 2 replaced the additive glycolic acid with an equal amount of glucose, while the other dissolution conditions remained the same.

[0036] Comparative Example 3

[0037] Compared with Example 1, Comparative Example 3 replaced the additive glycolic acid with an equal amount of wheat bran, while the other dissolution conditions remained the same.

[0038] Comparative Example 4

[0039] Compared with Example 1, Comparative Example 4 replaced the additive glycolic acid with an equal amount of 3-hydroxypropionic acid, while the other dissolution conditions remained the same.

[0040] The dissolution results of Examples 1-2 and Comparative Examples 1-4 using different reducing additives are shown in Table 1 below.

[0041] Table 1. Dissolution results of different additives in Examples 1-2 and Comparative Examples 1-4

[0042] Example 1 6% glycolic acid 84.64% 4.08% 11.02% 98.38% Example 2 6% lactic acid 82.59% 5.13% 10.32% 97.91% Comparative Example 1 / 71.50% 8.67% 9.13% 95.92% Comparative Example 2 6% glucose 70.01% 10.39% 8.97% 95.00% Comparative Example 3 6% wheat bran 69.03% 11.19% 8.89% 94.54% Comparative Example 4 6% 3-hydroxypropionic acid 70.98% 9.46% 8.79% 95.51%

[0043] The comparison results between Examples 1-2 and Comparative Example 1 in Table 1 show that the addition of glycolic acid or lactic acid significantly improved the direct dissolution rate of alumina and the total iron content of the leaching residue, effectively reducing the aluminum content in the leaching residue. Glycolic acid showed superior results. This may be because glycolic acid has a lower molecular weight, higher reducing activity, and a more direct reaction pathway. The comparison results between Examples 1-2 and Comparative Examples 2-4 show that the organic acid reducing agent containing a specific α-hydroxy acid structure used in this invention significantly improves the aluminum dissolution effect and the iron enrichment effect in the leaching residue compared to other organic reducing agents and those without an α-hydroxy acid structure. The comparison results between Example 2 and Comparative Example 4 further demonstrate that the organic acid reducing agent containing a specific α-hydroxy acid structure is key to improving the low-temperature dissolution effect. Furthermore, the comparison results between Comparative Examples 2-4 and Comparative Example 1 show that the dissolution effect of adding glucose, wheat bran, and 3-hydroxypropionic acid reducing agents was worse than that of Comparative Example 1 without any reducing agent. The reason is that the additives used not only fail to exert a reducing effect to promote the release of dissolved aluminum in goethite at a lower leaching temperature (220℃), but also reduce the alkalinity of the solution and increase the viscosity of the solution, which has a certain negative impact on the leaching process.

[0044] Examples 3-6

[0045] Examples 3-6 differed from Example 1 in that the amount of glycolic acid additive was adjusted, while the other leaching conditions remained the same. The total iron content, aluminum content, titanium content, and direct alumina leaching rate of the resulting leaching residue are listed in Table 2.

[0046] Table 2 Dissolution results with different amounts of glycolic acid added

[0047] Example 3 2% 72.52% 8.01% 8.47% 96.28% Example 4 4% 77.11% 6.62% 9.62% 97.11% Example 5 8% 81.70% 4.90% 10.77% 97.98% Example 6 10% 80.16% 5.22% 10.25% 97.81%

[0048] As can be seen from the results in Table 1-2 above, the addition of organic acid reducing agents containing α-hydroxy acid structures can achieve good dissolution effects in the range of 2 to 10 wt% of the mass of ferrous gibbsite bauxite. Furthermore, when the addition of reducing agents is 4 to 8 wt% of the mass of ferrous gibbsite bauxite, better dissolution efficiency and cost advantages can be achieved.

[0049] Examples 7-10

[0050] Examples 7-10 differed from Example 1 in that the leaching reaction temperature and time were adjusted, while the other leaching conditions remained the same. The total iron content, aluminum content, titanium content, and direct alumina leaching rate of the resulting leaching residue are listed in Table 3.

[0051] Table 3. Dissolution results at different dissolution temperatures and times.

[0052] Example 7 210℃, 100min 75.97% 7.78% 8.97% 96.55% Example 8 250℃, 100min 82.36% 5.07% 10.49% 97.93% Example 9 220℃, 60min 77.78% 6.57% 9.13% 97.16% Example 10 220℃, 120min 83.13% 4.52% 10.95% 98.17%

[0053] As can be seen from the results in Table 3, the reducing additive of the present invention can achieve a better dissolution effect at a lower temperature (210-250℃).

[0054] Example 11

[0055] Compared to Example 1, Example 11 replaced the additive glycolic acid with an equal amount of gluconic acid, increased the dissolution temperature to 250°C, and kept the other dissolution conditions the same.

[0056] Comparative Example 5

[0057] Compared to Example 11, Comparative Example 5 did not include the additive gluconic acid, but all other dissolution conditions were the same.

[0058] Comparative Example 6

[0059] Compared with Example 11, Comparative Example 6 replaced the additive gluconic acid with an equal amount of glucose, while the other dissolution conditions remained the same.

[0060] The dissolution results of Examples 11 and Comparative Examples 5-6 using different reducing additives are shown in Table 4 below.

[0061] Table 4. Dissolution results of different additives in Example 11 and Comparative Examples 5-6

[0062] Example 11 gluconic acid 250℃ 83.76% 4.49% 9.82% 98.19% Comparative Example 5 / 250℃ 73.67% 6.22% 9.53% 97.16% Comparative Example 6 glucose 250℃ 78.64% 5.41% 9.76% 97.68%

[0063] As can be seen from the results in Table 4 above, although increasing the dissolution temperature can improve the reduction and dissolution effect of glucose, it is still significantly lower than that of gluconic acid used in this invention. This once again proves that organic acid reducing agents containing specific α-hydroxy acid structures are the key to improving the dissolution effect of this invention.

[0064] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for enhancing the Bayer process leaching of high-iron trihydrate gibbsite bauxite with a reducing agent, characterized in that... Includes the following steps: (1) Prepare a mixed slurry by mixing high-speed iron trihydrate gibbsite type bauxite, sodium aluminate circulating mother liquor and organic acid reducing agent containing α-hydroxy acid structure; (2) The mixed slurry is heated to 210~250℃ to carry out a leaching reaction to obtain leaching slurry and leaching residue. The leaching residue is washed with hot water to obtain iron concentrate.

2. The method for reducing agent-enhanced Bayer process leaching of high-iron trihydrate gibbsite bauxite according to claim 1, characterized in that: The high-speed iron gibbsite type bauxite mentioned in step (1) refers to bauxite whose main component is gibbsite, iron mineral content is >15%, and iron mineral is mainly goethite.

3. The method for reducing agent-enhanced Bayer process leaching of high-iron trihydrate gibbsite bauxite according to claim 1, characterized in that: The Na2O in the sodium aluminate circulating mother liquor mentioned in step (1) k The concentration is 130~260 g / L, and the Al2O3 concentration is 71~143 g / L.

4. The method for reducing agent-enhanced Bayer process leaching of high-iron trihydrate gibbsite bauxite according to claim 1, characterized in that: The mass ratio of the added high-speed iron trihydrate gibbsite type bauxite in step (1) to the mass-volume ratio of the sodium aluminate circulating mother liquor is 142~251 g / L.

5. The method for reducing agent-enhanced Bayer process leaching of high-iron trihydrate gibbsite bauxite according to claim 1, characterized in that: The organic acid reducing agent containing the α-hydroxy acid structure mentioned in step (1) is at least one of glycolic acid, lactic acid, and gluconic acid, and the amount of the organic acid reducing agent containing the α-hydroxy acid structure added is 2 to 10 wt% of the mass of high-iron trihydrate gibbsite bauxite.

6. The method for reducing agent-enhanced Bayer process leaching of high-iron trihydrate gibbsite bauxite according to claim 5, characterized in that: The organic acid reducing agent containing the α-hydroxy acid structure is glycolic acid, and the amount of glycolic acid added is 4 to 8 wt% of the mass of high-iron trihydrate gibbsite-type bauxite.

7. The method for reducing agent-enhanced Bayer process leaching of high-iron trihydrate gibbsite bauxite according to claim 1, characterized in that: The dissolution reaction in step (2) takes 60 to 120 minutes.

8. The method for reducing agent-enhanced Bayer process leaching of high-iron trihydrate gibbsite bauxite according to claim 1, characterized in that: The hot water washing in step (2) uses 80~100℃ hot water for thorough washing.

9. The method for reducing agent-enhanced Bayer process leaching of high-iron trihydrate gibbsite bauxite according to claim 1, characterized in that: The slurry described in step (2) is first diluted and finely filtered. Then, aluminum hydroxide is added to the obtained filtrate as a seed crystal to induce the dissolved aluminum in the solution to precipitate as aluminum hydroxide. After filtration, aluminum hydroxide and filtrate are obtained. The aluminum hydroxide is further calcined to obtain alumina product. The filtrate is concentrated by evaporation and the alkali content is replenished before it is used as a circulating mother liquor for sodium aluminate.