Process for preparing aluminum oxide through coal gangue decarburization, activation and acid leaching

Abstract

The invention belongs to the technical field of coal gangue refined comprehensive utilization, and particularly relates to a process for preparing aluminum oxide by coal gangue decarburization activation acid leaching, which comprises the following steps: multi-stage activation, circular salt separation, catalytic alkalization, directional crystallization, oxygen-controlled roasting, magnetic separation impurity removal, flue gas reuse and the like. Efficient extraction of aluminum and deep removal of impurities in the coal gangue are achieved, and the final product aluminum oxide is high in purity, low in impurity content and fine and uniform in granularity and meets the metallurgical-grade aluminum oxide standard. The invention provides an industrial feasible scheme for high-value utilization of the coal gangue.

Description

Technical Field

[0001] The invention belongs to the technical field of refined comprehensive utilization of coal gangue, and particularly relates to a process for preparing alumina by utilizing coal gangue decarbonization activation acid leaching. Background Art

[0002] Gangue is the main solid waste generated during coal mining and washing. Its accumulation not only occupies a large amount of land, but also causes environmental pollution due to spontaneous combustion, leaching, etc. Gangue often contains a certain amount of alumina, which can be recycled as an aluminum resource. However, the traditional process of extracting alumina from gangue faces many challenges: First, the high content of organic carbon (residual carbon) and silicate minerals (such as silica) in the gangue hinders the effective leaching of aluminum; second, the consumption of hydrochloric acid during the acid leaching process is large and difficult to recover efficiently, resulting in high costs and high environmental pollution risks; third, impurity ions such as iron, titanium, and calcium in the leachate are difficult to remove deeply, affecting the final purity of alumina; fourth, the problem of residual chloride ions is prominent, and traditional high-temperature roasting dechlorination consumes a lot of energy and easily leads to uncontrollable alumina crystal form, making it difficult to meet the quality standards of metallurgical-grade products.

[0003] In the existing technology, coal gangue pretreatment mostly uses high-temperature calcination for decarbonization. However, calcination under a conventional air atmosphere can easily lead to sintering of aluminosilicate minerals, forming an insoluble phase, which significantly reduces the efficiency of acid leaching. In addition, the purification of the acid leaching solution and the hydrochloric acid recovery process mostly rely on atmospheric evaporation or chemical precipitation. The former has the problems of low HCl recovery rate and incomplete separation of impurity salts, while the latter causes sodium salt contamination due to the introduction of neutralizers, increasing the difficulty of subsequent treatment. In the dechlorination process, although direct high-temperature roasting can reduce the chloride ion content, it will cause the alumina particles to sinter and the specific surface area to decrease. In addition, the HCl concentration in the flue gas is high, requiring an additional exhaust gas treatment system, which is less economical.

[0004] In response to the above problems, it is urgent to develop an efficient, low-consumption, and environmentally friendly process for preparing alumina from coal gangue to achieve high-value utilization of aluminum resources, while solving key technical bottlenecks such as hydrochloric acid recycling, impurity salt separation, and chlorine residual control. Summary of the Invention

[0005] The purpose of the present invention is to provide a process for preparing alumina by utilizing coal gangue decarbonization activation acid leaching, which realizes the efficient extraction of aluminum in coal gangue and deep removal of impurities. The final product alumina has high purity, low impurity content, fine and uniform particle size, and meets the metallurgical grade alumina standards.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] S1, pretreatment of coal gangue, decarbonization and activation to obtain product 1

[0008] S2, magnetically separating product 1 to obtain product 2;

[0009] S3, reactivating product 2 to obtain product 3;

[0010] S4, acid leaching and dissolving the product 3, filtering to obtain a filtrate and a filter residue, wherein the filtrate is the product 4;

[0011] S5, evaporating the product 4 under negative pressure, recovering the hydrochloric acid, separating the impurity salts, and top flow crystallization to obtain the product 5;

[0012] S6, catalyzing the product 5 with a resin, and separating the crystals to obtain the product 6;

[0013] S7, thermally dechlorinating the product 6 to obtain the product 7;

[0014] S8, hydrothermally crystallizing product 7 to obtain product 8;

[0015] S9. The product 8 is calcined at high temperature to obtain metallurgical grade alumina.

[0016] Preferably, in step S1, the specific conditions for pre-treatment of the coal gangue are: crushing the coal gangue to a particle size of ≤5 mm and homogenizing it.

[0017] Preferably, the decarburization activation is oxygen-controlled roasting decarburization; the specific conditions of the oxygen-controlled roasting decarburization are: temperature of 700-900°C, roasting time of 30s-60min, roasting atmosphere of compressed air, oxygen concentration of 5%-10%, roasting to residual carbon ≤1.5%.

[0018] Raw material pretreatment and decarbonization activation can improve acid leaching efficiency and aluminum leaching rates. This is likely due to selective decarbonization under specific oxygen concentration conditions, which limits the oxidation of organic carbon and preserves alumina activity. High temperatures can also break down Al-Si bonds in the gangue, improving acid leaching efficiency. Furthermore, a low-oxygen environment inhibits the natural reaction between alumina and silica, preventing the formation of insoluble aluminosilicates.

[0019] Preferably, the specific steps of the secondary activation are: mixing the flue gas generated by the drying and roasting in step S7 and the gas generated by the high-temperature roasting in step S9 with the product 2 and reacting them for 25 seconds to 35 minutes.

[0020] Preferably, in step S4, the acid leaching uses the hydrochloric acid recovered in step S5, and the volume concentration of the hydrochloric acid is adjusted to 20%-30%. The liquid-solid ratio of the hydrochloric acid and the product 3 is (3-5) mL:1 g, the acid leaching temperature is 90-95° C., and the time is 1.5-2.5 h.

[0021] Preferably, in step S5, the negative pressure evaporation includes single-effect negative pressure evaporation and double-effect negative pressure evaporation.

[0022] Preferably, the specific conditions of the single-effect negative pressure evaporation and the double-effect negative pressure evaporation are: vacuum degree of 10-20 kPa, temperature of 40-70°C.

[0023] In some preferred embodiments, HCl and water can be evaporated by a single-effect negative pressure evaporation to recover hydrochloric acid with a volume concentration of 15%-22.4%, which is recycled for acid leaching. The mother liquor after the single-effect negative pressure evaporation is further subjected to a second-effect negative pressure evaporation to precipitate chlorinated salts, which are discharged by bottom flow and crystallized by top flow to obtain product 5.

[0024] Preferably, the chlorinated miscellaneous salts include ferric chloride and sodium chloride.

[0025] Preferably, the product 5 is PAC with a basicity of 36%-42%.

[0026] Through specific negative pressure evaporation, hydrochloric acid can be recovered, impure salts can be separated, and the aluminum chloride solution can be enriched for the preparation of polyaluminum chloride. This may be because under negative pressure conditions, the boiling point of hydrogen chloride is lower than that of water, so it evaporates preferentially, achieving efficient recovery of hydrogen chloride and direct use in the acid leaching step, reducing the amount of fresh acid used and lowering costs. The second-effect negative pressure evaporation concentrates the aluminum chloride solution, while metal ions such as iron and sodium ions crystallize due to the salting-out effect, achieving efficient separation of acid and salt, preventing the accumulation of impurities in the system and improving the efficiency of subsequent resin catalysis.

[0027] Preferably, the specific steps of step S6 are: subjecting the product 5 to catalytic alkalization treatment through a resin, and crystallizing it through a crystallization reactor until the alkalinity of the product is 60%-85%, that is, the product 6.

[0028] Preferably, the resin is a macroporous anion exchange resin with a specific surface area of ​​28-32 m 2 / g, particle size is 560-700μm, effective group is quaternary amino group, and exchange capacity is 0.8eq / L.

[0029] In some preferred embodiments, the macroporous anion exchange resin is from Sigma-Aldrich (Shanghai) Trading Co., Ltd. A26.

[0030] Preferably, the resin bed is filled with a thickness of 4% to 6% of the volume of the product 5.

[0031] Preferably, the product 6 includes Al(OH)3·mH2O, PAC and AlCl3.

[0032] By selecting a specific macroporous anion exchange resin for catalytic alkalinization and combining it with crystallization, aluminum chloride can be converted into highly basic polyaluminum chloride. The quaternary ammonium groups of the macroporous anion exchange resin selectively adsorb chloride ions and gradually release hydroxide ions, increasing the alkalinity of product 5 and promoting the crystallization of aluminum hydroxide. Simultaneously, by adjusting the resin bed thickness, the reaction rate is controlled, providing a uniform reaction field, suppressing side reactions, and improving the purity of product 6.

[0033] Preferably, in step S7, thermal dechlorination includes low-temperature dehydration and high-temperature dechlorination.

[0034] Preferably, the specific steps of the low-temperature dehydration are: heating to 200°C at a heating rate of 9-10°C / min, maintaining for 8-12 minutes, and turning on the steam when the furnace temperature is greater than 150°C.

[0035] Preferably, the specific steps of the high-temperature dechlorination are: heating to 400°C at a heating rate of 9-10°C / min, maintaining for 25-35 minutes, with a steam temperature of 200°C, a water vapor volume fraction of 0.5%-1%, and an inlet pressure of 0.18-0.22 MPa, until the chlorine content is ≤5%.

[0036] In some preferred embodiments, the pyrolysis process in step S7 generates flue gas containing hydrogen chloride, which can be used for secondary activation in step S3 after condensation and absorption.

[0037] Preferably, the product 7 is amorphous hydrated aluminum oxide with a chlorine content of ≤5%.

[0038] Through specific steam-assisted pyrolysis, the bound chlorine in product 6 can be removed. This may be because the physically adsorbed water and crystallized water can be removed first under low temperature conditions, avoiding the uncontrolled decomposition of aluminum hydroxide at a sudden high temperature; then, high-temperature dechlorination is performed, and water vapor acts as an oxidant to break the Al-Cl bond, generating HCl gas, which can be recycled to S3 for secondary activation, realizing the closed-loop utilization of chlorine and inhibiting the sintering of aluminum chloride.

[0039] Preferably, in step S8, the specific steps of hydrothermal crystallization are: hydrothermally reacting product 7 with γ-alumina for 1-3 hours and then filtering to obtain product 8.

[0040] Preferably, the mass of the γ-alumina is 1% of the mass of the product 7.

[0041] Preferably, in the hydrothermal reaction, the liquid-solid ratio of water to product 7 is (3-5) mL:1 g.

[0042] By adding a specific seed crystal of γ-alumina, it is possible to induce the conversion of amorphous alumina into α-alumina while shortening the crystallization time. Under hydrothermal conditions, the surface hydroxyl groups of γ-alumina and amorphous alumina rearrange to form α-alumina. At the same time, the lattice reorganization can lower the calcination energy barrier and reduce the defects during subsequent high-temperature calcination. The seed crystals can also guide the directional growth of alumina particles, reducing fine powder. In addition, by controlling the liquid-to-solid ratio during the hydrothermal crystallization process, the grain growth size can be controlled, obtaining a product with a uniform particle size distribution, and improving the calcination activity.

[0043] Preferably, in step S9, the high-temperature roasting conditions are: temperature of 940-960° C., time of 25-35 min, and roasting times of 2 times.

[0044] The second aspect of the present invention provides a product obtained by the process of preparing alumina by decarbonizing and activating coal gangue and acid leaching.

[0045] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0046] 1. The present invention provides a process for producing alumina by decarbonizing and activating coal gangue through acid leaching. Through multi-stage activation, cyclic salt separation, catalytic alkalization, and directional crystallization, combined with auxiliary steps such as oxygen-controlled roasting, magnetic separation, and flue gas recycling, this process achieves efficient extraction of aluminum from the gangue and deep removal of impurities. The final product, alumina, is high in purity, low in impurities, and has a fine and uniform particle size, meeting metallurgical-grade alumina standards. Furthermore, hydrochloric acid and flue gas can be recycled, improving the process's economic efficiency.

[0047] 2. The present invention can improve the acid leaching efficiency and the leaching rate of aluminum through pretreatment and decarbonization activation of raw materials.

[0048] 3. The present invention can recover hydrochloric acid, separate impurity salts, and enrich aluminum chloride solution for preparing polyaluminum chloride through specific negative pressure evaporation.

[0049] 4. The present invention uses a specific macroporous anion exchange resin for catalytic alkalization, combined with crystallization, to convert aluminum chloride into highly basic polyaluminum chloride.

[0050] 5. The present invention can remove the combined chlorine in product 6 through specific steam-assisted pyrolysis.

[0051] 6. The present invention can induce the conversion of amorphous alumina into α-alumina by adding a specific seed crystal γ-alumina, while shortening the crystallization time. DETAILED DESCRIPTION

[0052] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0053] The raw materials used in the present invention are all commercially available, specifically:

[0054] The main chemical composition of coal gangue (w / %) is shown in Table 1.

[0055] Table 1

[0056] <![CDATA[Al2O3]]> <![CDATA[SiO2]]> High <![CDATA[Fe2O3]]> <![CDATA[Na2O]]> <![CDATA[TiO2]]> MgO 36.48 37.36 0.246 0.31 0.10 0.7 0.17

[0057] Macroporous anion exchange resin, with a specific surface area of ​​28-32m 2 / g, particle size is 560-700μm, effective group is quaternary amine group, exchange capacity is 0.8eq / L, from Sigma-Aldrich (Shanghai) Trading Co., Ltd. A26.

[0058] Example 1

[0059] This embodiment provides a process for preparing alumina by acid leaching of coal gangue decarbonization activation, the steps being:

[0060] S1, pretreatment of coal gangue, decarbonization and activation to obtain product 1

[0061] S2, magnetically separating product 1 to obtain product 2;

[0062] S3, reactivating product 2 to obtain product 3;

[0063] S4, acid leaching and dissolving the product 3, filtering to obtain a filtrate and a filter residue, wherein the filtrate is the product 4;

[0064] S5, evaporating the product 4 under negative pressure, recovering the hydrochloric acid, separating the impurity salts, and top flow crystallization to obtain the product 5;

[0065] S6, catalyzing the product 5 with a resin, and separating the crystals to obtain the product 6;

[0066] S7, thermally dechlorinating the product 6 to obtain the product 7;

[0067] S8, hydrothermally crystallizing product 7 to obtain product 8;

[0068] S9. The product 8 is calcined at high temperature to obtain metallurgical grade alumina.

[0069] In step S1, the specific conditions for pre-treating the coal gangue are: crushing the coal gangue to a particle size of ≤5 mm and homogenizing it.

[0070] The decarburization activation is oxygen-controlled roasting decarburization; the specific conditions of the oxygen-controlled roasting decarburization are: temperature of 850°C, roasting time of 30 minutes, roasting atmosphere of compressed air, oxygen concentration of 8%, and roasting to residual carbon of 0.8%.

[0071] The specific steps of the secondary activation are: mixing the flue gas generated by the drying and roasting in step S7 and the gas generated by the high-temperature roasting in step S9 with the product 2 and reacting them for 25 minutes.

[0072] In step S4, the acid leaching uses the hydrochloric acid recovered in step S5, and the volume concentration of the hydrochloric acid is adjusted to 25%. The liquid-solid ratio of the hydrochloric acid and the product 3 is 4 mL:1 g. The acid leaching temperature is 90° C. and the time is 2 h.

[0073] In step S5, the negative pressure evaporation is single-effect negative pressure evaporation or double-effect negative pressure evaporation.

[0074] The specific conditions of the first-effect negative pressure evaporation and the second-effect negative pressure evaporation are: vacuum degree of 15 kPa and temperature of 55°C.

[0075] HCl and water are evaporated by a single negative pressure evaporation, and hydrochloric acid is recovered and recycled for acid leaching. The mother liquor after the single negative pressure evaporation is further evaporated by a second negative pressure evaporation to precipitate chlorinated salts, which are discharged by bottom flow and crystallized by top flow to obtain product 5.

[0076] The product 5 is PAC, and the basicity is 36.23%.

[0077] The specific steps of step S6 are: subjecting product 5 to catalytic alkalization treatment through resin, and crystallizing through a crystallization reactor until the alkalinity of the product reaches 65.48%, namely, product 6.

[0078] The resin is a macroporous anion exchange resin.

[0079] The resin bed was packed at a thickness of 5% of the volume of the product.

[0080] In step S7, the thermal dechlorination includes low-temperature dehydration and high-temperature dechlorination.

[0081] The specific steps of the low-temperature dehydration are: heating to 200°C at a heating rate of 9°C / min, maintaining for 10 minutes, and turning on the steam when the furnace temperature is greater than 150°C.

[0082] The specific steps of the high-temperature dechlorination are: heating to 400°C at a heating rate of 10°C / min, maintaining for 30 minutes, with a steam temperature of 200°C, a water vapor volume fraction of 0.5%, and an inlet pressure of 0.2MPa, until the chlorine content reaches 5%.

[0083] The flue gas containing hydrogen chloride generated during the pyrolysis process in step S7 can be used for secondary activation in step S3 after condensation and absorption.

[0084] In step S8, the specific steps of hydrothermal crystallization are: hydrothermally reacting product 7 with γ-alumina for 2 hours and then filtering to obtain product 8.

[0085] The mass of the γ-alumina is 1% of the mass of the product 7.

[0086] In the hydrothermal reaction, the liquid-to-solid ratio of water to product 7 was 4 mL:1 g.

[0087] In step S9, the high-temperature calcination conditions are: temperature of 950° C., time of 30 min, and calcination times of 2 times.

[0088] Example 2

[0089] The difference between this embodiment and embodiment 1 is that the decarburization activation is oxygen-controlled roasting decarburization; the specific conditions of the oxygen-controlled roasting decarburization are: temperature of 800°C, roasting time of 30 minutes, roasting atmosphere of compressed air, oxygen concentration of 8%, and roasting to a residual carbon of 1.2%.

[0090] Comparative Example 1

[0091] The difference between this comparative example and Example 1 is as follows: S5, product 4 is evaporated under normal pressure to obtain product 5;

[0092] The specific conditions of the atmospheric pressure evaporation are: vacuum degree of 100 kPa, temperature of 90°C;

[0093] In step S4, hydrochloric acid is additionally added to the acid leaching.

[0094] Comparative Example 2

[0095] The difference between this comparative example and Example 1 is that: S6, sodium hydroxide is used to adjust the alkalinity of product 5 to 65.48%, and product 6 is obtained by crystallization and separation.

[0096] Comparative Example 3

[0097] The difference between this comparative example and Example 1 is that the thermal dechlorination in step S7 is not performed, and the product 6 is directly hydrothermally crystallized and then calcined at high temperature.

[0098] Comparative Example 4

[0099] The difference between this comparative example and Example 1 is that in step S8, the specific steps of hydrothermal crystallization are: hydrothermally treating product 7 for 2 hours and then filtering to obtain product 8.

[0100] Comparative Example 5

[0101] The difference between this comparative example and Example 1 is that the specific conditions of the decarburization activation are: temperature of 850° C., calcination time of 30 min, and calcination atmosphere of air.

[0102] Comparative Example 6

[0103] The difference between this comparative example and Example 1 is that in step S9, the high-temperature calcination conditions are: temperature of 950° C., time of 30 min, and calcination times of 1 time.

[0104] Performance Testing

[0105] The purity of aluminum oxide and the residual chloride ion content in the product were tested, and the median particle size D50 was tested. The results are shown in Table 1.

[0106] Table 1 Measurement results

[0107]

[0108]

[0109] According to statistics, the alumina prepared in Examples 1-2 of the present invention has a high purity, the amount of residual aluminum ions is the lowest, and the particle size distribution is uniform and the particle size is small. Comparative Example 1 is evaporation at normal pressure; Comparative Example 2 is alkalization without using resin catalysis, and sodium hydroxide is used to adjust the alkalinity; Comparative Example 3 is high-temperature dechlorination for thermal dechlorination; Comparative Example 4 Step S8 does not add γ-alumina seeds; Comparative Example 5 decarbonization activation does not control oxygen, and air is freely burned; Comparative Example 6 Step S9 is a single high-temperature roasting. The purity of the alumina in the prepared product is low, and there are residual chloride ions, the particle size is high, and some particle size distributions are uneven. Therefore, the method described in this application is used to prepare alumina by acid leaching of coal gangue decarbonization activation, which realizes efficient extraction of aluminum in coal gangue and deep removal of impurities. The final product alumina has high purity, low impurity content, and fine and uniform particle size, meeting the metallurgical grade alumina standards.

[0110] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A process for preparing alumina by decarbonizing and activating coal gangue by acid leaching, characterized in that: The following steps are involved: S1, pretreatment of coal gangue, decarbonization and activation to obtain product 1 S2, magnetically separating product 1 to obtain product 2; S3, reactivating product 2 to obtain product 3; S4, acid leaching and dissolving the product 3, filtering to obtain a filtrate and a filter residue, wherein the filtrate is the product 4; S5, evaporating the product 4 under negative pressure, recovering the hydrochloric acid, separating the impurity salts, and top flow crystallization to obtain the product 5; S6, catalyzing the product 5 with a resin, and separating the crystals to obtain the product 6; S7, thermally dechlorinating the product 6 to obtain the product 7; S8, hydrothermally crystallizing product 7 to obtain product 8; S9, the product 8 is calcined at high temperature to obtain metallurgical grade alumina; In step S5, the negative pressure evaporation includes a first-effect negative pressure evaporation and a second-effect negative pressure evaporation. HCl and water are evaporated by the first-effect negative pressure evaporation, recovered, and recycled for acid leaching. The mother liquor after the first-effect negative pressure evaporation is further subjected to a second-effect negative pressure evaporation to precipitate chlorinated salts, discharge the salts in the bottom flow, and crystallize in the top flow to obtain product 5.

2. The process for preparing alumina by utilizing coal gangue decarbonization activation acid leaching according to claim 1, characterized in that: The decarburization activation is oxygen-controlled roasting decarburization; the specific conditions of the oxygen-controlled roasting decarburization are: temperature of 700-900°C, roasting time of 30s-60min, roasting atmosphere of compressed air, oxygen concentration of 5%-10%, roasting to residual carbon ≤1.5%.

3. The process for preparing alumina by utilizing coal gangue decarbonization activation acid leaching according to claim 1, characterized in that: The specific steps of the secondary activation are: mixing the flue gas generated by the drying and roasting step S7 and the gas generated by the high-temperature roasting step S9 with the product 2 and reacting them for 25 seconds to 35 minutes.

4. The process for preparing alumina by utilizing coal gangue decarbonization activation acid leaching according to claim 1, characterized in that: In step S4, the acid leaching uses the hydrochloric acid recovered in step S5, and the volume concentration of the hydrochloric acid is adjusted to 20%-30%. The liquid-solid ratio of the hydrochloric acid and the product 3 is (3-5) mL:1 g. The acid leaching temperature is 90-95° C. and the time is 1.5-2.5 h.

5. The process for preparing alumina by utilizing coal gangue decarbonization activation acid leaching according to claim 1, characterized in that: The specific conditions of the first-effect negative pressure evaporation and the second-effect negative pressure evaporation are: vacuum degree of 10-20 kPa, temperature of 40-70°C.

6. The process for preparing alumina by utilizing coal gangue decarbonization activation acid leaching according to claim 1, characterized in that: The specific steps of step S6 are: subjecting product 5 to catalytic alkalization treatment through resin, and crystallizing through a crystallization reactor until the alkalinity of the product reaches 60%-85%, namely product 6.

7. The process for preparing alumina by utilizing coal gangue decarbonization activation acid leaching according to claim 6, characterized in that: The resin is a macroporous anion exchange resin with a specific surface area of ​​28-32m 2 / g, particle size is 560-700μm, effective group is quaternary amino group, and exchange capacity is 0.8eq / L.

8. The process for preparing alumina by utilizing coal gangue decarbonization activation acid leaching according to claim 6, characterized in that: The filling thickness of the resin bed is 4%-6% of the volume of the product 5.

9. The process for preparing alumina by utilizing coal gangue decarbonization activation acid leaching according to claim 1, characterized in that: In step S7, thermal dechlorination includes low-temperature dehydration and high-temperature dechlorination.

10. A product obtained by the process for preparing alumina by decarbonization and activation acid leaching of coal gangue according to any one of claims 1 to 9.

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