Method for producing aluminum oxide from bauxite with high sulfur and low aluminum-silicon ratio

Abstract

The invention belongs to the technical field of mineral resource utilization, and particularly relates to a method for producing aluminum oxide from bauxite with high sulfur and low aluminum-silicon ratio. The method comprises the following steps: mixing pre-roasted bauxite, decomposition mother liquor containing sodium hydroxide, sodium hydroxide and lime slurry to form ore pulp, dissolving out sodium aluminate, adding a flocculating agent into the dissolved ore pulp, carrying out settling separation to obtain red mud and fine liquid containing sodium aluminate, carrying out seed crystal decomposition on the fine liquid to generate aluminum hydroxide and decomposition mother liquor containing sodium hydroxide, and carrying out solid-liquid separation on the aluminum hydroxide and the decomposition mother liquor containing sodium hydroxide. Roasting the aluminum hydroxide to generate aluminum oxide; the decomposition mother liquor is evaporated to increase the concentration of alkali liquor, and is returned to double decomposition reaction for cyclic utilization. According to the method, the dissolution rate of aluminum oxide can be increased, the recovery rate of aluminum is increased, the consumption of sodium hydrogen oxide is remarkably reduced, the acid-base reaction for dissolving out sodium aluminate can adopt lower temperature and lower concentration, the consumption of dissolved steam is reduced, and the method for producing aluminum oxide from bauxite with high sulfur and low aluminum-silicon ratio, which is simple, low in cost and high in efficiency, is provided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of mineral resources utilization, and particularly relates to a method for producing alumina from high-sulfur low-aluminum-silicon-ratio bauxite. BACKGROUND

[0002] The high-sulfur low-aluminum-silicon-ratio bauxite refers to bauxite with sulfur content greater than 0.7wt% (mainly between 0.8wt% and 2wt%) and aluminum-silicon ratio lower than 5 (mainly between 3 and 5), which cannot meet the requirements of producing alumina by the Bayer process. The sulfur in the high-sulfur bauxite mainly exists in the form of pyrite, and part of it exists in the form of marcasite or pyrrhotite, and a small part of it exists in the form of sulfate mineral. The harm of sulfur in bauxite includes: corroding production equipment, causing pollution of the leaching solution, and reducing product quality; reacting with alkali in the solution, increasing the consumption of alkali; being harmful to the dissolution of bauxite and the decomposition of seed, and endangering the safety of equipment; and reducing the sedimentation capacity of red mud. The alumina and silicon dioxide in the low-aluminum-silicon-ratio bauxite mainly exist in the form of crystalline kaolinite, which is dense and difficult to react with sodium hydroxide solution at low temperature, low alkali and low pressure, so it is difficult to be directly leached and utilized. Therefore, it is necessary to treat the bauxite by high-temperature activation roasting to decompose the silicon dioxide in kaolinite into amorphous state, improve the chemical reaction activity, and carry out desilication treatment to prepare high-aluminum-silicon-ratio compounds. Therefore, it is urgent to find a simple, low-cost and high-efficiency method for producing alumina from high-sulfur low-aluminum-silicon-ratio bauxite. SUMMARY

[0003] Therefore, the purpose of the present application is to provide a method for producing alumina from high-sulfur low-aluminum-silicon-ratio bauxite, which can improve the yield of alumina, reduce the consumption of sodium hydroxide, improve the efficiency, and reduce the cost.

[0004] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0005] The present application provides a method for producing alumina from high-sulfur low-aluminum-silicon-ratio bauxite, which comprises the following steps:

[0006] The high-sulfur low-aluminum-silicon-ratio bauxite is pre-roasted to obtain pre-roasted bauxite;

[0007] The pre-roasted bauxite, a decomposition mother liquor containing sodium hydroxide, sodium hydroxide and lime slurry are mixed, and the obtained slurry is subjected to a double decomposition reaction and an acid-base reaction in sequence to leach sodium aluminate and obtain a leached slurry;

[0008] The leached slurry is diluted with hot water and mixed with a flocculating agent, and then subjected to a sedimentation separation and a precision filtration in sequence to obtain a precision liquid containing sodium aluminate and red mud, respectively;

[0009] The precision liquid containing sodium aluminate is mixed with seed crystals to carry out a decomposition reaction, and then subjected to a solid-liquid separation to obtain aluminum hydroxide and a decomposition mother liquor containing sodium hydroxide, respectively;

[0010] roasting the aluminum hydroxide to obtain the aluminum oxide product;

[0011] The mass content of sulfur in the high-sulfur low-aluminum-silicon ratio bauxite is 0.8-2%; the aluminum-silicon ratio of the high-sulfur low-aluminum-silicon ratio bauxite is 3-5;

[0012] The decomposition mother liquor containing sodium hydroxide is returned to the double decomposition reaction for recycling.

[0013] Preferably, the pre-roasting comprises sequentially performing a first-stage pre-roasting and a second-stage pre-roasting; the temperature of the first-stage pre-roasting is 500-700℃, and the holding time is 1-10 min; the temperature of the second-stage pre-roasting is 900-1100℃, and the holding time is 20-40 min; the first-stage pre-roasting and the second-stage pre-roasting are independently performed in an oxidizing atmosphere; the volume content of oxygen in the oxidizing atmosphere is 2-5%.

[0014] Preferably, the temperature of the double decomposition reaction is 90-98℃, and the time is 6-10 h.

[0015] Preferably, the temperature of the acid-base reaction is 200-220℃, and the time is 50-70 min.

[0016] Preferably, the temperature of the hot water is 93-98℃; the content of aluminum oxide in the diluted ore slurry obtained by diluting the ore slurry after leaching with the hot water is 130-140 g / L.

[0017] Preferably, the flocculant comprises sodium polyacrylate and / or polyacrylamide; the mass of the flocculant is 0.01-0.03% of the mass of the diluted ore slurry obtained by diluting the ore slurry after leaching with the hot water.

[0018] Preferably, the seed crystal is aluminum hydroxide; the mass of the seed crystal is 2-3 times the mass of aluminum oxide in the sodium aluminate liquor.

[0019] Preferably, the temperature of the decomposition reaction is 40-60℃, and the time is 30-75 h.

[0020] Preferably, the temperature of the roasting is 900-1050℃, and the holding time is 2-10 s; the roasting is performed in an oxidizing atmosphere; the volume content of oxygen in the oxidizing atmosphere is 2-5%.

[0021] Preferably, the yield of the aluminum oxide product is 85-88%.

[0022] The application provides a method for producing alumina from high-sulfur low-aluminum-silicon bauxite, comprising the following steps: pre-roasting the high-sulfur low-aluminum-silicon bauxite to obtain pre-roasted bauxite; mixing the pre-roasted bauxite, a decomposition mother liquor containing sodium hydroxide, sodium hydroxide and lime slurry, and sequentially performing a double decomposition reaction and an acid-base reaction on the obtained ore slurry to dissolve sodium aluminate and obtain a post-dissolution ore slurry; mixing the post-dissolution ore slurry with a flocculating agent after diluting the post-dissolution ore slurry with hot water, and sequentially performing a sedimentation separation and a precision filtration to obtain a precision liquid containing sodium aluminate and red mud respectively; mixing the precision liquid containing sodium aluminate with a crystal seed, performing a decomposition reaction and a solid-liquid separation to obtain aluminum hydroxide and a decomposition mother liquor containing sodium hydroxide respectively; and roasting the aluminum hydroxide to obtain alumina products; the mass content of sulfur in the high-sulfur low-aluminum-silicon bauxite is 0.8-2%; the aluminum-silicon ratio of the high-sulfur low-aluminum-silicon bauxite is 3-5; and the decomposition mother liquor containing sodium hydroxide is recycled in the double decomposition reaction. In the application, the high-sulfur low-aluminum-silicon bauxite is pre-roasted, most of the sulfur in the bauxite is in the form of SO2 in flue gas, kaolinite is decomposed into aluminum spinel and amorphous silicon dioxide, and the pre-roasting can remove organic matter in the high-sulfur low-aluminum-silicon bauxite. The pre-roasted bauxite and the ore slurry mixed by the sodium hydroxide and the lime slurry are used to dissolve sodium aluminate, the post-dissolution ore slurry is separated into red mud and the precision liquid containing sodium aluminate after adding a flocculating agent, the precision liquid is decomposed by the crystal seed to generate aluminum hydroxide and the decomposition mother liquor containing sodium hydroxide, and the aluminum hydroxide is roasted to generate alumina. The decomposition mother liquor is evaporated to increase the concentration of the alkali liquor and recycled in the double decomposition reaction. The application increases the dissolution rate of alumina, increases the recovery rate of aluminum, significantly reduces the consumption of sodium hydroxide, the acid-base reaction for dissolving sodium aluminate can be performed at a lower temperature and a lower concentration, reduces the steam consumption in the dissolution, and provides a simple, low-cost and high-efficiency method for producing alumina from high-sulfur low-aluminum-silicon bauxite. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The application provides a method for producing alumina from high-sulfur low-aluminum-silicon bauxite. DETAILED DESCRIPTION

[0024] The application provides a method for producing alumina from high-sulfur low-aluminum-silicon bauxite, comprising the following steps:

[0025] Pre-roasting the high-sulfur low-aluminum-silicon bauxite to obtain pre-roasted bauxite;

[0026] Mixing the pre-roasted bauxite, a decomposition mother liquor containing sodium hydroxide, sodium hydroxide and lime slurry, and sequentially performing a double decomposition reaction and an acid-base reaction on the obtained ore slurry to dissolve sodium aluminate and obtain a post-dissolution ore slurry;

[0027] The post-dissolution slurry is diluted with hot water and mixed with a flocculant, and then subjected to sedimentation separation and precision filtration in sequence to obtain a precision liquid containing sodium aluminate and red mud, respectively;

[0028] The precision liquid containing sodium aluminate is mixed with seed crystals to perform a decomposition reaction, and then subjected to solid-liquid separation to obtain aluminum hydroxide and a decomposition mother liquor containing sodium hydroxide, respectively;

[0029] The aluminum hydroxide is calcined to obtain an aluminum oxide product;

[0030] The high-sulfur low-aluminum-silicon-ratio bauxite has a mass content of sulfur of 0.8-2%; and the high-sulfur low-aluminum-silicon-ratio bauxite has an aluminum-silicon ratio of 3-5.

[0031] The decomposition mother liquor containing sodium hydroxide is returned to a double decomposition reaction for recycling.

[0032] Unless otherwise specified, the source of the raw materials used in the present application is not particularly limited, and commercially available products known to those skilled in the art can be used.

[0033] The present application performs pre-calcination on the high-sulfur low-aluminum-silicon-ratio bauxite to obtain pre-calcined bauxite.

[0034] As an embodiment, the high-sulfur low-aluminum-silicon-ratio bauxite has a mass content of aluminum oxide of 45-70%, specifically 66% in an embodiment, a mass content of silicon dioxide of 9-15%, specifically 15% in an embodiment, a mass content of diiron trioxide of 2-6%, specifically 5% in an embodiment, and a mass content of sulfur of 0.8-2%, specifically 1.5% in an embodiment; and the high-sulfur low-aluminum-silicon-ratio bauxite has an aluminum-silicon ratio of 3-5, specifically 4.4 in an embodiment.

[0035] As an embodiment, the pre-calcination includes sequentially performing first-stage pre-calcination and second-stage pre-calcination; the first-stage pre-calcination has a temperature of 500-700°C, specifically 600°C in an embodiment, and a holding time of 1-10 min, specifically 5-8 min in an embodiment; the second-stage pre-calcination has a temperature of 900-1100°C, specifically 1070°C in an embodiment, and a holding time of 20-40 min, specifically 30 min in an embodiment; the first-stage pre-calcination and the second-stage pre-calcination are independently performed in an oxidizing atmosphere; and the oxidizing atmosphere has a volume content of oxygen of 2-5%, specifically 3% in an embodiment.

[0036] During the first-stage pre-calcination, 90% of the sulfur in the high-sulfur low-aluminum-silicon-ratio bauxite reacts with oxygen to generate sulfur dioxide into flue gas, which is discharged after desulfurization; and during the second-stage pre-calcination, kaolinite Al2O3·2SiO2·2H2O in the bauxite is converted into aluminum spinel Al2O3·SiO2 and amorphous silicon dioxide SiO2.

[0037] After obtaining the pre-calcined bauxite, the pre-calcined bauxite, the decomposition mother liquor containing sodium hydroxide, sodium hydroxide and lime slurry are mixed, and the obtained slurry is sequentially subjected to double decomposition reaction and acid-base reaction to dissolve sodium aluminate and obtain the slurry after dissolution.

[0038] As an embodiment, 4-6 t of the decomposition mother liquor containing sodium hydroxide, 0.2-0.4 t of sodium hydroxide and 0.06-0.09 t of lime are added per t of the pre-calcined bauxite, and in a specific embodiment, 5 t of the decomposition mother liquor containing sodium hydroxide, 0.3 t of sodium hydroxide and 0.08 t of lime are added per t of the pre-calcined bauxite; the lime slurry comprises lime and water; the mass content of calcium hydroxide in the lime slurry is 30-50%, and in a specific embodiment, 40%.

[0039] As an embodiment, the temperature of the double decomposition reaction is 90-98℃, and in a specific embodiment, 97℃, and the time is 6-10 h, and in a specific embodiment, 8 h; the double decomposition reaction is carried out at normal pressure. During the double decomposition reaction, amorphous silicon dioxide SiO2 is converted into sodium silicate and calcium silicate.

[0040] As an embodiment, the temperature of the acid-base reaction is 200-220℃, and in a specific embodiment, 210℃, and the time is 50-70 min, and in a specific embodiment, 60 min; after the double decomposition reaction, the slurry after the double decomposition reaction is heated to the temperature of the acid-base reaction by steam. Through steam heating, water evaporates, and the concentration of sodium hydroxide increases. The alumina in the slurry reacts with sodium hydroxide to generate sodium aluminate.

[0041] After obtaining the slurry after dissolution, the slurry after dissolution is diluted with hot water and mixed with a flocculating agent, and then subjected to sedimentation separation and precision filtration in sequence to obtain a precision liquid containing sodium aluminate and red mud, respectively.

[0042] As an embodiment, the temperature of the hot water is 93-98℃, and in a specific embodiment, 96℃; the content of alumina in the diluted slurry obtained after the slurry after dissolution is diluted with hot water is 130-140 g / L, and in a specific embodiment, 135 g / L; the flocculating agent comprises sodium polyacrylate and / or polyacrylamide, and in a specific embodiment, polyamine acrylamide; the mass of the flocculating agent is 0.01-0.03% of the mass of the diluted slurry obtained after the slurry after dissolution is diluted with hot water, and in a specific embodiment, 0.01-0.02%; the flocculating agent is used in the form of a flocculating agent aqueous solution; the mass concentration of the flocculating agent in the flocculating agent aqueous solution is 0.1%; the equipment used for precision filtration is a leaf filter.

[0043] After obtaining the sodium aluminate-containing liquor, the present application mixes the sodium aluminate-containing liquor with the seed crystal, carries out a decomposition reaction, solid-liquid separation, and obtains aluminum hydroxide and a sodium hydroxide-containing decomposition mother liquor, respectively.

[0044] As an embodiment, the seed crystal is aluminum hydroxide; the mass of the seed crystal is 2-3 times, and specifically 3 times, the mass of the aluminum oxide in the sodium aluminate-containing liquor; the temperature of the decomposition reaction is 40-60°C, and specifically 45°C, and the time is 30-75h, and specifically 40-50h; the solid-liquid separation is filtration; sodium aluminate is decomposed into aluminum hydroxide and sodium hydroxide, and the sodium hydroxide enters the decomposition mother liquor.

[0045] As an embodiment, the sodium hydroxide-containing decomposition mother liquor is returned to the double decomposition reaction for recycling; 4-6t, and specifically 5t, of the sodium hydroxide-containing decomposition mother liquor with a Na2O concentration of 280-300g / L is added to t of the pre-baked bauxite; before being returned to the double decomposition reaction, the sodium hydroxide-containing decomposition mother liquor is subjected to steam heating for water evaporation until the Na2O concentration is 280-300g / L, and specifically 300g / L; the steam used for the steam heating has a pressure of ≥0.6MPa, and specifically 0.6MPa; the equipment used for the steam heating is a multi-effect evaporator.

[0046] After obtaining the aluminum hydroxide, the present application calcines the aluminum hydroxide to obtain the aluminum oxide product.

[0047] As an embodiment, the calcination temperature is 900-1050°C, and specifically 1000-1050°C, and the holding time is 2-10s, and specifically 8s; the calcination is carried out in an oxidizing atmosphere.

[0048] As an embodiment, the yield of the aluminum oxide product is 85-88%, and specifically 86%.

[0049] Figure 1 This is a flowchart of the method for producing aluminum oxide from high-sulfur low-aluminum-silicon-ratio bauxite in the embodiments of the present application. After the high-sulfur low-aluminum-silicon-ratio bauxite is pre-baked, the present application dissolves sodium aluminate, separates by sedimentation, discharges red mud, obtains a sodium aluminate-containing liquor, adds seed crystal to carry out a decomposition reaction, generates aluminum hydroxide and a sodium hydroxide-containing decomposition mother liquor, calcines the aluminum hydroxide to obtain aluminum oxide, and returns the decomposition mother liquor to the dissolving procedure after the decomposition mother liquor is subjected to mother liquor evaporation to increase the concentration of the lye.

[0050] The present application increases the dissolving rate of aluminum oxide, increases the recovery rate of aluminum, significantly reduces the consumption of sodium hydroxide, and can use a lower temperature and a lower concentration for the acid-base reaction of the dissolved sodium aluminate, and reduces the steam consumption of the dissolving.

[0051] The technical solutions in the present application will be described clearly and completely below in combination with the embodiments in the present application, but they should not be understood as limitations to the protection scope of the present application.

[0052] Example 1

[0053] The high-sulfur low-aluminum-silicon-ratio bauxite is used as raw material, wherein the mass content of aluminum oxide is 66%, the mass content of silicon dioxide is 15%, the mass content of diiron trioxide is 5%, the mass content of sulfur is 1.5%, and the aluminum-silicon ratio is 4.4;

[0054] The high-sulfur low-aluminum-silicon-ratio bauxite is first precalcined at 600℃ for 5min in an oxidizing atmosphere (the volume content of oxygen is 3%) to remove sulfur, 90% of the sulfur and oxygen react to generate SO2 into flue gas, which is discharged after desulfurization; then precalcined at 1070℃ for 40min in an oxidizing atmosphere containing 3vol% oxygen, the kaolinite Al2O3·2SiO2·2H2O in the bauxite is converted into aluminum spinel Al2O3·SiO2 and amorphous silicon dioxide SiO2;

[0055] 5t of the decomposition mother liquor containing sodium hydroxide, 0.3t of sodium hydroxide and 0.08t of lime are added to each t of the precalcined bauxite, the lime and water are prepared into lime slurry (the mass content of calcium hydroxide is 40%) and mixed into the ore slurry, the ore slurry is first subjected to double decomposition reaction at normal pressure and 98℃ for 8h, the amorphous silicon dioxide is converted into sodium silicate and calcium silicate, and then subjected to acid-base reaction by steam heating to 210℃ for 60min, the aluminum oxide in the ore slurry reacts with sodium hydroxide to generate sodium aluminate to be dissolved, and the ore slurry after dissolution is obtained;

[0056] The ore slurry after dissolution is diluted by hot water to an aluminum oxide content of 135g / L, and then 0.01% of polyacrylamide flocculant of the diluted ore slurry after the ore slurry after dissolution is diluted by hot water is added, the polyacrylamide flocculant is prepared into an aqueous solution with a mass concentration of 0.1% for addition. After sedimentation separation and leaf filter precision filtration, red mud and refined liquid containing sodium aluminate are produced;

[0057] Hydroxide aluminum which is 3 times of the content of aluminum oxide in the refined liquid containing sodium aluminate is added to the refined liquid containing sodium aluminate as a seed crystal, and a decomposition reaction is carried out at 45℃, the sodium aluminate is decomposed into aluminum hydroxide and sodium hydroxide, and the aluminum hydroxide and the decomposition mother liquor containing sodium hydroxide are separated by filtration; the decomposition mother liquor containing sodium hydroxide is subjected to water evaporation by steam heating at 0.6MPa to a Na2O concentration of 300g / L, and then returned to the double decomposition reaction for recycling;

[0058] The aluminum hydroxide is calcined at 1000℃ in an oxidizing atmosphere containing 3vol% oxygen, and the total yield of the aluminum oxide product is 86%.

[0059] Although the above embodiments have been described in detail, they are only some embodiments of the present application but not all the embodiments. Other embodiments can be obtained according to the above embodiments without creativity, and these embodiments also belong to the protection scope of the present application.

Claims

1. A method for producing alumina from high-sulfur, low-alumina-silica ratio bauxite, characterized in that, Includes the following steps: High-sulfur, low-alumina-silicon ratio bauxite is pre-roasted to obtain pre-roasted bauxite. The pre-roasted bauxite, sodium hydroxide-containing decomposition mother liquor, sodium hydroxide and lime slurry are mixed, and the resulting slurry is subjected to a metathesis reaction and an acid-base reaction in sequence to dissolve sodium aluminate, thus obtaining the dissolved slurry. The dissolved slurry was diluted with hot water and mixed with flocculant, and then subjected to sedimentation separation and fine filtration in sequence to obtain sodium aluminate-containing concentrate and red mud, respectively. The sodium aluminate-containing liquid and seed crystals are mixed and subjected to a decomposition reaction. Solid-liquid separation is performed to obtain aluminum hydroxide and sodium hydroxide-containing decomposition mother liquor, respectively. The aluminum hydroxide is calcined to obtain the finished aluminum oxide product; The sulfur content in the high-sulfur, low-alumina-silicon ratio bauxite is 0.8-2% by mass; the alumina-silicon ratio in the high-sulfur, low-alumina-silicon ratio bauxite is 3-5. The mother liquor containing sodium hydroxide is returned to the metathesis reaction for recycling.

2. The method according to claim 1, characterized in that, The pre-calcination includes sequentially performing a first stage pre-calcination and a second stage pre-calcination; the temperature of the first stage pre-calcination is 500–700°C, and the holding time is 1–10 min; the temperature of the second stage pre-calcination is 900–1100°C, and the holding time is 20–40 min; the first stage pre-calcination and the second stage pre-calcination are carried out independently in an oxidizing atmosphere; the volume content of oxygen in the oxidizing atmosphere is 2–5%.

3. The method according to claim 1, characterized in that, The double displacement reaction is carried out at a temperature of 90–98°C for 6–10 hours.

4. The method according to claim 1, characterized in that, The acid-base reaction is carried out at a temperature of 200–220°C for 50–70 minutes.

5. The method according to claim 1, characterized in that, The temperature of the hot water is 93-98℃; the alumina content in the diluted slurry obtained after dilution with hot water is 130-140 g / L.

6. The method according to claim 1, characterized in that, The flocculant includes sodium polyacrylate and / or polyacrylamide; the mass of the flocculant is 0.01 to 0.03% of the mass of the diluted slurry obtained after dilution with hot water.

7. The method according to claim 1, characterized in that, The seed crystal is aluminum hydroxide; the mass of the seed crystal is 2 to 3 times the mass of aluminum oxide in the sodium aluminate-containing semen.

8. The method according to claim 1, characterized in that, The decomposition reaction is carried out at a temperature of 40–60°C for a time of 30–75 h.

9. The method according to claim 1, characterized in that, The calcination temperature is 900–1050°C, and the holding time is 2–10 seconds; the calcination is carried out in an oxidizing atmosphere; the volume content of oxygen in the oxidizing atmosphere is 2–5%.

10. The method according to claim 1, characterized in that, The yield of the alumina product is 85-88%.

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