A method for extracting alumina from medium- and low-grade aluminum-containing raw materials

Abstract

The present invention relates to the technical field of alumina production, and particularly relates to a method for extracting alumina from medium- and low-grade aluminum-containing raw materials. This method mixes medium- and low-grade aluminum-containing raw materials with sodium carbonate and calcium carbonate in a specific ratio, and sinters them to obtain clinker, which changes the occurrence state and phase composition of alumina and silica in the clinker, greatly reduces the dosage of sodium carbonate and the slag amount, reduces the energy consumption in the sintering process, and improves the dissolution rate of alumina in the clinker.

Description

Technical Field

[0001] The present invention belongs to the technical field of alumina production, and particularly relates to a method for extracting alumina from medium- and low-grade aluminum-containing raw materials. Background Art

[0002] The soda-lime sintering method for treating medium- and low-grade bauxite to produce alumina is one of the commonly used methods in domestic alumina enterprises at present. The main principle of this method is to add sodium carbonate and lime during the sintering process, so that gibbsite in the ore is converted into Na2O·Al2O3, iron-containing minerals are converted into sodium ferrate, and silicon-containing minerals are converted into β-2CaO·SiO2. This process has the advantages of low sintering temperature and high dissolution performance of the sintered clinker alumina.

[0003] However, in the actual production process, there are still some problems with this production process. For example, in order to form sodium aluminate and sodium ferrate, a large amount of sodium carbonate needs to be added during the sintering process, and it will volatilize and form scale during the rotary kiln sintering process; in addition, high-concentration sodium carbonate solution is required for alumina dissolution, and the large amount of sodium carbonate used makes there a large proportion of moisture in the subsequent evaporation process of the material, significantly increasing the energy consumption during the calcination process. Summary of the Invention

[0004] Aiming at the problems of high sodium carbonate addition amount in the current sintering method, which will cause scaling and increase energy consumption, the present invention provides a method for extracting alumina from medium- and low-grade aluminum-containing raw materials.

[0005] To achieve the above invention purpose, the embodiments of the present invention adopt the following technical solutions:

[0006] A method for extracting alumina from medium- and low-grade aluminum-containing raw materials, which comprises mixing the medium- and low-grade aluminum-containing raw materials with sodium carbonate and calcium carbonate, sintering to obtain a clinker, and subjecting the clinker to alumina dissolution to obtain the alumina; the aluminum element in the aluminum-containing raw materials is calculated as alumina (Al2O3), the silicon element is calculated as silicon dioxide (SiO2), the molar ratio of the sodium carbonate to the alumina is 0.3-0.5, and the molar ratio of the calcium carbonate to the sum of the molar numbers of the alumina and the silicon dioxide is 0.7-0.9.

[0007] By limiting the addition amounts of sodium carbonate and calcium carbonate, the present invention changes the occurrence states and phase compositions of alumina and silica in the clinker, converts the main occurrence phase of alumina in the sintered clinker from Na2O·Al2O3 in the clinker obtained by the traditional soda-lime sintering method to 2Na2O·3CaO·5Al2O3, and reduces the addition amount of sodium carbonate by 50-70%, and reduces the slag amount accordingly, realizing semi-dry sintering with relatively low energy consumption. Compared with the original process, it can reduce the energy consumption in the sintering process by 8-10%.

[0008] The phase composition of the obtained clinker reduces the requirement for the concentration of sodium carbonate for alumina digestion, and a lower concentration of sodium carbonate can be used, thus reducing the energy consumption of the subsequent evaporation process. Moreover, the digestion rate of alumina in this clinker (alumina in the digestion product / alumina in the clinker × 100%) can reach over 90%.

[0009] The method provided by the present invention can process medium and low-grade bauxite, and can also process low-grade aluminum-containing raw materials such as fly ash, thereby realizing the comprehensive utilization of resources. Among them, calcium carbonate can be replaced by limestone to reduce costs, and the calcium carbonate content in limestone still follows the above ratio.

[0010] Preferably, the molar ratio of the sodium carbonate to the alumina is 0.4, and the ratio of the molar number of the calcium carbonate to the sum of the molar numbers of the alumina and silica is 0.8.

[0011] Preferably, the sintering temperature is 1100 - 1250 °C.

[0012] Preferably, the heat preservation time after sintering to the above temperature is 15 - 60 min.

[0013] Preferably, the heating rate of the sintering is 15 - 30 °C / min. The co-limitation of this rapid heating system and the above heat preservation time can enable the clinker to form a loose and porous microstructure, enabling alumina to be rapidly digested in the subsequent digestion process. Too fast or too slow heating rates are not conducive to the formation of the porous structure, which may reduce or disappear the pore structure.

[0014] Preferably, the cooling system after sintering is natural cooling in the furnace.

[0015] Preferably, the alumina in the clinker is digested with an aqueous sodium carbonate solution with a concentration of 20 - 40 g / L. The phase composition of the clinker obtained by the present invention is 2Na2O·3CaO·5Al2O3, and sufficient digestion of alumina can be achieved without a sodium carbonate solution with too high a concentration, improving the situation where the energy consumption of the subsequent evaporation process increases due to too high a concentration of sodium carbonate and too much remaining sodium carbonate.

[0016] Preferably, the digestion temperature is 50 - 90 °C. Too high a temperature will increase unnecessary energy consumption and production costs, while too low a temperature will result in a slow reaction and incomplete digestion. Within this temperature range, the clinker can fully react with sodium carbonate in the solution to form aluminum hydroxide, and alumina can be obtained after further conventional calcination.

[0017] When the heating rate of sintering is 15 - 30 °C / min, preferably the digestion time is 10 - 30 min, which can not only ensure that alumina is digested as completely as possible, but also shorten the digestion time and reduce the time cost.

[0018] Preferably, the heat generated during sintering is used to heat the sodium carbonate solution, which can further reduce energy consumption, save resources and costs. Description of the Drawings

[0019] Figure 1 Schematic process flow diagrams of Examples 1 to 4 of the present invention;

[0020] Figure 2 Microscopic morphology of the clinker obtained in Example 1 of the present invention. Detailed Embodiments

[0021] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] Example 1

[0023] This example provides a method for extracting alumina from medium- and low-grade aluminum-containing raw materials. The specific operation is as follows:

[0024] A certain mass of bauxite is crushed and ground. The chemical composition of the bauxite in terms of mass percentage is: 52.5% Al2O3, 11.2% SiO2, 8.2% Fe2O3, and the rest are impurities; the proportion of particles with a particle size less than 0.074 mm after grinding reaches more than 85%; then sodium carbonate and limestone are added according to an alkali ratio (Na2CO3 / Al2O3, molar ratio) of 0.4 and a calcium ratio (CaCO3 / (Al2O3 + SiO2), molar ratio) of 0.8, and the materials are mixed; the temperature is raised to 1200 °C at a heating rate of 25 °C / min and held at this temperature for 30 minutes, and then naturally cooled in the furnace; the obtained clinker has a porous structure, and its phase composition is mainly 2Na2O·3CaO·5Al2O3 and β-2CaO·SiO2, and its microscopic morphology is as Figure 2 shown.

[0025] The obtained clinker is leached with a sodium carbonate solution with a concentration of 30 g / L. The leaching temperature is 70 °C and the time is 20 min, and the alumina leaching rate reaches 95.27%.

[0026] The amount of sodium carbonate added is reduced by 60% compared with the traditional soda-lime sintering method, and the energy consumption during the sintering process is reduced by 10%.

[0027] Example 2

[0028] This example provides a method for extracting alumina from medium- and low-grade aluminum-containing raw materials. The specific operation is as follows:

[0029] Crush and grind a certain mass of bauxite. The chemical composition of this bauxite in terms of mass percentage is: 50.8% Al2O3, 13.1% SiO2, 9.6% Fe2O3, and the rest are impurities; the proportion of particles with a particle size less than 0.074 mm after grinding reaches more than 85%; then add sodium carbonate and limestone according to a soda ratio of 0.5 and a lime ratio of 0.7, and mix the materials; raise the temperature to 1100 °C at a heating rate of 15 °C / min, and keep it at this temperature for 15 minutes, and then cool naturally in the furnace; the obtained clinker has a porous structure, and its phase composition is mainly 2Na2O·3CaO·5Al2O3 and β-2CaO·SiO2, and contains a small amount of Na2O·Al2O3.

[0030] Dissolve the obtained clinker with a sodium carbonate solution with a concentration of 20 g / L for alumina extraction. The extraction temperature is 50 °C and the time is 10 min. The alumina extraction rate reaches 90.48%.

[0031] The amount of sodium carbonate added is reduced by 50% compared with the traditional soda-lime sintering method, and the energy consumption in the sintering process is reduced by 8%.

[0032] Example 3

[0033] This example provides a method for extracting alumina from medium- and low-grade aluminum-containing raw materials. The specific operation is as follows:

[0034] Crush and grind a certain mass of bauxite. The chemical composition of this bauxite in terms of mass percentage is: 48.5% Al2O3, 16.3% SiO2, 9.1% Fe2O3, and the rest are impurities; the proportion of particles with a particle size less than 0.074 mm after grinding reaches more than 85%; then add sodium carbonate and limestone according to a soda ratio of 0.3 and a lime ratio of 0.9, and mix the materials; raise the temperature to 1250 °C at a heating rate of 30 °C / min, and keep it at this temperature for 60 minutes, and then cool naturally in the furnace; the obtained clinker has a porous structure, and its phase composition is mainly 2Na2O·3CaO·5Al2O3 and β-2CaO·SiO2, and contains a small amount of CaO·Al2O3.

[0035] Dissolve the obtained clinker with a sodium carbonate solution with a concentration of 40 g / L for alumina extraction. The extraction temperature is 90 °C and the time is 30 min. The alumina extraction rate reaches 92.15%.

[0036] The amount of sodium carbonate added is reduced by 70% compared with the traditional soda-lime sintering method, and the energy consumption in the sintering process is reduced by 9%.

[0037] Example 4

[0038] This example provides a method for extracting alumina from medium- and low-grade aluminum-containing raw materials. The specific operation is as follows:

[0039] Crush and grind a certain mass of high-aluminum fly ash. The chemical composition of this bauxite in terms of mass percentage is: Al2O3 49.2%, SiO2 35.8%, Fe2O3 5.6%, and the rest are impurities; the proportion of particles with a particle size less than 0.074 mm after grinding reaches more than 85%; then add sodium carbonate and limestone according to an alkali ratio of 0.4 and a calcium ratio of 0.8, and mix the materials; raise the temperature to 1200 °C at a heating rate of 25 °C / min, and keep it at this temperature for 30 minutes, and then cool naturally in the furnace; the obtained clinker has a porous structure, and its phase composition is mainly 2Na2O·3CaO·5Al2O3 and β-2CaO·SiO2, and contains a small amount of CaO·Al2O3.

[0040] Dissolve the obtained clinker with a sodium carbonate solution with a concentration of 30 g / L for alumina leaching. The leaching temperature is 70 °C and the time is 20 min, and the alumina leaching rate reaches 84.80%.

[0041] The amount of sodium carbonate added is reduced by 60% compared with the traditional alkali-lime sintering method, and the energy consumption in the sintering process is reduced by 9%.

[0042] The process flow diagrams of Examples 1 to 4 are as Figure 1 shown.

[0043] Comparative Example 1

[0044] This example provides a method for extracting alumina from medium- and low-grade aluminum-containing raw materials. The specific operation is as follows:

[0045] Crush and grind a certain mass of bauxite. The chemical composition of this bauxite in terms of mass percentage is: Al2O3 51.6%, SiO2 18.4%, Fe2O3 9.2%, and the rest are impurities; the proportion of particles with a particle size less than 0.074 mm after grinding reaches more than 85%; then add sodium carbonate and limestone according to an alkali ratio of 0.4 and a calcium ratio of 0.8, and mix the materials; raise the temperature to 1200 °C at a heating rate of 5 °C / min, and keep it at this temperature for 30 minutes, and then cool naturally in the furnace; the obtained clinker hardly shows a porous structure, and its phase composition is mainly 2Na2O·3CaO·5Al2O3 and β-2CaO·SiO2, but compared with the clinker obtained in Example 1, it also contains a larger amount of CaO·Al2O3 and 2CaO·Al2O3·SiO2.

[0046] Dissolve the obtained clinker with a sodium carbonate solution with a concentration of 40 g / L for alumina leaching. The leaching temperature is 80 °C and the time is 30 min, and the alumina leaching rate reaches 85.20%.

[0047] The amount of sodium carbonate added is reduced by 70% compared with the traditional alkali-lime sintering method, and the energy consumption in the sintering process is reduced by 8%.

[0048] Comparative Example 2

[0049] This comparative example provides a method for extracting alumina from medium- and low-grade aluminum-containing raw materials. The specific operation is as follows:

[0050] Crush and grind a certain mass of bauxite. The chemical composition of this bauxite in terms of mass percentage is: Al2O3 51.6%, SiO2 18.4%, Fe2O3 9.2%, and the rest are impurities; the proportion of particles with a particle size less than 0.074 mm after grinding reaches more than 85%; then add limestone according to a calcium ratio of 1.4, with an alkali ratio of 0 and no sodium carbonate added, and mix the materials; increase the temperature to 1350 °C at a heating rate of 10 °C / min and hold at this temperature for 60 minutes, and then cool naturally in the furnace; the obtained clinker has a porous structure, and its phase composition is mainly 12CaO·7Al2O3 and β-2CaO·SiO2, and contains a relatively large amount of CaO·Al2O3.

[0051] Dissolve the obtained clinker with a sodium carbonate solution with a concentration of 100 g / L for alumina extraction. The dissolution temperature is 80 °C and the time is 60 min, and the alumina dissolution rate reaches 86.20%. Sodium carbonate is not added during the sintering process, but the sintering temperature is significantly higher than that of the traditional soda-lime sintering method, resulting in increased energy consumption.

[0052] Comparative Example 3

[0053] This comparative example provides a method for extracting alumina from medium- and low-grade aluminum-containing raw materials. The specific operation is as follows:

[0054] Crush and grind a certain mass of bauxite. The chemical composition of this bauxite in terms of mass percentage is: Al2O3 51.6%, SiO2 18.4%, Fe2O3 9.2%, and the rest are impurities; the proportion of particles with a particle size less than 0.074 mm after grinding reaches more than 85%; then add sodium carbonate and limestone according to an alkali ratio of 1.0 and a calcium ratio of 0.5, and mix the materials; increase the temperature to 1200 °C at a heating rate of 10 °C / min and hold at this temperature for 30 minutes, and then cool naturally in the furnace; the obtained clinker has a porous structure, and its phase composition is mainly Na2O·Al2O3 and β-2CaO·SiO2.

[0055] Dissolve the obtained clinker with a sodium carbonate solution with a concentration of 20 g / L for alumina extraction. The dissolution temperature is 70 °C and the time is 30 min, and the alumina dissolution rate reaches 91.36%. A relatively large amount of sodium carbonate is added during the sintering process, resulting in high energy consumption and easy coking.

[0056] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for extracting alumina from medium- and low-grade aluminum-containing raw materials, characterized in that, Mix medium- and low-grade aluminum-containing raw materials with sodium carbonate and calcium carbonate, sinter them to obtain clinker, and then leach alumina from the clinker to obtain the product. Calculate the aluminum element in the aluminum-containing raw material as alumina and the silicon element as silicon dioxide. The molar ratio of the sodium carbonate to the alumina is 0.3 - 0.5, and the molar ratio of the calcium carbonate to the sum of the molar numbers of the alumina and silicon dioxide is 0.7 - 0.9; The sintering temperature is 1100 - 1250 °C; The heat preservation time after sintering to the above temperature is 15 - 60 min; The heating rate of the sintering is 15 - 30 °C / min; Leach alumina from the clinker with a sodium carbonate solution with a concentration of 20 - 40 g / L; The leaching temperature is 50 - 90 °C.

2. The method for extracting alumina from medium- and low-grade aluminum-containing raw materials according to claim 1, characterized in that, The molar ratio of the sodium carbonate to the alumina is 0.4, and the molar ratio of the calcium carbonate to the sum of the molar numbers of the alumina and silicon dioxide is 0.

8.

3. The method for extracting alumina from medium- and low-grade aluminum-containing raw materials according to claim 1, wherein The cooling system after sintering is natural cooling in the furnace.

4. The method for extracting alumina from medium- and low-grade aluminum-containing raw materials according to claim 1, characterized in that, Use the heat generated by sintering to heat the sodium carbonate solution.

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