RU2552414C2 - Production of alumina - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to production of alumina from man-made wastes, particularly, from mineral part of brown coal combustion ash. Charge is prepared by mixing of ash-slag wastes of thermal power plants and limestone taken in exceeds of 28.0-75.0% of stoichiometric amount and, thereafter, sintered. Obtained cake is leached at mixing to get cake pulp and desilicated by calcareous milk and filtered to obtain slime and filtrate. Slime is flushed and carbonized by CO₂-bearing gas-air mix to filter produced hydrate pulp to get aluminium hydroxide and mother soda solution recycled for cake leaching. Cake leaching is conducted by carbonate solution containing at least 52.0 g/dm³ of Na₂CO₃ at 75-80°C. At aluminium oxide leaching from cake, additional primary vibro-cavitation processing is performed. At desilicating of cake pulp by calcareous milk vibro-cavitation processing is reiterated.

EFFECT: higher yield and quality of aluminium oxide.

4 tbl

Description

The invention relates to a technology for producing alumina from alumina-containing industrial wastes, in particular from the mineral part of ash from slag burning of brown coal, and can be used for the needs of the aluminum, metallurgical and construction industries.

There is a method of processing energy coal ash into alumina and gypsum by calcining with a calcium compound and treating the cake with sulfuric acid, with calcium fluoride (CaF ₂ ) being used as a calcium compound, sulfuric acid treatment (sulfatization) is carried out at a temperature of 180-200 ° C, after treatment with sulfuric acid, sintering is carried out at a temperature of 200-300 ° C with a vacuum of 0.2-0.3 gc / cm ² with removal of the resulting gases, at a temperature of 120-150 ° C, followed by their processing with an ammonia solution and leaching of cake (Patent RU No. 2027669, 1995).

This method of processing steam coal ash does not provide their complex processing, is associated with the use of aggressive chemicals, i.e. It is an environmentally hazardous production and, in addition, the process is the dissolution of silicon oxide with the formation of silica gel, which makes it impossible for the subsequent process of separation of the resulting aluminate solution by filtration.

A known method for the integrated production of alumina and Portland cement from non-bauxite raw materials: brown coal ash and / or charred coal shale containing 30-40% Al ₂ O ₃ . The method consists in firing data of technogenic alumina-containing materials with limestone (52-53% CaO) at a dosage of the latter, based on the general stoichiometric ratio

CaO / Al ₂ O ₃ = 1.0 ± 0.05 and CaO / SiO ₂ = 2.0 ± 0.05

at a temperature of 1250 ° C to obtain a self-scattering cake, agitation leaching of aluminum oxide from the cake with soda solutions, filtering the leached pulp to obtain an aluminate solution and a "gray" sludge, 2-stage (the first stage is autoclaved at a temperature of 170-180 ° C, 2nd stage - in mixers at a temperature of 90-100 ° C), desalination of the aluminate solution with lime milk, filtration of the pulp to obtain a “whitened” sludge and a desilinated solution (the value of the _silicon modulus µ _Si = C _Al2O3 / C _SiO2 ≥1000, which is further carbonize flue gas CO ₂ -containing gases of sintering furnaces, are additionally fired to obtain a cement clinker containing mainly tricalcium silicate 3CaO · SiO ₂ [Goldstein L.Ya. - Complex methods for the production of cement. - Leningrad, "Stroyizdat", 1985 , p. 101-103].

Significant disadvantages of this method include, first of all, the complexity (multi-stage) of the technological scheme, which is expressed in the separation of the leaching of cake and desalination of the aluminate solution (with intermediate filtration) with milk of lime, which leads to additional losses of aluminum oxide and, therefore, insufficient through extraction of aluminum oxide the target product is alumina, comprising 83-85%.

The closest is a method for producing alumina from ash and slag of a thermal power plant, consisting of preparing and correcting a mixture for sintering, consisting of ash and slag of a thermal power plant and limestone, which in this case is taken in excess of 28.0-75.0% of the stoichiometric amount; sintering the mixture at a temperature of 1320-1400 ° C for 40-60 minutes to obtain a self-scattering cake; leaching cake with a reverse soda solution containing at least 5.0% Na ₂ CO ₃ at a temperature of 75-80 ° C for 6-8 hours; additional desiliconization of the heterophasic product (cake pulp after leaching) with milk of lime containing 10.0% Ca (OH) ₂ , at a flow rate of at least 0.10-0.20 dm ³ / dm ³ pulps, followed by filtration, washing the final sludge with water combining the promoter and the filtrate to obtain a silicified aluminate solution; carbonization of an aluminate solution with a CO ₂ -containing air-gas mixture to obtain aluminum hydroxide and a mother liquor, which is returned to the leaching of cake; calcining aluminum hydroxide to obtain the desired alumina product (patent RU No. 2200708, 2003). The sludge formed after leaching of cake in the form of dicalcium and tricalcium silicates is used to produce cement. In this case, metallurgical alumina of grade G3, GK according to GOST 6912-74 is obtained (the content of limiting impurities is as follows, wt.%: 0.040 Fe ₂ O ₃ and 0.13 SiO ₂ ), the through degree of extraction of aluminum oxide in the target product (from the content in the original ash) is 84-87%.

The known method is characterized by insufficient, on average, the degree of extraction of aluminum oxide in the target product and the insufficient quality of the obtained alumina for the production of aluminum of grade not less than A0 and higher.

The basis of the claimed invention is the task of developing a method for producing alumina from ash from burning brown coal, which ensures the achievement of a technical result - increasing the degree of through extraction of aluminum oxide in the target product while improving the quality of the obtained alumina.

The achievement of the above technical result is ensured by the fact that in the proposed method for producing alumina, the mineral part is used the mineral part of the brown coal burning ash with the preparation of the mixture by mixing it with limestone, which is taken in excess of 28.0-75.0% of the stoichiometric amount, sintering of the mixture with obtaining cake, leaching of alumina from cake with soda solution with stirring to obtain cake pulp and desalination with milk of lime, filtering cake cake with sludge and the filtrate, washing the sludge, combining the slurry and the filtrate to obtain an aluminate solution, carbonizing the latter with a CO ₂ -containing gas-air mixture, filtering the resulting hydrated pulp to obtain aluminum hydroxide and a mother liquor, turning to leach cake, calcining aluminum hydroxide to obtain alumina, when leaching aluminum oxide from the cake, primary vibrocavitation treatment is additionally carried out for 15-35 minutes at a peripheral speed of 30-55 m / s, and at Sintering of sinter pulp with lime milk results in repeated vibro-cavitation treatment for 20-30 minutes at a peripheral speed of 25-35 m / s.

Leaching of alumina from the cake is preferably carried out with a carbonate solution containing at least 52.0 g / dm ³ Na ₂ CO ₃ (5.0% solution) and providing a 25.0% molar excess of Na ₂ CO ₃ : Al ₂ O ₃ according to stoichiometry at a temperature of 75-80 ° C, the ratio T: W = 1.0: 4.0 and the duration of 5-6 hours. The primary vibrocavitation treatment of cake pulp is carried out at peripheral speeds with stirring of 30-55 m / s and a duration of 15-35 minutes.

After at least ¾ time duration of the leaching process, sintering of sinter pulp with lime milk is carried out, preferably containing at least 10.0 wt.% Ca (OH) ₂ , at a dosage of 0.10 dm ³ / dm ³ pulp, temperature 80 ° C, duration 1.25-1.5 hours. Repeated vibro-cavitation treatment of cake pulp at a peripheral speed (ω) of 25-35 m / s and a duration of 20-30 minutes.

Cavitation is a physicochemical process, which consists, in particular, in violation of the continuity of the liquid (in our case, it is a water-salt solution), associated with the formation and subsequent “collapse” of air (gas) microbubbles in the liquid. The energy of collapsing bubbles is spent, in particular, on the emission of shock waves, which, in turn, significantly intensifies mass transfer processes, and in each case (a specific solid-liquid heterophase system) there is a certain threshold value.

The implementation of the primary vibrocavitation treatment with soda leaching of aluminum oxide from the cake contributes, with other things comparable to the prototype, process parameters, increase the degree of extraction of Al ₂ O ₃ , on average, from 85.5% (prototype) to 87.5% , i.e. by 2.0%.

Repeated (final) vibro-cavitation treatment of cake pulp during desalination with lime milk helps to increase the value of the _silicon module (μ _Si ) of the resulting aluminate solution to μ _Si ≥1500, which, in the future, provides the target product - alumina, with a reduced content of limiting impurities, masses .%: 0.03 Fe ₂ O ₃ , 0.06 SiO ₂ (the prototype has 0.04% and 0.13%, respectively), i.e. at the level of brand F1 according to GOST 6912-74.

A method of obtaining alumina from the mineral part of the ash burning brown coal was carried out as follows.

The implementation of the proposed method is carried out in laboratory conditions. The raw materials used were the burning ash of Ekibastuz brown coal from the Reftinskaya CHPP, which has the following average chemical composition, wt.%: 55.0 SiO ₂ , 37.0 Al ₂ O ₃ , 3.0 Fe ₂ O ₃ , 2.50 TiO ₂ , 1.0 MgO, 1.0 CaO, 0.5 impurities. The phase composition of ash and slag, wt.%: 52.0 mullite (3Al ₂ O ₃ · 2SiO ₂ ), 25.0 α-quartz (SiO ₂ ) 8.0 kaolinite - Al ₂ Si ₂ O ₅ (OH) ₄ , 6, 0 titanium carbide (TiS ₂ ), 3.0 phase Mg ₂ Ca, the rest is impurities.

The weight of ash and slag in all experiments was 1.0 kg.

The dosage of limestone (CaO - 52.0 ÷ 53.0%), ground to a fraction - 45 μm, was made in the range of 28.0-75.0% in excess of the total stoichiometric ratio, including the following characteristic molar ratios:

CaO / Al ₂ O ₃ = 1.0 ± 0.05 and CaO / (SiO ₂ + Fe ₂ O ₃ + TiO ₂ ) = 2.0 ± 0.05.

Sintering was carried out in a laboratory tube furnace at temperatures of 1320-1400 ° C for 40-60 minutes depending on the dosage of limestone (calcium oxide) to obtain self-scattering cake (fraction content - 45 μm 100%).

Leaching of cake containing 11.8-14.5% Al ₂ O ₃ was carried out with a soda solution containing 52.0 ± 0.5 g / dm ³ Na ₂ CO ₃ ; other technological process parameters: temperature 80 ° C, T: W ratio in the initial pulp 1.0: 4.0, duration 5-6 hours depending on the intensity of vibro-cavitation treatment. The primary vibrocavitation treatment of cake pulp is carried out at peripheral speeds with stirring of 30-55 m / s and a duration of 15-35 minutes.

After at least ¾ of the total time duration of the leaching process, sintering of sinter pulp with lime milk was carried out at constant (in all experiments) technological parameters: the concentration of Ca (OH) ₂ in lime milk was 10.0%; dosage of 0.10 dm ³ / dm ³ pulps; temperature 80 ° C; duration 1.25-1.50 hours; repeated vibrocavitation treatment of the siliconized pulp at the value of the peripheral rotor speed (ω) of 25-35 m / s and the duration of 20-30 minutes.

The combined process “leaching + desiliconization” was carried out in a laboratory setup consisting of a mixer (V = 5.0 dm ³ ) with mechanical stirring and a vibro-cavitation mill combined with it in a closed loop (V = 5.0 dm ³ ), with a rotating rotor ⌀ = 100 mm in a fixed slit-like stator (the gap between the rotor and stator is 0.5 mm).

In the main mixer, a cake pulp is prepared, consisting of cake and soda solution, then it is driven in a closed loop “leaching mixer + vibro-cavitation mill” during the claimed time interval and at the claimed peripheral rotor speed (vibro-cavitation processing mode), i.e. At the same time, the process of primary vibration cavitation treatment and soda leaching of Al ₂ O ₃ from the cake are carried out. At the end of the vibro-cavitation treatment process, the mill is temporarily turned off and then only the main leaching process is carried out.

Similarly, the process of desalinization of the leached cakes is carried out with lime milk.

In the process of "leaching + desiliconization" on an industrial scale, vibrocavitation treatment can be carried out, for example, by commercially available rotary pulsation apparatuses (RPA) with obtaining the claimed technical result.

Upon completion of the leaching and desiliconization of the cake pulp, it was filtered to obtain sludge and filtrate. Filtration is carried out by any known methods.

The resulting slurry is washed with water, preferably washed with water at a rate of 1.5 dm ³ / kg. The obtained promoter is combined with the filtrate to obtain an aluminate solution, which is carbonized with a CO ₂ -containing air-gas mixture. CO _{2 is} supplied from the cylinder to the mixer (carbonizer), preferably with the following parameters: temperature 70 ° C; aeration rate - 4.0 ndm ³ / dm ^{3 of} solution per hour (under normal conditions); duration - 6.0 hours; the final pH is 8.50. The resulting hydrated pulp is subjected to filtration with the release of aluminum hydroxide and mother liquor soda solution, which is then used to leach cake. Calcination of aluminum hydroxide to obtain alumina is preferably carried out at a temperature of 1200 ° C for 2.0 hours.

The inventive method is illustrated by examples of specific performance.

Example 1. Sintering of ash and slag of the Reftinskaya TPP in the amount of 1.0 kg and a dosage of limestone in the amount of 2.94 kg (excess 28.0% by stoichiometry) at a temperature of 1350 ° C and a duration of 60 minutes

The obtained cake in the amount of 2.56 kg, containing 14.50% Al ₂ O ₃ , is leached with a soda solution, followed by desalination with milk of lime in vibro-cavitation mode under various technological conditions.

Table 1 shows the results obtained on the influence of the parameters of vibro-cavitation treatment on the degree of extraction of aluminum oxide from the cake - according to the claimed invention, as well as when going beyond the optimal limits of the parameters.

As can be seen from table 1, the claimed conditions for the primary vibrocavitation treatment of cake pulp at the stage of soda leaching: the value of the peripheral speed of 30-40 m / s and the duration of 15-20 minutes leads to the achievement of the claimed technical result when preparing the mixture with an excess of limestone of 28% against stoichiometric values.

Example 2. Sintering a mixture consisting of 1.0 kg of ash and slag of the Reftinskaya CHPP and 3.50 kg of limestone (55.0% of the stoichiometric ratio) at a temperature of 1320 ° C for 60 minutes.

The obtained cake in the amount of 2.85 kg, containing 13.0% Al ₂ O ₃ , is leached with a soda solution, followed by desalination with milk of lime in vibro-cavitation mode under the above technological conditions.

Table 2 shows the results on the influence of the parameters of vibro-cavitation treatment on the degree of extraction of Al ₂ O ₃ from the cake - according to the claimed invention, and when going beyond the optimal limits of the parameters.

As can be seen from table 2, the claimed conditions for the primary vibrocavitation treatment of cake pulp at the stage of soda leaching: the value of the peripheral speed of 35-45 m / s and the duration of 20-30 minutes leads to the achievement of the claimed technical result when preparing the mixture with an excess of limestone 55% against the stoichiometric value .

Example 3. Sintering of a mixture consisting of 1.0 kg of ash and slag of the Reftinskaya TPP and 4.0 kg of limestone (75.0% of the stoichiometric ratio) at a temperature of 1400 ° C for 40 minutes is carried out.

The obtained sinter in the amount of 3.15 kg, containing 11.75% Al ₂ O ₃ , is leached with a soda solution, followed by desalination with milk of lime in vibro-cavitation mode under the above technological conditions.

Table 3 shows the results on the influence of the parameters of vibro-cavitation treatment on the degree of extraction of Al ₂ O ₃ from the cake - according to the claimed invention, and when going beyond the optimal limits of the parameters.

As can be seen from table 3, the given example of a specific implementation confirms the validity of the stated conditions of the primary vibro-cavitation treatment at the stage of leaching the cake pulp obtained from a charge with an excess of limestone of 75.0% of the stoichiometric amount: the value of the peripheral speed is 40-55 m / s; the duration of 20-30 minutes, which ensure the achievement of the claimed technical result.

From the presented examples of specific performance it can be seen that going beyond the claimed intervals of the regimes of primary vibro-cavitation treatment of cake pulp during soda leaching to the lower side:

- at a dosage of limestone of 28.0% in excess of stoichiometric (Table 1) - values of the peripheral speed of 20-25 m / s (op.6, 7) and / or the processing time of 10 min (op.8, 10, 12);

- at a dosage of limestone of 55.0% in excess of stoichiometric (Table 2) - values of the peripheral speed of 25-30 m / s (op.6, 7) and / or processing time of 15 min (op.8, 10, 12);

- when the dosage of limestone is 75.0% in excess of stoichiometric (Table 3), the values of the peripheral speed are 30-35 m / s (op.6, 7) and / or the processing time is 10-15 min (op.8, 9, 10, eleven);

does not lead to the achievement of the claimed technical result, because the average value of the degree of extraction of aluminum oxide is 1.0-1.5% less than the corresponding values of the prototype (respectively 84.0, 86.0 and 87.0%). This is explained by the fact that in the diffusion process of leaching alumina from porous cakes, having a dosage of calcium-containing material in excess of the stoichiometric ratio with a significant coefficient, a sufficiently dense microstructure (porosity of 40-50% relative to ~ 60% with standard 5.0-10.0% - the dosage of limestone in excess of the stoichiometric ratio) the combination of the above technological parameters of vibro-cavitation treatment - the value of the peripheral speed and duration - has a lower threshold value, it necessary to intensify the main limiting step diffusion process: the chemical interaction with calcium aluminate soda solution.

When going beyond the claimed intervals of the regimes of primary vibro-cavitation treatment of pulp during soda leaching upwards:

- at a dosage of limestone of 28.0% in excess of stoichiometric (Table 1) - values of the peripheral speed of 50 m / s (op. 12, 13) and / or the processing time of 35 minutes (op. 6);

- at a dosage of limestone of 55.0% (Table 2) - values of the peripheral speed of 55-60 m / s (op.13, 14);

- at a dosage of limestone of 75.0% in excess of stoichiometric (table 3) - values of the peripheral speed of 60 m / s (op.14),

does not lead to the achievement of the claimed technical result, because the average value of the degree of extraction of aluminum oxide from the cake is either less than ~ 0.5%, or is practically at the same level as that of the prototype (84.0: 86.0 and 87.0%, respectively). This is explained by the fact that, ceteris paribus leaching (temperature, concentration of Na ₂ CO ₃ , duration) at the super-energy intensity of intensive vibro-cavitation treatment is a set of technological parameters: - the value of the peripheral speed and duration - there is a certain over-grinding of cake, i.e. the geometrical dimensions of the sinter pores (“tubules”) decrease and the following stages of the diffusion process of leaching of aluminum oxide slow down:

- penetration of the solvent (sodium carbonate) inside the porous skeleton of the sinter particle to the surface of the solute (calcium aluminate);

- removal of the reaction product (sodium aluminate) from the dissolution boundary to the surface of the sinter particle.

We also note that the duration of the combined process of "leaching + desiliconization" at all dosages of limestone for sintering is 5–6 hours (for the prototype 6–8 hours), i.e. vibration-cavitation treatment allows to reduce the duration of the process as a whole by an average of 1.5 hours as a result of, as noted, the intensification of mass transfer processes.

The duration of 4.0 hours (tab. 1 - op. 10, 13; tab. 2 - op. 11, 13 and tab. 3 - op. 13) is insufficient: the degree of extraction of Al ₂ O ₃ from the cake is, on average, , less by 0.5-0.7% than the prototype.

This is primarily due to the incompleteness of the limiting stage, the diffusion process of leaching Al ₂ O ₃ from the cake: the chemical interaction of calcium aluminate with sodium carbonate.

Example 4. Sintering a mixture consisting of 1.0 kg of ash and slag of the Reftinskaya CHPP and 3.50 kg of limestone (55.0% of the stoichiometric ratio) at a temperature of 1320 ° C for 60 minutes.

The obtained cake in an amount of 2.85 kg, containing 13.0% Al ₂ O ₃ , is leached with a soda solution under the following technological conditions: concentration of Na ₂ CO ₃ - 52.0 ± 0.5 g / dm ³ ; the ratio of T: W in the original cake pulp 1.0: 4.0; temperature 80 ° C; primary vibrocavitation treatment of cake pulp is carried out at a value of the peripheral rotor speed (ω) of 50 m / s and a duration of 20 minutes; total leaching time 5.0 hours

After 3.50 hours of soda leaching, the calcined pulp is desalted with lime milk under the following technological conditions: the concentration of Ca (OH) ₂ in the milk of lime is 10.0%; dosage of milk of lime 0.10 dm ³ / dm ³ pulp; temperature 80 ° C; duration of desalination 1.5 hours; repeated vibrocavitation treatment of siliceous pulp is carried out simultaneously with the input of milk of lime; after the general end of the process, the pulp is filtered to obtain the final slurry and siliceous aluminate solution.

After the general end of the process, the pulp is filtered to obtain the final "calcium-silicate" sludge and siliceous aluminate solution.

The resulting siliceous aluminate solutions were further subjected to carbonization with carbon dioxide (CO ₂ ) gas supplied to the mixer (carbonizer) from a cylinder at a temperature of 70 ° C; aeration rate - 4.0 ndm ³ / dm ^{3 of} solution per hour (under normal conditions); duration - 6.0 hours; the final pH is 8.50. Next, the hydrated pulps were filtered and the obtained precipitation of aluminum hydroxide (hereinafter - GOA) was dried at a temperature of 120 ° C for 2 hours and analyzed for the content of limiting impurity components: SiO ₂ and Fe ₂ O ₃ .

Table 4 shows the results of experiments on the influence of the parameters of vibro-cavitation treatment — the value of the peripheral speed and duration — on the value of the silicon modulus (the ratio of the concentrations of Al ₂ O ₃ and SiO ₂ ) in the solution obtained by silicon-free aluminate and on the content of impurity components in GOA sediments during subsequent carbonization .

The given example of a specific implementation confirms the validity of the stated conditions of vibro-cavitation treatment during desalination of cake pulp: the value of the peripheral speed is 25-35 m / s; duration 20-30 minutes

Moreover, the average value of μ _Si is ~ 1500 units. relative to µ _Si ~ 1100 in the prototype, and the average content of impurity components, mass. %: 0,055 SiO ₂ and 0,022 Fe ₂ O ₃ - relative to those of the prototype: 0,090% SiO ₂ and 0,027% Fe ₂ O ₃ , i.e. the decrease in the content of impurity components is, on average, ~ 39.0% and ~ 19.0%, respectively.

If you go beyond the declared limits of the parameters to a lower side - according to the value of the peripheral speed and / or duration of vibration cavitation treatment (op. 5, 6 and 8) - while maintaining a sufficiently high degree of extraction of aluminum oxide from the cake for the combined process "leaching = desilicon" at 87.43%, i.e. 1.43% more than in the prototype (µAl ₂ O ₃ = 86.0%), but the value of the _silicon module (µ _Si ) does not exceed the average value of 1040 units, i.e. almost on par with the prototype (µ _Si ~ 1100). This, in turn, determines the content of impurity components in GOA sediments at an average level of 0.095% SiO ₂ and 0.031% Fe ₂ O ₃ . Thus, it is not possible to improve the quality of the target product (alumina) by reducing the content of impurity components in it.

This is explained by the fact that the values of the parameters of vibro-cavitation treatment: the value of the peripheral speed of 20 m / s (op. 5) or the duration of the processing of 15 min (op. 6 and 8) are in aggregate less than the minimum threshold value for intensification of the process of desalination in vibro-cavitation mode.

When going beyond the declared limits of the parameters, the peripheral speed is 45 m / s (op. 9) and / or the processing time is 40 min (op. 7), the aluminate solution is deeply desalted: μ _Si is 1750-1850 units. (in the prototype, respectively, 1100) and, accordingly, the content of impurity components in GOA precipitates decreases to an average value of ~ 0.048% SiO ₂ and 0.020% Fe ₂ O ₃ (in the prototype, respectively, 0.090% SiO ₂ and 0.027% Fe ₂ O ₃ ) - however, the degree extraction of alumina from the cake is, on average, 85.8%, i.e. less than the prototype.

Example 5. Sintering of a mixture consisting of 1.0 kg of ash and slag of the Reftinskaya TPP and 3.50 kg of limestone (55.0% of the stoichiometric ratio) at a temperature of 1320 ° C for 60 minutes is carried out.

The obtained cake in the amount of 2.85 kg, containing 13.0% Al ₂ O ₃ , is leached with a soda solution under the following technological conditions: the concentration of Na ₂ CO ₃ is 52.0 ± 0.5 g / dm ³ (5.0% - solution); the ratio of T: W in the original cake pulp 1.0: 4.0; temperature 80 ° C; primary vibrocavitation treatment of cake pulp with the following constant parameters: the value of the peripheral speed of the rotor (ω) 50 m / s and the duration of 20 minutes; total leaching time 5.0 hours

Then, after 3.50 hours of soda leaching, the caking pulp is desalted with lime milk containing 10.0% Ca (OH) ₂ at a dosage of 0.10 dm ³ / dm ^{3 of} pulp and repeated vibro-cavitation treatment at a peripheral speed of 35 m / s and duration of 20 minutes with the simultaneous introduction of milk of lime.

After completion of the combined leaching + desiliconization process, the pulp is filtered, the final sludge in the amount of 2.60 kg is washed with water at the rate of 1.5 dm ³ / kg, the washer is combined with the filtrate and the resulting silicified aluminate solution (V ~ 15.0 dm ³ ) goes to carbonization.

An aluminate solution containing, g / dm ³ : 22.5 Na ₂ O _total , 18.5 Na ₂ O _cr , 22.0 Al ₂ O ₃ , α _cr = 1.40, 0.015 SiO ₂ , 0.01 Fe ₂ O ₃ , μ _Si ≥1500, pH 12.0 - is subjected to carbonization with carbon dioxide (CO ₂ ) gas supplied to the mixer (carbonizer) from a cylinder at the following specified process parameters: temperature 70 ° C; aeration rate - 4.0 ndm ³ / dm ^{3 of} solution per hour (under normal conditions); duration - 6.0 hours; the final pH is 8.50.

The control of the completeness of precipitation of aluminum hydroxide is additionally determined by the absence of turbidity (precipitation) in the filtered sample of the mother liquor by adding a 2.0% hydrochloric acid solution.

Next, the hydrated pulp was filtered and the resulting aluminum hydroxide (after drying at 120 ° C for 2 hours) was analyzed for the content of limiting impurities.

The impurity content is as follows,%: 0.23 Na ₂ O, 0.04 SiO ₂ , 0.020 Fe ₂ O ₃ .

The recovery of Al ₂ O ₃ in aluminum hydroxide during carbonization was 99.0%.

Next, the resulting aluminum hydroxide was calcined at a temperature of 1200 ° C for 2.0 hours.

The impurity content in the obtained target product — alumina — was as follows,%: 0.35 Na ₂ O, 0.06 SiO ₂ , 0.03 Fe ₂ O ₃ .

The obtained alumina in accordance with GOST 6912-74 corresponds to grade G1.

Thus, the sintering of the mineral part of the brown coal ash with limestone, introduced into the mixture with 28.0-75.0% excess from stoichiometry, leaching of the cake with a solution of sodium carbonate and primary vibro-cavitation treatment of cake pulp at a peripheral speed of 30-55 m / s for 15-35 min, desiliconization of cake pulp with lime milk and repeated vibrocavitation treatment of desiliconized pulp at peripheral speeds of 25-35 m / s for - 20-30 min, filtering the pulp to obtain the final slurry and skim belt aluminate solution, carbonization of the latter with a CO ₂ -containing gas, filtration and calcination of the extracted aluminum hydroxide, provide an implementation of the method for producing alumina with the achievement of the claimed technical result: increasing the degree of through extraction of aluminum oxide to an average of 87.5% (respectively, in the prototype 85.5%), i.e. an increase of ~ 2.0% and an increase in the quality of the obtained target product — alumina, with a reduced content of limiting impurities, wt.%: 0.03 Fe ₂ O ₃ , 0.06 SiO ₂ (the prototype has 0.04 and 0.130, respectively), which corresponds to grade G1 .

In addition, the primary vibration cavitation treatment during the leaching process and the repeated vibration cavitation treatment during the desilination of the cake pulp significantly reduce (by an average of 1.5 hours) the duration of the cake leaching process.

The specific modes of sinter leaching indicated in the description and examples of a specific implementation are made with a sodium carbonate solution containing at least 52.0 g / dm ³ Na ₂ CO ₃ (5.0% solution), at a temperature of 80 ° C, T: W ratio, equal to 1.0: 4.0, with a total duration of 5 ÷ 6 hours and regimes of desalination of cake pulp with milk of lime containing 10.0 wt.% Ca (OH) ₂ , at a dosage of the latter not less than 0.10 dm ³ / dm ³ pulps during the last 1.25-1.50 hours of the overall process, provide optimal parameters of the proposed method, allowing to obtain the highest possible technical effect with minimum raw material and energy costs.

Table 1 The results of the leaching of cake in vibrocavitation mode with a dosage of limestone of 28.0% in excess of the stoichiometric ratio No. p / p Process parameters The degree of extraction of Al ₂ O ₃ from cake,% The value of the peripheral speed (ω), m / s Processing time, min Leaching time, h According to the prototype 84.0 Optimal parameter limits one thirty 25 6.0 85.0 2 35 twenty 6.0 85.5 3 35 thirty 5,0 86.0 four 40 fifteen 6.0 86.5 5 40 25 5,0 86.5 When going beyond optimal limits 6 twenty 35 4.0 83.0 7 25 25 6.0 83.7 8 thirty 10 7.0 83.3 9 35 fifteen 6.0 84.2 10 40 fifteen 4.0 83.5 eleven 40 10 6.0 84.0 12 fifty 10 6.0 84.3 13 fifty twenty 4.0 83.7

table 2 The results of the leaching of cake in vibrocavitation mode with a dosage of limestone 55.0% in excess of the stoichiometric ratio No. p / p Process parameters The degree of extraction of Al ₂ O ₃ from cake,% The value of the peripheral speed (ω), m / s Processing time, min Leaching time, h According to the prototype 86.0 Optimal parameter limits one 35 twenty 6.0 86.7 2 35 25 6.0 87.0 3 40 thirty 5,0 87.0 four 45 thirty 5,0 87.5 5 fifty twenty 6.0 88.0 When going beyond optimal limits 6 25 25 5,0 84.5 7 thirty 25 6.0 85.5 8 35 fifteen 6.0 85.7 9 35 twenty 5,0 85.0 10 40 fifteen 6.0 85.0 eleven 45 thirty 4.0 85.6 12 55 fifteen 6.0 86.0 13 fifty thirty 4.0 85.5 fourteen 60 twenty 5,0 86.5

Table 3 The results of the leaching of cake in vibro-cavitation mode with a dosage of limestone 75.0% in excess of the stoichiometric ratio No. p / p Process parameters The degree of extraction of Al ₂ O ₃ from cake,% The value of the peripheral speed (ω), m / s Processing time, min Leaching time, h According to the prototype 87.0 Optimal parameter limits one 40 twenty 6.0 87.7 2 45 25 5,0 87.5 3 fifty twenty 6.0 88.0 four fifty thirty 5,0 88.5 5 55 twenty 5,0 88.7 When going beyond optimal limits 6 thirty twenty 5,0 85.8 7 35 25 6.0 86.5 8 40 10 6.0 85.7 9 40 fifteen 6.0 86.0 10 45 fifteen 6.0 86.6 eleven fifty fifteen 5,0 87.0 12 55 10 6.0 86.6 13 55 twenty 4.0 86.0 fourteen 60 thirty 7.0 87.5

Claims (1)

A method of producing alumina, including the preparation of a mixture by mixing ash and slag waste from a thermal power plant and limestone, which are taken in excess of 28.0-75.0% of the stoichiometric amount, sintering the mixture to obtain a cake, leaching aluminum oxide from cake with a soda solution with stirring to obtain cake cake and its desiliconization lime milk, filtering spekovoy slurry to prepare a slurry and filtrate, washing the slurry association promvody and filtrate to give aluminate solution, CO ₂ carbonization last -soderzhasche the air-gas mixture, filtering the resultant slurry to obtain a hydrate of aluminum hydroxide and mother soda solution, turns on the leach cake, calcination of aluminum hydroxide to obtain the alumina, characterized in that the leaching of lead carbonate cake with a solution containing not less than 52.0 g / dm ³ of Na ₂ CO ₃ at a temperature of 75-80 ° C, against T: M of 1.0: 4.0, with a total duration of the process is 5 ÷ 6 hours, and during the leaching of alumina cake additionally carried vibrokavitatsionnuyu primary processing Techa s 15-35 minutes at values of the circumferential speed of 30-55 m / s, lead desiliconization spekovoy pulp with lime milk comprising 10.0% of Ca (OH) _2, at a flow rate of 0.10 dm ³ / dm ³ slurry and the duration 1.25 ÷ 4.5 hours, and when the caking pulp is desilinated with lime milk, repeated vibro-cavitation treatment is carried out for 20-30 minutes at a peripheral speed of 25-35 m / s.