RU2835414C1 - Method for hydrochemical treatment of calcium silicate sludge - Google Patents

Abstract

FIELD: performing operations.

SUBSTANCE: invention relates to the technology of producing alumina by sintering during processing of aluminosilicates, including alkali-free aluminosilicates to obtain alumina and calcium silicate sludge, which needs additional processing to ensure the effect of complex use of the raw material. Method of hydrochemical treatment of calcium silicate sludge includes its division into two parts. One part is subjected to hydrochemical treatment by exposing the sludge to carbon dioxide in an aqueous medium at temperature of 25 to 95 °C, lasting from 2 to 6 hours and subsequent treatment with an alkaline solution. Further, it is mixed with the second part of the calcium silicate slurry until the composition of the crude mixture required for obtaining alite clinker is achieved. Raw material used is calcium silicate sludge containing γ-Ca₂SiO₄. One part is repulped with water to the ratio of liquid and solid components from 6/1 to 10/1. Hydrochemical treatment is carried out with a gas-air mixture with volume content of CO₂ from 15 to 50%.

EFFECT: higher efficiency of complex processing of kaolinite ores.

1 cl, 2 dwg, 1 tbl, 13 ex

Description

The invention relates to a technology for producing alumina by sintering during the processing of aluminosilicates, including alkali-free aluminosilicates, to obtain alumina and silicate-calcium sludge, which requires additional processing to ensure the effect of complex use of raw materials.

A method for the complex processing of nepheline raw materials is known (Layner A.I., Eremin N.I., Layner Yu.A., Pevzner I.Z. Alumina Production. Moscow: Metallurgy, 1978. pp. 184-192), the essence of which lies in the sintering of limestone-nepheline batch, leaching of the sinter to obtain an aluminate solution intended for the extraction of aluminum hydroxide, and nepheline sludge, which is used for the production of Portland cement.

The disadvantage of the method is the increased content of alkaline components in nepheline sludge and the need for complete utilization of sludge in the production of Portland cement to achieve the effect of complex waste-free processing of the original raw materials, which necessitates the introduction of an additional amount of lime component, such as limestone, and clearly determines the ratio of the main and by-products.

A method for processing alkali-free aluminosilicate raw materials is known (Layner A.I., Eremin N.I., Layner Yu.A., Pevzner I.Z. Alumina Production. Moscow: Metallurgy, 1978. pp. 317-319), which includes sintering a two-component limestone-aluminosilicate batch, leaching the sinter to obtain an aluminate solution intended for the extraction of aluminum hydroxide, and silicate-calcium sludge, which is used to produce Portland cement.

The disadvantage of this method is the need to introduce an additional amount of lime component, which clearly determines the yield of by-products for the utilization of the entire volume of silicate-calcium sludge in the production of alumina from kaolin raw materials.

A method of hydrochemical alkaline treatment of nepheline sludge containing β-2CaO SiO ₂ as the main component is known (Abramov V.Ya., Alekseev A.I., Badal'yants Kh.A. Complex processing of nepheline-apatite raw materials. Moscow: Metallurgy, 1990. Pp. 219-220), the essence of which lies in the treatment of nepheline sludge with a NaOH solution at a temperature of 95°C in order to form active decomposition products of the original dicalcium silicate.

The disadvantage of this method is the need for multi-stage washing of the treated sludge from alkali, while its content in the sludge remains at an unacceptably high level, as well as the achievement of relatively low indicators for the degree of conversion.

A method for hydrochemical treatment of nepheline sludge is known (author's certificate SU No. 1189833, published 07.11.1985), according to which the sludge is treated with a soda solution with a concentration of _{Na2CO3 of} 430 - 450 g/l with a ratio of liquid to solid in the pulp equal to (14.5-15):1.

The disadvantage of this method is the need for multi-stage washing of the treated sludge from alkali, while its content in the sludge remains at an unacceptably high level, as well as the achievement of relatively low indicators for the degree of conversion.

A method of hydrochemical treatment of nepheline sludge is known (author's certificate SU No. 981274, published on 17.12.1982), in which nepheline sludge is treated with a potash-soda solution with a concentration of Na ₂ CO ₃ 90-120 g / l, K ₂ CO ₃ 20-90 g / l. As in the previously considered analogs, this method is distinguished by a large number of technological operations necessary for separating the soda-silicate solution, its regeneration, washing the nepheline sludge and recycling the wash water.

The disadvantage of this method is the relatively low conversion rates and the preservation of an unacceptably high alkali content in the washed product.

A method of hydrochemical treatment of nepheline sludge is known (Abramov V.Ya., Alekseev A.I., Badal'yants Kh.A. Complex processing of nepheline-apatite raw materials. Moscow: Metallurgy. 1990. Pp. 224-227), according to which it is proposed to treat nepheline sludge with a soda-potash solution formed as a result of carbonization of aluminate solutions of alumina production.

The disadvantage of the method is the relatively low conversion rates of β-2CaO SiO ₂ with separate formation of the lime and silicate components, as well as the preservation of an unacceptably high alkali content in the washed product.

A method for hydrochemical treatment of nepheline sludge is known (RU Patent No. 2246458, filed 04.12.2003, published 20.02.2005), which consists of washing the sludge, treating it with an alkaline compound and lime milk with a dosage of 1.0-5.0 moles of active CaO per mole of the sum of alkalis in the nepheline sludge at a temperature of 25-95°C for 1-4 hours.

The disadvantage of this method is the need to introduce a significant number of additional technological operations, as well as the impossibility of separating the lime and silicate components, which eliminates the possibility of changing the ratio of the volumes of the main and by-products.

A method for hydrochemical treatment of nepheline sludge is known (RU Patent No. 2640071, published on 26.12.2017), adopted as a prototype, which consists of hydrochemical treatment of nepheline sludge for the production of Portland cement clinker by exposing the sludge to carbon dioxide in an aqueous medium at a temperature of 25-95 ° C for 2-6 hours and subsequent treatment with an alkaline solution. In this case, the initial flow of nepheline sludge is divided into two parts, one of which is subject to hydrochemical treatment to obtain a product corresponding to the molar ratio of CaO / SiO ₂ > 3, and then mixed with the second part of the nepheline sludge until the composition of the raw mixture required to obtain clinker of alite composition is achieved.

The disadvantage of this method is the retention of a fairly high alkali content in the washed product and its applicability only in the processing of nepheline sludges containing calcium orthosilicate as the main component in the metastable modification β-2CaO SiO ₂ .

The technical result is an increase in the efficiency of complex processing of kaolinite ores.

The technical result is achieved by using calcium silicate sludge as raw material, which contains γ-Ca ₂ SiO ₄ , while one part is repulped with water to a ratio by weight of liquid and solid components from 6/1 to 10/1, and hydrochemical treatment is carried out with a gas-air mixture with a volume content of CO ₂ from 15 to 50%.

The method is illustrated by the following figures:

Fig. 1 - graph of the dependence of the lime modulus of calcium silicate sludge after hydrochemical treatment on the degree of conversion of calcium orthosilicate;

Fig. 2 - graph of the dependence of the proportion of calcium silicate sludge entering hydrochemical treatment in the composition of the raw mixture on the degree of conversion of calcium orthosilicate.

The method is carried out as follows. The raw material used is calcium silicate sludge obtained during the processing of kaolinite ore by the sintering method, containing γ-Ca ₂ SiO ₄ , after its separation from the aluminate solution in a counter-current washing system with a humidity of about 50%, which is divided into two parts. One part is repulped with water to a ratio by weight of liquid and solid components from 4/1 to 10/1 and then subjected to hydrochemical treatment with carbon dioxide in the composition of a gas-air mixture with a concentration of CO ₂ from 15 to 50%, at a temperature of 25 to 95 ° C for a duration of 2 to 6 hours, which is accompanied by the following chemical interaction:

γ-Ca ₂ SiO ₄ + 2CO ₂ + 2H ₂ O = 2CaCO ₃ + H ₄ SiO ₄ (1)

After reaching the required degree of calcium orthosilicate conversion in the sludge, the pulp is filtered to obtain liquid and solid products. The liquid product, recycled water, is returned to the stage of repulping the silicate-calcium sludge. The solid product, the conversion silicate-calcium sludge, is placed in a reactor with mechanical mixing and a caustic alkali solution is added. After that, the resulting pulp is filtered to obtain solid and liquid products. The liquid product, a silicate-alkaline solution containing silica separated from the sludge, is sent for disposal. The solid product, the conversion sludge, after hydrochemical treatment is used to prepare raw Portland cement mixture.

The ratio of the components of the raw mix is determined by the value of the lime module of the silicate-calcium sludge of the initial composition and the value of the lime module of the conversion sludge after hydrochemical treatment, which are calculated based on the results of X-ray fluorescence analysis of the sludge for the content of CaO and SiO ₂ :

(α ^and ) _izv and (α ^k ) _izv are, respectively, the lime modulus of the silicate-calcium sludge of the original composition and the conversion sludge after hydrochemical treatment;

(CaO) ^and ,(SiO ₂ ) ^and and (CaO) ^k , (SiO ₂ ) ^k - respectively, the content of CaO and SiO ₂ in the original sludge and after hydrochemical treatment, %;

56 and 60 are the molecular weights of CaO and SiO ₂ , respectively, g/mol.

The conversion sludge after hydrochemical treatment and the second part of the silicate-calcium sludge of the original composition are mechanically mixed in a ratio that satisfies the stoichiometry of alite according to the following ratio:

α ^cm _izv = 60(CaO) ^cm / 56(SiO ₂ ) ^cm = 3 ± 0.03, where

(CaO) ^cm and (SiO ₂ ) ^cm - respectively, the content of CaO and SiO ₂ in the finished raw mix for obtaining clinker of alite composition;

to obtain a raw Portland cement mixture of uniform composition.

The method is illustrated by the following examples.

Example 1. A sample of calcium silicate sludge obtained during the processing of kaolinite ore by the sintering method is used, with the following composition, mass %: Al ₂ O ₃ - 31.9; SiO ₂ - 52.2; Fe ₂ O ₃ - 1.4; CaO - 0.59; LOI - 13.0. The sludge with a residual moisture content of 0.4-0.5% according to the MOC - 120H analyzer (Shimadzu) has the following chemical composition according to the results of X-ray fluorescence analysis on an XRF-1800 device (Shimadzu) and determination of the carbon content using a TOC-L analyzer (Shimadzu), mass %: Al ₂ O ₃ - 1.43; SiO ₂ - 25.69; Fe ₂ O ₃ - 0.63; CaO - 62.29; _CO2 - 9.69; = 2.60. The calcium silicate sludge is diluted with water to a liquid to solid mass ratio in the pulp of 4/1. The resulting pulp is heated to a process temperature of 25°C and treated with a gas-air mixture with a carbon dioxide concentration of 50% for 2 hours. The pulp is then separated using a Nutsche filter into liquid and solid products. The conversion sludge (solid product) is additionally treated with a caustic alkali solution to dissolve the silicate component formed during the carbon dioxide conversion, and the pulp is separated by filtration into solid and liquid products. The completeness of reaction (1) is estimated by the conversion degree index, which expresses the number of moles of SiO ₂ substituted in the polymorphic modification γ-2CaO SiO ₂ by an equivalent amount of carbonate ions. According to the results of the analysis, the degree of conversion of the silicate-calcium sludge is 9.5%, and the lime module of the conversion sludge after separation of the silicate component is 2.87. Calculations of the composition of the raw mix show that their results do not have physical meaning, and the preparation of a raw mix of alite composition using the original sludge and the one that has undergone hydrochemical treatment with the specified indicators is impossible (Table 1).

Examples 1-4 establish a noticeable influence of the mass ratio of the amount of liquid and solid components in the range of values from 4/1 to 11/1 on the parameters of the process of hydrochemical treatment of sludge and preparation of a two-component raw mix without introducing an additional amount of lime component. At the same time, an increase in liquid/solid in the range from 10/1 to 11/1 gives a noticeably smaller increase in the degree of conversion, which allows limiting the upper limit of this factor at the level of 10/1. The lower range of this factor at the level of 4/1 is limited by a noticeable increase in the viscosity of the pulp and a decrease in the rate of mass exchange processes, especially under conditions of low temperature, as in Example 1. This does not allow achieving the minimum required degree of conversion for the preparation of a raw mix of alite composition without introducing an additional amount of lime component. An increase in the process temperature significantly intensifies mass transfer with the achievement of the minimum required indicators as in Example 14, which makes it possible to limit the lower level of this factor to 4/1, ensuring the implementation of the process with a minimum volume of process materials (Table 1).

Examples 3, 5, 6 establish the influence of carbon dioxide concentration for the range of _CO2 concentrations in the gas-air mixture from 15 to 50%, which are the maximum possible for the exhaust gases of alumina and cement production. In this case, the upper level of concentration is determined by the composition of the exhaust gases during the calcination of limestone to obtain burnt lime, and the lower level by the composition of the exhaust gases in the production of alumina by sintering and during the calcination of raw mixtures of Portland cement production, which is supplemented by a noticeable intensification of the mass exchange processes of carbon dioxide hydrochemical treatment during their use.

Examples 5, 7-10 establish that the process temperature is a significant factor in the hydrochemical treatment of calcium silicate sludge, ensuring a stable increase in the calcium orthosilicate conversion rate in the temperature range from 25 to 95°C. In this case, the lower limit is limited by an increase in pulp viscosity and a noticeable decrease in conversion rates, and the upper level is limited by the implementation of the process in atmospheric conditions and the approach of the system to the boiling point of water (Table 1).

Examples 10-13 illustrate the effect of the duration of the hydrochemical conversion process against the background of other technologically significant factors that ensure the highest process indicators for the degree of calcium orthosilicate conversion. At the same time, analyzing the dynamics of the change in indicators, we can conclude that the process rate gradually slows down due to the growth of diffusion resistance to mass transfer and the approach of the indicators to the limit values for the magnitude of the conversion degree, the value of the lime module of the conversion sludge and its share in the composition of the two-component raw mix. Taking into account the wide range of process performance indicators, its duration in the range from 2 to 6 hours ensures the achievement of both the minimum required indicators for the degree of conversion and the maximum ones for the preparation of a two-component raw mix without introducing an additional amount of the lime component (Table 1).

Example 15. A sample of calcium silicate sludge obtained during the processing of kaolinite ore by the sintering method is used, which differs in composition from the ore in Examples 1-14, in mass %: Al ₂ O ₃ - 33.74; SiO ₂ - 46.77; Fe ₂ O ₃ - 1.65; TiO ₂ - 3.22; CaO - 0.17; LOI - 12.91. The sludge with a residual moisture content of 0.4-0.5% according to the MOC - 120H analyzer (Shimadzu) has the following chemical composition according to the results of X-ray fluorescence analysis on an XRF-1800 device (Shimadzu) and determination of the carbon content using a TOC-L analyzer (Shimadzu), in mass %: Al ₂ O ₃ - 1.55; SiO ₂ - 23.29; CaO - 61.39; TiO ₂ - 1.47; Fe ₂ O ₃ - 0.75; CO ₂ - 10.82; = 2.82. In this case, the process of hydrochemical treatment of calcium silicate sludge is implemented under conditions that ensure the achievement of maximum indicators as in Example 13. The results obtained establish an insignificant change in the process indicators compared to Example 13, despite the existing differences in the chemical composition of the raw materials associated with a high content of iron and titanium impurities. At the same time, the raw materials used have an increased lime module, compared to the previously used sample, which reduces the amount of calcium orthosilicate in the sludge and is a positive factor in its hydrochemical treatment (Table 1).

Example 16. A sample of aluminosilicate sludge with a process moisture content of 56.8% from the processing of kaolinite ore by the sintering method is used, the composition of which is given in Example 15. The process of hydrochemical treatment of calcium silicate sludge is implemented under the conditions as in Example 15. In this case, the indicators achieved are slightly different from the indicators of Example 15, which may be due to the absence of a drying operation causing additional changes in the structure and physicochemical properties of the surface of the aluminosilicate sludge participating in the heterogeneous interaction during its hydrochemical treatment (Table 1).

The method provides an increase in the technological efficiency of processing kaolin raw materials due to the separation of the silicate and lime components in the composition of the silicate-calcium sludge, which ensures the preparation of a two-component raw Portland cement mixture using only sludge components, reduces the consumption of the lime component, reduces the amount of greenhouse gas emissions and creates conditions for managing the ratio of the main and by-products in the complex processing of kaolinite ores.

Table 1 - Indicators of hydrochemical treatment of silicate-calcium sludge and preparation of raw Portland cement mixture during processing of kaolin raw materials by sintering method

Example, No. Technological mode of carbon dioxide treatment of calcium silicate sludge Indicators of hydrochemical treatment of calcium silicate sludge Indicators for the preparation of raw Portland cement mixture y/t pulp, kg/kg Process temperature, °C Process time, hour Concentration of _CO2 in the gas-air mixture, % Conversion rate (ε _conv ), % Lime module of sludge after hydrochemical treatment (α ^k _izv ) Sludge fraction after hydrochemical treatment (x _gx ) Proportion of sludge of the original composition (x _is ) Lime modulus of the mixture (α ^cm _izv ) 1 4/1 25 2 50 9.50 2.87 - - 0.423 - 2 6/1 25 2 50 15.7 3.08 0.859 0.141 2.98 3 10/1 25 2 50 21.3 3.30 0.631 0.369 2.97 4 11/1 25 2 50 21.9 3.33 0.612 0.388 3.02 5 10/1 25 2 15 25.1 3.47 0.535 0.465 2.98 6 10/1 25 2 30 22.7 3.36 0.593 0.407 3.03 7 10/1 50 2 15 42.7 4.53 0.316 0.684 3.01 8 10/1 70 2 15 61.3 6.71 0,220 0,780 2.99 9 10/1 80 2 15 72.0 9.28 0.187 0.813 3.00 10 10/1 95 2 15 80.5 13.32 0.168 0.832 3.02 11 10/1 95 4 15 87.9 21.47 0.153 0.847 3.01 12 10/1 95 5 15 89.3 24.28 0.151 0.849 3.02 13 10/1 95 6 15 92.4 34.18 0.146 0.854 3.00 14 4/1 95 2 50 23.4 3.41 0.598 0.402 2.98 15 10/1 95 6 15 91.6 33.57 0.067 0.933 3.02 16 10/1 95 6 15 92.8 39.17 0.066 0.934 3.03

Claims (1)

A method for hydrochemical treatment of calcium silicate sludge, including dividing it into two parts, one of which is subject to hydrochemical treatment by exposing the sludge to carbon dioxide in an aqueous medium at a temperature of 25 to 95°C, for a duration of 2 to 6 hours, and then treating it with an alkaline solution, mixing it with the second part of the calcium silicate sludge until the composition of the raw material mixture required to obtain alite clinker is achieved, characterized in that the raw material used is calcium silicate sludge, which contains γ-Ca ₂ SiO ₄ , wherein one part is repulped with water until the ratio by weight of the liquid and solid components is from 6/1 to 10/1, and the hydrochemical treatment is carried out with a gas-air mixture with a volume content of CO ₂ from 15 to 50%.