RU2119468C1 - Method of removing sulfate salting out products on ceramic facing article surface - Google Patents

Abstract

FIELD: building industry. SUBSTANCE: method involves addition of high-aluminous cement at amount 0.5-2.0 wt.-% of charge mass or 100-200% of SO₃ content in charge to raw charge. Then blanks are formed, dried and calcined. Method is used for production of ceramic bricks, stones, blocks, tiles and plates. Method ensures to eliminate salting out products on facing article surface completely. EFFECT: improved method of removing. 2 cl, 3 tbl, 2 ex

Description

 The invention relates to the building materials industry and allows to obtain ceramic products (ceramic bricks, stones, blocks, tiles, tiles) mainly on the basis of red-burning clays.

 One of the main sources of efflorescence on the surface of ceramic products is soluble sulfate salts in the molding composition. During the drying process, water-soluble salts are carried out by moisture to the surface of the raw material, where they are deposited. During firing, they are fixed on the surface and become noticeable against the background of the natural color of the crock in the form of white and colored spots, making the front surfaces of the products non-uniform.

 A known method of eliminating sulfate efflorescence [1], involving the introduction of additives of finely ground quartz feldspar sand, crushed in a vibratory mill, in an amount of 10-15% with or without coal dust (6-7 wt.%).

 The disadvantages of this method: does not provide a complete elimination of efflorescence, but only reduces them; has a limited scope only for loess and loesslike rocks.

 The closest in technical essence and the achieved effect is a method of preventing sulfate efflorescence by introducing barium compounds into the charge (prototype) [2], which bind soluble sulfate salts contained in the molding mass into an insoluble salt of barium sulfate.

Various compounds are used as barium-containing additives: BaCO ₃ , Ba (HCO ₃ ) ₂ , Ba (OH) ₂ • 8H ₂ O, BaCl ₂ • 2H ₂ O, BaF ₂ , etc., which are introduced into the molding composition as a dry powder or in the form of suspensions with mixing water. The best results were obtained with the introduction of additives in the form of a thin homogeneous suspension [3]. Barium-containing additives interact with soluble salts, for example, in the following reactions:
CaSO ₄ + BaCO ₃ _______ → BaSO ₄ + CaCO ₃ (1)
CaSO ₄ + Ba (OH) ₂ • 8H ₂ O __ → BaSO ₄ + Ca (OH) ₂ + 8H ₂ O (2)
CaSO ₄ + BaCl ₂ • 2H ₂ O __ → BaSO ₄ + CaCl ₂ + 2H ₂ O (3)
CaSO ₄ + BaF _________ → BaSO ₄ + CaF ₂ (4)
The formation of new soluble compounds [Ca (OH) ₂ , CaCl ₂ , CaF ₂ ] during the reactions does not guarantee the absence of efflorescence on the surface of fired ceramic products.

При этом BaCO₃ может сплавиться с черепком, а CaSO₄ - образовать высолы на обоженном кирпиче. Следовательно, введение солей бария в глины с высоким содержанием карбонатов нецелесообразно.In the presence of CaCO ₃ in the clay mass, the following metabolic reaction can occur with the formation of BaCO ₃ :

At the same time, BaCO ₃ can fuse with the shard, and CaSO _{4 can} form efflorescence on fired brick. Therefore, the introduction of barium salts in clay with a high content of carbonates is impractical.

Common disadvantages of this method are: limited scope, since the addition of barium salts does not give the desired effect for clay rocks with a high content of calcium carbonate [2, 4, 5]; there is secondary environmental pollution during firing due to dissociation, for example, CaCl ₂ , CaF ₂ (3,4) and the release of chlorides and fluorides; secondary efflorescence is possible due to the formation of new soluble compounds, for example, Ca (OH) ₂ (2).

 In addition, different methods of introducing additives have their drawbacks: when using a dry powder, its distribution in the mass is not evenly achieved, which leads to the formation of local efflorescences on the surface of the products or to excessive consumption of additives; when introducing an additive in the form of a suspension, the technology is complicated due to its additional preparation and stabilization.

 The aim of the invention is the complete elimination of efflorescence on ceramic cladding products made from a molding material containing soluble sulfate salts, based on any clay raw materials.

 This goal is achieved by the fact that in the method comprising introducing into the mixture additives that bind the soluble sulfate salts contained in the molding material into insoluble compounds, molding, drying and firing, high-alumina cement (VHC) in an amount of 0.5 - 2 is used as an additive, 0 wt.% By weight of the mixture (clay, clay-containing raw materials or a mixture of clay-containing raw materials and a detergent).

Взаимодействуя таким образом с растворимыми сульфатами, гидроалюминаты будут задерживать соли во внутренних слоях изделий, не допуская образования высолов на поверхности. С учетом молекулярных масс взаимодействующих по реакции (6) компонентов - 201 и 288, для образования гидросульфоалюмината кальция, содержание вводимых алюминатов должно приближаться к содержанию

в шихте. В ходе этой реакции не образуются новые растворимые соединения - источники вторичных высолов. Побочным продуктом является аморфный Al(OH)₃, который улучшает технологические параметры за счет расширения интервала спекания.The elimination of efflorescence is ensured by the following factors. Soluble sulfate salts in water dissociate, for example, on CaSO ₄ _____ → Ca ²⁺ + SO $\genfrac{}{}{0ex}{}{\text{2-}}{\text{4}}$ . The VHC contains active clinker minerals - calcium aluminates (CaO • Al ₂ O ₃ , CaO • 2Al ₂ O ₃ ), which, when hydrated for a short period of time, form positively charged micelles of calcium hydroaluminates. Ions SO $\genfrac{}{}{0ex}{}{\text{2-}}{\text{4}}$ interact in the molding mass with calcium hydroaluminates at ordinary temperature with the formation of insoluble calcium hydrosulfoaluminate, for example, by the reaction [6]:

Interacting in this way with soluble sulfates, hydroaluminates will retain salts in the inner layers of the products, preventing the formation of efflorescence on the surface. Taking into account the molecular masses of the components interacting by reaction (6), 201 and 288, for the formation of calcium hydrosulfoaluminate, the content of the introduced aluminates should approach the content

in the charge. In the course of this reaction, no new soluble compounds are formed - sources of secondary efflorescence. Amorphous Al (OH) ₃ , which improves process parameters by extending the sintering interval, is a by-product.

 A comparable analysis with the prototype shows that the inventive method differs from the known introduction of a new component of the HCV. The signs of the proposed solutions do not coincide with the signs of the known solutions (table. 1). Thanks to the differences in the solution, a new positive effect is achieved, expressed in the complete elimination of efflorescences on the surface of ceramic cladding products made from any clay raw materials.

 The method is as follows.

 A mixture is prepared from clay, clay-containing raw materials, or a mixture of clay-containing raw materials and a detergent, introducing a VHC technological additive into it, it is processed according to traditional technology and, for example, brick is prepared by plastic molding, dried and fired.

 Examples of experimental verification.

 Example 1

At the Chapaevsky brick factory in the Samara region. make the front ceramic brick from a mixture of the following composition, wt.%:
78% - white-burning clay (Chapaevsk);
22% of the red-burning clay of the Vozdvizhenskoye deposit.

Both clays have a significant carbonate content, the content of which is confirmed by intense boiling under the action of HCl. There are efflorescences on the surface of the brick due to the presence of sulfates in the raw material charge. The chemical compositions of the raw materials are given in table. 2. The total sulfate content in terms of SO ₃ in the mixture is ≈ 1%. VGTs of the Podolsky plant of brand 400 was introduced into the raw material charge of the factory composition in an amount of 0.5 to 3% by weight of the charge. The mixture was thoroughly mixed, moistened to a molding moisture, and, after daily aging, plastic samples were formed - tiles 60x30x10 mm in size. After drying under natural conditions, the samples were fired in a laboratory electric furnace (in an oxidizing environment) at a temperature of 950 ^o C. Firing mode: temperature rise - 7 hours, holding at maximum temperature - 1 hour, cooling to 50 ^o C - 15 hours. Analysis of efflorescence after firing was carried out visually. In the table. 3 shows indicators of the degree of elimination of efflorescence on the surface, depending on the composition. As can be seen from the table, with the introduction of 1-3% VHC (100 - 300% VHC of the content of SO ₃ ) efflorescence on the surface of the brick is completely eliminated. The introduction of BaCO ₃ (prototype) only reduces the intensity of efflorescence, because the feed contains many carbonate impurities and inclusions.

 Example 2

At the Togliatti brick factory, front ceramic bricks are made from the following mixture, wt.%:
35% of white-burning clay (Chapaevsk, Samara region);
58% clay Danilovskoye deposits;
7% phosphorus slag.

Clay of the Danilovsky deposit contains carbonate impurities and inclusions. The chemical composition is given in table. 2. The total content of sulfates in the mixture in terms of SO ₃ is 0.78%
The compositions of the charges, the method of formation, drying and firing are similar to those described in example 1. The results are presented in table. 3. As can be seen from the table, with the introduction of 0.78 - 3.0% HCV (100-256% HCV of the content of SO ₃ in the charge), the efflorescence is completely eliminated. The introduction of BaCO ₃ (prototype) only reduces the intensity of efflorescence formation, which is associated with the presence of carbonate impurities and inclusions in the feed.

 The data obtained suggest that the addition of VHC completely eliminates efflorescence and the optimal amount is 0.5 - 2.0 wt.%.

Sources of information:
1. 147514 (USSR), cl. 80c, 12 ₀₁ . A method of manufacturing burnt bricks from loesses and loesslike rocks / S.F. Lozitsky, K.Sh. Shatemirov. - Bull. N 10 // Bulletin of inventions, 1962.

 2. Zalmang G. Physical and chemical foundations of ceramics. -M.: Gosstroyizdat, 1959, - S. 90-91.

 3. Adamova Yu.S., Shaposhnikova AN, Reasons for the appearance of fading on the facing products // Transactions of NIISstrokeramiki. M., 1952, no. 6, p. 22-48.

 4. Filosofov P. S. Sulfate corrosion of ceramic products // Local building materials, 1947, N 6.

 5. Sokolov Ya. A., Yakopson TS, Bolshukhin VP The use of barite waste for binding soluble salts in clays // Glass and Ceramics, 1965, N 10, p. 35-37.

 6. Kuznetsova T.V. Aluminate and sulfoaluminate cements. - M.: Stroyizdat, 1986, p. 39.50.

Claims (1)

A method for eliminating sulfate efflorescences on the surface of ceramic cladding products by introducing additives into the raw material mixture, molding, drying and firing, characterized in that high-alumina cement is added to the mixture in the amount of 0.5 - 2.0 wt.% By weight of the mixture or 100 - 200% of the content of SO ₃ in the mixture.

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