RU2351557C2 - Method for production of gypsum binding agent - Google Patents

Abstract

FIELD: construction; chemistry.

SUBSTANCE: invention is related to methods for production of gypsum binding agents, including anhydrite, and also dry mixtures for production of construction products and structures, including monolithic wall partitions, ceiling slabs. In method for production of gypsum binding agent by means of processing of raw materials - carbonate or oxide of calcium - with sulfuric acid, dehydration of produced gypsum at normal pressure and temperature of 120-140°C or 400-500°C, or 800-900°C, or in autoclave at the pressure of 1.3 atm, with further crushing of produced product till residue on sieve 02 does not exceed 12%, specified raw materials are previously mixed with magnesium sulfate at the ratio of 500-1000:1 accordingly, specified treatment is realised by mixing with concentrated sulfuric acid at the ratio of 1:1, with spraying of water on reacting mixture, at that water is heated up to temperature of 70-80°C, in amount of 3-5% from mass of reacting mixture, soaking is realised to room temperature, prepared product is neutralised by magnesium oxide, and crushing is done in the presence of complex additive, which contains the following components, wt %: superplasticiser C-3 38-40, waterproofing agent "Sofexil" 48-60, alkali drain from production of caprolactam 0.8-2.0, foam suppressor "Norka" 0.01-0.05, water - the rest, taken in amount of 1 % of neutralised product.

EFFECT: higher strength and water resistance.

4 ex, 1 tbl

Description

The invention relates to the field of building materials widely used in mass and cottage housing construction, in particular to methods for producing gypsum binders: building gypsum binders, high strength gypsum binders, anhydrite and extreme gypsum.

Gypsum binders in industry are produced according to several basic technological schemes from quarried, averaged and enriched gypsum raw materials, usually containing at least 80% calcium sulfate dihydrate.

The crushed gypsum raw materials are subjected to heat treatment in gypsum boilers with preliminary drying in a drying drum at a moisture content of more than 5% or grinding and drying in a hammer mill with a moisture content of less than 5%. Drying of gypsum can be carried out in fluidized bed apparatus or in tube dryers. The product is a gypsum binder, presented in the main part by calcium sulfate hemihydrate (A.V. Ferronskaya. Reference. Plaster materials and products. Production and use. M., ASV publishing house, 2004, p.24 and 485).

A known scheme for producing gypsum binder by heat treatment of crushed stone of gypsum raw materials with natural humidity in an autoclave under pressure, followed by drying in a drying drum of heat treatment products, consisting mainly of hemihydrate alpha-modification of calcium sulfate (I. A. Perederni. High-strength gypsum GP, its technology and properties, Kuibyshev, 1960, p. 189).

According to another scheme, a suspension of gypsum raw materials with water is prepared, W: T = 1: 1, which is subjected to continuous autoclaving under pressure with stirring, followed by separation of the solid phase on the vacuum filter, which consists of calcium sulfate hemihydrate in alpha modification, then dried in a thermal unit and grind. The products are high-strength gypsum binders (P.F. Gordashevsky, A.V. Dolgorev. Production of gypsum binders from gypsum-containing wastes. M., Stroyizdat, 1987, 104 pp.).

Anhydrite is obtained by roasting gypsum raw materials in a thermal unit at a temperature of 600-700 ° C, and with the addition of lime astringent gypsum binder, which becomes waterproof after grinding and can completely and with great benefit replace Portland cement (P.P. Budnikov. Gypsum, its study and application. M., Stroyizdat Narkomstroy, 1943, p. 62 and 374).

From S. Nagai, J. Soc. Chem. Ind. Japan., Supol. Bind. 41, No. 1, 713-813 (cited from the book by P.P. Budnikov. Gypsum, its research and application, p. 120), a method for producing gypsum binders by sulfuric acid treatment of aqueous suspensions of calcium carbonates or oxides is known. In this case, dilute aqueous solutions of sulfuric acid (with a concentration of H ₂ SO ₄ monohydrate of less than 50%) are used, the gypsum formed is separated by filtration, sent to high-temperature drying with a coolant temperature of up to 600 ° C, and the heat treatment is completed by grinding (as well as A.A. Ulyanov, V.A. Tikhonov, E.I. Ved, Z. S. Litvinova. Molding gypsum. Kiev, Budevivilnik, 1970, p. 189).

The disadvantages of this method, selected for the prototype, are the low quality of the obtained gypsum raw materials due to incomplete opening of calcium carbonate and the strong phenomena of aggregation and sintering of particles of carbonate or calcium oxide in dilute solutions of sulfuric acid.

Dense films of calcium sulfate appear on the surface of the reacting particles, preventing the penetration of sulfuric acid into the particles to decompose carbonate or calcium oxide. The resulting gypsum is heavily contaminated with unreacted particles of carbonate or calcium oxide. The content of calcium sulfate in the resulting solid residues after filtration ranges from 60 to 75% of the basic substance. Such a low quality of the initial gypsum as a raw material for the production of a gypsum binder does not allow to obtain a high-quality product after heat treatment and drying.

Another disadvantage of this method is that the filtrate formed after separation of the gypsum mass must be disposed of using an additional heat consumption. Large amounts of salt water pollute the environment and are a serious obstacle to the industrial application of this method. In addition, it is impossible to process low-grade carbonate varieties with this method, since the crystal lattices of impurities are not destroyed in this process, and silicates, sulfides, oxides of other metals in the unchanged form enter the raw material, reducing its quality and astringent properties.

Our proposed method is devoid of these disadvantages and overcomes them.

The aim of the present invention is to expand the resource base, improve the environment, reduce heat and energy consumption, increase the yield of gypsum binder, its quality indicators, as well as the strength and water resistance of the products obtained from this binder.

This goal is achieved by the fact that low-grade carbonate industrial waste, screenings of limestone rocks, dusty limestone varieties, ground limestone, which are pre-mixed with magnesium sulfate powder at a ratio of 500-1000: 1, are used as raw materials, processing is carried out by mixing with concentrated sulfuric acid at a ratio 1: 1, spraying on a reacting mixture of water heated to a temperature of 70-80 ° C in an amount of 3-5% by weight of the reacting mixture, carry out exposure to room temperature, the resulting product is neutralized with magnesium oxide, and grinding is carried out in the presence of a complex additive containing, wt.%: superplasticizer C-3 -38-40, hydrophobizator Sofexil - 48-60, alkaline stock production of caprolactam - 0.8-2.0 , antifoam "Mink" - 0,01-0,05, the rest of the water taken in the amount of 1% of the neutralized product.

The resulting binder is ground to a residue of sieve 02 of not more than 12% or a specific surface area of at least 3250 cm ² / g.

The object of the proposed method is a gypsum binder.

Significant differences of the proposed technical solution are the feed for decomposition of raw materials containing calcium carbonate, pre-mixed with magnesium sulfate at a ratio of 500-100: 1, use concentrated (65-95%) sulfuric acid with a component mass ratio of 1: 1, as well as spraying on a reactive mixture of water heated to a temperature of 70-80 ° C in an amount of 3-5% by weight of the reacting mixture, holding the resulting reactive mass to room temperature, followed by neutralization of the resulting mass o magnesium oxide and grinding in the presence of a complex additive containing, wt.%: superplasticizer C-3 - 38-40, water-proofing agent Sofexil - 48-60, alkaline stock production of caprolactam - 0.8-2.0, antifoam "Nork" - 0.01-0.05, the rest of the water taken in an amount of 1% of the neutralized product.

As part of a complex additive, all components are produced by the domestic industry:

S-3 superplasticizer is a sodium product of polymer condensation of naphthalene sulfonic acid and formaldehyde, produced by Polyplast LLC according to TU 5870-002-58042865-03;

water-repellent Sofexil is potassium polymethylsiliconate, manufactured by CJSC NPK Sofeks in accordance with TU 2229-008-42942525-00;

the alkaline effluent of caprolactam production is a mixture of dicarboxylic acids, with a predominant content of adipates and sodium alkali, manufactured according to TU 113-03-488-84 of JSC Shchekinoazot;

Nork defoamer is a mixture of polyethylene glycol ethyl esters manufactured in accordance with TU 3467-006-567846-01 Salavatsintez OJSC.

A comparative analysis of the known and proposed methods shows that the proposed method has a significant novelty, inventive step and is useful for use in the construction industry and industry.

The proposed method provides:

- widespread use of carbonate-containing industrial wastes and local raw materials - ground limestones;

- the use of concentrated sulfuric acid in the process of producing gypsum and the use of the exothermic effects of the reaction to remove excess moisture from the processed material;

- the maximum yield of the target product is a gypsum binder, up to 99.5%;

- the use of magnesium sulfate in a mixture with carbonate-containing raw materials to increase the completeness of decomposition of raw materials;

- improving the environment through the involvement in industrial production of raw industrial waste and the implementation of technological methods that eliminate the discharge into the environment of water-salt wastewater;

- the use of complex additives in the process of grinding a gypsum binder, which increases the strength and moisture resistance of building products from the resulting binder.

Studies of the decomposition of diluted sulfuric acid carbonates, oxides, calcium silicates used in the known technical solutions (prototype) showed that the reaction products formed on the surface of the decomposed material - calcium carbonate, with sulfuric acid, primary gypsum calcifies the pores and does not allow completely opening the processed material.

The study of various additives in this process to overcome these negative phenomena has shown that magnesium sulfate, which has high solubility in concentrated sulfuric acid, is the best substance that can significantly improve the conditions of the reacting molecules, increase the degree of decomposition of the raw materials.

It was experimentally established that with increasing amounts of added magnesium sulfate in the raw material mixture, the degree of completeness of decomposition of calcium-containing minerals increases, this dependence is extreme in nature, reaching a maximum value of 99.8% in the range of ratios of raw materials and magnesium sulfate from 500-1000: 1, with an increase or decrease in this ratio, the degree of decomposition of the raw mix decreases to 58-65%.

It was found that the ratio of sulfuric acid to decomposable raw mix is optimal when the ratio of raw materials to sulfuric acid by mass is 1: 1 and meets the task of minimum acid consumption with a complete opening of the raw material.

Higher ratios lead to underdegradation of the material, and lower ratios lead to overspending of the acid and an increase in the expenditure coefficients of the neutralizing component — magnesium oxide.

Moistening the decomposition product of the feedstock with sulfuric acid with very small amounts of sprayed water allows, firstly, to suppress foaming during decomposition and, secondly, to obtain additional heat due to the exothermic effect of the reaction of the acid with hot water, taken in an amount of 3-5% from mass of the raw mix.

As comparative studies on the effectiveness of calcium oxide and magnesium oxide have shown, the latter is a more effective agent for neutralizing the residual sulfuric acid in the reaction product. Conducting neutralization with magnesium oxide can completely eliminate even trace amounts of sulfuric acid in the decomposition product.

The resulting binder was used to form samples, tests of which showed that the obtained binder has a compressive strength after 2 hours of 98 kgf / cm ² with a start time of setting of 12 minutes and an end of setting of 19 minutes. The water absorption of the samples after 2 days of soaking them in water was 14%. The resulting binder can be used in construction to obtain building envelopes inside buildings and to prepare dry building mixtures.

Very important were the results of studies of gypsum binder obtained after drying and grinding in the presence of a complex additive corresponding to the composition, wt.%: Superplasticizer C-3 - 38-40; water-repellent "Sofexil" - 48-60; alkaline runoff of caprolactam production - 0.8-2.0; antifoam - 0.01-0.05; the rest is water. The strength of the gypsum binder increases in the presence of additives by 100% or more, and water absorption decreases to 1.2 - 4%.

Examples of the method

Example 1. In a titanium mixer equipped with a mixing and abrasion device, 200 g of dry powdered powder of calcium carbonate (limestone) was loaded, 0.4 g of magnesium sulfate was added to it (the ratio of components in the mixture is 500: 1). To the resulting mixture, 200 g of sulfuric acid with a density of 1.84 g / cm ³ were added with stirring. Water was heated to 70 ° C in an amount of 2 g (5% by weight of the reacting mixture) using an ejector into the reaction mass. The resulting reaction mass was kept to room temperature, the dry mass was mixed with 0.23 g of magnesium oxide to finally neutralize it, controlling the process using a pH meter. The mixture was placed in a dehydrator, in which the material was heated at a temperature of 122 ° C (the optimal temperature of gypsum dehydration was determined using thermographic analysis on a derivatograph), maintaining the temperature of gypsum dehydration. Next, the resulting product is ground in a ball mill to a fineness corresponding to a residue of 12% on a sieve 02, or a specific surface of 6250 cm ² / g, in the presence of a complex additive containing, wt.%: Superplasticizer C-3 - 38; water-repellent "Sofexil" - 58; alkaline runoff of caprolactam production - 0.8; antifoam - 0.03; water - 3.17; taken from the total mass of the mixture in an amount of 1%. The resulting material was analyzed using physical and mechanical methods, forming standard samples in accordance with the requirements of GOST 125-79 and 23789-79. The research results are shown in table 1.

Example 2. They acted as in example 1, then 0.3 g of magnesium sulfate was added to 200 g of dry calcium carbonate powder, the mixture was stirred and 200 g of concentrated sulfuric acid was fed to it, as in example 1. The reaction mixture was sprayed with an ejector water heated to 80 ° C in an amount of 12 g (3% by weight of the reacting mixture), then neutralized 0.25 g of magnesium oxide, the mixture was placed in an autoclave, heated and kept at a pressure of 1.3 atm. The end of the transition of calcium sulfate to alpha hemihydrate was monitored by microscopic analysis according to the nature of the crystals formed. Next, the obtained gypsum binder milled in a ball mill, as in example 1, in the presence of a complex additive containing, wt.%: Superplasticizer C-3 - 39; water-repellent "Sofexil" - 48; alkaline runoff of caprolactam production - 0.8; antifoam - 0.05; water - 12.15, taken from the total mass of the mixture in an amount of 1%. Further, as in example 1.

Example 3. They acted as in example 1, then 0.2 g of magnesium sulfate was added to 200 g of dry powder of calcium carbonate, the mixture was stirred and 200 g of concentrated sulfuric acid was added to it with stirring, as in example 1. The mixture was sprayed with using a pulvilizer, water heated to 75 ° C in an amount of 16 g (4% by weight of the reacting mixture), then neutralized 0.2 g of magnesium oxide, the mixture was placed in a muffle furnace in which the material was heated at a temperature of 430 ° C (the optimum temperature for obtaining anhydrite determined using t derivatographic analysis), maintaining the temperature until the gypsum is completely dehydrated, then the obtained anhydrite is ground in a ball mill, as in example 1, in the presence of a complex additive containing, wt.%: superplasticizer C-3 -40; water-repellent "Sofexil" -52; alkaline runoff of caprolactam production - 2.0; antifoam - 0.05; water - 5.95, taken from the total mass of the mixture in an amount of 1%. Further, as in example 1.

Example 4. They acted as in example 1, then 0.2 g of magnesium sulfate was added to 200 g of dry powder of calcium carbonate, the mixture was stirred and 200 g of concentrated sulfuric acid was fed to it, as in example 1. It was sprayed into the reaction mass using an ejector water heated to 80 ° C in an amount of 12 g (3% by weight of the reacting mixture), then neutralized with 0.19 g of magnesium oxide, the mixture was placed in a muffle furnace in which the material was heated at a temperature of 810 ° C (the optimum temperature for obtaining the ext gypsum was determined using thermographic analysis aliza on a derivatograph), withstanding the temperature until the gypsum is completely dehydrated, then the obtained exirich gypsum is ground in a ball mill, as in example 1, in the presence of a complex additive containing, wt.%: superplasticizer C-3 -38.9; water-repellent "Sofexil" -60; alkaline runoff of caprolactam production - 1.0; antifoam - 0.05; water - 0.05, taken from the total mass of the mixture in an amount of 1%. Further, as in example 1.

The test results are shown in the table.

Example No. The degree of opening of raw materials,% Properties of the resulting gypsum binder Setting time start end min Strength: compress. bending, MPa Water absorption,% one 2 3 four 5 6 one. 99.8 10.5 18.5 38.8 1,6 2. 99.8 12.0 20,0 49.9 2.0 3. 98.9 38,0 52,5 40.9 0.8 four. 98.8 42.0 60.0 25.8 0.2

The results obtained suggest that the developed method for producing gypsum binder from carbonate-containing wastes by decomposing it with concentrated acid has advantages not only in terms of the best technological parameters, but also in the quality of the binder obtained, and in terms of environmental indicators, it allows involving large-tonnage calcium-containing wastes in industrial circulation and construction. and, most importantly, allows you to use sulfuric acid and utilize heat from the decomposition of raw sulfuric acid Oh.

Claims (1)

A method of producing a gypsum binder by treating raw materials such as carbonate or calcium oxide with sulfuric acid, dehydrating the obtained gypsum at normal pressure and temperature of 120-140 ° C, or 400-500 ° C, or 800-900 ° C, or in an autoclave at a pressure of 1, 3 atm, followed by grinding the resulting product to a residue on a sieve of 02 no more than 12%, characterized in that the said raw materials are pre-mixed with magnesium sulfate at a ratio of 500-1000: 1, respectively, this treatment is carried out by mixing with concentrated sulfuric acid in the ratio 1: 1, spraying on a reacting mixture of water heated to a temperature of 70-80 ° C, in an amount of 3-5% by weight of the reacting mixture, hold to room temperature, the resulting product is neutralized with magnesium oxide, and grinding is carried out in the presence of complex additives containing, wt.%: superplasticizer C-3 38-40, hydrophobizing agent "Sofexil" 48-60, alkaline stock production of caprolactam 0.8-2.0, antifoam "Nork" 0.01-0.05, water the rest taken in the amount of 1% neutralized product.