RU2375323C2 - Method of obtaining silicokieserite bonding material - Google Patents

Abstract

FIELD: construction industry.

SUBSTANCE: method of obtaining silicokieserite bonding material by mixing magnesium-containing production waste: powdered non-standard magnesite grade or serpentinite powder with strong sulphuric acid heated to 40°C in the ratio 1:1, by adding the decomposition of silica-containing addition and magnesium oxide to the obtained product in 'decomposition product : the above addition : magnesium oxide' ratio = 10:1-2:0.2-1.0 with further fine grinding. In the above method as silica-containing addition there can be used tripolite or filtered solid residue after being leached during 30 minutes with water heated to 90°C, at solid : liquid within 1:1-3 of the dried decomposition product, and from water phase, after the above leaching by means of magnesium sulphate crystallisation, drying and grinding there obtained is market product.

EFFECT: improving strength and water resistance at improving ecology owing to production wastes being used, decrease of energy consumption and increase of output of target product.

2 cl, 12 ex, 2 tbl

Description

The invention relates to the field of building materials, in particular to methods for preparing air binders used in the manufacture of monolithic concrete products in the construction of floors, wall structures of buildings and structures.

As a rule, in the construction business, in addition to Portland cement binders, the deficit of which in Russia is constantly growing at a speed of 3-3.5 million tons per year, air binder-gypsum and lime. The use of magnesia and kieserite binders, which have significantly higher (10 times) strength and hardness compared to gypsum in the production of building structures, is very limited due to the small volumes of their production in Russia and the need to import them from foreign suppliers.

The strength of products made from kieserite and silicokiserite binders reaches the strength of products made from Portland cement, amounting to 24-30 MPA after a day of curing, and 41-60 MPA after 28 days. These binders, consisting of magnesium monohydrosulfate (MgSO ₄ · H ₂ O) [1, 2], are not produced in Russia.

Currently, the production of magnesia binders is carried out using mining and geological work at the site of magnesite, which, after appropriate preparation and firing, is converted to burnt magnesia (magnesium oxide), which is closed to obtain concrete with solutions of magnesium chloride or magnesium sulfate. In practice, a salt of high purity magnesium sulfate heptahydrate is used.

The specified production of magnesia binders has serious drawbacks associated with the need for labor-intensive and thorough mining at brucite and magnesite deposits, high energy consumption for conducting processes of magnesite dissociation in high-temperature aggregates, environmental disruption: destruction of the soil forest cover of the earth and water sources, gas emissions and dust and gas emissions , and the release of low quality binder. Magnesium sulfates are prepared from dilute sulfate solutions associated with the need to perform an expensive closed-loop process.

One of the most important issues in the implementation of the priority national project “Affordable and Comfortable Housing for Russian Citizens” is the issue of increasing the capacity of the building materials industry (Portland cement, gypsum, magnesia, lime binders) and structural products based on the intensive use of strategic industrial products: industrial waste, secondary raw materials and local materials.

Industrial waste, the volume of which in total terms exceeds the value of 17.0 billion tons, is most significant for construction [3].

Russia has been confronted with an objective fact and circumstances of relentlessly developing industry capable of involving technogenic by-products into production processing.

At present, the need for normal economic activity in Russia (according to economists) can be satisfied by 60% only due to the industrial use of energy "reserves", the remaining 40% due to an increase in the production of fuel and energy resources (oil and gas).

Magnesium content industrial waste is energy “storage” in which up to 40-60% of the thermal and material energy of chemical processes, smelting technology, energy stripping and grinding, drying and labor energy of people that can be used to overcome the deficit of binders is invested. They amount to 3.0 billion tons, for the most part they are material already prepared for processing, which should be mastered only using new technological solutions. The stocks of technogenic products suitable for the production of new binders and building products from them are huge. Only in Bashkortostan and other regions there are about 2 billion tons of serpentinite. In Eastern Siberia, the Far East and Birobidzhan (the “Kuldurskoye” brucite deposit) there are large volumes of raw materials for the associated extraction of magnesium-containing components, which can be processed using low-cost technologies into building products and serpentinite cementless cementitious grades 750-1500 [4].

On the other hand, industrial wastes around the world are growing, associated with the accumulation of sulfur resulting from the refining of oil and gas, as well as gas emissions from metallurgical plants and thermal power plants. Sulfur-containing wastes are constantly growing, the production of elemental sulfur in 2006 according to IFA reached 23 million 760 thousand tons per year, but the sulfur market is constantly falling due to the reduction in the production of sulfuric acid used for the production of phosphate fertilizers [5].

It should be noted that sulfur is a relatively new energy source, its efficiency is 6 times higher than natural gas, but the intensive use of this fuel is constrained by the limited use of concentrated sulfuric acid, the commissioning of new capacities in the world exceeding 8 million 720 thousand tons per year (2001- 2003) to the existing ones.

One of the uses of sulfuric acid is the production of effective binders for construction.

Known methods for the production of binders are based on high-energy roasting or drying of the initial carbonate- or sulfate-containing rocks selectively produced in the mountains, the heat consumption in this case is (equivalent fuel per 1 ton of binder) in the production of Portland cement - 215 kg equivalent,

lime - 204,

magnesium oxide - 189,

extreme gypsum - 160,

anhydrite - 145,

silicokiserite - 107,

high strength gypsum binder - 106 and

Alabaster - 55 kg.t. [6].

Known methods for the production of magnesium oxide (3030 kJ per 1 kg of MgO at a firing temperature of 650-760 ° C) and the second necessary component of magnesium sulfate (MgSO ₄ · 7H ₂ O) are highly energy-intensive (more than 245 kg of equivalent fuel), mixtures of which are suitable to obtain magnesia concrete and products from them [7]. To obtain magnesia concrete, an aqueous solution of magnesium sulfate in an amount of 16-20% and magnesium oxide - 80-84% are used. The setting time is not earlier than 20-35 min, and the end of setting occurs no later than 6 hours from the start of mixing, the bending strength after 28 days is 2-4.5 MPA.

Kiserite or silicokiserite binder is a fine powder consisting of MgSO ₄ · H ₂ O · nSiO ₂ , the content in it: MgO from 28.7 to 20.4%; SO ₃ from 37.4 to 41.0%; amorphous SiO ₂ from 29.5 to 35.7%; H ₂ O bound from 8.4 to 9.2%. The content of kieserite in silicokizer is in the range of 64.5-70.5%. Like kieserite, silicokiserite is shut with water. The start of the setting of the silicokiserite test is not later than 5 minutes, and the end after 8-20 minutes. Normal density is 55%. Bending strength after 1 day is 1.5 MPA, and after 28 days 41.0 MPA.

There is a method of producing silicokiserite (kieserite) binder by dehydration of epsomite - seven-water magnesium sulfate or its mixtures with a finely ground siliceous component [4, 8]. Kieserite is also obtained as an insoluble waste in the water treatment of natural potassium salts [8] (see the chapter U. M.E. Pozin Technology of mineral salts, p. 160). The resulting waste contains kieserite and other impurities that reduce its effectiveness as a binder.

Another method for producing monohydrous magnesium sulfate is to heat magnesite or dolomite in an aqueous solution of ammonium sulfate. The resulting solution of MgSO ₄ · H ₂ O after distillation of ammonia is concentrated to precipitate CaSO ₄ , and then processed to magnesium sulfate [9]. The disadvantage of this method is its complexity and the need for processing large volumes of water and the gas-water phase. The resulting kieserite has low strength characteristics.

It is proposed to obtain magnesium sulfates by treating aqueous suspensions (T: W = 1: 1 by weight) of the finely divided serpentine mineral with a particle size of less than 0.075 mm sulfuric acid. The resulting mass is diluted with water and filtered, the resulting solution is subjected to evaporation and crystallization, amorphous silica is discarded [9, 10].

The disadvantages of the known methods and the method chosen for the prototype are: the high cost of heat treatment of the feedstock, the need to work with aqueous solutions and suspensions, which is associated with the processes of evaporation of large quantities of moisture, the need for disposal of wet waste, saline solutions and ammonia. The resulting kieserite or silicokiserite do not have high binders.

The aim of the present invention is to expand the raw material base and improve the environment through the use of industrial waste, reducing energy consumption, increasing the yield of the target product, increasing the strength and water resistance of building products from the resulting air binder, as well as obtaining highly standard magnesium sulfates.

This goal is achieved by the fact that magnesium-containing industrial wastes are used as raw materials: dusty and substandard varieties of magnesite and, first of all, serpentinite, milled to a fraction of 0.5 mm, which are fed in a dry state for decomposition with stirring in a heated to 40 ° With concentrated sulfuric acid, taken by weight to the magnesium-containing waste 1: 1; silica-containing additive (Tripoli) and magnesium oxide are added to the obtained reaction product in the ratio by weight of the decomposition product: Tripoli: magnesium oxide equal to 10: 1-2: 0.2-1.0; the mixture is sent to a fine grinding to obtain the desired silicokiserite binder. To obtain magnesium sulfates, the intermediate of the interaction of magnesium-containing waste with concentrated sulfuric acid is leached with water at T: G in the range 1: 1-3 and a temperature of 90 ° C, the aqueous phase is separated by filtration and magnesium sulfates are crystallized from it, which are dried and ground as a commercial product ; the aqueous phase is evaporated, and the solid residue after water leaching is dried and sent as a silica-containing additive to the grinding with the decomposition product.

The object of this method is a silicokiserite binder and magnesium sulfate salts.

A comparative analysis of known 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:

- the use of industrial wastes - primarily serpentinite or dusty and substandard magnesites;

- carrying out the process of producing silicokiserite in an anhydrous medium, directly in concentrated sulfuric acid, which immediately due to the exothermic effect of the reaction of reaction, accompanied by the destruction of the crystal lattices of minerals, allows you to get a mixture of kieserite and active silica in high yield, called silicokiserite, by the reaction:

Mg ₆ Si ₄ O ₁₀ (OH) ₈ + 6H ₂ SO ₄ = 6MgSO ₄ · H ₂ O + 4SiO ₂ + 4H ₂ O + 643 kcal, due to the heat of reaction, water evaporates during the decomposition of minerals;

- the presence of active silica increases the strength properties of the binder and its water resistance compared to pure kieserite;

- additional neutralization with magnesium oxide of unreacted acid in the decomposition product improves the quality of the target product;

- active silica, formed in the process of decomposition of serpentinite, adsorbs impurity elements on itself, which makes it possible to obtain high-purity magnesium sulfate when water leaching the decomposition product of serpentinite by sulfuric acid in comparison with other methods.

The chemical composition of serpentinite - a waste of asbestos-enrichment plants, is quite stable and varies slightly for various deposits. The content of the main components is as follows (wt.%): MgO - 35.5; CaO - 0.43; SiO ₂ 38.5; CO ₂ 0.77; checkpoint - 13.2; Fe ₂ O ₃ - 7.0.

Studies have shown that the process of decomposition of magnesium-containing waste: serpentinite or pulverized substandard magnesite proceeds quickly, the duration of decomposition of the material is in the range of 0.3-0.5 hours. The decomposition product is subject to thorough grinding and grinding in the presence of a silica-containing additive and magnesium oxide, which, when neutralized, forms an additional amount of kieserite. The optimal ratio of reacting components that correspond to a mass ratio of 1: 1 is established. At lower ratios, the yield of the target product is significantly reduced; at high sulfuric acid consumption, the reaction proceeds by 100%; however, to completely neutralize, it is necessary to increase the consumption of expensive magnesium oxide, which is not advisable. With the optimal ratio of magnesium-containing waste and concentrated sulfuric acid, the consumption for neutralization of the reaction product fits into the ratio of 10: 0.2-1.0.

In the process of researching the method of producing silicokiserite from serpentinite and sulfuric acid, it was found that the astringent properties, especially water resistance, of the products obtained from silicokiserite binder increase with an increase in the content of active silicon-containing additives in it. As siliceous additives used tripoli Kaluga deposits. It was found that with an optimal ratio by weight of the decomposition product and added tripoli in the range of 10: 1-2, stability of strength characteristics and water absorption of the experimental products from silicokiserite is observed. The results are shown in table 1.

Table 1 Product made of silicokiserite The ratio of decomposition product and tripoli Hardening time min Strength, MPA day Water absorption (%) Cubes 10: 0.5 2.5 4,5 6.0 15.0 10: 0.8 3.0 6.0 6.9 15.1 10 × 10 10: 1,0 10.0 23.0 34.0 8.0 10: 1,5 10.5 23.0 33.8 8.2 10: 1.8 11.0 24.0 35.0 8.0 10: 2.0 12.0 24.0 36.0 8.0 10: 2.2 12.0 24.3 29.5 8.5 10: 2.5 12.0 24.0 12.0 8.9 Kiserite Bead 4 × 4 × 16 - 4.0 7.0 7.2 20.6

All studies were carried out in titanium vessels and devices. Similar results were obtained when studying the process of decomposition of finely ground magnesite waste, adjusting the resulting intermediate using tripoli and magnesium oxide when grinding the resulting mixtures and testing the target product.

Studies of water leaching of the products of the interaction of magnesium-containing waste with sulfuric acid showed that the yield of magnesium sulfate salt depends on the following parameters: with an increase in the temperature of the suspension to 90 ° C, it grows and reaches its maximum value of 99.8%. For small W: T, the yield in the aqueous phase of the target product drops to 58.9%, and for large W: T there are large energy costs for evaporation and separation of magnesium sulfates. The optimum is T: W = 1: 1.

EXAMPLES OF IMPLEMENTING THE METHOD

Example 1. In a titanium mixer equipped with a stirrer and abrasion device, concentrated sulfuric acid, preheated to 40 ° C., weighing 200 g and a density of 1.84 g / cm ³ was charged. When the mixing device was turned on, dry powder serpentinite in an amount of 200 g was gradually loaded into the mixer. The mixture thickened, became very hot and began to boil; boiling of the suspension was accompanied by the release of gaseous water. The obtained pulverized and granular mass was analyzed by measuring pH, half of the mass was unloaded into a separate vessel for water leaching, and another equal share was sent to a ball porcelain mill equipped with porcelain balls, previously mixing the decomposition product with magnesium oxide and tripoli in a ratio of 10: 0. 2-1.0: 1.0-2.0. The resulting mixture was analyzed for the content of free hydrogen ions. After grinding the mixture to a particle fineness of 0.07 mm, it was unloaded and a silicokiserite binder was used to prepare a dough with water at a water-hard ratio of 0.57, cubes were formed, which after hardening were tested after 28 days. The second part of the product was leached with water at T: W = 1: 1 for 30 min and a temperature of leaching water equal to 90 ° C. The resulting suspension was filtered and the filtrate was evaporated to the maximum saturation of the solution with magnesium sulfate, from which a pure salt crystallized. Magnesium sulfate separated by filtration was dried and ground. The output of magnesium sulfate from the intermediate decomposition is equal to 99.8%. The residue after separation of magnesium sulfate was dried and sent to mix with the first part of the intermediate decomposition, observing the optimal ratio of siliceous additives added instead of tripoli.

Example 2. In a titanium mixer equipped with a mixing and abrasion device, sulfuric acid was loaded, as in Example 1, to which 200 mg of magnesite dusty waste was gradually sprinkled. The mixture immediately began to become very hot and boil. The reaction was accompanied by strong foaming due to the release of a large amount of carbon dioxide and vaporous water. After keeping the reaction mass with stirring and abrasion, it became loose and easily unloaded from the reactor. The resulting intermediate was unloaded and sent to a fine grinding in the presence of tripoli and magnesium oxide, as in example 1.

Example 3. Do as in example 1, adding to sulfuric acid 180 g of serpentinite, then, as in example 1.

Example 4. Do as in example 1, adding to sulfuric acid 220 g of serpentinite, then, as in example 1.

Example 5. Do as in example 1, mixing the resulting decomposition intermediate with tripoli and magnesium oxide, taken in proportion to the decomposition product of 10: 0.8: 0.5; further, as in example 1.

Example 6. Do as in example 1, mixing the resulting decomposition intermediate with tripoli and magnesium oxide, taken in proportion to the decomposition product of 10: 2.2: 0.5; then proceed as in example 1.

Example 7. Act as in example 1, mixing the resulting decomposition intermediate with tripoli and magnesium oxide, taken in proportion to the decomposition product 10: 1.5: 0.18; then proceed as in example 1.

Example 8. Act as in example 1, mixing the obtained decomposition intermediate with tripoli and magnesium oxide, taken in the ratio and with the decomposition product 10: 1,5: 1,2; then proceed as in example 1.

Example 9. Act as in example 1, separate half of the decomposition intermediate and leach it with water at a temperature of 90 ° C at T: W suspension of 1: 0.9; then proceed as in example 1.

Example 10. Act as in example 1, leaching with water the intermediate decomposition at T: W suspension 1: 1,2; then proceed as in example 1.

Example 11. Act as in example 1, leaching the intermediate decomposition of water heated to 80 ° C, and T: W suspension 1: 1, then, as in example 1.

Example 12. Heated in a drying drum at a temperature of 200 ° C for 5 hours, a pre-finely ground mixture of seven-water magnesium sulfate (epsomite) with tripoli, taken in a ratio of 1: 1, the mixture crumpled strongly, the dynamics of water removal from the mixture is controlled thermographically. The resulting product is cooled and again finely rubbed. The resulting powder is used to prepare a dough with water at a water-solid ratio of 0.58. The prepared concrete samples are studied. The test results are presented in table.2

table 2 Example No. The yield of silicokiserite,% The output of magnesium sulfate, with leaching,% Properties of the obtained silicokiserite Setting time, min Strength, MPA Water absorption,% one 2 3 four 5 6 one 100.0 99.8 12.0 36,2 8.0 2 100.0 99.8 10.5 30,2 8.6 3 95.2 90.1 3.0 6.0 20.5 four 100.0 95.6 2.5 4.0 20.3 5 98.9 98.3 3,5 3.0 19.0 6 100.0 89.2 3.0 3.0 21.6 7 100.0 92.1 5.5 4.0 19.0 8 100.0 92.0 4.2 3,5 20.1 9 100.0 68.0 10.0 30.6 9.0 10 100.0 71.0 11.5 36.0 8.4 eleven 100.0 60.0 12.0 35.8 8.8 12 67.0 - 2.5 5,6 14.8

The results obtained suggest that the developed method for the production of silicokiserite and magnesium sulfate salts has advantages not only in terms of the best technological parameters, but also in the quality of the binder, as well as in environmental indicators, allowing the inclusion of large tonnage magnesium-containing wastes in industrial circulation and construction, and that most importantly, it allows the use of concentrated sulfuric acid and to utilize heat from the use of sulfur waste.

Using the developed method, laboratory bench tests were carried out to obtain a silicokiserite binder for the manufacture of building elements and parts, as well as the manufacture of high-purity magnesium salts as a commercial product.

Claims (2)

1. A method of producing a silicokiserite binder by mixing a magnesium-containing industrial waste: a dusty substandard grade of magnesite or serpentinite powder with concentrated sulfuric acid heated to 40 ° C, in a 1: 1 ratio, adding to the obtained decomposition product a silica-containing additive and magnesium oxide in the ratio of decomposition product: specified additive; magnesium oxide = 10: 1-2: 0.2-1.0 followed by fine grinding. 2. The method according to claim 1, characterized in that as a silica-containing additive use tripoli or filtered solid residue after leaching for 30 minutes with water heated to 90 ° C, at T: G in the range 1: 1-3 of the decomposition product of dried and from the aqueous phase after the specified leaching by crystallization of magnesium sulfate, drying and grinding to obtain a marketable product.