RU2469004C1 - Method of producing magnesia cement and apparatus for realising said method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of structural materials and can be used to make building tiles, concrete, xylolite articles, fibreboard, foamed structural materials and plaster mortar. The method of producing magnesia cement involves decomposition of magnesite or dolomite to magnesium oxide and carbon dioxide during thermal treatment of crushed natural minerals at temperature 600-750°C for 1-2 hours in the presence of 0.5% sodium chloride from burnt dolomite or magnesite. Thermal treatment is carried out using magnesite along with dolomite and sodium chloride with the following composition, wt %: magnesite 12-17; dolomite 82.5-87.5; sodium chloride 0.5. The apparatus for realising the method of producing magnesia cement includes drum mixer, a vertical furnace, gas temperature control device and a ball mill. The vertical furnace, which is lined with firebrick, has a built-in cage, which is a grid of metal rods with diameter 20x20 mm, a hopper, a metallic container on wheels which facilitate continuous thermal treatment of the mixture of magnesite, dolomite and sodium chloride.

EFFECT: high quality of magnesia cement, continuous operation of the furnace, low capital and operational costs.

8 cl, 2 dwg, 1 tbl, 2 ex

Description

The invention relates to the production of building materials and can be used to obtain building boards, concrete, xylolithic products, fiberboard, building foam and gas materials, mortars for plastering.

A known method of producing magnesia binder from dolomite, intended for the production of building materials. The present invention proposes a regime of firing dolomite to control the quality factor of firing Kk.o = CO ₂ , wt.% / MgO, wt.%, Which should be equal in the range of 1.07-1.72 (RF Patent No. 2064905, published 08/10/1996 g).

The disadvantages of this method of obtaining magnesia binder are:

- the resulting magnesian binder has a low content of magnesium oxide, not more than 22%, which ensures the production of building materials with low mechanical properties, for example, compressive strength has a limit of 10-30 MPa, and if magnesia binder contains calcium oxide, which is not excluded formation at a firing temperature of dolomite 750-775 ° C, then the mechanical properties of the resulting building materials will be even lower;

- at a firing temperature of dolomite above 700 ° C, magnesium oxide activity decreases as a result of its recrystallization to periclase form, and this will lead to a decrease in the mechanical properties of the obtained building materials based on such a magnesian binder (L.G. Berg, Introduction to Thermography, ed. USSR Academy of Sciences, Moscow, 1961, pp. 206-211);

- determination in the process of firing the quality coefficient of firing of a magnesian binder (determination of the content of CO ₂ , MgO, CaO) is rather difficult.

A known method of producing magnesia binder by mixing caustic dolomite and Portland cement in the ratio: caustic dolomite 25-50 wt.%, Portland cement 50-75 wt.% (RF Patent No. 2102349, published 01.20.1998).

The disadvantage of this method of obtaining a magnesian binder is a significant increase in the cost of building materials obtained on the basis of caustic dolomite. With the indicated ratios of caustic dolomite and Portland cement, unbaked dolomite can be mixed with Portland cement without reducing the mechanical properties of building materials, but this can also be achieved by mixing Portland cement with sand.

A known method of producing caustic dolomite, adopted by us for the prototype, which consists in the fact that the production of caustic dolomite is carried out by two-stage heat treatment of crushed dolomite raw material by heating it first to 450-550 ° C for 20-100 minutes, and then to 600-720 ° C for 5-25 minutes, before being fed into the heat treatment, the crushed dolomite raw material is irrigated with a solution of magnesium chloride with a density of 1.2-1.3 g / cm ³ in an amount of 0.5-3.0% by weight of the calcined raw material (RF Patent No. 2158241, published 10/27/2000).

The disadvantages of this invention are:

- temperature instability along the height or length of the dolomite layer during heat treatment, since the nearby layers of dolomite to the flame of the gas burner will heat up above 800 ° C, and this will lead to the formation of a solid perekazny form of MgO crystals in caustic dolomite and the formation of CaO, which in turn will reduce the mechanical properties of building materials obtained on the basis of such caustic dolomite;

- to reduce the temperature and firing time of dolomite, it is irrigated with a solution of MgCl ₂ , but the irrigation of crushed dolomite with a solution of sodium chloride has the same effect, which is much simpler and cheaper.

The objectives of the proposed method for producing magnesia binder and installation for implementing the method are to eliminate the above disadvantages of the known methods and stabilize the conditions for obtaining highly effective magnesia binder, ensure continuous operation of the furnace, reduce capital and operating costs.

The solution to these problems is achieved as follows.

Crushed dolomite and magnesite are loaded onto a concrete site in a mass ratio (82.5-87.5) :( 12-17), which are irrigated with a nozzle and a pump with a 20% aqueous solution of sodium chloride having a specific gravity of 1.12 g / cm ³ , based on the content in the total mass of raw materials of 0.5 wt.% sodium chloride. For example. 82.5 kg of dolomite, 17 kg of magnesite are loaded onto the site, then 0.5 kg of sodium chloride must be added to this mass. This mass will be contained in 2.5 l of a 20% aqueous solution of sodium chloride having a specific gravity of 1.12 g / cm ³ . The irrigated mass of dolomite and magnesite with an aqueous solution of sodium chloride is loaded into a drum type mixer. Pieces of dolomite and magnesite should have a size of 30-60 mm. After mixing dolomite, magnesite and sodium chloride in a drum for 15-20 minutes, the resulting mixture is unloaded into a special hopper, from which, using an electric crane, a mixture of dolomite, magnesite and sodium chloride is loaded into a vertical furnace, which is shown in Fig. 1. The furnace includes the following elements:

1. The metal casing. 2. Refractory brick lining. 3. A cage made in the form of a grid of reinforcing rods with cells of 20 × 20 mm. 4. Metal inserts in the cage of the furnace for fastening the crate. 5. The bunker. 6. Shiber. 7. Metal inserts for securing the hopper. 8.9. Pipes for supplying a thermostatically controlled hot gas to a furnace having a temperature of 600-650 ° C. 10. A pipe for removing exhaust gas from the furnace. 11. The furnace lid made of heat-resistant steel and lined on both sides with refractory concrete. The thickness of the steel is 20 mm. The lid has a window for loading raw materials (not shown in the figure). 12. Rings for installing and removing the cover. 13. A metal container on wheels. 14. The mixture (a mixture of dolomite, magnesite and sodium chloride).

After the prepared charge is completely loaded into the furnace to the exhaust gas outlet level, as shown in Fig. 1, thermostatically controlled hot gas having a temperature of 600-650 ° C is supplied to the furnace from the thermostated gas device shown in Fig. 2 through pipes ( pos. 8, 9.)

The device includes the following elements:

1. The casing. 2. Refractory brick lining having a thickness of 400 mm. 3. A ring from heat resisting steel 20 mm thick. 4. A pipe for supplying thermostatically controlled hot gas to the furnace. The pipe has thermal insulation with mineral wool, not shown in Fig. 2. 5. A chamber for mixing gas and air. 6. Pipeline for supplying natural gas to the burner. 7. Gas burner mounted tangentially. 8. A pipeline for introducing air together with the exhaust gas after firing the charge in a furnace installed tangentially in one direction with a gas burner.

After heat treatment of the mixture for 1-1.5 hours, it is unloaded into a metal container on wheels (Fig. 1, item 13). The heat treatment time is specified in the production process, since it depends on the properties of natural dolomite and magnesite.

At the beginning of the process, the charge in the hopper volume (Fig. 1, pos. 5) is unloaded separately from the bulk of the charge and reloaded into the furnace. In the following operations, the last portions of the burnt charge are left in the hopper (Fig. 1. Item 5).

The unloaded burnt charge is loaded into a ball mill together with phosphoric acid and sodium tetraborate in a mass ratio of 1: 0.5 in the amount of 0.5-1.2 wt.% Of the obtained mass of the burnt charge. Grinding the calcined charge in a ball mill is carried out to obtain a particle size of 50-70 microns. The obtained magnesian binder is unloaded into a packaging container, analyzed for MgO and CaO content, and samples are taken for mixing the magnesia binder with an aqueous solution of magnesium chloride, having a specific gravity of 1.2 g / cm ³ , and obtaining samples for testing their mechanical properties.

The set of features of the proposed technical solution - a method of obtaining a magnesian binder and installation for implementing the method are different from the prototype and do not follow explicitly from the studied prior art, therefore, the authors believe that the method and installation are new and have an inventive step.

The method of producing a magnesian binder and the installation for implementing the method make it possible to use dolomite with a low content of magnesium carbonate to obtain a highly effective magnesian binder to reduce the capital and operating costs of introducing the method and installation into production, to increase the range of high-quality building materials.

An example implementation of the method of obtaining magnesia binder. As an example, take magnesite from the Savinsky deposit in the Irkutsk region, which has the following composition, wt.%:

MgCO ₃ - 97.48; SiO ₂ - 0.9; Al ₂ O ₃ - 0.6; Fe ₂ O ₃ - 0.8; CaO — 0.22 and dolomite of the Dankovsky deposit of the Lipetsk region, which has a composition, wt.%: MgCO ₃ - 38.74; CaCO ₃ - 58.96; SiO ₂ - 1.6; Al ₂ O ₃ - 0.3; Fe ₂ O ₃ - 0.4.

Option 1.

For heat treatment in an oven, we take 12 wt.% Magnesite, 87.5 wt.% Dolomite and 0.5 wt.% Sodium chloride. We load 12 kg of magnesite, 87.5 kg of dolomite onto a concrete site and irrigate with a 20% aqueous solution of sodium chloride having a specific gravity of 1.12 g / cm ³ based on the content of 0.5 kg of sodium chloride in the irrigated solution. For irrigation, sodium chloride is required:

V _p-pa = 500 g: 1.12 g / cm ³ × 0.2 = 2451 cm ³

or 2.5 l of solution

where 0.2 is a coefficient taking into account the 20% sodium chloride content in the solution.

Irrigated with a solution of sodium chloride, magnesite and dolomite are loaded into a drum-type mixer with a tilted axis of the drum from the horizontal by 40 °. After mixing the feedstock for 15-20 minutes, it is discharged into a hopper having a bottom opening device. Using a crane beam, the feedstock of the hopper is loaded into a vertical furnace. Thus, the furnace is fully loaded with feedstock for its heat treatment. The window in the lid of the furnace is closed with an insert. The gas thermostatting device is turned on and gas (a mixture of natural gas and atmospheric air combustion products) having a temperature of 600-650 ° C is fed into the furnace.

For this type of raw material, the optimal gas temperature and heat treatment time are preliminarily determined in the range of 1-1.5 hours, which allows maximum formation of magnesium oxide and the absence of calcium oxide. Under optimal conditions of heat treatment of a mixture of magnesite, dolomite and sodium chloride, the resulting products will have the following composition, wt.%: MgO - 28.73, CaCO ₃ - 67.58; CaO - 0.04; SiO ₂ - 1.98; Al ₂ O ₃ - 0.43; Fe ₂ O ₃ - 0.53; NaCl - 0.65.

As a result of heat treatment of 100 kg of magnesite, dolomite and sodium chloride, a mass of burnt charge equal to 76.11 kg is obtained, and 23.89 kg of CO _{2 is} removed from the furnace together with the exhaust gas.

It should be noted that at the beginning of the furnace commissioning, the mass of the loaded charge in the volume of the hopper remains unburnt, therefore, this charge is returned to the kiln, and in the following operations, the burnt charge is left in the hopper, so the mass of the loaded charge in the furnace will be equal to the mass of the burnt charge minus carbon dioxide as a result of dissociation of MgCO ₃ into MgO and CO ₂ . Thus, if 100 kg of the charge is loaded into the furnace, then each time they will receive 76.11 kg of burnt charge, provided that the initial charge contains 45.77 wt.% MgCO ₃ . The process of obtaining a magnesian binder can be carried out in this method and with this installation periodically with the furnace stopping for the duration of unloading the calcined charge from it and loading the initial charge, as well as continuously. During continuous operation of the furnace, a schedule is made for loading the initial charge and a schedule for unloading the calcined charge during the heat treatment time of the charge. During continuous operation, the furnace saves natural gas consumption by about 40-50% and increases the productivity of the furnace by 1-2 times. This will affect a significant reduction in the cost of magnesia binder.

The calcined charge from the furnace is unloaded into the container on wheels, and from the container to the concrete platform for cooling to a temperature of 60-100 ° C. Then, from the concrete site, the cooled calcined charge is loaded into a ball mill together with phosphoric acid and sodium tetraborate in a ratio of 1: 0.5. The mass of the loaded salts is 0.5-1.2 wt.% Of the mass of the loaded calcined charge from the furnace. As an example, we give a calculation of the loaded masses of sodium phosphate and tetraborate in a ball mill together with a burnt charge.

The total mass of the mixture of salts loaded into the ball mill will be:

m _C = 76.11 × 1.2%: 100% = 0.91 kg

где

Where

76.11 - the mass of the burnt charge loaded into the ball mill, kg;

1.2% - the proportion of the total mass of salts loaded into a ball mill;

3 - the cash fraction of Na ₂ OB ₄ O ₇ in the total mass of Na ₃ PO ₄ and Na ₂ B ₄ O ₇ loaded into the ball mill.

The finished dispersed product - magnesia binder should have the following composition, wt.%: MgO - 28.27; CaCO ₃ - 66.91; CaO - 0.03; SiO ₂ - 1.95; Al ₃ O ₃ - 0.43; Fe ₂ O ₃ - 0.58; NaCl - 0.65; Na ₃ PO ₄ - 0.79; Na ₂ B ₄ O ₇ - 0.39.

Option 2

For heat treatment in an oven, we take 17 wt.% Magnesite, 82.5 wt.% Dolomite and 0.5 wt.% Sodium chloride.

The compositions of magnesite and dolomite are similar to those in option 1.

The mixture of magnesite, dolomite and sodium chloride has the following composition, wt.%: MgCO ₃ - 48.53; CaCO ₃ - 48.64; CaO - 0.04; SiO ₂ - 1.47; Al ₂ O ₃ - 0.35; Fe ₂ O ₃ - 0.47; NaCl - 0.5.

All other operations for obtaining the burnt charge in the furnace are similar to those described in option 1.

The calcined charge in the furnace had a mass of 74.67 kg and the following composition, wt.%:

MgO - 31.07; CaCO ₃ - 65/14; CaO - 0.05; SiO ₂ - 1.97; Al ₂ O ₃ - 0.47; Fe ₂ O ₃ - 0.63; NaCl - 0.67

The calcined charge is loaded into a ball mill together with sodium phosphate and tetraborate in the amount of 1.2 wt.% Of the charge mixture, the loaded mass of sodium phosphate and tetraborate will be:

The mass of Na ₃ PO ₄ will be: mNa ₃ PO ₄ = 0.896 kg-0.896 kg: 3 = 0.597 kg,

The mass of Na ₂ B ₄ O ₇ will be: mNa ₂ B ₄ O ₇ = 0.896 kg-0.597 kg = 0.299 kg.

The dispersed powder obtained by grinding in a ball mill should have a dispersion of 50-70 microns and composition, wt.%:

MgO - 30.70; CaCO ₃ - 64.37; CaO - 0.05; SiO ₂ - 1.95; Al ₂ O ₃ - 0.46; Fe ₂ O ₃ - 0.62; NaCl - 0.65; Na ₃ PO ₄ - 0.80; Na ₂ B ₄ O ₇ - 0.39.

When the content in the magnesian binder of 28.1-30.7 wt.% Magnesium oxide, closed on an aqueous solution of MgCl ₂ , and aged for 7 days had a compressive strength of 50-60 MPa (RF Patent No. 10407 "Method for producing caustic dolomite" )

The results of laboratory tests of the obtained magnesia binder, carried out using an electrofusion, are presented in table 1.

Table 1 №№
p / p The composition of the feedstock received for heat treatment wt.% Heat treatment temperature, ° С Duration of heat treatment, min The composition of the resulting product wt.% Option 1 (magnesite 12%, dolomite 87.5%, sodium chloride 0.5%) MgCO ₃ 45.59 MgO 25.3 CaCO ₃ 51.60 MgCO ₃ 5.2 one. CaO 0.03 600 60 CaCO ₃ 65.9 NaCl 0.5 CaO 0.04 impurities NaCl 0.64 (SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ ) 2.28 impurities 2.92 MgCO ₃ 45.59 MgO 28.6 CaCO ₃ 51.60 CaCO ₃ 67.7 2. CaO 0.03 650 60 CaO 0.04 NaCl 0.5 NaCl 0.65 impurities 2.28 impurities 3.01 MgCO ₃ 45.59 MgO 28.6 CaCO ₃ 51.60 CaCO ₃ 67.7 3. CaO 0.03 600 90 CaO 0.04 NaCl 0.5 NaCl 0.65 impurities 2.28 impurities 3.01 Option 2 (magnesite 17%, dolomite 82.5%, sodium chloride 0.5%) MgCO ₃ 48.53 MgO 27.0 CaCO ₃ 48.64 MgCO ₃ 6.4 one. CaO 0.04 600 60 CaCO ₃ 63.0 NaCl 0.5 CaO 0.05 impurities NaCl 0.65 (SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ ) 2.74 impurities 2.9 MgCO ₃ 48.53 MgO 07/31 CaCO ₃ 48.64 CaCO ₃ 65.1 2. CaO 0.04 650 60 CaO 0.05 NaCl 0.5 NaCl 0.67 impurities 2.74 impurities 3.11 MgCO ₃ 48.53 MgO 07/31 CaCO ₃ 48.64 CaCO ₃ 65.1 3. CaO 0.04 600 90 CaO 0.05 NaCl 0.5 NaCl 0.67 impurities 2.74 impurities 3.11

As follows from the data in table 1, at a firing temperature of a mixture of magnesite, dolomite and sodium chloride of 600 ° C and a firing duration of 60 minutes, the dissociation of MgCO ₃ into MgO and CO ₂ does not occur completely regardless of the ratio of magnesite and dolomite.

At a temperature of 600 ° C and a duration of firing a mixture of magnesite, dolomite and sodium chloride for 90 min, the dissociation of MgCO ₃ into MgO and CO ₂ occurs completely regardless of the ratio of magnesite and dolomite.

At a temperature of 650 ° C and a firing duration of 60 minutes, the dissociation of magnesite and dolomite into MgO and CO ₂ occurs completely independently of the ratio of magnesite and dolomite.

In the temperature range 600-650 ° C, when firing a mixture of magnesite, dolomite and sodium chloride, CaCO ₃ dissociation into CaO and CO ₂ does not occur. The experimental results are valid only when firing a mixture of magnesite, dolomite and sodium chloride at a thermostated temperature.

Claims (8)

1. A method of producing a magnesian binder by decomposing magnesite or dolomite into magnesium oxide and carbon dioxide during the heat treatment of crushed natural minerals at a temperature of 600-750 ° C for 1-2 hours in the presence of 0.5% sodium chloride from calcined dolomite or magnesite , characterized in that for heat treatment use magnesite in conjunction with dolomite and sodium chloride of the following composition, wt.%:
magnesite 12-17 dolomite 82.5-87.5 sodium chloride 0.5 2. The method according to claim 1, characterized in that the crushed magnesite and dolomite are irrigated with a 20% aqueous solution of sodium chloride with a specific gravity of 1.12 g / cm ³ based on the content of sodium chloride in a mixture with magnesite and dolomite 0.5 wt. %, irrigated magnesite and dolomite are loaded into a drum-type mixer and mixed for 15-20 minutes. 3. The method according to claim 1, characterized in that for the heat treatment of a mixture of magnesite, dolomite and sodium chloride, a thermostated gas is used having a temperature of 600-650 ° C and obtained in a special thermostating device for the products of natural gas, air and exhaust gas after firing magnesite , dolomite and sodium chloride. 4. The method according to claim 1, characterized in that the duration of the heat treatment of crushed magnesite, dolomite with sodium chloride is 1-1.5 hours 5. The method according to claim 1, characterized in that the grinding of calcined magnesite, dolomite with sodium chloride is carried out with orthophosphoric and tetraborane sodium in a mass ratio of 1: 0.5 and constituting 0.5-1.2% of the loaded mass for grinding the calcined magnesite, dolomite with sodium chloride. 6. The method according to claim 1, characterized in that the grinding of calcined magnesite, dolomite with sodium chloride, phosphoric acid, sodium tetraborate is carried out to a dispersion of 50-70 microns. 7. Installation for implementing the method of producing magnesia binder, including a drum type mixer, a vertical furnace, a gas thermostat, a ball mill, characterized in that the vertical furnace, made of refractory bricks, has a built-in stand, which is a grid of metal rods with with a cell diameter of 20 × 20 mm, a hopper, a metal container on wheels that allow the heat treatment of a mixture of magnesite, dolomite and sodium chloride to be carried out continuously. 8. The installation according to claim 7, characterized in that it includes a gas thermostatting device, which allows to supply gas with a given temperature to the furnace, which eliminates the burning of magnesite and dolomite in the furnace and allows to obtain calcined magnesite and dolomite containing magnesium oxide in the active form and not containing calcium oxide.

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