RU2601962C1 - Method of producing gypsum binder, modified composite gypsum binder and method for production thereof - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: group of inventions relates to production of construction materials and specifically to a method of producing a gypsum binder, which can be used as a base during construction of road bases and as a binder in construction, from technical gypsum - phospho-semihydrate or phospho-dihydrate of calcium sulphate, as well as to production of a modified composite gypsum binder having a wide spectrum of application in construction. Method of producing a gypsum binder includes heating of initial raw material, which is technical gypsum - phospho-semihydrate or phospho-dihydrate of calcium sulphate, herewith the heating is carried out in two stages, at the first stage at the temperature of 85±5 °C, at the second stage at the temperature of 160±5 °C, herewith at the first stage the heating is carried out at continuous mixing the raw material for 40-60 minutes at the pressure of not less than 0.1 MPa, at the second stage the heating is carried out at continuous mixing the raw material for 30-60 minutes. Method of producing the gypsum binder may additionally include grinding of the gypsum binder at the end of the second stage of heating.

EFFECT: technical result is production of a stable binding product with stable physical and chemical parameters, in particular, higher strength.

6 cl, 2 dwg, 7 tbl

Description

The group of inventions relates to the field of production of building materials, and in particular to a method for producing a gypsum binder, which can be used as a base in the construction of road bases and as a binder in the construction industry, from gypsum technical - phospho-hemihydrate or phosphate dihydrate of calcium sulfate, as well as to obtain modified composite gypsum binder having a wide range of applications in construction.

A known invention that describes the production of a gypsum binder, which includes lime or shale ash 26.0-29.0 toluene diisocyanate 0.2-1.05 β-calcium sulfate hemihydrate and the rest of the phosphogypsum. The binder allows you to slow down the setting time: the beginning of 180-270 min, the end of 360-500 min (SU 1668330 A1, IPC C04B11 / 00, publ. 07.08.1991).

The disadvantage of this invention is the need for a large amount of lime and shale ash, which is currently not produced by industry.

A known additive for the modification of gypsum binders, including C-3 superplasticizer based on the sodium salts of the condensation product of naphthalene sulfonic acid with formaldehyde, as well as zeolite rock calcined at 800 ° C, and a silicate brick fight, while the additive contains C-3 superplasticizer in the form of dry powder in the following ratio of the components of the additive (% by weight): dry powder of superplasticizer C-3 - 1.5-4.0; zeolite additive calcined at 800 ° C 12-14; silica brick fight 82-86 (RU 2074137, IPC: C 04 V 11/00, C 04 V 111/20, publ. 02.27.1997).

Known gypsum binder in the form of semi-aquatic gypsum or anhydrite and a modifying additive, including (wt.%): A hydraulic binder 50-90, an active mineral component 10-45, a plasticizing additive 0.1-2, a setting time and hardening term 0.001-1, stabilizer 0.001-5. Moreover, as a hydraulic binder contains one of the following components or mixed in any proportion Portland cement of any kind, white cement, colored cement (RU 2260572, IPC C04B11 / 30, published on September 20, 2005).

The disadvantage of these inventions is the multicomponent composition.

Known additive for the modification of gypsum binders containing silica fume and superplasticizer C-3, obtained on the basis of sodium salts of the condensation product of naphthalenesulfonate and formaldehyde (RU 2081076, IPC С04В 11/00, publ. 10.06.1997).

A known method for the production of waterproof phosphogypsum binder (Plaster materials and products (production and use) ./ Under the general editorship of A.V. Ferronskaya. - M .: Publishing house ASV, p.152. - ISBN 5-93093-272-7), including the mixing of phosphogypsum dihydrate with quicklime in a ratio of 1: 0.8 - 1: 1.1, active pozzolanic additives (ash, tripoli, etc.) in an amount of 20 ... 40% by weight of all introduced components and the exposure of the mixture in a container in which the reaction of slaking lime and dehydration of phosphogypsum to hemihydrate proceeds. Obtained by this method, the binder has the brand G-5 - G-7.

The disadvantage of these methods is the significant consumption of quicklime and pozzolanic additives.

A known method of processing phosphogypsum, including mixing phosphogypsum with an additive containing lime, and water, granulation, after granulation, carry out drying with cold air at a temperature of 15-20 ° C. And further heat treatment to obtain calcium sulfate phospho-hemihydrate (RU 2309130 C1, publ. 10.27.2007).

A known method of utilizing phosphogypsum, including neutralizing it by introducing calcium hydroxide and water, followed by filtration pressing and removal of the filtrate. Filtration pressing is carried out with an effort that provides mechanical activation of phosphogypsum, exceeding the strength of the initial crystalline hydrates of phosphogypsum (RU 2215707 C1, publ. 10.11.2003).

A disadvantage of the known methods are the insufficient quality of the products obtained and the high energy consumption.

A known method of producing a gypsum binder by sintering at a temperature of 1100 ° C. Calcium sulfate hemihydrate 90.0-99.7% with calcium carbonate 0.3-10.0%. The result is a solid solution with a high content of calcium oxide. The compressive strength of dry samples is 10.7–13.7 MPa, the softening coefficient is 0.44–0.58 (SU 1530596 A1, IPC C04B11 / 00, publ. 12/23/1989). The disadvantage of this method is the significant energy consumption.

An invention is known that describes the production of a gypsum binder, including the introduction of a carbonate additive in phosphogypsum and subsequent dehydration and providing for preliminary mixing with the waste of production of pigment titanium dioxide based on monohydrous ferrous sulfate in the ratio of 1.00: 2.33 - 1.00-3.00. The resulting mixture is introduced in an amount of 1.01-4.17% by weight of phosphogypsum. The strength of the binder compressive 39 MPa. The start of setting is 10 minutes, the end is 19 minutes (SU 1502512 A1, IPC C04B11 / 00 publ. 08.23.1989). The disadvantage of this method is the complexity of the process.

The objective of the invention is the production of a stable environmentally friendly gypsum binder and a modified gypsum binder, used in the field of building materials for various purposes, at low energy consumption.

The technical result of the claimed group of inventions is to obtain a stable binder product with stable physico-chemical parameters, as well as significantly simplify the process of producing a gypsum binder, leading to a decrease in the total cost of energy and fuel and a decrease in the cost of the resulting binder product.

The claimed technical result is achieved by the fact that the method of producing a gypsum binder involves heating the feedstock, which is technical gypsum - calcium phosphate hemihydrate or phosphodihydrate calcium sulfate, and the heating is carried out in two stages, in the first stage at a temperature of 85 ± 5 ° C, in the second stage at a temperature of 160 ± 5 ° C, while in the first stage, heating is carried out with continuous stirring of the raw material for 40-60 minutes under a pressure of at least 0.1 MPa, in the second stage, heating is carried out with continuous stirring of the raw material I for 30-60 minutes. The method of producing a gypsum binder may further comprise a step of grinding the gypsum binder at the end of the second heating step.

A method of obtaining a modified composite gypsum binder, comprising the implementation of the method for producing a gypsum binder described above, in which, before the first stage of heating, the feedstock is mixed with calcium oxide and a crystal growth activator in the following ratio, wt.%:

- gypsum technical (phospho-hemihydrate or phosphate dihydrate of calcium sulfate) 92.5-99.8,

- calcium oxide 0.1-5.0,

- crystal growth activator 0.1-2.5,

where the crystal growth activator is a mixture of gas treatment dust from an electric steelmaking shop in the form of insoluble oxides of calcium, silicon, iron, magnesium, zincates and salts of iron sulfate, magnesium sulfate, calcium sulfate in the following ratio, wt.%:

- gas cleaning dust from the electric steelmaking shop in the form of insoluble oxides of calcium, silicon, iron, magnesium, zincates in an amount of 60-80, optimally 75,

- salts of iron sulfate, magnesium sulfate, zinc sulfate, calcium sulfate in an amount of 20-40, optimally 25.

As a result of the implementation of the inventive method for producing a modified composite gypsum binder, a modified composite gypsum binder is obtained, including a gypsum binder obtained by the method for producing a gypsum binder, a crystal growth activator, and also calcium oxide in the following ratio of components,%:

- gypsum binder 92.5-99.35,

- calcium oxide 0.1-5.0,

- activator of crystal growth 0.1-2.5.

The second method of obtaining a modified composite gypsum binder, comprising the implementation of a method of producing a gypsum binder, comprising the step of grinding a gypsum binder, while at the grinding stage, the gypsum binder is mixed with magnesia material and a diatomaceous filler in the following ratio, wt.%:

- gypsum binder 53-96,

- caustic magnesite powder, grade DTMC 1 ... 3MK 2-35,

- salt of sulfate or magnesium chloride 1-2,

- diatomaceous filler 1-10.

As a result of the second method of producing a modified composite gypsum binder, a modified composite gypsum binder is obtained, including a gypsum binder, obtained by the method of producing a gypsum binder, including the step of grinding a gypsum binder, caustic magnesite powder DTMC 1 ... 3MK, magnesium sulfate or magnesium chloride, diatom filler in the following ratio of components,%:

- gypsum binder 53-96,

- caustic magnesite powder, grade DTMC 1 ... 3MK 2-35,

- salt of sulfate or magnesium chloride 1-2,

- diatomaceous filler 1-10%.

The invention is illustrated by drawings, in which: FIG. 1 is a flow chart of the production of gypsum binder by a horizontal method of high-temperature drying; in FIG. 2 is a flow chart of the production of gypsum binder by the vertical method of high-temperature drying.

The positions in the drawings indicate:

1 - feed hopper,

2 - receiving hopper,

3 - rotating drum using infrared heaters,

4 - drying high-temperature drum using infrared heaters,

5 - refrigerator

6 - chopper of the finished product,

7 - silo for crushed finished product,

8 - silo for a product that has not passed the grinding process,

9 - hopper dispenser,

10 - hopper at the end of the process,

11 - conveyor belt

12 - infrared directional heaters,

13 - heat generator,

14 - a supercharger of hot air.

The inventive method of obtaining a gypsum binder includes the following steps.

The feedstock, which is phosphogypsum - technical gypsum, corresponding to TU 2141-693-00209438-2015 (calcium sulfate hemihydrate or calcium sulfate phosphodihydrate), with a total moisture content of not more than 30%, is uniformly fed from the feed hopper 1 equipped with a vibrator, according to the nutrient conveyor at the rate of 220-250 kg per minute in the receiving hopper 2.

From the receiving hopper 2, equipped with a vibrator, carry out a uniform supply of a given volume of raw materials into the drum 3.

The drum 3 consists of a housing, which is a welded structure made of separate shells. Inside the housing, to activate the heat transfer, a nozzle is first installed screw, on the rest of the drum lifting and blade. The casing is supported by two steel bands. A gear ring is attached to the drum casing by means of a traverse, by means of which the drum is driven into rotation by a drive. The drum is installed in relation to the horizon at an angle of 1 ° -4 °. Directional infrared heaters are installed in the lower part of the drum casing, providing uniform heating of the surface.

In the drum 3, the heating of the raw materials is carried out due to the return gases coming from the drum 4, and due to infrared directional heaters. The technological parameters of drum 3: processing temperature of raw materials, rotation speed, angle, humidity of raw materials, processing time of raw materials, pressure in the drying chamber, provide the process of forming complex chemical complexes with the simultaneous production of highly porous granules.

The inclination of the housing in combination with rotation around the axis provides movement and mixing of the material. In the drum 3, an overpressure of at least 0.1 MPa is provided due to the forced injection of return gases from the drum 4

The temperature of the raw material along the entire length of the drum is maintained at a level of 60-100 ± 10 ° C, optimally 85 ± 5 ° C. Drum 3 is conditionally divided into three equal zones. The heating of raw materials in the drum 3 is carried out:

- above due to the residual heat of the return gases from the drying drum 4, the temperature of which is 120-150 ° C,

- bottom by heating the lower surface of the drum 3 using infrared heaters directional,

- control of maintaining the temperature of the raw material 85 ± 5 ° C in conditional zones 2 and 3 is carried out using the control unit of infrared emitters, combined with a temperature controller,

- control of maintaining the temperature of the raw materials in conditional zone 1 (the beginning of the drum) is carried out using the temperature of the return gases coming from the drum 4,

- control of the temperature of the feedstock is carried out in all three zones of the drum 3, the deviation from the set temperature should not exceed more than ± 5 ° C.

At a temperature of 85 ± 5ºС, the rate of topochemical processes (interphase transitions) in the feedstock increases by 6-8 times, which leads to a redistribution of the components of the feedstock.

During the formation of calcium sulfate crystals at a temperature of 85 ° C, the crystallization rate increases by 4 times. The crystallization process in drum 3 lasts for 40-60 minutes, at the same time, the process of incorporating the components of the feedstock into the crystal lattice of calcium sulfate occurs, which leads to the formation of complex chemical complexes.

At the same time, at a temperature of 85ºС, granulation of the starting material takes place due to crystallization processes; the size of porous granules is 1-10 mm. Experimental data showed that at a temperature of 25 ° C the time of formation of granules is at least 10 hours, and at 85 ° C the time of formation of granules is 25-60 minutes, optimally 40 minutes.

The loading of the drum volume is carried out at 25-45% of the volume of the drum 3, optimally 35%. The rotation speed of the drum is 2-10 rpm, optimally 6 rpm.

At a raw material temperature of 85 ° C, a complex compound ((CaН) ₂ (SO ₄ ) ₃ CaHPO ₄ ) is formed in the drum 3, which acts as a retarder, and a complex complex (CaНPO ₄ CaSO ₄ SrSO ₄ ) is formed, which acts as a complex binder and conservative for long-term storage of the product.

At a temperature of 85 ° C for 40 minutes in the drum 3 there is a loss of excess moisture of the feedstock in the amount of 3-5%, which corresponds to 30-50 kg of H ₂ O per 1 ton of the starting product. The initial amount of excess moisture in the feedstock is 200-220 kg per 1 ton of feedstock.

The process of forming granules and complexes in the drum 3 is a key process for subsequent high-temperature processing in the drum 4.

After granulation of the raw materials in the drum 3, the resulting material — a complex for producing a binder — is fed into the drum 4. The material from the drum 3 to the drum 4 enters through the transition chamber without contact with the external environment.

There are two options for the location of the drum 4.

The first embodiment is shown in FIG. 1. Drum 4 consists of a housing and a heat generator. The body is a welded structure made of separate shells. Inside the housing, in order to activate the heat transfer, a nozzle is installed, first screw, in the middle of the drum lifting and blade and then chain. The casing is supported by two steel bands. A gear ring is attached to the drum casing by means of a traverse, by means of which the drum is driven into rotation by a drive. The drum is installed in relation to the horizon at an angle of 1 ° -4 °. The inclination of the housing in combination with rotation around the axis provides movement and mixing of the material.

A second arrangement of the drum 4 is shown in FIG. 2. The drum 4 is located vertically and consists of a housing, a heat generator and a screw auger. The body is a welded structure made of separate shells. The housing is mounted on a fixed platform. Inside the drum 4, in its lower part, a conical product trap is installed, which provides material supply to the screw screw, continuously rotating at a given speed and feeding the finished product to the cooling chamber 5. The speed of rotation of the screw is regulated depending on the performance of the installation. In the lower part of the drum 4 (Fig. 2), at a height of 1 meter from the base, four symmetrical hot air superchargers 14 are installed. Hot air superchargers 14 are metal ducts that are installed in relation to the horizontal at an angle of 7 degrees to rise and 30 degrees with respect to to the tangent of the drum 4. When hot air is supplied, vortex flows form. Due to the swirling process, the particle fall rate is slowed, while the particle fall rate can be controlled by the feed rate of hot air through the hot air blowers. Also, particles in the process of falling collide with the surface of the body, thereby increasing the speed of the heat transfer process.

The heat generator consists of a housing, inside of which there is a burner, a burner fan, an air flow regulator. The principle of operation of the heat generator is based on the formation of a mixture of air with the products of complete combustion of gaseous fuel and maintaining the set temperature in automatic mode.

In the lower part of the housing of the drum 3 (Fig. 1, Fig. 2) and the drum 4 (Fig. 1), directional infrared heaters are installed to ensure uniform heating of the surface. In the drum 4 (Fig. 1), the process of double-sided high-temperature heat treatment of highly porous granules obtained by processing raw materials in the drum 3, using flue gases and infrared heaters, is carried out. Flue gases are produced by mixing air with the products of complete combustion of fuel, such as natural gas.

The process of heat treatment of material coming from drum 3 to drum 4 occurs at a temperature of 150-190 ° C, optimally 160 ± 5 ° C. The processing time of the material continuously entering the drum 4 from the drum 3 is 30-60 minutes, optimally 40-45 minutes. During the heat treatment for 40-45 minutes, the excess moisture is completely removed and only crystallization water remains in an amount of not more than 7%. After completion of the heat treatment, the binder material consists of a mixture of α- and β-CaSO ₄ · 0.5H ₂ O. During the heat treatment, a stable complex CaHPO ₄ · CaHSO ₄ · SrSO ₄ · CaSO ₄ · 0,5H ₂ O is also formed - a complex gypsum binder .

The temperature of the flue gases at the inlet to the drum 4 is 600ºС at the outlet 120-150ºС

Drum 4 is conditionally divided into 4 zones. The temperature regime of the material 160 ± 5ºС in zones 2,3,4 is supported by directional infrared heaters and flue gases. In the first zone, the required temperature is maintained by the flue gases obtained by burning gas. When the material enters the drum 4 of the first zone, it comes into contact with the flue gases at an inlet temperature of 600 ° C; as a result, heat is transferred to the material at high speed. The temperature of the material within 5-10 minutes reaches 150-190ºС. Temperature control in all areas of the drum 4 is carried out using sensors that provide temperature measurement inside the material.

Material loading into the drum 4 is carried out at 15-35% of the volume of the drum 4, optimally 25%.

The rotation speed of the drum 4 is 2-6 rpm, optimally 4 rpm

The heat-treated material from the drum 4 enters the cooling chamber 5, where it cools to a temperature of 50-60 ° C at a speed of 10 ° C per minute.

The material cooled down to a temperature of 50-60ºC enters the material grinding unit 6, where crushing and pressure at the same time by the rolls of granules to a state of coarse grinding according to GOST 125-79 occur. The finished crushed material, which is a gypsum binder, is loaded into a silo 7 using a screw conveyor.

The finished gypsum binder from the refrigerating chamber 5 can be immediately shipped to the silo 8 without mechanical impact on the final product.

Ready gypsum binder from silos is packed up for a long storage period with unchanging properties for at least 1 year and the possibility of transportation to the application.

The described method for the production of gypsum binder has several advantages. At the first stage, at an optimal temperature of 85 ° C and a processing time of 40 minutes, the described method provides the process of forming a porous granule without using a granulator device. The porous granule can reduce the firing time in the second stage to 30-40 minutes, which makes it possible to reduce the consumption of thermal energy.

The implementation of the described method allows at the second stage to reduce the temperature of the optimal heat treatment to 160 ° C and the optimal heat treatment time to 40 minutes due to the formed porous granules and complex compounds in the first stage of the technological process. The reduction in energy consumption is achieved due to the fact that the granule from the drum 3 enters the drum 4 at a temperature of 85 ± 5 ° C, in contrast to the known methods in which the raw material at the inlet has an ambient temperature (20-25 ° C). The initial temperature difference between the known methods and the inventive method is 60 ± 5 ° C.

The inventive production method allows to obtain a composite gypsum binder with stable strength characteristics of 2-4 MPa / cm ² without the use of neutralizers and modified additives.

The exact parameters of the required temperature in the technological cycle in drums 3 and 4 are achieved by means of directional infrared heating of the outer shell of the drum containers, the temperature scatter in all zones is not more than ± 5ºС. Thermal purified gases from the drum 4 are sent to heat the raw materials in the drum 3, which significantly saves the cost of thermal energy.

To improve the strength characteristics of the gypsum binder and to preserve the binder properties for a long storage period, additives are used, thereby obtaining a modified composite gypsum binder.

When creating modified composite gypsum binders, additives that improve the properties of the finished material are added to the source material through the hopper 9.

The modified composite gypsum binder contains,% by weight:

Option number 1:

 - gypsum technical (phospho-hemihydrate or phosphate dihydrate of calcium sulfate) 92.5-99.8,

- calcium oxide (quicklime) 0.1-5.0,

- crystal growth activator 0.1-2.5,

the crystal growth activator satisfies the following requirements: the specific surface in the dehydrated (dry) state is not less than 6 m ² / g, with an average particle size of not more than 10 microns and contains crystals of sulfate salts.

Option number 2:

 - gypsum binder 53-96,

- caustic magnesite powder of the brand DTMC 1 ... 3, MK in an amount of 2-35,

- salts of magnesium sulfate or magnesium chloride 1-2,

- diatomaceous filler 1-10.

The use of crystal growth activators leads to an increase in strength characteristics to 8-10 MPa / cm ² and to an increase in the rate of setting of a knitting product when mixed with water at a ratio of 1: 0.15.

The composition of the crystal growth activator,% by weight:

- gas cleaning dust from the electric steelmaking shop in the form of insoluble oxides of calcium, silicon, iron, magnesium, zincates in an amount of 60-80, optimally 75,

- salts of iron sulfate, magnesium sulfate, zinc sulfate, calcium sulfate in an amount of 20-40, optimally 25.

Preparation of crystal growth activator

In a container with a mechanical stirrer, load 1 part by weight of 20% technical sulfuric acid (H ₂ SO ₄ ) and 3 parts by weight of PGESP (gas cleaning dust from electric arc furnaces). Stir the composition for 20 minutes. A chemical reaction occurs with the release of thermal energy.

After mixing, a friable mass in the form of small pellets is obtained - an activator of crystal growth.

Since PHESP has high porosity, therefore, excess moisture penetrates into the porous space, and the crystallizer turns out to be friable in the form of small granules. Due to the increase in concentration, crystals of salts of iron, magnesium, and zinc sulfates are formed on the surface of PHESP particles.

In the process of mixing sulfuric acid and PHESP, the following chemical processes occur:

Fe ₂ O ₃ + 3H ₂ SO ₄ = Fe ₂ (SO ₄ ) ₃ + 3H ₂ O

MgO + H ₂ SO ₄ = MgSO ₄ + H ₂ O

ZnO + H ₂ SO ₄ = ZnSO ₄ + H ₂ O

CaO + H ₂ SO ₄ = CaSO ₄ + H ₂ O

As a result of chemical reactions, iron sulfate Fe ₂ (SO ₄ ) ₃ , magnesium sulfate MgSO ₄ , zinc sulfate ZnSO _{4 are formed} .

The crystal growth activator at the rate of 3 kg and calcium oxide (CaO) at the rate of 3.5 kg per 1 ton of the initial technical gypsum are jointly loaded into the hopper 9. The material from the hopper 9 is simultaneously and continuously supplied with the technical gypsum to the drum 3, where mixing them and heating for 40 minutes. Further, the process occurs as described above for the production of a gypsum binder.

Due to the introduction of a crystal growth activator and calcium oxide (CaO), the growth rate and crystal size of calcium sulfate dihydrate increase upon mixing of the finished product with water. At the same time, the strength characteristics of the finished product increase by 1.5-2 times.

In this production method, at a raw material processing temperature of 85 ° C, calcium oxide (CaO) is also used as an activator of crystal growth in a minimum amount of 0.35% by weight of the feedstock, which reduces the cost of production technology compared to previously proposed methods by reducing the amount of CaO used from 30 kg to 3.5 kg per 1 ton of feedstock.

At a temperature of 85 ° C, the acid film is destroyed in the feedstock and the complex compound ((CaН) ₂ (SO ₄ ) ₃ CaHPO ₄ H ₃ PO ₄ ) is formed. The complex compound ((CaН) ₂ (SO ₄ ) ₃ CaHPO ₄ H ₃ PO ₄ ) acts as a retarder of the setting of the binder, the setting rate is regulated by the introduction of calcium oxide (CaO) crystal growth activator into the technological cycle in an amount of 0.1-5.0 % by weight of the feedstock, optimally 0.35%.

The use of diatomaceous filler and magnesia materials as modifying additives leads to an increase in the preservation time at high room humidity and an increase in strength characteristics to 10-15 MPa / cm ² .

Diatomite filler and magnesia materials are introduced into the composite gypsum binder at the grinding stage. Composite gypsum binder from the drum 4 enters the refrigeration chamber 5, where it cools to a temperature of 50-60 ° C at a rate of 10 ° C per minute. The cooled material enters the installation 6, where crushing and pressure are simultaneously carried out by the rollers of the granules to a powder state. At the same time in the installation 6 of the dispenser 10 add:

- caustic magnesite powder of the brand DTMC 1 ... 3MK, in an amount of 2-35% of the total mass of the modified composite gypsum binder,

 - salt of sulfate or magnesium chloride in an amount of 1-2% of the total mass of the modified composite gypsum binder,

- diatomaceous filler in an amount of 1-10% of the total weight of the modified composite gypsum binder.

Table 1. - The chemical composition of the diatomaceous filler and magnesia materials

The chemical composition of magnesia materials:
Caustic magnesite powder, grade DTMC 1 ... 3, MK
Mass fraction,% MgO ≥ 75 ... 90
Mass fraction,% CaO ≤ 2.2 ... 4.5
Mass fraction,% SiO ₂ ≤ 1.8 ... 3.5 The chemical composition of the diatomaceous aggregate:
SiO ₂ 74.80-88.15%
Al ₂ O ₃ 3.34-9.75%
Fe ₂ O ₃ 2.37-5.26%
CaO 0.47-0.85%
MgO 0.61-1.71%
Density 250-550 kg / m ³

With the simultaneous introduction of magnesia materials and a diatomaceous aggregate into the composite gypsum binder, the strength characteristics increase 2-4 times from the parameters of the gypsum binder obtained by two-stage heat treatment without adding modifiers.

Below are examples and experimental evidence of the achievement of the claimed result.

Theoretical and experimental studies of the process carried out in the drum 3, showed the following.

Upon transition to a temperature of 110 ° C, the course of the following reactions becomes possible:

a) CaSO ₄ · 2H ₂ O → b-CaSO ₄ · 0,5H ₂ O + 1,5H ₂ O _g (ΔG ⁰ ₃₈₃ = -836.77 J / mol);

b) CaSO ₄ · 2H ₂ O → β-CaSO ₄ · 0,5H ₂ O + 1,5H ₂ O _g (ΔG ⁰ ₃₈₃ = -6641.31 J / mol).

As can be seen from the value of the Gibbs energy, the formation of a semi-aquatic gypsum binder β-structure is more preferable under these conditions. As follows from the calculations, reaction (b) becomes possible even at a heat treatment temperature of 83 ° C, while reaction (a) becomes possible only at a temperature of 107 ° C.

Experimental studies have shown that the processes of granulation and the formation of complexes effectively begin to occur at a temperature of 85 ° C.

Table 2. - Strength indicators of gypsum binder obtained from technical gypsum

The processing temperature of the feedstock in the drum 3 for 45 min, ° C The setting time of the final product at a temperature of 25 ° C, min The strength of the final product, MPa / cm ²
The pressing method with a force of 20 MPa / cm ² for 3 min was used Gypsum ratio Start end bend compression Without the use of modifying additives 60 120 600 1.7 2,8 0.18 80 90 480 2.5 4.1 0.18 90 80 420 2.6 4,5 0.18 one hundred 60 300 2.9 5.5 0.18 110 60 300 3,5 6.0 0.18 Using a crystal growth activator (CaO) in a volume of 0.35% by weight of raw materials 60 120 600 2.2 3.0 0.18 80 75 420 3,1 5.2 0.18 90 60 300 3.2 5.8 0.18 one hundred thirty 240 3,5 6.5 0.18 110 thirty 240 3.6 6.8 0.18

The optimum processing temperature corresponds to 85 ° C.

A further increase in temperature leads to an increase in energy consumption with a slight increase in strength characteristics.

Theoretical and experimental studies of the process occurring in the drum 4, showed the following.

At a temperature of 180 ° C, the course of processes according to the following reactions becomes possible:

The temperature of the actual onset of the reaction (g) is 134 ° C, and the reaction (e) is 117 ° C (according to thermodynamic calculations).

a) CaSO ₄ · 2H ₂ O → CaSO ₄ b-· 0,5H ₂ O + 1,5H ₂ O _x (ΔG ⁰ ₄₅₃ = -3096.77 J / mol); b) CaSO ₄ · 2H ₂ O → CaSO ₄ b-+ 2H ₂ O _x (ΔG ⁰ ₄₅₃ = -1867.53 J / mol); c) b-CaSO ₄ · 0.5H ₂ O → b-CaSO ₄ + 0,5H ₂ O _g (ΔG ⁰ ₄₅₃ = -2959.18 J / mol); g) CaSO ₄ · 2H ₂ O → c-CaSO ₄ + 2H ₂ O _g (ΔG ⁰ ₄₅₃ = -13013 J / mol); d) CaSO ₄ · 2H ₂ O → b-CaSO ₄ + 2H ₂ O _g (ΔG ⁰ ₄₅₃ = -18621.2 J / mol).

According to the calculated Gibbs energies, for these reactions, the main reactions that occur at a given temperature are reactions (g) and (e), the rest of the reactions are background. As a result of the course of these reactions at 180 ° C, anhydrous calcium sulfate is obtained in various modifications of α and β. Therefore, to obtain hemihydrate of calcium sulfate, a heat treatment temperature in the range of 150-170 ° C is necessary.

Table 3. - The phase composition and strength characteristics of the processed gypsum technical in the drum (4)

Product name Drum heat treatment time 4 at _squ
MPa / cm ²
(7 days) The results of x-ray phase analysis, amount, wt.%
Main phases Gypsum binder obtained from gypsum by technical two-stage heat treatment at temperatures of 85 ° C and 160 ° C 15 minutes 3,1 Bassanite 60 Plaster 35 Celestine 5 30 minutes 3.6 Bassanite 80 Plaster 15 Celestine 5 45 min 4,5 Bassanite 88 Gypsum 7 Celestine 5 60 min 3,5 Bassanite 82 Anhydrite 8 Plaster 5 Celestine 5

Note: Bassanite - CaSO ₄ · 0,5H ₂ O; gypsum - CaSO ₄ · 2H ₂ O; celestin - SrSO ₄ ; anhydrite - CaSO ₄ .

We will study the strength characteristics of a composite gypsum binder, in which a crystal growth activator is added.

The hydration crystal growth activator acts in the declared binder as follows. The mixing of the finished product with water in a ratio of 1: 0.18 due to the dissolution of crystals of sulfate salts dramatically accelerates the hydration process of the main compound of calcium sulfate hemihydrate. The b-CaSO ₄ · 0.5H ₂ O molecule at the beginning of the hydration process extracts water molecules from sulfate salts, and the process of crystallization of sulfate salts occurs. Thus, crystallization centers are formed in which the growth of monoclinic, prismatic crystals begins. Crystallization processes grow significantly compared to a gypsum binder obtained without the addition of neutralizers and modifiers.

Material characteristics are shown in table 5.

Table 5. - Strength characteristics and setting time of the compositions

Composition number Strength after 7 days, MPa / cm ² Setting time, min Compression To bend Start end Composition 1 8.5 4.4 22 38 Composition 2 7.7 3.9 35 47 Composition 3 8.0 4.2 52 74 Composition 4 8.1 4.2 65 90 Composition 5 9.2 5.2 74 96 Gypsum binder without modifiers 4.1 2.5 98 480

The following conclusions can be made:

- an activator of crystal growth based on PHESP helps to increase the strength characteristics by a factor of 2 from 4 to 9 MPa / cm ² , the optimal composition is 5;

- the setting time of the material is reduced by 4 times due to the crystallization rate and the positive effect of calcium oxide on the composition.

To identify the role of magnesian materials and diatomite filler, we will conduct a study on the strength characteristics of the compositions in table 6. Thus, it was found that caustic magnesite powder of the DTMC 1 ... 3MK grade and magnesium salt work in conjunction as hydration activators. When tested according to the procedure for determining the strength characteristics found that when the content of MgCl ₂ 1.4% binder increases the strength of 3-fold compared to gypsum without addition of a binder modifier, which indicates the acceleration of hydration of the material. When the content of MgCl ₂ in the binder is more than 2.0%, the strength of the binder becomes at the level of the initial composition.

Table 7. - Strength characteristics and setting time of the compositions

Composition number Strength after 7 days, MPa / cm ² Setting time, min Compression To bend Start end Composition 1 18.0 11.0 28 54 Composition 2 12.0 8.6 42 88 Composition 3 14.8 8.9 54 96 Composition 4 11.0 8.0 56 110 Composition 5 6.0 4.8 65 130 Gypsum binder without modifiers 4.1 2.5 98 480

The following conclusions can be made:

- modifiers based on DTMC 1 ... 3MK magnesia material and salts of chloride or magnesium sulfate create a composite gypsum binder, in their strength characteristics 3-4 times higher than a gypsum binder without the addition of modifiers;

- the combination of magnesian material and a deatomite filler ensures the safety of the adhesive properties of the material for a long period of at least a year, even if the material was in an unheated room;

- the mass fraction of water-soluble phosphates in terms of P ₂ O ₅ is not more than 0.2%, which indicates the interaction of the compounds of the diatomite filler and magnesian material with orthophosphoric acid, which is in the technical gypsum.

Claims (6)

1. A method of producing a gypsum binder, including heating the feedstock, which is technical gypsum - calcium phosphate hemihydrate or phosphate dihydrate, characterized in that the heating is carried out in two stages, in the first stage at a temperature of 85 ± 5 ° C, in the second stage at a temperature of 160 ± 5 ° C, while in the first stage, heating is carried out with continuous stirring of the raw material for 40-60 minutes under a pressure of at least 0.1 MPa, in the second stage, heating is carried out with continuous stirring of the raw material for 30-60 minutes. 2. A method of obtaining a gypsum binder according to claim 1, characterized in that at the end of the second stage of heating, the gypsum binder is crushed. 3. A method of obtaining a modified composite gypsum binder, comprising the implementation of the method according to claim 1, wherein before starting the first heating step, the feedstock is mixed with calcium oxide and a crystal growth activator in the following ratio, wt.%:
- gypsum technical (phospho-hemihydrate or phosphate dihydrate of calcium sulfate) 92.5-99.8,
- calcium oxide 0.1-5.0,
- crystal growth activator 0.1-2.5,
where the crystal growth activator is a mixture of gas treatment dust from an electric steelmaking shop in the form of insoluble oxides of calcium, silicon, iron, magnesium, zincates and salts of iron sulfate, magnesium sulfate, calcium sulfate in the following ratio, wt.%:
- gas cleaning dust from the electric steelmaking shop in the form of insoluble oxides of calcium, silicon, iron, magnesium, zincates in an amount of 60-80, optimally 75,
- salts of iron sulfate, magnesium sulfate, zinc sulfate, calcium sulfate in an amount of 20-40, optimally 25. 4. A modified composite gypsum binder, including a gypsum binder obtained by the method according to claim 1, a crystal growth activator, as well as calcium oxide in the following ratio of components,%:
- gypsum binder 92.5-99.35,
- calcium oxide 0.1-5.0,
- activator of crystal growth 0.1-2.5. 5. A method of obtaining a modified composite gypsum binder, comprising the implementation of the method according to claim 2, wherein at the grinding stage, the gypsum binder is mixed with magnesia material and a diatomaceous filler in the following ratio, wt.%:
- gypsum binder 53-96,
- caustic magnesite powder, grade DTMC 1 ... 3MK 2-35,
- salt of sulfate or magnesium chloride 1-2,
- diatomaceous filler 1-10. 6. A modified composite gypsum binder, including a gypsum binder, obtained by the method according to claim 2, caustic magnesite powder of the DTMC 1 ... 3MK grade, salt of magnesium sulfate or chloride, diatomite filler in the following ratio,%:
- gypsum binder 53-96,
- caustic magnesite powder, grade DTMC 1 ... 3MK 2-35,
- salt of sulfate or magnesium chloride 1-2,
- diatomaceous filler 1-10.

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