RU2469970C2 - Method for production of magnesia binder - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: in the method for production of a magnesia binder - brucite is ground, burnt and milled into a powder, besides, the specified raw materials are ground to the fraction of 0-0.5 mm, then mixed with the technical lignosulfonate binder in the amount of 3-4% of brucite weight, sealed with water with bischofite dissolved in it in the amount of 3-5% of brucite weight, granules are formed and baked at the temperature of 800-850°C for 1.5-2 hours, cooled and ground until residue on a sieve of 0.08 is not more than 15%.

EFFECT: higher strength and evenness of volume variation with simultaneous reduction of baking temperature.

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Description

The invention relates to the field of building materials, in particular the production of magnesia binders.

As a raw material for the production of magnesia binder, various high-magnesian rocks are used: magnesite, brucite and dolomite. The highest quality binder for construction purposes can be obtained by roasting brucite. It is known that the material obtained by roasting brucite rock at a temperature of 400-450 ° C possesses astringent properties; it is referred to as burnt magnesia. The disadvantages of such a binder when used in construction are high activity and exothermicity, leading to uneven volume changes and the formation of cracks in the stone during hardening, which is not allowed by the requirements of TU 5745-004-70828456-2005 “Magnesia binder”.

A known method of producing lime, in which to reduce the firing temperature, limestone is impregnated with saline solution - natural brine in an amount of 0.9-1.6% by weight of the material to be calcined. The brine includes: CaCl ₂ , NaCl, MgCl ₂ , KCl, SrBr ₂ , Na ₂ SO ₄ (RF Patent No. 2098369, application. 04.03.1996, publ. 10.12.1997). Impregnated with brine, the raw materials are calcined at a temperature of 850-900 ° C and high-quality lime is obtained.

A known method for producing calcined magnesia chloride cement, which consists in high-temperature processing of magnesium carbonate with the addition of magnesium chloride, introduced in an amount of 1 ... 3% by weight of the source rock. The firing is carried out by thermal shock, using a solid heat carrier (Fedorov N.F. Calcined magnesia chloride cement / N.F. Fedorov, M.A. Andreev // Cement and its application. - May-June 2006 - P.76-78) . The disadvantage of this method is the lack of data on the uniformity of changes in the volume of binder samples.

Closest to the claimed technical essence is a method of producing a magnesian binder, in which high-magnesian rocks containing 15-40 wt.% Magnesium hydrosilicates are crushed to a fraction of less than 60 mm, calcined at a temperature of 1050-1100 ° C for 2-3 hours , then grinded into powder - passage through a sieve of 0.08 - 78-84% (RF Patent No. 2286965, filed May 23, 2005, publ. November 10, 2006). The magnesian binder obtained by this method has high strength, has a uniform volume change, that is, is not prone to cracking during hardening, and also has low linear shrinkage, but is energy intensive due to the high firing temperature of the feedstock.

The present invention solves the problem of obtaining magnesia binder with high strength and uniformity of volume change while reducing the firing temperature.

This is achieved by the fact that brucite raw materials are crushed to a fraction of 0-0.5 mm, mixed with a dry binder - technical lignosulfonate (LST) in an amount of 3-4% by weight of brucite, shut with a bischofite solution, granules are formed, burned at a temperature of 800-850 ° C, then the calcined granules are cooled and ground to a powder state.

Additive LST allows you to hold together the particles of crushed material and form granules to reduce the dust dust of the calcined material from the furnace and increase its efficiency (efficiency).

The amount of LST is less than 3% of the mass of brucite insufficient for bonding particles of crushed material and forming granules. An increase in the amount of LFB more than 4% of the mass of brucite is irrational, leading to unnecessary waste of material.

Bischofite is a modifying mineralizing additive that activates the dehydration of both brucite and serpentines at the stage of brucite rock heating due to the destabilizing effect of magnesium ions on the crystal lattice and the formation of a liquid phase, and during cooling it promotes the formation of magnesium oxide crystals due to the appearance of crystallization nuclei.

Firing at a temperature of 800-850 ° C, with the addition of 3-5% bischofite, allows you to get a binder with a uniform volume change and brand strength of at least 40 MPa.

When bischofite is introduced into the brucite mixture, less than 3% firing at a temperature of 800-850 ° C and holding at this temperature for 1.5 ... 2 hours does not allow to obtain a moderately active binder. When firing such a mixture, a highly active binder is obtained, and the stone obtained after mixing it with a bischofite solution has an uneven volume change and is destroyed during hardening.

The introduction of bischofite additives in an amount of more than 5% and firing at 800-850 ° C leads to the formation of a low-activity binder (burnout), prone to cracking due to late hydration of the burnout during hardening.

Firing the source rock at temperatures up to 800 ° C, with the introduction of bischofite 3-5%, leads to a highly active binder, characterized by a uniform volume change during hardening. The binder, calcined at a temperature of more than 850 ° C with the addition of bischofite in an amount of 3-5%, is inactive, has low strength, contains a significant amount of burnout, which leads to the formation of cracks in the resulting stone in the later stages of hardening.

Examples of specific implementation of the method.

Example 1

Brucite was milled to a residue of 0.5 no more than 5% on a sieve, a weighed quantity of 1000 g was taken, which corresponded to 100%, the brucite sample was mixed dry to a homogeneous state with 3% LST. The dry mixture was closed with 17% water with the addition of bischofite taken in an amount of 6% by weight of brucite. Granules with a diameter of 3-4 cm were formed from the resulting mixture, then they were placed in a furnace, and the furnace with granules was heated to 800 ° C, and then the granules were kept at this temperature for 1.5 hours, cooling was carried out in air for 3 hours. Then the granules were crushed to a residue on a sieve of 0.08 no more than 15%, cubed samples with a 2 cm rib were made from the obtained powder to determine strength and pellet samples to determine the uniformity of volume change. The binder test was carried out in accordance with GOST 1216.

Hardening occurred at an air humidity of 60-80% and an air temperature of 20 ± 2 ° C for 28 days.

Example 2

We took the following composition,%:

Brucite one hundred LST 3.0 Bischofite 4.0 Water 17.0 Firing temperature 800 ° C Isothermal exposure time 1.5 h

Samples were prepared according to the method described in example 1.

Example 3

We took the following composition,%:

Brucite one hundred LST 3.0 Bischofite 4.0 Water 17.0 Firing temperature 800 ° C Isothermal exposure time 2 h

Samples were prepared according to the method described in example 1.

Example 4

We took the following composition,%:

Brucite one hundred LST 3.0 Bischofite 4.0 Water 17.0 Firing temperature 850 ° C Isothermal exposure time 1.5 h

Samples were prepared according to the method described in example 1.

Example 5

We took the following composition,%:

Brucite one hundred LST 3.0 Bischofite 4.0 Water 17.0 Firing temperature 850 ° C Isothermal exposure time 2 h

Samples were prepared according to the method described in example 1.

Example 6

We took the following composition,%:

Brucite one hundred LST 3.0 Bischofite 2.0 Water 17.0 Firing temperature 850 ° C Isothermal exposure time 2 h

Samples were prepared according to the method described in example 1.

The results obtained are illustrated by the data given in the table.

No. p / p Composition, wt.% The compressive strength after 1 day, MPa The compressive strength after 28 days, MPa Volume uniformity one Example 1 1-2 28-30 Through cracks 2 Example 2 13-16 45-47 No cracks 3 Example 3 12-15 41-44 No cracks four Example 4 12-14 41-43 No cracks 5 Example 5 10-13 40-42 No cracks 6 Example 6 27-30 35-38 Crack network, breaking into separate blocks

The binder obtained by the claimed method has high strength and uniformity of volume change. The possibility of firing at low temperatures can reduce energy consumption in the production of binder.

Claims (1)

A method of obtaining a magnesian binder, in which the raw material - brucite is crushed, calcined and ground into powder, characterized in that the specified raw material is crushed to a fraction of 0-0.5 mm, then mixed with a binder LST in the amount of 3-4% by weight of brucite, shut water with bischofite dissolved in it in an amount of 3-5% by weight of brucite, form granules and burn at a temperature of 800-850 ° C for 1.5-2 hours, cool and grind to a residue on a sieve of 0.08 no more than 15%.