RU2757876C1 - Method for production of chemically deposited chalk - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in the pulp and paper, food, perfume and cosmetics, medical, pharmaceutical, chemical, rubber, paint and varnish industries. The method for producing chemically precipitated chalk involves grinding calcite and heating it in a furnace. Calcium oxide obtained as a result of calcite heating is mixed with water to obtain slaked lime in a ratio of 11-15 wt. %, of calcium oxide and 85-89 wt. %, of water. Mixing of calcium oxide with water is accompanied by bubbling of ozone through lime milk with mechanical intensification. Next, filtration from impurities is carried out, slaked lime is treated with carbon dioxide to obtain chemically precipitated chalk in the sediment, drying and grinding.

EFFECT: invention makes it possible to increase the purity and whiteness of chemically precipitated chalk by removing coloring impurities from slaked lime.

1 cl

Description

The invention relates to the production of chemically precipitated chalk. The main consuming industries: pulp and paper, food, perfumery and cosmetic, medical, pharmaceutical, chemical, industrial rubber, paint and varnish and polymer.

There is a known method of producing chemically precipitated chalk (patent for invention of the Russian Federation No. 2390496, publ. 05/27/2010), including the preparation of water containing calcium hydroxide, treatment of water in a carbonizer with gas - carbon dioxide or its mixture with another gas, removal of the chalk suspension from the carbonizer , its separation from the aqueous medium, drying, according to the invention, a flow-through reactor is used as a carbonizer, made in the form of a cylindrical body with its inner space divided by porous partitions into two coaxial longitudinal cavities communicating with each other through the pores of the partitions, the outer cavity is supplied under pressure containing calcium hydroxide water, and gas is also fed into the inner cavity under pressure, while the pressure in the gas cavity is higher than the pressure in the cavity with water containing calcium hydroxide. Lime water or milk of lime is used as the water containing calcium hydroxide.

The disadvantage of this method is the relatively low quality of products, the need to use a large number of carbonizers to ensure the continuity of the lime milk carbonation process, as well as insufficient productivity.

There is a known method of producing chemically precipitated chalk (patent for invention of the Russian Federation No. 2156737, publ. 09/27/2000), including slaking lime with water at 80-90 ° C, carbonization of lime milk with the formation of a chalk suspension, separation and drying of the product, according to the invention, quenching lime with water is carried out until 10-14% of a suspension of milk of lime is formed, before carbonization, the suspension of milk of lime is purified, carbonization is carried out with a gas of lime-kilns with a volume fraction of carbon dioxide of at least 20%, the separation of the chalk product is carried out at a rarefaction of 80-90 Pa, and drying - until the bulk density is not more than 0.25-0.35 g / cm ³ . The optimal conditions are the following: lump technological lime is slaked with a mass fraction of the sum of active calcium oxide and magnesium oxide in terms of calcium oxide not less than 70%; a suspension of milk of lime is purified to achieve a density at 20 ° C, equal to 1.06-1.11 g / cm ³ ; lime gas of kilns is preliminarily purified in a dust-settling chamber, a cyclone and water counter-current precipitators; drying of the product is carried out in loop dryers; drying of the product in loop dryers is carried out with the help of a heat carrier - products of natural gas combustion; after drying, the product is ground. The technical result of the invention is to reduce energy consumption while increasing the degree of whiteness of the chalk.

The disadvantages of this method are the need to use a large number of carbonizers to ensure the continuity of the lime milk carbonization process, as well as insufficient productivity due to the technology of the carbonization stage by bubbling carbon dioxide through the milk of lime, in which each carbonizer operates in a batch mode.

The object of the present invention is to provide a highly productive method for the production of chemically precipitated chalk.

The technical result of the claimed invention is to improve the quality of slaked lime purification due to exposure to ozone as an additional oxidizing agent, which allows colourant impurities to be removed into the sediment.

The claimed technical result is achieved due to the fact that according to the invention, the mixing of calcium oxide with water is carried out in the presence of ozone and with a large excess of water.

The basis of the proposed method is the process of preparing carbonate rocks: roasting, obtaining water containing calcium hydroxide, treating water in a carbonizer with gas - carbon dioxide and ozone, removing a chalk suspension from a carbonizer, separating it from an aqueous medium, washing, drying and grinding. The invention reduces the cost and increases the market value of the finished product, the total economic effect corresponds to a decrease in the cost by 15-25%. This is achieved by improving the main characteristics - purity and whiteness. The intensification of the process occurs due to ozonization of water containing calcium hydroxide and impurities included in its composition, while the process time is further reduced due to the presence of mechanical process intensifiers at each operation from lime slaking to lime milk recovery, drying of finished products and final grinding of particles.

Operations of ozonation and mechanical intensification of the process make it possible to obtain products significantly superior to the characteristics of GOST 8253-79 "Chemically precipitated chalk", first grade. That allows you to confidently compete with international leaders in this field.

To implement the claimed method, a line is used, which includes:

- the stage of preparation of raw materials (grinding of natural chalk);

- the stage of burning natural chalk;

- the stage of ozone generation;

- stage of extinguishing;

- stage of carbonization;

- the stage of concentration of carbon dioxide;

- drying stage;

- grinding stage.

The technology for the production of chemically precipitated chalk includes the following stages.

The mined rock is crushed (fraction 5-10 mm) and cleaned of impurities for subsequent processing - extraction of large iron-containing impurities.

Calcite is heated in an oven. In this case, calcite decomposes into calcium oxide (CaO) and carbon dioxide (CO2). Carbon dioxide is cooled, cleaned from mechanical impurities and captured for subsequent use. The optimal time for firing natural chalk to obtain chemically precipitated chalk is 3 hours from the moment the temperature reaches 900 ° C in the zone where the raw material is located.

Calcium oxide is mixed with water and ozone to produce slaked lime. To exclude the slowdown in quenching due to the formation of a pasty layer of hydration products on the surface of the lime particles, which prevents water from accessing the inner layers of the original grain, the process proceeds with ozone bubbling and mechanical intensification. The optimal ratio of lime and water: 11-15 wt.% Quicklime and 85-89 wt.% Purified water. To remove the main coloring impurities that affect the whiteness and purity of the final product, chemical cleaning is carried out when processing lime milk with ozone. Ozone, as a strong oxidant, affects the elements that make up the coloring impurities, which can lead to the transfer of these elements from a soluble state to an insoluble one. And this, in turn, will allow them to be removed into the sediment, from which the milk of lime is separated by filtration. The generated ozone is fed into the technological process, the concentration is assigned from the chemical composition of the raw material and the requirements for the final product.

Impurities are separated from the slaked lime using the principle of vibration separation.

Slaked lime is treated with carbon dioxide obtained earlier. As a result of the carbonization reaction, chemically precipitated chalk precipitates.

Impurities are separated from chemically precipitated chalk by additional washing.

After accumulating the required volume of chalk milk, it is sent to the press filter. The press filter allows the most complete separation of water from the filtered medium. Then the chalk after the press filter enters the washing reactor. For filtration of chalk milk after the stage of carbonization, one unit of press filters is allocated, and for filtration of chalk milk after washing, two. Then wet chalk undergoes a drying stage at temperatures up to 200 ° C, the duration of the process depends on the initial water content of the product, drying is carried out to the mass fraction of moisture less than 1%.

The finished chalk suspension is dried, crushed and packaged.

Claims (1)

A method for the production of chemically precipitated chalk, including grinding calcite, heating calcite in a furnace, mixing calcium oxide obtained as a result of heating calcite with water to obtain slaked lime in a ratio of 11-15 wt.% Calcium oxide and 85-89 wt.% Water, filtration from impurities, treatment of slaked lime with carbon dioxide to obtain chalk chemically precipitated in a sediment, drying and grinding, characterized in that mixing calcium oxide with water is accompanied by ozone bubbling through milk of lime with mechanical intensification.