RU2246445C2 - Method of producing coarse chemically precipitated calcium carbonate with plate shape of particles - Google Patents

Abstract

FIELD: industrial inorganic synthesis.

SUBSTANCE: soda ash production waste, namely 2.58% calcium chloride solution, is carbonized at continuous stirring with soda ash solution containing 18.7% Na₂CO₃, or 10.58% carbonate ion. During the synthesis conducted at 60-70^оС, continuous streams of reactants are maintained so that sodium carbonate consumption were not higher than 103.5 kg/m³· h to keep constant excess of carbonate ions at level of 2.35. Precipitate is filtered, reslurried, washed at stirring, refiltered, and dried. Content of CaCO₃ in product is at least 99%. Plate-shaped particles of product have average size 10-12.5 μm and maximum size 25 x 5 μm.

EFFECT: increased purity of product.

1 tbl, 6 ex

Description

A method for producing coarse chemically precipitated calcium carbonate with a lamellar particle shape relates to the technology for producing chalk, which is used in the production of pigments, varnishes, paints. It can be used in chemical plants producing high-quality calcium carbonate.

The known method / 1 / for the preparation of monodisperse calcium carbonate in plate form, comprising the stepwise addition of 5-20 times the amount of water to a suspension of quicklime and / or slaked lime in methanol containing 0.5-12% by weight. lime, passing carbon dioxide through the mixture, controlling the temperature within 30 ° C during the process of saturation of the system with carbonic acid and setting the reaction time of the saturation of carbonic acid (less than 1.0 minute). The disadvantage of this method is the toxicity of the reagents used and the contamination of the product with impurities present in calcium hydroxide.

There is also known a method / 2 / for the production of coarse particles of plate-shaped calcium carbonate, which comprises the steps of periodically or continuously adding an aqueous solution of calcium hydrogen carbonate having a constant temperature of less than 50 ° C, at a rate of 10-300 ml / min, in 1000 ml of an aqueous medium with a concentration Ca (HCO ₃ ) ₂ 0.1-0.4% by weight, in an aqueous solution maintained at temperatures of 65-90 ° C, followed by separation of the obtained lamellar particles of calcium carbonate from the solution. The disadvantage of this method is the low uniformity of the obtained particles of CaCO ₃ in size (particle size ranges from 3 to 20 microns).

To eliminate these drawbacks, a method for producing coarse chemically precipitated calcium carbonate with a lamellar particle shape is proposed, which involves synthesizing a precipitate by feeding a reagent containing calcium ions into a mixed mixture, separating the precipitate from the solution and drying the product, characterized in that as a reagent containing calcium ions, use an aqueous solution of calcium chloride, at the same time introduce a carbonizing reagent - an aqueous solution of sodium carbonate, and during the synthesis process they maintain constant flow of reagents with a flow rate of sodium carbonate of not more than 103.5 kg / m ³ · hour and a constant excess of carbonate ions of not less than 2.35, and the temperature of the synthesis process is maintained in the range of 60-70 ° C.

The use of aqueous solutions of calcium chloride and sodium carbonate as reagents makes it possible to obtain high-quality calcium carbonate containing at least 99.0% of the basic substance, to utilize the CaCl ₂ effluent solutions produced by soda ash.

Maintaining in the synthesis of constant flows of calcium chloride and sodium carbonate at a flow rate of sodium carbonate is not more than 103.5 kg / m ³ · h and a constant excess of carbonate ions is not less than 2.35 promotes formation of lamellar coarse particulate calcium carbonate with high uniformity obtained particles of CaCO ₃ in size.

The restriction of the flow of sodium carbonate to not more than 103.5 kg / m ³ · hour allows you to support the possibility of growth of large lamellar particles of CaCO ₃ on the already formed particles of calcium carbonate during the synthesis of CaCO ₃ .

A decrease in the excess of carbonate ions of less than 2.35 during the synthesis leads to the appearance of bulk (non-lamellar) CaCO ₃ particles, which impairs the physicochemical characteristics of calcium carbonate.

The synthesis in the temperature range of 60-70 ° C accelerates the growth of plate coarse crystals of CaCO ₃ . At temperatures below 60 ° C, the particle size decreases, and at temperatures above 70 ° C, the fraction of small particles in the sediment increases due to their destruction.

Examples of the method

Example No. 1. The reagent was a filtered solution of calcium chloride with a concentration of CaCl _{2 of} 77 g / l (7.15 wt.%), Which corresponds to a concentration of calcium ion of 2.58% by weight. Such a solution is formed as waste in the production of soda ash. A solution of soda ash containing Na ₂ CO ₃ 230 g / l (18.7% wt.) Was used as the second reagent, which corresponded to a concentration of carbonation of 10.58% wt.

An aqueous solution of calcium chloride at a volumetric rate of 0.18 l / h and an aqueous solution of sodium carbonate at a rate of 0.09 l / hour. The value of the flow Wi in terms of an industrial reactor is calculated by the formula:

Wi = vi × C / Vp,

where vi is the volumetric rate of the solution of the i-th substance, m ³ / hour;

C is the concentration of the i-th substance, kg / m ³ ;

Vp is the working volume of the reactor, m ³ .

The flow rate of the sodium carbonate solution was a constant value:

Wi = vi × C / Vp = 0.09 × 230 / 0.200 = 103.5 kg / m ³

The flow rate of the calcium chloride solution was a constant value:

Wi = vi × C / Vp = 0.18 × 77 / 0.200 = 69.3 kg / m ³ · hour

The mass ratio between carbonate ions and calcium ions in the synthesis process was:

- масса карбонат-иона;Where

- mass of carbonate ion;

- молекулярная масса карбоната натрия;

- molecular weight of sodium carbonate;

- масса иона кальция;

- mass of calcium ion;

- молекулярная масса хлорида кальция.

- molecular weight of calcium chloride.

The resulting precipitate was filtered on a Buchner funnel. The calcium carbonate precipitate was repulped and washed 3 times. To do this, the filter cake was placed in a glass reactor thermostatically controlled at 60 ° C and poured with distilled water in the ratio W: T = 5. Washing was carried out with stirring for 20 minutes. Then the precipitate was filtered on a Buchner funnel. The sludge washing process was carried out in three stages, each time filtering the sludge. Then, the calcium carbonate paste was dried in an oven at a temperature of 100 ° C, placing the paste in a thin layer on filter paper on a flat metal substrate. The dried precipitate of calcium carbonate was analyzed using an optical microscope and also subjected to chemical analysis. The results of the experiment are shown in the table. A precipitate of CaCO ₃ with coarse particles of only a plate shape and an average size of 12.5 μm was obtained. The content of CaCO ₃ in the product was 99.12%.

Table.
The parameters of the particles of calcium carbonate obtained under various synthesis conditions No. The consumption of sodium carbonate kg / m ³ · hour Excess Carbonate Ions The temperature of the synthesis process, ° С The shape of the resulting particles The minimum particle size, microns The maximum particle size, microns The average particle size, microns 1 103.5 2.35 60 Lamellar 5 17.5 × 5 12.5 2 103.5 3.90 60 Lamellar 7.5x2.5 25 × 5 10 3 103.5 2.03 60 Spherical and plate 3 nine 5 4 155.0 2.35 60 Spherical and plate 1 8 4.5 5 103.5 2.35 70 Lamellar 5 15 × 5 eleven 6 103.5 2.35 75 Lamellar and spherical 3 10 6

Example No. 2. The method of producing calcium carbonate was carried out analogously to example 1 with the difference that in the synthesis process an excess of carbonate ions was maintained by maintaining the mass ratio between carbonate ions and calcium ions 3.9. As a result, a precipitate of coarse lamellar particles of CaCO _{3 was} obtained with dimensions: maximum size 25 × 5 μm, average size 10 μm. The content of CaCO ₃ in the product was 99.09%.

Example No. 3. The method of producing calcium carbonate was carried out analogously to example 1 with the difference that during the synthesis the mass ratio between calcium ions and carbonate ions was maintained at 2.03. As a result, a precipitate of plate and bulk spherical CaCO ₃ particles with smaller sizes was obtained: the maximum size is 9 μm, the average size is 5 μm. The content of CaCO ₃ in the product was 99.21%.

Example No. 4. The method of producing calcium carbonate was carried out analogously to example 1 with the difference that in the synthesis process the flow of sodium carbonate was maintained at 155 kg / m ³ · hour. As a result, a precipitate of spherical and lamellar particles of CaCO _{3 was} obtained with sizes: maximum size 8 μm, average size 4.5 μm. The content of CaCO ₃ in the product was 99.04%.

Example No. 5. The method of producing calcium carbonate was carried out analogously to example 1 with the difference that the synthesis process was carried out at a temperature of 70 ° C. As a result, a coarse precipitate of only CaCO ₃ lamellar particles was obtained with dimensions: maximum size 15 × 5 μm, average size 11 μm. The content of CaCO ₃ in the product was 99.15%.

Example No. 6. The method of producing calcium carbonate was carried out analogously to example 1 with the difference that the synthesis process was carried out at a temperature of 75 ° C. As a result, a precipitate of plate and spherical particles of CaCO _{3 was} obtained with sizes: maximum size 10 μm, average size 6 μm. The content of CaCO ₃ in the product was 99.16%.

Thus, the proposed method allows to obtain a homogeneous coarse chemically precipitated calcium carbonate with a particle size of 10-12.5 μm only lamellar form (examples No. 1, 2, 5), while the product contains at least 99.0% of the main substance, which allows its use in production pigments, varnishes, paints with high hiding power.

List of sources used:

1. US patent 5275651, C 01 F 11/18 Minayoshi, et. al. Monodisperse vaterite, the method of its production and the method of controlling the growth of particles during its formation. Jan. 4, 1994.

2. U.S. Patent 4,857,291 C 09 C 001/02; C 01 F 005/24; C 01 F 011/18. Ota, et al. The process for the production of lamellar particles of calcium carbonate, August 15, 1989.

Claims (1)

A method of producing coarse chemically precipitated calcium carbonate with a plate-like particle form, comprising synthesizing a precipitate by feeding a reagent containing calcium ions into a stirred mixture, separating the precipitate from the solution and drying the product, characterized in that an aqueous solution of chloride is used as a reagent containing calcium ions calcium, at the same time a carbonizing reagent is introduced - an aqueous solution of sodium carbonate, and during the synthesis process, constant flows of reagents are maintained with a flow rate of sodium carbonate n over 103.5 kg / m ³ · h and a constant excess of carbonate ions is not less than 2.35, and the synthesis process the temperature is maintained in the range of 60-70 ° C.