RU2047631C1 - Method of iron oxide pigment preparing - Google Patents

Abstract

FIELD: pigments, inorganic chemistry. SUBSTANCE: iron oxide pigments were prepared from the red slime, alumina production waste by its separation by size class in hydrocyclone. Particle fraction of size 0.02 mm (not above) were selected and calcined at 290-850 C. The end product shows clean red color, increased homogeneity of dispersed composition and improved covering power (7-11 g/m²). EFFECT: enhanced quality of pigment. 1 tbl

Description

 The invention relates to the production of inorganic pigments, namely iron oxide pigments of red color, and can be used in the paint industry.

A known method of producing iron oxide pigments with a gamma structure Fe ₂ O ₃ containing 0.1-12.0% SiO ₂ and 0.02-5.0% Al ₂ O ₃ , by burning a mixture of Fe ₃ O ₄ , SiO ₂ , Al ₂ O ₃ at 200-700 ^about With the supply of air and oxygen.

 The method is intended to produce brown pigments.

 Closest to the technical nature of the claimed invention is a method for producing red iron oxide pigment from red mud, waste from alumina production, by calcining it in a mixture with phosphomel.

 The disadvantages of this method are the high content of sulfide sulfur in the initial product before calcination, the low content of iron trioxide in the composition of the obtained pigment and the heterogeneity of its dispersed composition, which results in low hiding power, as well as a dirty brown tint of the color of the obtained pigment.

 The objective of the invention is to reduce the content of sulfide sulfur in the initial product before calcination, increase the content of iron trioxide in the composition of the obtained pigment and increase the uniformity of its dispersed composition, which provides a pigment of a pure red color and increases its hiding power.

This problem is solved by the method of obtaining iron oxide pigments from red mud, the waste of alumina production, by calcining it, while before calcining the red mud is subjected to separation by size class in a hydrocyclone with selection of a fraction no larger than 0.02 mm, and this fraction is calcined at 290-850 ^about S.

 The separation of red mud by size classes in a hydrocyclone with the selection of fractions no larger than 0.02 mm ensures the separation of iron trioxide concentrated in small size classes (<0.02 mm) and sulfide sulfur concentrated in large classes (> 0.02 mm) .

 The increase in the content of iron trioxide provides a pure red color of the obtained pigment. Reducing the content of sulfide sulfur, which is a strong reducing agent, prevents the formation of black ferrous oxide and brown ferrous oxide when calcined, which ensures a pure red color of the obtained pigment. In addition, the separation of red mud by size classes in a hydrocyclone with selection of fractions no larger than 0.02 mm provides an increase in the uniformity of the dispersed composition and the hiding power of the obtained pigment.

The lower limit of the calcination temperature range is due to the fact that when the calcination temperature below 290 ^{° C} does not occur the structural changes of the starting material, the color and dispersibility remain unchanged, the upper limit is due to the fact that at temperatures above ^about 850 C are formed coarsely-crystalline structure.

 The claimed method was obtained iron oxide pigments from red mud, the departure of the Bayer branch of the Bogoslovsky aluminum plant, the following chemical composition in terms of oxides, wt.

Fe ₂ O ₃ 39.0; Al ₂ O ₃ 15.9; CaO 14.0; S 1.5; TiO ₂ 3.9; SiO ₂ 7.3; Na ₂ O 3,4; CO ₂ 3.5.

A sample of red mud weight of 35 kg with a moisture content of 35% were separated by size classes in a laboratory hydrocyclone TSNIGRI construction at an angle of taper of ^about 10 and 20; diameters of the drain union 6, 8, 10 and 12 mm; diameters of passage openings of sand unions 2, 3, 4,5; 5.5 mm and an inlet 3 mm high and 16 mm wide.

Hydrocyclone was carried out at a liquid (water) solid ratio of 5.0. The fraction selected during hydrocyclonation (0.2 mm and below) was 68.7 wt. the original sludge and had the following chemical composition in terms of oxides, wt. Fe ₂ O ₃ 53.0; Al ₂ O ₃ 13.5; CaO 7.0; S 0.4; TiO ₂ 3.5; SiO ₂ 6.5.

After separation by size classes, the selected fraction was filtered off, washed to a pH of wash water of 8.5, and dried, after which a sample weighing 24 kg was calcined in a rotary drum furnace. The resulting pigment has the following chemical composition in terms of oxides, wt. F ₂ O ₃ 53.0; Al ₂ O ₃ 13.5; CaO 7.0; S 0.4; TiO ₂ 3.5; SiO ₂ 6.5.

 The technological parameters of obtaining iron oxide pigments and the characteristics of the target product obtained by the claimed method, as well as by the method taken as a prototype, are given in the table.

 The determination of color and hiding power of the obtained pigment was carried out on the basis of standard methods (see Dobrovolsky I. Bolshakov A. et al. Methods of technical analysis of pigment production, Chelyabinsk, South Ural Book Publishing House, 1973, pp. 212-213).

As can be seen from the above examples, the inventive method allows to increase the content of iron trioxide in the composition of the obtained pigment from 39.0 to 53.0 wt. to exclude the content of sulfide sulfur in the initial product before calcination (residual sulfur in the amount of 0.4 wt. is sulfate, present in the form of calcium sulfate), which ensures that after calcination at 290-850 ^о С a pure red pigment, uniform in disperse composition with hiding power of 7 g / m ² . Using the proposed method provides the following advantages:
obtaining iron oxide pigments of a pure red color with a hiding power of 7 g / m ² ;
as a result of the use of waste from the production of alumina-red mud, the absence of the need for additional raw materials, additives;
an exception when obtaining environmental pollution pigments with sulfur dioxide due to the removal of sulfide sulfur from the process.

Claims (1)

METHOD FOR PRODUCING IRON OXYGEN PIGMENTS from red mud from alumina production waste, including calcining it, characterized in that the red mud before calcination is subjected to separation by size class in a hydrocyclone with a particle fraction not larger than 0.02 mm and calcined at 290-850 ^o WITH.

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