HIGH-PURITY MAGNESIUM OXIDE AND METHOD FOR PRODUCTION THEREOF

Abstract

The invention relates to chemical technology for producing high-purity magnesium oxide used in the pharmaceutical, cosmetic, and food industries, in the production of ceramics, glasses, optical materials, electronic materials, catalysts, polymer materials, transformer steel.

High-purity magnesium oxide having a specific surface area, determined by the BET method, in the range from 5 to 70 m.sup.2/g, an average particle size (d50), determined by laser diffraction, of not more than 5 m, characterized in that it has a mass fraction of impurity elements of each of Pb, Cd, As, Hg of not more than 0.1 ppm, a mass fraction of impurity elements of each of Ba, Zn, Ti, Mn, Co, Mo, V, Sb, Sr of not more than 1 ppm, a mass fraction of impurity elements of each of Al, F of not more than 5 ppm, a mass fraction of impurity elements of each of P, Cr, Ni, K, Li of not more than 10 ppm, a mass fraction of Fe of not more than 50 ppm, a mass fraction of Si of not more than 0.01%, a mass fraction of impurity elements of each of Ca, B of not more than 0.02%, a mass fraction of sulphates SO.sub.4.sup.2k of not more than 0.02%, a mass fraction of Na impurity of not more than 0.05%, a mass fraction of chloride impurity of not more than 0.05% and includes primary particles and agglomerates consisting of primary particles.

High-purity magnesium oxide is obtained by calcination of magnesium hydroxide obtained by reacting a purified concentrated aqueous solution of magnesium chloride with an aqueous solution of sodium hydroxide in a continuous manner at a temperature of 40-90 C., stirring at a speed of 20-300 rpm at a molar ratio of OH.sup.:Mg.sup.++ ions within the range (1.92.1):1 with the continuous supply of a suspension of magnesium hydroxide seed crystals into the reaction mass in an amount of 5-200% of the total mass of the supplied initial reagents, and the magnesium hydroxide seed crystals are pre-treated with a concentrated aqueous solution of magnesium chloride, after interaction of the reagents, a suspension of magnesium hydroxide is sent for aging at a temperature of 40-90 C., then hydrothermal crystallization of magnesium hydroxide particles is carried out in the presence of dihydric alcohol: ethylene glycol or propylene glycol, at a temperature in the range from 120 to 220 C., pressure in the range from 0.1 to 2.3 MPa, and a duration ranging from 1 to 10 hours, the resulting suspension of magnesium hydroxide is filtered, washed, and calcination of magnesium hydroxide is carried out at a temperature of 700-1100 C.

The obtained high-purity magnesium oxide has high chemical purity, adjustable specific surface area, pore volume and pore size distribution, particle size distribution and activity.

Claims

1. High-purity magnesium oxide, having a specific surface area, determined by the BET method, in the range from 5 to 70 m.sup.2/g, an average particle size (d50), determined by laser diffraction, of not more than 5 m, wherein the high-purity magnesium oxide has a mass fraction of impurity elements of each of Pb, Cd, As, Hg of not more than 0.1 ppm, a mass fraction of impurity elements of each of Ba, Zn, Ti, Mn, Co, Mo, V, Sb, Sr of not more than 1 ppm, a mass fraction of impurity elements of each of Al, F of not more than 5 ppm, a mass fraction of impurity elements of each of P, Cr, Ni, K, Li of not more than 10 ppm, a mass fraction of Fe of not more than 50 ppm, a mass fraction of Si of not more than 0.01%, a mass fraction of impurity elements of each of Ca, B of not more than 0.02%, a mass fraction of sulphates SO.sub.4.sup.2 of not more than 0.02%, a mass fraction of Na impurity of not more than 0.05%, a mass fraction of chloride impurity of not more than 0.05%, and wherein the high-purity magnesium oxide includes primary particles and agglomerates consisting of primary particles.

2. High-purity magnesium oxide of claim 1, characterized in that it has a mass fraction of chlorides of not more than 0.025%.

3. High-purity magnesium oxide of claim 1, characterized in that it has a mass fraction of iron of not more than 20 ppm.

4. High-purity magnesium oxide of claim 1, characterized in that it has a specific surface area, determined by the BET method, in the range from 10 to 30 m.sup.2/g.

5. High-purity magnesium oxide of claim 1, characterized in that it has a pore volume determined by mercury porosimetry in the range from 0.910.sup.6 to 1.510.sup.6 m.sup.3/g.

6. High-purity magnesium oxide of claim 1, characterized in that it has a macropore volume in the range of 85-93 vol %, a mesopore volume in the range of 6.5-14 vol %, a micropore volume in the range of 0.5-1.5 vol % based on the total pore volume.

7. High-purity magnesium oxide of claim 1, characterized in that it has a modal pore diameter, determined by mercury porosimetry, in the range from 150 to 400 nm.

8. High-purity magnesium oxide of claim 1, characterized in that it has an average particle size (d50), determined by laser diffraction, of not more than 3.5 m.

9. High-purity magnesium oxide of claim 1, characterized in that 10% of the particles have a diameter of not more than 2 m, and 90% of the particles have a diameter of not more than 30 m, determined by laser diffraction.

10. High-purity magnesium oxide of claim 1, characterized in that it has a residue on a 325 mesh sieve of not more than 0.1%.

11. High-purity magnesium oxide of claim 1, characterized in that it has a citric acid activity in the range from 40 to 200 s.

12. High-purity magnesium oxide of claim 1, characterized in that it has a viscosity of the aqueous suspension of not more than 400 cP.

13. High-purity magnesium oxide of claim 1, characterized in that it is modified by one or several surface-treating agents selected from the group of saturated and unsaturated fatty acids containing from 8 to 20 carbon atoms, and/or their alkaline and alkaline earth metals, and/or silane coupling agents selected from the group of organofunctional trialkoxysilanes, tetraalkoxysilanes, and/or additives selected from the group including inorganic silicon compounds: salts of silicic acids and alkali and alkaline earth metals, silicon dioxide or mixtures thereof; boron: boric acid and its alkali and alkaline earth metal salts or mixtures thereof; calcium: calcium carbonate, calcium phosphate, calcium borates or mixtures thereof; antimony: antimony oxide, antimony sulphate or mixtures thereof; organic and inorganic compounds phosphorus: phosphoric acid, phosphonic acids, their alkali and alkaline earth metal salts or mixtures thereof; titanium: titanium dioxide and organofunctional titanates or mixtures thereof; or mixtures thereof in an amount from 0.001 to 5.0% by weight of magnesium oxide.

14. A method for producing high-purity magnesium oxide by calcination of magnesium hydroxide, comprising,: reacting an aqueous solution of magnesium chloride with an aqueous solution of sodium hydroxide, characterized in that the interaction of a purified concentrated aqueous solution of magnesium chloride with an aqueous solution of sodium hydroxide is carried out in a continuous manner at a temperature of 40-90 C., stirring at a speed of 20-300 rpm, with a molar ratio of OH.sup.:Mg.sup.++ ions in the range of (1.92.1): 1 with continuous feeding of a suspension of magnesium hydroxide seed crystals into the reaction mass in an amount of 5-200% of the total mass of supplied initial reagents, wherein the magnesium hydroxide seed crystals are pre-treated with a concentrated aqueous solution of magnesium chloride, aging a suspension of magnesium hydroxide at a temperature of 40-90 C., hydrothermal crystallization of magnesium hydroxide particles in carried out in the presence of dihydric alcohol: ethylene glycol or propylene glycol at a temperature in the range from 120 to 220 C., a pressure in the range from 0.1 to 2.3 MPa, and a duration in the range from 1 to 10 hours, filtering and washing of the resulting magnesium hydroxide suspension, calcining of magnesium hydroxide at a temperature of 700-1100 C.

15. The method of claim 14, characterized in that an aqueous solution of magnesium chloride of synthetic or natural origin preliminarily purified from impurities of heavy metals and/or iron, and/or sulphates, and/or boron, and/or bromine, and/or mixtures thereof, and the final stage of purification being ion exchange purification, is used as a concentrated aqueous solution of magnesium chloride.

16. The method of claim 14, characterized in that an aqueous solution of sodium hydroxide obtained by an electrochemical method is used as an aqueous solution of sodium hydroxide.

17. The method of claim 14, characterized in that hydrothermal crystallization of magnesium hydroxide is carried out in the presence of dihydric alcohol in an amount of 0.01-1.0 wt. %.

18. The method of claim 14, characterized in that deionized water and/or alkaline water, which is an aqueous solution of sodium hydroxide with a mass fraction in the range of 0.01-0.1%, is used to wash magnesium hydroxide crystals.

19. The method of claim 14, characterized in that magnesium oxide is modified by one or several surface-treating agents selected from the group of saturated and unsaturated fatty acids containing from 8 to 20 carbon atoms, and/or their alkaline and alkaline earth metals, and/or silane coupling agents selected from the group of organofunctional trialkoxysilanes, tetraalkoxysilanes, and/or additives selected from the group including inorganic silicon compounds: salts of silicic acids and alkali and alkaline earth metals, silicon dioxide or mixtures thereof; boron: boric acid and its alkali and alkaline earth metal salts or mixtures thereof; calcium: calcium carbonate, calcium phosphate, calcium borates or mixtures thereof; antimony: antimony oxide, antimony sulphate or mixtures thereof; organic and inorganic compounds phosphorus: phosphoric acid, phosphonic acids, their alkali and alkaline earth metal salts or mixtures thereof; titanium: titanium dioxide and organofunctional titanates or mixtures thereof; or mixtures thereof in an amount from 0.001 to 5.0% by weight of magnesium oxide.

Description

EXAMPLE 1

[0098] A magnesium chloride solution is prepared by dissolving magnesium chloride hexahydrate in deionized water, then purified from iron and sulphates and passed through a column filled with Lanxess TP 208 MonoPlus ion exchange resin. In the purified solution, the mass fraction of magnesium chloride is 32.1%.

[0099] The sodium hydroxide solution obtained by electrolysis with a mercury cathode is diluted with deionized water to a mass fraction of sodium hydroxide of 16.6%.

[0100] The first reactor of the cascade is simultaneously fed with a purified solution of magnesium chloride at a flow rate of 33.5 kg/h and a suspension of seed crystals with a flow rate of 44 kg/h, sent after aging from the third reactor of the cascade.

[0101] The second reactor of the cascade is simultaneously fed with a solution of sodium hydroxide at a flow rate of 54.4 kg/h and a suspension of seed crystals treated with a solution of magnesium chloride from the first reactor. The resulting suspension of magnesium hydroxide crystals is continuously sent for aging to the third reactor of the cascade.

[0102] The temperature in all reactors of the cascade is maintained in the range of 50-60 C.

[0103] The residence time in the reactor cascade is 2 hours.

[0104] After aging, a suspension of magnesium hydroxide crystals is sent for hydrothermal crystallization at a temperature of 170 C. in the presence of 0.1 wt. % propylene glycol by weight of magnesium hydroxide for 3 hours.

[0105] The magnesium hydroxide suspension is filtered. Wet magnesium hydroxide crystals are washed on a filter with alkaline water with a mass fraction of sodium hydroxide of 0.02%. The magnesium hydroxide cake with a moisture content of 48% is calcined at a temperature of 950 C. for 2 hours and ground.

[0106] The characteristics of the obtained high-purity magnesium oxide are given in Tables 1-2.

EXAMPLE 2

[0107] The bischofite solution, purified from sulphates and boron, is passed through a column filled with TP 208 MonoPlus ion exchange resin manufactured by Lanxess. In the purified solution, the mass fraction of magnesium chloride is 30.5%.

[0108] The sodium hydroxide solution obtained by diaphragm electrolysis is diluted with deionized water to a mass fraction of sodium hydroxide of 10.0%.

[0109] The first reactor of the cascade is simultaneously fed with a purified solution of magnesium chloride with a flow rate of 35.3 kg/h and a suspension of seed crystals with a flow rate of 12.6 kg/h, sent after aging from the third reactor of the cascade.

[0110] The second reactor of the cascade is simultaneously fed with a solution of sodium hydroxide at a flow rate of 90.8 kg/h and a suspension of seed crystals treated with a bischofite solution from the first reactor. The resulting suspension of magnesium hydroxide crystals is continuously sent for aging to the third reactor of the cascade.

[0111] The temperature in all reactors of the cascade is maintained in the range of 50-60 C.

[0112] The residence time in the reactor cascade is about 2 hours.

[0113] After aging, a suspension of magnesium hydroxide crystals is sent for hydrothermal crystallization at a temperature of 200 C. in the presence of 0.05 wt. % ethylene glycol by weight of magnesium hydroxide for 1 hour.

[0114] The magnesium hydroxide suspension is filtered. Wet magnesium hydroxide crystals are washed on a filter with alkaline water with a mass fraction of sodium hydroxide of 0.02%. The magnesium hydroxide cake with a moisture content of 38% is calcined at a temperature of 850 C. for 2 hours and ground in a hammer mill.

[0115] The characteristics of the obtained high-purity magnesium oxide are given in Tables 1-2.

EXAMPLE 3

[0116] A magnesium chloride solution is prepared by dissolving magnesium chloride hexahydrate in deionized water, then purified from sulphates and passed through a column filled with AMBERLITE IRC 748 ion exchange resin manufactured by ROHM 15 and HAAS. In the purified solution, the mass fraction of magnesium chloride is 32.1%.

[0117] The sodium hydroxide solution obtained by membrane electrolysis is diluted with deionized water to a mass fraction of sodium hydroxide of 12.5%.

[0118] The first reactor of the cascade is simultaneously fed with a purified solution of magnesium chloride with a flow rate of 31.8 kg/h and a suspension of seed crystals with a flow rate of 33.3 kg/h, sent from the second reactor of the cascade.

[0119] The second reactor of the cascade is simultaneously fed with a solution of sodium hydroxide at a flow rate of 68.1 kg/h and a suspension of seed crystals treated with a bischofite solution from the first reactor. The resulting suspension of magnesium hydroxide crystals is continuously sent for aging to the third reactor of the cascade.

[0120] The temperature in all reactors of the cascade is maintained in the range of 70-80 C.

[0121] The residence time in the reactor cascade is 2 hours.

[0122] After aging, a suspension of magnesium hydroxide crystals is sent for hydrothermal crystallization at a temperature of 130 C. in the presence of 0.02 wt. % ethylene glycol by weight of magnesium hydroxide for 2 hours.

[0123] The magnesium hydroxide suspension is filtered. Wet magnesium hydroxide crystals are washed on a filter with alkaline water with a mass fraction of sodium hydroxide of 0.02%. The magnesium hydroxide cake with a moisture content of 48% is calcined at a temperature of 750 C. for 3 hours and ground in a hammer mill.

[0124] The characteristics of the obtained high-purity magnesium oxide are given in Tables 1-2.

EXAMPLE 4

[0125] The bischofite solution is purified from bromine and passed through a column filled with AMBERLITE IRC 748 ion exchange resin manufactured by ROHM and HAAS. In the purified solution, the mass fraction of magnesium chloride is 28.0%.

[0126] The sodium hydroxide solution obtained by diaphragm electrolysis is diluted with deionized water to a mass fraction of sodium hydroxide of 13.5%.

[0127] The first reactor of the cascade is simultaneously fed with a purified solution of magnesium chloride with a flow rate of 63.6 kg/h and a suspension of seed crystals with a flow rate of 85.5 kg/h, sent from the second reactor of the cascade.

[0128] The second reactor of the cascade is simultaneously fed with a sodium hydroxide solution at a flow rate of 110.5 kg/h and a suspension of seed crystals treated with a bischofite solution from the first reactor. The resulting suspension of magnesium hydroxide crystals is continuously sent for aging to the third reactor of the cascade.

[0129] The temperature in all reactors of the cascade is maintained in the range of 50-60 C.

[0130] The residence time in the reactor cascade is 1 hour.

[0131] After aging, a suspension of magnesium hydroxide crystals is sent for hydrothermal crystallization at a temperature of 150 C. in the presence of 0.5 wt. % propylene glycol by weight of magnesium hydroxide for 4 hours.

[0132] The magnesium hydroxide suspension is filtered. Wet magnesium hydroxide crystals are washed on a filter with deionized water. The magnesium hydroxide cake with a moisture content of 39% is calcined at a temperature of 900 C. for 2 hours and ground in a hammer mill.

[0133] The characteristics of the obtained high-purity magnesium oxide are given in Tables 1-2.

Comparative Example

[0134] 45 kg of magnesium chloride solution with a mass fraction of 32% is loaded into the reactor and 82 kg of lime milk with a mass fraction of calcium hydroxide of 15% is dosed with continuous stirring for 1 hour. Stirring is continued for 24 hours at a temperature of 20-30 C.

[0135] The magnesium hydroxide suspension is filtered, and the wet magnesium hydroxide crystals are washed on the filter with deionized water. The magnesium hydroxide cake with a moisture content of 65% is calcined in a muffle furnace at a temperature of 900 C. for 2 hours and ground in a hammer mill.

[0136] The characteristics of the obtained magnesium oxide are provided in Table 1.

TABLE-US-00001 TABLE 1 Magnesium oxide characteristics Comparative Characteristic name Example 1 Example 2 Example 3 Example 4 example Mass fraction of iron Fe, ppm 11 34 20 50 300 Mass fraction of chlorides Cl, % 0.01 0.03 0.04 0.02 0.1 Mass fraction of calcium Ca, % 0.01 0.015 0.01 0.01 0.32 Mass fraction of sodium Na, % 30 100 300 80 10 Mass fraction of boron B, % 0.02 0.0005 0.02 0.02 0.02 Mass fraction of sulphates SO.sub.4.sup.2, % 0.002 0.002 0.002 0.017 0.025 Mass fraction of silicon Si, % 0.006 0.009 0.007 0.009 0.12 Specific surface area, m.sup.2/g 20 35 62 15 30 Citric acid activity, s 70 65 45 65 54 Pore volume, m.sup.3/g 0.918 10.sup.6 1.392 10.sup.6 1.488 10.sup.6 1.275 10.sup.6 1.83 10.sup.6 Volume fraction of macropore 89 83 91 92 67 volume, % Volume fraction of mesopore 9.9 10.5 7.8 7.2 28.1 volume, % Volume fraction of micropore 1.1 1.5 1.2 0.77 4.9 volume, % Modal pore diameter, nm 280 200 340 285 135 Particle size distribution, m d10 0.8 0.7 0.6 0.9 3.4 d50 2.3 1.6 1.2 2.0 8.7 d90 17.7 16.5 15.4 17.3 32.8 Residue on a 325 mesh sieve, % 0.02 0.01 0.02 0.03 1.5 Aqueous suspension viscosity, cP 135 180 200 140 370 Whiteness, % 98 100 99 99 67 Suspension sedimentation rate, 4 1 2 2 1 vol % per hour

TABLE-US-00002 TABLE 2 Impurities content in high purity magnesium oxide obtained according to Examples 1-5. Characteristic name Mass fraction Lead, Pb Less than 0.1 ppm Cadmium, Cd Less than 0.1 ppm Arsenic, As Less than 0.1 ppm Mercury, Hg Less than 0.1 ppm Barium, Ba Less than 1 ppm Zinc, Zn Less than 1 ppm Titanium, Ti Less than 1 ppm Manganese, Mn Less than 1 ppm Cobalt, Co Less than 1 ppm Molybdenum, Mo Less than 1 ppm Vanadium, V Less than 1 ppm Antimony, Sb Less than 1 ppm Strontium, Sr Less than 1 ppm Aluminium, Al Less than 5 ppm Fluorine, F Less than 5 ppm Phosphorus, P Less than 10 ppm Lithium, Li Less than 10 ppm Potassium, K Less than 10 ppm Chromium, Cr Less than 10 ppm Nickel, Ni Less than 10 ppm

Modification Example 1

[0137] 100 g of high-purity magnesium oxide obtained according to Example 1 and 0.5 g of vinyltrimethoxysilane are loaded into a Henschel-type mixer and stirred for 10-15 minutes at a temperature of not more than 70 C. Modified magnesium oxide is obtained.

Modification Example 2

[0138] 100 g of high-purity magnesium oxide obtained according to Example 1 and 2.0 g of calcium stearate are loaded into a Henschel-type mixer and mixed for 10-15 minutes at a temperature of not more than 100 C. Modified magnesium oxide is obtained.

Modification Example 3

[0139] 100 g of high-purity magnesium oxide obtained according to Example 1 and 0.5 g of boric acid are loaded into a Henschel-type mixer and stirred for 10-15 minutes at a temperature of not more than 80 C. Modified magnesium oxide is obtained.

[0140] The given examples illustrate the essence of the presented invention and do not limit the scope of the claimed invention.

[0141] The above examples show that the proposed production method allows obtaining high-purity magnesium oxide with a low content of impurities, controlled activity, pore volume and pore size distribution, and particle size distribution.