Active high purity magnesium oxide and its production method

Abstract

The invention is referred to chemical technology, namely to active high-purity magnesium oxide and its production method. Active high-purity magnesium oxide, including the surface treated one, has BET specific surface area from 70 to 200 m.sup.2/g, average particle size (d50) determined by laser diffraction method not more than 10 microns, iodine activity in the range from 70 to 200 mg J/g MgO, citric activity not more than 40 s, pore volume in the range from 3.2?10.sup.?2 cm.sup.3/g to 10.2?10.sup.?2 cm.sup.3/g, diameter of 10% of the particles not more than 2 microns, diameter of 90% of the particles not more than 30 microns, mass fraction of residue on the 150 micron sieve not more than 1%, mass fraction of residue on the 45 micron sieve not more than 2%, mass fraction of chlorides not more than 0.1%, mass fraction of calcium not more than 0.1%, mass fraction of substances insoluble in hydrochloric acid not more than 0.05%, mass fraction of iron not more than 0.005%, mass fraction of impurities of each of Ti, Co, Mo, V, Sb, Ba cations not more than 1 ppm, Pb, Cd, As, Hg not more than 0.1 ppm.

Claims

1. Active high-purity magnesium oxide having: BET specific surface area from 70 to 200 m.sup.2/g, average particle size (d50) determined by laser diffraction method not more than 10 microns, characterized by having iodine activity in the range from 70 to 200 mg J/g MgO, citric acid activity not more than 40 s, pore volume in the range from 3.2?10.sup.?2 cm.sup.3/g to 10.2?10.sup.?2 cm.sup.3/g, diameter of 10% of the particles not more than 2 microns, diameter of 90% of the particles not more than 30 microns, mass fraction of residue on the 150 micron sieve not more than 1%, mass fraction of residue on the 45 micron sieve not more than 2%, dynamic viscosity of an aqueous suspension of not more than 30 cP, mass fraction of chlorides not more than 0.1%, mass fraction of calcium not more than 0.1%, mass fraction of substances insoluble in hydrochloric acid not more than 0.05%, mass fraction of iron not more than 0.005%, mass fraction of impurities of each of Ti, Co, Mo, V, Sb, Ba cations not more than 1 ppm, and mass fraction of impurities of each of Pb, Cd, As, Hg not more than 0.1 ppm.

2. Active high-purity magnesium oxide according to claim 1 characterized by having BET specific surface area within the range from 130 to 180 m.sup.2/g.

3. Active high-purity magnesium oxide according to claim 1 characterized by having the average particle size (d50) determined by laser diffraction method not more than 2 microns.

4. Active high-purity magnesium oxide according to claim 1 characterized by having a mass fraction of chlorides not more than 0.02% wt.

5. Active high-purity magnesium oxide according to claim 1 characterized by having a mass fraction of calcium not more than 0.05% wt.

6. Active high-purity magnesium oxide according to claim 1 characterized by having a mass fraction of carbonates wt not more than 1% wt.

7. Active high-purity magnesium oxide according to claim 1 characterized by having a mass fraction of sulphates not more than 0.01%.

8. Active high-purity magnesium oxide according to claim 1 characterized by having a mass fraction of Iron (Fe) not more than 0.003%.

9. Active high-purity magnesium oxide according to claim 1 characterized by having a mass fraction of manganese (Mn) not more than 2 ppm.

10. Active high-purity magnesium oxide according to claim 1 characterized by having a mass of residue on the 150 micron sieve 0.05% not more than 0.05%.

11. Active high-purity magnesium oxide according to claim 1 characterized by having a mass fraction of residue on the 45 micron sieve not more than 0.1%.

12. Active high-purity magnesium oxide according to claim 1 characterized by surface treatment with one or several silane coupling agents, selected from organofunctional trialkoxysilanes group, which includes alkyl triethoxysilane, alkyl trimethoxysilanes, alkenyl triethoxysilanes, and alkenyl trimethoxysilanes and/or one or several surface treating agents selected from saturated and unsaturated fatty acids group, containing from 8 to 20 carbon atoms, which includes stearic acid, oleic acid, palmitic acid, behenic acid, myristic acid, fatty acids of tall oil and/or their salts of alkali and/or alkaline-earth metals and/or their mixtures in the amount of 0.1-5.0% of the magnesium oxide mass.

Description

EXAMPLE 1

(1) Magnesium hydroxide crystals production process is carried out in a continuous mode at the installation, which is a cascade of three reactors equipped with anchor-type stirrers with a number of revolutions equal to 37. Operating volume of the reactors is 120 dm.sup.3. Temperature of 50-60? C. is maintained in all reactors of the cascade.

(2) Bischofite solution pre-cleaned from heavy metals and iron with mass fraction of magnesium chloride equal to 31.6%, mass fraction of diesel fuel equal to 0.001% and flow rate of 24.8 kg/h and seed with flow rate of 38.5 kg/h are continuously fed to the first reactor of the cascade. The seed is a suspension of finished crystals coming from the last reactor of the cascade.

(3) Suspension of magnesium hydroxide seed crystals treated with bischofite solution enters from the first reactor to the second reactor of the cascade. At the same time sodium hydroxide solution with mass fraction of 9.3% and flow rate of 70.7 kg/h is fed to the second reactor of the cascade. The resulting suspension of magnesium hydroxide crystals is sent from the second reactor to the third reactor of the cascade containing suspension of formed magnesium hydroxide crystals. Residence time in the reactor cascade is 1 h.

(4) Magnesium hydroxide crystals are filtered, washed with alkaline water which is an aqueous solution of sodium hydroxide with mass fraction of 0.05%, mass ratio of alkaline water/magnesium hydroxide equal to 10/1 using a filter, then dispersed in alkaline water, which is an aqueous solution of sodium hydroxide with mass fraction of 0.01%, mass ratio of alkaline water/magnesium hydroxide equal to 20/1 to form a suspension of magnesium hydroxide and then filtered.

(5) After final washing the magnesium hydroxide crystals are heated in the furnace at a rate of 10? C./min, calcined for 2 hours at a temperature of 600? C., ground with a hammer mill and active high-purity magnesium oxide is obtained. Characteristics of the obtained magnesium oxide are given in Tables 1-2.

Example 2

(6) Production of magnesium oxide is similar to the example 1, except that the bischofite solution with mass fraction of low-viscosity marine fuel 0.0002% is fed; sodium hydroxide solution with mass fraction of 9.3% and flow rate of 71.1 kg/h is fed into the second reactor of the cascade; washing with demineralized water at mass ratio of demineralized water/magnesium hydroxide equal to 6/1 is carried out using the filter, after filter washing magnesium hydroxide crystals are dispersed in demineralized water and filtered. Magnesium hydroxide cake is calcined at 450? C. Characteristics of the obtained magnesium oxide are given in Tables 1-2.

Example 3

(7) Production of magnesium oxide is carried out similarly to example 1, except that bischofite solution, purified from heavy metals, iron and sulfates with mass fraction of low-viscosity marine fuel of 0.0002% is fed. The magnesium hydroxide suspension from the third reactor of the cascade is directed to hydrothermal recrystallization for 2 hours at temperature of 170? C. and pressure of 0.6 MPa; washing of magnesium hydroxide crystals is done with a filter, mass ratio of alkaline water/magnesium hydroxide equal to 6/1, dispersion of crystals is not carried out. Magnesium hydroxide cake is calcined at 450? C. Characteristics of the obtained magnesium oxide are given in Tables 1-2.

Example 4

(8) Magnesium oxide is obtained similarly to Example 3, except that after washing magnesium hydroxide crystals are dispersed in alkaline water, which is an aqueous sodium hydroxide solution with mass fraction of 0.05%, mass ratio of alkaline water/magnesium hydroxide equal to 20/1, to form a magnesium hydroxide suspension and then filtered. Magnesium hydroxide cake is calcined at 450? C. Characteristics of the obtained magnesium oxide are given in Tables 1-2.

Example of Comparison

(9) 361.5 kg of sodium hydroxide solution with mass fraction of 9.2% is loaded into a reactor with a working volume of 500 dm.sup.3 and 118.5 kg of bischofite solution with magnesium chloride mass fraction of 33.46% is dosed. The reaction mixture shall be kept stirred for 2 hours at 20-30? C. Then magnesium hydroxide crystals are filtered and washed with demineralized water at mass ratio of alkaline water/magnesium hydroxide equal to 10/1 using a filter. Magnesium hydroxide crystals are heated in a furnace at a rate of 10? C./min, calcined for 2 hours at temperature of 600? C., ground with a hammer mill and magnesium oxide is obtained. Characteristics of the obtained magnesium oxide are shown in Table 1.

Example of Surface Treatment

(10) 200 g of magnesium oxide obtained as described in example 3 is loaded into a Henschel mixer, 7 g of stearic acid is fed in, and the mixture is stirred at 80? C. for 10-20 min. Surface-treated magnesium oxide with mass fraction of stearic acid equal to 3.5% is obtained.

(11) The above examples illustrate the essence of the invention, are illustrative and do not limit the field of the claimed invention.

(12) 5 The given examples demonstrate that the proposed production method allows obtaining active high-purity magnesium oxide with adjustable activity, chemical purity and particle size distribution.

(13) TABLE-US-00001 TABLE 1 Magnesium oxide characteristics Example of Characteristic Name Example 1 Example 2 Example 3 Example 4 Comparison Specific surface area, 78 160 183 180 55 m.sup.2/g Iodine activity, mg I/g 75 158 175 173 52 MgO Citric activity, s 28 12 8 8 42 Pore volume, cm.sup.3/g 3.7 ? 10.sup.?2 8.0 ? 10.sup.?2 7.2 ? 10.sup.?2 7.2 ? 10.sup.?2 2.5 ? 10.sup.?2 Mass fraction of 0.07 0.08 0.08 0.018 0.25 chlorides Cl.sup.?, % Mass fraction of calcium 0.003 0.017 0.003 0.003 ? Ca, % Mass fraction of 0.02 0.02 0,01 0.01 0.2 substances insoluble in hydrochloric acid, % Mass fraction of iron, Fe, 48 45 20 20 490 ppm Mass fraction of 0.6 0.8 0.2 0.3 0.7 carbonates CO3.sup.2- Mass fraction of sulfates 0.03 0.03 0.006 0.006 0.06 SO.sub.4.sup.2?, % Dynamic viscosity, cP 25 20 12 8 590 Mass fraction of losses 2.5 5.1 4.8 4.7 8.5 on ignition at 900? C. Particle size distribution, ?m D10 1.2 1.4 0.7 0.7 3.5 D50 5.1 6.5 1.3 1.4 22.5 D90 15.8 30.2 2.6 4.9 48.6 residue on 150 ?m 0.22 0.37 <0.1 <0.1 1.5 sieve, % residue on 45 ?m 0.9 0.9 <0.1 <0.1 10.8 sieve, %

(14) TABLE-US-00002 TABLE 2 Content of heavy metals and toxic substances in magnesium oxide, obtained according to the examples 1-4 Name Mass fraction, ppm Lead, Pb less than 0.1 Cadmium, Cd less than 0.1 Arsenic, As less than 0.1 Mercury, Hg less than 0.1 Titanium, Ti less than 1 Cobalt, Co less than 1 Molybdenum, Mo less than 1 Vanadium, V less than 1 Antimony, Sb less than 1 Barium, Ba less than 1 Manganese, Mn less than 2