CS196294B2 - Process for preparing high pure synthetic magnesia - Google Patents

Description

(54) Method for producing very pure synthetic magnesium oxide

The invention relates to a process for the production of very pure synthetic magnesium oxide containing calcium silicates by thermal decomposition of purified magnesium chloride solutions, but preferably containing calcium chloride, while respecting the quality requirements for basic refractory bricks with respect to the content of certain impurities. An essential advantage of the invention is, besides the substantial simplification of the process control, the prevention of unwanted waste water.

Various processes proposing a solution to the problem of large-scale and economical production of very pure synthetic magnesium oxide from natural raw materials have not yet offered a solution for the removal of calcium chloride that would satisfy in all directions.

Some ways, such as DT-OS

107 844 or DT-OS 2,137,573 suggest the separation of calcium contained in the purified magnesium chloride solution by precipitation in the form of gypsum. The technical feasibility of this process is limited by the solubility of calcium in magnesium chloride solutions. In addition, the controllable separation of the calcium sulphate resulting from this process is problematic.

In other processes, such as the recovery of magnesia from seawater or the recovery of magnesium oxide by thermal decomposition of brine, the water-soluble calcium chloride is removed by water scrubbing. Again, the amount of calcium chloride that has been dropped again creates a landfill problem. A further drawback of these processes is the necessity of calcinating magnesium hydroxide, which is associated with considerable expense of thermal energy. ......

DT-OS 1 592 085 proposes a process for removing the calcium chloride contained in magnesium chloride solutions by solvent extraction. Here too, a dilute calcium chloride solution is formed as a by-product.

In contrast to known methods, a process for the production of very pure synthetic magnesium oxide containing. 0.5 to 5% by weight, in particular 0.75 to 3.25% by weight, of calcium silicates and / or calcium titanates and / or of the X-ray phases of the MgO-CaO-SiO 2 -NaO-K 2 O -BaO -SrO- system TlOz-Al2O3 by thermal decomposition of the purified magnesium chloride solutions, but preferably containing 0.5 to 5 g / l of calcium chloride, and above 50 g, preferably 80 to 110 g Mg, calculated as metal per liter of solution, characterized in that calcium chloride, optionally also NaCl, KCl, BaCl2, SrCL ·

19B294

In addition, the additions of SiO2 or, respectively, TiO2 and Al2O3, calculated as moles in the molar ratio, are added in the chloride / magnesium solution.

CaO + (Na? O + K2O -j- BaO + SrO)

SiOz + (TiOz - (- AI2O5))

1: 1 to 4: 1, in particular in a molar ratio of 2.0 to 2.8: 1, and thereafter thermal decomposition of the metal chloride into magnesium oxide, calcium silicates and / or calcium titanates and / or x-ray amorphous mixtures of metal oxides of the aforementioned of the type while at the same time releasing hydrogen chloride at temperatures of 650 to 1600 ° C, in particular between 800 and 1350 ° C, within 0.5 to 15 seconds while adjusting the predetermined surface area of the reaction product to 0.01 to 20 m ² / g, in particular between 0.05 and 2 m ² / g, as determined by the BET method, the fissionable decomposition being carried out in the fluidized state and the metered magnesium chloride solution before the decomposition is converted to magnesium chlorohydrates and then thermally decomposed, S1O2 and T1O2 being added as surfactant powders .

The original contents of calcium chloride, possibly NaCl, KCl and others, after thermal decomposition of the magnesium chloride solution in the roasting product, are predominantly in the form of calcium silicates. Repairs of the calcium-containing roasting product to approximately dicalcium silicate (2 CaO, SiO 2) can be achieved without difficulty with a suitable additive. The residual chloride contents are reduced by about 2.1% by weight compared to the unadditioned sample. % residual chloride below 0.15 wt. residual chloride.

Thus, in addition to the production of refractory bases, no additive S1O2 wt.

with intentionally predetermined ratio

CaO

SlO2 + T1O2 eliminates the process of scrubbing or precipitation to remove calcium from the magnesium chloride solution.

Substantial economic benefits are obtained by substantially simplifying the process of the present invention. The process is of particular importance for all natural magnesia raw materials whose calcium content of the roasting product is not more than 3% by weight. CaO.

The process according to the invention is illustrated by the following examples. He did

The purified magnesium chloride solution, made from natural raw materials, has the following composition;

G Mg / 1 80.2 mg Na / 1 0.5 G Ca / 1 1.5 mg Ni / 1 0.5 G Na / 1 0.1 mg Co / 1 0.04 G K / l 0.1 mg Mn / 1 0.3 mg Fe / 1 0.4 mg SIO2 / I 32 mg Al / 1 0.2

Without appropriate adjustment of ratio

CaO

S102-I-T102 exhibits a roasting product as compared to the starting solution and the adjusted ratio

CaO

SIO2 4- T1O ₂ following ¹ values of chemical analysis:

With additive ^:

SiO 2 / wt.

MgO 96.46 97.1 CaO - 1.53 NazO - 0.14 K2O - 0.12 Fe2O3 tracks tracks AI2O3 tracks tracks Mn _x O _y tracks tracks NiO tracks tracks CO _X Oy tracks tracks S1O2 tracks 0.94 Residual chlorides including free HCl . 3.46 0.15 Reaction temperature. 980 ° C 980 ° C Excess oxygen 3.5 wt. 3.5 wt. Bulk weight 350 g / l 350 g / l

A further advantage of the magnesium oxide produced by said process is that the product can be processed directly into ceramic moldings after the previous deagglomeration. At a relatively low press pressure of 400 MPa, a green compact density of 2.85 g.cnr ³ can be achieved. Subsequent heat treatment for 2 hours at 1850 ° C results in a pellicle density of 3.35 to 3.50 g / m ³ , giving excellent shape stability to the shaped body.

Example 2

The purified magnesium chloride solution of 80 g of Mg / 1 thermally decomposed during 10 seconds at 850 ^P C (or 950 ° C), consisted of the following ingredients, oxides or chlorides of metals:

Present as oxides:

MgO 95.7 % wt. SiOz 0,035 % wt. AI2O3 0.04 % wt. TiO2 0.05 % wt. FezOs 0.1 % wt. CrzOs 0.02 % wt. Present as chlorides: CaCl2 3.5 % wt. KC1 0.18 % wt. NaCl 0.15 % wt. BaCl ₂ 0.01 % wt. SrCl2 0.01 % wt. HCl 0.15 % wt. Expressed in the form of oxides corresponds

the above composition molar ratio

CaO / (NazO + K2O + BaO SrO)

SiO ₂ + (TiO 2 + Al 2 O 3)

70: 1. In this context, it can be found that even raising the temperature at 950 ° C does not affect the roasting of the chloride. The roasting product has a specific surface area of 2.86 m ² / g.

In contrast, 0.95 g / l is obtained

SiO2 with a specific surface area of 50 m ² / g and consisting of 99% of S1O2 according to the invention

CaO

S1O2 to a molar ratio of 2.8. The surface-active silica is suspended in an acidic magnesium chloride solution. The turbid magnesium chloride solution is then thermally decomposed at 950 ° C for 10 seconds by spraying into a spray roasting reactor.

The solid roasting product obtained as described above has a specific surface area of 1.68 m ² / g and the MgO produced has a residual chloride content of 0.12% by weight, a substantial proportion consisting of the surface-absorbed hydrogen chloride gas. The calcium content is present in the form of an oxide together with the silica. Based on microscopic examination, it can be found that about 65 wt. The calcium is present in the form of dicalcium silicate (2 CaO, SiO 2). The remainder of the calcium content is divided into portions of tricalcium silicate (3CaO.SiO2) and calcium oxide in solid solution with magnesium oxide.

The MgO produced by the above process has the following chemical composition:

% MgO 96.7

Al 2 O 3 0.04

TiO 0.05

0,01'β2θ3 0,01

Cr2O3 0.02

Na 2 O 0.08

K2O 0.13

BaO < 0.01

SrO <0.01

SiO2 0.75

CaO 1.96

HCl 0.12 Subject

Claims (1)

Process for producing a very pure synthetic magnesium oxide containing 0.5 to 5% by weight, in particular 0.75 to 3.25% by weight, of calcium silicates and / or calcium titanates and / or x-ray amorphous phases of the MgO-CaO-SiOž-NazO system —K2O — BaO — SrO— Τίθ2 — Al2O3 by thermal decomposition of purified magnesium chloride solutions, but containing preferably 0,5 to 5 g / l calcium chloride as well as above 50 g, preferably 80 to 110 g Mg, calculated as metal per liter of solution characterized in that the additions of S1O2 or T1O2 and Al2O3 are also added to the calcium chloride, optionally also NaCl, CaCl2, KCl, SrCl2 present in the magnesium chloride solution, calculated as oxides in a molar ratio CaO + (NaaO + K 2 O + BaO + SrO) S1O2 + (TiO2 + AI2O3) YNALEZU 1: 1 to 4: 1, in particular in a molar ratio of 2.0 to 2.8: 1, and thereafter thermal decomposition of the metal chlorides to magnesium oxide, calcium silicates and / or calcium titanates and / or an X-ray amorphous mixture of metal oxides of the above of the type while releasing hydrogen chloride at temperatures of 650 to 1600 ° C, in particular between 800 and 1350 ° C, within 0.5 to 15 seconds while adjusting the predetermined specific surface area of the reaction product to 0.01 to 20 m ² / g, in particular 0, 05 to 2 m ² / g, the thermal decomposition being carried out in the fluidized state and the metered magnesium chloride solution before the decomposition is converted to magnesium chloride hydrates and then thermally decomposed, whereby S1O2 and T1O2 are added as surfactant powders.