CS243848B1 - Process for producing magnesium oxide - Google Patents

Abstract

The aim is to produce MgO suitable for clinker production, which is achieved by carbonated or hydrated magnesium raw material, such as semi-burnt dolomite or hydrated burnt magnesite, in an aqueous suspension at a temperature of up to 35 °C and a partial pressure of CO up to 2 MPa so intensively that a calculated MgO concentration in the solution of at least 12 g MgO/liter is achieved in less than 120 minutes. The separated leachate is decarbonated at a temperature below 35 °C and the precipitated magnesium carbonate pentahydrate is calcined to magnesium oxide.

Description

The invention relates to a process for producing magnesium oxide.

One possibility of chemically converting impure magnesium raw materials into pure magnesium oxide is the carbonate (sometimes called bicarbonate) process. It was designed in several variations. Věechny but have in common the intermediate refined magnesium trihydrate, magnesium carbonate MgCO ₃ .3 H ₂ O.

The original Pattison bicarbonate process was developed for dolomite. Dolomite is first calcined to form semi-calcined dolomite, which is a mixture of magnesium oxide and calcium carbonate, which is quenched with water to a mixture of magnesium hydroxide + calcium carbonate which disperses in water and carbonates with carbon dioxide to form a suspension of calcium carbonate and other impurities in .

After separation of the solid phases by filtration, the magnesium bicarbonate solution is precipitated by heating and aerating the magnesium carbonate trihydrate, which is filtered off, dried and calcined to technical magnesium oxide.

A disadvantage of the carbonate processes known hitherto is that the needle-shaped trihydrate crystals have a low bulk density, and since drying and calcination products retain this shape, it is very difficult to produce high density clinkers, which is one of the main quality parameters of magnesite refractory materials.

The process according to the invention appears to be more advantageous in that the semi-calcined dolomite or calcined magnesite or the hydrated semi-calcined dolomite or the hydrated calcined magnesite are carbonated in an aqueous suspension at a temperature of up to 35 DEG C. and steam. a CO ₂ pressure of up to 2 MPa, so intensely that in less than 120 minutes, preferably within 20 minutes, the Mg concentration in the solution, calculated as MgO, is greater than 12 g MgO / L, whereupon the extract is separated from the and the precipitated magnesium carbonate pentahydrate is separated from the mother liquor, dried and calcined to magnesium oxide.

The carbonation can be carried out in one or more stages by the process according to the invention, the decarbonation of the solution can be carried out by introducing an inert gas, the inert gas can be air and the decarbonation can be carried out by reducing the pressure above the solution.

Rapid elimination during carbonation and achieving a high concentration (above 12 g MgO / l) in the bicarbonate solution is a prerequisite for obtaining a metastable magnesium carbonate pentahydrate solution when operating at about 10 ° C.

It is only from such a metastable solution that partial magnesium carbonate pentahydrate can be obtained. Another condition is the presence of a well reactive magnesium oxide or magnesium hydroxide in the carbonation starting material.

Well reactive burnt magnesite is characterized by a loss on ignition of at least 6% by weight. and must be finely ground or extinguished with water. The finely ground material has a min.

% by weight of grain below 0.1 mm. Also semi-fired dolomite can be hyrated either slaked or ground.

The carbonation temperature may reach normal. pare. at a pressure of CO ₂ not more than 27 ° C, at a pressure of 200 kPa not more than 35 ° C. In decarbonation, cooling below 22 ° C should be rapidly achieved to eliminate the pentahydrate and not the trihydrate.

Burnt magnesite should be carbonated by steam. of a CO ₂ pressure of about 100 kPa because, under increased CO ₂ pressure, a disproportionately increased amount of iron passes into solution and then into pentahydrate. In the case of semi-fired dolomite, there is usually no danger of this, since the dolomites are very clean.

partial decarbonation / decomposition of bicarbonate to carbonate and carbon dioxide / metastable solution so as to precipitate the pentahydrate and not the trihydrate can be accomplished either by introducing an inert gas or by vacuum, not by heating.

Inert gas in this case means a gas with a lower partial pressure of CO ₂ than the equilibrium pressure of CO ₂ above the decarbonated bicarbonate solution, eg air. The wet pentahydrate should be processed immediately and as quickly as possible by drying and calcination, since only a rapid processing will retain the particulate form.

An advantage of the process according to the invention is, besides the granular form of the product particles, a high concentration of magnesium oxide in the metastable bicarbonate solution. E.g. at 26 ° C is normal. pare. CO ₂ metastabile equilibrium concentration around 20 g MgO (1), stable equilibrium (in equilibrium with the solid trihydrate) only 9 g / l.

At a CO ₂ pressure of 200 kPa, up to 48 g of MgO / L can be achieved at 30 ° C, while the equilibrium concentration under these conditions is only about 12 g of MgO / L. In order to more readily achieve the desired carbonation parameters that guarantee the formation of a metastable pentahydrate solution, i.e. a temperature of up to 35 ° C and a reaction time of less than 120 minutes, it is advantageous to work in two or more countercurrent stages.

E.g.' in the two-stage carbonation process, the solid particles of the first carbonation containing the undissolved magnesium oxide residues separated from the leachate are dispersed in water and carbonate in the second stage, and the second stage leachate is returned to the first stage.

The advantage of the two-stage carbonation is also that in the second stage, possibly dilute carbon dioxide from decarbonation can be used for carbonation and that the completely precipitated sludge can be separated from the weak magnesium bicarbonate solution by sedimentation, which is especially important in the processing of burnt magnesite very difficult to filter here. For single-stage carbonation, the temperature must not exceed 35 ° C. In the case of two _{in the} AO stage carbonation, the temperature in the second stage can be up to 45 ° C.

The carbonate processes have a great advantage over other chemical processes for the treatment of magnesium raw materials in that they have no problems with harmful exhalations and defective solid wastes, respectively. with by-products. Solid wastes from carbonate processes are absolutely safe in terms of hygiene.

In the process according to the invention, the content of impurities in the product is higher in the case of fired natural magnesite as raw material. When leaching beyond the norm. a pressure of CO ₂ to an extract concentration of about 20 g MgO / l extracts so much impurities from the calcined magnesite that treatment of the precipitated pentahydrate yields magnesium oxide containing by weight: MgO 97.0 to 98.0, CaO 0.5 to 1.2, Azθ2®3 θ'® ^{and from} UO, Mn 0.01 to 0.02, SiO ₂ 0.1. This purity is sufficient for high-quality refractory materials.

Examples

He did

Into a slurry of 0.1 kg of burnt magnesite with a composition by weight: MgO 75.18, CaO 6.44,

Fe ₂ Oj 5.64, R ₂ ° 3 7.26, S10 ₂ 1.03, l. 10.16, in 1 liter of water, CO ₂ was introduced under stirring at 200 kPa for 15 minutes with stirring.

The suspension was cooled to a final temperature of 30 ° C. The reacted suspension was filtered. The filtrate contained (g / l): MgO 48.0, CaO 0.45, Fe ₂ O ₃ 1.7. Air was introduced into the filtrate for 2 h, the final temperature being 19 ° C.

The precipitated granular crystals were filtered off, the filtrate containing 4.2 g MgO / L. Crystallization gave 43 g of a product containing% by weight: MgO 95.8, CaO 0.48, R ₂ O ₃ 2.71, S _{10 2} 0.30.

Example 2

To a suspension of 50 g of calcined magnesite in 1 liter of water was added CO ₂ at 200 kPa pressure with stirring for 15 min. The final temperature was 30 ° C. The reacted mixture was filtered. The filtrate contained (g / l): MgO 27.9, CaO 0.22, Fe ₂ O ₃ Air was introduced into the filtrate for 130 minutes, the final temperature being 18 ° C.

The precipitated granular crystals were filtered off, the filtrate containing 3.55 g MgO / L. Crystallization gave 25 g of a product with a weight% composition: MgO 95.5, CaO 0.29, R 10 -J 2.18, SiO ₂ 0.22.

Example 3

To a suspension of 75 g of burnt magnesite in 3 liters of a 5.4 g MgO / l solution of magnesium bicarbonate CO ₂ was introduced under stirring at normal pressure for 20 minutes, the maximum temperature being 26 ° C.

The reacted suspension was filtered, the filtrate containing 19.8 g MgO / L. The filtrate was bubbled with air for 90 minutes to a final temperature of 18.5 ° C. The granular crystals were filtered off, the filtrate containing 2.3 g MgO / L.

Calcination of the crystals gave 53 g of a product with a% by weight composition: MgO 97.2, CaO 0.53, R ₂ O ₃ 1.13, SiO ₂ 0.12.

Claims (5)

SUBJECT OF THE INVENTION A process for the production of magnesium oxide, characterized in that semi-calcined dolomite or calcined magnesite or hydrated semi-calcined dolomite or hydrated calcined magnesite is carbonated in an aqueous suspension at a temperature of up to 35 ° C and par.c. a CO ₂ pressure of up to 2 MPa in such a way that, in less than 120 minutes, preferably 20 minutes, the Mg concentration in the solutions calculated as MgO is greater than 12 g MgO / l, whereupon the extract is separated from the solid particles and decarbonate at a temperature below 35 ° C, preferably below 21 ° C, the precipitated magnesium carbonate pentahydrate is separated from the mother liquor, dried and calcined to magnesium oxide. 2. The method according to claim 1, wherein the steps are:. 3. The process of claim 1 wherein the inert gas. 4. The method of claim 3, wherein: 5. A method according to claim 1, characterized in that above the solution. wherein the carbonation is carried out in at least one decarbonation of the solution is carried out by introducing the inert gas as air. decarbonation is performed by reducing the pressure Severography, n. P., MOST