CS199323B1 - Process for preparing magnesium oxide from dolomites and dolomite calcites - Google Patents

Description

(54) Method of production of magnesium oxide from dolomites and dolomitic limestones

SUMMARY OF THE INVENTION The present invention provides a method for producing magnesium oxide from dolomite and dolomite limestone.

The basic raw material for the production of refractory magnesite materials is magnesite, MgCOy In addition to magnesium carbonate, magnesite, as well as the usual magnesium oxide, alumina, alumina, calcium oxide and mainly iron oxide are present in the raw magnesite. As long as these impurities are present in a limited small amount in magnesite, they affect the final properties of the refractory materials only relatively little.

However, due to the continuing depletion of sources of high-quality magnesia and the forced transition to ever-less valuable raw materials, it becomes more difficult to maintain the quality of the refractory products at the desired level. Therefore, it is necessary to gradually and gradually proceed to the physical and especially chemical methods of enrichment of crude magnesite. It is mainly about the removal of high proportions of silica and especially iron oxide.

Recently, a new trend of direct production from pure magnesium oxide prepared by chemical processes has begun to be applied in the production of magnesium oxide-based materials. So eg. Magnesia production from seawater has been elaborated where magnesium chloride present in seawater precipitates with calcium hydroxide to magnesium hydroxide. The disadvantage of this method of magnesium oxide production is the considerable low concentration of the starting magnesium chloride and the problems of unwanted coprecipitation of some

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199,323 other oxides present in seawater (eg boric oxide).

Therefore, most of the proposed methods for producing pure magnesium oxide are based on auric magnesite, which is usually calcined at temperatures of 1100-1200 ° C to reduce the solubility of ferric oxide, and then dissolves magnesite in acids. When nitric acid is used for dissolution, the resulting magnesium dilate is converted to magnesium hydroxide by precipitation with liquid ammonia. When using hydrochloric acid as the solvent, the resulting magnesium chloride solution is thickened in the reactor at 600 ° C, where it is cleaved directly onto magnesium oxide and hydrogen chloride.

There is also a bicarbonate process wherein ea suspension is carbonated on cooling with carbon dioxide and the resulting soluble magnesium bicarbonate decomposes at elevated temperature to insoluble magnesium carbonate trihydrate.

The deficiencies of these methods are - in addition to the rather complicated technology and unresolved problems in the field of construction materials - mainly in environmental pollution and in the problems of using waste products.

Recently, processes for the production of basic magnesium carbonate by selective leaching of spent magnesite with aqueous solutions of ammonium salts of some organic acids, preferably formates and ammonium oxalates have been described. The basic magnesium carbonate precipitates from the ammonium formate solution after removal of the insoluble impurities by injecting ammonia and carbon dioxide.

There is also a method of producing magnesium oxide from dolomite; for example, according to Romanian patent no. 59 712 prepares magnesium oxide by a two-stage treatment of dolomite: in the first stage, the fired dolomite is treated with waste solutions from the ammonia production process e <3dy to form magnesium hydroxide; in the second step, this salc is treated by adding waste solutions to form a magnesium chloride solution which precipitates upon removal of the calcium chloride by sodium bicarbonate, thereby forming magnesium carbonate, which gives magnesium oxide by leaching.

Another method described in Romanian patent no. 59 779 consists of treating dolomite with ammonia-free solutions of soda water, saturating the resulting solution with carbon tetrachloride, and after filtering and separating the traces of calcium chloride with magnesium carbonate, the magnesium chloride solution is treated with sodium bicarbonate at 25 ° C to form magnesium carbonate.

The above-mentioned drawbacks have no method for producing magnesium oxide from dolomites and dolomitic limestones according to the invention, which consists in that dolomite or dolomitic limestone, preferably in the form of dolomitic sands, or waste dolomitic powders and lump dolomites is subjected to selective calcination at temperatures from 650 ° C to 850 ° C, whereupon the annealed product is leached with solutions, preferably 10-40% aqueous solutions, of ammonium salts of inorganic acids, preferably of sulphate a) or of nitrate a) or of ammonium chloride containing an ammonium salt of 100 to 200 mole%, based on the magnesium oxide content of the semi-calcined dolomite, the leaching being carried out at a temperature of 50 to 110 ° C for 5 to 20 minutes, preferably 5 to 10 minutes, where in use

After leaching and separating the solid phase, 199 323 ammonium sulphate for leaching semi-calcined dolomite is subjected to crystallization, preferably by cooling the hot solution below 5 ° C, after which the crystallized magnesium sulphate after decomposition is decomposed by calcination at a temperature of 1000 to 1200 ° C. magnesium oxide, because with the use of sulphate a) or nitrate a) or ammonium chloride to precipitate, after leaching and separation of the solid phase, the basic magnesium carbonate precipitates from the obtained magnesium salt solution with simultaneous or successive ammonia and carbon dioxide. and drying calcines at a temperature above 400 ° C for magnesium oxide, or precipitates on the leachate oxalic acid or ammonium oxalate to magnesium oxalate, which after separation from the mother liquor is subjected to calcination at a temperature above 550 ° C to magnesium oxide.

Selective calcination is carried out so that all of the dolomite contained magnesium carbonate is converted to MgO and CaCO2 remains decomposed.

An advantage of the process for producing magnesium oxide according to the invention is that it solves the production of magnesium oxide by using, in particular, inferior or waste magnesium-containing carbonate raw materials. Advantageously, sand dolomites may be used which, although chemically very pure, are unsuitable for most applications in terms of their euphony. Furthermore, waste resulting from the treatment of high-value dolomites can be treated in this way.

The material remaining after the leaching of magnesium oxide is essentially pure calcium carbonate, which can be used as a full-value raw material (cement, clinker, glass, etc.). In this context, consideration may be given to using the invention to remove higher levels of magnesium oxide from limestone where the presence of magnesium oxide is undesirable calcium oxide for construction, cement production, lightweight building materials, etc.).

Example 1

The burning of 5 kg of dolomite at 825 ° C resulted in semi-fired dolomite containing 27.21% magnesium oxide. The material so obtained was ground and sieved through a 0.5 mm screen.

Example 2

In each case 100 g of semi-baked dolomite prepared according to Example 1 were subjected to leaching in 230 ml of a 40% ammonium sulfate solution for 5 min at 100 [deg.] C., after filtration and washing, the magnesium and calcium oxides were analyzed analytically in the mother liquor. Table 1 shows the results for the respective temperatures and leaching times.

Table 1

Extraction temperature Mp 100 ° C 90 ° C 70 ° 0 leaching time (min) 5 10 20 5 10 20 5 10 20 MgO content in the leachate, on a semi-burnt mine. (%) 26.75 26.94 27,02 26.19 26.82 26.94 25.05 26,32 26.74 CaO content in the leachate, in a semi-burnt mine. (%) 1.00 2.14 6.16 0.85 1.17 2.47 0.75 1.10 1.74

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Example 3

100 g of semi-baked dolomite prepared according to Example 1 was subjected to leaching in 230 ml of a 40% ammonium sulfate solution for 20 minutes at 70 ° C. The procedure was as in Example 2.

Example 4

100 g of semi-fired dolomite prepared according to Example 1 were subjected to leaching in 230 ml of a 40% ammonium sulfate solution for 10 minutes at 90 ° C. The eco procedure of Example 2 was then followed.

Example 5

In each case 100 g of semi-fired dolomite prepared according to Example 1 were subjected to leaching in 1 l of a 10% ammonium sulfate solution for 5 minutes at 100 ° C, after which the magnesium oxide and calcium oxide were analyzed analytically in the extract. Table 2 shows the results for the respective leaching temperatures and times.

Table 2

-y η ----- Extraction temperature ICO ° c 90 ° C 70 ° C Deň: 32 ° C leaching time and Amin) 5 10 20 5 10 20 5 10 20 7 ^ 5 10 20 the content of IgO in the leachate per half. dol. ίίϋ 25.92 26.47 26.83 24.85 25.56 26.14 25.31 25.94 26.36 19.43 22.62 23.73 content of OaQ in the extract, per half. dol. ( «) 0.96 1.49 3.42 0.38 0.75 1.10 0.35 0.69 0.88 0.28 0.45 0.65

Example 6

100 g of semi-fired dolomite prepared according to Example 1 were subjected to leaching in 1 liter of 10% ammonium sulfate solution for 20 minutes at 50 ° C.

Next, aa proceeded as in Example 5.

Example 7

100 g of semi-baked dolomite prepared according to Example 1 aa was subjected to leaching in 1 liter of 10% ammonium sulfate solution for 10 minutes at 70 ° C. The procedure was as in Example 5.

Example 8

0.5 kg of dolomite aa is calcined at 690 ° C, after which the material obtained is ground and sieved through a 0.5 mm sieve and leached in 2.5 liters of 30% ammonium nitrate solution for 10 min at 85 ° C. After filtering and cooling, the solution is treated simultaneously with ammonia gas and carbon dioxide for 30 min at a flow rate of 200 ml / min for each of the gases.

The resulting precipitate of basic magnesium carbonate is separated from the solution by filtration. The dried material is calibrated at 440 ° C. This gave 95 g of magnesium oxide, which is about 92% yield of the total magnesium oxide content of dolomite.

Example 9

The burned dolomite of Example 1 weighing 0.5 kg was subjected to leaching in 1.75 liters of a 30% ammonium sulfate solution at 90 ° C for 8 min. After filtration, the hot solution was cooled to 15 ° C, after crystallization for 30 minutes, the formed crystals were collected by filtration. The magnesium sulfate obtained was calcined at 1050 ° C. Burnt magnesium was obtained containing 98.60% of magnesium oxide.

Example 10

To 0.5 kg of the semi-baked dolomite of Example 1 was added 2 liters of 20% ammonium chloride solution. Extraction was carried out at 70 ° C for 10 min. After filtration, 500 g of ammonium oxalate was added to the solution. Upon dissolution and reaction, a precipitate of magnesium oxalate was obtained, which, after filtration and washing, and calcined at 600 ° C. The product was obtained in an amount of 129 g, containing 95.37% of magnesium oxide.

Claims (1)

OBJECT OF THE INVENTION Process for producing magnesium oxide from dolomites and dolomitic limestones, characterized in that dolomite or dolomitic limestone, preferably in the form of dolomitic sands or waste dolomitic powders and lump dolomites unsuitable for other uses, is subjected to selective calcination at temperatures from 650 ° C to 850 ° C ° C, after which the annealed product is leached with solutions, preferably 10 to 40% aqueous solutions, of ammonium salts of inorganic acids, preferably of sulfate a) or of nitrate a) or of ammonium chloride, containing an ammonium salt in an amount of 100 to 200 mole% based on the magnesium oxide content of the semi-fired dolomite, the leaching being carried out at a temperature of 50 to 110 ° C for 5 to 20 minutes, preferably 5 to 10 minutes, after which the ammonium sulphate for leaching the semi-burned dolomite is subjected to solution by crystallization, preferably about cooling the hot solution below 15 ° C, whereupon the crystallized magnesium sulphate after drying is decomposed into magnesium oxide by calcination at a temperature of 1000 to 1200 ° C, because using a) or nitrate a) or ammonium chloride for leaching after leaching and separation The solid phase precipitates the basic magnesium carbonate from the obtained magnesium salt solution with simultaneous or successively introduced ammonia and carbon dioxide, which after separation and drying is calcined at a temperature above 400 ° C for magnesium oxide, or precipitated on the leach by oxalic acid or ammonium oxalate to magnesium oxalate which, after separation from the mother liquor, is subjected to calcination at a temperature above 550 ° C to produce magnesium oxide.