CS265971B1 - Process for preparing anhydrous magnesium carbonate - Google Patents

Description

(57) The solution is to obtain anhydrous magnesium carbonate from a solution of magnesium salts or from suspensions of sparingly soluble magnesium compounds such as nesquehonite, magnesium hydroxide, etc. The solution or suspension is mixed with ammonium carbonate or alkali metal carbonates or carbon dioxide to a MgO molar ratio. The CO2 in the reaction mixture did not exceed 2 and then decomposed in the autoclave at a temperature above 110 ° C. The anhydrous magnesium carbonate is separated from the mother liquor from which ammonia is regenerated by the addition of calcium hydroxide, alkali metal hydroxide or calcined magnesium feedstock, thereby simultaneously obtaining a magnesium salt solution.

The invention relates to a process for obtaining anhydrous magnesium carbonate from solutions of salts of natural or synthetic origin or from aqueous suspensions of sparingly soluble magnesium compounds of natural origin or synthetically produced, for example, nesquehonite MgCO ₃ .3H ₂ O, lansfordite MgCO ₃ .5H ₂ O; hydromagnesite Mg ₂ / MgOH / ₂ . (C0 _{3) 3} .3H ₂ O, artinite / MgOH / .C0 ₂ .3H ₂ 0 _{3 of the} decomposition products of magnesium bicarbonate example 5MgO.4CO ₂ .5H ₂ O, 3MgCO _3, Mg / OH / ₂ .5H ₂ O etc., magnesium oxide, magnesium hydroxide, etc., or a suspension of low soluble magnesium compounds in magnesium salt solutions by decomposing the reaction mixture after adjusting the MgO: CO ₂ molar ratio to a maximum of 2 by adding carbonate or ammonium carbonate or alkali metal carbonate or mixtures or carbon dioxide , event. with the addition of ammonia or an alkali metal hydroxide at an elevated temperature of at least 110 ° C and a corresponding pressure.

In the present state, several technological processes have been developed according to which magnesium compounds are obtained from industrial solutions and whose ultimate goal is mostly the production of magnesium oxide, magnesium clinkers or magnesium compounds. The precipitation of hydrated magnesium carbonate or basic magnesium carbonates of different compositions from magnesium salt solutions is known and is incorporated as a technological node in industrially used magnesium oxide production technologies either to obtain a suitable intermediate or is designed as a refining operation for separating magnesium from calcium.

The precipitation of hydrated magnesium carbonate with an ammonium carbonate solution at temperatures up to 50 ° C and at a controlled pH of the reaction mixture is carried out in the treatment of magnesium chloride solutions. A well filterable crystalline product is obtained - nesquehonite MgCO ₃ .3H ₂ O, which is dried and thermally decomposed to magnesium oxide. Due nesquehonitu solubility in a given medium is the residual concentration of MgCl ₂ in the filtrate was 16 to 18 g.dm \ so that the processing solution concentration is industrially acceptable yield in the precipitation of magnesium 85, max. 88%. The filtered unsquehonite from the vacuum filtration contains more than 30% moisture, the bound water in MgCO3. %. Another method for the production of magnesium carbonate ^J * 2+ is given by АО SU 702 943. According to this process, a basic magnesium carbonate is precipitated from a Mg-containing solution by the addition of a soda solution. The precipitation product is dried to a anhydrous carbonate in a gas stream containing 7-12% carbon dioxide at 200-250 ° C.

The subject of technological interest is solutions of acidic magnesium carbonate, the decomposition of which is carried out by removing excess carbon dioxide under reduced pressure or by heating the solution in the range of 30 to 100 ° C. In this case, nesquehonite, basic magnesium carbonates, for example hydromagnesite, artinite, basic carbonate 3MgCO ₃ .Mg / OH / ₂ · 5H ₂ O, or mixtures of these, or mixtures thereof, may be formed. of similar compounds. All of these compounds, referred to as magnesium carbonates, can be an intermediate, the so-called bicarbonate technology for the production of magnesium oxide. However, anhydrous MgCO ₃ cannot be formed when decarbonizing solutions of acidic magnesium carbonate to decomposition temperatures of 100 ° C. In order to achieve the separation of magnesium from calcium, АО SU 368 188 utilizes the formation of magnesium bicarbonate and its decomposition at elevated temperature. Likewise, according to DOS 3 101 101 293, the magnesium hydroxide in the mash is converted by means of carbon dioxide to magnesium acid carbonate. Magnesium and calcium carbonate are formed and precipitated from the solution. After separation, the solution is decarbonised either by heating or under vacuum and the precipitated hydrated magnesium carbonate is separated from the liquid phase. A special form of foliar base magnesium carbonate with calcium carbonate for papermaking purposes is obtained according to patent application EP 10 643 by subsequent pressure decomposition of a dilute carbonated suspension of fired dolomite.

To achieve a durable Nesquehonite product, АО SU 622 497 is recommended. The product is basic magnesium carbonate. In the process of chemical production of magnesium oxide, relatively dilute magnesium salt solutions are sometimes treated. This is the case, for example, in the production of magnesium oxide from seawater or natural low magnesium solutions.

In these cases, magnesium hydroxide precipitates, which is drained in a very demanding manner and, in addition to the constitutional water, has a residual moisture content of 30 to 50%. In all of the above cases, in the production of magnesium oxide, intermediates with relatively high constitutional water and moisture contents are consumed in the process of dewatering, respectively. calcination a considerable amount of thermal energy. In addition, in some cases these intermediates are difficult to dewater, a large filtration area is required for filtration, and a considerable amount of dilute wash solutions is produced. In addition, when the nesquehonite is precipitated, relatively low magnesium yields are achieved. All these drawbacks are overcome by the process according to the invention, in which anhydrous magnesium carbonate is obtained from magnesium salt solutions or from suspensions of sparingly soluble magnesium compounds such as nesquehonite, lansfordite, basic carbonates, magnesium hydroxide, etc. in water or magnesium salt solutions. the solution or suspension is mixed with carbonate or acidic ammonium carbonate or alkali metals or mixtures thereof, or with carbon dioxide, respectively. with the addition of ammonia or an alkali metal hydroxide. The amount of added compounds is chosen such that the molar ratio of MgO: CO ₂ in the reaction mixture does not exceed 2, and the reaction mixture is, after the reaction mixture, optionally. preheating the components in an enclosed space to a temperature of at least 110 ° C. The reaction, which is carried out continuously or batchwise, takes place depending on the temperature of 2 - 600 minutes. After decompression, evnt is released. ammonia and carbon dioxide present in excess and both gases are obtained by absorption. After the anhydrous magnesium carbonate has been separated, ammonia is recovered from the ammonium salt solution by addition of calcium hydroxide or alkali metal hydroxide, or by reaction with the calcined magnesium oxide-containing feedstock at the same time bringing the magnesium into solution.

Example 1

A 5,000 ml autoclave was charged with 2,000 ml of the magnesium chloride composition

167.7 g MgCl ₂ .dm ³

28.9 g NH ₄ Cl.dm ³

0.03 g CaCl ₂ .dm ³

0.005 g Fe.dm &^lt; ³ > and 340 g ammonium carbonate was added to adjust the mol. the MgO: CO ₂ ratio in the reaction mixture to 1.0. Thereafter, the reaction mixture was heated to 180 ° C with stirring and the pressure reached 1.9 MPa. The reaction time in the temperature range of 110 to 180 ° C was 135 min. After cooling the solid was filtered and washed, the filtrate returned 8.1 g MgCl ₂ .dm ^third The filter cake was subjected to fine structure X-ray determination, DTA, GTA and chemical analysis. The magnesium carbonate content of this product was 99.6%. The wash water filtrate was hot decomposed with 175 g of calcined magnesite containing 87% MgO; 4.5% of CaO and 6.25% _Fe ^ O. After boiling the ammonia and evaporating the solution to 2000 ml, the solution contained 165 g

-3 ^J -3

MgCl ₂ .dm and 7.0 g CaCl ₂ .dm

Example 2

Into a 5,000 ml autoclave, 2,000 ml of a 195 g MgSO ⁴ solution was introduced and the solution was heated to 110 ° C with stirring. Then ammonia and carbon dioxide were introduced into the reaction space so that the final MgO: CO ₂ molar ratio in the reaction mixture was 0.89. Ammonia was metered in a molar ratio of NH ₃ : CO ₂ = ^δ 1.80. The reaction mixture was heated to 155 ° C, the maximum pressure reached was 3.2 MPa, after stabilization the pressure was 1.6 MPa. After cooling, the resulting solid phase was analyzed, the X-ray fine structure

-3 corresponds to crystalline MgCO ₃ · The concentration of MgSO ₄ in the filtrate was 11.34 g.dm. Sulphate ions were precipitated in the form of gypsum by the addition of a small excess of calcium hydroxide suspension, and after boiling ammonia, the liquid phase contained 0.03 g NH ₃ / dm

Example 3

Autoclave 5000 ml was put 2,000 ml solution of magnesium nitrate -3 '3, composition 441 g Mg / NO _3/2 .dm and 9.40 g of Ca / NO _3/2 .dm was added 880 g of potash. The reaction mixture, which had a MgO: CO ₂ ratio of 0.95, was heated to 195 ° C at 2.1 MPa and was immediately withdrawn from the reaction space. The solid phase contained 98.0% MgCO ₃ and 1.8% CaCO ₃ , the magnesium yield was 98.2%.

Example 4

A 2000 ml autoclave was charged with 2000 ml of a suspension of nesquehonite-3 MgCO ₃ .3H ₂ O in distilled water. The solids concentration in the slurry was 150.0 g.dm. The reaction mixture was heated without the addition of additional reagents, the MgO: CO ₂ ratio was equal to 1. The maximum temperature reached was 180 ° C at 1.6 MPa. After cooling, pure MgCO ₃ was detected by X-ray analysis of fine structure, the MgO concentration in the filtrate was 0.15 g.dm.

Example 5

A 5,000 ml autoclave was charged with 2,000 ml of 100 g solids / liter of magnesium hydroxide in distilled water. At the same time, 200 g of carbon dioxide was metered into the reaction space, so that mol. the MgO: CO ₂ ratio was 0.75. After heating the reaction mixture to 155 [deg.] C., it was 1.8 MPa and after cooling in the solid phase only anhydrous magnesium carbonate was detected. In the liquid phase, the MgO concentration was 0.22 g.dm ³ .

Example 6

To the operating pressure of the mixing reactor 2.8 m ³ heated to 155 ° C for 3 and a pressure of 1.2 MPa was fed magnesium chloride solution composed of 158.2 g MgCl .dm _9,

-3 -3 ^W -3

0.08 g CaCl ₂ .dm and 28.0 g of NH? Cl.dm and a solution of ammonium carbonate having a concentration of 309 g.dm dosing was done in such manner that in 10 minutes the reactor was injected 50 1 magnesium chloride solution and 20 1 solution of ammonium carbonate, which represents mol. MgO: CO ₂ ratio about 1.3. The withdrawn suspension was filtered and washed, the solid phase contained 99.2% MgCO ₃ , and a residual concentration of 48.4 g MgCl ₂ was determined in the solution.

SUBJECT OF THE INVENTION

Claims (4)

A process for obtaining anhydrous magnesium carbonate from a magnesium salt solution or from a suspension of low soluble magnesium compounds such as nesquehonite MgCO ₃ .3H ₂ O, basic carbonates, magnesium hydroxide, etc. in water or magnesium salt solutions, characterized in that the solution or suspension admixed with carbonate, or ammonium carbonate or alkali metal carbonate or mixtures thereof, or with carbon dioxide; with the addition of ammonia or an alkali metal hydroxide such that the molar ratio of MgO: CO ₂ in the reaction mixture does not exceed 2; the preheating of the components is heated in an enclosed space and at a temperature of at least 110 ° C and the corresponding pressure is allowed to react depending on the temperature of the reaction mixture for 2 to 600 minutes, after which the solid phase is separated from the mother liquor after decompression. 2. The method according to item. ammonia present and 1, characterized in that from the gases after decompression, the reaction carbon dioxide is absorbed by absorption. mixture 1 and 2, characterized in that the mother liquors and washings are used 3. The process according to the point containing predominantly ammonium salts is decomposed by calcium hydroxide or alkali hydroxide or by calcined magnesium raw material and the liberated ammonia is recovered by absorption. 4. Process according to claim 1, characterized in that the decomposition of the magnesium salt solutions or of the suspensions of low soluble magnesium compounds is carried out in batches or in a continuous process.