CS251463B1 - A method of obtaining precipitated calcium carbonate on an industrial scale - Google Patents

Abstract

The use of calcium salt solutions, waste from production processes, as starting materials for the production of precipitated CaCO3 on an industrial scale, which is achieved by mixing solutions containing calcium salts, for example CaCl2 or Ca(NO3)2, with a magnesium bicarbonate solution, which results in the precipitation of Ca2+ ions from the reaction mixture in the form of CaCCb.

Description

The invention relates to a method for obtaining precipitated calcium carbonate from solutions of calcium salts.

A method for producing precipitated CaCO3 by absorbing CO2 into an aqueous suspension of CaO and/or CaOH is known — for example, see: Juvekar V. A., Sharma M. M.; Chem. Eng. Sci., vol. 28, p. 825, 1973.

There are a number of cases, for example the production of soda by the Solvay process or the chemical production of pure magnesium oxide, when the production processes produce aqueous solutions of calcium salts that it is desirable to further utilize in a suitable way.

H2O

Ca ²⁺ + Mg(HCO3) ₂ = CaCO3 + Mg ²⁺ +

Precipitated CaCO3 is required in various industries, for example as a filler in the production of rubber and plastics, or as a pigment.

Example 1

A solution of magnesium hydrogen carbonate with a concentration of 0.103 mol/l MgJHCCbJa was mixed at a temperature of 30 °C with a solution of CaCl2 with a concentration of 3.463 mol/l. CaCl2 in a volume ratio of 53:1. The reaction mixture was mechanically stirred in air at a temperature of 30 °C for 20 minutes. A sample of the reaction mixture was then filtered to remove the precipitate of GaCCb and subjected to chemical analysis. The results are shown in Table 1.

Example 2

A solution of magnesium hydrogen carbonate with a concentration of 0.047 mol/l Mg(HCO3)2 was

The essence of the invention lies in the fact that aqueous solutions containing calcium salts are used as a raw material for the production of precipitated CaCO3.

The method of obtaining precipitated CaCCb according to the invention is characterized in that a solution containing a calcium salt, for example CaCl2 or Ca(NO3)2, is mixed with a solution of magnesium hydrogen carbonate, Mg(HCO3)2, under such conditions that the value of the product of the solubility of CaCCb for the parameters of the reaction mixture is exceeded and the solid phase of CaCCb is precipitated from the reaction mixture according to the overall equation

CO2 + H2O.

mixed at 30 °C with a solution containing 2.551 mol/l CaCl 2 and 0.950 mol/l MgCl 2 in a volume ratio of 55.6:1. The reaction mixture was mechanically stirred in air at 30 °C for 20 minutes. A sample of the reaction mixture was then processed as in Example 1. The results are shown in Table 1.

Example 3

A solution of magnesium bicarbonate with a concentration of 0.047 mol/l Mg(HCO3)2 was mixed at 30 °C with a solution containing 1.075 mol/l CaCl2 and 2.275 mol/l MgCl2 in a volume ratio of 23.3:1. The reaction mixture was mechanically stirred in air at 30 °C for 20 minutes. A sample of the reaction mixture was then processed as in Examples 1 and 2. The results are shown in Table 1.

Table 1

The data on the composition of the reaction mixture at the moment of mixing the solutions and after 20 minutes of reaction duration are as follows for examples 1, 2 and 3:

Component Concentration of component in reaction mixture (mol/l) at time point after 20 minutes Example of mixing reaction duration

CaCh Mg(HCO3)2 MgClz 0.064 0.101 0 0.010 0.047 0.054 1 CaCl2 0.045 0.030 Mg(HCO3)2 0.046 ,0.031 2 MgCl2 0.017 0.032 CaCh 0.044 0.029 Mg(HCO3)2 0.045 0.030 3 MgCl ₂ (0.094 0.109

The difference in the concentrations of CaCl2 at the moment of mixing the solutions and after 20 minutes of reaction corresponds to the amount of precipitated CaCCb — in moles — obtained from 1 liter of reaction mixture for the experimental conditions described in examples 1, 2 and 3.

The Mg(HCO3)2 solution can be advantageously prepared by a known method: by absorption of CO2, for example from the flue gases of furnace units, into an aqueous suspension of a mineral magnesium material containing MgO, Mg(OH)2 and/or MgCO3, for example magnesite fly ash. The insoluble residue of the magnesium material is separated from the solution by sedimentation and/or filtration.

The obtained Mg(HCO3)2 solution with a Mg(HCO3)2 concentration above 2.10“ ² mol/1, preferably above 4. 10~ ² mol/1, is then mixed at a temperature above 10 °C, preferably above 30 °C, in a crystallization reactor with a calcium salt solution with a pH value of >3, preferably with a pH value of >6, and with a Ca ²⁺ ion concentration such that after mixing both solutions the solubility product value is exceeded.

CaCO3, given by the parameters of the reaction mixture, and to the precipitation of a solid phase of calcium carbonate.

The rate of precipitation of CaCO3 in the crystallizer can be increased by mechanically stirring the reaction mixture in an atmosphere with a minimum CO2 content, and/or by bubbling fresh air through the reaction mixture, and/or by adding CaO and/or Ca (OH)2 to the reaction mixture and/or to the calcium salt solution before it enters the crystallizer.

The precipitated CaCO3 is separated from the solution by sedimentation and/or filtration.

The method according to the invention, enabling the production of precipitated CaCO3 from solutions containing Ca ²⁺ ions, is advantageously feasible, especially within the industrial production of pure magnesium oxide from mineral magnesium substances containing calcium compounds as impurities, for example from magnesite, dolomite or from waste from the magnesite industry, or within the industrial production of soda by the Solvay process, associated with the production of pure MgO.

Claims (2)

231463 The difference in the concentration of CaCl 2 at the time of mixing of the solutions and after 20 minutes of the reaction corresponds to the amount of CaCl 2 precipitated in moles obtained from 1 liter of the reaction mixture described in Examples 1, 2 and 3. Advantageously, it is prepared by known methods: absorption of CO 2, for example from flue gases of furnace aggregates, an aqueous suspension of mineral magnesium material containing MgO, Mg (OH) 2 and / or MgCO 3, for example magnesite dust. The insoluble residue of the magnesium material is separated from the solution by sedimentation and / or filtration. The obtained Mg (HCO3) 2 solution with a Mg (HCO3) 2 concentration above 2.10-2 mol / l, preferably above 4.times.10@-2 mol / l, is then mixed with a temperature of over 10 DEG C., preferably above. 30 ° C, in a crystallization reactor with a calcium salt solution having a pH> 3, preferably spH> 6, and a Ga 2+ ion concentration such that upon mixing of the two solutions, the product of the solubility of CaCO 3, determined by the parameters of the reaction mixture, and to the excretion solid phase carbonate carbonate. The precipitation rate of CaCO 3 in the crystallizer can be increased by mechanically agitating the reaction mixture in an atmosphere with a minimum CO 2 content, and / or by bubbling the reaction mixture with fresh air, and / or adding CaO and / or Ca (OH) 2 to the reaction mixture and / or the calcium solution. salt prior to entering the crystallizer. The precipitated Ca, CO 3 is separated from the solution by sedimentation and / or filtration. The process according to the invention, which makes it possible to produce precipitated CaCO3 from Ca2 + -containing solutions, is advantageously feasible in the industrial production of pure magnesium oxide from mineral magnesium compounds containing calcium compounds such as magnesite, dolomite. or from the wastes of the magnesia industry, in the industrial production of Solvay process, associated with the production of pure MgO. P R E D Μ E T A process for obtaining precipitated calcium carbonate on an industrial scale, characterized in that the GaCCb solid phase is formed in the reaction mixture obtained by mixing the magnesium bicarbonate solution with a Mg (HCO 3) 2 concentration of at least 0.01 mol / well. 1 with a solution containing, in addition to the calcium hydrogen carbonate present, at least 0.02 mole / l of another soluble calcium salt, preferably calcium chloride or nitrate. 2. Process according to claim 1, characterized in that calcium oxide or calcium hydroxide or both are added to the reaction mixture and / or to the starting solutions - either to one or both - before mixing. these substances in any form, preferably as calcareous or lime milk.