EP2742000A1

EP2742000A1 - Method for producing ultrapure magnesium hydroxide and magnesium oxide

Info

Publication number: EP2742000A1
Application number: EP12705865.9A
Authority: EP
Inventors: Marcus Georg Schrems; Anna Katharina DÜRR; Günther Huber; Jesus Enrique ZERPA UNDA; Katrin Freitag; Michael Karcher; Axel Salden
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2011-08-08
Filing date: 2012-02-27
Publication date: 2014-06-18
Also published as: KR20140052013A; CN104066685A; SG2014009716A; JP2014524401A; IL230613A0; WO2013020717A1

Abstract

The invention relates to a method for producing magnesium compounds by means of precipitation, wherein (1) an aqueous solution or suspension of a magnesium compound is mixed with a precipitant, selected from the group of alkali, oxin, inorganic phosphate and inorganic salt of carbonic acid, and the corresponding magnesium compound precipitates, (2) the mixture from step (1) is mixed with a flocculating agent as applicable, (3) the solid is separated from the liquid from the mixture from step (1) and step (2), as applicable, (4) the separated solid is mixed with water in the presence or in the absence of a flocculating agent, (5) the solid is separated from the liquid from the mixture from step (4) as applicable, (6) steps (4) and (5) are repeated once or repeatedly as applicable, (7) and the separated solid is dried as applicable, after the addition of further compounds as applicable, characterized in that the aqueous solution or suspension of a magnesium compound in step (1) is obtained (i) by reacting an organo-magnesium compound with aldehyde or a ketone or another electrophile and subsequent aqueous preprocessing of the reaction mixture at a pH value of 10 at maximum or (ii) from a magnesium salt having a calcium content and/or potassium content of 200 ppm each at maximum, relative to the magnesium salt used.

Description

The present invention relates to a process for producing high-purity magnesium compounds, preferably high-purity magnesium hydroxide and high-purity magnesium oxide, and to the use of the magnesium compound thus obtained, preferably the magnesium hydroxide or magnesium oxide thus obtained, as defined in the claims, respectively. Magnesium hydroxide Mg (OH) 2 and magnesium oxide MgO are known per se.

Magnesium hydroxide Mg (OH) 2 and magnesium oxide MgO with a very high degree of purity (for example about 99% by weight MgO content) are, for example, important additives for the production of ion-conducting ceramics and are also used in other fields, for example the Production of crucibles for the production of ion-conducting ceramics, for heating cartridges, spiral tube cartridges, heating cables, fire-proof cables, jacket thermocouples or in general in electrical heating technology or temperature measurement, as an additive in animal nutrition, in the production of catalysts, in papermaking, as an additive to rubber and plastics. Ion-conducting ceramics are described, for example, in J.L. Sudworth and A.R. Tilley, The Sodium Sulfur Battery, Chapman and Hall, New York (1985) and are used inter alia as an electrolyte in electrochemical cells, for example as electric batteries or synthesis cells for alkali metals. As a rule, ion-conducting ceramics are usually produced as follows: alumina, an alkali metal source, generally alkali metal salts, and further additives are formed (green body) and sintered at a very high temperature.

In particular, for use as an additive for the production of ion-conductive ceramics, it is advantageous if the content of certain alkali, alkaline earth and transition metals, for example of strontium, barium, beryllium, calcium, potassium, cesium in the corresponding magnesium or magnesium oxide , in particular calcium and / or potassium is not greater than 50 ppm each. Even lower contents are preferred. It is also advantageous to keep the halide concentration, preferably chloride concentration, as low as possible in the corresponding magnesium hydroxide or magnesium oxide.

Although such relatively pure magnesium oxide or magnesium oxide products are commercially available, they are usually so expensive that their price hinders a technical application.

JH Canterford, Mineral Processing and Extractive Metallurgy Review, 1985, 2 (1-2), 57-102, Gordon and Breach Science Publishers, Ltd., describe the precipitation of magnesium hydroxide. xid from seawater with a base and the calcination of magnesium hydroxide to magnesium oxide. This reference, inter alia, does not disclose organomagnesium compounds.

The object of the present invention was to remedy the disadvantages of the prior art and to provide magnesium hydroxide or magnesium oxide at low cost, which is particularly suitable for use as an additive in the production of ion-conducting ceramics.

The object was achieved by the method defined in the claims and the use defined in the claims.

A water-containing solution or suspension of a magnesium compound in step (1) which is suitable for the process according to the invention is obtained

(i) by reacting an organomagnesium compound with an aldehyde or a ketone or another electrophile and subsequent aqueous workup of the reaction mixture at a pH of at most 10 or

(ii) from a magnesium salt whose calcium content and / or potassium content is in each case at most 100 ppm, based on the magnesium salt used. According to variant (i), the aqueous solution or suspension of a magnesium compound is obtained in step (1) of the process according to the invention by reacting an organomagnesium compound.

For the preparation of the organomagnesium compound, for example, commercially available magnesium can be brought into a form by reaction with organic compounds, which makes it possible to dissolve or suspend the resulting organomagnesium compound such as RMgX or R2Mg in an organic solvent.

This can be done, for example, by reacting magnesium with an alkyl halide, aryl halide, vinyl halide, aralkyl halide or alkaryl halide or another organic halide (also known as the "Grignard reaction"), with organomagnesium halides (RMgX) or diorganomagnesium compounds R2Mg generally being formed Preferred organic compounds here are organic chlorides, such as alkyl chlorides, aryl chlorides, aryl chlorides, alkaryl chlorides, for example C 1 -C 10 -alkyl chlorides, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl The Grignard reaction preferably takes place in aprotic ethereal solvents such as diethyl ether, methyl tert-butyl ether, tetrahydrofuran or 2-methyltetrahydrofuran, but may also be carried out in other suitable solvents known to the person skilled in the art ,

By reaction with a further compound and subsequent workup, the previously organically bound magnesium can be released as a salt. For example, the organomagnesium compound RMgX or F ^ Mg are reacted with an aldehyde or a ketone or another electrophile, which generally leads to cleavage of the magnesium-carbon bond in the R-Mg part of the organomagnesium compound. Preference is given to aldehydes and ketones.

Subsequently, the reaction mixture is usually worked up aqueous and the aqueous phase separated from the organic phase by conventional methods. Aqueous work-up with respect to this reaction mixture is known to the person skilled in the art and usually means that the reaction mixture is admixed with water and / or an aqueous protic acid, for example inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid or organic acids such as acetic acid Separate organic and the aqueous phase.

The aqueous work-up takes place at a pH of at most 10, preferably at most 9.5. Examples of work-up pHs are 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9.5, 10.

The aqueous phase contains, in addition to residues of organic components, for example solvents, magnesium salts, as a rule mixed magnesium salts, for example

Mg (OH) 2, Mg (CI) 2 or Mg (OH) Cl. The water content of the aqueous phase is usually above 50% by weight, preferably above 80% by weight, in each case based on the aqueous phase, including dissolved and / or suspended constituents.

If necessary, the aqueous phase can be freed from organic solvent residues by heating or stripping.

A source of such aqueous phases which is also well suited on an industrial scale is the magnesium-containing aqueous phase (wastewater) obtained during the workup of Grignard reactions, for example from industrial synthesis processes in which organic electrophiles are reacted with Grignard compounds and then worked up in water as described above isolate organic target molecule. According to variant (ii), the water-containing solution or suspension of a magnesium compound in step (1) of the process according to the invention is obtained from a magnesium salt.

Suitable magnesium salts are: salts of magnesium with inorganic or organic acids, for example magnesium chloride, magnesium sulfate, magnesium carbonate, magnesium hydrogencarbonate, in each case with or without water of crystallization, preference is given to magnesium chloride with or without water of crystallization (also referred to below as MgC).

The magnesium salts mentioned in the above paragraph advantageously each have a calcium content and / or potassium content of (in each case based on calcium content or potassium content) at most 200 ppm, preferably at most 100 ppm, particularly preferably at most 50 ppm, in each case based on that for step 1 The magnesium salt used in the process according to the invention. The calcium content or potassium content is understood here as ppm by weight. The calci- content and potassium content are both determined by the known method ICP-OES (Ion Coupled Plasma - Optical Emission Spectroscopy). In this case, the sample to be examined is dissolved and introduced into the spectrometer and their emission measured against a quantitative standard.

In step (1) of the process according to the invention, the aqueous solution or suspension of a magnesium compound described under variant (i) above is mixed with a precipitating agent. The mixing can be carried out by the methods known to the person skilled in the art, without or preferably with stirring, for example in an open stirred vessel.

During or after mixing, the sparingly soluble magnesium compound corresponding to the precipitant is precipitated, for example when using an aqueous base, the magnesium hydroxide (also referred to herein as Mg (OH) 2).

The precipitation usually takes place at temperatures in the range of 10 to 100 ° C and at an ambient pressure of 1 atm (abs.), But also overpressure can be applied.

Suitable precipitating agents are base, oxine, inorganic phosphate and inorganic carbonic acid salt or any mixtures thereof. Preferred precipitants are bases.

Sodium hydroxide or ammonium hydroxide (aqueous ammonia solution) are advantageously used as base if the magnesium hydroxide according to the invention or the magnesium oxide obtainable therefrom is to be used for the production of ion-conducting ceramics, in particular sodium-ion-conducting ceramics.

For other applications, however, the reaction can also be carried out with other hydroxides, such as potassium hydroxide.

Suitable bases are aqueous dilute bases or mixtures thereof whose water content is in the range from 30 to 99% by weight, for example sodium hydroxide solution, potassium hydroxide solution, ammonium hydroxide solution, preferably sodium hydroxide solution or ammonium hydroxide solution.

Ammonia can also be used as the base gas, from which an aqueous solution of ammonium hydroxide forms, for example, when it is introduced into the aqueous solution or suspension of a magnesium compound in step (1).

Also suitable as precipitant is oxine (8-hydroxyquinoline), which precipitates magnesium as magnesium oxinate. Also suitable as precipitating agents are inorganic phosphates such as water-soluble alkali metal phosphates, water-soluble alkali metal hydrogenphosphates, water-soluble alkali metal dihydrogen phosphates, preferably disodium hydrogenphosphate and / or ammonium dihydrogenphosphate, diammonium hydrogenphosphate.

In a well-suited process for the precipitation of magnesium ammonium phosphate, the aqueous solution or suspension of a magnesium compound in step (1) of the process according to the invention is buffered to pH 8 to 9 with ammonia and ammonium chloride and then treated with aqueous disodium hydrogen phosphate solution, whereby the magnesium ammonium phosphate as a white, acid-soluble precipitate is obtained.

The magnesium can also be precipitated by adding inorganic salts of carbonic acid, preferably alkali metal carbonates, for example disodium carbonate (Na 2 CO ₃ ), as carbonate from the aqueous solution or suspension of a magnesium compound in step (1) of the process according to the invention.

Step (2) of the method according to the invention is optional. If it is carried out, which is preferred, then the mixture from step (1) of the process according to the invention is mixed with a flocculant, wherein the addition type, flocculant for mixing or mixing to the flocculant or other variants is not critical. The displacement can be done, for example, in the stirred tank from step (1), or during the transfer into a second tank.

Flocculants are known in principle. They are usually high molecular weight organic substances such as polymers or polyelectrolytes.

The flocculation aid according to the invention is, for example, an anionic or cationic or neutral (synonymous: nonionic) organic high molecular flocculation aid or a combination thereof. Examples of anionic flocculants according to the invention are polyacrylic acid salts of the alkali metals - such as poly (sodium acrylate) - and carboxyl-substituted polyacrylamide.

Examples of neutral (synonymous: nonionic) flocculation aids according to the invention are polyacrylamide, poly (ethylene oxide) or polymers of 1-vinyl-2-pyrrolidone, N-vinylformamide.

Flocculation aids according to the invention are described, for example, in the brochure "Sedipur® types for water treatment" of TENSID CHEMIE / BASF Group of August 2002. Examples of such flocculation aids are polyacrylamide (nonionic), carboxyl-substituted polyacrylamide (anionic), with COR- Groups substituted polyacrylamide (R = O-CH ₂ -CH ₂ -N (CH ₃ ) ₃ Cl) (cationic), polyethylenimine (PEI), poly-DADMAC, polyamines (see page 7 of said booklet). Preferred flocculation aids according to the invention are nonionic or anionic flocculants, for example polyacrylamide (nonionic), polyacrylamide substituted with carboxyl groups (anionic), polyacrylic acid salts of the alkali metals (anionic), particularly preferred are nonionic flocculation aids, for example polyacrylamide.

The amount of flocculation aid based on the mass of magnesium contained in the mixture of step (1) is variable, with 1 mg of pure precipitant per g of magnesium should not fall below and more than 10 mg of pure precipitant per gram of magnesium usually no effect improvement to provide more.

By adding aqueous bases such as NaOH or aqueous Nh solution or Nh gas, the pH of the aqueous phase can be raised so that magnesium hydroxide precipitates. This can be separated from the mother liquor by methods known to those skilled in the art and further processed in the present form.

Alternatively, the magnesium hydroxide may be washed with water to lower, for example, the level of unwanted ions. For example, the chloride content of the magnesium hydroxide can be lowered by washing with water. The separation of the magnesium hydroxide (Mg (OH) 2) precipitated from the alkaline aqueous medium, for example by sedimentation, can be accelerated when a flocculant is added to the aqueous medium in which the magnesium hydroxide is contained. In step (3) of the process according to the invention, the solid is separated from the liquid from the mixture of step (1) and optionally step (2). This can be done by conventional methods known to those skilled in the art, such as filtration, sedimentation, centrifugation or the like, preferably sedimentation. For example, the mixture from step (1) and optionally step (2) is transferred to a container, for example pumped and allowed to rest, with sedimentation taking place (sedimentation 1) in which the solid separates from the liquid. This container is for example a gravitational separator, for example a sedimentation tank.

The separated liquid (waste water 1) can be completely or partially used again as an extractant or discarded. In a preferred embodiment, the liquid is partially recycled or discarded, in a particularly preferred embodiment, the liquid is discarded.

Step (4) of the method according to the invention is optional. If it is carried out, which is preferred, the solid separated in step (3) is mixed with water, preferably with stirring. This can be done, for example, in an open stirred tank. The resulting mixture can then be mixed with a flocculation aid according to the invention, the addition type, flocculant for mixing or mixing to the flocculant or other variants being not critical. The displacement can be done for example in said stirred tank, or during the transfer into a second container. As flocculation aids according to the invention, those described above, including those mentioned as preferred or particularly preferred groups or individuals, are used. It is preferred that the resulting mixture is admixed with a flocculation aid according to the invention as described above. Step (5) of the process of the invention is optional. When applied, the mixture of step (4) separates the solid from the liquid as described in step (3) above.

The separated liquid (waste water 2) can be used in whole or in part again in step 1 instead of the water, or discarded. In a preferred embodiment, the liquid is partially recycled or discarded, in a particularly preferred embodiment the liquid is partially recycled.

Step (6) of the method according to the invention is optional. If it is used, steps (4) and (5) of the method according to the invention are repeated once or several times.

In a preferred embodiment, steps (4) and (5) are each executed once and not repeated, step (6) thus not applied.

The steps (1) to (6) of the method according to the invention are generally carried out in a temperature range of 10 ° C to 100 ° C. Preferably, these steps are carried out in a temperature range of 15 ° C to 50 ° C, most preferably, these steps are carried out in a temperature range of 15 ° C to 30 ° C. In an alternative embodiment, step three can also be carried out in the temperature range from 30 C to the boiling point of the mixture. Steps one, two, three and four can be carried out in a pressure range from 100 mbar to 10000 mbar. The implementation is preferably carried out at atmospheric pressure.

In step (7) of the process according to the invention, the separated magnesium compound obtained by the above-mentioned steps, preferably of the magnesium hydroxide

(Mg (OH) 2), for example, together with the residues of the water contained in it by the usual methods for drying inorganic suspensions or pastes, for example, spray drying, fluidized bed drying, dried. If the drying in step (7) is not carried out, the magnesium compound separated off after the last process step, preferably the magnesium hydroxide (Mg (OH) 2), still contains residues of water.

This hydrous magnesium compound, or the magnesium compound obtained by the step (7) of the process of the present invention, preferably the magnesium hydroxide (Mg (OH) 2) can be used for the production of magnesium oxide by thermal treatment of the magnesium compound, preferably magnesium hydroxide (Mg (OH) 2) in the range of 600 to 3000 ° C and / or for the production of sintered molded articles, such as by way of example in the following, described a little further below.

If the magnesium compound obtainable by the present process, preferably the magnesium hydroxide (Mg (OH) 2), for example, a thermal treatment in the range of 600 to 1000 ° C, preferably at about 900 ° C, subjected to usually obtains a calcined magnesium oxide, the Binds with water and which can be used for example for the production of ion-conducting ceramics.

If the magnesium compound obtainable by the present process, preferably the magnesium hydroxide (Mg (OH) 2), for example, subjected to a thermal treatment in the range of 1200 to 2800 ° C usually gives a magnesium oxide, which no longer binds with water. This is also referred to in the art as "sintered magnesia." This sintered magnesia, preferably that which is obtainable at a temperature of about 1200 to about 1500 ° C., is used, for example, for the production of refractory materials, for example, magnesium oxide crucibles.

Such magnesia crucibles may in turn be used to make ion conducting ceramics such that the green bodies of the ion conducting ceramics are sintered in the magnesia crucibles, for example as described below.

If the magnesium compound obtainable by the present process, preferably the magnesium hydroxide (Mg (OH) 2), for example, a thermal treatment in the range of 2800 to 3000 ° C, for example in an electric arc furnace, subjected to usually obtains a magnesium oxide, which does not bind with water , This is referred to in the art as "fused magnesia." This material usually has the highest hardness.

As sintered shaped bodies, which are also referred to as "ceramics", basically all bodies with regular or irregular shape are suitable, for example cylinders open on both sides, such as tubes, cylinders closed on one side, for example so-called crucibles, round discs, angular plates, rods and tubes with lace pattern.

For example, the sintered shaped bodies, preferably cylinders closed on one side; Round disks or square plates Ion-conducting ceramics, preferably alkali metal ion-conducting ceramics, ion-conducting ceramics are described, for example, in JL Sudworth and AR Tilley, The Sodium Sulfur Battery, Chapman and Hall, New York (1985). They are used for example in electrochemical processes, such as electrolysis cells or electric batteries. In a first embodiment, the hydrous magnesium compound or the magnesium compound obtained after step (7) of the process according to the invention, preferably in each case the magnesium hydroxide (Mg (OH) 2, in the temperature range from 600 to 3000 ° C, bei- For example, 600 to 1000 ° C, 1200 to 2800 ° C, 2800 to 3000 ° C generally in an oxygen-containing atmosphere, preferably air, thermally treated. The thermal treatment, also referred to in the art as "calcining", usually takes place in the apparatus known to those skilled in the art, such as rotary kilns, muffle furnaces, electric arc furnaces (the latter especially for the temperatures in the range from 2800 to 3000 ° C.) Treatment converts the magnesium compound obtained by the process according to the invention into magnesium oxide (MgO), also called magnesia, as described above, in calcined magnesium oxide which bonds with water, sintered magnesia or fused magnesia For example, the magnesium oxide according to the invention, preferably that which is obtainable at a temperature of about 1200 to about 1500 ° C, for the production of sintered moldings, preferably closed on one side ssenen cylinders, so-called "crucibles" are used.

These crucibles can also have a modular design, for example, they contain a cylinder closed on one side as a base on the open side of a cylinder open on both sides or a plurality of cylinders open on both sides and can be connected and these crucibles can be covered with a lid, no matter what geometry ,

The sintered bodies of the present invention, preferably the crucibles described herein, may be used, for example, to make ionically conductive ceramics, for example, by placing and subjecting the precursor green body of the ion conducting ceramic in the magnesium oxide crucible of the present invention described herein to thermal treatment. In a variant of the first embodiment, the magnesium compound is precipitated in step (1) of the process according to the invention with an aqueous ammonia solution and then in the temperature range of 600 to 3000 ° C, for example 600 to 1000 ° C, 1200 to 2800 ° C, 2800 to 3000 ° C generally in an oxygen-containing atmosphere, preferably air, thermally treated. This thermal treatment converts the magnesium compound obtained by the process according to the invention into magnesium oxide (MgO), which is distinguished by particularly low chloride contents. The magnesia may then be used to make the sintered bodies described above, including their preferred or particularly preferred embodiments. In a second embodiment, the hydrous magnesium compound obtained by the process of the invention or the magnesium compound dried in step 7, preferably the magnesium hydroxide (Mg (OH) 2), may also be mixed with other additives, for example alumina (Al 2 O 3) and / or sodium salts and binders and ground, for example, in aqueous suspension and then dried, preferably spray-dried. This modified magnesium compound, preferably magnesium hydroxide (Mg (OH) 2), can then be used for the production of the above-described sintered shaped bodies, including their preferred or particularly preferred embodiments, for example wise ion-conducting ceramics, preferably alkali metal ion-conducting ceramics, or the crucibles described herein, continue to be used.

Examples

Example 0

That from the large-scale implementation of a Grignard reagent (RMgX) with a

Electrophilic and subsequent acidic, aqueous work-up of the reaction mixture obtained wastewater (pH = 9.3) was evaporated and the residue analyzed. The calcium content was <10 ppm. A typical composition of other components was: Mg about 19 g / 100 g and about 35 g / 100 g of chlorine as chloride.

example 1

The wastewater according to Example 0 was adjusted to pH = 10.4 with 25% strength aqueous ammonia solution and stirred for one hour at room temperature. Thereafter, the mixture of solid and liquid was filtered for about 5 hours over a membrane chute. Thereafter, the solid was mixed with 100 ml of water and heated to about 100 C (15 min). Thereafter, the mixture was cooled and filtered through a membrane chute. The wash with water was repeated twice more. The residue was then dried from magnesium hydroxide (120 C, 10 mbar) and analyzed: magnesium content 41 g / 100 g of substance; Chlorine content 1000 ppm.

The example shows, among other things, that the filtration is slow. Example 2

The material obtained from Example 1 was heated for one hour at 1000 C in an air atmosphere in a muffle furnace. An analysis of the resulting magnesium oxide showed: about 59 g Mg / 100 g; 10 ppm Cl.

This example shows that by calcining the Mg (OH) ₂ precipitated with aqueous ammonia solution at 1000 ° C, the Mg (OH) _{2 is converted} into MgO and the chlorine content can be lowered to very low values.

Example 3

The wastewater according to Example 0 was adjusted to pH = 1 1.5 with 25% strength aqueous NaOH solution (sodium hydroxide solution) and stirred for one hour at room temperature. Thereafter, the mixture of solid and liquid was filtered through a membrane chute. A portion of the solid of the crude magnesium hydroxide was dried and analyzed: magnesium content: 32 g / 100 g; Chlorine content: 13.1 g / 100 g.

Thereafter, the residual solid of the crude magnesium hydroxide was washed four times with 50 mL each of water. The residue was then dried (120 ° C., 10 mbar) and analyzed: magnesium content 40 g / 100 g of substance; Chlorine content 1000 ppm. Example 4

The wastewater according to Example 0 was adjusted to pH = 1, 5 with 25% strength aqueous ammonia solution and stirred for one hour at room temperature. Thereafter, the mixture was filtered through a membrane chute. A portion of the solid of the crude magnesium hydroxide was dried and analyzed: magnesium content: 39 g / 100 g; Chlorine content: 2.5 g / 100 g.

Thereafter, the residual solid of the crude magnesium hydroxide was washed four times with 50 mL each of water. The residue was then dried (120 C, 10 mbar) and analyzed: magnesium content 41 g / 100 g of substance; Chlorine content 1400 ppm. Examples 3 and 4 show that the magnesium hydroxide can be obtained by adding sodium hydroxide solution or ammonia solution. The washing can also be done at room temperature and lowers the chlorine content.

Example 5

The wastewater according to Example 0 (1 kg) was mixed with 25% aqueous ammonia solution (224 g) (pH = 10.3) and stirred for 30 min at room temperature. The product does not sediment after switching off the stirrer.

Subsequently, 50 g of a 0.1% by weight aqueous Sedipurt® NF106 (medium to high molecular weight nonionic polyacrylamide) solution was added. The mixture was stirred for 7 minutes. After about 30 seconds, the precipitated Mg (OH) 2 sat down completely. The Mg content of the supernatant is <1000 ppm. The Mg (OH) 2 thus obtained could be easily separated from the supernatant by filtration.

Example 6

The wastewater according to Example 0 (100 g) was mixed with 20 g of a 25% ammonia solution.

By adding various flocculant types, as described below, the resulting Mg (OH) _{2 was} precipitated. When using a 0.1% aqueous solution of the non-ionic flocculant Sedi- pur®NF 104 (medium to high molecular weight), 1.7 mL of Sedipur solution was needed to give good visible flocculation with the addition of total 5 mL of this solution showed rapid precipitation to give large flakes. When using a 0.1% aqueous solution of Sedipur® NF 106 non-ionic flocculant (medium to high molecular weight), 1.7 mL of Sedipur solution was required to give good visible flocculation with a total of 4 mL added This solution was a rapid precipitation to form large flakes to recognize. When using a 0.1% aqueous solution of the anionic flocculant Sedipur® AF 900, about 10 mL of Sedipur solution was needed to obtain visible flocculation and longer precipitation. When using a 0.1% aqueous solution of the cationic flocculant Sedipur CF 803, no visible flocculation was seen after addition of> 15 mL Sedipur solution. This example shows that nonionic and anionic flocculants are suitable for the separation of the recovered Mg (OH) 2 from the mother liquor. Particularly suitable are nonionic flocculants having a medium to high molecular weight, which can be seen, inter alia, from the fact that it is necessary to add smaller amounts thereof in order to achieve a rapid precipitation.

Example 7

The wastewater according to Example 0 (300 g) was mixed with 25% aqueous sodium hydroxide (29 g) (pH = 1 1, 65) and stirred for 60 min at room temperature. The product does not sediment after switching off the stirrer. To 90 mL of this suspension was then added 2 g of 0.1% (w / w) aqueous Sedipur® NF104 (medium to high molecular weight nonionic polyacrylamide). The mixture was stirred for 7 minutes. After about 30 seconds, the precipitated Mg (OH) 2 sat down completely. The Mg (OH) 2 thus obtained could be easily separated from the supernatant by filtration. The filter cake was dried at 120 ° C in vacuo (10 mbar) and then calcined at 1200 ° C. Before calcining, the chloride content was 2900 ppm, and after calcining, the chloride content was 30 ppm. The Mg content of the MgO thus obtained corresponded to the theoretical content of 59 g / 100 g.

This example shows that the combined use of NaOH solution (caustic soda) and flocculant leads to a rapid precipitation as Mg (OH) 2 and the product after calcination has a lower chlorine content of <50 ppm,

Claims

claims

1 . Process for the preparation of magnesium compounds by precipitation, wherein

(1) a water-containing solution or suspension of a magnesium compound is mixed with a precipitant selected from the group consisting of base, oxine, inorganic phosphate and inorganic salt of carbonic acid, and the corresponding magnesium compound precipitates,

(2) optionally adding a flocculation aid to the mixture of step (1),

(3) separating the solid from the liquid from the mixture of step (1) and optionally step (2),

(4) optionally mixing the separated solid with water in the presence or absence of a flocculant aid,

(5) optionally separating the solid from the liquid from the mixture of step (4)

(6) optionally repeating steps (4) and (5) once or several times

(7) and optionally the separated solid, optionally after addition of further compounds, drying,

characterized in that the aqueous solution or suspension of a magnesium compound in step (1) is obtained (i) by reacting an organomagnesium compound with an aldehyde or a ketone or other electrophile and subsequent aqueous workup of the reaction mixture at a pH of at most 10 or (ii) from a magnesium salt whose calcium content and / or potassium content is in each case at most 200 ppm, based on the magnesium salt used.

2. The method of claim 1, wherein the precipitating agent in step (1) is a base.

3. The method of claim 1 to 2, wherein the base are hydroxides and the magnesium compound is magnesium hydroxide.

4. The method of claim 1 to 3, wherein the base is sodium hydroxide or ammonium hydroxide.

5. The method of claim 1 to 4, wherein the separation of the solid from the liquid in steps (3) and / or (5) is done by sedimentation.

6. The method of claim 1 to 5, wherein step (4) is performed mandatory.

7. The method of claim 1 to 6, wherein step (2) and / or (4) is obligatory and carried out in the presence of a flocculant.

8. The method of claim 1 to 7, wherein the flocculant is selected from the group of anionic, cationic, neutral flocculants.

9. The method of claim 1 to 8, wherein the flocculant is selected from the group consisting of polyacrylamide (non-ionic), carboxyl-substituted polyacrylamide (anionic), COR-substituted polyacrylamide (R = 0-CH2-CH2-N (CH ₃ ) 3CI) (cationic), polyethylenimine (PEI), poly-DADMAC, polyamines.

A process according to claims 1 to 9, wherein the liquid from step (5) is recycled in whole or in part in step (4) as a medium for mixing.

1 1. Use of, according to the method defined in claim 1 to 10, obtained magnesium compound for the production of magnesium oxide by thermal treatment of the magnesium compound in the range of 600 to 3000 ° C.

12. Use of, according to the method defined in claim 1 to 10, the obtained magnesium compound or the obtained according to claim 1 1 magnesium oxide for the production of sintered moldings.

13. Use of, according to the method defined in claim 3 to 10, obtained magnesium hydroxide or obtained according to claim 1 1 magnesium oxide for the production of sintered moldings.

14. Use according to claim 12 to 13, wherein the moldings are open cylinders or cylinders closed on one side, round discs or square plates.

15. Use according to claim 12 to 14, wherein the moldings are ion-conducting ceramics.

16. Use according to claim 12 to 15, wherein the moldings are alkali metal ion conducting ceramics.

17. Use according to claim 12 to 16, wherein the magnesium compound or the magnesium oxide is used together with other components.

18. Use according to claim 12 to 14, wherein the sintered moldings are used for the production of ion-conducting ceramics.

19. Use of the defined in claim 12 to 14 and 17 sintered moldings for the production of ion-conducting ceramics.