DE4302539C2 - Lime and / or magnesium hydroxide slurry and its manufacture - Google Patents

Description

The invention relates to a lime and / or magnesium hydroxide Slurry with a dry matter content of more than 60%.

It is known to use lime and / or magnesium hydroxide slurry by reaction of CaO, MgO, CaO-MgO with water or by mixing calcium hydroxide and / or magnesium hydroxide to be prepared in an aqueous medium.

In the production of milk of lime or a lime slurry through the reaction of unslaked or burnt lime with water the mean particle size of the calcium hydroxide particles is very large low, so that the content of calcium hydroxide particles in the Slurry must be less than 20 to 30 wt% in order for it to be sufficient flowability or sufficient pumpability ability of the slurry is ensured.

In order to increase this content up to 50% by weight, EP-A- 0 313 483 the use of a polymer and / or copolymer from at least one ethylenic monocarboxylic acid monomer recommended.

It is also known that as the particle size increases, the Calcium hydroxide particles have the specific surface area of these Particle decreases and that by increasing the diameter of the calcium hydroxide particles, the viscosity of the lime slurry decrease or even at a predetermined viscosity can increase the solids content of the slurry.

In order to increase the particle size of Ca (OH) ₂ and thus reduce the viscosity of the lime slurry, it has already been proposed in US Pat. No. 4,464,353 to use quicklime in an aqueous medium in the presence of 0.5 to 5% by weight. Calcium sulphate, based on the weight of the quick lime that is to be extinguished. According to this publication, the burnt lime is extinguished until the temperature of the reaction medium is about 85 ° C.

Tests have shown that according to such a method he keep lime slurries a dry matter content in the Can have a maximum of 40-45% by weight.

As stated on page 335 of "Chemistry and Technology of Lime and Limestone", the use of water containing SO ₂ to extinguish quick lime reduces the hydration speed of the lime and promotes the formation of large or thick particles sediment quickly. Lime slurries that have been produced by slaking quicklime in the presence of CaSO ₄ only have a relative stability or resistance over time due to this rapid sedimentation.

The present invention aims to overcome these disadvantages to lift. It therefore concerns a lime and / or magnesium hy droxide slurry with a dry matter content of more than 60% by weight, but this slurry is stable over time, d. H. that with the help of this slurry the problem of Sedi mentation of particles is avoided or prevented. The he finding therefore concerns a lime and / or magnesium hydroxide Slurry having a viscosity of less than 1.5 Pa.s and has a dry matter content of more than 60% by weight.

Such a slurry is obtained by quenching CaO, MgO, CaO-MgO, preferably CaO, with water in the presence of an anion selected from SO ₃ ^- and SO ₄ ^2- and in the presence of a polyanion.

According to a particular feature, the invention contains Slurry at least one anion of an inorganic acid, which have been selected from sulfuric acid and sulphurous acid is, as well as at least one polyanion.

The anion of the inorganic acid, which is SO ₃ ^- or SO ₄ ^2- or a mixture of these, is present in the calcium slurry in a concentration which is generally 1 to 50 g / l, advantageously 6 to 50 g / l and preferably 6 to 30 g / l.

This anion advantageously comes from a calcium or magnesium salt of an inorganic acid, in particular from CaSO ₄ (preferably in the form of CaSO _4. 1 / 2H ₂ O), MgSO ₄ (preferably in the form of MgSO _4. 7H ₂ O) and their mixtures .

That in the invention The polyanion present in the slurry is a polymer or copolymer containing anionic monomer units, derived from monomers of the following group: acrylic acid and its salts, methacrylic acid and its salts, vinylbenzenesulfone acid and its salts, 2-acrylamino-2-methylpropanesulfonic acid and its salts, 2-sulfoethyl methacrylate and its salts. the Concentration of this polyanion in the slurry is for example 1 to 50 g / l, but preferably 10 to 30 g / l.

Preferred polyanions are the acrylic polymers or copolymers ren, especially the polyacrylates, polymethacrylates, the Copo polymers made from acrylic acid esters and methacrylic acid esters and their Mixtures.

Slurries according to the invention can in their embodiment form a viscosity in the range of 0.5 Pa.s and 1.5 Pa.s and a dry matter content of more than 60% by weight.

According to another feature of the slurry of the invention gen, they contain a considerable amount of thick part chen, such as particles with a grain size above 100 microns. So ent in its embodiments holds the slurry after the Er finding calcium hydroxide and / or magnesium hydroxide particles of considerable grain size. The Invention's Slurries dung are characterized by good stability or high resistance compared to sedimentation, what their transport and their Use or their use is facilitated.

Advantageously, at least 20%, preferably at least at least 30% of the calcium hydroxide particles have a grain size or egg a diameter of more than 100 µm. According to a special feature such a lime slurry have more than 80% of the Cal Calcium hydroxide particles have a grain size above 20 microns.

In one embodiment, the slurry of the invention is a slurry that contains _{essentially only Ca (OH) 2.} Thus, according to a special feature of this embodiment, the slurry contains less than 5 wt .-%, preferably less than 1 wt .-% and even about only 0 wt .-% magnesium hydroxide, based on the total weight of calcium hydroxide and magnesium hydroxide.

The invention also relates to a method of manufacture a lime and / or magnesium hydroxide slurry, which have a dry matter content of greater than 60 wt% and a viscosity less than 1.5 Pa.s. H. a lime slurry according to the Er finding.

According to the method according to the invention, calcium oxide and / or magnesium oxide is quenched with at least one aqueous solution which contains at least one anion selected from SO ₃ ^- or SO ₄ ^2- ; during or at the end of the reaction of the quenching of the calcium oxide and / or magnesium oxide to the aqueous solution, a polyanion of a polymer or copolymer which comprises anionic monomer units which originate from monomers belonging to the group consisting of acrylic acid and theirs Salts, methacrylic acid and its salts, 2-acrylamino-2-methylpropanesulfonic acid and its salts, 2-sulfoethyl methacrylate and its salts belong to.

The reaction of the quenching of CaO, MgO or one of their mixtures is advantageously carried out with the aid of a solution containing 1 to 50 g / l, preferably 6 to 50 g / l and in particular 6 to 30 g / l SO ₄ ^2- contains.

During this quenching reaction, the reaction medium is in motion and the temperature of the medium at below 30 ° C, preferably held at 20 ° C.

Advantageously, the reaction of the erasure is measured by measuring the viscosity of the reaction medium is controlled or regulated. For example, calcium oxide and / or magnesium oxide are used Solution until a viscosity in the range of 0.3 to 1.2 Pa.s. is reached.

According to one embodiment of the method according to the invention, calcium oxide and / or magnesium oxide are extinguished with an aqueous solution containing an SO ₄ ^2- anion until the reaction mixture has a viscosity in the range from 0.3 to 1.2 Pa.s. then an acrylic polymer or copolymer is added to the mixture, preferably selected from a polyacrylate or polymethacrylate or a copolymer of acrylic and methacrylic esters or a mixture of these, so that said viscosity is reduced; then calcium oxide and / or magnesium oxide is added to the mixture in order to quench it until a viscosity in the range from 0.3 to 1.2 Pa.s. is obtained.

The slurry of lime and / or magnesium hydroxide that for example in the manner described above has been established, a phase separation (e.g. wise to a filtration) are subjected to a solid phase (which contains the particles) and a liquid phase obtain.

According to one embodiment in which the inventive Auf slurry only a phase separation, for example a Fil tration, is subjected to a liquid phase and obtained a solid phase, being grains of calcium hydroxide and / or Magnesium hydroxide in the form of a mixture of micro-flakes can be obtained.

These micro-flakes advantageously have a thickness of less than 0.5 μm, preferably less than 0.3 μm, and in embodiments can have lower and upper sides parallel to one another, the surface of these (two) sides being less than 200 μm ² , preferably less than 100 microns ² be.

The invention therefore also relates to a method for production of flakes of the slurry of the invention.

The solid phase obtained by this process is before partly dried.

According to one embodiment, the solid phase can be ground in order to form micro-leaflets, in particular of calcium hydroxide. These flakes can then be dried if necessary. These micro-leaflets advantageously have a thickness of less than 0.5 microns, preferably less than 0.3 microns, and in Ausführungsfor men can have mutually parallel lower and upper sides, the surface of these (two) sides less than 200 μm ² , preferably less than 100 μm ² .

According to one embodiment, the granules comprise calcium hydro xide and / or magnesium hydroxide in the form of a mixture of Mi Kroblättchen a mean grain size of more than 20 microns, before preferably of more than 50 µm. The mean grain size was determined by sieving. The grain size of more than 80% of the Particles or grains should be above 20 µm.

Particularly advantageous grains or granules are those with an average grain size of more than 100 µm, preferably of more than 200 µm.

These granules according to the invention are large in size Pores (for example from 30 to 35 microns), so that they are advantageous can also be used to capture thick particles.

Further details and features of the invention can be found in FIG following description, in which on the production games and reference is made to the accompanying drawings will.

In the drawings show:

Fig. 1 is a schematic view of a plant that can be used for the preparation of a slurry according to the inven tion and

Fig. 2 and 3 views and recordings of a Calciumhy droxidkorns according to the invention.

The ge for the preparation of the slurry according to the invention used plant comprises a tub 1 , provided with a cooling jacket 11 and an agitator 12 (preferably of the Ankerrüh type). The calcium and / or magnesium oxide or the calcium and / or magnesium hydroxide is filled into a funnel 2 and fed to the tub 1 via an endless screw 3. The speed of the agitator is, for example, 200 to 600 rpm.

Water, the anion of an inorganic acid and the polyanion are supplied to the tub 1 via lines 41 and 42 and 43, respectively.

The tub 1 has at its bottom a discharge line 5 for the resulting lime and / or magnesium hydroxide slurry.

The tub 1 is advantageously also equipped with a device 6 for measuring the viscosity, which is connected to a control system 7 which acts on the motor 8 which drives the endless screw 3. This system 7 then enables the rate of addition of CaO, MgO, Ca (OH) ₂ and / or Mg (OH) ₂ to be controlled in order to obtain the predetermined viscosity level, ie to obtain a product with a predetermined viscosity at the end of the operation .

A temperature sensor 9 is connected to a control system 10 of an inlet valve 21 for a cooling liquid in the jacket 11 of the bot tich 1 . In this way it can be ensured that the temperature of the mixture contained in the vat does not exceed a predetermined temperature, for example 40.degree. C., preferably 30.degree.

Manufacturing examples example 1

To an aqueous solution containing 10 g / l CaSO ₄ . 1 / 2H ₂ O, calcium oxide was added. During the exothermic hydration reaction, the temperature of the medium was kept at about 30 ° C. This hydration reaction was carried out with stirring (rotational speed: 400 rpm).

The calcium sulfate present in the solution inhibited the hydrates tion reaction, d. H. decreased the rate of hydration and thus enabled better discharge of the reac tion released heat.

As soon as the viscosity of the reaction mixture was 0.8 Pa.s. was sodium polyacrylate in an amount corresponding to 1% des target weight of calcium hydroxide in the lime added slurry. After this addition, the stirred Mixture has a viscosity of 0.3 Pa.s. Then became continue adding calcium oxide to the mixture until viscosity was about 0.8 Pa.s. During the hydration reaction of the Cal cium oxide, the temperature of the reaction medium was about Maintained 30 ° C.

The slurry prepared in this way had a concentration of Ca (OH) ₂ of about 65% by weight.

Example 2

Example 1 was repeated with the modification that initially a solution containing 10 g / l CaSO ₄ . 1 / 2H ₂ O and 6 g / l sodium polyacrylate and then the unslaked lime was slaked with the help of this solution until a viscosity of 800 cP was obtained. The slurry thus obtained had a Ca (OH) ₂ concentration of about 65-70% by weight.

_{Ca (OH) 2} particles as shown in FIGS. 2 and 3 were obtained from this slurry by filtration. These particles appeared in the form of a whole or a mixture of micro-flakes. The thickness of these micro-leaflets was on the order of 0.1-0.2 µm. These microsheets had a lower outside and an upper outside that were parallel to each other. The surface of these sides was about 25 to 50 μm ² .

The following table shows the grain size distributions of the in lime slurry prepared in this example and one Classical type slurry, i.e. H. according to the state of the art nik, listed.

Tabel

As the table shows, the slurry of the present invention is this example by the presence of particles or grains nern with a mean grain size of well over 20 µm (around 50 µm more). In fact, more than 80% by weight the particles have a grain size of more than 20 µm. A be the substantial number of particles has a grain size greater than this than 250 µm.

Example 3

Example 1 was repeated with the modification that a solution containing 20 g / l MgSO ₄ . 7H ₂ O instead of a solution containing 10 g / l CaSO ₄ . 1 / 2H ₂ O was used. In this way it was possible to produce a lime slurry which contained about 65% by weight Ca (OH) ₂ .

Despite the presence of a considerable amount of grains with a grain size over 200 microns it was found that a such lime slurry has excellent stability of more than 24 hours without stirring and more than 15 days gentle stirring (100 rpm).

The following table shows the values for the viscosity of the Lime slurry in a vat and stirring gently listed.

Dwell time (days) Viscosity (cP) 1 315 2 310 3rd 320 4th 315 5 307 6th 315

Such a lime slurry can be easily thanks to its stability be transported in tank trucks and released from them.

Example 4

Example 2 was repeated with the modification that the tempera ture of the medium or mixture not at a temperature un below 40 ° C was kept.

The table below shows the temperatures of the medium after adding 150 g of CaO in 600 ml of an aqueous solution which optionally contained CaSO ₄ and sodium polycarbonate.

This example shows that although it is not possible to produce a Ca (OH) ₂ granulate according to the invention in the absence of a poly anion (sodium polycarbonate), the CaSO ₄ allows the rate of hydration of the (unslaked) lime and thus the rate the release of heat in this reaction.

The lime slurry according to the invention is mainly thanks to The shape and size of their particles (micro-leaflets, macropores, considerable grain size, low water content (25 to 30 wt. %)) with advantage for the treatment of industrial waste set, for example from industrial waste (liquid or gaseous), waste containing heavy metals, etc.

The grains or granules, in particular the part thereof with a grain size of over 200 microns, are / is advantageously used to produce filter beds. Such grains or granules have a low specific surface area (9 m ² / g versus 20 to 25 m ² / g for Ca (OH) _{2 of} a known slurry), but macropores or cages of 20 to 50 μm.

Finally, by grinding the granules of a lime slurry obtained by filtering and drying, a mixture of micro-flakes of Ca (OH) _{2 was} obtained. Because of their small thickness (0.2 to 0.3 µm and because of their surface area (25 to 30 µm ² )), such micro-flakes are advantageously used in the production of films and foils from plastic materials, cellulosic materials (paper...), Etc. Such micro-flakes act as flame retardants.

The viscosity values given in the description are values after Brookfield, determined with the needle no. 3 and at an Um rotation speed of 60 rpm.

Claims (23)

1. Lime and / or magnesium hydroxide slurry with a dry matter content of more than 60 wt .-% and a viscosity of less than 1.5 Pa.s., characterized in that it has an anion selected from SO ₃ ^- and SO ₄ ^2- and contains a polyanion, the polyanion being a polymer or copolymer which contains anionic monomer units, those of monomers from the group comprising acrylic acid and its salts, methacrylic acid and its salts, vinylbenzylsulphonic acid and its salts, acrylamino-2-methylpropanesulphonic acid and their salts, 2-sulfoethyl methacrylate and its salts. 2. slurry according to claim 1, characterized in that it ent ent 1 to 50 g / l of the anion holds. 3. slurry according to claim 2, characterized in that it is 6 to 50 g / l, preferably 6 contains up to 30 g / l of the anion. 4. slurry according to claim 1, characterized in that it contains 1 to 50 g / l, preferably 5 contains up to 30 g / l polyanion. 5. slurry according to any one of claims 1 to 4, characterized in that at least 20 wt .-%, preferably min at least 30% by weight of the calcium hydroxide particles have a grain size of more than 100 µm. 6. slurry according to claim 5, characterized in that more than 80% of the calcium hydro oxide particles have a grain size of more than 20 microns. 7. slurry according to any one of claims 1 to 6, characterized in that they contain micro-leaflets from Calciumhy contains droxide. 8. Slurry according to claim 7, characterized in that the micro-leaflets have a thickness of less than 0.5 µm, preferably less than 0.3 µm sen. 9. Slurry according to claim 8, characterized in that the micro-leaflets have a lower Au and an upper outer side which run parallel to each other and that the surface of these sides is less than 200 microns ² , preferably less than 100 microns ² . 10. Slurry according to one of the preceding claims, there characterized in that it is less than 5% by weight, preferably se less than 1 wt .-% magnesium hydroxide, based on the Ge total weight of calcium hydroxide and magnesium hydroxide. 11. A method for producing a lime and / or magnesium hydroxide slurry according to any one of claims 1 to 10, characterized in that calcium oxide and / or Magnesi umoxid with the help of an aqueous solution extinguishes the SO ₃ ^- or SO ₄ ^2- contains and that the aqueous solution is added before, during or at the end of the quenching reaction, an aforementioned polyanion. 12. The method according to claim 11, characterized in that the calcium oxide is deleted with a solution that contains 1 to 50 g / l, preferably 6 to 30 g / l, SO ₄ ^2- . 13. The method according to claim 11, characterized in that one in the course or at the end of Reaction an aforementioned polyanion adds so that the Konzen tration of polyanion in the range from 1 to 50 g / l, preferably in the range from 5 to 30 g / l. 14. The method according to any one of claims 11 to 13, characterized in that the reaction mixture is stirred and the temperature of the reaction mixture below 30 ° C, preferably wisely below 20 ° C. 15. The method according to any one of claims 11 to 14, characterized in that the viscosity of the reaction me diums regulates. 16. The method according to claim 15, characterized in that calcium oxide is added to the solution up to a viscosity in the range of 0.3 to 1.2 Pa.s. 17. The method according to claim 15, characterized in that calcium oxide and / or Magnesiu moxid with an aqueous solution containing an SO ₄ ^2- anion, extinguishes until the reaction mixture has a viscosity in the range from 0.3 to 1.2 Pa.s and that a polyanion mentioned above is then added to the mixture in order to reduce the viscosity and that calcium oxide and / or magnesium oxide is then added to the mixture until a viscosity in the range from 0.3 to 1.2 is obtained Pa.s. Receives. 18. Process for the production of micro-leaflets, characterized in that one has a lime and / or magnesium hydroxide slurry according to any one of claims 1 to 10 Phase separation subjects, in which a liquid phase and a solid phase is obtained, the solid phase being granules of calcium hydroxide and / or Magnesium hydroxide in the form of a mixture of micro-flakes having. 19. The method according to claim 18, characterized in that the solid phase is dried. 20. The method according to any one of claims 18 or 19, characterized in that the solid phase is ground. 21. The method according to claim 20, characterized in that the ground solid phase dries. 22. The method according to any one of claims 18 to 21, characterized in that the grains are produced so that they have an average grain size dimensions of more than 20 µm, preferably of more than 50 µm, exhibit. 23. The method according to any one of claims 18 to 21, characterized in that the grains are made to have an average grain size of more than 100 µm, preferably of more than 200 µm, exhibit.