DE2512246C3 - Process for the continuous production of concentrated magnesium sulphate solutions from kieserite - Google Patents

Description

It is known that Epsom salt, MgSO ₄ · 7H ₂ O, can be produced from the mineral kieserite by dissolving and crystallizing, which is required in medical and technical quality. This requires a highly concentrated MgSO ₄ solution, which is obtained by dissolving kieserite in water or in dilute MgSO ₄ solution, from which Epsom salt is obtained by crystallization in a vacuum cooling system by cooling and evaporation.

The rate of dissolution of the kieserite depends on the grain size, the dissolution temperature and the concentration the solution and its cloud density. Also the technological implementation of the dissolution process significantly influences the rate of dissolution of the kieserite.

According to the state of the art, kieserite is dissolved in vats in a continuous process, in which the clear, hot magnesium sulfate solution which runs off is separated from the residue by means of suitable filter mats. Since the magnesium sulphate content of the kieserite produced from crude potash salts is around 78 to 84% by weight, a magnesium sulphate solution with 430 g / l MgSO ₄ at around 353 ° K with a throughput of 5 can be used ^{in such dissolving vats with a volume of around 100 m 3} m '/ h to generate. This dissolution process has the disadvantages of a low throughput in the case of a discontinuous procedure. Due to the accumulation of anhydrite in the dissolving vat, the throughput drops after a few days. The backlog after the business interruption must therefore be cleared up and, if necessary, a reserve capacity must be kept. When using fine-grain kieserite, dense layers can form on the filter mat, which stop the kieserite from dissolving. Another disadvantage of this procedure is the sensitivity to residual amounts of potassium chloride, which can lead to the formation of polyhalite, which seals the bottom of the dissolving tub against further dissolution of kieserite.

Dissolution processes for kieserite which are carried out in stirred vessels have also become known have been. Since the kieserite, due to its special hardness, causes considerable wear and tear on the stirring elements caused, this approach has never been able to establish itself on an industrial scale. This is also the case here a direct current process in which the kieserite and solvents are fed overhead into tower-like dissolving chambers while the solution is at the FuIi taken from these chambers winl.

The US-PS 2635 94 ° describes a gas-solid reactor, in which the solids are kept in a quasi-liquid state by the gas. The subject of US-PS 3,524,820 is a direct current

reactor, which the reaction components overhead are fed, while the reaction product is withdrawn from the bottom of the reactor. Subject of US-PS 3,752,653 is also a direct current reactor, to which the reaction components are fed in a mixture at the foot, while the reaction products drain overhead. A countercurrent dissolution process, as proposed below, cannot be carried out in any of these previously known reactors will.

The invention is based on the object of producing a highly concentrated MgSO ₄ solution from kieserite with a considerably higher throughput (M ³ solution volume / m ³ MgSO ₄ solution / h) than according to the prior art, which is used as a starting product for the production of Epsom salt can be used.

A process has been found for the continuous production of concentrated magnesium sulfate solutions from kieserite in several stirring chambers connected in series. Then kieseril is continuously introduced into the first of the series-connected stirred vessels and water is continuously introduced into the last in quantities sufficient to completely dissolve the kieserite in a residence time of 1 to 2 hours, with a temperature of 338 to 363 ° K and a Maintained the pulp density of 50 to 70% and a hot concentrated magnesium sulfate solution with over 400 g / l MgSO _{4 is} removed from the first stirred vessel and removed in a clarifying zone to a solids content of about 10 to 20 g / l and in a downstream clarifier free of solids and finally removed , while a residue with 50 to 75 wt .-% calcium sulfate is drawn off from the last stirring chamber and separated from the magnesium sulfate solution, which is returned to the penultimate stirring chamber.

The flow rate of the magnesium sulfate solution in the stirring chamber cascade should be advantageous 0.075 to 0.016 m / sec. The pulp density in the chambers of the stirred chamber cascade can be increased by Change the stirring speed and the flow rate of the magnesium sulfate solution can be set to the specified value of 50 to 70%.

To carry out this method, a device has been found, an embodiment of which is shown schematically in FIGS. 1 and 2. A characteristic of this device is that an inlet pipe 2 cooperating with a metering device 1 leads through a clarification chamber 3 with overflow into the first chamber I ^{1 of} a stirring chamber cascade 4 consisting of several centrically superposed stirring chambers I ¹ to I ⁶ , which is equipped with a stirrer 5 is, which in each agitation chamber 1 'to l ^{fi has} two symmetrically arranged agitator blades 6 with two divided, angularly offset agitator blades, in which the ratio of the length of the axially close agitator blade to the length of the axially distant agitator blade is about 2: 1 and the lower Chamber I ^{6 is} equipped with a removal device for residue (anhydrite), while the stirring chamber I ² with a supply device for solids and the stirring chamber I ^{5 have} a supply device for liquids and the overflow of the clarification chamber is connected to a downstream Kliircr, whose discharge for pre-thickened Solid with the stirrer mer I ² is connected.

The discharge for thickened solids of the downstream clarifier is advantageously connected to a hydrocyclone, the solids discharge of which is connected ^{to the stirring chamber I 2.}

"> A stirred chamber cascade 4 with has proven itself 4 to 8 stirring chambers.

It is also beneficial if in the clarification zone 3 several, designed as downward sloping surfaces are arranged flow breaker 7, which the

i "Serve retention of entrained solids.

A turbulence of the contents of the agitation chambers which is particularly favorable for the method of the invention results when the agitator blades of the agitator blades 6 are designed as trapezoidal and flat surfaces

ι> are at an angle of 50 to 60 ° to each other are arranged.

For carrying out the method according to the invention, it is also advantageous if the stirrer 5 has a peripheral speed during operation.

- <> has a speed of 3.5 to 4.5 m / sec.

The method of the invention rrit the device for its implementation offers the technical advantages that by dissolving the kieserite in countercurrent in a multi-stage stirring chamber cascade

- '"> significantly higher throughput (m ³ / h) is achieved than according to the prior art, it being possible to work in a high pulp density which is advantageous for dissolving the kieserite. The low stirring speed according to the process of the invention

«Ι allows to keep the drive power of the stirrer lower and has the consequence that the mechanical wear of the stirrer is significantly reduced.

By adjusting the flow speed of the magnesium to be generated in countercurrent

>> sulfate solution with the speed of the stirrer, according to the teaching of the invention, it is entirely possible to carry out the process of the invention in a continuous manner perform.

The method of the invention is thus independent

4 "of changes in the chemical and physical properties of the kieserite used, and the magnesium sulfate yield of the concentrated magnesium sulfate solution is compared to the dissolution of the Kieserites in vats about 10% higher. Essential

However, the technical progress of the space-time yield is ^{improved from 20 m 3 of} solution volume / m ^{3 of} magnesium sulfate solution and hours to 1.4 m ³ and hours.

- _{) (l} example

To produce 40.7 m ³ / h of concentrated magnesium sulphate solution in a stirring chamber cascade with a ^{volume of 60 m 3} and equipped with multi-stage countercurrent stirrers, the following are used:

v> 15.5 t / h kieserite with 75.3% by weight MgSO ₄ (7% by weight adhering moisture). To dissolve it, 14.4 mVh of water are introduced and 20.94 m ^{3 of} magnesium sulfate solution with 295 g / l of MgSO ₄ from the crystallization of Epsom salt are returned.

By dissolving the kieserite according to the method of the invention, 40.7 mVh of magnesium sulphate solution with 427 g / l MgSO _{4 are} produced and 0.3 mVh of anhydrite beet containing 55% by weight of Feslsfoft with a calcium sulphate content of 56.8% is carried out .

From the dehydration of the anhydrite, 0.13 m / h of dilute magnesium sulfate solution with 245 g of MgSO ₄ /! together with the mother liquor from the Epsom salt liquor crystallization in the second lowest

Stirring chamber l ⁵ returned.

In this mode of operation, according to the invention, is the solids concentration in the one carried out from the clarification zone 3 of the stirring chamber cascade 4, concentrated magnesium sulphate solution 0.44 t / h according to K), S g / l with a magnesium sulphate content of 61.4%.

In the process of finding the pulp density in all chambers of the stirring chamber cascade is about 65 wt. ^R / _f solids.

For this purpose 2 sheets of drawings

Claims (7)

Patent claims: 1. A process for the continuous production of concentrated magnesium sulphate solutions from kieserite in several stirring chambers connected in series, characterized in that kieserite is continuously introduced into the first of series-connected mixing vessels and the water is continuously introduced into the last in quantities necessary to completely dissolve the kieserite in a residence time of 1 up to 2 hours are sufficient, with a temperature of 338 to 363 ° K and a cloud density of 50 to 70% being maintained in the stirred vessels and a hot concentrated magnesium sulfate solution with over 400 g / l MgSO ₄ removed from the first stirred vessel and transferred to a clarifying zone Solids content of about 10 to 20 g / l and clarified free of solids in a downstream clarifier and finally removed, while a residue with 50 to 75 wt .-% calcium sulfate is drawn off from the last stirring chamber and separated from the magnesium sulfate solution, which is in the penultimate Stirring chamber is returned . 2. The method according to claim 1, characterized in that the flow rate of the solution in the stirring chamber cascade is 0.075 to 0.016 m / sec. 3. Device for carrying out the method according to claims 1 to 2, characterized in that a metering device (1) cooperating E'ilaufrohr (2) through a clarification chamber (3) with overflow into the first chamber (I ¹ ) from one Mehrr-sn centrally arranged one above the other agitator chambers (I ¹ ) to (I ⁶ ) existing agitator chamber cascade (4), which is equipped with a stirrer (S), the two symmetrically arranged agitator blades ^{in each agitator chamber (I 1} ) to (I ⁶⁾ with two divided agitator blades offset from one another at an angle, in which the ratio of the length of the axially close agitator blade to the length of the axially fine agitator blade is about 2: 1 and whose lower chamber (I ⁶ ) is equipped with a removal device for residue (anhydrite), while the agitation chamber (I ² ) with a feed device for solids and the agitation chamber (I ⁵ ) have a feed device for liquids and the overflow of the clarification chamber with a downstream one th clarifier is connected, the discharge of which is connected to the pre-thickened solids with the stirring chamber (I ² ). 4. Apparatus according to claim 3, characterized in that the discharge for thickened solids of the downstream clarifier is in connection with a hydrocyclone, the solids discharge of which is connected ^{to the stirring chamber (I 2).} 5. Device according to claims 3 to 4, characterized in that the Ruhr chamber cascade (4) has 4-8 stirring chambers. 6. Device according to claims 3 to 5, characterized in that in the clear zone (3) a plurality of flow breakers (7) designed as downward sloping surfaces are arranged are. 7. Device according to ilen claims 3 to 6, characterized in that the stirring blades of the stirring blades (6) are designed as trapezoidal and flat surfaces which ^{are arranged at an angle of 50 to 60 e} to one another. 8, device according to claims 3 to 7, characterized in that the stirrer (5) during of operation has a peripheral speed of 3.5 to 4.5 m / sec.