DE913535C - Process for the production of easily filterable magnesia and ammonium-magnesium double salt - Google Patents

Description

Process for obtaining easily filterable magnesia and ammonium-magnesium double salt The patent 908 014 relates to a process for obtaining easily filterable magnesia and magnesium-ammonium double salt from ammonium salt-containing magnesium salt solution and ammonia and is characterized in that, using gaseous and aqueous ammonia , preferably in an excess of 1 equivalent, the two starting materials are continuously introduced with stirring into a magnesium salt-rich mother liquor returning from the process, which was converted back into a magnesium salt-rich starting liquor by stirring in, for example, kieserite.

It has already been proposed to use magnesium sulfate solutions Ammonia to precipitate magnesium hydroxide and from the resulting ammonium sulfate Solution to obtain the double salt magnesium ammonium sulfate by evaporation, which then finally treated again with ammonia in a further process stage and can be converted to ammonium sulfate.

The specified method according to the main patent offers the great technical Advantage that there is no need for evaporation to obtain the double salt and through a closed cycle process not only in terms of energy efficiency, but also offers significant advantages in terms of exploitation.

According to the further development of this method according to the invention a way is now also shown in order to be able to use ammonium sulphate as well as possibly also separately, to win, in a manner different from that according to the state the technology described above is completely different.

It has been successful, with recycling of the circulating liquor to work with significantly higher Mg SO4 concentrations and thus economically to close the cycle. The filter properties of the magnesia obtained in this way are excellent. It has even become possible (what for the yield of the process is of particular importance) to accommodate the detergents in the circuit.

Ammonia sulphate can be obtained in addition to ammonia by the following measures: An ammonia concentration of 10 to 100 g / 1 NH ", preferably ao g f 1, is produced in the mother liquor that has been submitted to it, preferably ao g f 1 Achieved gaseous as well as aqueous ammonia and maintained or increased during the precipitation process with the continuous supply of ammonia together with the magnesium salt solution, preferably to 40 gil, or even further increased after the mother liquor has been fed in.

The ammoniacal mother liquor resulting after the magnesia precipitation has ended depends on the reaction temperature lying between 5o and 8o ° C, preferably 6o ° C cooled down to below 30 ° C, expediently to 15 ° C. It is thereby achieved that the point representing the solution is from the area of existence of magnesium hydroxide moves out and thus falls into the ammonium sulfate area. The underlying equilibrium relationships are illustrated by the drawing, which is based on our own investigations was produced.

In triangular coordinates in the system (N H4) 2 S 04-M9 S 04- (N H3) 2, the areas of existence of ammonia, ammonium sulfate and magnesium hydroxide are shown for temperatures 60 and 15 ° C. It can be seen from this that the three-salt point with lowering of the temperature tends to move much closer to the ammonia corner and thereby a larger ammonia field is created. The magnesia precipitation carried out at 60 ° C is represented by the path from I to II in a triangle and initially runs a short distance in the ammoniacal field, although there is no sediment in the unsaturated liquor. By cooling from 60 ° to below 30 ° C, point II moves into the ammonium sulphate field after the magnesia has been separated from the reaction liquor, and it is possible, with further cooling to about 15 ° C, while stirring at the same time, to remove the Schönite supersaturation, which is the state point shifts from II to III. With the introduction of ammonia, the state point moves into the ammonia corner up to point IV. As a result of the strong supersaturation of ammonia, the solubility of the ammonia sulfate is lowered to such an extent that ammonium sulfate is separated on the way from III to IV. A noteworthy transformation of the ammonite on the way from III to IV within the ammonium sulphate field does not take place, if it is left in the solution, because of the onset of encrustation.

The procedural path given on the basis of the triangular coordinate drawing corresponds to the operational mode of operation in the example. The obtained ammonium sulfate can be obtained together with the ammonite crystallized during cooling and a product containing nitrogen magnesia, which can be used, for example, for fertilization purposes is suitable to be processed, or else it can be the Ammonschönit after finished Cooling removed from the solution and the process route III-IV for recovery of ammonium sulfate alone can be used.

In further training of the process it has now been shown that this the precipitation intensifying cooling by applying the following measures even more effective and can be made more economical. It is first used during the precipitation of salt with and without pressure, the heat generated from the salt-solution mixture with cooling water Discharged in a known manner up to a temperature that can be achieved therewith. - Partially at the same time or preferably subsequently, the cold effect of the can be used for precipitation required ammonia can be exploited by this before it is introduced into the salt precipitation for example, in a cooling coil inside the vessel, relaxed or directly is expanded as liquid ammonia in the salt-solution mixture and thereby its Removes heat of evaporation from the solution.

With this method of operation according to the invention, it is possible to further lower the temperatures by about 15 ° C. and thereby bring the salt precipitation to practically ammonium hydroxide, using a much smaller amount of free NH to precipitate, for example up to a concentration of 32o g /1. The cooling by relaxation after the salt precipitation has ended can also be combined with the procedure according to the invention. The effect can be further increased by pumping.

After separating the salts from the solution under the high excess of ammonia over 300 g / l, it is removed from it by stripping it off by means of indirect heating and the ammonia obtained is reused in the next precipitation of magnesia or ammonia sulfate. The mother liquor freed from ammonia, together with the wash water coming from the process, is used to obtain the starting solution I (see scheme) by dissolving new MgSO4, preferably in the form of the mineral kieserite. This completes the cycle. Example In 10.5 t aqueous lye with the composition 0.56 t (NH4) 2S04, 2.56 t Mg S 04, 7.38 t H, 0 at 70 ° C 1.28 t NH3 and 2.02 t 11, 0 initiated, with 1.53 t of rapidly settling magnesium hydroxide precipitating with 61.50 /, water. After separation of the hydroxide remaining 12.5 t 2.34 t liquor with (NH4) 1S04, o, t 8 Mg 04 S, O, N 9 t H "8.46 t H20, from the by cooling to i5 ° C 2 .31 t of ammonite are obtained, resulting in 10.2 t of mother liquor with 1.5 t of (N H4) 2 S 04, 0.03 t of Mg S 04, 0.9 t of NH, 7.76 t of H20.

By introducing 4.4 t of N H3 with or without prior separation of the ammonia, 1.33 t of ammonium sulphate are obtained. This produces 13.3 t of a precipitated liquor with 0.17 t (NH4) 2S04, 0.03 t of Mg S 04, 5.3 t of N H3, 7.76 t of H20, from which N H3 is separated in a known manner and used again Precipitation is used.

After saturation with Mg S 04, the lye is expediently stirred in von Kieserite used again as the starting liquor in the cycle with the addition of the The water excreted by the precipitated salts and the removed ammonia.

Claims (7)

PATENT CLAIMS: i. Process for obtaining easily filterable magnesia and ammonium-magnesium double salt according to patent 9o8 014 by combining ammonia and ammonium salt-containing magnesium salt solution, characterized in that a mother liquor rich in magnesium salt with an ammonia concentration of 10 to 100 g / 1, preferably 20 g / 1, is presented and during the precipitation process the magnesium hydroxide is increased, preferably to about 40 g! 1, or even further increased after the mother liquor has been added and this precipitation is carried out at temperatures between 50 and 80 ° C., the mother liquor after separation of the precipitated magnesium hydroxide is cooled down to below 30 ° C, preferably to 15 ° C, with ammonia precipitating with stirring and after which ammonia is again passed into this lye and either ammonium sulfate is obtained together with the ammonium sulfate obtained beforehand by cooling or, after separate separation, ammonia sulfate alone w earth. 2. The method according to claim i, characterized characterized in that the washing water required for washing out the magnesium hydroxide is fed to the process for the liquor cycle. 3. The method according to claim i and 2, characterized in that after a pre-cooling with water on one with the Cooling water achievable temperature partially simultaneously or subsequently a further cooling takes place through the ammonia required for precipitation. q .. procedure according to claims i to 3, characterized in that the ammonia is used for indirect cooling inside the precipitation vessel or directly as liquid ammonia in the salt solution mixture is expanded. 5. The method according to claim i to q., Characterized in that After the precipitated salt or salt mixture has been separated off, the free ammonia is driven off and fed back into the process. 6. The method according to claim i to 5, characterized characterized in that the cooling effect associated with the relaxation of the free ammonia is increased by pumping. 7. The method according to claim i to 6, characterized in that that the liquor freed from ammonia after uptake of new Mg S 04 and after Claim: 2 resulting wash water withdrawn in the process for magnesium hydroxide precipitation will.