DE956304C - Process for the direct production of potassium sulfate from calcium sulfate and potassium chloride in the presence of concentrated aqueous ammonia solutions - Google Patents

Description

Process for the direct production of potassium sulfate from calcium sulfate and potassium chloride in the presence of concentrated aqueous ammonia solutions Die The production of potassium sulfate from calcium sulfate and potassium chloride is known. It Numerous processes have been proposed in which the calium sulfate such as it is or after activation or also after conversion into other intermediate sulfates, such as magnesium sulfate or ammonium sulfate is used.

Work from the procedures that use untreated calcium sulfate various in aqueous solution, however, the implementation of. Potassium chloride with Calcium sulphate with a more or less high yield for the formation of double salts, like syngenite Ca S 04 - K2 S 04 - H2 O or penta salt 5 Ca S 04 * K2 S 04 - H2 O, which are then decomposed to obtain the K2 S 04.

It is also known to work in the presence of an aqueous ammonia solution, either obtaining a double salt when working with a very small excess of potassium chloride over the stoichiometric amount required for the reaction, but obtaining better yields than when working in aqueous solution , or K2 S 04 is obtained directly if a very large excess of potassium chloride is used over the amount stoichiometrically required for the reaction. In the latter case, the considerable amounts of the mother liquor contain a borrowed portion of potassium chloride, which can only be recovered in difficult processes by precipitating the double salts which have to be post-treated.

The German patent specification 925 466 also describes a method described, after which potassium sulfate is obtained directly when in practically stoichiometric Ratio of potassium chloride with calcium sulfate at about room temperature in ammoniacal-aqueous Solution with a concentration of about 5o% and more of ammonia when using a sufficiently increased pressure of about 3 kg absolute.

It has been found that it is possible to obtain the minimum concentration required to reduce ammonia in the aqueous solutions if one is at temperatures below works from room temperature. According to the invention, the minimum ammonia concentration to .4o%, if you work at temperatures below 5 °.

Such an improvement could not be foreseen on the basis of the state of the art, as given by the German patent specification 925.466. The method according to the invention also provides the following particular advantages: i. It is possible to work with very reduced amounts of ammoniacal solutions, since the ratio of ammoniacal solution to Ca S 04 is always below 2.6o.

2. The amount of ammonia needed to convert an equal amount of calcium sulfate Used in potassium sulfate can be reduced in two ways. because you have the amount of the solution and also the ammonia concentration of this Solution decreased.

Several of these benefits obtained without purifying excess of K Cl over the ratio stoichiometrically required for implementation must apply are interesting factors for the recovery of the ammonia the mother liquor, either by distillation or by known methods of precipitation of ammonia from Ca C12 and decomposition of these ammonia.

In addition, the special temperature and pressure conditions allow of the process according to the invention to carry out the reaction at atmospheric pressure, whereby losses of ammonia can be avoided as far as possible. Also join the import of the solid substances into the otherwise pressurized containers and no difficulties in emptying them.

It was further found that the process results improved can be if the manufacture of the K2 S 04 is continuous in a two-stage Process takes place in the manner described below: In: a first process stage Ca S 04 is used and the unit is smaller than the stoichiometrically required for implementation Amount of potassium chloride in an ammoniacal solution containing K Cl and Ca C12, which were produced in the second process stage described below.

Towards the end of the first reaction stage, ie when the conversion slows down, the solid product is separated off. The mother liquor is distilled - and the solid moist residue. treated in a second process stage with a fresh ammoniacal solution and a new batch of K Cl, the sum of the potassium chloride additives introduced in both process stages corresponding to the stoichiometric amount required for the reaction with CaS 04. The addition of new ammoniacal solution and new potassium chloride in the second process stage allows a better conversion rate, compared to a moderate one, until the end of the reaction. Process to obtain in a single process step. In fact, the accumulation of CaC12 in the mother liquor significantly slows down the rate of conversion between Ca S O 4 and K Cl. In particular, these disadvantages are overcome by the inclusion of partially converted solid moist mass in a fresh ammoniacal solution.

When carrying out this 2-step process at temperatures below 5 ° is also the amount of ammonia required to convert a given amount of Ca S O4 still significantly reduced.

In the method described above, the calcium sulfate can be used in any form, e.g. B. as plaster of paris, as a hemihydrate or as anhydrite.

The invention is illustrated by the following examples however, it is not restricted.

i. It was 3 hours at a temperature of -3 ° at atmospheric pressure with moderate agitation, 100 parts of plaster of paris with a content of 79 parts of Ca S 04.87 Parts of K Cl, 113 parts of water and 93 parts of N H3 reacted. Then the Filtered off mother liquor and after washing with an aqueous ammonia solution, K2 S 04 received. Contributes to the yields in the conversion of gypsum into K2 S 04 98 0/0. 2 mature K Cl were entrained by the mother liquor.

The method described above can be carried out under the same concentration conditions (the same amount of ammoniacal solution and the same ammonia content of the solution) but at room temperature (20 to 25 °), ie at an absolute pressure of about 2 kg / cm2. After washing with pure ammoniacal solution, a solid mass is obtained which consists of a mixture of Syngenit Ca S 04 ' K2 S 04 - H2 O and K Cl. The yield from the conversion of gypsum into K2S04 is 50/0 in this case.

To go directly to K2 S 04 with good yield when working at room temperature In order to obtain it, one has to use the ratio of the amount of ammoniacal solution the processed -Ca S 04 and, secondly, the ammonia concentration of these solution increase, according to the method described in German Patent 925 466. To process 100 parts of plaster you need: 100 parts of water and 127 parts N H3.

Compared with this process, with the K2 S 04 directly at room temperature is obtained, one gains an essential one when working at a lower temperature Amount of ammonia. Comparing the ratio of Ca S 04 to N H3 in these two Cases, a ratio of 0.85 is maintained at -3 ° and at room temperature a ratio of o.62, i.e. H. a difference of 23 0/0, which is an N H3 saving of 37 '/ o.

2. In a first stage of the process, the following were implemented: 108 parts more natural Gypsum with a content of 92a6% Ca S 04.2 H2 O, 65 parts K Cl, containing 58 to 6o% K.0, mother liquor from the second process stage of the reaction according to the invention with a content of 105 parts of H20, 86 parts of N H3, 2i, 5 parts of Ca C12, 3 parts K C1. After less than an hour of reaction under atmospheric pressure at one temperature of - 3 ° with moderate agitation, the conversion yield from the plaster of paris is approximately 72%, and a) a moist cake with a content of 28 parts was separated off Ca S 04.:2 H2 O, 72.7 parts of K2 S 041 8 parts of insoluble residue, 4.7 parts K Cl, i parts H2 O, 7 parts N H3, 6 parts Ca Cl ".

b) Mother liquor -with a content of 109 parts of H2 O, 79 parts of N H3, 62 parts of Ca C12, 0.8 parts of K Cl.

Ammonia is recovered from this mother liquor using known processes, z. B. by distillation, by precipitation of CaC12 ammonia and decomposition of these ammoniaates.

In a second stage of the process, the moist cake is made with 95 parts H2 O, 78 parts of N H3 and 2o, 8 parts of K Cl were taken up again. Noise for an hour Reaction at -3 ° below atmospheric pressure with moderate agitation is the conversion yield from the plaster of paris about 90%, and one obtains a) a moist cake with a content of 2 parts of Ca S 04.2 H2 O, 99.2 parts of K2 S 041 8 parts of insoluble residue, 6.5 parts H2 O, 5 parts I \ TH3, i, 3 parts Ca C12; b) mother liquor with a content of 105 parts of H20. 80 parts of NH3, 3 parts of K Cl, 2-i, 5 parts of CaC12, which after addition of ammonia. is returned.

The ratio of Ca S 04 to N H3 is under these conditions at letwa o, 92, d. This means that the difference to the one-step process is -3 ° 70/0, for the process at room temperature 300/0, which means NH.- savings of 8 or q.80 / 0 is equivalent to.

Claims (3)

PATENT CLAIMS: i. Process for the direct production of potassium sulphate from Calei @ umsulfat and potassium chloride in the presence of concentrated aqueous ammonia solution, characterized in that sat stoichiometric amounts of potassium chloride and calcium sulfate in the presence of concentrated aqueous ammonia solutions in a manner known per se be implemented, but the reaction at temperatures below 5 ° he follows. 2. The method according to claim i, characterized in that the reaction was carried out in the presence of an ammonia solution containing at least qo percent by weight of NH . 3. The method according to claims i and 2, characterized in that the reaction sat continuously in a two-step process he follows. Documents considered: German Patent No. 925 q.66.