DE2911413C2 - Process for the production of potassium magnesium phosphate - Google Patents

Description

The (patent application P 28 31 672.5) proposes a process for the production of potassium magnesium phosphate by reacting acidic aqueous solutions containing phosphate ions with potassium chloride and basic magnesium compounds. After that, the amount of basic magnesium compound stoichiometrically required for the formation of dimagnesium phosphate and a partial amount of the total amount of potassium chloride required are stirred _{into an acidic phosphate solution with a P 2} O ₅ content of 20 to 167 g P ₂ O _{5 per 1000 g of water} into the resulting suspension after adding the remaining amount of potassium chloride, whereby the total amount of added potassium chloride is increased to a molar ratio K ₂ O · P ₂ O ₅ of more than 1: 1 to a little below the saturation concentration, at a temperature of below 40 ^° C. the stoichiometrically required amount of basic magnesium compound to form the tertiary magnesium phosphate is slowly added, whereby a concentration of 130 g of MgCl ₂ in 1000 g of water in the reaction mixture must not be exceeded and whereupon the potassium magnesium phosphate formed is separated from the mother liquor, washed with water and dried will.

As a further development of this process, it has now been found that it is advantageous as a base reacting Magnesium compound to use magnesium oxide, which by means of a dispersing device of high

Shear action is dispersed in a portion of the mother liquor, which after separating the Potassium magnesium phosphate remains.

The invention is based on the observation that when using some magnesium oxides, their Iodine number significantly exceeds 100, according to that proposed in (patent application P 28 31 672Jj) Process products are obtained which have little or no potassium content.

These highly active types of magnesium oxide therefore direct them to potassium magnesium phosphate leading implementations apparently in the wrong direction.

It has surprisingly been found that these difficulties do not arise if the preferably active. Magnesium oxide before its use in the mother liquor, which after separation of the Potassium magnesium phosphate remains, "according to one Dispersion device is dispersed, which is able to exert high shear effects. As a dispersing device A paste mill with high shear stress fields has proven particularly useful instead of the mother liquor A potassium chloride solution can also be used as a dispersing agent The potassium chloride content should be added to the total amount of potassium chloride to be introduced into the reaction mixture is. The cloud density of the dispersion should be between 40 g / l and 230 g / l. It depends on the Thickening during the period of use.

The process of the invention is advantageously carried out in such a way that the acidic phosphate solution is placed in an upstream reaction vessel with vigorous stirring using a turbine or toothed disc stirrer with a portion of the magnesium oxide dispersion to form a Suspension of dimagnesium phosphate is implemented. This suspension is then transferred to a second reaction vessel transferred and there the remaining amount of the magnesium oxide dispersion at such a feed rate stirred in so that the pH of the reaction mixture is kept between 7.2 and 8.5. At the same time, potassium chloride is added to the reaction mixture in such an amount and at a rate that that the potassium chloride concentration of the liquid phase of the reaction mixture is always in the vicinity of the Saturation concentration remains. In this reaction vessel, the potassium magnesium phosphate crystallizes as Hexahydrate.

The crystallization of the potassium magnesium hexahydrate is complete after a maturing time of about 30 minutes.

This ripening time is determined by character-wise implementation of the method of the invention, the batch cycle and, if carried out continuously, the volume and the throughput speed of the stirred vessel cascade.

The crystallized potassium magnesium phosphate is then separated from the mother liquor, washed and calcined. The remaining mother liquor is fed to the potassium chloride recovery process depending on its new formation, while the remainder is returned to the process again to disperse the active magnesium oxide and, if necessary, to reduce the pulp density .

The method of the invention is - with the exception of dead burned magnesium oxide - with all Magnesium oxide grades can be carried out without incorrect reactions occurring.

The following examples are intended to demonstrate this technical advantage of the process according to the invention

occupy. For these examples, a magnesium oxide is used, which for a period of 60 minutes in water with a temperature of 353 "K and after separation of the liquid phase for the duration of Is fired for 30 min at a temperature of 773 "K. The fired product is finally in a Cross beater mill to an activated magnesium oxide powder, the particles of which are 95% smaller than 0.1 mm and whose iodine number is 133.

Example 1 (comparison)

First, 56.6 kg of H ₃ PO ₄ in 297 kg of H ₂ O were reacted together with 12 kg of magnesium oxide and 45 kg of KCL to form a basic solution which essentially contained dissolved monomagnesium phosphate and potassium chloride. This basic solution was slowly run into a flow reactor with a toothed disk stirrer. To this was added in a stoichiometric ratio of 11.5 kg of the activated magnesium oxide in the form trockensr eingeriesei 'and at the same time to dilute the slurry approximately 0.5 m ³ of fine recycled mother liquor, which in 1000 g H ₂ O hog MgCl ₂ and 190 g KCL dissolved contained , supplied. During the preparation time, a suspension of dimagnesium phosphate in a solution containing calcium chloride flowed off steadily.

The suspension of dimagnesium flowed into the crystallizer for Kaliummagnesrumphosphat hexahydrate was stirred in which a template of a further 0.5 m ^J recycled mother liquor, and 30 kg of potassium chloride. A further 11 ^ 5 kg of MgO were trickled into this with constant pH control. The pri value was between 7.4 and 7.8 and the reaction temperature was 30S. K guarded. The introduction of the suspension and the MgO extended over one

A period of approximately 20 minutes. The reaction mixture was then stirred in the crystallizer for a further 30 minutes. Then 136 kg of a potassium magnesium hexahydrate product (calculated without moisture) were separated from 1.3 m ^{3 of} mother liquor, washed and dried at 313 K. It contained 6.4% KjO; 24.5% MgO; 30.3% P ₂ O ₅ ; 0.3% Cl.

Example 2 (invention)

The base solution and the reactor for the dimagnesium phosphate stage were the same as in Example 1. The MgO was not fed dry to the reactor and the crystallizer for the potassium _{magnesium phosphate, but finely dispersed in the recycled mother liquor, which was dissolved in 1000 g H 2} O HOg MgCl ₂ and contained 190 g of KCL. In this case where 23 kg of the activated magnesium oxide having a turbomixer with toothed rotor and stator in 0.5 m ^J of this mother liquor dispersed (pulp density, 46 g / l). Half of this was fed to the dimagnesium phosphate reactor and the other half to the crystallizer for the potassium magnesium phosphate hexahydrate. pH control and temperature control are the same as in Example 1.

The time from the production of the magnesium oxide dispersion in the mother liquor to its full consumption was 22 minutes. It thickened, but was still sufficiently flowable for a crush.

After stirring for a further 30 minutes, 153 kg of potassium magnesium phosphate hexahydrate product were separated from 1.27 m ^{3 of} mother liquor from the crystallization mixer. This product contained 14.9% K ₂ O as hexahydrate; 16.8% MgO and 26.8% P2O5 and comes much closer to the theoretical composition than the product from Example 1.

Claims (1)

Claim: Process for the production of potassium magnesium phosphate by reacting acidic aqueous solutions containing phosphate ions with potassium chloride and basic magnesium compounds, in which an acid phosphate solution with a P ₂ Os gel of 20 to 167 g P2O5 per 1000 g water is necessary for the formation of Dimagnesium phosphate stoichiometrically required amount of basic magnesium compound and a portion of the total amount of potassium chloride required are stirred into the resulting suspension after adding the remaining amount of potassium chloride, bringing the total amount of potassium chloride added to a molar ratio K2O: P2O5 of more than 1: 1 to slightly below Saturation concentration is increased, at a temperature of below 40 ⁰ C the stoichiometrically required amount of basic magnesium compound to form the tertiary magnesium phosphate is slowly entered, a concentration of 130 g MgCl ₂ in 1000 g water i n the reaction mixture must not be exceeded, whereupon the potassium magnesium phosphate formed is separated from the mother liquor, washed with water and dried, according to (patent application P28 31 672.5-41), characterized in that magnesium oxide is used as the basic magnesium compound, which by means of a dispersing device is dispersed by high shear in a portion of the mother liquor that remains after separating the potassium magnesium phosphate.