CS265806B1 - A method for producing a composition comprising predominantly phosphoric acid or NP or NPK fertilizers - Google Patents

Abstract

The essence of the method is that the decomposition of the phosphorus raw material is carried out with nitric acid and sulfuric acid or/and sulfuric acid is used to partially adjust the ratio of calcium to phosphorus oxide, while the resulting calcium sulfate, together with the difficultly decomposable components of the phosphorus raw material, is separated from the resulting suspension before adjusting the ratio between calcium and phosphorus oxide by direct freezing. In the case of the production of NP or NPK fertilizers, this phase can be added back to the produced fertilizer in one of the other operations, after adjusting the ratio of calcium to phosphorus oxide, leading to the formation of the final product. The effect of the proposed production method is to limit the formation of so-called villi and the associated technological difficulties when mixing the organic and inorganic phases during direct freezing of the decomposed slurry.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the preparation of a mixture comprising predominantly phosphoric acid and / or NP and / or NPK fertilizers.

In the manufacture of NP or NPK fertilizers based on natural phosphates, using a direct freeze-drying method to adjust the ratio between calcium and phosphorus pentoxide to remove CatNOglg from the system. 4 HgO, ^{the decomposition of the} phosphate feedstock is carried out with nitric acid. The principle of direct freezing consists in the undercooling of the decomposed slurry being in direct contact with the cooled and immiscible liquid, such as petrol. For more details on this technology, see books by I. Harmaniak: Industrial Fertilizers, Alfa 1975 and V. Lakota: Production of Combined Fertilizers, SNTL 1964. 2a. phases. One of the causes of this difficulty is the hardly degradable impurities contained in the phosphate feedstock, the removal of which from the decomposed slurry is a very difficult process, since they are particles of very small dimensions, some of which are colloidal in nature.

As is evident, the lack of direct freeze-drying methods hitherto used is mainly that there is no effective purification of decomposed sludge from the hardly decomposable impurities contained in the phosphate feedstock prior to adjusting the ratio between calcium and phosphorus pentoxide.

This disadvantage is solved by a process for the production of a mixture containing predominantly phosphoric acid and / or NP and / or NPK fertilizers based on natural phosphates and nitric acid,

-2.265 806 and including the adjustment of the ratio between calcium and phosphorus pentoxide by direct freezing, for NP fertilizers also by ammoniacalization of the frozen slurry, for NPK fertilizers besides ammoniaization also by calibrating the frozen slurry, which consists in and / or a partial adjustment of the calcium to phosphorus pentoxide ratio is carried out by means of sulfuric acid or a raw material containing said acid, the resulting calcium sulphate together with poorly decomposable phosphate feedstocks separated from the resulting slurry prior to adjusting the calcium / phosphorus pentoxide ratio by direct freezing.

The basic effect of the process according to the invention is that the formation of so-called villi is reduced when the organic and inorganic phases are mixed. As a result, the process according to the invention becomes more advantageous than the hitherto known processes.

For example, the proposed process is such that all of the nitric acid and the phosphate feedstock are metered into the first reactor of the decomposition plant, consisting of four sequential reactors.

The sulfuric acid is fed to the third reactor. The resulting calcium sulfate, along with the poorly degradable phosphate feedstocks, is separated from the resulting slurry by filtration and can be added back to the fertilizer in the production of solid NP or NPK fertilizers in one of the following operations after adjusting the calcium to phosphorus pentoxide ratio.

The above process is described in more detail below with reference to specific embodiments.

Example 1

In a batch stirred reactor, apatite Kola was decomposed at a temperature of about 60 ° C by a concentration of 54% by weight nitric acid. in a quantity corresponding to a 10% surplus from the consumption standard. After 60 minutes of decomposition, 70 wt% sulfuric acid was added. in an amount corresponding to 10% of the calcium present in the apatite Kola. Decomposition

- 3,265,806 was terminated after 120 minutes. Calcium sulphate together with the hardly decomposable components from the apatite Kqla was separated by filtration. The remaining clear filtrate after cooling was mixed further with shaking with cooled gasoline. The freezing temperature was maintained at about -10 ° C. Upon shaking, the gasoline spontaneously separated from the remaining slurry, containing predominantly phosphoric acid and calcium nitrate tetrahydrate crystals. These were further separated by filtration. The product was a solution containing predominantly phosphoric acid, non-frozen calcium nitrate and the remaining nitric acid.

Frost-free slurries without addition of sulfuric acid and separation of the solid phase give rise to so-called villi in an amount of approx. 0.5% by volume. As the industrial process is continuous, the villi volume gradually increases and thus technological difficulties in the freezing equipment.

Example 2

The process was conducted as in Example 1 except that Senegal phosphate was used instead of the Wheel apatite.

Frost-free slurries without addition of sulfuric acid and solid-phase separation give rise to so-called villi in an amount of 15% by volume. Since the industrial process is continuous, the villi volume rapidly increases, thereby gradually freezing the freezer.

Example 3

The process was conducted as in Example 1, with the difference that Togo phosphite was used instead of the Wheel apatite.

In the freeze-drying process without the addition of sulfuric acid and separation of the solid phase,

villi in quantities of «ca 11% vol.

Example 4,265,806

The process was conducted as in Example 1 except that the filtered calcium sulfate along with the hardly decomposable components from apatite. The wheels were added to the purified frozen and ammonia to pH = 4.6 neutralized slurries. After drying the product, the product was a fertilizer containing mainly dicalcium phosphate, ammonium dihydrogen phosphate and ammonium nitrate. Almost all of the P 2 O 8 content was soluble in citric acid. The physical properties of the obtained NP fertilizer were approximately comparable to the corresponding types of industrially produced fertilizers.

Example 5

The process was conducted as in Example 1 except that the filtered calcium sulfate together with the hardly decomposable components from apatite was added to the purified frozen and ammonia to pH = 4.6 neutralized slurries together with potassium chloride. The product was fertilizer after drying the NPK. The physical and chemical properties of the fertilizers obtained were comparable to the corresponding types of industrially produced fertilizers.

Claims (1)

THE INVENTION Process for producing a mixture containing predominantly trihydrogenphosphoric acid and / or NP and / or NPK fertilizers, starting from natural phosphates and nitric acid, and comprising adjusting the ratio between calcium and phosphorus pentoxide by direct freeze drying, ammoniacalization and quenching of a frozen slurry, characterized in that the decomposition of the phosphorous feedstock is carried out with nitric acid and sulfuric acid or / and the partial adjustment of the ratio of calcium to phosphorous pentoxide is carried out with sulfuric acid or a feedstock containing this acid. the phosphate feed components are separated from the resulting suspension by direct freeze-drying before adjusting the ratio between calcium and phosphorus pentoxide.