CS197845B1 - Method of producing ammonium phosphates - Google Patents

Description

The invention relates to a process for the production of ammonium phosphates with a low content of fluorine, arsenic and heavy metals.

For example, ammonium phosphates are produced by neutralizing ammonia extraction phosphoric acid with the addition of calcium salts in excess of the fluorine contained in the phosphoric acid used. The addition of calcium salts also partially reduces the content of arsenic and heavy metals. Perfect removal of arsenic and heavy metals is achieved by adding hydrogen sulfide or soluble sulfides. Excess hydrogen sulphide must be removed from the reaction mixture in a rather complicated manner. If, according to the reaction conditions, ammonium hydrophosphate predominates in the final filtrate prior to drying, ammonia losses occur on drying.

The above-mentioned disadvantages have no process for the production of ammonium phosphates with a low content of fluorine, arsenic and heavy metals, in which arsenic and heavy metals are removed by the addition of sulfide ions, fluorine is removed by the addition of at least 0.1% by weight. soluble calcium salts and neutralization is carried out by the addition of ammonia, which is based on the fact that the excess hydrogen sulfide is removed from the reaction mixture by the addition of an oxidizing agent with an oxidizing agent.

197 845 with a reduction potential greater than +0,4 V, measured at unit activity of the reagents and at 25 ° C, such as hydrogen peroxide or potassium permanganate, in an amount equal to at least twice the excess hydrogen sulfide present expressed in equivalents and pH of the filtrate after removal insoluble calcium salts are brought to a value of at most 7.8, preferably by the addition of phosphoric acid.

The process according to the invention simplifies the entire manufacturing process, since the disposal of excess hydrogen sulfide is solved by simply adding an oxidizing agent which oxidizes hydrogen sulfide to harmless elemental sulfur. By correcting the pH of the solution before drying, the ammonia is exhaled and thereby lost.

The production process can also be based on technical extraction phosphoric acid, characterized by a high content of impurities (fluorine, arsenic and heavy metals). In this case, 1 to 1.5 kg of sodium sulfide is added per 1 ton of acid heated to 60 [deg.] C., for better filtration of the excreted sulfides and heavy metals, the suspension is supplemented with diatomaceous earth and activated carbon. After 30 minutes of stirring, the suspension is filtered to remove 92% of the initially present heavy metal salts and 95% of the originally present arsenic according to the tests performed. If at least twice the equivalent of the oxidizing agent to the hydrogen sulfide present is used, oxidation takes place quantitatively within about 10 minutes, the oxides and sulfur precipitated being separated by subsequent filtration of the fluoride and calcium phosphate.

Since the calcium contained in the acid used is under equivalent to the fluorine present, the calcium content is supplemented with a soluble calcium salt (eg calcium oxide) such that there is an excess of calcium relative to fluorine (at least 1 mole of calcium oxide per 2 moles of fluorine). This neutralization eliminates fluorine as insoluble calcium fluoride and excess calcium as insoluble calcium hydrophosphate. These impurities are separated by filtration, and the filtrate obtained is a solution of ammonium phosphates having a maximum content of 0.02% by weight. fluorine.

In order to reduce the loss of ammonia during drying of the filtrate thus obtained, the pH is lowered to a maximum of 7.8, preferably to 5-2. The pH can be lowered with any acid, in order to maintain a high phosphorus content in the product, the use of thermal phosphoric acid *

After drying the product (e.g., in a spray drier), a product is obtained containing 60% by weight Ρ ₂ θ5 and not more than 0.04% by weight. P and 0.2 ppm As.

Due to the high purity of the product, it can be used to enrich phosphorus feed rations *

197 845

Exemplary embodiment

The reactor was charged with 568 kg of phosphoric acid extraction (25 wt.

1.5 wt. % P and 0.002 wt. As). 0.5 kg of activated carbon, 0.6 kg of diatomaceous earth and 0.8 kg of sodium sulfide were added with stirring. The whole was heated to 60 ° C and after stirring for 30 minutes the suspension was filtered. To the still warm filtrate was added 2 kg of a 30% hydrogen peroxide solution and after stirring for 10 minutes 11.93 kg of calcium oxide and 51.1 kg of ammonia gas. The neutralized solution was filtered, and the pH of the filtrate was adjusted to 5.2 with the addition of thermal phosphoric acid, and then dried in a spray drier. 345 kg of product were obtained with a content of 59.1% by weight. % Wt. P, 0.16 ppm As and 0.29 ppm heavy metals, expressed as lead.

Claims (1)

SUBJECT OF THE INVENTION A process for the production of ammonium phosphates having a low content of fluorine, arsenic and heavy metals, wherein arsenic and heavy metals are removed by the addition of Sim ions, fluorine is removed by the addition of at least 0.1 wt. soluble calcium salts and neutralization is carried out by the addition of ammonia, characterized in that excess hydrogen sulfide is removed from the reaction mixture by the addition of an oxidizing agent with an oxidation-reduction potential of greater than +0.4 V, measured at unit activity of the reactants and at 25 ° C, such as hydrogen peroxide or potassium permanganate, in an amount equal to at least twice the excess hydrogen sulfide present, expressed in equivalents, and the pH of the filtrate after removal of insoluble calcium salts is adjusted to a value of at most 7.8, preferably by addition of phosphoric acid.