CS206641B1 - Treatment method of indecomposed residues after acid decomposition of phosphoric raw materials - Google Patents

Description

It is an object of the present invention to provide a process for the treatment of non-decomposed residues after the acidic decomposition of a phosphorous feedstock in the production of combined fertilizers by a freeze-drying technology.

The non-decomposed part of the phosphorous raw material (apatite, phosphite), non-decomposed residues, must be separated from the solution due to further processing of the mother liquor. Separation, mainly carried out on sedimentation centrifuges, results in undecomposed residues concentrated to a pasty consistency with a liquid phase content of up to 30%. The reaction of thickened, non-decomposed residues is strongly acidic due to the broken liquid phase.

Thickened non-decomposed residues can theoretically be directly metered into a further process for the production of a combined fertilizer, but this method encounters major difficulties.

First of all, it is the considerable compactness of the thickened non-decomposed residues, which causes difficulties in homogenizing the non-decomposed residues, which causes difficulties in homogenizing the non-decomposed residues with the process medium in the process reactor. For a long time, the strongly acidic reaction of undigested residues, which, due to the inhomogeneity of the mixture, causes the formation of acid centers in the process media - which is unacceptable from the viewpoint of the combined fertilizer technology.

206 641

For these reasons, the return of non-decomposed residues to the production process is by-passed and the residues are exported as waste to landfill even at the cost of economic losses.

These drawbacks are overcome by the method of treating the undecomposed residues according to the present invention.

SUMMARY OF THE INVENTION The present invention relates to a process for the treatment of decomposed residues after the decomposition of phosphorous raw material by acid in the production of combined fertilizers by a freeze-drying process, characterized in that the separated concentrated decomposed residues are liquefied in water the non-decomposed residues are preferably returned to the combined fertilizer production process.

The effect of the treatment of the non-decomposed residues according to the invention is that their physical and chemical properties are altered by the treatment. By liquefying the concentrated non-decomposed residues with water, their compactness is removed. Neutralization with ammonia removes the acidity of the residues and, on the other hand, the pH changes to precipitate the hydroxides of some elements (Al, Fe, etc.) present in the residues coming from the phosphorus feedstock. The presence of these precipitates partially stabilizes the liquefied residues and limits their sedimentation.

Due to the newly acquired properties, it is then easy to return the processed non-decomposed residues to the combined fertilizer production process without affecting and disrupting the technological parameters. This will not only increase the economic efficiency of combined fertilizer production, but will also improve the working and living environment.

As an example of a possible practical application of the process according to the invention, the treatment of non-decomposed residues after the decomposition of the apatite wheel with nitric acid on the combined fertilizer production plant by freezing technology is further described.

The non-decomposed residues are separated from the solution of the Wheel of apatite in nitric acid on a decanter centrifuge. Below the centrifuge is a tank with a capacity of 0.7 to 1.2 m, equipped with a cage stirrer, water supply, ammonia and overflow. Concentrated, non-decomposed residues containing mother liquors 20 to 30, 56, fall from the centrifuge directly into the stirred tank, while supplying water and ammonia. The amount of water supplied is controlled according to the decomposition node performance (ratio control), the amount of ammonia automatically according to the temperature of the reaction mixture in the tank. Liquid and neutralized non-decomposed residues are discharged from the tank via an overflow into the process stirred reactor, where they are mixed with the melt of the combined fertilizer before its granulation.

Claims (2)

Process for the treatment of decomposed residues after acid decomposition of a phosphorous raw material with an acid, in the production of a combined fertilizer by a freeze-drying process, characterized in that the separated concentrated decomposed residues are liquefied in water in a ratio of 1:10 to 1: 1. 2. A process according to claim 1, characterized in that the liquefied and neutralized non-decomposed residues are returned to the combined fertilizer production process.