RU2250197C1 - Method of recovering strontium-containing concentrate - Google Patents

Abstract

FIELD: inorganic compounds technology.

SUBSTANCE: invention relates to production of strontium compounds and can be used in manufacture of complex fertilizers. Apatite is decomposed by nitric acid, nitric acid extract is diluted with water, concentrated, and filtered. Consumption of water 0.03-0.12 t per 1 t apatite is maintained in apatite decomposition reactor.

EFFECT: reduced loss of strontium nitrate with clarified solution more by 20% during operation under optimum conditions.

3 cl, 3 ex

Description

The invention relates to the field of production of strontium compounds and may find application in the preparation of complex fertilizers using the nitric acid processing technology of apatite.

Strontium isomorphically replaces part of the calcium in apatite and, in the process of its decomposition with nitric acid, passes into the nitrate salt. The latter has limited solubility in a nitric acid extract. Therefore, part of the strontium nitrate formed is in a nitric acid extract in crystalline form and can be separated together with an insoluble residue in the form of a so-called strontium-containing concentrate.

There is a method of separating strontium-containing concentrate in the process of producing complex fertilizers by decomposing apatite with nitric acid in the presence of manganese dioxide, thickening the resulting nitric acid extract and filtering the condensed product [Complex nitric acid processing of phosphate raw materials. Ed. A. L. Goldinova and B. A. Kopyleva, L., "Chemistry", 1982, pp. 75-79]. The disadvantage of this method is the contamination of fertilizers with manganese salts, which reduce the thermal stability of fertilizers, as they catalyze the process of their spontaneous decomposition when heated.

The closest in the set of essential features and the achieved result to the present invention is a method for separating strontium-containing concentrate from a nitric acid extract obtained in a reactor of nitric acid decomposition of apatite, including thickening the nitric acid extract and filtering the condensed product [US Pat. RF №2032622, С 01 F 11/38, publ. 04/10/95].

The disadvantage of this method is the significant loss of strontium nitrate with a clarified solution during thickening of nitric acid extract.

The technical problem solved by the claimed method is to reduce the loss of strontium nitrate with a clarified solution.

The stated technical problem is solved by the fact that in the method for separating strontium-containing concentrate from a nitric acid extract obtained in a nitric acid decomposition reactor of apatite, including thickening the nitric acid extract and filtering the condensed product, according to the invention, water is added to the nitric acid extract at a rate of 0.03-0 12 tons per 1 ton of apatite.

Water is added to the apatite nitric acid decomposition reactor.

Example 1

Apatite, containing 39.4% phosphorus pentoxide (hereinafter,% by mass), 36.0% calcium and 2.5% strontium, is decomposed in an amount of 34 t / h in two reactors operating in parallel with nitric acid. As the source of nitric acid, the so-called reverse nitric acid is used, which is formed in the production of complex fertilizers as a result of washing the crystals of calcium nitrate tetrahydrate with the initial cooled 58% nitric acid and mixing the resulting washing solution with other technological circulating solutions containing nitric and phosphoric acids, nitrates calcium and strontium. The composition of the working acid,%: nitric acid - 40.1, phosphorus pentoxide - 2.8, calcium - 2.4, strontium - 0.1. The consumption of circulating acid is 123 t / h. Water is also added to the apatite decomposition reactor, namely steam condensate in an amount of 2.5 t / h. The resulting nitric acid extract in an amount of 159.5 t / h is sent to two simultaneously operating thickeners with a thickening surface of 254 m ² each. The thickened product in an amount of 6.5 t / h is filtered on two disk filters with a surface of 68 m ² and get 2 t / h of strontium-containing concentrate, which contains 29% strontium in the form of strontium nitrate. The filtrate in an amount of 4.5 t / h is used for the preparation of circulating nitric acid. The clarified solution (top drain from the thickener) in the amount of 153 t / h is sent for further processing into complex fertilizers. The content of strontium nitrate in the clarified solution in terms of strontium 0.22%, including dissolved 0.15%, crystalline - 0.07%. Loss of strontium with a clarified solution of 9.9 kg per 1 ton of apatite. The flow rate of water added to the nitric acid extract is 0.074 tons per 1 ton of apatite, while water is added to the decomposition reactor of apatite, that is, in the process of obtaining a nitric acid extract.

Example 2

Change the flow of water and the order of its addition to the nitric acid extract, namely:

- the average daily water consumption is maintained in the range of 0.03-0.12 tons per 1 ton of apatite;

- water is added to the nitric acid extract at the outlet of the apatite decomposition reactor.

The loss of strontium with a clarified solution after the thickener is 9.1-12.0 kg per 1 ton of apatite when water is supplied to the nitric acid decomposition reactor and 11.5-13.0 kg per 1 ton of apatite when water is introduced into the nitric acid extract at the reactor outlet .

Example 3

Carry out a prototype experiment. To do this, exclude the addition of water to the aero acid extract, but add water to the condensed product before filtering it. With nitric acid decomposition of 34 t / h of apatite and the addition of water to the condensed product in an amount of 0.6 m ³ / h, 1.95 t / h of strontium-containing concentrate and 150.5 t / h of clarified solution are obtained. The content of strontium nitrate in terms of strontium,%:

- in strontium-containing concentrate - 28.6

- in the clarified solution - 0.31,

including - 0.15 dissolved

and 0.16 crystalline

Loss of strontium with a clarified solution of 13.7 kg per 1 ton of apatite.

The data show that the proposed method in comparison with the prototype can significantly reduce the loss of strontium with a clarified solution by more than 20 rel.% When operating in optimal mode. The reduction in losses is due to a decrease in the content of crystalline strontium nitrate in the clarified solution.

The positive effect is provided by the addition of water to the nitric acid extract before it is thickened and, apparently, due to the fact that the addition of water provides favorable conditions for the formation of larger crystals of strontium nitrate, which are more fully condensed.

The optimum water flow rate is 0.03-0.12 t per 1 ton of apatite. With less water consumption, the positive effect decreases due to an increase in the loss of crystalline strontium nitrate. With a water flow rate of more than 0.12 tons per 1 ton of apatite, the positive effect decreases due to an increase in losses of dissolved strontium nitrate.

It is advisable to add water directly to the apatite decomposition reactor. With the introduction of water into the nitric acid extract at the outlet of the decomposition reactor, the positive effect decreases.

Claims (2)

1. The method of separation of strontium-containing concentrate from a nitrogen-acid extract obtained in a reactor of nitrogen-acid decomposition of apatite, including thickening the nitrogen-acid extract and filtering the condensed product, characterized in that water is added to the nitrogen-acid extract before it is condensed with a flow rate within 0.03-0.12 t per 1 t of apatite 2. The method according to claim 1, characterized in that water is added to the apatite nitric acid decomposition reactor.