RU2240284C1 - Calcium nitrate crystalline hydrate isolation method - Google Patents

Abstract

FIELD: inorganic compounds technology.

SUBSTANCE: invention relates to complex fertilizer production technology via decomposition of naturally occurring phosphates with nitric acid, more specifically to isolation of calcium nitrate crystalline hydrate from nitric-phosphoric acid solution. Method comprises cooling acid solution, crystallization, separating crystals from mother liquor and treating them with nitric acid followed by washing crystals with 35-60% ammonium nitrate solution cooled to temperature between -10 and +10^оС, consumption of the latter being maintained within a range of 0.1 to 0.25 wt parts per 1 wt part crystals.

EFFECT: increased purity of product with regard to nitric acid impurity.

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Description

The invention relates to the production technology of complex fertilizers by the nitric acid method.

A known method for the separation of crystalline hydrate of calcium nitrate, providing for the cooling of a nitric phosphate solution, crystallization, filtering or centrifugation of the resulting suspension and washing the crystals with nitric acid from the mother liquor [M.E. Posin The technology of mineral salts. Part II, L., Chemistry, 1974, S. 1339-1342].

The disadvantage of this method is the significant loss of nitric acid with crystalline hydrate of calcium nitrate.

The closest set of essential features and the achieved result to the present invention is a method for the separation of calcium nitrate crystalline hydrate, comprising cooling the nitric phosphate solution, crystallization, separating the crystals from the mother liquor by filtration, followed by their treatment with nitric acid and washing the crystals from nitric acid with an aqueous solution of calcium nitrate with a concentration 20-40 wt.% And a temperature of from plus 5 to minus 10 ° C [and.with. USSR No. 644733, class C 01 F 11/44, publ. 01/30/79].

The disadvantage of this method is the low washing efficiency. When trying to implement the method in an industrial environment, it turned out that upon contact of the wash solution with a layer of crystals on the filter, a crust forms on the surface of the layer, in appearance similar to ice and prevents the penetration of the wash solution into the layer. As a result, the washing solution flows down the crust into the trough of the drum filter, and the washing ratio is only 15 rel.%.

The technical problem solved by the claimed method is to increase the efficiency of washing crystals.

The stated technical problem is solved by the fact that in the method for the separation of calcium nitrate crystalline hydrate from a nitric phosphate solution, including cooling, crystallization, separation of crystals from the mother liquor, their treatment with nitric acid and subsequent washing with a cooled nitrate-containing saline solution, according to the invention, ammonium nitrate solution is used as the latter . While the flow rate of the solution of ammonium nitrate is maintained in the range of 0.1-0.25 wt.h. per 1 part by weight crystals, the temperature of the solution of ammonium nitrate is in the range from minus 10 to plus 10 ° C, and its concentration is in the range of 35-60 wt.%.

Example 1

Nitrogen-phosphate solution containing, wt.%: P ₂ O ₅ - 10.8, Ca - 9.8, HNO ₃ - 7.0, in an amount of 80 t / h, cooled in a cascade of three circulating crystallizers to a temperature of minus 4 ° С , crystals of calcium nitrate tetrahydrate, separated on the drum vacuum filter from the mother liquor, in an amount of 43.4 t / h, and containing 79% calcium nitrate tetrahydrate and 21% of the liquid phase, are placed in a repulpator, where it is processed cooled to minus 5 ° With a solution of nitric acid with a concentration of 58% in an amount of 24 t / h The crystals treated with nitric acid are separated from the washing nitric acid solution in a second drum filter. The number of crystals is 34.7 t / h; they contain 85% calcium nitrate tetrahydrate and 15% liquid phase, including 8.8% nitric acid. Next, the crystals directly on the filter are washed with a cooled to minus 5 ° C 40% solution of ammonium nitrate, taken in an amount of 7 t / h The washing of crystals on the filter takes place without any visible complications. In this case, 32.4 t / h of washed crystals of calcium nitrate tetrahydrate and 9.3 t / h of washed nitrate solution are obtained. The composition of the washed crystals, wt.%:

Calcium Nitrate Tetrahydrate 86

Liquid phase 14

including:

Nitric acid 1.2

Ammonium Nitrate 4.8

The composition of the washing nitrate solution, wt.%:

Nitric acid 29.0

Ammonium nitrate 13.1

Calcium Nitrate 15.8

The washed crystals are sent for processing into synthetic chalk and ammonium nitrate, and the washing solution is sent to the nitric acid opening unit of the apatite concentrate.

Example 2

The washing regime of the crystals of calcium nitrate tetrahydrate is changed, namely, the flow rate of the ammonium nitrate solution is maintained within 3.5-9 t / h, which corresponds to a specific flow rate of 0.1-0.25 t per 1 ton of crystals entering the washing; the temperature of the solution is in the range from plus 10 to minus 10 ° C; the concentration of the solution is in the range of 35-60 wt.%. The washing of the crystals on the filter takes place without any apparent complications, while washing crystals of calcium nitrate tetrahydrate are obtained, containing, wt.%:

Calcium Nitrate Tetrahydrate 84-87

Liquid phase 13-16

including:

Nitric acid 1-2.8

Ammonium Nitrate 3-6

Example 3

Carry out a prototype experiment. For this, the washing of crystals is carried out cooled to a temperature of minus 5 ° C with a 35% solution of calcium nitrate. During washing, a monolithic layer is formed on the surface of the crystals, which in appearance resembles an ice crust. As a result, the calcium nitrate solution supplied to the crystal bed flows into the trough of the drum filter without washing the crystals. The residual content of nitric acid in the crystals is 7-7.5 wt.%. The experience is terminated.

From the presented data it can be seen that the inventive method, in contrast to the prototype method, provides high efficiency washing crystals of calcium nitrate tetrahydrate from nitric acid.

A positive effect is provided by the use of a solution of ammonium nitrate for washing the crystals, which does not undergo any transformations on the crystal surface that impede washing.

The optimal specific consumption of a solution of ammonium nitrate is 0.1-0.25 tons per 1 ton of crystals. At a lower flow rate, efficiency decreases, an increase in flow rate of more than 0.25 tons per 1 ton of crystals unreasonably increases the amount of water introduced into the process, and then it must be evaporated, which is not economically feasible.

The optimal temperature range of the solution of ammonium nitrate is from minus 10 to plus 10 ° C. When using a solution with a temperature above plus 10 ° С, the washing efficiency of crystals decreases due to the formation of channels in the sediment layer due to the dissolution of calcium nitrate at the points of entry of the solution jets. The use of a solution cooled to a temperature below minus 10 ° C does not increase the washing efficiency, but causes an increased cold consumption.

The optimal concentration range of the solution of ammonium nitrate is 35-60 wt.%. The use of a more dilute solution will cause additional watering of the technological process, and the use of a more concentrated (above 60 wt.%) Solution will cause difficulty in cooling it.

Claims (1)

The method of separation of crystalline hydrate of calcium nitrate from nitric phosphate solution, including cooling, crystallization, separation of crystals from the mother liquor, their treatment with nitric acid and subsequent washing with chilled nitrate-containing saline solution, characterized in that the solution used is ammonium nitrate with a concentration of 35-60 wt. .%, a temperature in the range from minus 10 to plus 10 ° C, while the flow rate of the solution of ammonium nitrate is maintained in the range of 0.1-0.25 wt.h. per 1 part by weight crystals.