GB366970A - Improvements in or relating to the solution of phosphate rock in nitric acid - Google Patents

Abstract

In the process of the parent Specification for dissolving phosphate rock in nitric acid of the order of 50 per cent concentration and separating calcium nitrate by cooling, the phosphate rock is treated first with a quantity of nitric acid materially less than that required for complete solution to form, without frothing, a viscous or plastic mass which is subsequently subjected to mechanical treatment such as kneading or stirring to release most of the gases, the further quantities of acid required to form a solution containing all the phosphoric acid in the free state then being added. The first portion of acid should be at least sufficient to react with the whole of the gas-producing impurities, such as calcium carbonate or fluoride, and may be added as a fine spray. Apparatus for continuous working may comprise a mixer provided with stirrers to which the initial quantity of acid is added, the mass then passing to a series of tanks or the like, to each of which a portion of the main acid supply is fed. A counter-current process, for example as described in Specification 316,428, [Class 1 (ii), Inorganic compounds, other than &c.], may however be used. The reaction with the initial quantity of acid may be continued until a solid, friable product is obtained which is stored and further pulverized before treating with the remaining acid. A solution of phosphate rock in nitric acid, or the mother liquor obtained after crystallization of calcium nitrate therefrom, may be used in place of nitric acid for the first stage of the treatment. The Specification as open to inspection under Sect. 91 (3) (a) comprises the treatment of solid substances with acids in general, in which an initial quantity of acid is added to decompose gas-producing impurities. This subject-matter does not appear in the Specification as accepted.ALSO:In the process of the parent Specification for dissolving phosphate rock in nitric acid of the order of 50 per cent concentration and separating calcium nitrate by cooling, the phosphate rock is treated first with a quantity of nitric acid materially less than that required for complete solution to form, without frothing, a viscous or plastic mass which is subsequently subjected to mechanical treatment such as kneading or stirring to release most of the gases, the further quantities of acid required to form a solution containing all the phosphoric acid in the free state then being added. The first portion of acid should be at least sufficient to react with the whole of the gas-producing impurities, such as calcium carbonate or fluoride, and may be added as a fine spray. Apparatus for continuous working may comprise a mixer provided with stirrers to which the initial quantity of acid is added, the mass then passing to a series of tanks or the like, to each of which a portion of the main acid supply is fed. A countercurrent process, for example as described in Specification 316,428, [Class 1 (ii), Inorganic compounds, other than &c.], may however be used. The reaction with the initial quantity of acid may be continued until a solid, friable product is obtained which is stored and further pulverized before treating with the remaining acid. A solution of phosphate rock in nitric acid, or the mother liquor obtained after crystallization of calcium nitrate therefrom may be used in place of nitric acid for the first stage of the treatment. The Specification as open to inspection under Sect. 91 (3) (a) comprises the treatment of solid substances with acids in general, in which an initial quantity of acid is added to decompose p gas-producing impurities. This subject-matter does not appear in the Specification as accepted.