Method for the production of phosphoric acid with high contents of fertilizer-nutrients

摘要

Phosphoric acid with a high fertilizer-nutrient content is produced by decomposing phosphate rock with nitric acid followed by precipitation of calcium ions with sulfate. The steps of the process are as follows: PPA. Decomposing phosphate rock with (7-2x) to (17-2x) mol nitric acid and x mols sulfuric acid per mol phosphorous pentoxide P PA.sub.1 whereby x may take on any values between 0 and a maximum value X, which is limitedPPA.sub. 2 by the condition that the mol ratio H.sub.2 SO.sub.4 :HNO.sub.3 may never exceed the value 8:1 and P PA.sub.3 by the condition that in the decomposition solution, into which, if need be, also ammonium sulfate is introduced, the content of sulfate ions after precipitation of the semihydrate gypsum is between 10 to 150 g/l solution;P PB. Adding--if no or not enough sulfuric acid has been used for precipitating calcium sulfate--ammonium sulfate in amounts corresponding to condition A. sub.3 in the beginning, while or after the decomposition process in this way choosing by step A and B a proportion between the use of sulfuric acid and ammonium sulfate corresponding to the economical situation of the day or the N:P proportion wanted in the produced N- containing phosphoric acid;PPC. Adjusting the acid decomposition mixture for decomposing the phosphate rock in the beginning of the process corresponding to the available acids by admixing with corresponding portions of the aqueous filtrates in a way that the developing nitrogen containing phosphoric acid has a total water contentPPC.sub.1 of 65 to 40% by weight, if only (NH.sub. 4)SO.sub.4 is used for supplying sulfate,PPC.sub.2 of 55 to 20% by weight, if only H.sub.2 SO.sub.4 is used for supplying sulfate orPPC.sub.3 of 65 to 20% by weight, if mixtures of (NH. sub.4).sub.2 SO.sub.4 and H.sub.2 SO.sub.4 are used for supplying sulfate; PPD. Separating the purified calcium sulfate semihydrate from the acid solution by filtration or centrifugation;PP E. Carrying out steps A, B and D at a temperature of about 60° to 100° C.