Phosphoric acid contg. high levels of fertilising elements - prepd. by digesting crude phosphate with nitric acid and adding sulphate

摘要

In making phosphoric acid contg. a high level of fertilising elements, crude phosphate is digested with 7-17 moles HNO3/mole P2O5, in which the HNO3 or nitric acid washing water filtrates contain 35-60% by wt HNO3 and to which (NH4)2SO4 has been added to give 10-150 g SO4--/1, at 60-100 degrees C. Alternatively (NH4)2SO4 is partly or wholly replaced by H2SO4 and the water content of the acid digesting mixt is adjusted by adding washing filtrates so that the phosphoric a acid contg. 55% of N-prod contains 20-55% water. The phosphoric acid, used in fertiliser mfr is economically prepd without the need for a lengthy purification.