ABSTRACT
Concentrated superphosphate is made by the acidulation of natural phosphate material with phosphoric acid. High-analysis superphosphate is also referred to as “anhydrous superphosphate,” or “high-analysis triple superphosphate.” The high-analysis superphosphate is made with superphosphoric acid containing approximately 75 to 76% phosphorous pentoxide. Triple superphosphate made from electric furnace acid contains considerably reduced impurities, and the sulfate is practically eliminated. The electric furnace acid is comparatively pure concentrated phosphoric acid made from elemental phosphorous evolved by smelting phosphate rock in an electric or blast furnace. The initial stages of reaction of phosphoric acid with phosphate rock proceed from a fluid stage through a plastic stage into a dry stage. The lengths of the fluid and plastic stages vary with the conditions of manufacture; the fluid stage depends upon the acid concentration, acid temperature, rock particle size, impurities, and the percent P2O5 in the rock.
