Superphosphates

Use

Normal superphosphate is made by treating ground rock phosphate with sulphuric acid. The above reaction yields monocalcium phosphate and gypsum. For the manufacture of normal superphosphates, a continuous process rather than a batch process is in vogue. Some of these processes are named after their inventors, for example, the Tennessee Valley Authority process, the Maxitz-Standard Den process, the Broadfield Den process and the Kuhlman Den process. The treated mass is sent to a curing shed and stored for 3 to 4 weeks for curing and final drying. The dried product is excavated, milled, screened, and either bagged for marketing or sent for granulation. Granulation is done in a granulator in the presence of steam and the finished product is then bagged. It contains 16 to 21% phosphorus pentoxide (P2O5) in a watersoluble form. In addition, it contains 11 to 12% sulphur as calcium sulphate.