Triple superphosphate (TSP) was one of the first high-analysis phosphorus (P) fertilizers that became widely used in the 20th century. Technically, it is known as calcium dihydrogen phosphate and as monocalcium phosphate, [Ca(H2PO4)2 .H2O]. Triple superphosphate (TSP) is the more concentrated fertilizer than ordinary superphosphate, containing from 44 to 51% of available P2O5 or nearly three times the amount in the regular superphosphate. Triple superphosphate, also known as concentrated superphosphate, contains 45 to 50% monocalcium or water-soluble phosphate.
TSP is manufactured by adding phosphoric acid to rock phosphate, producing mainly water-soluble monocalcium phosphate with no calcium sulfate.
CaF2 + 3Ca3(PO4)2 + 14H3PO4 →10Ca(H2PO4)2 + 2HF
The concept of TSP production is relatively simple. Manufacturers make nongranular TSP typically by reacting finely ground phosphate rock with liquid phosphoric acid in a cone-type mixer. Granular TSP is made similarly, but the resulting slurry is sprayed as a coating onto small particles to build granules of the desired size. The product from both production methods then cures for several weeks as the chemical reactions are slowly completed. The chemistry and process of the reaction will vary somewhat depending on the properties of the phosphate rock.
95 to 98% of the ground rock phosphate, passed through 100 mesh sieve, is mixed with phosphoric acid (1kg rock phosphate of 34% P2O5 is mixed with 2.6kg acid). The acid is of commercial grade with P2O5 content of 52%. Finely ground phosphate rock and 62% H3PO4 are charged continuously to the granulator, where reaction and granulation take place. The den step, of TSP is faster (10-30min) than that for SSP (30-120min). The mixture from the reaction vessel goes to the den where it solidifies. Fines from the product screen are recycled to the granulator, and the moisture and temperature required for proper granulation are maintained by addition of water and/or steam.
TSP has several agronomic advantages that made it such a popular P source for many years. It has the highest P content of dry fertilizers that don’t contain nitrogen (N). Over 90 percent of the total P in TSP is water soluble, so it becomes rapidly available for plant uptake. As soil moisture dissolves the granule, the concentrated soil solution becomes acidic. TSP also contains 15 percent calcium (Ca), providing an additional plant nutrient.
A major use of TSP is in situations where several solid fertilizers are blended together for broadcasting on the soil surface or for application in a concentrated band beneath the surface. It’s also desirable for fertilization of leguminous crops, such as alfalfa or beans, where no additional N fertilization is needed to supplement biological N fixation.
Phosphate is one of the soil components that is vital to help promote root growth of all kinds of plants, so that the roots will be thicker, stronger and healthier. Phosphate will thus strengthen the trunk and increase its resistance against disease and pests, as well as reduce the risk of uprooting and spur flower development and seed maturity, thus accelerating harvest times. Phosphorous deficiency may cause a plant to have stunted growth, dark green color on leaves, fewer seedlings, long period of maturation and low productivity.
Monocalcium phosphate is an important ingredient in baking powder. The acidic monocalcium phosphate reacts with an alkaline component to produce carbon dioxide, the leavening for many baked products. Monocalcium phosphate is commonly added to animal diets as an important mineral supplement of both P and Ca.