Stable suspension fertilizers from monoammonium phosphate

Research studies conducted at the Tennessee Valley Authority (TVA) have shown that the addition of fluoride ion can improve the physical properties of suspension fertilizers made from monoammonium phosphate (MAP) containing metallic impurities. In the past, compounds of high cost, such as ammonium fluoride or bifluoride, have been used as the source of fluorine. Because of the cost of these compounds, a study was carried out using fluorosilicic acid, which is a by-product of the phosphate fertilizer industry, as the fluorine source in the production of suspension fertilizers from MAP. In the study, three commercial MAPs of medium- to high-impurity levels were evaluated. The experimental data showed improvements in both viscosity and pourability of 10-30-0 (N-P₂O₅-K₂O) and 11-33-0 grade suspensions made from 11-52-0 grade MAPs using as little as 0.6% fluorine added as fluorosilicic acid. Products of grades 10-30-0 and 11-33-0 (fluorine added) had satisfactory storage at both 27 and 38°C for up to 90 days, while the control sample (no fluorine added) had satisfactory storage for only 30 days at 27°C and less than 15 days at 38°C.