Agronomic use of aluminum thermophosphates with slag addition

Abstract

Phosphate minerals are the main source of phosphorus and are used as raw materials for most phosphate fertilizer industries worldwide. However, the production of thermophosphates improves phosphorus solubility in the soil. In this study, thermophosphates were produced from lateritic phosphates with the addition of ironmaking and steelmaking slags at ten temperatures, ranging from 100 °C to 1,000 °C, to evaluate the effect of temperature on these products and their feasibility as fertilizers. The mineralogical and chemical compositions of the samples were characterized by X-ray diffraction and X-ray fluorescence, respectively. Crandallite is the main Al-phosphate in the ore, with amorphous and iron oxide phases present in the slags. Agronomic efficiency experiments of thermophosphates produced at 300 °C, 600 °C, and 1,000 °C were carried out. Thermophosphates, both in natura and with slag at 600 °C, showed amorphous phases with better results in plant development due to the solubility of phosphorus and other nutrients available for crop absorption, thereby enhancing growth and regulating soil fertility. The agronomic efficiency index of thermophosphates plus slags at 600 °C showed results superior to in natura phosphate in all variables, primarily due to the high levels of CaO and MgO in the slags, which may have nutritionally benefited the maize plants.  The aluminum thermophosphates with slag addition are a viable alternative to traditional phosphate fertilizers, offering both agronomic and environmental benefits.