Formulation of a slow-release fertilizer by mechanical activation of smectite/glauconite and urea mixtures

This study demonstrates the formulation of slow-release fertilizers by the mechanical activation of a mixture of powdered clays and urea in the ratio 2:3, using planetary or ring milling techniques. The activation produces micro-aggregates of composites with intercalated clay and urea and is rimmed by the latter. Smectite-urea and glauconite-urea mixture shows an intercalation between urea and clay from the beginning of activation. A shift of X-Ray Diffractional parameters and the intensities of FTIR peaks record the systematic structural changes of the composites with increasing duration of activation. The maximum intercalation of clays and urea requires operation times of 20 and 60 min in planetary and ring mills, respectively. The external urea forms a uniform coating around the intercalated structure using the planetary mill, and it keeps on growing as the operation time increases. Therefore, this investigation reveals the optimum activation conditions for the formation of composites with layered structures. While the direct application of urea releases nitrogen to the soil at a fast rate, the resulting composites are likely to liberate the nutrient at a slow rate. Additionally, the composites made from a mixture of glauconite and urea releases potassium at a slow rate. The resultant composites meet the criteria of multifunctional slow-release fertilizers.