Effects of Milling Time and Speed on Nutrient Availability of KH2PO4 with Kaolinite as Physical Type Slow/Controlled Release Fertilizers

Mechanochemical processing was applied to produce slow-release fertilizers consisting of kaolinite as clay material and (KDP) KH2PO4 in 3:1 weight ratio by grinding the contents in a planetary ball mill at milling rotational speeds ranging from 200 to 700 rpm for 2 h and at different milling times ranging between 1-3 h at 600 rpm milling speed. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and coupled ion chromatography (IC) were used to characterize the prepared samples. It was shown that the mechanochemical process succeeded to incorporate KDP into the kaolinite structure. The K+ and PO43- ions released from the kaolinite–KH2PO4 system when dispersed in distilled water for 24 h were measured. The results indicate that the prepared kaolinite–KH2PO4 system acts as a carrier of K+ and PO43- nutrients to be used as slow-released fertilizers