Clean and efficient synthesis using mechanochemistry: Preparation of kaolinite–KH2PO4 and kaolinite–(NH4)2HPO4 complexes as slow released fertilizer

This study investigated a mechanochemical process for synthesizing slow-release fertilizers of kaolinite and KH2PO4/(NH4)2HPO4 in separate systems by milling in a planetary ball mill. Tests with kaolinite contents ranging from 25 to 75 wt % and mill rotational speeds at 600 rpm for 2 h were performed to evaluate incorporation of KH2PO4 and (NH4)2HPO4 and release of K+, NH4+ and PO43− ions into solution. X-ray diffraction (XRD), Thermal gravimetric analysis (TGA), Fourier transformation infrared spectrometry (FTIR) and ion chromatography (IC) were used to analyze the synthesized samples and indicated that the mechanochemistry (MC) process was successfully applied to incorporate both KH2PO4 and (NH4)2HPO4 into the amorphous kaolinite structure. Release of K+ and PO43− ions from the system (kaolinite–KH2PO4) when dispersed in water for 24 h reached up to 15 to 40 ppm respectively. Under similar conditions for the system (kaolinite–(NH4)2HPO4), release of NH4+ and PO43− ions reached between 303.2 and 415.1 (ppm) respectively. These results indicated that the MC process could developed to allow amorphous kaolinite to act as a carrier of K+, NH4+ and PO43− nutrients to be released slowly for use as fertilizer.