Mechanochemical formation of K–Si–Ca–O compound as a slow-release fertilizer

• Mechanochemical process was used to synthesize a slow-release potassium fertilizer.
• KOH, CaO and amorphous SiO2 were directly as the starting materials for synthesis.
• The synthesized fertilizer (K–Si–Ca–O system) was an amorphous glass phase.
• K+ and Ca2 + were incorporated into the framework structure of SiO4 tetrahedron.
• The release rate of nutrient K+ from the synthesized fertilizer was about 25%.

This study investigated a mechanochemical process for synthesizing slow-release potassium fertilizer by co-grinding starting materials of KOH, CaO and amorphous SiO2 in a planetary ball mill. X-ray diffraction (XRD), differential thermal analysis (DTA), Fourier transformation infrared spectrometry (FTIR) and ion chromatography (IC) were used to analyze the synthesized samples. The milled sample reached an amorphous glass phase of the K–Si–Ca–O system through the incorporation of K+ and Ca2 + into the SiO2 network. The release rate of nutrient K+ decreased with increases in the amount of added silica oxide and in the rotational milling speed. For a synthesized sample dispersed in water for 24 h and milled at 400 rpm, the release rate of K+ was approximately 25%. All the results indicate that mechanochemical synthesis using starting materials of hydroxides or oxides is a simple and feasible process for producing slow-release fertilizer.

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