In this study, a novel slow-release fertilizer (SRF) consisting of kaolinite and K2SO4 was prepared, employing the process of mechanochemical milling in a planetary ball mill. To obtain the optimum milling time and speed, several samples were made at fixed mass ratios of kaolinite: K2SO4 (3:1). The milling rotational speed ranged from 200 to 700 rpm for 120 min. Different milling times ranging from 60 to 180 min at fixed 600 rpm milling speed were also investigated to evaluate the incorporation of K2SO4 and to measure the liberation of K+ and SO42− ions into solution. The properties of the studied samples were analyzed by Fourier transformation infrared spectrometry (FTIR), thermal gravimetric analysis (TGA), and ion chromatography (IC). The mechanochemical process is a green chemistry procedure that is successfully applied to incorporate K2SO4 into the amorphous kaolinite structure. The slow-release performance was evaluated by determining the K+ and SO42− content in the aqueous solution upon leaching. The optimum released amount of K+ after 24 h was 32 mg L−1 for the milling conditions of 180 min and 700 rpm, indicating that K2SO4-kaolinite has good slow-release properties. The novel SRF is cost-effective, environmentally friendly, and improves the fertilizer’s efficiency in many agricultural applications.
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