Microcrystalline apatite minerals: Mechanochemical activation for agricultural application

Abstract

Phosphate minerals of apatite from three mines with different amounts of gangue minerals were activated by milling to increase their microcrystallinity and subsequent dissolution in a citric acid solution to serve as slow-release fertilizers for agricultural production. XRD (X-ray diffraction), FTIR (Fourier Transform Infrared), and SEM (Scanning electron microscope) were employed to characterize the properties of the prepared samples, such as changes in microcrystallinity, mineral composition, lattice structure, and granule morphology during the milling. With prolonged milling time, accompanied with the progress in microcrystallinity, the ratio of the formed amorphous compositions increased, resulting in higher dissolution in citric acid solution. In the case of carrot plants, the addition of the microcrystalline phosphate rock together with phosphorus bacteria allowed an efficient nutrient (P, K, and N) uptake as high as 77.0%, 36.7%, and 32.2%, which increased by 91.3%, 123.0%, and 105.2%, respectively, from the growth on an original soil without any addition, demonstrating clear contribution of the activated apatites in agricultural production.