Physicochemical and structural characteristics of nano eggshell calcium prepared by wet ball milling

Nano eggshell calcium (NEC) powder was prepared from biowaste chicken eggshells using wet ball milling. The characteristics of the NEC, including the zeta potential, micromorphology, elemental composition, particle size distribution, Ca2+ concentration, and chemical structure, were investigated. According to the results, the optimum process parameters were determined to be as follows: a milling time of 13 h, rotation speed of 400 rpm, ball-to-powder ratio of 5:1, solid-to-liquid ratio of 1:2 and filling ratio of 20%. Under these conditions, the eggshell particles were reached a minimum median particle size (D50) of 500 nm after 13 h of milling. NEC particles were negatively charged and the zeta potential notably reduced as the particle size decreased. Homogeneous, aggregated and polyhedron crystals morphology of NEC particles were observed through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, the selected area electron diffraction (SAED) analysis performed during TEM showed that the NEC particles were polycrystalline in nature. The FT-IR and XRD analysis revealed that the milling process did not cause significant changes to the chemical structure of the NEC. The Ca2+ concentration in the NEC suspension increased after milling, suggesting that calcium was steadily released from the particles to the suspension during milling.