The milling process was performed with high-energy ball mill, Fritsch Pulverisette 7, with a 250 ml zirconia bowl, 5 zirconia balls of 15 mm diameter. The essays were performed using the weight ratio of 1:1 (w/w) of eggshell and KH2PO4 were performed firstly for 15 min, 30 min, 1 h, 2 h, 3 h, 6 h, 12 h and 24 h at 600 rpm, and secondly at 100, 200, 400 and 600 rpm for 2 h, in order to evaluate acid-basic reactions between these precursors to form potassium calcium phosphates. Considering the purity of KH2PO4 and assuming that the eggshells are mainly composed by CaCO3, the mixture corresponds to 0.75 mmol of KH2PO4 and 1 mmol of CaCO3. After milled, the samples were characterized by X-ray diffraction (XRD), nuclear magnetic resonance, magic-angle spinning (NMR) MAS, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Details of each characterization are described in Supplementary Material.