Based on the reverse logistic and green chemistry this study proposes the use of eggshell, a food industry residue, and KH2PO4 to design an eco-friendly fertilizer that guarantee a better nutrient management, playing on the solubility of calcium, potassium and phosphorus. To reach this aim a mechanochemical process was used, free of solvent, and presenting no unwanted subproduct. The results indicate new phosphate phases such as K3CaH(PO4)2 and KCaPO4, that present in citric acid solution (wt 2%) a slower release character of potassium and phosphorus compared to the precursor KH2PO4, and a faster release character compared to the precursor CaCO3 from eggshell.