Agricultural wastes as renewable fillers in physical granulation of NPK fertilizers: Evaluation of on-size granules and comparison to conventional filler

Purpose This research aimed to evaluate the yield and quality of granular NPK fertilizers prepared by physical granulation with eggshell, snail shell, and cow bone as fillers and to compare them to conventional filler. Methods Urea, DAP, KCl, and fillers were milled separately and mixed to the desired formula. About 150 g of mixed powders were granulated on a disc granulator in 9 minutes, at a rotation speed of 35 rpm and a disc slope of 45°. Water at a desired additional moisture was sprayed on the tumbled powders to facilitate the granulation. The obtained granules were then dried and screened into three fractions: undersize ( 4 mm). Results Snail shells and eggshells as fillers were found to give on-size NPK granules having yield and compressive strength which were comparable to that with limestone as a conventional filler. For NPK 15-15-15, using snail shells and eggshells as fillers, the yields of on-size granules achieved 46% and 56%, respectively, and the compressive strengths of on-size granules reached 2.4 and 2.1 MPa, respectively. Cow bones as fillers resulted in low compressive strength. The distribution of nutrients in the NPK granules was found to be close to the targeted formula. Conclusion Snail shells and eggshells as fillers have good yield and quality of on-size NPK granules and are very potential alternatives to limestone.