Eggshell as an alternative source of calcium for nitrate fertilizer bead gel

The chicken eggshell was applied as an alternative calcium source to produce calcium nitrate fertilizer. 12 g of eggshell waste was used as raw material for extraction into liquid calcium nitrate by a 100 mL of 10%(v/v) nitric acid solution. The liquid calcium nitrate fertilizer was encapsulated through the wet-extrusion process, in which calcium ions from liquid calcium nitrate as crosslinking agents and sodium alginate as an absorbent polymer. 73.57% of nitrate was absorbed by the droplet of 2%(w/v) sodium alginate, forming sphericallike gel structures. The optimal hardening time for bead gel formation was 120 min. The average size of wet bead gels was 4.29 ± 0.34 mm. The bead gels were oven-dried at 45◦C for 1 hour to maintain their shapes. Among other controlled release agents, pectin showed the slowest nitrate release from fertilizer bead gel. The chemical nature of bead gels characterized by FTIR indicated that nitrate was absorbed by alginate polymer incorporated with pectin, binding with the Ca2+ ions.