NPK fertilizer is multi-nutrient fertilizer which contains primary macronutrients needed by plants including nitrogen (N), phosphor (P), and potassium (K). Bulk production of NPK fertilizer is mainly in granular form with the advantages in terms of simplicity of storage, handling, and transporting properties. Granular NPK fertilizer is synthesized by either reactive granulation or physical granulation. In preceding process, phosphoric acid was made to react with ammonia vapor to produce ammonium phosphate slurry. The slurry was then sprayed upon a tumbling bed of potassium chloride, recycled solid, filler, and other solid materials to form NPK granules. The mixed fertilizer was subsequently tumbled with the binder. These two processes are called as slurry and solid routes respectively (Hallsworth et.al., 1984).
Filler is used to adjust the percentage of the nutrients to a desired ratio, prevent fertilizer caking, and increase fertilizer weight (Gowariker et.al., 2009). Filler is usually from inorganic minerals, such as zeolite, clay, dolomite, phosphate rock, and bentonite. These materials are non-renewable and their stocks are limited. An alternative for conventional filler materials is required. Livestock wastes and their derivatives, such as eggshell and compost, could be considered as the alternative for conventional filler. A previous study showed that these two renewable materials could be granulated with mixed fertilizer (urea, DAP, and KCl), however the obtained granules do not have adequate compressive strength. Incapable method in spraying water and absence of external binder could be the causes.
The objective of this research is to prepare NPK granular fertilizer with renewable filler that has compressive strength comparable to NPK granular fertilizer with conventional filler. Eggshell and compost were used as the renewable filler. Granulation performance was evaluated by measuring yield and compressive strength of the granules and comparing the results with limestone as conventional NPK filler. The granulation was carried out by using a laboratory pan granulator. The granulator consists of an inclined disc equipped with a scrapper, supported on a metal frame which allows slope adjustment. The pan is rotated by a motor equipped with a speed reducer and an inverter. The pan is made from flexiglass. In contrast to the previous method which used a needle to delivery water in initiating granulation, in this research, water was delivered by using a sparger. Carboxymethyl cellulose, known having binding properties, was involved and added to solid particles.
Contact Person:
Dr. I Dewa Gede Arsa Putrawan (idewa@che.itb.ac.id)