Caking processes in granular NPK fertilizer

This investigation into the caking of granular NPK fertilizer examines three specific areas, namely, accelerated caking tests, the role of unbound water, and the effect of ammonium chloride on caking. The caking propensity of granular fertilizer was characterized by two accelerated caking tests, with the caking propensity being correlated with the tensile properties of the fertilizer granules and the theory of capillary adhesion. The concentration of saturated fertilizer salts in free water found within the granules was determined and gave a good correlation with the caking propensity as determined by the accelerated caking tests. It also indicated that high levels of ammonium and chloride ions were found in the free water within fertilizer granules. X-ray diffraction analysis revealed that high concentrations of ammonium chloride were found on the surface of fertilizer having a high caking propensity. A further investigation using X-ray microanalysis indicated complete conversion of potassium chloride to ammonium chloride within fertilizer granules.