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 u nbound water, and the effect of ammonium chloride on caking. The cakin g propensity of granular fertilizer was characterized by two accelerat ed caking tests, with the caking propensity being correlated with the tensile properties of the fertilizer granules and the theory of capill ary adhesion. The concentration of saturated fertilizer salts in free water found within the granules was determined and gave a good correla tion with the caking propensity as determined by the accelerated cakin g tests. It also indicated that high levels of ammonium and chloride i ons were found in the free water within fertilizer granules. X-ray dif fraction analysis revealed that high concentrations of ammonium chlori de were found on the surface of fertilizer having a high caking propen sity. A further investigation using X-ray microanalysis indicated comp lete conversion of potassium chloride to ammonium chloride within fert ilizer granules.