Investigation of factors affecting caking tendency of calcium ammonium nitrate fertilizer and coating experiments

Abstract

Caking of fertilizers is an important problem both to manufacturers and users. Manufacturers must recycle the caked fertilizer to the process resulting in an extra cost and users may have difficulties during the application of the fertilizer to the soil. In the first part of this study major factors which influence caking of a commercial grade calcium ammonium nitrate (CAN) fertilizer were investigated with a laboratory caking apparatus kept in a controlled atmosphere. It was observed that the caking tendency of CAN fertilizer increases almost linearly with pressure exerted on the fertilizer and with moisture content of the fertilizer at a temperature of 35 °C. The results indicate that the phase transition of ammonium nitrate between crystalline forms IV and III plays a significant role in caking of CAN since caking tendency is greatly reduced below the phase transition temperature which occurs at about 32 °C. In the second part of the study, the effectiveness of some coating materials to reduce the caking tendency of CAN fertilizer were tested. Among the materials tested, kieselguhr gave the most satisfactory result under the experimental conditions employed.