Effect of process parameters and agglomeration mechanisms on NPK compound fertiliser

The granulation characteristics of a calcium carbonate–industrial sulphuric acid-based NPK compound fertiliser have been investigated in a bench scale drum granulation unit. It was found that the granulation of the fertiliser was correlated with both the calcium carbonateʹs properties and the systemʹs operating parameters, especially the industrial sulphuric acid content and viscosity which were found to govern the granulation process. The surface structure and characteristics of the NPK granules were analysed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that calcium sulphate formed the coalescence kernel with its high porosity and strength generated by a chemical reaction in the granulation process. Meanwhile, urea sulphate, as a liquid binder, improved the solution–solid phase ratios and binder viscosity.