Production of mechanically activated rock flour fertilizer by high intensive ultrafine grinding

This paper provides a first assessment of the use of mechanical activation to enhance the availability (i.e., leachability) of potassium from K-feldspar containing materials for soil improvement and agricultural purposes. A planetary mono mill was used to achieve high intensive dry grinding of both a K-feldspar concentrate and a nepheline syenite concentrate that served as a reference material. The K-feldspar concentrate was also milled in a pilot-scale HiCOM 15 nutating mill. The mill products were characterised with respect to their size distributions, specific surface areas and their relative degree of structural disordering as calculated from X-ray diffraction analysis. The enhanced solubility of the products in terms of potassium was determined directly through a three-step cascade leaching test. The results show that high intensive dry grinding could be used to increase the release of potassium from K-feldspar containing materials by more than an order of magnitude. When subjected to planetary milling, less than 10 min of milling was required to make the K-feldspar mineral more reactive than the intrinsically more soluble nepheline. The enhanced reactivity of the mill products is predominantly a function of their specific surface areas, but a significant part of the observed increase in reactivity must be attributed to structural disordering. The use of water as a grinding aid makes it possible to produce very reactive structurally disordered products with high specific surface areas.