Combined milling–dissolution of Panzhihua ilmenite in sulfuric acid

Simultaneous milling and dissolution in a stirred mill was tested on Panzhihua ilmenite in a 50% sulfuric acid solution. The results show that the dissolution of ilmenite was greatly enhanced by in situ milling, which continuously produced new surface and new crystal defects on the surface of unreacted particles. The milling–dissolution resulted in a high leaching conversion of 80% under an industrially used ore/acid ratio at 120 °C over 2 h. The characterization revealed that the reaction was likely to start from the surface perpendicular to the c-axis of the ilmenite crystal since increased lattice strain in the c-direction significantly accelerated the dissolution. Kinetic experiments show that the milling–dissolution probably consists of three competing kinetics, surface area increase due to milling, surface area decrease due to dissolution and hydrolysis increase due to induction of fresh surface and active sites on the surface of the particles freshly broken by milling. However, within the initial 50% the dissolution followed the shrinking core model with an apparent activation energy of 38 kJ/mol.