Modelling of the sulfuric acid leaching of mechanically activated titanite

摘要

A titanite CaTiSiO5 concentrate was mechanically activated in a laboratory centrifugal-planetary mill for up to 10 min at dry and wet conditions. XRD analysis showed the weakening and broadening of diffraction peaks are mainly due to dry mechanical activation (MA) than due to wet MA. Leaching experiments were carried out using 30% H_2SO_4 at 20, 40, and 60 ℃. Preliminary MA of titanite concentrate lead to significant increase in the leaching rate. Dry MA of titanite for 10 min resulted in ～90% Ti dissolved at 60 ℃ for 2.5 h. Leaching efficiency of unactivated titanite at similar conditions was about 1% Ti dissolved. Wet MA was found to be less effective than dry MA, despite the former attaining significantly larger surface area. This is due to greater degree of amorphization induced by dry MA in comparison to wet MA. In the suggested kinetic model an attempt was made to take into consideration the influence of BET surface area, amorphization of mineral and decrease in average energy stored by mineral due to MA in the course of leaching on the rate of dissolution. Small size crystallites and regions with large lattice strain which are typical of outer particle layers dissolve at a higher reaction rate. As the leaching time increases, the average degree of structure imperfections of the remaining powder decreases. Consequently, the average energy stored by mineral due to MA decreases and activation energy increases leading to decreasing the dissolution rate. The activation energy derived from the model indicates that the reaction of titanite with sulfuric acid is chemically controlled.