Abstract
In this study, the impact of vertical shaft impactor (VSI) crusher on fine and ultrafine production during crushing of South African Middle group (MG) chromite seam was investigated. The chromite ore was subjected to size reduction with VSI crusher at varied rotor tip speed (30, 35 &40 Hz) and particle size distribution analysis was done on all the three products. The VSI crusher product particle size distribution indicated that as the VSI rotor speed was increased, the amount of ultrafine generated also increased. The product at rotor speed of 35Hz revealed a lower percentage of ultrafines at 6.16% in the -212+150μm and 0.85% in the -150+53μm particle size range. Ball mill product from the Plant was analysed and the results revealed that the ball mill is more efficient for chromite ore liberation as 84% of the -425+300μm was produced compared to the VSI which only produced 51.27% -425+300μm. However, the amount of ultrafines produced was high at 9.2% of -150+106μm size fraction, with most ultrafine particle size of 4.42% in the -53+26μm size fraction. The mineral liberation analysis conducted on the -425+300 and -300+212μm VSI crusher products indicated that the degree of chromite liberation was higher at 95% on the -300+212μm size fraction compared to 78% liberation on the -425+300 μm size fraction. From the liberation analysis conducted in this investigation, it can be concluded that VSI crusher has a greater potential in chromite size reduction as it has shown to produce a liberated product with reduced percentage of ultrafines. However more test needs to be done on the VSI residence time to improve the percentage mass of the required liberated product particle size.