Comminution effects on mineral grade distribution

Every mining operations is followed by a beneficiation process aimed to deliver quality material to the transformation industry. Most of mineral processing is focused on comminution and grinding of extracted ore that is crucial for the following separation steps in order to divide gangue from valuable minerals. Comminution is the most energy consuming phase and the quality of the results is strictly related to the characteristic of the material under treatment. A preliminary study has been performed to understand the crushing behaviour of a mixed sulphide ore, containing galena and sphalerite, and how target minerals grade distributes among the different sized products of the process. Ore samples have been examined and characterized by means of thin sections observation and SEM analyses for the determination of the grain liberation size, while XRD quantitative analyses have been performed for the definition of the grades. The crushing circuit selected comprises lab-scale impact crusher, jaw crusher, disk mill and rod mill. The products collected are below the free grain size threshold and granulometric analyses have been performed. Comminution products have been divided in size classes suitable for flotation separation, ranging between 0.250 and 0.075mm and XRD analyses showed a variable mineral grade distribution varying with the reduction in dimension of the products. This important trend should be considered for further investigation related to an efficient froth flotation separation.