Dissolution of gangue minerals in the grinding stage

The aim of this thesis work was to investigate how the water chemistry was affected as a result of ore grinding. A new experimental set-up was designed and constructed to monitor the dissolution of the ore during the grinding. This was done by monitoring changes in pH, Eh, DO, conductivity and temperature of the water and by analysing the dissolved species in water samples taken after specific grinding times. The operation of this new set-up was successful, as evidenced by the experimental data collected. Six different water types were tested of which three at Aalto and three at Kevitsa Mine in Sodankylä, Finland. The water types included Purified water, Tap water, River water and Thickener overflow water and water from the Tailings pond. The experiments were done between the 3th and 25th of May, 2016. It was hypothesized that the dissolution of minerals would be the fastest in the cleaner waters, such as tap and purified water. This was expected because the presence of soluble species in the process waters decrease the amount of minerals that can be further dissolved before saturation is reached. It was found, that the dissolution of minerals in the grinding stage is not governed entirely by the chemistry of the water. The energy that is put into the system by grinding, as well as the presence and concentration of specific species might have a larger impact on the dissolution speed. The Thickener overflow was identified as being the most active water, being dynamically unstable and it showed the largest variation in dissolved species concentration over time. This finding, proving that the thickener overflow water is not in equilibrium, highlights that closing the water circuits and recirculating water in short loops within the flotation plants needs to be carefully considered and planned in order to avoid negative effects on the flotation performance. Based on the experimental results, the hypothesis was rejected