Investigation of the effect of particle size in gravity concentration equipment

In this thesis, it was aimed to determine the separation efficiencies of gravity concentration equipment and to reveal the concentration behavior of particles by investigating the separation mechanisms of coarse and fine sizes. With this purpose, shaking tables, spiral concentrators, Falcon concentrator and MGS (Multi-gravity separator) were tested by using artificial feed, consisted of magnetite and quartz mixture. Sampling data, obtained from a chromite concentration plant using spiral concentrators, was also used in the results. In the experimental studies, samples taken from feed, concentrate and tailings were sieved, grades of the size fractions were analyzed and recoveries, separation efficiencies, grades and grade ratios were evaluated on size basis. As a result of the studies, it was observed that, in every condition, the separation efficiencies, due to particle sizes, increased as the particle size increased up to a certain point. After the maximum separation efficiency was obtained, the separation efficiency decreased as the particle size increased. In the evaluation of the average size-by-size separation efficiencies, maximum values were obtained as 95% in shaking tables, 78% in spiral concentrators and 48% in Falcon concentrator. Low concentration results was obtained in MGS tests with -150+38 μm feed material. Relations between the particle sizes and the separation efficiencies can be explained by quadratic polynomials. In the region where the separation efficiencies increased due to the particle sizes, linear relations were observed between the settling rates of the particles and their separation efficiencies. Decreases in the separation efficiencies of the coarse particles, though, could be explained by Bagnold forces, which are directly proportional to the specific gravities of the particles and increase with the square of the particles' diameter.