| Overgrinding is a critical problem commonly encountered in size reduction circuits. Size reduction is seldom performed without one or more classification stages. In the case of heterogeneous ores, the difference in the classification properties of the ore has been found to greatly influence hydrocyclone performance. A study of an iron ore size reduction circuit processing magnetite identified the presence of a large fraction of fine valuable material in the hydrocyclone undertow feeding a pebble mill. The presence of fine material in the pebble mill feed resulted in reduced mill capacity and wasted energy.; Laboratory and plant hydrocyclones experimental work was carried out to evaluate the effect of the difference in classification properties of the components of heterogeneous ores to understand this phenomenon and to develop methods to improve performance. During the experimental work, fine and coarse fish-hooks were observed on the hydrocyclone efficiency curves. Even though both anomalies in the efficiency curves had been previously observed, they had not been observed simultaneously; neither origin of these anomalies is fully understood.; The results from the laboratory experiments indicated that the coarse fish-hook occurred due to the difference in size distribution and specific gravity of the components of heterogeneous ores and the operating conditions. Magnetic agglomeration, on the other hand, was responsible for an increase in the size of the fine fish-hook.; Reviewing hydrocyclones theory, laminar flow was observed to have been assumed as the normal operating regime for hydrocyclones. The hydrocyclone experimental results indicated that the assumption of laminar flow might be an incorrect assumption for hydrocyclone models, and a correction to Plitt's hydrocyclone model was made to account for non-laminar flow. A second equation adjustment was made to model the coarse fish-hook because current model corrections are focused on fine fish-hooks rather than the coarse fish-hooks.; Finally, a model for a size reduction circuit was used to examine an alternative circuit configuration based on the knowledge gained during the project. |
