Mathematical modeling of taconite circuits

Comminution accounts for a large percentage of the energy used in mineral processing. Therefore, improvements in comminution efficiency result in decreased energy costs. Taconite comminution circuits are often inefficient due to over-grinding, where product-sized material is re-circulated and re-ground unnecessarily. Over-grinding is a problem because it reduces circuit throughput and causes excess energy usage.; Computer modeling allows ideas for reducing over-grind to be tested before incurring the considerable expense of changing the actual circuit. An industrial taconite comminution circuit was analyzed to determine the sources of over-grinding at the ball mill. MatlabRTM was used to simulate alternate circuits that were proposed with the goal of reducing over-grinding. The most successful alternate circuit involved the removal of a screen and a magnetic separator, and the re-location the hydrocyclones up-stream of the ball mill. This resulted in a simulated 15% increase in throughput and a 50% reduction in over-grind, but a 6% decrease in the circuit product assay.; Hydrocyclone inefficiencies called "coarse fish-hooks" are sometimes the cause of over-grinding. Very few studies regarding the elimination or reduction of coarse fish-hooks have been included in literature. Therefore, experiments were run to explore the possibility of reducing coarse fish-hooks by: (1) Varying common hydrocyclone operating parameters; (2) Changing the chemical environment of the hydrocyclone feed slurry by adding surfactants.; Varying the hydrocyclone feed solids concentration and decreasing the feed flowrate both reduced the coarse fish-hook. However, it was found that reducing the coarse fish-hook did not necessarily reduce over-grinding. Increasing the feed solids concentration and increasing the feed flowrate were both effective methods of reducing over-grinding, regardless of their affect on the coarse fish-hook. Increasing the feed solids concentration 100% and 75% decreased the over-grind material originating from the hydrocyclone by 20%. Increasing the feed pressure 350% decreased the over-grind material originating from the hydrocyclone by 35%.; The primary contribution of this project was a comprehensive study on the effects of varying the chemical environment of the hydrocyclone feed slurry on hydrocyclone performance. Surfactants were carefully chosen to represent the different mechanisms for changing the coagulation, flocculation, and dispersion of the hydrocyclone feed slurry. It was found that varying the chemical environment, as measured in terms of pH, viscosity, and zeta potential, did not change hydrocyclone performance with statistical significance. This meant that varying the chemical environment of the slurry was not considered a viable option for the reduction of coarse fish-hooks or over-grinding.