THE TRANSPORT AND GRINDING OF MATERIAL IN A CONTINUOUS, WET, OVERFLOW BALL MILL.

摘要

A study of the transport and size reduction of material in a continuous, wet, overflow ball mill was conducted. A mathematical simulation of the process was developed.; The contents of a laboratory mill were experimentally sampled at a steady state. Radioactive tracing experiments were conducted with detectors corresponding to different locations along the mill in addition to the conventional discharge location. The following was found.; The hold-up of solids is almost uniform along the mill. The concentration of solids within the mill is higher than that in the feed. Two regions were observed in the rotating mill: the ball charge and the "pool." This "pool" is typical for steady state operations, except at very low feed rates with high percent solids where the pool disappears.; The particle size distribution within the mill is much finer than the feed. Starting from the inlet, it has a small gradient until the outlet, while at the discharge it is considerably finer than in the region immediately adjacent to the outlet.; Two mathematical simulation models were developed. The first predicts the transport in the mill while the second predicts the particle size distributions and the hold-up along the mill.; The transport model assumes that the axial motion occurs only in the "pool," but with continuous interchange of the slurry between the balls and the "pool" due to rotation of the mill. Settling of the solid particles in the pool gives rise to preferential transport of solids into the ball charge, leading to a higher mean residence time for solids than water.; The particle size distribution model uses a diffusion-convection-grinding approach analogous to the analysis of chemical reactors. The model allows size-dependent velocity distributions (extracted from the transport model) within the mill, as well as exit classification based on particle size.; Another part of the simulation work was the extension of a convection-diffusion model for pulse tracing at the mill exit to cover all locations along the mill.; As a result, this work offers a convenient method of predicting the steady-state product of any size of open-circuit, wet, overflow ball mill under any operating conditions.