The axial mixing model applied to ball mills

Abstract

The unsteady-state, one-dimensional convective mixing equation was solved with finite end boundary conditions for a pulse of tracer admitted into a steady flow, assuming a constant dimensionless mixing factor D*. Radiotracer tests were performed on two continuous wet overflow ball mills, a laboratory mill of 0.3 m i.d. and a pilot-scale mill of 0.91 m i.d. Counting through the mill case enabled the tracer concentration to be measured at L/3, 2L/3 and L for the small mill, and L/2 and L for the pilot-scale mill. The results were consistent with the mixing model with D* = 0.5 and 0.3, respectively, with D* constant along the mill. The mean residence time of water was about 0.85 that of the solid, showing the slurry density in a mill to be higher than that of the feed and product streams.