Abstract
The current practice of assessing the efficiency of recovery of magnetite and ferrosilicon by drum magnetic separators is to conduct Davis tube tests at a magnetic induction equal to that on the surface of the drum. It is, however, the magnetic force or the force index, and not the magnetic field strength, that are decisive in the operation of a magneticseparator. Since the magneticfield gradients generated by Davis tube and drum magnetic separators are generally different, it is unlikely that the above practice would yield correct information. This article analyses the patterns of the force index generated by drum magnetic separators and a Davis tube operated at different field strengths. It is shown that in order to obtain a correct assessment of the efficiency of separation by a ferrite drum magnetic separator, a Davis tube should be operated at the field of about 0.1 T, which is lower than the current practice suggests. For a rare-earth drum separator the Davis tube operating field should be at least 0.3 T.