Critical pressure drop and flow velocity in axial HGMS matrices

The material throughput per unit area, v, is an important parameter for magnetic separation. Another is the pressure drop (as head loss due to flow per unit length of matrix, P
n
. The value of v for which P
n
= 1 is designated v
c
which depends on the characteristics of the slurry and on matrix construction but not on matrix length or area. In the absence of magnetic field, data can be matched to a curve of the form:
p_{n} = (\frac {v}{v_{c}})^{2}
for relatively open matrices and high velocity. When slurry "pours" through a matrix, as in the present experiment, with no velocity control, the flow tends to satisfy a condition of balance between head and head loss corresponding to P
n
= 1. In a magnetic field there is a value of P
n
, P
c
, which controls the trapping of magnetics. Experiments indicate that magnetics trapping of efficiency is high only for P
n
< P
c
. Three screen spacings were used in batch experiments on the recovery of magnetite from magnetite/coal slurries from coal cleaning plants. Two of these have been transferred to continuous carousel separator matrices. Pressure drop as a function of velocity was measured on the batch matrices to help in the design and in the operation of continuous tests.