Abstract:
The Kumba Resources Sishen Iron Ore Mine is one of the biggest iron ore producers in South
A6ica, where beneficiation of the iron ore is done using a dense medium separation process.
Ferrosilicon is used as the dense medium separation material.
About 7 years ago, Kumba Resources decided to produce its own ferrosilicon, whereas the
previous supplier was Samancor. The new ferrosilicon produced by Kumba Resources,
however, had different characteristics and thus caused different problems in the dense medium
separation process, as was the case with the previously used ferrosilicon.
A study was undertaken to identify the changes that occur in the new ferrosilicon and to
understand the reasons why certain losses occur. Tests were done in the laboratory to identify
the effect of attrition on the ferrosilicon used as a dense medium separation material, and the
results obtained via the use of SEM analyses and Mossbauer spectroscopy, were compared
with the results obtained from samples taken in the Sishen plant itself.
No definite change could be observed in the magnetic properties of the ferrosilicon during
use, but rather a difference in magnetic recoverability of individual particles was found. The
difference in the magnetic recoverability was assigned to the fact that the chemical
compositions of individual size fractions may be different from the bulk chemical
composition. Furthermore, due to a difference in magnetic recoverability, it was found that
one of the main pathways of loss for the ferrosilicon was the inefficient magnetic recovery of
the ferrosilicon. The abrasion process that takes place during normal use of the ferrosilicon,
was also identified as a large contributing factor to the loss of ferrosilicon.
It is recommended that manufacturers should ensure that the bulk chemical composition of the
ferrosilicon produced be an accurate reflection of the chemical composition of individual
ferrosilicon particles. This would ensure more efficient reclaiming of the used ferrosilicon.
