|The Kumba Resources Sishen Iron Ore Mine is one of the biggest iron ore producers in South Afica, 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.