Abstract
The Brockman Iron Formation is one of the most important sources of iron ore in Australia. The usable reserves are limited, however, by high phosphorus levels within some of the orebodies. Understanding of the nature and distribution of this phosphorus is critical when techniques are being devised to upgrade the ores for ironmaking. Although some of the phosphorus is present as secondary apatite and other less common phosphates, it has been known for some time that the majority of the phosphorus in Brockman iron ores is associated with goethite, in amounts often exceeding 1%. It has now been shown that phosphorus levels are dependent not only on the amount of goethite but also on the microtextural types of goethite in the ore. Extensive microanalytical studies of a wide range of ore types have established that the highest phosphorus levels are consistently associated with late-formed colloform goethite in cracks and pore networks. Preliminary studies by scanning transmision electron microscopy reveal that high phosphorus levels are limited to goethite composed of ultrafine crystallites. Where dehydration or recrystallization of the goethite has occurred it typically results in expulsion of the contained phosphorus. The implications of these findings for phosphorus removal are discussed.
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