Characterisation of phosphorus and other impurities in goethite-rich iron ores - Possible P incorporation mechanisms

Phosphorus is one of the most deleterious elements in iron ore as it follows irorl during downstream reduction processes, forming iron phosphides that make steel brittle. Excess phosphorus increases the cost of steelmaking and the steel industry has placed an upper limit of 0.07-0.08 wt-% P on the iron ore feed. Goethite grains containing high levels of phosphorus are abundant in many iron ores and can be difficult to remove without also discarding valuable iron-containing units. The goethite forms during supergene metasomatic enrichment of BIF-derived ores and the phosphorus is typically associated in goethite with other impurity elements such as Si and Al. The current study focusses on determining the distribution and association of phosphorus within goethite present in a high-P Brockman type iron ore from the Pilbara region of Western Australia. Detailed characterisation of the chemistry and mineralogy of the goethite-rich ore was conducted using XRF, optical microscopy and EPMA to determine the distribution of phosphorus and other impurity elements. Using this knowledge, we speculate on the possible P substitution mechanisms in goethite. The latter has important implications in designing strategies for beneficiating high-P goethitic iron ores.