Upgrade of SLon concentrate with the use of froth flotation on an iron ore sample from Anglo American Kumba iron ore

Abstract

Pollution caused by mining practices is a growing concern worldwide. Although there are numerous contributing factors, discarded ultra-fine (-150 micron) material is regarded as one of the major challenges. Geological footprints, water pollution and dust generation are but some of the environmental challenges that are associated with the generation of ultrafine (-150 micron) material. To overcome the arising challenges, extensive research into the reduction of fines generation, as well as ultra-fines beneficiation, has been investigated. Although crushing circuits have been made more efficient by making use of improved mining techniques and novel processing technologies, the presence and the generation of ultra-fines are unavoidable. The environmental impact and the loss of material is thus forcing mining practices to consider new beneficiation techniques. Great benefits can be realised, as the ultra-fine material has no associated mining cost and has the potential of increasing production, effectively generating revenue. Several techniques have been investigated over the last few decades to upgrade ultra-fine iron ore by making use of various differences in mineral characteristics. The major difference between beneficiation technologies is the cost involved and many technologies have therefore been uneconomical in the past. However, with the development of technologies, the beneficiation of iron ore ultra-fines has become more and more economically attractive. The most popular of these techniques include froth flotation, as well as magnetic separation - specifically the SLon concentrator. Due to the selectivity and low operational costs, froth flotation has been used worldwide to produce a saleable product from the ultra-fine material. The use of flotation in South Africa’s iron ore industry has been unsuccessful in the past, due to the complexity of the ore body. The ore mineralogy complicates the use of flotation and the circuits involved. Therefore, Anglo American Kumba Iron Ore has conducted extensive research on the use of the SLon concentrator to upgrade the material found at its Sishen mine. However, this process alone has proved to be unsuccessful in producing a high grade product. This study therefore investigated the use of froth flotation as a final upgrading process, after the SLon concentrator, to produce a high grade iron ore product with an iron content of more than 66,5%. Mineralogical studies of the feed material indicated that the material in the +38 micron material was unliberated and required milling of this size fraction prior to the use of flotation. Additionally, the -38 micron material was well liberated and was assayed to be close to the required product specification with a total Fe content of 66,3%. Based on the results, the process was determined to include de-sliming of the feed material (SLon concentrate) at 38 micron, andmilling of the +38 micron material, which is then followed by froth flotation. The use of starch, amines and inorganic chemicals as a depressant, collector and pH modifiers respectively, have proven successful in upgrading Sishen’s iron ore ultra-fines during flotation. Results showed selective depression of hematite and the activation of quartz and kaolinite under specific conditions. Laboratory results indicated that the milled material can be upgraded to a Fe content of approximately 67% from a feed material containing less than 65% Fe at a yield to product of 60 to 65%. Finally, combining the flotation concentrate with the de-slimed -38 micron material, a total circuit yield of 82 % can be achieved with an Fe content of 66,5 % (w/w) and a total SiO2 content of less than 2% as required for a high grade iron ore product. Therefore it was concluded that the SLon concentrate at Sishen can successfully be upgraded using froth flotation as a final concentrating step.