Processing of high alumina iron ore slimes using classification and flotation

The generation of iron ore slimes in India is estimated to be 10–15% by weight of the total iron ore mined. The iron ore values are lost to the tune of 10–15 million tons per year. Moreover these slimes which are stored in slime ponds at mine site pose threat to the environment. Considering the present magnitude of the iron ore slimes generation annually, quantity of slime accumulated over the years, depletion of high grade ore reserves, acute shortage of land at mining lease areas and stringent government norms, these slimes can be considered as a national resource if properly beneficiated using innovative technology. These slimes are readily available in finer size typically assaying 55–60% Fe and 6–8% alumina eliminating the need for crushing to finer sizes. This paper presents the research work carried out to recover Fe values with low alumina and silica content from high alumina iron ore slimes of India, using combination of hydrocyclone and flotation. Fine particle size, complex mineralogy and presence of locked particles determine the impossibility of direct production of hematite concentrate by froth flotation. Classification of slimes with two stage hydrocyclone gives a concentrate containing 61.99% Fe, 4.0% Al2O3 and 3.22% SiO2, with Fe recovery of 54.55% in Stage-I. Concentrate from Stage-II hydrocyclone contains 62.19% Fe, 3.45% Al2O3 and 2.79% SiO2 with Fe recovery of 47.45% with respect to initial feed. Further the concentrate from Stage-II hydrocyclone is beneficiated using reverse cationic flotation by using amines and direct flotation with fatty acid. A final concentrate of 64.46% Fe, 2.66% Al2O3, and 2.05% SiO2 with Fe recovery of 69.03% in flotation stage and 34.13% with respect to the initial feed was obtained with reverse cationic flotation. While conducting flotation of aluminosilicates by using amines as a collector and starch as a depressant for iron ore, starch adsorption occurred on aluminosilicate particles covered by iron oxides and on minerals which contains Al and Si ions in their structure; consequently an entire flotation of mineral complex is possible by controlling electrokinetic phenomenon.