High intensity magnetic separation of iron ore slime and its limitations

Abstract

India is endowed with large reserves of high grade hematitic iron ores. However, steady depletion of these iron ores is now a concern forcing to develop beneficiation strategies to utilize low grade iron ores. In India, iron ores are generally washed to remove the high alumina containing clayey matter. Conventionally, after washing, the lumps are directly fed to blast furnace and the fines are used after agglomerating them into sinter. However, the slimes are being rejected in the tailing ponds. These slimes in most cases contain substantial iron values in the range of 54–58% Fe. Therefore, it is imperative to recover iron values from these slimes because of high demand on the good grade iron ores day-by-day. Also, it is expected that the iron bearing minerals will be in liberated state in the slime because of their fine particle size and will be amenable to beneficiation. National Metallurgical Laboratory is engaged in developing strategies for beneficiating iron ore slimes and during one such beneficiation studies, the slimes were processed through gravity and magnetic methods of separation. The slime under investigation contains Fe 58.64%, SiO2 3.41%, Al2O3 4.85% and LOI 7.57%. The mineralogy of the slime sample though indicated that hematite is the major iron bearing phase, goethite also occurs in substantial quantity. A systematic study on this slime sample using wet high intensity magnetic separation at higher intensities was carried out and the products were analyzed both chemically and mineralogically. The results indicated that stage wise magnetic separation with increasing intensity improves the total iron recovery. However, increasing the intensity over 1.31 Tesla again deteriorates the grade of the product. The results of this investigation are presented in this paper.