Laboratory Column flotation studies for reduction of alumina and silica in iron ore slimes of an operating plant

Abstract

A typical iron ore washing plant for treating iron ore fines (<10 mm) consist of sizing of the ore by dry / wet screening, washing, classification by screw classifiers followed by single or multi-stage hydrocycloning of screw classifiers overflow. The underflow of the hydrocyclones forms the concentrate which is suitable for pellets making. Since the cut-point of hydrocyclones is usually at 20 µm or less, relatively lower diameter cyclones in a cluster with parallel feeding are used. This is found to, often, result in choking of the spigots, at times, by extraneous material reporting along with the slurry. It is observed to lead to sub-optimum performance of the cyclones with loss of iron values into cyclone overflow and thereafter into tailings. Analysis of the data of an operating beneficiation plant (Beneficiation plant - 1) of M/s Jindal South West (JSW) Steel Limited, Karnataka, India over a period of one year indicated that weight recovery of the concentrate from two-stage hydrocycloning was 45.9% (with respect to feed to the cyclones) and assaying 63.43% Fe, 4.43% SiO2 and 2.23% Al2O3. Considering the fineness of the slimes (d80: 40.5 µm), generated as screw classifier overflow, flotation is thought to be better alternative vis-à-vis hydrocyclones to recover iron values from it. The present study aims at improving the recovery of the iron values from the screw classifier overflow by adopting reverse cationic column flotation technology. After selecting a suitable collector, process parameters like collector and depressant dosages are optimized by statistically designed experiments on a Denver D12 flotation cell. Later, the effect of important operating parameters of flotation column like air flow-rate, froth depth and wash water on the separation process is studied and optimized. It was established that a typical screw classifier overflow analyzing 60.43% Fe, 6.88% SiO2 and 3.26% Al2O3 could be improved to 63.30% Fe, 4.04% SiO2 and 2.32% Al2O3 with 59.10% weight and 61.70% Fe recovery. This is an improvement of 29% in weight recovery of the concentrate at equivalent metallurgy compared to what is being obtained, by two-stage cycloning.