A Beneficiation Scheme for Reduction of Alumina in Iron Ores from Barsua

Abstract

In order to improve blast furnace productivity by reducing the alumina of iron ore fines from the present level of 3.3-3.9% to the desired level of 2.5%, a detailed characterisation followed by beneficiation studies compris-ing crushing, dry screening, washing, gravity separation of fines and slimes, on the seven individual 'type' and a 'composite' iron ore samples from Barsua Iron Mines were carried out at NML, Jamshedpur to find the amenability of beneficiation and develop a flow-sheet. Based on the find-ings from the studies, two conceptual flowsheets were designed.The first one consisted of crushing the composite sample (62.26% Fe, 2.01% Si02 and 4.22% A1203) to 25 mm followed by wet processing comprising scrubbing & wet screening at 8 mm and classification of -8mm fraction into sand (+100#) and slime (-100#). The -8+1 mm fraction of the sand would be subjected to jigging and -1mm+100 # fraction to tabling. The cyclone underflow obtained by treating the slime would be subjected to tabling as well. The yield of the combined concentrate of fines would be 28% and analyse 64.09% Fe, 1.9% Si02 and 2.95% A1203. The +8 mm lumps, 45% by weight would analyse 63.69% Fe, 1.52% Si02 and 3.8% A1203. Based on mainly grade and physical characteristics of individual type samples, the Second Flowsheet consists of separate proportioning, blending and treatment of two group of ores viz., Direct Ore (Friable, Mineable Transi-tional and Blue Dust) and Beneficiable Ore (Soft Lamina-ted , Lateritic , Hard Laminated and Massive). The flow-sheet consists of dry processing of Direct Ore (29% by weight with 63.55% Fe, 1.69% Si02 and 2.45% A1203) and wet processing of Beneficiable Ore (71% by weight with 61.39% Fe, 2.22% Si02 and 5.09% A1203). The Dry Circuit would consist of crushing the Direct to -25 mm and screening at 8 mm. The lumps and fines would weigh 8% and 21% and analyse 62.62% Fe, 1.79% Si02 and 2.92% A1203 and 63.9% Fe, 1.65% SiO2 and 2.27% Al2O3 respectively. The Benefic-iable will go through the wet circuit as described for the first flowsheet. The washed lump would be 36.43% by weight and analyse 63.4% Fe, 1.38% Si02 and 4.05% Al2O3. The combined lumps from Dry Circuit and Wet Circuit would be 44.43% by weight and analyse 63.25% Fe, 1.45% Si02 and 3.85% A1203.The combined fines from Dry Circuit and Wet Circuit (without concentrates from slime) would weigh 35.62% and analyse 64.1% Fe, 1.59% Si02 and 2.56% A1203. The yield will improve by an additional amount of 5-6% with slight increase in Al2O3 (2.85%) if table con-centrates from cyclone underflow and overflow are recovered. Although quality or quantity of lumps remain almost same in both the cases, there is substantial improvement in grade and yield of fines in the second flowsheet.