UP GRADATION OF DILBAND IRON ORE

Abstract

Dilband iron ore deposits, discovered in 1997 by Geological Survey of Pakistan (GSP) in Kalat Division Balochistan, Pakistan, is of significant importance from socio-economical point of view among the rest indigenous iron ore deposits discovered so far in Pakistan. Because of its relatively low iron content, high gangue minerals specially quartz and more importantly high phosphorous ( i.e. steel polutant) content, it requires an adequate concentration method, in order to meet the requirements of Pakistan SteelMills ore specification (i.e. 57-60% Fe (min.), 8.5% SiO 2 (max.), 0.5% Al 2 O 3 (max.), 0.1% P (max.), and 0.05% S. This work, therefore, is aimed to up-grade Dilband iron ore through an adequate physical concentration methods. This calls for detailed mineralogical, petrological, elemental, and intergrown investigations as these studies are widely recognized to be the mandatory steps in the selection of an appropriate concentration method and play significant role in developing the cost effective process flow sheets. For mineralogical, petrographic, and elemental analysis XRD, thin section and SEM attached with EDS, and Atomic Absorption Spectrometer and XRF techniques were used. Mineralogical study revealed that Dilband iron ore is mainly composed of 46.27% hematite, 17.41% quartz 14.47% calcite, 9.24% chlinochlore, 10.5% kaolinite, and 1.75% fluorapatite minerals. Three types of iron stones namely hematite-ooides, hematite-peloids, and hematite biosparite were identified from petrographic study. Elemental analysis of different size fractions ranging from 600 xivμm down to 38 μm indicated that Dilband iron ore contains average of 40.18% Fe, 18.34% SiO 2 , 5.32% Ca, and 2.262% Al. Whereas, average analysis of different size fractions on XRF indicated 44.3% Fe, 20.4% SiO 2 , 8.8% CaO, 6.35% Al 2 O 3 , 1.3% P 2 O 5 , and 0.065% SO 2 . From the mineralogical, X-ray mapping with EDS, and elemental analysis data finely dissemination of impurities specially quartz, and fluorapatite in hematite phase was conceived, suggesting that Dilband iron ore is not amenable to upgrade with conventional physical techniques. For assessing the mesh of liberation the physico-chemical attributes of different size fractions along with the examination of coarser to ultra fine particles under reflected microscope, polarized microscope, stereomicroscope and scanning electron microscope attached with EDS at different accelerating voltages and magnifications was conducted. The results of density, magnetic susceptibility, and elemental analysis revealed that mesh of liberation of Dilband iron ore exists below 15 μm particle size. The image analysis of particles and x-ray mapping results confirmed that gangue minerals are so finely disseminated that complete liberation of hematite phase is seldom to achieve even below 10 μm. Particularly quartz (SiO 2 ) phase is so finely disseminated within the matrix of hematite that even in the particles of 2 to 5 μm the 100% hematite phase was not observed. Interlocking of quartz and calcite within the 80% hematite enriched particles was observed in the most of the particles finer than 15 μm. Acid treatment tests of the ore using hydrofluoric acid and hydrochloric acid further confirmed that exact mesh of liberation exist below 2μm. Based on these studies selective flocculation process was envisaged to be the adequate process for beneficiation of Dilband iron ore. For this, determination of energy required for comminuting to probable mesh of liberation, zetapotential measurement, xvcontent of polyvalent metal ions, slurry stablization and finally the selective flocculation was performed. Besides this ore enrichment by means of density and magnetic separation prior to subsequent selective flocculation tests were also attempted. Work index of two size classes of Dilband iron ore was calculated from grindability tests. Based on grindability test results the work index value calculated for 3800μm 80% passing was 11.85 kwh/t and that for 5200μm 80% passing was 9.3 kwh/ton. Ball mill grinding test indicated that dry grinding in open circuit is not efficient and consumes energy of 88.48kwh/t of ore for grinding 1000/40μm to 80% <40μm size. In dispersion tests effect of particle size, solid concentration, pH, dispersants and their doses, stirring speed, and sonication, has been extensively studied. The point of zero charge (PZC) of Dilband iron ore system was determined by using the Zetaphormeter III (CAD E400), and found at 4.25 in acid range. The dispersion results confirmed the significant role of particle size in the slurry stabilization and the optimal conditions for <38 μm Dilband iron ore slurry were found at 10% solid concentration, 10.5 pH , 2000 rpm stirring speed and 5min stirring time. The optimization of dispersant and its dose found quite difficult due to marginal change in sediment wt% , however on the basis of elemental analysis and sediment wt% 6.4k g/ton (i.e. 400% of stacheometric amount of Ca +2 cation present in Dilband iron ore) of EDTA was recommended. Selective flocculation tests of Dilband iron ore slurry using corn starch, potato starch and polyacrylamide (PAA) flocculants were conducted. The selective flocculation results carried out on Dilbnad iron ore suggest that either the selective flocculation process is not the adequate beneficiating technique to upgrade the ore upto the xvirequirements of the Pakistan SteelMills or it achieves nearly half of the beneficiation results expected. Applying flotation to selectively flocculated ore do not upgrade it further due to high intergrowth status of impurities. Pre enrichment attempts were also made to check magnetic susceptibility attribute. It was found to give some better results in separating less intergrwon from highly intergrwon particles of -500 and +315μm size fraction. Results indicated that 60% removal of P 2 O 5 and 30% of SiO 2 is possible with density followed by magnetic separation. Substential decrease in silica and phosphorous content in less intergronwn part suggest that a process flow sheet based on magnetic susceptibility attribute would be a suitable route to some exent for Dilband iron ore.