Characterisation and Processing of Some Iron Ores of India

Lack of process characterization data of the ores based on the granulometry, texture, mineralogy, physical, chemical, properties, merits and limitations of process, market and local conditions may mislead the mineral processing entrepreneur. The proper implementation of process characterization and geotechnical map data will result in optimized sustainable utilization of resource by processing. A few case studies of process characterization of some Indian iron ores are dealt with. The tentative ascending order of process refractoriness of iron ores is massive hematite/magnetite < marine black iron oxide sands < laminated soft friable siliceous ore fines < massive banded magnetite quartzite < laminated soft friable clayey aluminous ore fines < massive banded hematite quartzite/jasper < massive clayey hydrated iron oxide ore < manganese bearing iron ores massive < Ti–V bearing magnetite magmatic ore < ferruginous cherty quartzite. Based on diagnostic process characterization, the ores have been classified and generic process have been adopted for some Indian iron ores.


Introduction
The exponential demand, improved socio-economic conditions, stringent environmental regulations on mining industry and depletion of massive compact high grade anhydrous iron oxide ores necessitated the processing and utilization of sub and low grade iron ore lumps and fines and mine waste dumps. The previous works by IBM [1,2], FIMI [3] and Sahoo et al. [4] on iron ore processing comprises of size reduction-sizing, washing-classification of fines, jigging of fine-chips, crushing-closed circuit grinding to liberate values followed by classification, gravity concentration, magnetic concentration, selective dispersion of gangue-flocculation of iron ore slimes followed by desliming, inverse flotation of iron minerals, selective magnetic collector adsorption followed by magnetic separation, pyro-processing followed by desliming, gravity concentration, magnetic concentration and agglomeration of concentrates. The industrial trend is to reduce the cost, both capital and operative, by enhancing unit capacities, reducing energy consumption, giving flexible flow sheet for pre-concentration of values at coarse sizes at site, as indicated by some of previous reviews of IBM [1,2] and FIMI [3]. Iron ores are categorized as anhydrous iron oxide ores, hydrated iron oxide ores, iron carbonate and iron silicate ores based on iron ore mineralogy. It is also categorized as massive hematite, banded anhydrous iron oxide quartz [BHQ/banded magnetite quartzite (BMQ)], friable hard/soft laminated ores, laterites, beach black iron ore sands, marine oolitic ores, massive magmatic Ti/V magnetite ores, manganese bearing iron ores and ferruginous cherty quartzite by IBM [1,2] and FIMI [3].
The process characterization data of the ores based on granulometry, texture, mineralogy, physical, chemical properties, merits and limitation of process, costs, market and local conditions may aid the mineral processing entrepreneur. The proper implementation of process characterization and geotechnical map data will result in pragmatic sustainable utilization of resource by processing. The onus for solutions to the problems associated with the assemblage of minerals and processes lie with them only. Hence, the paper briefly enumerates the mineral-process characteristics of some iron ores mainly from India, based on ore characteristics, diagnostic amenability test (DAT) and generic process results.

Materials and Methods
Iron ore samples from Donimalai [1], Bellary [3], Chitradurga [4], Hospet [5], CN Halli [6], Sandur [6] from Karnataka, Gonda, Ratnagiri [2] from Maharashtra, Odisha and Goa [7] were collected for the above study. The samples were subjected to standard feed preparation and sampling methods. The DAT is as follows. The original sample was subjected to detailed mineralogical and chemical analysis. A representative portion of the sample as received was dry ground to -0.2 to 0.1 mm based on degree of liberation, wet sieved over 500 mesh to reject slimes [-500 mesh]. The sand fraction was subjected to heavy liquid separation at 2.96 specific gravity using TBE and also the sand fractions, sink and float products were subjected to hand magnet, Frantz Iso dynamic separator at various intensities. Mineral processing studies comprised of controlled crushing and grinding (if needed), wet screening for particle size refining to study the amenability of sample to washing and particle size refining for high grade massive ores and friable clayey iron ores and WLIMS for alluvial sands. The siliceous iron ores and BMQ were subjected to controlled closed circuit grinding with screens to liberation size followed by gravity and magnetic separation processes. The BHQ was subjected to fine grinding to unlock quartz followed by wet high intensity high gradient magnetic separations. The complicated ores like massive hydrated iron oxide ores, Mn bearing iron ores and Ti magnetite were subjected to chemical processing methods.   Table 3. The grade was low at MOG coarser than 0.2 mm due to interlocking and Fe recovery was low at size finer than 0.074 mm due to slime constraints on gravity and WLIMS, leading to pre-concentration at coarse size followed by cleaner step after regrinding to -0.1 mm. The flotation of gangue minerals using xanthate, oleate and amine sequentially from concentrate reduced the impurity level in non float significantly. The ganuge content and fine interlocking nature complicates the process though the processing of BMQ appears simple. Haran et al. [6] produced similar and better results employing dry cobbing at coarse sizes of -6 mm, gravity and concentration at -0.1 mm and inverse flotation to remove S and P after grinding the concentrate to -0.075 mm.   The results are given in Table 5. Figure 1 shows the intimate association of clay with iron minerals. The sample is amenable to simple attrition and washing yielding only sinter grade concentrates.    Table 8 and very fine mineralogical assemblage is given in Fig. 3. Requisite grade concentrates could not be produced due to very fine mutual interlocking and inclusions of chert with hematite. The process comprising of WHIMS with cleaning stage   Figure 4 shows the mineralogical assemblage of the sample. Table 9 gives the DAT and OD test data. Conventional rougher WLIMS at -0.5 mm followed by two stages of cleaner WLIMS of rougher concentrate reground to -0.05 mm could yield a concentrate assaying 55.96 % Fe, 13.86 % TiO 2 , 1.08 % SiO 2 , 9.04 % FeO, 3.05 % Al 2 O 3 , 0.03 % P, 0.03 % S, 1.52 % V 2 O 5 , 0.15 % LOI concentrate with 85 % Fe recovery at 79 wt% yield. Only special plasma metallurgical processes may use this pelletized concentrates. Based on the above chemical, mineralogical characterization and DAT the ores were categorized. The mineral processing test was done based on generic process    [7]. The refractoriness is attributed to chemically bound deleterious values within the lattice of iron minerals besides ultra fine dissemination of gangue at micron-sub micron levels with iron minerals.

Conclusions
The process characterization studies indicated that the tentative ascending process refractoriness of iron ores are massive hematite/magnetite \ marine black iron oxide sands \ laminated soft friable siliceous ore fines \ massive BMQ \ laminated soft friable clayey aluminous ore fines \ massive banded hematite quartzite/jasper \ massive clayey hydrated iron oxide ore \ manganese bearing iron ores massive \ Ti-V bearing magnetite magmatic ore \ ferruginous cherty quartzite. Each ore is unique.
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