A peep into the stratigraphy of iron ore can give some scope of locating iron ore at deeper level, which is not mineable with present mining technology. There are other resources in the freehold areas which could be included in the mining leases to add to the dwindling resources. The crises of meeting the needs of steel making industries, we need to focus on other areas within the existing mines, for recovery of iron ore.
The iron ore forms one of the most important commodities for economic growth of a country. India is bestowed with substantially large deposits of iron ore. As per UNFC system, the total resources of haematite as on 1.4.2010 are estimated at 17,882 million tonnes of which 8,093 million tonnes (45%) are under ‘reserves’ category and the balance 9,789 million tonnes (55%) are under ‘remaining resources’ category. By grades, lumps constitute about 56% followed by fines (21%), lumps with fines (13%) and the remaining 10% are black iron ore, unclassified, not-known and other grades. Major resources of haematite are located in Odisha – 5930 million tonnes (33%) (IBM MYB 2014). In Odisha the iron ore deposits are spread over four different areas, viz: Hirapur in Nabarangpur, Daitari-Tomka in Jajpur, Badampahar – Suleipat – Gorumahisani in Mayurbhanj and Joda-Koira in Keonjhar and Sundergarh districts of Odisha. Growth of iron ore mining was very sluggish till about 1992. However, with the gradual unfolding of economic liberalization in early nineties the iron ore market saw an increase in the demand for iron ore due to setting up of sponge iron industries and to some extent expansion of steel plant capacities. After 2001-02 there was a spurt in the production of iron ore in India and other iron ore producing countries, when domestic demand and export to China in particular increased rapidly. Odisha used to produce just 2 million tonnes of iron ore in 1955 which was raised to 77 million tonnes in 2011.
In the recent past, multiple issues have also adversely influenced the steel sector, viz. cancellations of iron ore and coal mine allocations, delays in land acquisition, sluggish environmental clearances, which resulted in many of the projects facing significant time overruns which manifested in financial liabilities. Post 2011, global prices of steel began to decline, signaling the beginning of a slow-down in the global steel industry triggered by slump in global demand and over capacities in a number of countries including China. By July 2015, prices of Indian iron ore had fallen by 50% compared to January 2011. This significant structural imbalance between demand and supply also affected large number of Indian companies.
PROJECTED REQUIREMENT OF IRON ORE
It won’t be overstatement to say that rapid industrial development, from a small capacity of 22 MT in FY 1991-92 of steel, India has become one of the five the largest steel producers in the world with a production of 91 MT in FY 2015-16. There is significant potential for growth given the low per capita steel consumption of 61 Kg in India, as compared to world average of 208 Kg. Indian economy is growing, though wobbly, with focus on infrastructure and construction sector, affordable housing, expansion of railway networks and development of ports and domestic shipbuilding industry, are expected to create significant demand for steel in the country. It is predicted that at the current rate of GDP growth, the steel demand will grow threefold in next 15 years to reach a demand of 212 – 247 MT by 2030. However, even with this demand of finished steel by 2030, India’s per capita consumption would reach only to 160 Kg, lower than the current global average of 208 kg. About 300 Mt of good grade iron ore (+63% Fe) goes to make 200 Mt of finished steel. It has been estimated that at this rate of mining the proven reserve of iron ore in India may last about 27 years only, not counting the reserves of magnetite though.
Odisha alone has 5930.232 million tonnes of iron ore resources with a cutoff grade of 60% Fe. In the beginning of mining for iron ore there was a tendency to mine out the high grade massive ore and hard laminated ore, not caring to blend with the relatively lower grades. With the fast depletion of proved reserves of high grade, the available resources and the grade have now dwindled down. The scanning for new deposits of iron ore is a distant possibility but to upgrade the low grade iron ore can be a practical alternative. A peep into the stratigraphy of iron ore can give some scope of locating iron ore at deeper level, which is not mineable with present mining technology. There are other resources in the freehold areas which could be included in the mining leases to add to the dwindling resources. The crises of meeting the needs of steel making industries, we need to focus on other areas within the existing mines, for recovery of iron ore, such as: 1. Remove the overburden if it consists of protolith or subgrade ore and beneficiate, 2. Utilise iron ore fines. 3. Mining the float which in many cases is high grade ore after wash, 5. Look for iron ore underlying the stratigraphically younger formation the Upper Shale.
IRON ORE FINES AND SLIMES
During washing and sizing of the ore, slimes with less than 0.21 mm size are generated and disposed off into tailing ponds. It is estimated that around 10 million tonnes of slimes are being generated per year in the processing of hematite ore and dumped as tailings containing around 48-62% of Fe. Beneficiation and utilization of these slimes still remains a challenge for the metallurgist.
The increasing need to utilize the slimes is reflected in the shift in steel production from basic blast furnaces to electric arc furnace technology. In the USA, around 40% of steel is produced in electric arc furnaces by using iron ore pellets. Pellets are ideal feed material for direct reduction iron (DRI) plants. However the use of pellet in Indian steel plants is very limited. The fines and tailings are potential sources to produce pellet grade concentrate after suitable upgradation. Another source of pellet feed concentrate is from low and off grade ores such as banded haematite quartzite (BHQ) and banded haematite jasper (BHJ). All these materials can be beneficiated to yield the pellet making material. (Nayak, 2013) There is a pressing need to utilize low grade iron ores including slimes and dump fines which are stockpiled at different mine heads. Hence, optimal use of existing low grade iron ore resources with special emphasis on conservation of high grade ores will be encouraged. Because of the finer particle size (<0.15 mm) it is expected that the mineral phases present in the slimes will be in liberated forms which may ease the beneficiation process without applying any comminuting action. Alumina in Indian iron ore slimes occurs in the form of two distinct mineral constituents namely, gibbsite (hydrated aluminum oxides) and kaolinite (hydrated aluminium silicate) (Nayak, 2013). Impetus should be given to Pellet industry as it helps in mineral conservation by acting as direct feedstock in Blast Furnace in place of high grade iron ore.
SUBGRADE IRON ORE
Lessees of iron ore mines are under instruction from Indian Bureau of Mines to explore and assess the low grade iron ores at different cut off, upto the threshold grade of 45% Fe. A large part of the Iron ore mineralized zone in Odisha has been leased out with small freehold areas lying in between. There are pockets of low grade ores in these areas which have not been explored. It is essential to define a clear cut picture of the resources of low grade (45%Fe to 55%Fe) iron ores in different cut off categories, so that blue print for beneficiation of these ores could be prepared with the participation of the lessees and private exploration agencies. Unless done in a war footing, it may take a decade from now to have a complete panoramic view of the sub-grade iron resources and other occurrences which have not been mineable for some reason or the other.
In several mines a part of the high grade ores are not mineable due huge thickness of overlying low grade ores. Attempts have been made by mineral processing engineers in some laboratories to upgrade the banded haematite quartzite/jasper successfully. It may not be economic in the present downturn in the iron ore market, though it can be applied in the future. But in a changed scenario when the steel market grows beneficiation can be economically effective means of removing the overburden and beneficiate while the high grade ore below the overburden is mineable. Overburdens in many cases are either banded haematite jasper, banded magnetite quartzite or ferruginous laterite. Attempts have been made by mineral processing engineers in some laboratories to upgrade the banded haematite quartzite/jasper successfully. It may not be economic in the present depression in the iron ore market, though it can be applied in the future. Mishra et al (2007) have observed that beneficiation studies undertaken on the BHQ iron ore sample of Hospet area to enrich the iron content and make it suitable for pellet making. The sample on an average contains around 38% Fe, 45 % SiO2 and 0.5% Al2 O3. The XRD studies reveals that the minerals associated in the sample are magnetite, hematite and quartz. Mishra et al (2007) attempted various beneficiation studies such as hydrocyclone, magnetic separation, spiral, and column flotation have been carried out to recover good grade iron concentrate. Their studies indicate that the sample needs to be ground to finer sizes to be conducive for liberation of gangue materials. The results of their studies indicated that an iron concentrate of 64-66% Fe at 42-44 % recovery, could be obtained.
UPPER SHALE: The occurrence of iron ore in association with the stratigraphically younger Upper Shale horizon (Sagasahi deposit) has come to light during the exploration by GSI in the Koira sector of the Horse Shoe belt of Odisha. The iron ore is different texturally and genetically and its grade is above 60% Fe. It also has opened the vistas of finding BHJ associated iron ore, stratigraphically below the Upper Shale. Though an expensive proposal it may be worthwhile to attempt at stratigraphic drilling purely an academic exercise to ascertain the depth of iron ore underlying the Upper Shale associated iron ore in the core of the Horse Shoe belt. Such exercises if proved the occurrence of iron ore underlying ferruginous Upper Shale, should be supported by eco-friendly viable underground mining technique for gainful exploitation of haematite/magnetite ore deposits locked under huge thickness of Upper Shale or BHQ/BMQ.
Conclusion: The National Mineral Policy 2008 emphasises the importance of beneficiation. Attention will be given to beneficiation and agglomeration techniques to bring lower grades and finer size material into use. Research organisations, including the National Mineral Processing Laboratories of the Indian Bureau of Mines will be strengthened for development of processes for beneficiation and mineral and elemental analysis of ores and ore dressing products. The total resources of iron ore (hematite) in the state as on 1.4.2010 are estimated at 5930 million tonnes (IBM Mineral Year Book 2014) as against 3,789 million tonnes inventoried by IBM in 2005. As per the compendium of mineral resources of Orissa, Govt of Orissa (2009) the total resource was 5231 million tonnes. So there has been steady increase of resources in view of continued exploration. The total resource increase by as much as 2141 million tonnes over 5 years is substantial largely contributed by depth-wise drilling. Orissa has the lion`s share of iron ore resources in the country. A programme should be drawn up for re-assessment of iron ore resources both in the leasehold and free hold areas taking the cut off grade of 45% Fe, with the GSI as the nodal agency, in association with MECL IBM and Directorate of Geology, Odisha. All other stakeholders like FIMI, EZMA, OMC, SAIL, Tata Steel, NMDC, IMMT, MECON should also be associated in such exercise. There is no talk of evaluation of iron ore deposit like Hirapur in Nawrangpur district and magnetite in Mayurbhanj diistrict. Huge resources of float iron ore need to be explored to add to the resources of high grade iron ore. Assessment of BMQ is emphasized owing to its amenability to beneficiation. The exploration for iron ore can now be supported by the National Mineral Exploration Trust hence one can be optimistic about results. All these measures taken without much delay will not be enough if the infrastructure in the mining areas does get a facelift. This includes more roads in and out of the mineralised belt, railways network and water for beneficiation of low grade ores.
Nayak Nirlipta. P. 2013 Mineralogical Constraints in Beneficiation Of Low Grade Iron Ores of Barsua, Eastern India. IJEIT,V3/5 p109-113.
Mishra, B.K., Reddy, P.S., Das, B., Biswal, S.K., Prakash, S., Das, S.K. 2007 Issues relating to characterization and beneficiation of low grade iron ore fines. Steel World.
IBM 2014 Indian Mineral Year Book. Iron Ores.