Dr. RK Upadhyay

In the recent past a paradigm shift has taken place in ore evaluation from manual execution of geological procedures, ore reserve estimation, mine planning and related activities to computer-aided resource evaluation and mine planning and scheduling processes in the Indian mining and mineral sector. Noamundi and Joda East Iron ore mines of Tata Steel are no exception and a culture of continuous improvement is practiced extensively in those areas. The paper discusses the major improvements in those areas which were launched to refine the ore evaluation processes and grade assurance methods in the iron ore mines of TSL. Also discussed are the structural-cum-topographic control in understanding the genesis of iron ore occurrences in adjoining areas as well as its implications in exploration programs. Noamundi and Joda East Iron mines, situated on the eastern limb of the major Iron Ore Group (IOG) synclinorium within Singhbhum-Orissa Iron Ore Cratonic block (SOIOC), together cater to 100% of iron ore requirements of Tata Steel's Plant at Jamshedpur. These high grade hematite deposits are being extracted by open pit mining methods to meet the plant's requirement. Owing to the complex geological structure, the grades and beneficiation characteristics of the ore differ markedly over short distances. Thus, continual advancement of geological knowledge as a result of new exploration and pit-mapping with an overview of ore genesis provides a new and improved solution to the varied geological and grade problem thus helping to define the mineable ore reserves.

During the mining of iron ore at Khondbond Mines, Tata Steel, some flaky ores are produced which could not be used for sponge grade applications. High alumina content of these ores also prevents them from sintermaking applications. Studies were undertaken at R&D to develop a suitable process flowsheet for upgrading the ore for lowering the alumina to below 2% for use in sintermaking. Characterisation studies of the ores revealed that the alumina was contributed mostly by platy shale clay, the iron minerals mostly by martite and hematite and silica by quartz. Clay and iron minerals were the main contributors of phosphorus in the ores. Studies showed that crushing the particles to even below 1 mm size and de-dusting, the liberation of alumina would not improve significantly. Presence of martite indicated that magnetic separation could be a viable beneficiation process. Considering the paucity of water at Khondbond mines, dry beneficiation process was first attempted. Two-stage dry classification followed by dry magnetic separation (at-1 mm size) is expected to produce concentrate with less than 2% alumina product with a weight recovery of 55% from a feed having 4.3% alumina. Due to the low yield expected from dry beneficiation process, wet beneficiation techniques were also explored. Crushing followed by a combination of Jig for-10 +1 mm size fraction, Spiral for-1+ 0.15 mm size fraction and Multi Gravity Separator for-0.15 mm fraction process could produce a concentrate of about 2.35% alumina with 70% recovery from a feed of 3.8% alumina.

Geological aspects, particularly mineralogy and ore genesis of different iron ores have important roles to play in understanding their behaviour during processing and decide suitable beneficiation method for particular type of ore so to produce desired quality end products. The implications of different geological aspects and mineralogical characteristics specific to ore types in mineral beneficiation have been outlined in this paper. Experiments indicated that iron ores, such as massive hard ores, laminated hard ores, fine powdery ore and blue dust ore, do not require complicated processing, however at the other end; sub grade ores, such as flaky, friable, shaly, ochrous, powdery, lateritic and goethitic ores having low iron and high alumina content, require specific beneficiation treatments before their use as direct or as agglomerates in the blast furnace feed. While processing, different ore types need treatment differently for their up gradation. Hence, in addition to the conventional methods of processing such as crushing, screening and washing, advanced beneficiation techniques using concepts of gravity and magnetic separation have found their specific applications for beneficiation of different types of ores, based upon their physicochemical and mineralogical characteristics. Geological setup of the deposits and mode of occurrences of different ore types, physical, chemical and mineralogical characterisation and extensive beneficiation experiments conducted on Indian iron ores have established that quality of lumps can substantially be up graded through simple processing and log washing. On the other hand, for fines ores, Jigging has been found to be the best suitable method. Slime beneficiation requires combination of processes and treatment through hydrocyclones, multigravity separation, magnetic separation and sink float methods, etc. These applications would help not only to recover more values from the inferior grades of iron ores but also to conserve and preserve the natural resources too.