DONIMALAI IRON ORE MINE
Donimalai deposit of NMDC is located in Bellary district of Karnatka state,bounded by latitude 15° 2’ 00” & 15° 86’ 30” and longitude 76° 36’ 00” & 76° 38’ 30”, covered under survey of India toposheet no. 57A/12. The deposit is well connected by air/rail & road. The nearest railhead & airport are Toranagallu, which is about 25 km. from the deposit.
The deposit is located on the high lofty parallel ridges rising from a level of 580 mRL with peaks ranging between 975 m RL. to 1050 m RL.The iron ore range of Donimalai belongs to Precamberian Dharwarian rocks of Sandur hill range & runs for a strike length of about 7 km & trending NW-SW with steep dips of 70°-75° towards East.
Geologically the deposit has been divided into two distinct blocks namely South Block & North Block separated by a band of lateritised shale & BHJ of about 50-60 m width. The south block stretches for a total strike length of about 4.0 Km. The southern most part of the south block, commonly known as ‘Beyond MM Section (BMM)’ covers a length of around 2.0 km after which it splits into two limbs. The eastern limb of the splitted ore body is exposed for a length of about 1 km & is called deposit-1, whereas, the western limb, commonly known as deposit 1A, is further extended for about 0.4km. The south block ends to the south against private leasehold in which the main ore body is found to extend for about 100 m.
In north block, considering general strike continuity of deposit 1(of south block) two isolated ore bodies are observed which are commonly known as 2 West (2W) & 3 West (3W) respectively. Similarly on the basis of general strike continuity of deposit 1A (of south block) two isolated ore bodies are observed in this block which are commonly known as 2 East (2E) & 3 East (3E) respectively.
The main ore types encountered in different blocks have been classified as follows:
- Massive ore
- Hard laminated ore
- Soft laminated / biscuity ore
- Blue dust
Donimalai mine commissioned in October 1977 was designed to process 4 Mt/yr ROM ore to produce 1.6Mt of -30+10 mm lumps for export to Japan. It is a highly mechanised open cast mine with 12m (max) bench height and 30m (min) bench width. As the workings have attained grea ter depth the problem of accumulation of water and removal of huge accumula ted was te rock are being faced. Left out ore specially at south block involves considerable development work at the higher horizons (in both the flanges) so that the ore available at lower levels can be exposed for its exploitation. Presently 4.6 m 3 electrical / 4.5 to 5.5 m 3 hydraulic & rope shovel are being deployed in the mines. For transport of ore to the crushing plant and was te to the was te dumps, dumpers of 50t / 85t capacity are being used. For drilling, 152mm diame ter blast hole electrical drills/diesel drills are in use, whereas slurry explosive finds application as blasting agent. The targe ted production from Donimalai mechanized mine is to the tune of 5.9 Mt during 2006-07.
Mining at Donimalai is an in tegra ted sys tem comprising of various discre te activities like Drilling, Blasting, Excavation, Haulage, Crushing, Downhill Conveying, Screening and Loading operations which themselves are sys tems on their own.
Feeding and primary crushing
ROM from mine working benches lif ted to stockpile or directly dumped to the feed hopper (200/250T capacity) of primary crusher (54″x 80″, NORDBERG Make) having capacity 1800 TPH capacity. Dumper platform of primary crusher is having the facilities of EOT crane (100/20T) to carry the weight up to 100 tons. Oversized boulders are handled using rock grapple and J-hook. Crusher is equipped with the hydroset for lifting the mantle and lubricating arrangement with geared oil pumps for pumping the oil in to inner-ou ter bushing of lower and upper mantle section. Hopper below the primary crusher is having the arrangement of high level and low level indicator facilities as well as the window door for repair and inspection.
Scalping and Secondary Crushing
An apron feeder (107) (size w=2000mm X L=6570mm) of capacity 1800 t/h is placed for intermediate feeding of ore from hopper to first belt conveyor no.108 (w=1200mm). Belt Conveyor no.108 is equipped with weightometer, metal detector, and hanging magnet as auxiliary sub assemblies for the measuring of tonnage on the weight, trapping of metal and tromp iron pieces respectively.
Primary scalping screen of medium heavy duty (1830mmx4880mm) of capacity 1800TPH is used to separa te the -100mm ma terial from the primary crushed ore from secondary cone crusher (Standard 7 feet, Set:105 mm, SYMONS Make) of 750 t/h capacity. The oversize ore of +100 mm is crushed in cone crusher at the set of 75mm in open circuit. Cone crusher is connec ted to lubrication sys tem for the need of oil in bushing and hydraulic sys tem for setting the gape of the crusher.
Transportation of ore
Undersize from scalping screen falls on the apron feeder no.115 (1800mm X 3000mm) of capacities 1500 t/h. Apron feeder deliver the ore to belt conveyor no.118(w=1200 mm) capacity=1800 t/h. The combined ma terials from apron feeder and secondary crusher are conveyed through the belt conveyor no.118 to the S teel cord Belt conveyor no.121 (w=1050 mm) in down terrain. Belt conveyor no.121 delivers the ore on to tripper conveyor no.122. Trippers loca ted at the end of belt conveyor no.122 stack the ore in the stockpile of 16000 live capacity. All the downhill conveyors are attached with proper braking arrangements and the skirt rubber sealing to avoid spillage of ma terials from the belt.
Screening plant has four input lines A, B, C & D using Apron feeder and belt conveyors. The old screening plant has three processing circuits (A, B & C) of capacity 600 t/h each. Consequent on modification, the fourth line (D) is added in circuit with the capacity of 800 t/h totaling 2600 t/h designed capacity. Circuit arrangement contains the discharge chu tes of primary stock pile deliver the ore onto the three numbers of apron feeders (No.201) of size 1400 X 4170 mm in series. This arrangement exists in three parallel lines (A, B & C). Two numbers of apron feeders in 4 th line (D) are provided. Three numbers of apron feeders in line A, B & C deliver the ore onto the single belt conveyor (No.202)width=1200mm of capacity 600 t/h. Fourth line D is using two pool of belt conveyors 202D1 and 202D2 of width=1200mm. It is having capacity of 1000 t/h.
Primary and secondary screening
Ore screening is designed to process two stages of screening for sharp and effective separation of lump and fines. Enough screening lengths are provided for higher screening efficiency and ore bed height on the pan.
Primary double deck vibrating screen no. 205 of size 2450 X 5470 mm with aperture 40 mm top deck and 20 mm bottom deck is available in three lines A, B & C while the fourth line has the bigger size 2440 X 6100 mm receive the ore from belt conveyor no. 202 and wash the ore onto the pans. Spray wa ter arrangements are provided on the top of screen through pipes and nozzle assembly. Top deck fraction of ore size +40 mm is oversize product and fed to two stage tertiary cone crusher no.213 through the belt conveyor no.206 for further reduction in size below 40 mm. The middle fraction on the screen is sized lump ore and delivered onto the belt conveyor no.208 for the final dispatch to loading plant through the belt conveyor no.501 (Lump Conveyor). The bottom deck undersize fraction of size -20 mm along with the wa ter on screen is fed to next stage of screening through the launder onto the secondary double deck vibrating screen no.209 of same size of primary screens with aperture 15 mm top deck and 4 mm bottom deck. Top deck fraction of screen no.209 -20 +15 mm is sized lump product and fed to belt conveyor no.210 delivering ore onto belt conveyor no.501 for final dispatch as lump ore. The middle fraction on the screen i.e.-15+4 mm is sized fine ore and delivered onto the belt conveyor no.211 for the final dispatch to loading plant through the belt conveyor no.400 (Fine Ore Conveyor). The bottom deck undersize fraction of size -4 mm along with the water on screen is fed to next stage of density wise size separation through the launder into the classifier.
Ore of +40 mm size is fed to belt conveyor no.206.1 from belt conveyor no.206. Conveyor206.1 fed the ore into tertiary cone crusher no.213(CSS=22 mm) through chu te for size reduction and the reduced product is directly fed to a double deck vibrating screen no.214 with top deck 40 mm & bottom deck 12 mm aperture. Oversize product of the top deck of the screen no.214 is +40 mm and fed to the next tertiary crusher (CSS=20 mm) via belt conveyors no.215 & 216 for further crushing. Crushed product of this tertiary crusher is having the similar arrangement as first tertiary crusher and product distribution of screen af ter second tertiary cone crusher is taken on the same belt conveyor as the screen no.214. Middle fraction product of screen no.214 is taken to belt conveyor no.217 and fed to belt conveyor no.210 through the belt conveyor no.218. The bottom fraction -12mm is taken to conveyor no. 219 and fed to belt conveyor no.400.
Application of spiral classifier is widely available in iron ore fines processing below 4 mm world wide. Spiral classifier no.301.1 of size length 11000mm and fin dia.1830mm has a Cut size=100# is available four in numbers. The coarse fraction of spiral classifier is the underflow of the sys tem and fed onto the dewa tering screen no.301.3 of size=2400 X 4880 mm. The dewa tered ore from the screen no.301.3 is fed onto the belt conveyor no.303 for final dispatch of fines through the belt conveyor no.400. Above described arrangement is similar to all four lines A, B, C & D. The overflow from the spiral classifiers are collec ted in tank no.304 having rich amount of iron value to be recovered. The ultra fine range recovery of iron value is envisaged through the hydrocyclone. Tank no.304 is having two pumps for feeding of slurry from tank to hydrocyclones. There are arrangements of two banks of four hydrocyclones no.306 (Size=600 mm, capacity=60 TPH solid each) with the provision of one working and one standby. One pump from the collection tank feed the slurry in to the bank of four hydrocyclone as per the capacity demands. Overflow from the hydrocyclone directly delivered to the thickener through the pipeline. Underflow of the hydro cyclone is taken to the slow speed classifier no.308. (1, 2) of capacity 60t/h and rotation between 1 to 4 rpm. Overflow of the slow speed classifier is diver ted to the thickener through the pipeline and underflow sand is taken to belt conveyor no.400 directly.
There are two thickener of size 35000 mm diame ter is installed for the recovery of wa ter in circuit and slime disposal. Thickeners are having arrangements of the rake movement and mixing of reagent to the slurry in thickening tank.
Thickener collects the entire slurry genera ted in overflow of hydrocyclones and slow speed classifiers and thickens it up to 45-50% solid w/w. The clean wa ter is collected and pumped to the water tank of capacity 2500 m 3. The thick mud collected in thickener bottom is pumped to the slime pond through the slurry pump.