From ore to yellow cake
Uranium Corporation of India's mining and processing facilities in Bihar's Singhbhum district present a range of capabilities in the specialised field.
SUHRID SANKAR CHATTOPADHYAY
Pictures: Sushanto Patronobish
NATURAL uranium converted into pellets is the vital fuel for eight nuclear reactors in the country, called Pressurised Heavy Water Reactors (PHWRs), two each at Rawatbhatta in Rajasthan, Kalpakkam in Tamil Nadu, Narora in Uttar Pradesh and Kakrapar in Gu
jarat. Heavy water is both the moderator and the coolant in these reactors.
The mining and milling (that is, processing) of uranium ore, the first steps leading to nuclear power generation, are undertaken in India by the public sector Uranium Corporation of India Limited (UCIL), which comes under the administrative control of th
e Department of Atomic Energy (DAE). UCIL itself was founded in 1967 with its headquarters at Jaduguda in east Singhbhum district of Bihar, where the country's first underground uranium mine was established the same year. UCIL manages the mining of urani
um ore and its processing into uranium oxide concentrates, or yellow cake. Yellow cake is sintered and made into fuel pellets at the Nuclear Fuel Complex, Hyderabad.
Rising over the underground mine shaft at Jaduguda, a 41-metre concrete tower housing equipment that enables the movement of men and materials through the shaft.
Uranium is found in nature in the form of minerals. There are more than 100 such minerals present in almost all rocks. The German scientist Martin Heinrich Klaproth isolated uranium in 1789 in a sample of pitchblende. (It was only in 1896 that A.H. Becqu
erel discovered that uranium underwent radioactive decay. The discovery of nuclear fission by Otto Hahn and F. Strassmann in 1939 brought uranium into the limelight.)
The Atomic Minerals Division of the DAE is responsible for uranium prospecting; UCIL mines and processes the ore. Commercially exploitable levels of ore deposits were found at Jaduguda in 1950 and at nearby Bhatin and Narwapahar later in the 160-km-long
and 2-km-wide Singhbhum thrust belt.
Picturesque Jaduguda is 230 km from Calcutta and 24 km from Jamshedpur. It is hemmed in by the Chhotanagpur hills. The valley is awash with paddyfields. The Subarnarekha flows nearby. People belonging to the Santhal, Munda and Ho tribes live in the area.
An overall view of the uranium processing mill and allied facilities in a verdant setting in the Chhotanagpur area.
Although the ore is mined at all the three underground mines, all milling is carried out at Jaduguda. Here the mine and the mill are next to each other.
AS you step into the "cage" in the shaft and the switch is thrown, it is dark all around. The lift speeds down. In a couple of minutes, you step out - 605 metres below the surface of the earth, in an area that is well lit and ventilated. Now you are in t
he heart of the Jaduguda mine.
The tunnels go in different directions. Occasionally, miners with their machinery appear. A conveyor belt transports lumps of uranium ore into a measuring bin which, in turn, empties the ore into a skip. The skip, a huge bucket, is hoisted and the ore is
emptied on the surface.
R.P. Sengupta, General Manager of the Narwapahar mine.
The circular, concrete-lined main mine shaft has a diameter of 5 metres and it is sunk to a depth of 640 m. It was sunk in two stages - the first stage went to a depth of 315 m and the second stage from 315 m. Later, an auxiliary third shaft to a further
depth of 350 m was sunk. The three shafts together go to a depth of 990 m.
J.L. Bhasin, who until his death on August 2 of a heart attack, was the Chairman and Managing Director of UCIL, was in charge of the design of the three shafts. (Bhasin had briefed a group of visiting journalists on the activities of UCIL, just last mont
On top of the shaft and on the surface is a 41-m concrete tower that houses machinery. Two multi-rope friction winders control the skip and the cage. The skip can haul 5 tonnes of ore at a time from a loading station situated 605 m below the surface. The
cage has two decks to transport men and materials.
The Narwapahar mine, one of the most modern in the country, is the only underground mine in India where a ramp as well as a shaft is in use to go down the mine. A signalling system controls the traffic of trucks that go down hundreds of metres to tran
sport mining personnel and the ore.
As you go down the shaft, there is an operating level every 65 m, which is connected to the ore drives. At every alternate level there is a pumping station.
One sub-station with high tension lines of 6,600 volts could be spotted at a depth of 434 m. Elsewhere, in a rock-cut "temple", is a control room with automatic panels.
S.C. Bhowmik, Mines Superintendent, explained how the uranium ore bodies are prised out. "Earlier, we used the hand-drill jack hammer. Now we use electrically operated jumbo drills."
J.L. Bhasin, who was Chairman and Managing Director of UCIL.
The ore extracted from different levels is collected in a central crushing station, 580 m below the ground. The crushing is done in the mine itself. At a nearby washing station, the rocks are sprayed with water. Then a big jaw crusher breaks the ore lum
ps to a size of about 200 mm. The crushed ore is stored in ore pockets below the crushing station, at a depth of 605 m. Here a conveyor belt loads the crushed ore into a measuring bin which, in turn, loads the ore into the skip. The ore is finally hoiste
d to the surface in the skip. This ore is transported to the mill. About 750 tonnes of ore a day is extracted at Jaduguda.
Bhasin stressed the importance given to the safety of the workers. He said: "We lay great emphasis on providing adequate ventilation in all the three mines. The most effective way of controlling radon and airborne radioactive dust from the mine air is pr
oper ventilation." At Jaduguda, the main shaft is used to supply fresh air. There are also two exhaust fans, located on the surface of the eastern and western ends of the mine, which get rid of impure air.
LOCATED 4 km west of Jaduguda is the much smaller Bhatin mine. Entry into this mine, which goes to a depth of 135 m, is by means of an adit and two winzes. Bhatin's uranium deposit is the western extension of the Jaduguda ore body. This mine has been pro
ducing ore since 1986-87 and production now is around 150 tonnes a day. This ore is transported to the Jaduguda mill.
Uranium ore being collected in bins at a depth of 580 metres.
The Narwapahar mine is 12 km away from Jaduguda. It is one of the most modern mines in the country. Bhasin said state-of-the-art technology involving "trackless mining with decline" and "ramps in stopes" was utilised here for ore extraction from depths o
f up to 140 m.
The Narwapahar mine is also an underground one, but the preferred entry here is down a ramp rather than through the shaft. This is the only underground mine in India where such dual-type access is possible. At a production point, a jumbo drill bores into
the rock that contains uranium ore. Trucks transport the ore outside.
The Narwapahar mine was set up at a cost of Rs.216 crores. The 5-m diameter shaft here is sunk to a depth of 355 m. The working level is up to 275 m. The mine now produces about 650 tonnes of ore a day; it is planned to increase production to about 1,00
Yellow cake, or magnesium diuranate, the end product of uranium processing, is sent to the Nuclear Fuel Complex in Hyderabad where it is sintered and made into fuel pellets which power Pressurised Heavy Water Reactors.
According to R.P. Sengupta, General Manager of the Narwapahar mine, trackless mining equipment such as jumbo drill, low profile dump trucks and passenger carriers were introduced for the first time in the country here.
D. Acharya, mine manager, said the jumbo drill used drill bits made of tungsten carbide. As these drill bits cut into the rock, rock particles flew out.
THE mill at Jaduguda is a modern complex with a massive chemical house. It can process 1,000 tonnes of ore a day. Here there is also a sulphuric acid manufacturing unit and a plant to recover byproducts.
A jumbo drill cuts the earth deep down the Narwapahar mine.
According to K.K. Beri, Director (Technical), UCIL, the processing is done in three stages: crushing, grinding and leaching. The ore is crushed and ground and uranium leached into solution by sulphuric acid. The solution is filtered, concentrated and pur
ified, and uranium is precipitated in the form of magnesium diuranate, or yellow cake. Crushing is done in stages in rollers with 4-inch-diameter iron rods and steel balls. The rods and the steel balls impact on the ore, smashing it. The smashed ore is s
ieved into 4-inch, 2.5-inch, and one-inch particles. The 4-inch and 2.5-inch particles are again crushed, to produce one-inch particles, which are mixed with water (to prevent dust formation) and ground.
The grinding produces a slurry which is 40 per cent solid; it is thickened into 60 per cent solid state. This is filtered to 80 per cent solid state." This ore pulp is dissolved in sulphuric acid in a process that lasts about 12 hours at a temperature of
40-to 50-C. Thus, the uranium gets oxidised and dissolved. The left-out solids are gangue minerals - waste products. The uranium-bearing solution is filtered and purified by the ion exchange process of clarification. Subsequently, the uranium is separat
ed as magnesium diuranate after a reaction with magnesia slurry.
A.R. Ray, General Manager (Electrical), UCIL, said that at a certain percentage of the hydrogen value, the uranium gets precipitated. The yellow cake thus formed is sent to the NFC to be sintered into uranium bundles. Once uranium is extracted, magnetite
is recovered. Magnetite has applications in the coal industry.
All the processes after leaching take place in the chemical house. Double filtration is also done in the chemical house and its main purpose is to take out the uranium solution.