Edmund Halley

Born November 8th, 1656 in Haggerston, England to a prosperous family, young Edmund Halley received a private education before enrolling in St. Paul's school. While in school, Edmund excelled in mathematics and astronomy. At the young age of 17, he enrolled at The Queen's College, Oxford to study under the Astronomer Royal of the time John Flamsteed

By 1676, Halley had dropped out of university to begin making his own contributions to the field of astronomy. After publishing his star chart of the southern oceans in 1678, he was granted a Master of Arts from Oxford by decree of King Charles II. Anchoring his position as a great astronomer, Halley was also elected fellow of the Royal Society as one of the youngest members.

At the young age of 22, he sailed to St. Helena where he discovered a star cluster in Centaurus and mapped the stars of the southern hemisphere, allowing sailors to navigate the world's oceans. Halley devised a clever way to calculate the distance from the Earth to the Sun. By carefully timing how long it took Venus to cross the Sun's disk, he was able to give a real distance to the astronomical unit; about 93 million miles. He used this newfound information to accurately calculate the size of the solar system for the first time.

Pouring over ancient Greek recordings of stars, Halley compared their observations to what he saw in the night sky some 1800 years later. He discovered that the stars the Greeks had cataloged were not in the same position as the stars he observed, but had moved. Halley concluded that the stars are not fixed in one position as once thought, their motion only apparent to the observer after many centuries.

Continuing his pioneering work in observational astronomy, Halley published in 1705 A Synopsis of the Astronomy of Comets, in which he described the parabolic orbits of 24 comets that had been observed from 1337 to 1698. He showed that the three historic comets of 1531, 1607, and 1682 were so similar in characteristics that they must have been successive returns of the same visitant—now known as Halley’s Comet—and accurately predicted its return in 1758.

His Early Career and Travels

In 1675, Halley became the assistant for John Flamsteed who was first Astronomer Royal at Greenwich Observatory. One of Halley’s many tasks was to assign numbers to stars using Flamsteed’s number system for identification and cataloguing purposes. A year later, he travelled to the volcanic tropical island Saint Helena, in the South Atlantic Ocean. He brought with him a large sextant and some telescopic sights so he could set up an observatory and study and catalogue the stars in the Southern Hemisphere. It was during his stay in St. Helena that he carefully observed the transit of Mercury across the sky. He realized that Venus, moving in the same way, could then be used to calculate the size of the Solar System.

Halley returned to England in 1678 and a year later he went to Danzig at the request of the Royal Society to help resolve a dispute between Robert Hooke and Johannes Hevelius. As Hevelius did not utilize a telescope in his observations, Robert Hooke questioned his findings. Halley stayed with Hevelius to observe his findings and verify his conclusions

That same year in 1679, Halley published “Catalogue Stellarum Australium”, a catalogue of the Southern Hemisphere stars which he observed while in St. Helena. His publication was so extensive that it included 341 stars that could be viewed only in the Southern Hemisphere. Flamsteed gave him the title “The Southern Tycho” in reference to the well-known sixteenth century astronomer, Tycho Brahe. Halley also attained his Master’s Degree from Oxford and was elected as a Royal Society Fellow aged 22.

Halley conducted many lunar observations which took up most of his time. Aside from his lunar studies, he also became interested with problems relating to gravity. One issue in particular that concerned him was finding a proof for the laws of planetary motion. In 1684, he travelled to Cambridge to talk the issue over with Sir Isaac Newton, only to find out that Newton had already managed to solve the problem, stating that the planets’ orbits would be elliptical. Halley naturally wanted to see the calculations Newton used but Newton wasn’t able to locate them. Newton then wrote a short treatise entitled “On the Motion of Bodies in an Orbit” in 1684 which explained his calculations. This work was later expanded on by Newton, becoming the famous work “Philosophiæ Naturalis Principia Mathematica” in 1687 which Halley helped to publish.

Later Life and Comet Predictions

In 1698, he was given permission to take command of the sailing ship Paramour and travel to the South Atlantic Ocean to find out more about the laws that govern the variation of the compass. The first expedition was cut short due to unrest among the crew and a second expedition began in 1699. His magnetic charts of Atlantic Ocean and parts of the Pacific Ocean were published in “General Chart of the Variation of the Compass” in 1701.

In 1704, Halley finally became Savilian Professor of Geometry at the University of Oxford, after missing out on this prestigious appointment earlier in his career. He published “Synopsis Astronomia Cometicae” (A Synopsis of the Astronomy of Comets) in 1705. This work detailed the parabolic orbits of 24 comets that had been observed from 1337 to 1698. It also stated that the comet sightings of 1531, 1607, and 1682 were of the same comet, which orbits the sun every 75-76 years and he correctly predicted it would return in 1758. When the comet did return it became known as Halley’s Comet.

He devised a method of observing the transit of Venus across the sun which would next be observed in 1761 and 1769. These observations would then be used to make an accurate calculation of the distance from the Earth from the sun.

Halley became Astronomer Royal at Greenwich Observatory, succeeding John Flamsteed in 1720.

His death

He died on January 14, 1742 aged 86 and sadly, did not live to see the return of the comet that was named in his honor. Halley’s Comet will next appear in the night sky in the year 2062.

 

Tycho Brahe

Tycho Ottesen Brahe was born into a highly aristocratic, very wealthy family on December 14, 1546. Tycho was the second of the couple’s 12 children. Something rather remarkable happened to Tycho in his second year of life – he was kidnapped by his uncle and aunt, Jørgen Brahe and Inger Oxe, when his parents were away from home. Tycho’s uncle and aunt were childless, and they believed that Jørgen was entitled to a lawful son and heir to his estates. Tycho’s natural parents eventually agreed to this, so Tycho was raised by his uncle and aunt as if he were their own son.

  Tycho’s foster mother, Inger, had come from an academic family and she persuaded her husband that Tycho should receive an academic education. Tycho began school aged six or seven, a grammar school where he probably learned the classical languages, mathematics, and the Lutheran religion.

In April 1559, aged 12, Tycho matriculated at the University of Copenhagen. He studied a general classical curriculum for three years, during which time he became increasingly absorbed in astronomy. He bought a number of important books in the field, including Johannes de Sacrobosco’s On the Spheres, Peter Abian’s Cosmography, and Regiomantus’s Trigonometry.

Tycho’s interest in astronomy began with the solar eclipse of August 21, 1560. In Copenhagen this eclipse was barely noticeable – less than half of the sun was covered. The eclipse inspired Tycho not because it was spectacular, but because astronomers had predicted exactly when it would happen. Tycho was fascinated, and wanted to learn how he too could make predictions like this.

Using just a basic, fist-sized celestial sphere and string, Tycho discovered that tables of predictions of planet positions sourced from the works of both Ptolemy and Nicolaus Copernicus were rather unsatisfactory.

In August 1563, aged 16, Tycho began his first logbook of astronomical observations. He observed a one-in-twenty-year conjunction of Jupiter and Saturn, and again noted errors in both Copernicus’s and Ptolemy’s predictions. Using Ptolemy’s data tables, the conjunction timing was wrong by a month!

It became Tycho’s goal to produce truly accurate predictions of planetary positions based on accurate observations. Although he did not quite succeed in his ambition to make all his measurements accurate to within one arc minute, many of them did meet this standard, and his observations were a phenomenal five times more accurate than his peers made.

Tycho made his first significant discovery on November 11, 1572. Observing the night sky from an uncle’s home, Tycho was amazed to see a new light brighter than Venus in the sky.

He studied the new heavenly body for a year. He deduced that it was a star because, unlike closer bodies such as the planets, its position relative to the other stars did not change.

In 1573, Tycho’s name became well-known in astronomical circles when he published De nova stella – The New Star. Although other people had also observed the new star, Tycho published the most comprehensive study of it. Tycho’s new star gradually faded until, after a year, it was no longer visible to the naked eye.

The Great Comet of 1577 made people fearful, because comets were seen as bad omens.

Tycho recorded the comet’s positions between November 13, 1577 and January 26, 1578, after which he could no longer see it.

Tycho used Hipparchus’s parallax method to measure the comet’s distance from the earth.

Unfortunately, there was insufficient parallax for him to pin down the distance, but he was able to say that:-

The comet was much farther away from our planet than the moon is – at least six times as far. This refuted the popular idea that comets traveled within the earth’s atmosphere.

The comet’s tail always pointed away from the sun.

The comet’s path was associated with the sun, not the earth.

The comet had another far-reaching consequence for Tycho and science. It prompted him to begin making observations with a view to producing his own star catalogue to replace Ptolemy’s ancient work.

Tycho accurately recorded the positions of 777 stars by 1592, and he eventually amassed data for 1,006 stars. Tycho’s catalog was later worked on and published by Johannes Kepler. 

In Prague, Tycho gave Johannes Kepler a job as his assistant. Together, they began working on a new star catalog, but it was slow work. Tycho Brahe died aged 54 on October 24, 1601 in Prague. The catalog was eventually published by Kepler in 1627 as the Rudolphine Tables. These were by far the most accurate astronomical data tables ever published, with planetary data and 1,006 star positions. The majority of stars were cataloged to within one arc minute accuracy, which had been Tycho’s ambition.

Kepler's Laws of Planetary Motion

Kepler was assigned the task by Tycho Brahe to analyze the observations that Tycho had made of Mars. Of all the planets, the predicted position of Mars had the largest errors and therefore posed the greatest problem. Tycho's data were the best available before the invention of the telescope and the accuracy was good enough for Kepler to show that Mars' orbit would precisely fit an ellipse. In 1605 he announced The First Law:

Planets move in ellipses with the Sun at one focus.

The radius vector describes equal areas in equal times. (The Second Law)

Kepler published these two laws in 1609 in his book Astronomia Nova.

For a circle the motion is uniform, but in order for an object along an elliptical orbit to sweep out the area at a uniform rate, the object moves quickly when the radius vector is short and the object moves slowly when the radius vector is long.

On May 15, 1618 he discovered The Third Law:

The squares of the periodic times are to each other as the cubes of the mean distances.

This law he published in 1619 in his Harmonices Mundi . It was this law, not an apple, that led Newton to his law of gravitation. Kepler can truly be called the founder of celestial mechanics.

 

Nicolaus Copernicus

Nicolaus Copernicus was a Polish astronomer known as the father of modern astronomy. He was the first modern European scientist to propose that Earth and other planets revolve around the sun, or the Heliocentric Theory of the universe. 

Prior to the publication of his major astronomical work, “Six Books Concerning the Revolutions of the Heavenly Orbs,” in 1543, European astronomers argued that Earth lay at the center of the universe, the view also held by most ancient philosophers and biblical writers. 

In addition to correctly postulating the order of the known planets, including Earth, from the sun, and estimating their orbital periods relatively accurately, Copernicus argued that Earth turned daily on its axis and that gradual shifts of this axis accounted for the changing seasons. 

Nicolaus Copernicus was born on February 19, 1473 in Torun, a city in north-central Poland on the Vistula River. Copernicus was born into a family of well-to-do merchants, and after his father’s death, his uncle–soon to be a bishop–took the boy under his wing. He was given the best education of the day and bred for a career in canon (church) law. At the University of Krakow, he studied liberal arts, including astronomy and astrology, and then, like many Poles of his social class, was sent to Italy to study medicine and law. 

The cosmology of early 16th-century Europe held that Earth sat stationary and motionless at the center of several rotating, concentric spheres that bore the celestial bodies: the sun, the moon, the known planets, and the stars. From ancient times, philosophers adhered to the belief that the heavens were arranged in circles (which by definition are perfectly round), causing confusion among astronomers who recorded the often eccentric motion of the planets, which sometimes appeared to halt in their orbit of Earth and move retrograde across the sky. 

In the second century A.D., the Alexandrian geographer and astronomer Ptolemy sought to resolve this problem by arguing that the sun, planets, and moon move in small circles around much larger circles that revolve around Earth. These small circles he called epicycles, and by incorporating numerous epicycles rotating at varying speeds he made his celestial system correspond with most astronomical observations on record. 

The Ptolemaic system remained Europe’s accepted cosmology for more than 1,000 years, but by Copernicus’ day accumulated astronomical evidence had thrown some of his theories into confusion. Astronomers disagreed on the order of the planets from Earth, and it was this problem that Copernicus addressed at the beginning of the 16th century. 

Sometime between 1508 and 1514, Nicolaus Copernicus wrote a short astronomical treatise commonly called the Commentariolus, or “Little Commentary,” which laid the basis for his heliocentric (sun-centered) system. The work was not published in his lifetime. In the treatise, he correctly postulated the order of the known planets, including Earth, from the sun, and estimated their orbital periods relatively accurately. 

In “Six Books Concerning the Revolutions of the Heavenly Orbs,” Copernicus’ groundbreaking argument that Earth and the planets revolve around the sun led him to make a number of other major astronomical discoveries. While revolving around the sun, Earth, he argued, spins on its axis daily. Earth takes one year to orbit the sun and during this time wobbles gradually on its axis, which accounts for the precession of the equinoxes. 

Nicolaus Copernicus died on May 24, 1543 in what is now Frombork, Poland. He died the year his major work was published, saving him from the outrage of some religious leaders who later condemned his heliocentric view of the universe as heresy. 

It was not until the early 17th century that Galileo and Johannes Kepler developed and popularized the Copernican theory, which for Galileo resulted in a trial and conviction for heresy. Following Isaac Newton’s work in celestial mechanics in the late 17th century, acceptance of the Copernican theory spread rapidly in non-Catholic countries, and by the late 18th century the Copernican view of the solar system, it was almost universally accepted. 

Evolution of Telecom Industry in India

Evolution of Telecom Industry in India

Telephone services in India began on a small scale with the commissioning of a 50-line manual telephone exchange in 1882 in Kolkata. This was less than five years after the invention of the telephone by Alexander Graham Bell. 

Independent India, after partition, on 31st March 1948 was left with very few (7330)

telegraph offices. Departmental exchanges were 321 with 82985 telephones and

2166 private branch exchanges with another 38155 telephones (DoT Publications).

During that time some systems were installed and operated by the princely states. 

The urgency of self-rule inspired opening of public call offices in cities and

important towns. “There were 537 such public call offices throughout the country.

The combined Post and Telegraph Department then had a fixed assets to the tune

of Rs. 315.1 million, of which Rs. 292.6 million were for telecommunication

services. There were 80873 miles (129395 km. approximately) of telegraph and

trunk telephones lines and 9746 miles of local telephone lines on that date”.

The telecommunication development of a country is best judged by the number of

its telephones. On the 1st January, 1951, there were approximately about 74.8

million telephones in the entire world. Out of these, India had only about 160,000.

(Refer table). United States had almost half of the total telephones all over the

world. This was one reasons for its international dominance in communication

technology at the time.

 Number of Phones in Big Cities of India

S.no.        City No. of Phones

1 Bombay     46,181

2 Calcutta     35,794

3 Delhi     14,852

4 Madras     11,102

5 Ahmedabad  13,782

6 Hyderabad      2,376

7 Bangalore      2,333

8 Lucknow      2,327

9 Kanpur      2,285

10 Nagpur      1,116

 

India’s poor showing in the field of telephones at the time of freedom was as much

a reflection of the state of the national economy as of its backwardness. Initially for

the government, postal department was the priority area. Yet it was the earnings of 

the telephones that made up for the loss of the posts. Universalization of phone had

a long way to go, at that time money was the main problem. 

After the implementation of the Federal Financial Integration Scheme on 1st April, 1950, the administration of the entire network of telegraphs and telephone systems of the nation, including those that previously existed in the former princely state became a major adventure. In 1950 the number of telephone exchanges absorbed from princely states was 196. This system which was working with different degrees of efficiency could fit into the general telecommunication network. The installed capacity of these 196 exchanges was 13,362 lines with 11,296 working connections. Soon after the absorption an attempt was made to improve their technical efficiency by replacing absolute and unserviceable equipment and lending well-qualified and experienced staff. Isolated exchanges were integrated with the general pool. The more complicated task was the accusation of the staff. Their final absorption into the different cadres of service in posts and telegraph was a major step. By April, 1972, the telecommunications accounts were separated. Simultaneously the department also started preparing the balance sheet annually. 

In 1975 the department of telecom was separated from P & T. DOT was

responsible for telecom services in entire country until 1985 when Mahanagar

telephone Nigam Ltd was carved out of DOT to run the telecom service of Delhi &

Mumbai.

India had approx. 82 000 telephone connections at the time of independence (1947) and by 1984 the number of connections had slowly risen to 3.05 million. India's telecom network was notoriously unreliable and only available to a small section of households along with the corporate sector.

In the year 1985, the DOT was set up to provide domestic and long distance telephone services. The telecom services have been recognized the world-over as an important tool for socio-economic development of a nation and hence telecom infrastructure is treated as a crucial factor to realize the socio-economic objective in India. Accordingly, the DOT has been formulating development policies and projects for the accelerated growth of the telecommunication services. The Department is also responsible for frequency management in the field of radio connection in close coordination with the international bodies. It also enforces wireless regulatory measures by monitoring wireless transmission of all uses in the country. The DOT has been the premier telecom service provider in India with its presents through the length and breadth of the country. The Department in 1986 reorganized the Telecommunication circles with the SSAs as basic units. It was implemented in a phased manner. With a view to deciding matters of policy, a separate telecom Board, named the Telecom Commission, was also setup. The telecom commission was constituted in 1989. The Telecom commission was set up by the government of India with necessary executive, administrative and financial powers to deal with various aspects of Telecommunications.

In 1990 the telecom sector was opened by the government for private investment as a part of Liberalization Privatization Globalization policy.

The telecom sector was a government monopoly until 1994 when liberalisation gradually took place. Cellular service was launched in November 1995 in Kolkata. Therefore, it became a necessary to separate the Government’s policy wing from its operations wing. The Government of India seperated the operations wing of DoT on October 01, 2000 and named it as Bharat Sanchar Nigam Limited. Many private operators, such as Reliance India Mobile, Tata Telecom, Hutch, BPL, Bharti, idea etc., successfully entered the high potential Indian telecom market.

Homi Jahabgir Bhabha

Bhabha Homi Jehangir

Homi Jehangir Bhabha was born on 30 October 1909 in a wealthy Parsi family of Bombay

Bhabha attended the Cathedral and John Connon Schools in Bombay. After passing Senior Cambridge Examination at the age of 15 Bhabha entered the Elphinstone College in Bombay and later the Royal Institute of Science, also in Bombay. In 1927 Bhabha joined the Gonville and Caius College in Cambridge.

 Bhabha was taught by Paul Adrien Maurice Dirac (1902-84), who was Lucasian Professor of Mathematics (1932-69) at Cambridge and awarded the Nobel Prize in Physics in 1933 with Erwin Schrodinger (1887-1961) for their work in quantum theory. Bhabha joined the Cavendish Laboratory, from where he obtained his Ph.D. in theoretical physics.

The important contributions made by Bhabha while working at Cambridge have been summarised by G. Venkataraman (in his book, Bhabha and His Magnificent Obsessions, Universities Press, Hyderabad, 1994) as :

The explanation of relativistic exchange scattering (Bhabha Scattering).

• The theory of production of electron and positron showers in cosmic rays (Bhabha-Heitler theory).
• Speculation about the Yukawa particle related to which was his suggestion of the name meson.
• Prediction of relativistic time dilatation effects in the decay of the meson.

In 1939 when the Second World War broke out, Bhabha was in India. He came for a short holiday. However, the war changed his plan. Most of the scientists in England had to take part in war activities and there was no scope for doing basic research. So Bhabha had to abandon his plan to return to England to resume his research work at Cambridge. It may be recalled here that Prasanta Chandra Mahalanobis (1893-1972) who after completing the Physics Tripos made arrangement to work under C.T.R. Wilson, the inventor of the cloud chamber, at the Cavendish Laboratory came back to India for a short vacation. He also could not go back because the First World War broke out. In 1940 Bhabha joined the Indian Institute of Science at Bangalore where a Readership in Theoretical Physics was specially created for him. Chandrasekhara Venkata Raman (1888-1970) was then the Director of the Institute. Bhabha was made a Professor in 1944. Vikram Sarabhai (1919-71) also spent a short period at the Institute when Bhabha was there. At the Indian Institute of Science Bhabha guided research on cosmic rays. He organised a group of young researchers in experimental and theoretical aspects of cosmic ray research. After spending a few years in India Bhabha was no longer interested in going back to England. Perhaps this was because of his growing sense of responsibility towards his motherland. Gradually he became convinced that it was his duty to build up research groups in the frontier of scientific knowledge. On April 20, 1944, Bhabha in a letter to Subrahmanyan Chandrasekhar (1910-95) wrote: “…I have recently come to the view that provided proper appreciation and financial support are forthcoming, ‘it was one’s duty to stay in one’s country and build up schools comparable with those that other countries are fortunate in possessing.”

The first three things that Bhabha felt necessary for putting India’s nuclear programme on a sound footing were:

• The survey of natural resources, particularly materials of interest to atomic energy programme such as uranium, thorium, beryllium, graphite etc. To achieve this a special unit, Rare Minerals Division was created at Delhi with the help of Darashaw Nosherwan Wadia (1883-1969).
• Development of strong research schools in basic sciences particularly physics, chemistry and biology by providing facilities to and training up high quality research scientists.
• Development of a programme for instrumentation particularly in electronics. A unit called Electronics Production Unit was started in TIFR, which later formed the nucleus of the large corporation known as Electronics Corporation of India Limited (ECIL) at Hyderabad.

When Bhabha realised that technology development for the atomic energy programme could no longer be carried out within TIFR he decided to build a new laboratory entirely devoted to this purpose. He managed to acquire 1200 acres of land at Trombay, near Bombay for this purpose. Thus the Atomic Energy Establishment started functioning in 1954. The same year the Department of Atomic Energy (DAE) was also established.

Bhabha was elected a Fellow of the Royal Society in 1941. In 1943 he was awarded the Adams Prize by the Cambridge University for his work on cosmic rays, and in 1948 the Hopkins prize of the Cambridge Philosophical Society. In 1963 he was elected Foreign Associate of the U.S. National Academy of Sciences, and Honorary Life Member of the New York Academy of Sciences. In 1964 he was made Foreign Corresponding Academician of the Royal Academy of Sciences, Madrid. From 1960 until 1963 he was President of the International Union of Pure and Applied Physics. He was president of the historic International Conference of the Peaceful uses of atomic energy held, under U.N. auspices, at Geneva in August, 1955. Bhabha was President of the National Institute of Sciences of India in 1963 and President of the Indian Science Congress Association in 1951. He was awarded the title of Padma Bhushan by the Government of India in 1954.

Uranium Minerals

Kadapa district of Andhra Pradesh

Oxidative pressure leaching of uranium from a dolomitic limestone ore:

India has a medium-tonnage, low-grade uranium ore deposit of siliceous dolomitic phosphatic limestone type, in Kadapa district of Andhra Pradesh. Detailed exploration carried out in a stretch of about 9 km in this area, established a resource of 29000 t of U3 O8 with a cut-off grade of 0.025% U3 O8. Mineralogical studies on an exploratory mine ore sample from this area, indicated the occurrence of uranium values predominantly as ultra-fine dissemination, in lighter gangue minerals (specific gravity less than 3.2). It also occurs, albeit to a minor extent, in the form of ultra-fine pitchblende in association with pyrite, as disseminations in collophane-rich parts, coffinite and as U-Ti complex. Carbonate minerals constitute the major gangue present in the form of dolostone (~80%). Siliceous minerals in the ore are quartz, feldspar and chlorite (13%). Collophane (4%) is the only phosphate bearing phase. Pyrite is the predominant sulphide ore mineral, along with few grains of chalcopyrite and galena. The iron bearing oxides are magnetite, ilmenite and goethite. Heavy media separation of various closely-sized feed fractions, using bromoform (BR) and methylene iodide (MI) liquids, have indicated that about 91% of the uranium values are present in lighter minerals (specific gravity <3.2), as ultra-fine disseminations. The remaining 9% of uranium values reported in methylene iodide heavy fraction, are accounted by discrete pitchblende, which is mostly associated with pyrite and collophane. Pitchblende occurring with pyrite is present as fine orbicular cluster, separated by thin disconnected rims of pyrite or as garlands around pyrite.

Leaching Chemistry of Uranium Minerals

The common oxidation states of uranium, in its minerals like uraninite, pitchblende, coffinite and numerous others, are +4 and +6. Amongst the two oxidation states, U+6 is soluble in aqueous media under suitable EH – pH conditions, while U+4 is practically insoluble. The uranium minerals occurring in various ore deposits consist predominantly of uranous ion (U+4), necessitating the use of an oxidant and other lixiviants, for quantitative dissolution during leaching. The type of leaching - acid or alkaline mode depends upon the host rock. Sulfuric acid is the common leachant in acid leaching process, while Na2 CO3 - NaHCO3 , (NH4 ) 2CO3 and NH4 HCO3 are the widely used lixiviants in alkaline leaching of uranium ores. The oxidant reagents could be either chemical or gaseous in nature. A typical chemical reaction in alkaline leaching of UO2 with carbonate ions and oxidant (X) is given in Equation 1, a similar equation can be written for the sulfuric acid leaching process. UO2 + 3CO3 -2 + X  [UO2(CO3) 3 ] -4 + X-2 .

Atmospheric alkaline leaching studies, carried out on this ore sample, by varying important process parameters like mesh-of-grind, temperature, contact time, dosages of leachants - sodium carbonate and sodium bicarbonate, solids concentration and type of oxidant, gave a maximum U3O8 leachability of 65%. Studies with other oxidants like NaOCl, Cu-NH3, oxygen and air gave poor leachability in comparison to KMnO4, emphasizing the need for strong oxidizing conditions during the dissolution process. However, as KMnO4 cannot be used as an oxidant on commercial scale due to its expensive nature, the only alternative is to carryout the leaching reaction in a pressure reactor, using a gaseous oxidant. Since the solubility of oxygen diminishes with increasing temperature, adoption of higher partial pressure aids in increased dissolved oxygen concentration. Detailed analysis of the leach residue obtained in the atmospheric leaching experiments indicated, that uranium values associated with pyrite are not completely leached at temperatures <1000 C. Further, some of the locked-up uranium values in various gangue phases, require more aggressive diffusion conditions for penetration of the leachant to the desired mineral interface. Both these requirements can be realized only at elevated temperature and under sustained oxidizing conditions, possible in an autoclave reactor. Leaching at elevated temperature and pressure was initially carried out in a laboratory, 5 liter S.S. autoclave reactor equipped with necessary instrumentation and control to maintain preset temperature, overpressure and agitation speed of the impeller. All the autoclave leaching experiments were carried out, at optimum dosage combination of sodium carbonate and sodium bicarbonate evolved in atmospheric leaching, that is - 50 kg/ton and - 70 kg/ton respectively. The autoclave leaching studies mainly addressed the dissolution of uranium associated with pyrite and the scope of replacing KMnO4 with industrial oxygen. Figs. 3 and 4, illustrate the effect of temperature and contact time on the leachability of uranium values, observed under aggressive conditions. About 75% of uranium values were leached at a reaction temperature of 125 - 130°C in 3 h of contact time, using a feed ground to 65% weight finer than 200#. Increasing the fineness of grind in -200# to 85% showed, an enhancement in leachability to about 80%. Based on these results, large-scale leaching studies were carried out, both on batch and continuous leach reactor, to generate necessary scale-up and engineering data for industrial scale reactor, besides verifying the reproducibility of results at higher-scale of operation. Both the batch and cigar type continuous reactor were of 850 liter capacity with inconel 600 as material of construction. Largescale studies confirmed the results generated in batch scale experiments. At present, DAE is setting-up a 3000 tpd capacity uranium mill at site, wherein two 720 m3 capacity autoclave reactors with inconel 600 cladding for the wetted parts will be used. This will be the first uranium plant, using autoclave leaching technology in India.

Uranium extraction of its ore

Leaching

Roasted uranium ores are leached of their uranium values by both acidic and alkaline aqueous solutions. For the successful operation of all leaching systems, uranium must either be initially present in the more stable hexavalent state or be oxidized to that state in the leaching process.

Acid leaching is commonly performed by agitating an ore-leach mixture for 4 to as long as 48 hours at ambient temperature. Except in special circumstances, sulfuric acid is the leachant used; it is supplied in amounts sufficient to obtain a final leach liquor at about pH 1.5. Sulfuric acid leaching circuits commonly employ either manganese dioxide or chlorate ion to oxidize the tetravalent uranium ion (U4+) to the hexavalent uranyl ion (UO22+). Typically, about 5 kilograms (11 pounds) of manganese dioxide or 1.5 kilograms of sodium chlorate per ton suffice to oxidize tetravalent uranium. In any case, the oxidized uranium reacts with the sulfuric acid to form a uranyl sulfate complex anion, [UO2(SO4)3]4-.

Uranium ores that contain significant amounts of basic minerals such as calcite or dolomite are leached with 0.5 to 1 molar sodium carbonate solutions. Although a variety of reagents has been studied and tested, oxygen is the uranium oxidant of choice. Typically, candidate ores are leached in air at atmospheric pressureand at 75° to 80° C (167° to 175° F) for periods that vary with the particular ore. The alkaline leachant reacts with uranium to form a readily soluble uranyl carbonate complex ion, [UO2(CO3)3]4-.

Treatment of uranium leachates

The complex ions [UO2(CO3)3]4- and [UO2(SO4)3]4- can be sorbed from their respective leach solutions by ion-exchange resins. These special resins—characterized by their sorption and elution kinetics, particle size, stability, and hydraulic properties—can be used in a variety of processing equipment—e.g., fixed-bed, moving-bed, basket resin-in-pulp, and continuous resin-in-pulp. Conventionally, sodium and ammonium chloride or nitrate solutions are then used to elute the sorbed uranium from the exchange resins.

Uranium can also be removed from acidic ore leach-liquors through solvent extraction. In industrial methods, alkyl phosphoric acids—e.g., di(2-ethylhexyl) phosphoric acid—and secondary and tertiary alkyl amines are the usual solvents. As a general rule, solvent extraction is preferred over ion-exchange methods for acidic leachates containing more than one gram of uranium per litre. Solvent extraction is not useful for recovery of uranium from carbonate leach liquors, however.

Precipitation of yellow cake

Prior to final purification, uranium present in acidic solutions produced by the ion-exchange or solvent-extraction processes described above, as well as uranium dissolved in carbonate ore leach solutions, is typically precipitated as a polyuranate. From acidic solutions, uranium is precipitated by addition of neutralizers such as sodium hydroxide, magnesia, or (most commonly) aqueous ammonia. Uranium is usually precipitated as ammonium diuranate, (NH4)2U2O7. From alkaline solutions, uranium is most often precipitated by addition of sodium hydroxide, producing an insoluble sodium diuranate, Na2U2O7. It can also be precipitated by acidification (to remove carbon dioxide) and then neutralization (to remove the uranium) or by reduction to less soluble tetravalent uranium. In all cases, the final uranium precipitate, commonly referred to as yellow cake, is dried. In some cases—e.g., with ammonium diuranate—the yellow cake is ignited, driving off the ammonia and oxidizing the uranium to produce uranium trioxide (UO3) or the more complex triuranium octoxide (U3O8). In all cases, the final product is shipped to a central uranium-purification facility.

Refining of yellow cake

Uranium meeting nuclear-grade specifications is usually obtained from yellow cake through a tributyl phosphate solvent-extraction process. First, the yellow cake is dissolved in nitric acid to prepare a feed solution. Uranium is then selectively extracted from this acid feed by tributyl phosphate diluted with kerosene or some other suitable hydrocarbon mixture. Finally, uranium is stripped from the tributyl phosphate extract into acidified water to yield a highly purified uranyl nitrate, UO2(NO3)2.

Conversion and isotopic enrichment

Uranyl nitrate is produced by the ore-processing operations described above as well as by solvent extraction from irradiated nuclear reactor fuel (described below, see Conversion to plutonium). In either case, it is an excellent starting material for conversion to uranium metal or for eventual enrichment of the uranium-235 content. Both of these routes conventionally begin with calcining the nitrate to UO3 and then reducing the trioxide with hydrogen to uranium dioxide (UO2). Subsequent treatment of powdered UO2with gaseous hydrogen fluoride (HF) at 550° C (1,025° F) produces uranium tetrafluoride (UF4) and water vapour, as in the following reaction:

This hydrofluorination process is usually performed in a fluidized-bed reactor.

Uranium tetrafluoride can also be fluorinated at 350° C (660° F) with fluorine gas to volatile uranium hexafluoride (UF6), which is fractionally distilled to produce high-purity feedstock for isotopic enrichment. Any of several methods—gaseous diffusion, gas centrifugation, liquid thermal diffusion—can be employed to separate and concentrate the fissile uranium-235 isotope into several grades, from low-enrichment (2 to 3 percent uranium-235) to fully enriched (97 to 99 percent uranium-235). Low-enrichment uranium is typically used as fuel for light-water nuclear reactors.

After enrichment, UF6 is reacted in the gaseous state with water vapour to yield hydrated uranyl fluoride (UO2F2 · H2O). Hydrogen reduction of the uranyl fluoride produces powdered UO2, which can be used to prepare ceramic nuclear reactor fuel