Uranium ore processing

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 pressure and 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-.

Prior to further processing, solutions resulting from either acidic or carbonate leaching must be clarified. Large-scale separation of clays and other ore slimes is accomplished through the use of effective flocculants, including polyacrylamides, guar gum, and animal glue.

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.

Abundance:

Uranium is more plentiful than antimony, tin, cadmium, mercury, or silver, and it is about as abundant as arsenic or molybdenum.Uranium is found in hundreds of minerals, including uraninite (the most common uranium ore), carnotite, autunite, uranophane, torbernite, and coffinite.

The discovery of the element is credited to the German chemist Martin Heinrich Klaproth. While he was working in his experimental laboratory in Berlin in 1789, Klaproth was able to precipitate a yellow compound (likely sodium diuranate) by dissolving pitchblende in nitric acid and neutralizing the solution with sodium hydroxide.[27] Klaproth assumed the yellow substance was the oxide of a yet-undiscovered element and heated it with charcoal to obtain a black powder, which he thought was the newly discovered metal itself (in fact, that powder was an oxide of uranium).He named the newly discovered element after the planet Uranus.

Worldwide production of U3O8 (yellowcake) in 2013 amounted to 70,015 tonnes, of which 22,451 t (32%) was mined in Kazakhstan. Other important uranium mining countries are Canada (9,331 t), Australia (6,350 t), Niger (4,518 t), Namibia(4,323 t) and Russia (3,135 t).

Mining:

Uranium ore is mined in several ways: by open pit, underground, in-situ leaching, and borehole mining (see uranium mining).Low-grade uranium ore mined typically contains 0.01 to 0.25% uranium oxides. Extensive measures must be employed to extract the metal from its ore.High-grade ores found in Athabasca Basin deposits in Saskatchewan, Canada can contain up to 23% uranium oxides on average.Uranium ore is crushed and rendered into a fine powder and then leached with either an acid or alkali. The leachate is subjected to one of several sequences of precipitation, solvent extraction, and ion exchange. The resulting mixture, called yellowcake, contains at least 75% uranium oxides U3O8. Yellowcake is then calcined to remove impurities from the milling process before refining and conversion.

The most common forms of uranium oxide are triuranium octoxide (U3O8) and UO2.Both oxide forms are solids that have low solubility in water and are relatively stable over a wide range of environmental conditions. Triuranium octoxide is (depending on conditions) the most stable compound of uranium and is the form most commonly found in nature. Uranium dioxide is the form in which uranium is most commonly used as a nuclear reactor fuel.At ambient temperatures, UO2 will gradually convert to U3O8. Because of their stability, uranium oxides are generally considered the preferred chemical form for storage or disposal.

Enrichment:

In nature, uranium is found as uranium-238 (99.2742%) and uranium-235 (0.7204%). Isotope separation concentrates (enriches) the fissionable uranium-235 for nuclear weapons and most nuclear power plants, except for gas cooled reactors and pressurised heavy water reactors. Most neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain the nuclear chain reaction. The concentration and amount of uranium-235 needed to achieve this is called a 'critical mass'.

To be considered 'enriched', the uranium-235 fraction should be between 3% and 5%.This process produces huge quantities of uranium that is depleted of uranium-235 and with a correspondingly increased fraction of uranium-238, called depleted uranium or 'DU'. To be considered 'depleted', the uranium-235 isotope concentration should be no more than 0.3%.

At room temperatures, UF6 has a high vapor pressure, making it useful in the gaseous diffusion process to separate the rare uranium-235 from the common uranium-238 isotope. This compound can be prepared from uranium dioxide and uranium hydride by the following process:

UO2 + 4 HF → UF4 + 2 H2O (500 °C, endothermic)

UF4 + F2 → UF6 (350 °C, endothermic)

The resulting UF6, a white solid, is highly reactive (by fluorination), easily sublimes (emitting a vapor that behaves as a nearly ideal gas), and is the most volatile compound of uranium known to exist.

Natural farming

You should have a little water source. This helps to give jeevambritham.

No fertilizers are needed, no pesticides are required.

You require only one Desi cow, for cultivation up to thirty acres of land.

Cow dung is needed for making jeevmbritham which is used for micro organisms multiplication through fermentation and supply to the soil.

Micro-organisms enhance the automatic production of plant needs[nitrogen fixing] from the soil fertility. Micro organisms convert unusable minerals into usable ones for plants.The earth-worms themselves till[ make holes] the soil and make it porous to hold maximum rain water in the inner layers of the field. The land becomes fertile so that any crop can be grown. The earth's water level also improves. The soil erosion is also reduced, because of lesser surface tilling activity.

You need not purchase any thing from market for cultivation including fertilisers, pesticides and seeds. Hence it is called zero budget cultivation process. But labour cost is involved to some extent. When bulls are used, you need not go for tractor tilling. The bulls also give additional dung and they can also be used to transport goods to and fro the field. If there are any pests, they can be controlled by multi cropping and using Neem, Dhatturi, Seetafal, Besermy and others leaves. The farmers can be saved from debt and his prosperity increases on more food grains production.

Zero budget cultivation means no pesticides, no fertilisers. It also means pure food grains without chemicals to consumers. It also means good return to farmers, as investment expenditure is limited to only labour cost. It adds to Health improvement, wealth creation and happiness. Water requirement is also reduced.

Jeevambritham needs cow dung, cow urine, jaggery, floor of pulses and a little good soil.

Production cost is nil. Nothing is wasted other than labouring, for up keeping plants and harvesting. The micro organisms supply the needs of the plants. There is no mineral shortage in the earth. You see how does the forests grow for themselves? Nature is self curing, self protecting, and self producing.

It is better to do cultivation than say. Your action should tell and show results. Mr.Subhash Paleker toiled on this problem from 1985 to 2000 while he was a student of agriculture science, to make experiments and conclude the results of zero budget farming.

Basic science:

Plants take 98.5% of their requirement from air, water and sun light and they take only 1.5% from the soil. It was also confirmed that natural seeds are more powerful to the modified ones.

Modified seeds are used in modern methods and they can not grow without fertilizers and pesticide. In this method, the soil fertility is lost and unwanted chemicals are added to the food grains. Such grains destroy the heath of people causing many un-natural deaths.

The natural farming generate lot of profit if done systematically. Multi cropping bagvani gives lot of profit, at the rate of more than one lakh per acre net after expenses.

I had found the truth

I had discovered science after 21 years of my graduation in science, probably in 1994.Though I was science graduate, I could not make out what science really was all about! I had completed my B.Sc. From Karkataka university during 1973.

When I was at Raichur, I had encountered a book called” Vaignanika manodharma” which taught me all about what exactly science is and all about science history.The book was written by one Mr. G. T. Narayanarao, in Kannada language which is my mother tongue. The book contained all about, How the heliocentric universe was confirmed. How the speed of light was enumerated by Romer and all. How Galileo Galilee confirmed that the earth rotates around the Sun. I was enlightened, The Newton’s universal law of gravitation fascinated me as it relates to supernova, the science of destroying atoms into enormous energy and the death of stars. The true story of nature started revealing before me. I questioned to myself, “Does the so called God really exist?” The probable answer was no, there is no God as we define it. But the notion of God was needed for peaceful co-existence of social life.

 I had one more question in my mind that “what would be the height at which the clouds form above earth surface?” With some reference, I came to know that temperature falls by two degrees, at the height of every 1000 feet above the ground level. By some calculations, I could guess that probably at the height of about 5 to 6 kilometers height , the temperature falls to zero degree Celsius. Therefore the clouds should form at that height. I found that my argument was roughly good. I attempted to calculate the diameter of Sun by some experiment assuming that the distance to Sun from earth being 150000000 kilometers. I applied Trigonometric formula and radian measure to do so. I calculated the geostationary orbit of satellites as 36000 kilometers. at about 43000 feet above the earth surface, there is no oxygen to breath. things can not burn at such hight.

Thus my journey started in that direction. I calculated the speed of earth around the Sun by applying elliptical motion to earth. This result was almost nearer to actual one. Most of the superstitions vanished of my mind.I became a thinker in new direction. Started reading to understand the nature in a better way. Every day I spend reading and taking some notes of science when ever time permits to do so after my duty hours. The journey is still in progress even after two decades.

I had retired from my duty and once I went to my sister’s village casually. One day, I happened to visit the new government high school in that village. I came to know that there was no maths teacher available to teach the students of that new high school. I attempted to teach them. Somehow I became a teacher there and taught there till a new teacher was appointed for that school after a lapse of two long years. I still visit that school regularly and if a period is found vacant without a teacher, I teach the students something about maths, science, or the English language. People started addressing me as a teacher. Little kids would salute me in respect. Some of the students occasionally visit me at my residence. They seek and learn maths basics at my private coaching location in the evening hours after school time.

  

I had understood many truths of nature and wanted to teach the interested people. But it was difficult to come across such curious people in a rural environment. Most of the education is all about scoring good grades, getting a good job, and earning money for livelihood.

 Once I visited a private high school in a neighboring town, and met the management, and expressed my desire to teach science to the students. The manager introduced me to the headmaster. But the headmaster did not care for what I was saying. There was a girls' high school, on the same premises, where I was given a last period to teach. By the time I started some introduction, the students from villages would request that they need to leave the school to catch a bus to their villages and I was forced to terminate my lesson.

I happened to read photosynthesis. The breakdown of a water molecule into hydrogen ions, electrons, and oxygen due to sunlight absorption was interesting. When an electron absorbs sufficient energy, it is ejected gaining momentum and this energy is transferred to the ADP molecule to form ATP, the electron again gets energy and moves further, where it is captured to form the NADPH molecule. This activity made me to think about the nature of electrons that electrons can be ejected and can be absorbed in some other molecules in photosynthesis. I had learned about the nature of electrons.

My interest then turned to chemistry. I studied the nature of covalent bonds and ionic bonds. How metals and nonmetals combine to form salts and all. Noble gases have a special property in that they do not take part in compound formation. They have a completely filled valence shell. They are stable and inert.

In fact, the octate-rule made them stable. The other elements try to form stable by farming octane structures. Thus they interact with one another and form stable structure.

Initially, I concluded that bond formation liberates energy and to break a bond external energy is needed. But this rule could not be applied to carbon. Carbon-to-carbon bond formation takes energy from outside. Photosynthesis is an example of taking photon energy from Sunlight to make glucose by carbon to carbon fixation process.

The exothermic and endothermic reactions and Gibb's law of free energy concept for spontaneous reactions, were all interesting concepts of chemistry.

Classification of elements and their properties fit into a table called the periodic table.

Electronic configuration of an atom and valence shell and valency was analyzed by Schrodinger wave equation. This complex wave equation when solved gave quantum numbers relating to energy levels of an atom. Multiple valency was explained by hybridization process of Linus Poling to form different types of compounds. Carbon monoxide and carbon dioxide are two different gases of the same two elements combined in different ratio, their valency differ.

Organic chemistry and biochemistry, rest on carbon to carbon chain formation called catenation. The hydrocarbons, the carbohydrates, proteins, the enzymes, the lipids, amino-acids and many other molecules are all carbon compounds. It seems that life evolved by the interaction of water and air. The self replication of DNA and cell division leads to growth of living things [organisms]. All information of a species is held as triple-codon information in the DNA of each cell of an organism. The metabolism is; changing molecules into one another in water medium due to enzyme interactions at normal temperature. Complex processes like digestion of food, protein synthesis, break down of glucose in mitochondria to generate ATP molecules and all such processes occur in living organisms.

The TCA cycle, the core cycle, the urea cycle, protein synthesis, lipids synthesis and so many others reactions occur in biology. The all such interactions were termed metabolism. The metabolism includes catabolism and anabolism.

Applied science:[technology]

As the science grew, its application for human profit started.

The telescope was invented which opened the knowledge of space science. The microscope was invented which opened the knowledge of micro-organisms and the life science. The ores smelting was done to extract metals like copper and then pig iron.They made soft iron and then steel out of pig iron. This they used to make the watt’s steam engine. Thus industrial world of mass production resulted which made some countries more rich with materials and technology. They dominated the other undeveloped counties. Then the greed to acquire more land made people to fight world was one and world was two. After second world war, the wars had been almost stopped because of the fear of atomic explosion used to kill humanity. The world leaders established UNO. Most of the colonies were given freedom. Elections were held to get democratic order in the world. By this time telegraph,telephone the radio, the flying objects were invented. The quantum theory of the nature was applied to study the smallest of small particle, the Atom. They understood the crystal structure of minerals.they made semiconducting materials to make logic gates and applied to build the calculating machines. Then came the information era in which we are dwelling.

Silicon crystals were manipulated [doped] to make semi conductors.The semi conductor crystal of silicon could be used to make ICs to build logic gates and they can then be used to make calculations and the solid state amplifiers and all the solid state electronics began which oped a new field of science.

The 1980 saw the advent of personal computers and internet services were the result of modern world.

Technical institutions grew world wide to make research in all walks of life.

The Indian IITs have lot of demand as it produces technocrats.

Some land marks:

The iron smelting using blast furnace in which coke was used instead of charcoal.

The watt’s steam Engine

The Leblanc process for Soda ash which convert salt[NaCl] into sodium carbonate and washing soda. This soda was needed for glass industry and paper industry and in other chemical manufacturing process. The first such facroty was installed in 1823 in Great Britain. The watt’s steam engines made were used to weave cloths automatically. The textile flourished in England to accumulate money. They grew rich and dominated the other population. Mass transport was a reality which employed rail roads and locomotives.

Ford’s motor car.

The aeroplane invention.

The helicopter invention

Satellite launching and its applications.

Birth of chemistry

1660-the royal society was founded in England

Robert Boyle

1661-Robert Boyle defined element, acid and base. He also discovered the gas law called Boyle.s law.

1666- The French academy of science was founded.

1735-Georg Brandt discovered Cobalt in his Swedish laboratory.

[Miners in the Harz mountains have often been frustrated by a substance which appears to be copper ore but which, when heated, yields none of the expected metal. Even worse, it emits noxious fumes.]

1751- Axel Cronstedt discovered Nickel in Sweden.

A similar demon is blamed by miners in Saxony for another ore which yields a brittle substance instead of copper. The impurity in ore of this type is analyzed in Sweden in 1751 by Axel Cronstedt. He identifies its components as arsenic and a previously unknown hard white metal, quite distinct from copper.

Joseph Black, the Scottish Chemist

1761-Black explored the properties of a gas produced in various reactions. He found that limestone could be heated or treated with acids to yield a gas he called "fixed air." He observed that the fixed air was denser than air and did not support either flame or animal life. Black also found that when bubbled through an aqueous solution of lime (calcium hydroxide), it would precipitate calcium carbonate. He used this phenomenon to illustrate that carbon dioxide is produced by animal respiration and microbial fermentation.

Henry Cavendish

1766-Henry Cavendish had set up a small laboratory in his house. He collected some iron, lead and tin pieces, besides hydrochloric acid. He then put an equal number of iron pieces in both acids. He did the same with the lead and tin piece producing hydrogen. As a result of the chemical process some bubbles surfaced. He collected the gas bubbles in separate balloons. He noticed that all the balloons contained samples of inflammable gases and they all produced similar blue flame. On further observation he found that the gases weighed the same and the volume of inflammable gas produced was proportionate to the metal pieces.

1774- Joseph Priestley and discovery of Oxygen.

On August 1, 1774, he conducted his most famous experiment. Using a 12-inch-wide glass "burning lens," he focused sunlight on a lump of reddish mercuric oxide in an inverted glass container placed in a pool of mercury. The gas emitted, he found, was "five or six times as good as common air." In succeeding tests, it caused a flame to burn intensely and kept a mouse alive about four times as long as a similar quantity of air.

In October 1774, Priestley visiting Paris with his noble patron, he describes his discovery to a gathering of French scientists. Among them is Lavoisier, who develops Priestley's experiments in his own laboratory and realizes that he has the evidence to disprove the phlogiston theory. He named it oxygen [meaning acid maker].

Antoine Lavoisier, the French Chemist.

In 1779 Lavoisier coined the name oxygen for the element released by mercury oxide. He found oxygen made up 20 percent of air and was vital for combustion and respiration. He also concluded that when phosphorus or sulfur are burned in air, the products are formed by the reaction of these elements with oxygen.

In 1777 Lavoisier correctly identified sulfur as an element. He had carried out extensive experiments involving this substance and observed that it could not be broken down into any simpler substances.

In 1778 Lavoisier found that when mercury oxide is heated its weight decreases. The oxygen gas it releases has exactly the same weight as the weight lost by the mercury oxide.

While this may seem obvious to us today, it was less so in those days (hence the general support for the phlogiston theory). After carrying out work with a number of different substances, and recalling earlier work such as his work in 1772 with carbon, Lavoisier announced a new fundamental law of nature:

The law of conservation of mass:

· matter is conserved in chemical reactions

or stated in another way:

· the total mass of a chemical reaction’s products is identical to the total mass of the starting materials

The law of mass conservation only became firmly established after Lavoisier independently discovered it.

In 1783 Lavoisier coined the name ‘hydrogen’ for the gas which Henry Cavendish had recognized as a new element in 1766; Cavendish had called the gas inflammable air.

Working again with Pierre-Simon Laplace, Lavoisier burned hydrogen with oxygen and found that water was produced, establishing that water is not an element, but is actually a compound made from the elements hydrogen and oxygen. This result astonished many people, because at that time ‘everyone knew’ that water was itself one of the ‘indivisible’ element

In1789 Lavoisier published his groundbreaking Elementary Treatise on Chemistry.

Elementary Treatise on Chemistry detailed his oxygen theory of chemistry (banishing phlostigon), made clear the difference between a compound and an element, and contained a list of chemical elements. The list included oxygen, nitrogen, hydrogen, sulfur, phosphorus, carbon, antimony, cobalt, copper, gold, iron, manganese, molybdenum, nickel, platinum, silver, tin, tungsten, and zinc.

Antoine Lavoisier is called the father of modern chemistry.

Experimental science

Van Helmont weighs out 200 lbs of dried earth, places it in an earthenware container and plants a willow tree weighing 5 lbs. For five years he waters the plant daily. At the end of the experiment the willow tree weighs 169lbs and the earth, when dried, not much less than 200 lbs. Van Helmont concludes, reasonably that the wood, bark and leaves of the tree must be composed of water, which he therefore considers to be the chief constituent of all matter.

He is half right - any willow tree is about 50% water. What van Helmont is unaware of is that the tree has also absorbed carbon and oxygen, as carbon dioxide or CO2, from the air. 

Ironically, Van Helmont himself becomes the first scientist to postulate the existence of carbon dioxide. He burns 62 lbs of charcoal and finds that he is left with only 1 lb of ash. What has happened to the rest? Van Helmont is convinced, ahead of his time, of the indestructibility of matter. Indeed he is able to demonstrate that metal dissolved in acid can be recovered without loss of weight. 

So he now reasons that the missing 61 lbs have escaped in the form of an airy substance to which he gives the name gas sylvestre (wood gas).

Demons in the ore: 1742-1751

Miners in the Harz mountains have often been frustrated by a substance which appears to be copper ore but which, when heated, yields none of the expected metal. Even worse, it emits noxious fumes. In about 1735 Georg Brandt is able to show in his Swedish laboratory that the  previously unknown substance was Cobalt. It has been identified, and Brandt gives its name to the new substance - as cobalt

A similar demon is blamed by miners in Saxony for another ore which yields a brittle substance instead of copper. The impurity in ore of this type is analyzed in Sweden in 1751 by Axel Cronstedt. He identifies its components as arsenic and a previously unknown hard white metal, quite distinct from copper. He honours the new substance and calls it nickel.

Joseph Black and fixed air: 1754-1756
Black has observed that if he heats chalk (calcium carbonate), he gets quicklime (calcium oxide) and a gas, the presence of which he can identify by its weight. Unwilling as yet to speculate on its identity, he calls it fixed air - because it exists in solid form until released.

In 1766 Henry Cavendish presents his first paper to the Royal Society. Under the title Factitious Airs he describes his experiments with two gases. One is the 'fixed air' identified by Joseph Black. The other is a gas which Cavendish calls 'inflammable air', soon to be given the name hydrogen by Lavoisier

Hydrogen has been observed as a phenomenon for at least two centuries. The 16th-century alchemist and charlatan Paracelsus finds that the dissolving of a metal in acid releases a form of air which will burn. But Cavendish is the first to identify it as specific substance. He believes that he has found the inflammable essence, phlogiston. 

Priestley and oxygen: 1774

In August 1774 Priestley directs his lens at some mercury oxide. He discovers that it gives off a colourless gas in which a candle burns with an unusually brilliant light.

In October 1774, visiting Paris with his noble patron, he describes his discovery to a gathering of French scientists. Among them is Lavoisier, who develops Priestley's experiments in his own laboratory and realizes that he has the evidence to disprove the phlogiston theory.

Cavendish and water: 1784

During the last three decades of the 18th century, with more and more chemical substances becoming identified, there is great interest in which of them may be elements - in Boyle's sense of being pure substances unmixed with anything else. Of the four ancient Greek elements, earth is clearly no longer a candidate. Air is separated in 1773 by Scheele into oxygen and nitrogen. Water receives its dismissal from the club at Cavendish's hands in a paper entitled Experiments in Air (1784).

Cavendish mixes hydrogen and oxygen, in the proportion 2:1, in a glass globe through which he passes an electric spark. The resulting chemical reaction leaves him with water, which stands revealed as a compound (H2O). 

Lavoisier: 1777-1794

Although Antoine Laurent Lavoisier has no single glamorous discovery to add lustre to his name (such as identifying oxygen), he is regarded as the father of modern chemistry. The reason is that during the last two decades of the 18th century he interprets the findings of his colleagues with more scientific clarity than they have mustered, and creates the rational framework within which chemistry can develop.

He gives evidence of this in his response to Priestley's discovery of 'dephlogisticated air'. He undertakes a series of experiments which reveal the involvement of this new gas in the processes where phlogiston has been assumed to play a key role.

He is able to show that Priestley's gas is involved in chemical reactions in the processes of burning and rusting, and that it is transformed in both burning and breathing into the 'fixed air' discovered by Joseph Black. His researches with phosphorus and sulphur cause him to believe that the new gas is invariably a component of acids. He therefore gives it in 1777 the name oxygen ( 'acid maker'). On a similar principle Lavoisier coins the word hydrogen ('water maker') for the very light gas isolated by Cavendish.

With these two names chemistry takes a clear and decisive step into the modern era. It is an advance which Lavoisier soon consolidates. 

With three other French colleagues Lavoisier publishes in 1787 Méthode de nomenclature chimique (Method of Chemical Nomenclature). Their scheme, soon universally accepted, sweeps away the muddled naming of substances which has descended from alchemy and replaces it with a logical system of classification. This is an achievement of French rationalism comparable to the metric system, in the planning of which Lavoisier is also involved

In 1789 Lavoisier follows this book on chemical methodology with the related fruits of his own researches - Traité élémentaire de chimie (Elementary Treatise of Chemistry). In this he attempts a list of the known elements. 

Lavoisier names more than thirty elements, which he defines - in the tradition begun by Boyle a century earlier - as substances which can be broken down no further by any known method of analysis. The majority are metals, but there are by now three gases which Lavoisier identifies as elements - oxygen, hydrogen and nitrogen (which he calls azote, 'without life').

Oxygen theory of combustion

The oxygen theory of combustion resulted from a demanding and sustained campaign to construct an experimentally grounded chemical theory of combustion, respiration, and calcination. The theory that emerged was in many respects a mirror image of the phlogiston theory, but gaining evidence to support the new theory involved more than merely demonstrating the errors and inadequacies of the previous theory. From the early 1770s until 1785, when the last important pieces of the theory fell into place, Lavoisier and his collaborators performed a wide range of experiments designed to advance many points on their research frontier.

Lavoisier’s research in the early 1770s focused upon weight gains and losses in calcination. It was known that when metals slowly changed into powders (calxes), as was observed in the rusting of iron, the calx actually weighed more than the original metal, whereas when the calx was “reduced” to a metal, a loss of weight occurred. The phlogiston theory did not account for these weight changes, for fire itself could not be isolated and weighed. Lavoisier hypothesized that it was probably the fixation and release of air, rather than fire, that caused the observed gains and losses in weight. This idea set the course of his research for the next decade.

Along the way, he encountered related phenomena that had to be explained. Mineral acids, for instance, were made by roasting a mineral such as sulfur in fire and then mixing the resultant calx with water. Lavoisier had initially conjectured that the sulfur combined with air in the fire and that the air was the cause of acidity. However, it was not at all obvious just what kind of air made sulfur acidic. The problem was further complicated by the concurrent discovery of new kinds of airs within the atmosphere. British pneumatic chemists made most of these discoveries, with Joseph Priestley leading the effort. And it was Priestley, despite his unrelenting adherence to the phlogiston theory, who ultimately helped Lavoisier unravel the mystery of oxygen. Priestley isolated oxygen in August 1774 after recognizing several properties that distinguished it from atmospheric air. In Paris at the same time, Lavoisier and his colleagues were experimenting with a set of reactions identical to those that Priestley was studying, but they failed to notice the novel properties of the air they collected. Priestley visited Paris later that year and at a dinner held in his honour at the Academy of Sciences informed his French colleagues about the properties of this new air. Lavoisier, who was familiar with Priestley’s research and held him in high regard, hurried back to his laboratory, repeated the experiment, and found that it produced precisely the kind of air he needed to complete his theory. He called the gas that was produced oxygen, the generator of acids. Isolating oxygen allowed him to explain both the quantitative and qualitative changes that occurred in combustion, respiration, and calcination.