Uranium

Uranium ore is mined in several ways: by open pit, underground, in-situ leaching, and borehole mining. Low-grade uranium ore typically contains 0.1 to 0.25% of actual uranium oxides, so 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 70% uranium oxides, and therefore must be diluted with waste rock prior to milling, in order to reduce radiation exposure to workers. Uranium ore is crushed and rendered into a fine powder and then leached with either an acid or alkali. The leachate is then subjected to one of several sequences of precipitation, solvent extraction, and ion exchange. The resulting mixture, called yellowcake, contains at least 75% uranium oxides. Yellowcake is then calcined to remove impurities from the milling process prior to refining and conversion.

Commercial-grade uranium can be produced through the reduction of uranium halides with alkali or alkaline earth metals. Uranium metal can also be made through electrolysis of KU5 or UF4, dissolved in a molten calcium chloride (CaCl2) and sodium chloride (NaCl) solution.Very pure uranium can be produced through the thermal decomposition of uranium halides on a hot filament.

Oxides

Calcined uranium yellowcake as produced in many large mills contains a distribution of uranium oxidation species in various forms ranging from most oxidized to least oxidized. Particles with short residence times in a calciner will generally be less oxidized than particles that have long retention times or are recovered in the stack scrubber. While uranium content is referred to for U3O8 content, to do so is inaccurate and dates to the days of the Manhattan project when U3O8 was used as an analytical chemistry reporting standard.

Phase relationships in the uranium-oxygen system are highly complex. The most important oxidation states of uranium are uranium(IV) and uranium(VI), and their two corresponding oxides are, respectively, uranium dioxide (UO2) and uranium trioxide (UO3). Other uranium oxides such as uranium monoxide (UO), diuranium pentoxide (U2O5), and uranium peroxide (UO4•2H2O) are also known to exist.

The most common forms of uranium oxide are triuranium octaoxide (U3O8) and the aforementioned UO2. Both oxide forms are solids that have low solubility in water and are relatively stable over a wide range of environmental conditions. Triuranium octaoxide 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.

Aqueous chemistry

Ions that represent the four different oxidation states of uranium are soluble and therefore can be studied in aqueous solutions. They are: U3+ (red), U4+ (green), UO2+ (unstable), and UO22+ (yellow).[48] A few solid and semi-metallic compounds such as UO and US exist for the formal oxidation state uranium(II), but no simple ions are known to exist in solution for that state. Ions of U3+ liberate hydrogen from water and are therefore considered to be highly unstable. The UO22+ ion represents the uranium(VI) state and is known to form compounds such as the carbonate, chloride and sulfate. UO22+ also forms complexes with various organic chelating agents, the most commonly encountered of which is uranyl acetate.

Carbonates 

The interactions of carbonate anions with uranium(VI) cause the Pourbaix diagram to change greatly when the medium is changed from water to a carbonate containing solution. It is interesting to note that while the vast majority of carbonates are insoluble in water (students are often taught that all carbonates other than those of alkali metals are insoluble in water), uranium carbonates are often soluble in water. This is due to the fact that a U(VI) cation is able to bind two terminal oxides and three or more carbonates to form anionic complexes.

The effect of pH

The uranium fraction diagrams in the presence of carbonate illustrate this further: it may be seen that when the pH of a uranium(VI) solution is increased that the uranium is converted to a hydrated uranium oxide hydroxide and then at high pHs to an anionic hydroxide complex.

On addition of carbonate to the system the uranium is converted to a series of carbonate complexes when the pH is increased, one important overall effect of these reactions is to increase the solubility of the uranium in the range pH 6 to 8. This is important when considering the long term stability of used uranium dioxide nuclear fuels.

Hydrides, carbides and nitrides

Uranium metal heated to 250 to 300 °C (482 to 572 °F) reacts with hydrogen to form uranium hydride. Even higher temperatures will reversibly remove the hydrogen. This property makes uranium hydrides convenient starting materials to create reactive uranium powder along with various uranium carbide, nitride, and halide compounds. Two crystal modifications of uranium hydride exist: an α form that is obtained at low temperatures and a β form that is created when the formation temperature is above 250 °C.

Uranium carbides and uranium nitrides are both relatively inert semimetallic compounds that are minimally soluble in acids, react with water, and can ignite in air to form U3O8. Carbides of uranium include uranium monocarbide (UC), uranium dicarbide (UC2), and diuranium tricarbide (U2C3). Both UC and UC2 are formed by adding carbon to molten uranium or by exposing the metal to carbon monoxide at high temperatures. Stable below 1800 °C, U2C3 is prepared by subjecting a heated mixture of UC and UC2 to mechanical stress. Uranium nitrides obtained by direct exposure of the metal to nitrogen include uranium mononitride (UN), uranium dinitride (UN2), and diuranium trinitride (U2N3).

Halides

All uranium fluorides are created using uranium tetrafluoride (UF4); UF4 itself is prepared by hydrofluorination of uranium dioxide. Reduction of UF4 with hydrogen at 1000 °C produces uranium trifluoride (UF3). Under the right conditions of temperature and pressure, the reaction of solid UF4 with gaseous uranium hexafluoride (UF6) can form the intermediate fluorides of U2F9, U4F17, and UF5.

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

UO2 + 4HF + heat (500 °C) → UF4 + 2H2O
UF4 + F2 + heat (350 °C) → UF6

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

One method of preparing uranium tetrachloride (UCl4) is to directly combine chlorine with either uranium metal or uranium hydride. The reduction of UCl4 by hydrogen produces uranium trichloride (UCl3) while the higher chlorides of uranium are prepared by reaction with additional chlorine. All uranium chlorides react with water and air.

Bromides and iodides of uranium are formed by direct reaction of, respectively, bromine and iodine with uranium or by adding UH3 to those element's acids. Known examples include: UBr3, UBr4, UI3, and UI4. Uranium oxyhalides are water-soluble and include UO2F2, UOCl2, UO2Cl2, and UO2Br2. Stability of the oxyhalides decrease as the atomic weight of the component halide increases.

Enrichment

Enrichment of uranium ore through isotope separation to concentrate the fissionable uranium-235 is needed for use in nuclear weapons and most nuclear power plants with the exception of gas cooled reactors and pressurised heavy water reactors. A majority of neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain the nuclear chain reaction needed for these applications. The concentration and amount of uranium-235 needed to achieve this is called a 'critical mass.'

To be considered 'enriched', the uranium-235 fraction has to be increased to significantly greater than its concentration in naturally occurring uranium. Enriched uranium typically has a uranium-235 concentration of between 3 and 5%. The 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 has to have been decreased to significantly less than its natural concentration. Typically the amount of uranium-235 left in depleted uranium is 0.2% to 0.3%. As the price of uranium has risen since 2001, some enrichment tailings containing more than 0.35% uranium-235 are being considered for re-enrichment, driving the price of these depleted uranium hexafluoride stores above $130 per kilogram in July, 2007 from just $5 in 2001.

The gas centrifuge process, where gaseous uranium hexafluoride (UF6) is separated by the difference in molecular weight between 235UF6 and 238UF6 using high-speed centrifuges, has become the cheapest and leading enrichment process (lighter UF6 concentrates in the center of the centrifuge). The gaseous diffusion process was the previous leading method for enrichment and the one used in the Manhattan Project. In this process, uranium hexafluoride is repeatedly diffused through a silver-zinc membrane, and the different isotopes of uranium are separated by diffusion rate (uranium 238 is heavier and thus diffuses slightly slower than uranium-235). The molecular laser isotope separation method employs a laser beam of precise energy to sever the bond between uranium-235 and fluorine. This leaves uranium-238 bonded to fluorine and allows uranium-235 metal to precipitate from the solution. Another method is called liquid thermal diffusion

Minerals processing

Mineral processing, otherwise known as mineral dressing, is the practice of beneficiating valuable minerals from their ores. Industrial mineral treatment processes usually combine a number of unit operations in order to liberate and separate minerals by exploiting the differences in physical properties of the different minerals that make up an ore.

Many plants also incorporate hydrometallurgical or pyrometallurgical processes as part of an extractive metallurgical operation.

Mineral processing involves four general types of operations: comminution or particle size reduction, sizing or separation of particle sizes by screening or classification, concentration by taking advantage of physical and surface chemical properties, and dewatering or solid/liquid separation.

A number of auxiliary materials handling operations are also considered a branch of mineral processing such as storage (as in bin design), conveying, sampling, weighing, slurry transport, and pneumatic transport.

Comminution

Comminution is particle size reduction of materials. Comminution may be carried out on either dry materials or slurries. Crushing and grinding are the two primary comminution processes. Crushing is normally carried out on "run-of-mine" ore, while grinding (normally carried out after crushing) may be conducted on dry or slurried material.

Sizing

Sizing is the general term for separation of particles according to size.

The simplest of sizing processes is screening, or passing the particles to be sized through a screen or number of screens. Screening equipment can include grizzlies, bar screens, and wire mesh screens. Screens can be static (typically the case for very coarse material), or they can incorporate mechanisms to shake or vibrate the screen.

Classification refers to sizing operations that exploits the differences in settling velocities exhibited by particles of different size. Classification equipment may include ore sorters, gas cyclones, hydrocyclones, rake classifiers, rotating trommels, or fluidized classifers. When the feed material contains particles of different densities as well as particles of different size, a degree of concentration takes place during classification because settling velocities are also dependent on particle density.

Froth flotation

Froth flotation is achieved when particles are separated based on their surface potential. Hydrophobic particles are recovered to the froth, whereas hydrophilic particles are discharged with the tailings stream. Some mineral particles are naturally hydrophobic, whereas others require specific reagent additions to change their surface potentials. Oxide ores, such as spodumene and tantalite can be treated using oxalic acid based collectors. Sulfide ores can be recovered using xanthate or dithiophosphate type collectors.

Gravity concentration

Particles can be classified based on their specific gravity. Gravity concentration processes include:

• Heavy media or dense media separation
• Shaking tables, such as the wilfely table
• Spiral separators
• Centrifugal bowl concentrators
• Jig concentrators are continuous processing gravity concentration devices
• Multi gravity separators
  
  

Electrostatic separation

Non-conducting particles maintain an electrostatic charge induced electrically, and so remain pinned to a charged drum. Conducting particles do not maintain the electrostatic charge and so fall off the drum, thus minerals such as ilmenite and rutile can be separated.

Magnetic separation

Minerals such as magnetite and pyrrhotite are naturally magnetic, and so can be separated from non-magnetic particles using strong magnets.

Bayer Process

The process of producing pure alumina from bauxite - the Bayer Process - has changed very little since the first plant was opened in 1893. The Bayer process can be considered in three stages:

Extraction

The aluminium-bearing minerals in bauxite - Gibbsite, Böhmite and Diaspore - are selectively extracted from the insoluble components (mostly oxides) by dissolving them in a solution of sodium hydroxide (caustic soda):

Gibbsite: 

Al(OH)3 + Na+ + OH- ---> Al(OH)4- + Na+

Böhmite and Diaspore: 

AlO(OH) + Na+ + OH - + H2O ---> Al(OH)4- + Na+

Depending on the quality of the ore it may be washed to beneficiate it prior to processing. The ore is crushed and milled to reduce the particle size and make the minerals more available for extraction. It is then combined with the process liquor and sent in a slurry to a heated pressure digester.

Conditions within the digester (concentration, temperature and pressure) are set according to the properties of the bauxite ore. Ores with a high Gibbsite content can be processed at 140oC. Processing of Böhmite on the other hand requires between 200 and 240°c. The pressure is not important for the process, as such but is defined by the steam pressure during the actual process conditions. At 240°c tl the pressure is approximately 35 atmospheres (atm).

Although higher temperatures are often theoretically advantageous there are several disadvantages including corrosion problems and the possibility of oxides other than alumina dissolving into the caustic liquor.

After the extraction stage the insoluble bauxite residue must be separated from the Aluminium-containing liquor by a process known as settling. The liquor is purified as much as possible through filters before being transferred to the precipitators. The insoluble mud from the first settling stage is thickened and washed to recover the caustic soda, which is then recycled back into the main process.

Precipitation

Crystalline aluminium trihydroxide (Gibbsite), conveniently named "hydrate", is then precipitated from the digestion liquor:

Al(OH)4- + Na+ ---> Al(OH)3 + Na+ + OH-

This is basically the reverse of the extraction process, except that the product's nature is carefully controlled by plant conditions, including seeding or selective nucleation, precipitation temperature and cooling rate. The "hydrate" crystals are then classified into size fractions and fed into a rotary or fluidised bed calcination kiln. Undersize particles are fed back into the precipitation stage.

Calcination

"Hydrate", is calcined to form alumina for the aluminium smelting process. In the calcination process water is driven off to form alumina:

2Al(OH)3 ---> Al2O3 + 3H2O

The calcination process must be carefully controlled since it dictates the properties of the final product.

About gold

Gold is a chemical element with the symbol Au (from its Latin name aurum) and atomic number 79. It is a highly sought-after precious metal, having been used as money, as a store of value, in jewelry, in sculpture, and for ornamentation since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, underground "veins" and in alluvial deposits. It is one of the coinage metals. Gold is dense, soft, shiny and the most malleable and ductile substance known. Pure gold has a bright yellow color traditionally considered attractive. Gold formed the basis for the gold standard used before the collapse of the Bretton Woods system in 1971. The ISO currency code of gold bullion is XAU.

Modern industrial uses include dentistry and electronics, where gold has traditionally found use because of its good resistance to oxidative corrosion.Chemically, gold is a transition metal and can form trivalent and univalent cations upon solvation. At STP it is attacked by aqua regia, forming chloroauric acid and by alkaline solutions of cyanide but not by hydrochloric, nitric or sulphuric acids. Gold dissolves in mercury, forming amalgam alloys, but does not react with it. Gold is insoluble in nitric acid, which will dissolve silver and base metals, and is the basis of the gold refining technique known as "inquartation and parting". Nitric acid has long been used to confirm the presence of gold in items, and this is the origin of the colloquial term "acid test," referring to a gold standard test for genuine value.

Gold is the most malleable and ductile metal; a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become translucent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red.

Gold readily creates alloys with many other metals. These alloys can be produced to increase the hardness or to create exotic colors (see below). Gold is a good conductor of heat and electricity, and is not affected by air and most reagents. Heat, moisture, oxygen, and most corrosive agents have very little chemical effect on gold, making it well-suited for use in coins and jewelry; conversely, halogens will chemically alter gold, and aqua regia dissolves it via formation of the chloraurate ion.

Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated out as gold metal by adding any other metal as the reducing agent. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.

High quality pure metallic gold is tasteless; in keeping with its resistance to corrosion (it is metal ions which confer taste to metals).In addition, gold is very dense, a cubic meter weighing 19300 kg. By comparison, the density of lead is 11340 kg/m³, and that of the densest element, osmium, is 22610 kg/m³.

In various countries, gold is used as a standard for monetary exchange, in coinage and in jewelry. Pure gold is too soft for ordinary use and is typically hardened by alloying with copper or other base metals. The gold content of gold alloys is measured in carats (k), pure gold being designated as 24k.

Gold coins intended for circulation from 1526 into the 1930s were typically a standard 22k alloy called crown gold, for hardness. Modern collector/investment bullion coins (which do not require good mechanical wear properties) are typically 24k, although the American Gold Eagle and British gold sovereign continue to be made at 22k, on historical tradition. The Canadian Gold Maple Leaf coin contains the highest purity gold of any popular bullion coin, at 99.999% (.99999 fine). Several other 99.99% pure gold coins are currently available, including Australia's Gold Kangaroos (first appearing in 1986 as the Australian Gold Nugget, with the kangaroo theme appearing in 1989), the several coins of the Australian Lunar Calendar series, and the Austrian Philharmonic. In 2006, the U.S. Mint began production of the American Buffalo gold bullion coin also at 99.99% purity.

Because of the softness of pure (24k) gold, it is usually alloyed with base metals for use in jewelry, altering its hardness and ductility, melting point, color and other properties. Alloys with lower caratage, typically 22k, 18k, 14k or 10k, contain higher percentages of copper, or other base metals or silver or palladium in the alloy. Copper is the most commonly used base metal, yielding a redder color. Eighteen carat gold containing 25% copper is found in antique and Russian jewellery and has a distinct, though not dominant, copper cast, creating rose gold. Fourteen carat gold-copper alloy is nearly identical in color to certain bronze alloys, and both may be used to produce police and other badges. Blue gold can be made by alloying with iron and purple gold can be made by alloying with aluminium, although rarely done except in specialized jewelry. Blue gold is more brittle and therefore more difficult to work with when making jewelry. Fourteen and eighteen carat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. White gold alloys can be made with palladium or nickel. White 18 carat gold containing 17.3% nickel, 5.5% zinc and 2.2% copper is silver in appearance

Gold leaching method

Any method of treating gold ores must take advantage of the natural characteristics of the metal. Cyanide solution, unlike most other liquids, is able to dissolve gold, and thus, is used in the processing of gold ore. When in solution (and in the presence of oxygen), cyanide slowly attacks fine particles of gold and ultimately dissolves them. It is strange, but fortunate (because cyanide is extremely toxic), that a weak cyanide solution attacks the gold particles faster than a strong solutions. 

For the cyanide to attack the gold particles, it is necessary that the gold first be liberated from the worthless gangue rock which surrounds it because cyanide will not attack or dissolve most other minerals.

Overall, the cyanide process is very efficient. A gold ore containing less than one gram of gold per ton can, in some cases (and depending on the gold price), be profitably treated. A modern cyanide mill recovers or extracts 95% to 98% of the gold in the ore.

In a cyanide mill, lime and cyanide are added to the ore pulp in the grinding circuit. The lime has several functions: it protects the cyanide from being destroyed by naturally occurring chemicals called cyanicides and improves the settlement rate of the pulp in the thickening stage.

Cyanidation (the actual dissolution of the gold) begins in the grinding step. Cyanide and lime solutions are introduced here, where newly liberated gold particles are constantly being polished by the grinding action and the solutions are heated by the friction. Depending on the ore and fineness of grind, from 30% to 70% of the gold may be dissolved during the grinding process.

Additional time is required to place the balance of the liberated gold into solution. This is done by pumping the gold-bearing pulp to a number of mixing tanks, known as agitators. Here the pulp is aerated either mechanically or by compressed air, or by a combination of both, for a predetermined period of time. This varies any where from 24 to 48 hours.

Heap leaching avoids most of the above steps, and does not even require that a mill be built, making it a very low-cost method of processing ore. Here, broken ore is heaped onto a thick polyethylene sheet, called a liner, and then dilute cyanide solution is sprinkled on top of the heap. As the solution trickles down through the ore, the gold is dissolved. Before the heap is constructed, the polyethylene liner is laid down in such a way that the cyanide solution will drain to a central point. From here the gold-laden solution is channeled into a man-made pond.

One downside of heap leaching is lower recovery — just 65% to 85% of the gold in the ore ends up in the gold bars a heap-leach mine produces.

Extractive metallurgy

Extractive metallurgy is the practice of extracting metal from ore, purifying it, and recycling it. Most metals found in the Earth's crust exist as oxide and sulfide compounds. These mineral compounds must be reduced to liberate the desired metal. The reduction of these compounds can be carried out through either electrolytic or chemical processes, and extraction of some metals employ both methods. Chemical reduction includes reductive smelting and autoclave hydrogen reduction. Electrolytic reduction consists of simply passing a current through a dissolved or molten metal oxide to produce the neutral metal. Before the reduction of the compounds can be undertaken however, it is often necessary to separate the metal compounds from the raw ore. This mineral processing can consist of both physical and chemical treatment of the metal ore.

Mineral processing involves the use of physical and chemical processes to manipulate ore particle size, and concentrate valuable minerals using the processes of separation, based on such properties of the ore, as density, chemical composition, electrostatic, magnetic or fluorescence properties. A good example of a separation process is froth flotation. Also of interest to the mineral processor is the separation of mineral solids from water and aqueous solutions by thickening, filtering and drying.

Pyrometallurgy involves the treatment of ores at high temperature to convert ore minerals to raw metals, or intermediate compounds for further refining. Roasting, smelting and converting are the most common pyrometallurgical processes.

A roasting process is used to extract metals from sulfide ores: in this process the ore is heated in the presence of oxygen and the sulfur is oxidised and driven off as sulfur dioxide. Some metals in this process remain in the sulfide form, while other metals are turned into an oxide form. The desired metal may be in either product.

Oxidative smelting and converting are similar to the roasting process, but differ slightly in the way that the processes' temperatures are high enough to promote melting of materials. Some minerals are more resistant to oxidation, so they remain in the sulfide form, while other minerals are completely oxidized and form compounds with additives, often called flux. Molten sulfides and oxide compounds split in two layers because of the different specific weights. The byproducts created in these operations, sulfur dioxide and carbon dioxide, are major pollutants.

Hydrometallurgy involves the use of aqueous solutions to extract metals or compounds from their ores. Some of the hydrometallurgical processes include leaching, precipitation of insoluble compounds, pressure reduction. Biohydrometallurgy is a sub topic of hydrometallurgy; this uses microbes to extract metals or metal compounds from the raw ore. Leaching is a process for chemical dissolution of the desired minerals in aqueous solutions. Due to the difference in the dissolution rates, it is possible to separate the compounds of different metals. Often, some oxidative reagents need to be added to promote leaching.

Chemical reduction can be carried out in a variety of processes, including reductive smelting - the process of heating an ore with reducing agent (often, coke or charcoal) and purifying agents to separate the pure molten metal from the waste products. Some other processes for chemical reduction include autoclave hydrogen reduction and converting. The latter though does not produce the pure metal, therefore requiring further treatment of its product.

Electrolytic reduction involves passing a large current through a molten metal oxide or an aqueous solution of the metal's salt. For example, aluminium is electrolysed from bauxite dissolved in molten cryolite via the Hall-Héroult process.

Extractive metallurgical technologies are divided into mineral processing, hydrometallurgy and pyrometallurgy areas. Extractive metallurgical and mineral dressing operations can be divided into two main categories, ferrous metallurgy, which includes reduction of iron ore into iron, and further refinement and alloying with other metals to make steel and non-ferrous metallurgy, which includes all other metals. The non-ferrous category can be further broken down into extraction of precious metals, or the recovery of gold and silver and the platinum group metals; extractive metallurgy of base metals which is the recovery of lead, zinc, copper, and nickel. Extraction of light metals includes the recovery of magnesium, aluminium, tin, and titanium while minor element recovery includes arsenic, selenium, bismuth, tellurium, and antimony.

What is Metallurgy ?

Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their compounds, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use. Metallurgy is commonly used in the craft of metalworking.

The earliest recorded metal employed by humans appears to be gold which can be found free or "native". Small amounts of natural gold have been found in Spanish caves used during the late Paleolithic period, c. 40,000 BC.

Silver, copper, tin and meteoric iron can also be found native, allowing a limited amount of metalworking in early cultures. Egyptian weapons made from meteoric iron in about 3000 B.C. were highly prized as "Daggers from Heaven". However, by learning to get copper and tin by heating rocks and combining copper and tin to make an alloy called bronze, the technology of metallurgy began about 3500 B.C. with the Bronze Age.

The extraction of iron from its ore into a workable metal is much more difficult. It appears to have been invented by the Hittites in about 1200 B.C., beginning the Iron Age. The secret of extracting and working iron was a key factor in the success of the Philistines.

Historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. This includes the ancient and medieval kingdoms and empires of the Middle East and Near East, ancient Egypt and Anatolia (Turkey), Carthage, the Greeks and Romans of ancient Europe, medieval Europe, ancient and medieval China, ancient and medieval India, ancient and medieval Japan, etc. Of interest to note is that many applications, practices, and devices associated or involved in metallurgy were possibly established in ancient China before Europeans mastered these crafts (such as the innovation of the blast furnace, cast iron, steel, hydraulic-powered trip hammers, etc.). However, modern research suggests that Roman technology was far more sophisticated than hitherto supposed, especially in mining methods, metal extraction and forging. They were for example expert in hydraulic mining methods well before the Chinese, or any other civilization of the time[citation needed].

A 16th century book by Georg Agricola called De re metallica describes the highly developed and complex processes of mining metal ores, metal extraction and metallurgy of the time. Agricola has been described as the "father of metallurgy"