Calcination

The IUPAC defines calcination as "heating to high temperatures in air or oxygen".[1] However, calcination is also used to mean a thermal treatment process in the absence or limited supply of air or oxygen applied to ores and other solid materials to bring about a thermal decomposition. A calciner is a steel cylinder that rotates inside a heated furnace and performs indirect high-temperature processing (550–1150 °C, or 1000–2100 °F) within a controlled atmosphere.[2]

Industrial processes

LDLimeShaftKilnBasic
An oven for calcination of limestone

The process of calcination derives its name from the Latin calcinare (to burn lime)[3] due to its most common application, the decomposition of calcium carbonate (limestone) to calcium oxide (lime) and carbon dioxide, in order to create cement. The product of calcination is usually referred to in general as "calcine", regardless of the actual minerals undergoing thermal treatment. Calcination is carried out in furnaces or reactors (sometimes referred to as kilns or calciners) of various designs including shaft furnaces, rotary kilns, multiple hearth furnaces, and fluidized bed reactors.

Examples of calcination processes include the following:

Reactions

Calcination reactions usually take place at or above the thermal decomposition temperature (for decomposition and volatilization reactions) or the transition temperature (for phase transitions). This temperature is usually defined as the temperature at which the standard Gibbs free energy for a particular calcination reaction is equal to zero.

Limestone calcination

In limestone calcination, a decomposition process, the chemical reaction is

CaCO3 → CaO + CO2(g)

The standard Gibbs free energy of reaction is approximated as ΔG°r = 177,100 − 158 T (J/mol).[4] The standard free energy of reaction is 0 in this case when the temperature, T, is equal to 1121 K, or 848 °C.

Oxidation

In some cases, calcination of a metal results in oxidation of the metal. Jean Rey noted that lead and tin when calcinated gained weight, presumably as they were being oxidized.

Alchemy

In alchemy, calcination was believed to be one of the 12 vital processes required for the transformation of a substance.

Alchemists distinguished two kinds of calcination, actual and potential. Actual calcination is that brought about by actual fire, from wood, coals, or other fuel, raised to a certain temperature. Potential calcination is that brought about by potential fire, such as corrosive chemicals; for example, gold was calcined in a reverberatory furnace with mercury and sal ammoniac; silver with common salt and alkali salt; copper with salt and sulfur; iron with sal ammoniac and vinegar; tin with antimony; lead with sulfur; and mercury with aqua fortis.[5]

There was also philosophical calcination, which was said to occur when horns, hooves, etc., were hung over boiling water, or other liquor, until they had lost their mucilage, and were easily reducible into powder.[5]

References

  1. ^ IUPAC. "Calcination".
  2. ^ "High-Temperature Processing with Calciners".
  3. ^ Mosby's Medical, Nursing and Allied Health Dictionary, Fourth Edition, Mosby-Year Book Inc., 1994, p. 243
  4. ^ Gilchrist, J.D. (1989). Extraction Metallurgy (3rd ed.). Oxford: Pergamon Press. p. 145. ISBN 978-0-08-036612-8.
  5. ^ a b  This article incorporates text from a publication now in the public domainChambers, Ephraim, ed. (1728). "Calcination". Cyclopædia, or an Universal Dictionary of Arts and Sciences (first ed.). James and John Knapton, et al.
Ammonium uranyl carbonate

Ammonium uranyl carbonate (UO2CO3·2(NH4)2CO3) is known in the uranium processing industry as AUC and is also called uranyl ammonium carbonate. This compound is important as a component in the conversion process of uranium hexafluoride (UF6) to uranium dioxide (UO2). The ammonium uranyl carbonate is combined with steam and hydrogen at 500–600 °C to yield UO2. In another process aqueous uranyl nitrate, known as uranyl nitrate liquor (UNL) is treated with ammonium bicarbonate to form ammonium uranyl carbonate as a solid precipitate. This is separated from the solution, dried with methanol and then calcinated with hydrogen directly to UO2 to obtain a sinterable grade powder. The ex-AUC uranium dioxide powder is free-flowing, relatively coarse (10 µ) and porous with specific surface area in the range of 5 m2/g and suitable for direct pelletisation, avoiding the granulation step. Conversion to UO2 is often performed as the first stage of nuclear fuel fabrication.The AUC process is followed in South Korea and Argentina. In the AUC route, calcination, reduction and stabilization are simultaneously carried out in a vertical fluidized bed reactor. In most countries, sinterable grade UO2 powder for nuclear fuel is obtained by the ammonium diuranate (ADU) process, which requires several more steps.

Ammonium uranyl carbonate is also one of the many forms called yellowcake; in this case it is the product obtained by the heap leach process.

Bhasma

Bhasma in Ayurveda has been defined as a substance obtained by calcination.

Bhasma (residue after incineration – calcined preparation) and pishti (powdered gem or metal) are used with herbs for the treatment of critical ailments as a medicinal preparation in Ayurveda and to some extent Unani (both Indian branches of medical science using natural curative methods). The procedures for preparing these medicines are time-consuming and complicated.

Bhasma is a calcined preparation in which the gem or metal is converted into ash. Gems or metals are purified to remove impurities and treated by triturating and macerating in herbal extracts. The dough so obtained is calcinated to obtain the ashes.^

Bone ash

Bone ash is a white material produced by the calcination of bones. Typical bone ash consists of about 55.82% calcium oxide, 42.39% phosphorus pentoxide, and 1.79% water. The exact composition of these compounds varies depending upon the type of bones being used, but generally the formula for bone ash is: Ca5(OH)(PO4)3. Bone ash usually has a density around 3.10 g/mL and a melting point of 1670 °C (3038 °F). Most bones retain their cellular structure through calcination.

Calcium carbonate

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone, which is a type of sedimentary rock consisting mainly of calcite) and is the main component of pearls and the shells of marine organisms, snails, and eggs. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a calcium supplement or as an antacid, but excessive consumption can be hazardous.

Calcium looping

Calcium looping (CaL), or the regenerative calcium cycle (RCC), is a second-generation carbon capture technology. It is the most developed form of carbonate looping, where a metal (M) is reversibly reacted between its carbonate form (MCO3) and its oxide form (MO) to separate carbon dioxide from other gases coming from either power generation or an industrial plant. In the calcium looping process, the two species are calcium carbonate (CaCO3) and calcium oxide (CaO). The captured carbon dioxide can then be transported to a storage site, used in enhanced oil recovery or used as a chemical feedstock. Calcium oxide is often referred to as the sorbent.

Calcium looping is being developed as it is a more efficient, less toxic alternative to current post-combustion capture processes such as amine scrubbing. It also has interesting potential for integration with the cement industry.

Deville process

The Deville process was the first industrial process used to produce alumina from bauxite.

The Frenchman Henri Sainte-Claire Deville invented the process in 1859. It is sometimes called the Deville-Pechiney process.

It is based on the extraction of alumina with sodium carbonate.

The first stage is the calcination of the bauxite at 1200 °C with sodium carbonate and coke. The alumina is converted in sodium aluminate. Iron oxide remains unchanged and silica forms a polysilicate.

In the second stage sodium hydroxide solution is added, which dissolves the sodium aluminate, leaving the impurities as a solid residue. The amount of sodium hydroxide solution needed depends upon the amount of silica present in the raw material. The solution is filtered off; carbon dioxide is bubbled through the solution, causing aluminium hydroxide to precipitate, leaving a solution of sodium carbonate. The latter can be recovered and reused in the first stage.

The aluminium hydroxide is calcined to produce alumina.

The process was used in France at Salindres until 1923 and in Germany and Great Britain until the outbreak of the Second World War.It has now been replaced by the Bayer process.

FDU materials

FDU Materials are a class of regularly structured mesoporous organic materials first synthesized at Fudan University in Shanghai, China (hence FDU). FDU-14 -15 and -16 are formed by polymerizing resol around a lyotropic liquid crystal template and then removing the template by calcination.

Lime (material)

Lime is a calcium-containing inorganic mineral composed primarily of oxides, and hydroxide, usually calcium oxide and/ or calcium hydroxide. It is also the name for calcium oxide which occurs as a product of coal seam fires and in altered limestone xenoliths in volcanic ejecta. The word lime originates with its earliest use as building mortar and has the sense of sticking or adhering.These materials are still used in large quantities as building and engineering materials (including limestone products, cement, concrete, and mortar), as chemical feedstocks, and for sugar refining, among other uses. Lime industries and the use of many of the resulting products date from prehistoric times in both the Old World and the New World. Lime is used extensively for wastewater treatment with ferrous sulfate.

The rocks and minerals from which these materials are derived, typically limestone or chalk, are composed primarily of calcium carbonate. They may be cut, crushed, or pulverized and chemically altered. Burning (calcination) of these minerals in a lime kiln converts them into the highly caustic material burnt lime, unslaked lime or quicklime (calcium oxide) and, through subsequent addition of water, into the less caustic (but still strongly alkaline) slaked lime or hydrated lime (calcium hydroxide, Ca(OH)2), the process of which is called slaking of lime.

When the term is encountered in an agricultural context, it usually refers to agricultural lime, which is crushed limestone, not a product of a lime kiln. Otherwise it most commonly means slaked lime, as the more dangerous form is usually described more specifically as quicklime or burnt lime.

Lime kiln

A lime kiln is a kiln used for the calcination of limestone (calcium carbonate) to produce the form of lime called quicklime (calcium oxide). The chemical equation for this reaction is

CaCO3 + heat → CaO + CO2This reaction takes place at 900 °C (1650 °F; at which temperature the partial pressure of CO2 is 1 atmosphere), but a temperature around 1000 °C (1800 °F; at which temperature the partial pressure of CO2 is 3.8 atmospheres) is usually used to make the reaction proceed quickly. Excessive temperature is avoided because it produces unreactive, "dead-burned" lime.

Slaked lime (calcium hydroxide) can be formed by mixing water with quicklime.

Lithium platinate

Lithium platinate, Li2PtO3, is a chemical compound of lithium, platinum and oxygen. It is a semiconductor with a layered honeycomb crystal structure and a band gap of 2.3 eV, and can be prepared by direct calcination of Pt metal and lithium carbonate at ca. 600 °C. Lithium platinate is a potential lithium-ion battery electrode material, though this application is hindered by the high costs of Pt, as compared to the cheaper Li2MnO3 alternative.

Lithium ruthenate

Lithium ruthenate, Li2RuO3, is a chemical compound of lithium, ruthenium and oxygen. It has a layered honeycomb crystal structure, and can be prepared by direct calcination of Ru metal and lithium carbonate at ca. 700 °C. It is a potential lithium-ion battery electrode material, though this application is hindered by the high costs of Ru, as compared to the cheaper Li2MnO3 alternative.

Phenyl acetate

Phenyl acetate is the ester of phenol and acetyl chloride. One way that it can be produced by decarboxylation of aspirin. Another way that it can be produced is by reacting phenol with acetic anhydride.

Phenyl acetate can be separated into phenol and an acetate salt, via saponification: heating the phenyl acetate with a strong base, such as sodium hydroxide, will produce phenol and sodium acetate. The two chemicals can be separated by heating and calcination of carbon or heat and filtration.

Pyrometallurgy

Pyrometallurgy is a branch of extractive metallurgy. It consists of the thermal treatment of minerals and metallurgical ores and concentrates to bring about physical and chemical transformations in the materials to enable recovery of valuable metals. Pyrometallurgical treatment may produce products able to be sold such as pure metals, or intermediate compounds or alloys, suitable as feed for further processing. Examples of elements extracted by pyrometallurgical processes include the oxides of less reactive elements like iron, copper, zinc, chromium, tin, and manganese.Pyrometallurgical processes are generally grouped into one or more of the following categories:

calcining,

roasting,

smelting,

refining.Most pyrometallurgical processes require energy input to sustain the temperature at which the process takes place. The energy is usually provided in the form of combustion or from electrical heat. When sufficient material is present in the feed to sustain the process temperature solely by exothermic reaction (i.e. without the addition of fuel or electrical heat), the process is said to be "autogenous". Processing of some sulfide ores exploit the exothermicity of their combustion

Pyroprocessing

Pyroprocessing (from Greek Πυρος = fire) is a process in which materials are subjected to high temperatures (typically over 800 °C) in order to bring about a chemical or physical change. Pyroprocessing includes such terms as ore-roasting, calcination and sintering. Equipment for pyroprocessing includes kilns, electric arc furnaces and reverberatory furnaces.

Cement manufacturing is a very common example of pyroprocessing. The raw material mix (raw meal) is fed to a kiln where pyroprocessing takes place. As with most industries, pyroprocessing is the most energy-intensive part of the industrial process.

Rosendale cement

Rosendale cement is a natural hydraulic cement that was produced in and around Rosendale, New York, beginning in 1825. From 1818 to 1970 natural cements were produced in over 70 locations in the United States and Canada. More than half of the 35 million tons of natural cement produced in the United States originated with cement rock mined in Ulster County, New York, in and around the Town of Rosendale in the Hudson River Valley. The Rosendale region of southeastern New York State is widely recognized as the source of the highest quality natural cement in North America. The Rosendale region was also coveted by geologists, such as W. W. Mather, a geologist working for the State of New York, for its unusual exposed bedrock.` Because of its reputation, Rosendale cement was used as both a trade name and as a generic term referring to any natural hydraulic cement in the US. It was used in the construction of many of the United States' most important landmarks, including the Brooklyn Bridge, the pedestal of the Statue of Liberty, Federal Hall National Memorial, and the west wing of the United States Capitol building.

Rotary kiln

A rotary kiln is a pyroprocessing device used to raise materials to a high temperature (calcination) in a continuous process. Materials produced using rotary kilns include:

Cement

Lime

Refractories

Metakaolin

Titanium dioxide

Alumina

Vermiculite

Iron ore pelletsThey are also used for roasting a wide variety of sulfide ores prior to metal extraction.

Spagyric

Spagyric is a word in English that means "alchemy". Some people have coined the use of the word to mean an herbal medicine produced by alchemical procedures. These procedures involve fermentation, distillation, and extraction of mineral components from the ash of the plant. These processes were in use in medieval alchemy generally for the separation and purification of metals from ores (see Calcination), and salts from brines and other aqueous solutions.

Suspicions about the Hidden Realities of the Air

Suspicions about the Hidden Realities of the Air is a book on alchemy by 17th-century philosopher Robert Boyle. It was written in 1674 concerning ideas about the agency of the air in chemical reactions. Air at this time was considered homogenous, empty and inactive.

I have often suspected, that there may be in the Air some yet more latent Qualities or Powers differing enough from all these, and principally due to the Substantial Parts or Ingredients, whereof it consists.

For this is not as many imagine a simple and elementary body, but a confused aggregate of 'effluviums' from such differing bodies, that, though they all agree in constituting by their minuteness and various motions one great mass of fluid matter, yet perhaps there is scarce a more heterogeneous body in the world.

Although his research and personal philosophy clearly has its roots in the alchemical tradition, Boyle is largely regarded today as the first modern chemist, and therefore one of the founders of modern chemistry. It was by examining the part played by the air in processes of calcination and burning that it became possible to give approximately complete descriptions of these processes, which led to the gradual scientific rejection of Phlogiston.Among Boyle's more popular works is The Sceptical Chymist, seen as a cornerstone book in the field of chemistry.

The Calcination of Scout Niblett

The Calcination of Scout Niblett is the fifth studio album by singer-songwriter Scout Niblett, and was her first release on Drag City records. The album was Niblett's fourth collaboration with producer Steve Albini.

Mineral processing
(by physical means)
Pyrometallurgy
(by heat)
Hydrometallurgy
(by aqueous solution)
Electrometallurgy
(by electricity)
Co-products

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.