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31-405: It is produced on a large scale by pyrometallurgy , as one stage in extracting copper from its ores. The ores are treated with an aqueous mixture of ammonium carbonate , ammonia , and oxygen to ultimately give copper(II) ammine complex carbonates, such as [Cu(NH 3 ) 4 ]CO 3 . After extraction from the residues and after separation from iron, lead, etc. impurities, the carbonate salt

62-428: A reducing agent that liberates the oxygen as carbon dioxide leaving a refined mineral. Concern about the production of carbon dioxide is only a recent worry, following the identification of the enhanced greenhouse effect . Carbonate ores are also smelted with charcoal, but sometimes need to be calcined first. Other materials may need to be added as flux , aiding the melting of the oxide ores and assisting in

93-505: A flame inside the kiln. Such a flame is projected from a burner-pipe (or "firing pipe") which acts like a large bunsen burner . The fuel for this may be gas, oil, pulverized petroleum coke or pulverized coal. The basic components of a rotary kiln are the shell, the refractory lining, support tyres (riding rings) and rollers, drive gear and internal heat exchangers. The rotary kiln was invented in 1873 by Frederick Ransome . He filed several patents in 1885-1887, but his experiments with

124-420: A mixed sulfide feed (for instance a feed containing both copper sulfide and iron sulfide) reacts such that one metal forms a sulfate and the other forms an oxide, the process is known as " selective roasting " or " selective sulfation ". Smelting involves thermal reactions in which at least one product is a molten phase. Metal oxides can then be smelted by heating with coke or charcoal (forms of carbon ),

155-453: A typical 6 m × 60 m (20 ft × 197 ft) kiln, including refractories and feed, is around 1,100 t (2,400,000 lb), and would be carried on three tyres and sets of rollers, spaced along the length of the kiln. The longest kilns may have 8 sets of rollers, while very short and small kilns may have none. Kilns usually rotate at 0.5 to 2 rpm. The Kilns of modern cement plants are running at 4 to 5 rpm. The bearings of

186-406: A variety of furnaces, including shaft furnaces , rotary kilns , and fluidized bed reactors . Roasting consists of thermal gas–solid reactions, which can include oxidation, reduction, chlorination, sulfation, and pyrohydrolysis. The most common example of roasting is the oxidation of metal sulfide ores. The metal sulfide is heated in the presence of air to a temperature that allows the oxygen in

217-414: Is a pyroprocessing device used to raise materials to a high temperature ( calcination ) in a continuous process. Materials produced using rotary kilns include: They are also used for roasting a wide variety of sulfide ores prior to metal extraction. The kiln is a cylindrical vessel, inclined slightly from the horizontal, which is rotated slowly about its longitudinal axis. The process feedstock

248-461: Is coordinated by 4 oxygen atoms in an approximately square planar configuration. The work function of bulk CuO is 5.3 eV . As a significant product of copper mining, copper(II) oxide is the starting point for the production of many other copper salts. For example, many wood preservatives are produced from copper oxide. Cupric oxide is used as a pigment in ceramics to produce blue, red, and green, and sometimes gray, pink, or black glazes. It

279-411: Is damaged. Hence, normal practice is to provide an auxiliary drive for use during power cuts. This may be a small electric motor with an independent power supply, or a diesel engine . This turns the kiln very slowly, but enough to prevent damage. Heat exchange in a rotary kiln may be by conduction , convection and radiation , in descending order of efficiency. In low-temperature processes, and in

310-428: Is decomposed with steam to give CuO. It can be formed by heating copper in air at around 300–800 °C: For laboratory uses, copper(II) oxide is conveniently prepared by pyrolysis of copper(II) nitrate or basic copper(II) carbonate : Dehydration of cupric hydroxide has also been demonstrated: Copper(II) oxide reacts with mineral acids such as hydrochloric acid , sulfuric acid , and nitric acid to give

341-411: Is fed into the upper end of the cylinder. As the kiln rotates, material gradually moves down toward the lower end, and may undergo a certain amount of stirring and mixing. Hot gases pass along the kiln, sometimes in the same direction as the process material (co-current), but usually in the opposite direction (counter-current). The hot gases may be generated in an external furnace, or may be generated by

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372-686: Is incorrectly used as a dietary supplement in animal feed . Due to low bioactivity, negligible copper is absorbed. It is used when welding with copper alloys . A copper oxide electrode formed part of the early battery type known as the Edison–Lalande cell . Copper oxide was also used in a lithium battery type ( IEC 60086 code "G"). Used as moderate blue coloring agent in blue flame compositions with additional chlorine donors and oxidizers such as chlorates and perchlorates. Providing oxygen it can be used as flash powder oxidizer with metal fuels such as magnesium, aluminium, or magnalium powder. Sometimes it

403-423: Is said to be "autogenous". Processing of some sulfide ores exploit the exothermicity of their combustion. Calcination is thermal decomposition of a material. Examples include decomposition of hydrates such as ferric hydroxide to ferric oxide and water vapor, the decomposition of calcium carbonate to calcium oxide and carbon dioxide as well as iron carbonate to iron oxide: Calcination processes are carried out in

434-411: Is used in strobe effects and thermite compositions as crackling stars effect. An example of natural copper (I,II) oxide is the mineral paramelaconite , Cu 2 Cu 2 O 3 . 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

465-455: Is usually turned by means of a single Girth Gear surrounding a cooler part of the kiln tube, but sometimes it is turned by driven rollers. The gear is connected through a gear train to a variable-speed electric motor . This must have high starting torque to start the kiln with a large eccentric load. A 6 m × 60 m (20 ft × 197 ft) kiln requires around 800 kW to turn at 3 rpm. The speed of material flow through

496-399: The air to react with the sulfide to form sulfur dioxide gas and solid metal oxide. The solid product from roasting is often called " calcine ". In oxidizing roasting, if the temperature and gas conditions are such that the sulfide feed is completely oxidized, the process is known as " dead roasting ". Sometimes, as in the case of pre-treating reverberatory or electric smelting furnace feed,

527-565: The cooler parts of long kilns lacking preheaters, the kiln is often furnished with internal heat exchangers to encourage heat exchange between the gas and the feed. These may consist of scoops or "lifters" that cascade the feed through the gas stream, or may be metallic inserts that heat up in the upper part of the kiln, and impart the heat to the feed as they dip below the feed surface as the kiln rotates. The latter are favoured where lifters would cause excessive dust pick-up. The most common heat exchanger consists of chains hanging in curtains across

558-445: The corresponding hydrated copper(II) salts: In presence of water it reacts with concentrated alkali to form the corresponding cuprate salts: It can also be reduced to copper metal using hydrogen , carbon monoxide , and carbon : When cupric oxide is substituted for iron oxide in thermite the resulting mixture is a low explosive, not an incendiary. Copper(II) oxide belongs to the monoclinic crystal system . The copper atom

589-408: The following categories: 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

620-639: The formation of a slag , as the flux reacts with impurities, such as silicon compounds. Smelting usually takes place at a temperature above the melting point of the metal, but processes vary considerably according to the ore involved and other matters. Refining is the removal of impurities from materials by a thermal process. This covers a wide range of processes, involving different kinds of furnace or other plant. The term " refining " can also refer to certain electrolytic processes. Accordingly, some kinds of pyrometallurgical refining are referred to as " fire refining ". Rotary kiln A rotary kiln

651-430: The gas stream. The kiln connects with a material exit hood at the lower end and ducts for waste gases. This requires gas-tight seals at either end of the kiln. The exhaust gas may go to waste, or may enter a preheater, which further exchanges heat with the entering feed. The gases must be drawn through the kiln, and the preheater if fitted, by a fan situated at the exhaust end. In preheater installations which may have

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682-475: The idea were not a commercial success. Nevertheless, his designs provided the basis for successful kilns in the US from 1891, subsequently emulated worldwide. This is made from rolled mild steel plate, usually between 15 and 30 mm (0.6 and 1.2 in), welded to form a cylinder which may be up to 230 m (750 ft) in length and up to 6 m (20 ft) in diameter. Upper limits on diameter are set by

713-421: The kiln is proportional to rotation speed; a variable-speed drive is needed to control this. When driving through rollers, hydraulic drives may be used. These have the advantage of developing extremely high torque. In many processes, it is dangerous to allow a hot kiln to stand still if the drive power fails. Temperature differences between the top and bottom of the kiln may cause the kiln to warp, and refractory

744-404: The kiln, and to protect it from the corrosive properties of the process material. It may consist of refractory bricks or cast refractory concrete, or may be absent in zones of the kiln that are below approximately 250 °C (482 °F). The refractory selected depends upon the temperature inside the kiln and the chemical nature of the material being processed. In some processes, such as cement,

775-468: 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

806-442: The refractory life is prolonged by maintaining a coating of the processed material on the refractory surface. The thickness of the lining is generally in the range 80 to 300 mm (3 to 12 in). A typical refractory will be capable of maintaining a temperature drop of 1000 °C (1,800 °F) or more between its hot and cold faces. The shell temperature needs to be maintained below around 350 °C (662 °F) to protect

837-480: The roasting process is performed with less than the required amount of oxygen to fully oxidize the feed. In this case, the process is called " partial roasting " because the sulfur is only partially removed. Finally, if the temperature and gas conditions are controlled such that the sulfides in the feed react to form metal sulfates instead of metal oxides, the process is known as " sulfation roasting ". Sometimes, temperature and gas conditions can be maintained such that

868-428: The rollers must be capable of withstanding the large static and live loads involved and must be carefully protected from the heat of the kiln and the ingress of dust. Since the kiln is at an angle, it also needs support to prevent it from walking off the support rollers. Usually upper and lower "retaining (or thrust) rollers" bearing against the side of tyres prevent the kiln from walking off the support rollers. The kiln

899-399: The steel from damage, and continuous infrared scanners are used to give early warning of "hot-spots" indicative of refractory failure. Tyres, sometimes called riding rings, usually consist of a single annular steel casting, machined to a smooth cylindrical surface, which attach loosely to the kiln shell through a variety of "chair" arrangements. These require some ingenuity of design, since

930-413: The tendency of the shell to deform under its own weight to an oval cross section, with consequent flexure during rotation. Length is not necessarily limited, but it becomes difficult to cope with changes in length on heating and cooling (typically around 0.1 to 0.5% of the length) if the kiln is very long. The purpose of the refractory lining is to insulate the steel shell from the high temperatures inside

961-421: The tyre must fit the shell snugly, but also allow thermal movement. The tyre rides on pairs of steel rollers, also machined to a smooth cylindrical surface, and set about half a kiln-diameter apart. The rollers must support the kiln, and allow rotation that is as nearly frictionless as possible. A well-engineered kiln, when the power is cut off, will swing pendulum-like many times before coming to rest. The mass of

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