Calcium Metal Producers

It is recovered commercially from monazite sand, which contains about 3%, and from bastnasite, which contains about 0.2%. Wohler obtained the impure element in 1828 by reduction of the anhydrous chloride with potassium. The metal is now produced commercially by reduction of the fluoride with calcium metal. It can also be prepared by other techniques. 

Terbium has been isolated only in recent years with the development of ion-exchange techniques for separating the rare-earth elements. As with other rare earths, it can be produced by reducing the anhydrous chloride or fluoride with calcium metal in a tantalum crucible. Calcium and tantalum impurities can be removed by vacuum remelting. Other methods of isolation are possible. 

Other Reductions. Ductile, pure zirconium has been made by a two-stage sodium reduction of zirconium tetrachloride (68) in which the tetrachloride and sodium are continuously fed into a stirred reactor to form zirconium dichloride [13762-26-0], heating with additional sodium yields zirconium metal. Leaching with water removes the sodium chloride from the zirconium. Bomb reduction of pure zirconium tetrafluoride with calcium also produces pure metal (69). 

Barium reduces the oxides, haUdes, and sulfides of most of the less reactive metals, thereby producing the corresponding metal. It has reportedly been used to prepare metallic americium via reduction of americium trifluoride (13). However, calcium metal can, in most cases, be used for similar purposes and is usually preferred over barium because of lower cost per equivalent weight and nontoxicity (see Actinides and transactinides). 

Calcium metal was produced in 1855 by electrolysis of a mixture of calcium, strontium, and ammonium chlorides, but the product was highly contaminated with chlorides (1). By 1904 fairly large quantities of calcium were obtained by the electrolysis of molten calcium chloride held at a temperature above the melting point of the salt but below the melting point of calcium metal. An iron cathode just touched the surface of the bath and was raised slowly as the relatively chloride-free calcium solidified on the end. This process became the basis for commercial production of calcium metal until World War II. 

Commercially produced calcium metal is analyzed for metallic impurities by emission spectroscopy. Carbon content is determined by combustion, whereas nitrogen is measured by Kjeldahl determination. 

Aluminothermal Method. Calcium metal is produced by high temperature vacuum reduction of calcium oxide in the aluminothermal process. This process, in which aluminum [7429-90-5] metal serves as the reducing agent, was commercialized in the 1940s. The reactions, which are thermodynamically unfavorable at temperatures below 2000°C, have been summarized as ... 

The calcium crowns can be sold as such for certain appHcations. However, further processing may be required, and the crowns can be reduced in size to pieces of about 25 cm or nodules of about 3 mm. They can also be melted under a protective atmosphere of argon and cast into billets or ingots. Calcium wire can be made by extmsion, and calcium turnings are produced as lathe cuttings from cast billets. Technologies have also been developed to manufacture calcium metal particulates and powders by atomization, comminution, and grinding processes. 

Calcium metal is produced in the United States by Pfizer Inc., Canaan, Coimecticut, and in Canada by Timminco Metals, Toronto, Ontario. In France it is produced by Pechiney ElectrometaHurgie. It is also produced in the Commonwealth of Independent States (CIS) and the People s RepubHc of China. Both Pfizer and Timminco supply the various grades in a variety of sizes and forms. In addition, Pfizer suppHes an 80% Ca—20% Mg alloy and a steel-clad calcium wire for use in deoxidation of steel and other metals. Timminco and Pfizer both supply ca 75% Ca—25% Al alloy for use in lead alloying. Timminco also suppHes a 70% Mg—30% Ca alloy for use in lead debismuthizing (18), and calcium particulate products, which are purchased by several companies for the manufacture of cored wire for use in the steel industry. 

U.S. imports of calcium metals fluctuate greatiy. Since the mid-1980s, the avadabiHty of very low priced calcium metal from China and the CIS has led to substantial reductions in calcium production by Western producers. This has been compensated to a certain extent by an increase in sales of processed materials, ie, alloys and particulates, by the Western companies. In 1991, more than 700 tons of calcium metal were imported to the United States from the People s RepubHc of China. Significant quantities of calcium alloys and particulates have also been imported from France and Canada. 

Although the exact chemical mechanism for the direct oxide reduction reaction has not yet been fully characterized, it has been well established that the reaction goes to completion when excess calcium is present, sufficient CaCl2 is available to dissolve the CaO produced, and adequate stirring is used. As calcium metal is soluble to about 1 wt% in CaC12 at 835°C, excess Ca insures that the reaction is driven to completion by mass-action effects. 

Krafft temperatures depend not only on chain length but on the cation. Eth-oxylation of the base alcohol reduces the Krafft temperature due to the higher solubility of the sulfate. Calcium and other earth alkaline metals produce an increase of the Krafft temperature that is significantly reduced by ethoxylation of the alcohol. The decrease is more significant for alkaline earth metals than for alkaline cations as shown in Table 6 [81,82], although it should be noted that, according to other workers, sodium dodecyl sulfate has a Krafft temperature of 16°C. 

H.7 Write a balanced chemical equation for each of the following reactions, (a) Calcium metal reacts with water to produce hydrogen gas and aqueous calcium hydroxide. 

Ca3(BN2)2 is readily formed when (distilled) calcium metal is melted in the presence of (layer-type) boron nitride. This reaction provides some insight on how alkaline-earth metals like calcium may act as a catalyst in the phase transformation of layered a-BN into its cubic modification. Instead of metals, nowadays alkaline-earth (Ca, Sr, Ba) nitridoborates can be used as a flux catalyst in high-pressure and high-temperature transformation reactions to produce cubic boron nitride [15]. 

C19-0116. Calcium metal is obtained by the direct electrolysis of molten CaCl2. If a metallurgical electrolysis apparatus operates at 27.6 A and 1.2 V, what mass of calcium metal will it produce in 24 hours of operation ... 

Preparation. Sodium can be produced by electrolysis of a mixture of NaCl (40%) and calcium chloride, CaCl2 (60%), melting at about 580°C. The electrolysis is carried out as a melt in a Downs cell , producing also calcium metal as well, which is solidified in a collection pipe and returned back to the melt. Since 1950 a modified Downs cell has been used with an electrolyte consisting of a ternary mixture of NaCl, BaCl2 and CaCl2. 

Calcium is produced by two methods. One method is the electrolysis of calcium chloride (Ca + 2C1 —> CaCy as the electrolyte at a temperature of 800°C, during which process metallic calcium cations (Ca ) are deposited at the cathode as elemental calcium metal. Calcium can also be produced through a thermal process under very low pressure (vacuum) in which lime is reduced by using aluminum. 

Cerium is separated from other rare-earth elements by an ion-exchange process in which it reacts with fluoride. This compound is then reduced with calcium metal (3Ca +2CeF — 2Ce + 3CaFj). Cerium can also be produced by the electrolysis of molten cerium salts. The metal ion collects at the cathode, and the chlorine or fluorine gases of the salt compound at the anode. 

It requires twice as much electricity to produce one mole of calcium metal as one mole of sodium metal. 

Electrolytic reduction involves electrolysis of partially molten calcium chloride at 780° to 800°C in a graphite lined steel vessel. The method requires precise control of temperature and current. The sohd deposit of metal produced may contain entrapped salt and impurities such as chlorine and nitrogen. It is re-melted to reduce impurity levels. 

Plutonium is recovered from uranium and fission products by solvent extraction, precipitation, and other chemical methods. In most chemical processes, plutonium first is converted to one of its salts, usually plutonium fluoride, before it is recovered in purified metallic form. The fluoride is reduced with calcium metal to yield plutonium. Electrorefining may produce material of higher purity. 

A method for the commercial production of acetylene was discovered accidentally in 1892 by Thomas Willson (1860-1915). Willson was experimenting on aluminum production at his company in Spray, North Carolina. He was attempting to produce calcium in order to reduce aluminum in aluminum oxide, A1203. Willson combined coal tar and quicklime in an electric furnace and, instead of producing metallic calcium, he produced a brittle gray substance. The substance was calcium carbide, CaC2, which when reacted with water, produced acetylene. Willsons work led to the establishment of a number of acetylene plants in the United States and Europe during the next decade. 

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