Alkali Metals Production (Li, Na, K) availability and high potential yield of oxide (Li2O). Large reserves of spodumene can be found in North Carolina in the United States and in Quebec 1. Introduction and Manitoba in Canada. Spodumene theoretically contains 8.03% of Li2O. Amblygonite, (LiAl(PO4)F, Lithium (Li: atomic number 3), (Na:11), and OH) contains 10.1% Li2O, and is mostly available in (K:19) are very reactive, monovalent alkali Europe, Africa, and South America for commercial metals that occupy the Group 1A position on the extraction. Substantial amounts of petalite (Li2O periodic table. These metals find extensive applica- Al2O3 8SiO2: 4.09% Li2O) and lepidolite (K2(LiAl)5–6 tions in many industries, both as pure metal as well as (Si6–7Al2–1O20): 4.89% Li2O) are also found in compounds. Application in compound forms is Rhodesia, Africa. The other nonmineral source of significant for all alkali metals, as some of the most lithium is brines. The concentration of lithium found important commercial chemicals contain these metals. in seawater is B0.1 ppm. It is also prevalent in other Lithium is used as a stearate in lubricating greases, as mineral waters such as Searles Lake in California. oxide in ceramics and porcelain, as halides in welding fluxes and as salts in medical treatment. Recent applications of lithium metal include batteries and 2.2 Extraction and Purification of Lithium energy storage devices. Aluminum–lithium alloys Flotation is primary used for mineral extraction from have found extensive use in aerospace applications. lithium ores. In this process, lithium ores are Sodium is primarily used in the synthesis of anti- concentrated with respect to lithium oxide from knock agent for automotive gasoline. Other uses 1–3% Li2O to 4–6% Li2O through heavy medium include reductant for zirconium, titanium, and potas- separation using dense nonaqueous liquids in a froth sium metal production and as a reductant of oils to flotation process. Silicate ores are most widely fatty alcohols for detergent applications. Its com- processed using the flotation method, those products pounds, particularly the chloride and hydroxide are are subsequently chemically cleaned by an acid or important industrial chemicals. Potassium in the form alkaline process. of chloride is mainly used in fertilizers. In the acid cleaning process, the concentrated The primary production method of sodium and spodumene ore is placed in a kiln and heated to lithium is by molten salt while potassium is elevated temperatures between 1075 1C and 1100 1C. produced using sodium in a metallothermic reduction This process changes the naturally occurring alpha- process. Lithium cell uses a salt mixture of lithium spodumene into beta-spodumene, which can be more chloride and potassium chloride whereas sodium cell readily attacked by the acid. The beta-spodumene is () uses a mixture of sodium chloride and further cooled and ball-milled. This powder is then chloride. The occurrence, metallurgical ex- roasted in a second kiln under an excess of sulfuric traction methods, chemical properties, and prominent acid at a temperature between 200 1C and 250 1C. The applications, including those of the compounds of following reaction occurs at this stage: alkali metals—lithium, sodium, and potassium—have been described. Alkali metals are excellent reductants for other metal compounds, since alkali metals form Li2OAl2O34SiO2 þ H2SO4 some of the most stable compounds. Thus, a hybrid -H2OAl2O34SiO2 þ Li2SO4 at 2002250 1C ð1Þ process has been outlined where the alkali metal is electrochemically produced and used as a pyrochem- Once this reaction has taken place, the kiln is then ical reductant in situ. In this scheme, alkali metal leached with water. This yields a lithium sulfate serves as a nonconsumable reducing metal. product to be treated with sodium carbonate to convert it into lithium carbonate. Hydrochloric acid can then be used to react with the lithium carbonate to 2. Lithium form lithium chloride. 2.1 Sources of Lithium Li2SO4 þ Na2CO3-Li2CO3 þ Na2SO4 ð2Þ Lithium in nature, is primarily obtained from lithium-bearing pegmatites and brines. The lithium Li2CO3 þ 2HCl-2LiCl þ H2CO3 ð3Þ found within the pegmatite formations is in the mineral forms of spodumene, petalite, lepidolite, and In the alkaline cleaning process, either a spodumene amblygonite. These pegmatites are found as veins or a lepidolite concentrated ore is ground and calcined within or associated with granites and feldspar and with a mixture of 3.5 parts limestone to 1 part lithium. are generally the primary sources for extraction This is done at a temperature between 900 1Cand of lithium. The mineral, spodumene (Li2OAl2O3 1000 1C. In this process, the kiln is then hot-leached 4SiO2), is of primary interest for the commercial with water and the product is lithium hydroxide, production of lithium in North America due to its which can be converted to lithium chloride using

1 Alkali Metals Production (Li, Na, K) hydrochloric acid: cathode with cast iron collectors and a graphite anode is employed. Tables 1 and 2 show that lithium has a

Li 2OAl2O34SiO2 þ CaO lower density than the electrolytes. Therefore, the metal floats on top. The collector is helpful in the -CaOAl2O34SiO2 þ Li2Oat90021000 1C ð4Þ recovery of the metal. The electrical and ionic conductivities in the cell and the fluidity of the Li O þ H O þ 2HCl-2LiCl þ 2H O ð5Þ electrolyte, are critical parameters that control the 2 2 2 material and energy balance of the process. Electrolytic lithium is refined by remelting, when Lithium chloride is thus the source for electrolytic the insolubles either float to the surface or sink extraction of lithium. Metallic lithium can be obtained to the bottom of the melt pot. Potassium is only by the electrolysis of a melt, comprising of an equal slightly miscible in lithium. The remelting step mixture of lithium chloride and potassium chloride. A produces lithium metal with less than 100 ppm of schematic diagram of this cell can be seen in Fig. 1 potassium. (Freitas 2000). Lithium chloride is fed into the cell, which is operated at a temperature between 400 1C and 420 1C. The voltage across the cell of molten 2.3 Applications of Lithium lithium chloride and potassium chloride, is typically between 8 V and 9 V with a current consumption of Table 1 lists some of the physicochemical properties 40 kWh kg1 of lithium that is produced. A steel of the alkali metals. Its low density makes it a very useful alloying agent. The major industrial use of lithium is for lubricating greases in the form of lithium stearate. Lithium-based greases provide high temperature and water resistance as well as having good low temperature properties. A relatively new, but very popular application of lithium is for lightweight alkaline batteries in which the anode is comprised of lithium. Metallic lithium is also added to certain types of glasses and ceramics, as a flux to lower melting and sintering temperatures, as well as to lower the coefficient of expansion in the finished product (Fishwick 1974). Lithium can also be added to electrolytic cells in the production of aluminum to increase yield and reduce fluorine. Lithium also finds many uses in inorganic compounds, particularly in the form of chlorides and fluorides. Table 3 lists the prominent applications (Roskill 1979).

3. Sodium 3.1 Sources of Sodium Figure 1 Illustration of a cell for electrolytic production of As one of the most abundant minerals on earth, lithium (Freitas 2000). sodium is most commonly derived from natural salts.

Table 1 Physicochemical properties of lithium, sodium, and potassium. Properties Lithium Sodium Potassium At. weight (At. no) 6.94 (3) 22.98 (11) 39.1 (19) Melting point, 1C 180.5 97.8 63.7 Boiling point, 1C 1336 892 760 Density, g cm3 0.53 0.97 0.86 Thermal conductivity, cal/(s.cm.1C) 0.17 0.334 0.107 Specific heat (250 1C), cal g1 0.849 0.295 0.177 Heat of fusion, cal g1 103.2 27.05 14.6 Electronegativity, Pauling’s 1.0 0.9 0.8 Atomic volume, W/D 13.1 23.7 45.3

2 Alkali Metals Production (Li, Na, K)

Table 2 Physicochemical properties of relevant metal chlorides.

Properties LiCl NaCl KCl CaCl2 Melting point, 1C 610 800.7 771 775 Boiling point, 1C 1383 1465 1500 (sub) 1935 Density, g cm3 2.068 2.17 1.988 2.15 Mol. wt. 42.4 58.5 74.6 111 Std. free energy of formation (25 1C), kJ mol1 384.4 384.1 408.5 748.8 Std. dissociation potential, V 3.98 3.98 4.23 3.88 Elec. conductivity, O1cm1 5.814 3.657 2.303

Table 3 Applications of lithium compounds. Compound Application Lithium acetate Organic synthesis. Lithium aluminate Flux in highly refractory porcelain enamels. Lithium aluminum Preparation of vitamins, steroids, and Ziegler catalysts. Solvent drying and generation hydride of . Lithium tetraborate Ceramics. Lithium bromide Reconstitution of brines, catalyst and dehydro-halogenating agent, swelling agent for proteins. Lithium carbonate Enamels, glasses, glazes, and ceramic specialties. Extractive metallurgy of aluminum and uranium. Pharmaceutical. Lithium chloride Preparation of lithium metal, brazing fluxes, electrolytes of low-temperature dry cell batteries, fire extinguishing solutions. Lithium chromate brine Corrosion inhibitor for lithium chloride and bromide brines, industrial battery additive, paint remover. Lithium fluoride Strong flux for enamels, glasses and glazes, welding and brazing fluxes, of aluminum, heat sink material. Lithium hydride Amide and double hydrides of lithium, catalyst in polymerization reactions, hydrogen generation, radiation shielding, high energy fuels, fuel cells, heat sink, silane gas production. Lithium hydroxide Multi-purpose lubricating greases, additive to the KOH electrolyte of alkaline batteries, anhydrous lithium hydroxide used as a CO2 absorbent in air purification systems of submarines and space capsules, alkaline reagent for corrosion inhibition in steam boilers, component of copper electroplating baths, absorption of CO2 in air conditioning systems. Lithium manganite Bonding agent in ceramic bonded grinding wheels. Lithium molybdate Ceramics, corrosion inhibitor, metal surface treatment. Lithium nitrate Ammonia absorbent in refrigeration systems, oxidizing agent, flame colorant in fireworks. Lithium oxide Carbon dioxide absorption. Lithium peroxide Atmosphere regenerant, chemical oxidant. Lithium perchlorate Electrolyte constituent for lithium batteries, solid propellant mixtures for rockets, oxygen source. Lithium silicate Vehicle for water-based protective coatings, concrete sealant, adhesive, binder for welding rod coatings. Lithium sulphate High strength glass, photographic developer composition, tracer ingredient in chemical products.

The important sodium salts are sodium chloride commonly found in seawater, salt lakes, alkaline (rock salt), sodium carbonate (soda), sodium sulfate lakes, and mineral springs. Sodium chloride is the (thenardite), sodium nitrate (Chile salt peter), and typical starting material for the manufacture and sodium borate (borax). These sodium salts are extraction of sodium metal. Deposits of sodium

3 Alkali Metals Production (Li, Na, K) chloride in the United States are also in the form of salt domes and are found in Virginia, West Virginia, Texas, and Louisiana. Since these salts were depos- ited many years ago by pre-existing seas and lakes, most of the deposits are located underground. Therefore, these salts are typically flushed out of underground mines by solution mining with water in the form of brines.

3.2 Extraction and Purification Current commercial practice for manufacturing of metallic sodium is based almost entirely on the reduction of sodium chloride. The most important technique for reducing this salt is by electrolytic reduction using the Downs process. Direct electro- lysis of by the Castner process produced sodium prior to the advent of the Downs process. Carbothermic reduction of soda ash is also practiced as shown below: Figure 2 Illustration of a cell for electrolytic production of Na2CO3 þ 2C-2Na þ 3CO ð6Þ sodium (Freitas 2000).

Equation (6) is associated with an enthalpy change 3.3 Applications of Sodium 1 1 of DH298 ¼ 231 kcal g mol . Chalk is often added The greatest single demand for sodium in the world to keep the charge material pasty and to prevent the today is for the synthesis of tetraethyllead (Sittig separation of the molten sodium carbonate from 1956). This is used as an automotive gasoline additive carbon on heating in the thermochemical reduction to prevent engine knocking. This single application system. accounts for 60% of the metallic sodium that is In industry today, the most common way manufactured. In this process, a sodium–lead inter- of producing metallic sodium is through the use of metallic alloy is reacted with an ethyl chloride that a Downs cell. A Downs cell is comprised of a large yields tetraethyllead by the following reaction: steel vessel that is lined with refractory firebricks and is operated at 590 1C. The cell has a large, vertical, 4PbNa 4C H Cl- C H Pb 3Pb 4NaCl 7 central graphite anode descending from the bottom þ 2 5 ð 2 5Þ4 þ þ ð Þ of the cell that is surrounded by cylindrical steel cathodes. This creates an annular electrolysis zone. The lead that is not used in the reaction is recycled Figure 2 shows a schematic illustration of this cell back into the process. (Freitas 2000). A eutectic mixture of NaCl and CaCl2 Another major use of sodium is in the reduction of is used as the electrolyte. When this cell is activated, animal and vegetable oils into long-chain fatty gas is produced and must be removed from alcohols. These alcohols are then used in the the cell. As the product of sodium metal is lighter production of detergents and soaps. A third major than the bath material, it floats to the surface of the consumer of sodium is the Hunter’s process for the bath where it is collected by an inverted collector ring reduction of titanium and zirconium halides to their and forced up the collector tube. The resulting respective metals. The process of reducing these sodium that is collected in the reservoir is 99.8% halides with sodium has become more and more pure. The primary limitation of the Downs process is popular due to the cost of (Kroll process) the contamination of the product by calcium, which over the cost of sodium. The high thermodynamic has a solubility of 4–5 wt.%. At the cell oper- stability of sodium chloride with respect to the ating temperature. Holding the sodium at just above titanium or zirconium chloride makes it a useful its melting point, lowers calcium solubility to reductant. Metallic sodium also finds many uses in B100 ppm. Calcium contamination restricts the use inorganic compounds and solutions such as sodium of sodium as a reactor coolant due to its high affinity hydride, sodium amide, and sodium cyanide. Sodium for oxygen and nitrogen. Electrochemical reactions rock salt can also be used for curing fish and meat in are similar to that of a lithium cell where chlorine the packing and food preparation industry. Minor evolves at the anode and the metal deposits at the applications of sodium are found in a heat treating cathode (Foust 1979). medium, high temperature reactor kettles, fractional

4 Alkali Metals Production (Li, Na, K) condensers for metallic vapors, bus bars, sodium of potassium in the salt that causes short-circuiting in vapor lamps, photocells, modified aluminum alloys, the cell and the formation of metal fog. Salt mixtures and the hardening of bearing metals. with halides that are more stable than KCl have not been found, thus a low melting eutectic cannot be employed (Mausteller et al. 1967). Potassium can 4. Potassium only be formed using thermochemical techniques where sodium is used as the reductant. In this 4.1 Sources of Potassium process, commercial molten potassium chloride is The most important potassium compound in industry continuously fed to a packed distillation column is potassium chloride (KCl). Potassium chloride is where it is further heated (Fig. 3). The molten also found as potash, which is used as a fertilizer. chloride then encounters sodium vapors that are Potassium is abundant in seawater, as well as in flowing up through the column produced by a gas- mineral form in the Earth’s crust. Seawater contains fired reboiler (Freitas 2000). The resulting products 380 ppm potassium and the Earth’s crust contains of this interaction are sodium chloride and potassium 2.6% combined potassium (Dalrymple and Lanphere metal at equilibrium: 1969). Some of the important minerals of potassium 1 are sylvite (KCl), carnallite (MgCl2KCl), and poly- Na þ KCl-NaCl þ K; DGð871 1CÞ¼3 kcal mol ð8Þ halite (2CaSO4K2SO42H2O). From these minerals, some important compounds can be extracted, such as Equation (8) indicates that formation of pure potas- potassium hydroxide (KOH), potassium carbonate sium is not favorable. However, vaporization and (K CO ), and potassium nitrate (KNO ). 2 3 3 condensation of volatile potassium drives the reac- tion to the right. Variation in condenser temperature 4.2 Extraction and Purification and a sluggish removal of potassium can result in the production of NaK or potassium with sodium Potassium chloride (KCl) is the most important content of 1 wt.%. Sodium can be lowered to below potassium source, due to its wide use in fertilizers. 50 ppm by distillation in a multiplate tower. The Production of potassium by electrolysis, like sodium sodium chloride that is produced must be continu- and lithium is grossly inefficient due to back diffusion ously removed from the system.

Figure 3 Illustration of a cell for electrolytic production of potassium (Freitas 2000).

5 Alkali Metals Production (Li, Na, K)

4.3 Applications insolubility of titanium and titanium chloride in the salt, lower thermodynamic stability of titanium Most of the potassium that is processed goes chloride and lack of desire for intermetallic forma- into fertilizers in the form of potassium chloride. tion. In such a process, the metal compound can be Potassium chloride is also used in the production of continuously fed into the cell as lithium is being other potassium compounds and solutions such as electrolytically generated. potassium hydroxide. Potash also accounts for a lot of the potassium that is consumed for agricultural purposes. Finally, potassium can also be found in 6. Summary some explosives and as a coloring agent in fireworks. Lithium, sodium, and potassium are reactive alkali 5. Hybrid Processing metals that are produced from their chlorides. Due to the high thermodynamic stability of the chlorides, Lithium and sodium are very reactive metals that are electrolytic reduction at lower temperatures is com- produced by electrolytic means. Potassium is pro- mercially used by employing a eutectic salt mixture. duced by sodium reduction. These metals find Potassium chloride is pyrochemically reduced by applications in industry, particularly in the nuclear sodium, where potassium must be removed con- industry, as a reductant for other metal compounds stantly from the reaction site to enable the reduction. since the alkali metals form some of the most These alkali metals find extensive applications in thermodynamically stable compounds. This fact industry, mostly in the compound form and as a allows the development of a hybrid process where reducing agent and a coolant in the metallic form. the electrolytically produced metal can be used in situ These metals must be handled with care due to their to reduce another metal compound. The general strong affinity for oxygen and moisture. chemical scheme is given as follows:

þ 4LiCl-4Li þ 4Cl ð9aÞ Bibliography

4Cl-2Cl m þ 4e ð9bÞ Dalrymple G B, Lanphere M A 1969 Potassium–Argon Dating: 2 Principles, Techniques and Applications to Geochronology. W H Freeman and Company, San Francisco, CA 4Liþ þ 4e-4Li ð9cÞ Fishwick J H 1974 Applications of Lithium in Ceramics. Cahners Publishing Company, Boston, MA - Foust O J (ed.) 1979 Sodium-NaK Engineering Handbook. TiCl4 þ 4Li Ti þ 4LiCl ð9dÞ Gordon and Breach, New York, Vol. 5, Chap. 1, pp. 1–51 Freitas D M 2000 McGraw-Hill Science and Technology Encyclopedia. McGraw-Hill, New York TiCl4-Ti þ 2Cl2 ð10Þ Mausteller J W, Tepper F, Rodgers S J 1967 Alkali Metal Titanium tetrachloride has been used as an exam- Handling and Systems Operating Techniques. Gordon and ple of a metal compound. The equations indicate Breach, New York, pp. 4–7 that lithium is a nonconsumable reductant in this Roskill 1979 The Economics of Lithium, 3rd edn. Roskill process where titanium metal can be produced Information Services, London, UK Sittig M 1956 Sodium: Its Manufacture, Properties, and Uses. along with anodically discharged chlorine gas. This Reinhold Publishing Corporation, New York type of electrochemical/chemical hybrid reaction schemes is being extensively researched. Some of the requirements for using such a process include B. Mishra

Published by Elsevier Science Ltd 2003. Encyclopedia of Materials: Science and Technology ISBN: 0-08-043152-6 pp. 1–6

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