48 | The History and Use of Our Earth’s Chemical Elements AbundanceandSource
48 | The History and Use of Our Earth’s Chemical Elements AbundanceandSource
Lithium ranks 33rd among the most abundant elements found on Earth. It does not exist in pure metallic form in nature because it reacts with water and air. It is always combined with other elements in compound forms. These lithium mineral ores make up only about 0.0007%, or about 65 ppm, of the Earth’s crust.
Lithium is contained in minute amounts in the mineral ores of spodumene, lepidolite, and amblygonite, which are found in the United States and several countries in Europe, Africa, and South America. High temperatures are required to extract lithium from its compounds and by electrolysis of lithium chloride. It is also concentrated by solar evaporation of salt brine in lakes.
Metallic lithium is produced on a commercial scale by electrolysis of molten lithium chlo- ride (LiCl) that is heated as a mixture with potassium chloride (KCl). Both have a rather high melting point, but when mixed, the temperature required to melt them (400°C) is several hundred degrees lower than their individual melting points. This liquid mixture of LiCl and KCl becomes the electrolyte. The anode is graphite (carbon) and the cathode is steel. The molten liquid positive lithium cations collect at the cathode while negative chlorine anions collect at the anode, and the potassium chloride remains in the electrolyte. Each positive ion of lithium that collects at the cathode gains an electron, thus producing neutral atoms of molten lithium metal, which is then further purified.
History The mineral petalite was mined as an ore in Sweden. In 1817 Johan August Arfwedson
(1792–1841) analyzed this new mineral. After identifying several compounds in the ore, he realized there was a small percentage of the ore that could not be identified. After applying more analytical procedures, he determined it was a new alkali. It turned out that petalite
contains lithium aluminum silicate, LiAl(Si 2 O 5 ) 2 . In 1818 the first lithium metal was pre- pared independently by two scientists, Sir Humphry Davy (1778–1892) and W. T. Brande (1788–1866). Lithium was discovered at a time in the early nineteenth century when numer- ous “new” elements were discovered and identified by other scientists. Many of these newly named elements were predicted by the use of the periodic table of the chemical elements.
CommonUses Lithium has many uses in today’s industrial society. It is used as a flux to promote the fus-
ing of metals during welding and soldering. It also eliminates the formation of oxides during welding by absorbing impurities. This fusing quality is also important as a flux for producing ceramics, enamels, and glass.
A major use is as lithium stearate for lubricating greases. It makes a solid grease that can withstand hard use and high temperatures. Lithium is used to manufacture electric storage cells (batteries) that have a long shelf life for use in heart pacemakers, cameras, and so forth. Some lithium compounds are used as rocket propellants, nuclear reactor coolants, alloy hardeners, and deoxidizers and to make special ceramics. Lithium is a source of alpha particles when bombarded in a nuclear accelerator. The fol- lowing occurs: lithium nuclei (3 protons + 4 neutrons) are targeted by high-speed protons (hydrogen nuclei), resulting in lithium absorbing a proton to form 4 protons + 4 neutrons,
Guide to the Elements | 49
1 H+ 3 Li = 2 He + 2 He. This is an example of the first man-made nuclear reaction produced by Sir John Cockcroft (1897–1967) and Ernest Walton (1903–1995) in 1929. Several compounds of lithium are used as pharmaceuticals to treat severe psychotic depression (as antidepressant agents). And lithium carbonate is also used as a sedative or mild tranquilizer to treat less severe anxiety, which is a general feeling of uneasiness or distress about present condition or future uncertainties. Lithium is also used in the production of vitamin A.
ExamplesofCompounds There are numerous compounds of lithium. Its atoms combine with many other elements
to form a variety of compound molecules. Some form as single oxidation states, with one lithium cation combining with one anion (+1 combines with –1), and the more complex compounds involve two positive lithium cations combining with two negative anions (+2 combines with –2). Some examples follow:
Lithium chloride (Li + + Cl - → LICl) is used as an antidepressant, especially in the treatment of manic depression and bipolar disorders. Lithium hydroxide (Li + + OH - → LiOH) is used in storage batteries and soaps and as CO 2 absorber in spacecrafts. Lithium hydride (Li + +H - → LiH) is a bluish-white crystal that is flammable in moisture. Used as a source of hydrogen gas that is liberated when LiH becomes wet. LiH is an excel- lent desiccant and reducing agent as well as a shield that protects from radiation created by nuclear reactions.
Lithium Fluoride (Li + +F - → LiF) is used to produce ceramics and rocket fuel and is used as welding and soldering flux and in light-sensitive scientific instruments (e.g., X-ray diffraction, which is the scattering of X-rays by crystals that produce a specific pattern of that crystal’s atoms, thus producing a technique for identifying different elements).
Lithium oxide (2Li ++ +O – → Li 2 O) is a strong alkali that absorbs carbon dioxide and water from the atmosphere. It is used in manufacturing ceramics and special types of glass. Lithium carbonate (2Li ++ + (CO 3 ) – → Li 2 CO 3 ) is used as a compound for producing metal- lic lithium. Lithium carbonate is the result of treating the mineral spodumene with sulfuric acid and then adding calcium carbonate. It is used as an antidepressant.
Lithium aluminum deuteride (LiAlD 4 ) is used as a source of deuterium atoms (heavy hydro- gen, 1 D-2) to produce tritium ( 1 T-3) (super heavy hydrogen) for cooling nuclear reactors.
Hazards Lithium metal is highly flammable, explosive, and toxic. It will ignite when exposed to
water, acids, and even damp air. Metallic lithium is a reducing agent that readily gives up an electron to active oxidizing agents that require an electron to complete their outer valence shell—thus the violent chemical reaction that follows. Lithium will even burn in nitrogen gas, which is relatively stable. In addition, many of its compounds also react violently when exposed to water.