Platinum

Uses

Jewelry; oxygen sensor in internal combustion engines; chemical and electrical industries; dentistry; windings of hightemperature furnaces; electroplating; photography; cancer chemotherapeutic agents

Chemical Properties

Platinum is a silvery to whitish-gray metal, that is malleable and ductile (Weast, 1988; Krebs, 2006). It is estimated that the average platinum concentration in the earth’s lithosphere ranges from 0.001 to 0.005 mg/kg (WHO, 1991). It has a vapor pressure of approximately 0mmHg (NIOSH, 2005). Platinum, depending on mining location, is found in sperrylite, cooperite, braggite, and copper–nickel sulfide ores, and in alloys with other members of the platinum group elements (PGE; iridium, osmium, palladium, ruthenium, and rhodium) (Dubiella-Jackowska et al., 2009; Weast, 1988; WHO, 1991). Both elemental platinum and platinum salts are used in industry. Elemental platinum is insoluble in water whereas many of the platinum salts are water soluble to varying degrees, depending on their specific chemical properties (WHO, 1991). Platinum metal is inert and resists corrosion (Krebs, 2006). However, platinum halide salts are considered potent allergens that have a high risk of causing sensitization (Linnett, 2005). Platinum bonds with halogens in its +2 and +4 oxidation state (Krebs, 2006). The charge of the salt and the presence and number of halides, especially chloride, in a complex platinum salt may affect the degree of mammalian sensitivity to a specific salt (Cleare et al., 1976; Mapp et al., 1999; Merget et al., 2000; Ravindra et al., 2004; Pepys, 1980).

Uses

Platinum is found in the environment naturally and from anthropogenic sources. Platinum is primarily used in industry as a catalyst, predominately for the production of vehicle catalytic converters. Platinum is also used in the chemical, electrical, glass, dental, healthcare, pharmaceutical, petroleum, and jewelry fields. In addition to its catalytic properties, platinum, in combination with cobalt, has powerful magnetic properties.
Platinum metal and its alloys have numerous applications. As a precious metal it is used extensively in jewelry. Other important applications include construction of laboratory crucibles and high temperature electric furnaces; in instruments as thermocouple elements; as wire; for electrical contacts; as electrodes; in dentistry; in cigarette lighters; and for coating missile and jet engine parts.
Platinum also is used extensively as a catalyst in hydrogenation, dehydrogenation, oxidation, isomerization, carbonylation, and hydrocracking. Also, it is used in organic synthesis and petroleum refining. Like palladium, platinum also exhibits remarkable ability to absorb hydrogen. An important application of platinum is in the catalytic oxidation of ammonia in Ostwald's process in the manufacture of nitric acid. Platinum is installed in the catalytic converters in automobile engines for pollution control.

Description

Platinum was discovered in Colombia, South America by Ulloa in 1735 and six years later in 1741 by Wood. The metal was isolated from native platinum by Delisle in 1775 and produced in malleable form by Chabaneau in 1786. Wollaston in 1803 developed a method of obtaining pure malleable platinum from crude platinum by extraction with aqua regia. The process led to the discovery of two other platinum group metals, palladium and rhodium, that were found in the aqua regia extract after platinum precipitated. Platinum derived its name from platina originating from the Spanish word plata for silver, because it was thought to be a trivial unwanted material associated with gold in gold mines of Central America.
Platinum occurs in nature as a bright-white cubic crystalline solid with metallic luster associated with other noble metals of its group. Platinum also occurs as the mineral sperrylite, PtAs2, found as tin-white brittle cubic crystals containing 52−57% platinum in certain nickel-bearing deposits. Some other minerals of platinum are cooperite PtS (Pt 80-86%); and braggite(Pt, Pd, Ni)S (Pt 58-60%). The abundance of platinum in the earth’s crust is estimated to be 0.005 mg/kg.

Chemical Properties

Platinum is a soft, ductile, malleable, silverwhite metal. It is found in the metallic form and as the arsenide, sperrylite. It forms complex soluble salts, such as Na2PtCl6. It also forms halides. Metallic platinum is insoluble in water. Platinum(IV) chloride is red-brown crystals or powder.

Chemical Properties

silvery gray, lustrous, ductile metal; fcc, a=0.39231nm; also has black powder(s) and spongy mass forms; vapor pressure at mp 0.0187Pa; electrical resistivity, μohm· cm: 10.6 (20°C), 9.85 (0°C); Brinell hardness 97; does not corrode or tarnish; attacked by Cl2 at high temperatures; Poisson’s ratio 0.39; enthalpy of fusion 22.17kJ/mol; used as a catalyst for chemical, automotive, and petroleum industries [KIR82] [HAW93] [MER06] [CRC10]

Physical properties

Platinum is classed by tradition and commercial usefulness as a precious metal that is soft,dense, dull, and silvery-white in color, and it is both malleable and ductile and can be formedinto many shapes. Platinum is considered part of the “precious” metals group that includesgold, silver, iridium, and palladium. It is noncorrosive at room temperature and is not solublein any acid except aqua regia. It does not oxidize in air, which is the reason that it is foundin its elemental metallic form in nature. Its melting point is 1,772°C, its boiling point is3,827°C, and its density is 195.09g/cm³.

Isotopes

There are a total of 43 isotopes for platinum. Five of these are stable, andanother has such a long half-life that it is considered practically stable (Pt-190 with ahalf-life of 6.5×10⁺¹¹ years). Pt-190 contributes just 0.014% to the proportion of platinumfound on Earth. The stable isotopes and their contributions to platinum’s existenceon Earth are as follows: Pt-192 = 0.782%, Pt-194 = 32.967%, Pt-195 = 33.832%, Pt-196 = 25.242%, and Pt-198 = 7.163%. All the other isotopes are radioactive and areproduced artificially. They have half-lives ranging from a few microseconds to minutes tohours, and one has a half-life of 50 years (Pt-193).

Origin of Name

The name “platinum” is derived from the Spanish word platina, which means “silver.”

Occurrence

Platinum is the 75th most abundant element and, unlike many elements, is found in itspure elemental form in nature, as are deposits of silver and gold. Platinum is widely distributedover the Earth and is mined mainly in the Ural Mountains in Russia and in South Africa,Alaska, the western United States, Columbia in South America, and Ontario in Canada.When found in the mineral sperrylite (PtAs₂), it is dissolved with aqua regia to form a precipitatecalled “sponge” that is then converted into platinum metal. It is also recovered as aby-product of nickel mining, mainly in Ontario, Canada.

Characteristics

Platinum is the main metal in the platinum group, which consists of metals in both period5 and period 6. They are ruthenium (Ru), rhodium (Ro), and palladium (Pd) in period 5 andosmium (Os), iridium (Ir), and platinum (Pt) in period 6. All six of these metals share someof the same physical and chemical properties. Also, the other metals in the group are usuallyfound in platinum ore deposits.
Platinum can absorb great quantities of hydrogen gas, which makes it useful as a catalystin industry to speed up chemical reactions.

History

Discovered in South America by Ulloa in 1735 and by Wood in 1741. Platinum was used by pre-Columbian Indians. Platinum occurs native, accompanied by small quantities of iridium, osmium, palladium, ruthenium, and rhodium, all belonging to the same group of metals. These are found in the alluvial deposits of the Ural mountains and in Columbia. Sperrylite (PtAs2), occurring with the nickel-bearing deposits of Sudbury, Ontario, is a source of a considerable amount of metal. The large production of nickel offsets there being only one part of the platinum metals in two million parts of ore. The largest supplier of the platinum group of metals is now South Africa, followed by Russia and Canada. Platinum is a beautiful silvery-white metal, when pure, and is malleable and ductile. It has a coefficient of expansion almost equal to that of soda–lime–silica glass, and is therefore used to make sealed electrodes in glass systems. The metal does not oxidize in air at any temperature, but is corroded by halogens, cyanides, sulfur, and caustic alkalis. It is insoluble in hydrochloric and nitric acid, but dissolves when they are mixed as aqua regia, forming chloroplatinic acid (H2PtCl6), an important compound. Natural platinum contains six isotopes, one of which, 190Pt, is radioactive with a long half-life. Thirtyseven other radioactive isotopes and isomers are recognized. The metal is used extensively in jewelry, wire, and vessels for laboratory use, and in many valuable instruments including thermocouple elements. It is also used for electrical contacts, corrosion-resistant apparatus, and in dentistry. Platinum–cobalt alloys have magnetic properties. One such alloy made of 76.7% Pt and 23.3% Co, by weight, is an extremely powerful magnet that offers a B-H (max) almost twice that of Alnico V. Platinum resistance wires are used for constructing hightemperature electric furnaces. The metal is used for coating missile nose cones, jet engine fuel nozzles, etc., which must perform reliably for long periods of time at high temperatures. The metal, like palladium, absorbs large volumes of hydrogen, retaining it at ordinary temperatures but giving it up at red heat. In the finely divided state platinum is an excellent catalyst, having long been used in the contact process for producing sulfuric acid. It is also used as a catalyst in cracking petroleum products. There is also much current interest in the use of platinum as a catalyst in fuel cells and in its use as antipollution devices for automobiles. Platinum anodes are extensively used in cathodic protection systems for large ships and ocean-going vessels, pipelines, steel piers, etc. Pure platinum wire will glow red hot when placed in the vapor of methyl alcohol. It acts here as a catalyst, converting the alcohol to formaldehyde. This phenomenon has been used commercially to produce cigarette lighters and hand warmers. Hydrogen and oxygen explode in the presence of platinum. The price of platinum has varied widely; more than a century ago it was used to adulterate gold. It was nearly eight times as valuable as gold in 1920. The price in January 2002 was about $430/troy oz. ($15/g), higher than the price of gold.

Uses

Because of its chemical and physical properties, platinum has many uses. It is used widelyin jewelry making and is often mixed with gold to improve gold’s strength and durability.
In the early 1800s it was known that when hydrogen is passed over powdered platinum, thehydrogen ignites without being heated and without consuming the platinum. This propertyled to a major use of platinum as a catalyst to speed up chemical reactions. An example is presentin the internal combustion engine that produces harmful gases. Gasoline fuel burns insidethe engine, as compared to the steam engine, where the fuel is burned outside the engine. Thecatalytic converter in automobiles uses a platinum-coated ceramic grid in the exhaust systemto convert unburned fuel to carbon dioxide and water. The platinum in the converter will lastas long as the car since a catalyst is not consumed by the chemical reaction.
As a catalyst, platinum is used for hydrogenation of liquid vegetable oils to produce solidforms of the oil, such as margarine. It is also used in the cracking process that breaks downlarge crude oil molecules into smaller, more useful molecules, such as gasoline. The catalyticproperties of platinum make it useful in the production of sulfuric acid (H₂SO₄) and in fuelcells that unite hydrogen and oxygen to produce electricity.

Uses

Platinum is a white noble metal that looks very much like metallic silver found in copper ore. The name platinum comes from the Spanish word plata, meaning silver. Platinum compounds were used in the platinum printing process and for toning silver images.

Uses

manufacture of apparatus for laboratory and industrial use, thermocouples, platinum resistance thermometers, acidproof containers, electrodes, etc. In dentistry; jewelry; electroplating. As oxidation catalyst in manufacture of acetic acid, nitric acid from ammonia, manufacture of sulfuric acid; control of automotive emissions.

Production Methods

Platinum is obtained mainly from copper and nickel ores, and platinum alloys and by recovery from the catalyst and other waste. The main stages of platinum production include extraction of the precious metal concentrate from the ore followed by separation through a complex refining process, during which the concentrate is dissolved in aqua regia, and the platinum is precipitated in the form of ammonium(IV) hexachloroplatinate. The precipitate is then calcinated at 600–700 °C to give platinum sponge, which is then hardened by melting at high temperatures, such as in the electric arc. The resultant gray platinum sponge contains 99.95–99.9% pure metal. Another method of platinum production involves its reduction to metal from the aqueous platinum salts by zinc, magnesium, iron, or aluminum. Similar procedures are used to recover platinum from the catalytic converters and other waste. The hexachloroplatinic(IV) acid produced by treating platinum with aqua regia is an important chemical platinum compound used to obtain various platinum salts.

Definition

platinum: Symbol Pt. A silverywhite metallic transition element(see also platinum metals); a.n. 78;r.a.m. 195.09; r.d. 21.45; m.p. 1772°C;b.p. 3827±100°C. It occurs in somenickel and copper ores and is alsofound native in some deposits. Themain source is the anode sludge obtainedin copper–nickel refining. Theelement is used in jewellery, laboratoryapparatus (e.g. thermocouples,electrodes, etc.), electrical contacts,and in certain alloys (e.g. with iridium or rhodium). It is also a hydrogenationcatalyst. The elementdoes not oxidize nor dissolve inhydrochloric acid. Most of its compoundsare platinum(II) orplatinum(IV) complexes.

Definition

A silvery-white malleable ductile transition metal. It occurs naturally in Australia and Canada, either free or in association with other platinum metals. It is resistant to oxidation and is not attacked by acids (except aqua regia) or alkalis. Platinum is used as a catalyst for ammonia oxidation (to make nitric acid) and in catalytic converters. It is also used in jewelry. Symbol: Pt; m.p. 1772°C; b.p. 3830 ± 100°C; r.d. 21.45 (20°C); p.n. 78; r.a.m. 195.08.

General Description

Silvery, whitish-gray, malleable, ductile metal. Mp: 1772°C; bp: 2187°C. Density: 21.45 g cm-3 at room conditions (very dense). Also shipped as a finely divided powder (Platinum black), as a sponge, and as particles deposited on a supporting material such as alumina. Has strong catalytic activity in these forms; finely divided Platinum can be dangerous to handle in the vicinity of other chemicals on this account. Used Platinum catalysts are particularly dangerous and can be explosive.

Reactivity Profile

Massive Platinum (lump, ingot, etc.) is generally inert. Dissolves readily in aqua regia (mixture of concentrated hydrochloride and concentrated nitric acids). Reacts rapidly with molten alkali metal oxides and peroxides. Reacts with F2 and Cl2 at red heat. Absorbs large volumes of hydrogen when hot. Catalyzes the exothermic oxidation of ammonia by air. Finely divided Platinum is incompatible with aluminum, acetone, arsenic, ethane, hydrazine, hydrogen peroxide, lithium, phosphorus, selenium, tellurium and many fluorides. Explosion can occur upon contact with hydrogen peroxide. Platinum black, sponge and supported catalysts have strong catalytic activity; can be dangerous to handle in the vicinity of other chemicals on this account. Used Platinum catalysts are particularly dangerous and can cause explosions. Ethanol or methanol can ignite on contact with a Platinum-black catalyst. (Urben 1794).

Hazard

Fine platinum powder may explode if near an open flame. Because platinum is rather inertin its elemental metallic form, it is not poisonous to humans, but some of its compounds,particularly its soluble salts, are toxic if inhaled or ingested.

Health Hazard

Exposure to the complex salts of platinum, especially ammonium hexachloroplatinate and ammonium tetrachloroplatinate, but not elemental platinum, may cause skin sensitization and a progressive allergic reaction that may lead to pronounced asthmatic symptoms.
The signs and symptoms of hypersensitivity include urticaria, contact dermatitis of the skin, and respiratory disorders ranging from sneezing, shortness of breath, and cyanosis to severe asthma. The latency period from the first contact with platinum to the occurrence of the first symptoms varies from a few weeks to several years.

Flammability and Explosibility

Non flammable

Safety Profile

Questionable carcinogen with experimental tumorigenic data by implant route. Finely divided platinum is a powerful catalyst and can be dangerous to handle. Used catalysts are especially dangerous and may be explosive. May undergo hazardous reactions with aluminum, acetone, arsenic, carbon + methanol, nitrosyl chloride, dioxygen difluoride, ethanol, hydrazine, hydrogen + air, hydrogen peroxide, lithium, methyl hydroperoxide, ozonides, peroxpmonosulfuric acid, phosphorus, selenium, tellurium, vanadium dichloride + water. See also PLATINUM COMPOUNDS.

Potential Exposure

Platinum and its alloys have high electrical conductivity and excellent catalytic properties. They are used in relays, contacts and tubes in electronic equipment, in spark plug electrodes for aircraft; and windings in high-temperature electrical furnaces. Platinum alloys are used for standards for weight, length, and temperature measurement. Platinum and platinum catalysts, for example, hexachloroplatinic acid and H2PtCl6, are widely used in the chemical industry in persulfuric, nitric, and sulfuric acid production, in the synthesis of organic compounds and vitamins, and for producing higher octane gasoline. They are coming into use in catalyst systems for control of exhaust pollutants from automobiles. They are used in the equipment for handling molten glass and manufacturing fibrous glass; in laboratory, medical, and dental apparatus; in electroplating; in photography; in jewelry; and in X-ray fluorescent screens. Because platinum complexes are used as antitumor agents, the potential for carcinogenic activity is present; tests to clarify this aspect should be conducted. While low levels of emissions of platinum particulate have been observed from some catalyst-equipped automobiles, the major potential source of Pt is from the disposal of spent catalysts.

Environmental Fate

Inhalation of industrial platinum compounds may be a problem. The general population is exposed to platinum by the dermal route, especially from jewelry. The oral route is not significant because the absorption is very poor.
Platinum can enter the environment through automobile emissions from the platinum-containing catalytic converter.Relatively high levels of platinum can be found along congested roadways. A number of chemotherapeutic agents contain platinum and thus their disposal can lead to environmental contamination. In industrialized regions, relatively high concentrations can be found in waterway sediments. Organic matter binds to the metal. In soil, mobility depends on pH, redox potential, and chloride concentration. Platinum will likely only mobilize under highly acidic conditions or in soil water with high chloride content. Some platinum (IV) complexes, in the presence of platinum (II), may undergo methylation by microorganisms.

Shipping

UN3089 Metal powders, flammable, n.o.s., Hazard Class: 4.1; Labels: 4.1-Flammable solid.

Toxicity evaluation

While the metal itself is systemically of little concern, its salts are very toxic. The cis-platinum compounds can react with disulfides and amino groups and form adducts with some bases in nucleic acids. Platinum compounds inhibit a few enzymes, including leucine aminopeptidase, and the hydrogenases of malate, alcohol, and lactate. Cisplatin can form crosslinks between strands of DNA.

Incompatibilities

Dust or powder may form explosive mixture with air. Platinum metal is incompatible with aluminum; acetone, arsenic, ethane, hydrazine, hydrogen peroxide; lithium, phosphorus, selenium, tellurium, various fluorides.

Waste Disposal

Catalyst disposal is expected to be the largest contributor of Pt to the environment. The value of the metal would help to offset the cost of reclaiming the Pt from discarded catalysts. If direct vehicular emissions of Pt are found to be significant, particulate taps, which are available at reasonable cost, may provide a technological solution. In any event, recovery and recycling is the preferred technique for both health and economic reasons. Details of platinum recovery and recycling from plating wastes, platinum metal refinery effluents; spent catalysts and precious metals scrap have been published.