Platinum: An Invaluable Earth Resource Essay, Research Paper
Platinum: An Invaluable Earth Resource
The advent of the Industrial Revolution sparked worldwide large-scale use of minerals in the mid 18th and early 19th centuries, as well as continued growth during the next several hundred years. Over a period of 150 years from 1750-1900, global mineral use saw an increase of roughly 1000 percent while the world population merely doubled. Since 1900, mineral production has increased roughly 1300 percent (Young 6), and the world has become completely dependent upon the various uses of limited mineral resources. One mineral which has provided numerous uses for several diverse industrial markets is the valuable metal platinum (Pt).
Platinum is the most well known and widely used member of the six platinum metals of Group VIII, Period 6, of the periodic table. In order of increasing atomic weight, the platinum group metals are ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and the focus metal, platinum (Pt). Excluding osmium, all the aforementioned elements are silvery white in color.
According to historical record, gold artifacts containing platinum have been dated to approximately 700 BC; however, the presence of platinum in these materials was most likely accidental, or unknown. Similarly, 16th century Jesuits made reference to unidentified metallic pebbles contained within gold bars, making them brittle and hard to refine. These pebbles were most likely platinum based metals. Despite early sightings of platinum group metals, the pure, malleable platinum known and used today was not discovered until 1789 by French physicist P.F. Chabaneau. Upon its discovery, Chabaneau felt it worthy to present before Pope Pius VI in the form of a chalice, or trophy.
Geographic distribution of platinum is quite limited and appears in large quantities in a select few sites. The largest known deposit of platinum is found in the Bushveld Complex of South Africa, a country well known for its exquisite diamonds. Additional large deposits are located in the Sudbury deposit of Ontario, Canada, and the Norilsk-Talnakh deposit of Siberia in the former USSR. Montana’s Stillwater Complex is the major U.S. excavator of platinum-based metals, however, in comparison, U.S. production is miniscule compared to the aforementioned countries.
Three individual layered reefs of the Bushveld Complex in South Africa–the Merensky Reef, the UG2 Chromite Layer, and the Platreef–produce the country’s most significant amounts of platinum group metals (PGM). The PGM occur as alloyed native metals, as platinoid minerals, and in copper, nickel, cobalt, and iron sulfide minerals. (Hilliard FFF4) South Africa produced roughly 174,000 kilograms of PGM in 1998, a 2 percent increase from 1997 figures. In 1998, the Krasnoyarsk nonferrous metals plant produced 95 percent of all Russian PGM and most likely exported every ounce of the total 100, 000 kilograms that were recovered. (Hilliard FFF4) The Krasnoyarsk plant reportedly struck a deal with Impala Platinum Holdings Ltd., a South African based mining company, to ship platinum ores to be refined in Russia and then exported as pure metal beginning in 1999. Supposedly the deal would increase Krasnoyarsk plant operating capacity 5 percent to a total of 35 percent. (Hilliard FFF4) Canadian PGM output was much smaller in comparison to Russia and South Africa, coming in a distant third at 7,570 kilograms for 1998 production. The United States rounded out the top four with 1998 annual production at 3,240 kilograms of PGM. (Hilliard Table 2)
Mineral reserves are defined as “known and identified deposits of earth materials that can be extracted legally with economic efficiency, by using existing technology.” It is estimated that world reserves of platinum group metals in mineral concentrations presently or potentially economic to mine are in excess of 100 million kilograms. (Hilliard 127) South Africa alone is believed to hold around 63 percent of the world’s PGM reserves , which equates to nearly 63 million kilograms of the precious metals. This figure places South Africa at the top of the world reserve list for PGM. Russia captures the number two spot with a mere 6.9 million kilograms of reserves, while the United States follows in third with about 800,000 kilograms. These figures indicate that the supply of platinum and its PGM counterparts will be unlikely to run out in the near future.
Aside from small alluvial deposits of platinum, practically no ores exist where platinum is the major metal. Usually, platinum based minerals are widely dispersed in sulfide ores such as pentlandite [(Ni, Fe)9S8], laurite (RuS2), irarsite [(Ir, Ru, Rh, Pt)AsS], osmiridium (Ir, Os), cooperite (PtS), and braggite [(Pt, Pd)S]. (Brittanica, Platinum Group) Most of the major platinum deposits are exploited through underground mining techniques. As mentioned prior, basically all platinum group metals are extracted from copper or nickel sulfide minerals that are concentrated by floatation separation. Smelting of the concentrate produces a matte that is filtered of copper and nickel sulfides in an autoclave. (Brittanica, Platinum Group) The filtered material is composed of 15 to 20 percent platinum group metals.
Of all metals, the platinum group is among the most difficult and time consuming to separate from ore. Separation of platinum ores traditionally begins with a mineral concentrate as described above, in a process called “individual solubilization.” The concentrate is leached with aqua regia (Brittanica, Platinum Group), that dissolves the platinum (and palladium) and leaves other metals in solid form. Using ammonium chloride, the platinum is precipitated from solution, and the ensuing platinum salt is captured by filtration and heated to form a metallic powder. The powder is then redissolved in aqua regia and reprecipitated with ammonium chloride and calcined to pure platinum metal. (Brittanica, Platinum Group) The palladium which resided with the platinum in the original ore is recovered in a similar fashion by converting it to salt form, and then altering it to metallic form.
Similarly, a second form of recovering platinum is the “simultaneous solubilization” technique. Simultaneous solubilization is achieved by fusing the mineral concentrate gathered from the copper and nickel sulfide ores with aluminum metal. The aluminum is dissolved, and the leftover material is treated with hydrochloric acid and chlorine. This, in turn, dissolves all platinum group metals within the material which are then separated by solvent extraction. (Brittanica, Platinum Group) Individual metal suspensions are then treated by standard techniques to recover the metals in a pure state.
Reprocessing procedures to recover platinum group metal scrap is dependent upon the type of metal desired. In the case of platinum itself, the scrap can be redissolved in aqua regia and recovered from solution by previously discussed methods. Most platinum scrap is gathered from automotive catalytic converters. Other popular techniques to recover minerals, such as assaying, are not practical with platinum due to its extremely weak concentration in ore, often less than one part per million. Therefore, most processing of platinum is done with individual or simultaneous solubilization.
Structural uses of platinum range from jewelry, to electronics, to cancer therapy; however, most platinum is consumed by the auto industry for use in catalytic converters. Ironically, despite its resistance to most chemical reagents, platinum is an outstanding catalyst that easily accelerates or controls oxidation, reduction, and hydrogenation reaction rates. For this reason, 90 percent of platinum produced in the Western world, and 35 percent worldwide, is employed in the use of automobile catalytic converters to promote conversion of unburned hydrocarbons. (Hilliard FFF1) However, due to stricter hydrocarbon standards stemming from the Clean Air Act of 1990, platinum share of the automobile catalyst market is being eroded by palladium, another significant PGM, because of its superior hydrocarbon control and smaller price tag.
Recently, demand for platinum has drastically increased in the electronics and glass industries where the unique physical and chemical properties of platinum can be fully exploited. A need for high-quality glass for use in liquid crystal displays and cathode ray tubes drove demand for platinum in the glass industry, while increases in computer hard disk production (surface coated with platinum alloys) fueled demand in the electronic industry. Likewise, demand for platinum in biotechnology has increased due to the expanding use of platinum salts in cancer chemotherapy.
As mentioned throughout, platinum has been subject to fluctuations in demand throughout recent history; however, changes in supply have also had major effects upon platinum distribution, prices, and applications. For the third consecutive year, slow shipments from Russia in the first half of 1998 caused tightness in the major PGM market that resulted in higher prices. (Hilliard FFF3) The auto industry maintained its role as the leading consumer of PGM metals in 1998, accumulating 35 percent of platinum sales worldwide. Yet, despite growth in auto sales during this time period, demand for platinum by the auto industry fell almost 5 percent to 56,900 kilograms. This change in consumption is a direct result of tighter control upon hydrocarbon emissions from the Clean Air Act of 1990. Platinum based catalyst technology is now being traded on a large scale for palladium-based catalysts due to palladium’s increased hydrocarbon emission control and cheaper price tag. Therefore, over time, it will be likely that platinum use will be slowly phased out of the automobile industry for use in catalytic converters, and more platinum will be bought for use in the electronic, glass, and jewelry industries.
In summary, platinum is a relatively young element in terms of geological discovery, but is also a very productive element in terms of industry uses. The world owes much to platinum and other platinum-based metals for their effective regulation of hydrocarbon emissions from automobiles in the last 25 years. The explosion of the personal computer industry has also felt the need of platinum within its product lines and has much invested in platinum technologies. Recently, platinum jewelry has also become very popular as a substitute for such precious metals as gold and silver, and demand will certainly increase in this market in the following years. Platinum reserves are steady and do not display any shortage of the valuable metal in the near or distant future. For these reasons and more, platinum will continue to be an important metal in the lives of humans now, and in the future, claiming more market demand and industry use.
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“Platinum Group.” Britannica Online. Vers. 99.1.1. Encyclopaedia Britannica. [http://www.brittanica.com/]. February 2000.
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