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Flow of Platinum and the

Platinum Group Metals

in the United States 
 
 

1. Introduction
2. Uses of PGM
3. Sources of PGM
4. Releases to the environment
5. Conclusion
6. References

I.  Introduction 

Platinum (Pt) is a malleable, silvery metal found at trace quantities in the lithosphere.  It is commonly grouped with five other elements:  Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Osmium (Os) and Irridium (Ir).  These metals, which exhibit similar properties, are referred to as the Platinum Group Metals (PGM) or Platinum Group Elements (PGE).  Mineral deposits containing platinum will contain portions of the other PGMs in varying amounts.  The following diagram depicts the location of PGMs in the periodic table: 
 
 

The platinum group metals are often referred to as “noble metals” due to their resistance to oxidation.  These metals are also characterized as exhibiting high melting points, mechanical strength at high temperatures, stable electrical properties, high density, and non-contaminating behavior.   Platinum is highly resistant to discoloration and wear. 

The primary use of PGM is in automobile catalytic converters.  These devices are used to reduce harmful automobile emissions which impact air quality.  It is therefore interesting to look at the material flows associated with the generation of PGM, since the primary application of these materials is associated with environmental protection. 
 

II.  Uses of platinum and PGMs 

PGMs are most commonly used as catalysts.  In the United States, PGM consumption is primarily as coatings in automotive catalytic converters, followed by catalysts for various industrial processes.¹  Other applications of platinum and the PGM include electrical conductors, extrusion devices, dental and medical prostheses and jewelry.  A significant amount of platinum is used to make equipment for handling molten glass during glass manufacturing, including the manufacturing of fiberoptic cable. Over ninety percent of today’s computer disk drives contain a Pt-Co magnetic layer.  A portion of platinum consumption is attributable to speculation (coins).  Platinum compounds are used in the treatment of certain cancers.  A more recent application is as a catalyst in fuel cells. 

The following table summarizes year 2001 consumption of platinum and palladium in North America (Johnson Matthey, 2003): 

The following is a discussion of the most prevalent applications of PGM: 

Catalytic converters:  Catalytic converters have been required in cars since 1974, and today constitute the most common application of PGM.  Catalytic converters are used to treat automobile emissions by catalyzing the oxidation of carbon monoxide and hydrocarbons, and the reduction of NOx (transforming them to less toxic substances including CO2, water and nitrogen gas).  They are constructed by applying a film of platinum, palladium and ruthenium on a ceramic “monolith”.  It is estimated that the average catalytic converter on the market contains 1.5 g of PGM (USGS, 1998).  The proportion of the three metals varies considerably.   The following diagrams depicts the location of catalytic converters in an automobile, and a common “honeycomb” catalyst design: 
 

Source: http://www.howstuffworks.com/catalytic-converter.htm 

Petroleum refining catalysts: PGM are used in as catalysts in reforming processes, in which organic molecules are upgraded into more valuable products under heat and pressure.  In these applications, catalysts will over time develop a coating of coke, which may be removed to restore the catalyst surface.  After a catalyst has been restored several times it begins to lose its efficiency and is considered to be “spent”.  PGM group metals used for this application have an exceptionally high recovery rate. 

Chemical process catalysts:  The chemical industry uses PGM as catalysts in a variety of reactions.  A common application is the oxidation of ammonia to nitric oxide (the raw material for fertilizers, explosives and nitric acid).  This reaction is performed in the presence of pure platinum or platinum-rhodium alloy gauze (USGS website).  A small amount of catalyst material may be transferred the reaction products during these reactions. 
 

III.  Sources of PGM 

Mining:

Platinum and PGM ores are found in Canada, South Africa, Russia, and the United States.  South Africa is the largest producer of platinum, and Russia is the largest producer of palladium. In Canada and Russia, PGM are produced as a byproduct of nickel-copper mining.  In 2001, worldwide PGM production consisted of 44% platinum, 43% palladium, and 13% other (by weight).  (USGS, 2001)  In 2001, the United States relied on imports for 90% of platinum consumption, and 87% of palladium consumption.

PGM production in the United States is limited to the Stillwater Complex located in Montana.  In 2000, 5% of the world’s supply of palladium, and 2% of the world’s supply of platinum came from this mine (Stillwater Mining Company, 2003).  The Complex includes facilities for mining, milling, smelting and refining of PGM ores.  Stillwater also processes spent auto catalysts. 

At the Stillwater Complex, ore is first smelted to produce a matte (metal sulphide mixture).  The matte is refined to form a “filter cake”, in which the combined platinum and palladium content has been enriched to 60%.  The cake is sent to smelters in California, New Jersey and Germany for refining.   

In 2001, Stillwater produced 12,100 kg of palladium and 3,610 kg of platinum.  These metals were refined from 827,000 metric tons of ore, indicating that roughly 52 tons of ore were required to recover one kilogram of PGM. Or, inversely, 19 g of PGM were recovered per ton of ore.  

Wastes generated during mining:

Stillwater’s operations have resulted in the generation of hazardous wastes that are recorded in TRI.  Air emissions from the mine and solid wastes impounded at the mine site have included barium, barium compounds, chromium compounts, copper, copper compounds, mercury, nickel, nickel compounds, and nitrate compounds.  Air emissions from the smelter have included chromium compounds, copper, nickel and nickel compounds.  The TRI also indicates that solid wastes from the smelter and refinery are disposed of at the mine.  In 1999, 135,000 pounds of chromium waste was transported from the smelter to the mine for storage. 

The following charts shows the release of toxic materials from Stillwater facilities in recent years.  These values eclipse the total production of refined platinum and palladium, which in 2001 was approximately 35,000 lbs. 

TRI Release Summary For Stillwater Mine (in pounds): 

TRI Release Summary For Stillwater Smelter and Refinery (in pounds): 

Recovery of PGM from Post-Consumer Scrap:

The high value of PGM makes recovery from discarded products profitable.  In 2001, it was estimated that 16,200 kg of platinum and 9,000 kg of palladium were recovered from scrap in the United States. (USGS, 2001)   These values represent 31% of platinum demand and 9% of palladium demand.  The recovery of these materials is driven by high demand for catalytic converters, as well as high commodity prices.   

Prior to the requirement for catalytic converters, the PGM recycling rate in the United States was approximately 85%.(Frosch, R., 1989)  In 1998, the overall recycling efficiency of platinum scrap (amount recovered and reused relative to the amount available) was 76%.   Platinum recovery rates were over 98% for chemical and petroleum refining catalysts.  Recovery rates for platinum in automobile catalysts were lower, due to an inferior collection system.   In 2001, platinum recovery from catalytic converters in North America was approximately 47% of the amount that was embedded in new converters (derived from Johnson-Matthey, 2003).  Although recovery rates are lower than for other sources of scrap, most recycled platinum is recovered from catalytic converters.   

Sources of PGM for secondary refining include spent reforming and chemical-process catalysts, electronic scrap, jewelry, used equipment from glass industry. Some PGM can potentially be recovered from disk drive coatings.  The USGS estimates that 6000 kg of PGM were recovered from scrap domestically in 2001.   

Recovery of PGM from automobile catalysts:

Recovery of PGM from automobile catalytic converters continues to rise as the network of recycling facilities expands and the number of pre-1974 vehicles going out of service dwindles.    In 1998, PGM recovered from catalytic converters constituted 8% of US demand.  An even larger portion was recovered by shipping discarded catalysts to other countries for PGM recovery. 

The ability to recover PGM from automobile catalysts is limited by the scrap recovery infrastructure.  In general, the recovery of PGM from catalytic converters is a function of the materials composition of the catalyst, the percent of the catalyst that is recoverable, the likelihood of vehicles going out of service, and the probability that out of service vehicles will be scrapped.  In 1983, of all scrapped catalytic converters, 30% were recovered domestically, 30% were stored to await higher prices, 20% were shipped overseas for reprocessing and 20% were disposed unrecovered. (USGS, 1998)   

Low PGM content per car has required the development of technologies and logistical practices to streamline the recovery process.  The primary technologies for recovering PGM from catalytic converters include: 1) dissolving PGM coating with aqua regia (mixture of HCl and HNO3), then reducing the salts to recover metals;  2) dissolving the ceramic support media in sulfuric acid;  3) volatization of the substrate.   Another recovery process, which is practiced at the Stillwater Refinery, involves introducing the scrap catalysts to the PGM concentrate flow to be refined in the same process. 

There are currently several companies in the US market which purchase used catalytic converters for recovery of PGM.  In addition, a significant number of converters are shipped overseas for materials recovery.

The following diagram summarizes the materials flow of platinum in 1998: 
 
 

This diagram can be used to estimate total 1998 stocks of platinum.  It appears that  platinum reserves were embedded in post-consumer scrap (12,200 kg), and finished products (46,000 kg). The 1998 USGS Commodity Summary for PGM indicates a US stockpile of raw platinum of 13,700 kg.   Thus total platinum stores are on the order of 70,000 kg. 
 
 

IV.  Releases to the environment  

PGM toxicity has recently become a concern.  Releases of PGM to the environment occur through dissipative uses, discarded products, loss of catalyst materials during chemical processing, and loss of PGM from automotive catalysts during vehicle operation.   

Background concentrations of PGM are extremely low.  Measurements of ambient platinum concentrations in air are on the order of picograms per cubic meter (the detection limit is 0.05 pg/m³).  Platinum concentrations in the Pacific Ocean are on the order of 100-200 picograms per liter.   Platinum concentrations in the lithosphere average 0.001-0.005 ppm.  Concentration of platinum in some ores can be as high as 500 ppm.  Asteroids contribute a significant amount of platinum, approximately 10 kg per day. (WHO, 2000)    

In the 1998 materials flow, total losses of platinum in the form of dissipative uses and unrecovered scrap were 4000 and 8500 kg, respectively.  Together, these values constituted approximately 11% of US platinum production. 

Of growing concern is the loss of PGM from catalytic converters during vehicle operation.  Recent research has indicated that concentrations of palladium, platinum and rhodium appear in roadside soils in excess of background levels within 50 feet of roadways (Ely et al, 2001).  Some have suggested that concentrations of these materials are high enough that recovery of PGM from roadside soils may be economically viable.    PGM particles are emitted at rates on the order of 10^-9 grams per kilometer traveled.  Assuming each vehicle averages 12,000 miles per year (19,300 km), the 150 million vehicles in the United States emit: 

150,000,000 cars * 19,300 km/car * 10^-9 g/km ≈ 3 kg of PGM per year 

While this is enough PGM to build 2000 new catalytic converters, it is an insignificant quantity compared to the annual recovery of PGM from scrapped vehicles (25,500 kg).   

Although leakage of PGM to the environment by this process is low, there is still concern about the potential impacts of these releases.  Studies have shown that platinum emitted on roadsides can be taken up by plants.  This leads to concern for the PGM content of crops grown adjacent to roadways.  Evidence also suggests that palladium is soluble in water, suggesting that it has the potential to move through the environment after being deposited near a road.  While exposure to metallic platinum produces no negative effects, exposure platinum’s halogen salts can produce severe allergic reactions at very low concentrations. 
 
 

V.  Conclusion 

PGMs are rare materials with numerous critical applications.  The high value of these materials continues to drive high recovery rates, and as a result, minimize leakage to the environment.  Increased recovery of PGM from catalytic converters may help to avoid some of the toxic releases associated with mining.  Additional research is required to determine whether the leakage of PGM to the environment may produce toxicity.  
 
 
 
 
 
 
 
 

VI.  References 

Platinum Group Metals:  Statistics and Information (USGS) http://minerals.usgs.gov/minerals/pubs/commodity/platinum/index.html. last modified 2/12/2003 

Mineral Commodity Summary, Platinum-Group Metals, USGS 2003 

Hilliard, Henry E.  Minerals Yearbook:  Platinum-Group Metals.  USGS   2001 

WHO Air Quality Guidelines for Europe – 2^nd Edition.  Chapter 6.11 Platinum.  http://www.who.dk/air/Activities/20020620_1  2000 

Hilliard, Henry E.  Platinum Recycling in the United States in 1998.  USGS Survey Circular 1196-B.  1998. 

Stillwater Mining Company www.stillwatermining.com 

Johnson Matthey Company (http://www.platinum.matthey.com) 

Ely, J. et al.  “Implications of Platinum-Group Element Accumulation along U.S. Roads from Catalytic-Converter Attrition”  Environ. Sci. Technol.2001, 35,3816-3822 

Frosch, J.  Strategies for Manufacturing. Scientific American, 1989

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