Residents of Cardiff, Wales, were bemused (and probably amused) not to long ago to see a respected geologist out on the streets of town early one Sunday morning, sweeping road dust into a dustpan.

Fortunately, Dr. Hazel Prichard hadn’t been forced to take up stree-sweeping because she had lost her job at Cardiff University; instead, she was testing a theory that the streets of Cardiff–and most other major Western cities–are slowly becoming paved with platinum.

Dr. Prichard told a conference in Cardiff last week that the amount of platinum spewed out on city streets from the catalytic convertors used to control pollution is approaching the point where it might be economical to recycle it. Platinum, which is far rarer than gold, is currently priced at $370 U.S. an ounce.

Dr. Prichard figures that in places road dust in Cardiff is approaching 1500 parts per billion of platinum. (By contrast, the solid rock from which platinum is normally retrieved typically only contains 4000 parts per billion.) She also suspects that road dust in major North American cities, where catalytic convertors have been used much longer, could have even higher levels of platinum.

Recycling platinum from road dust might sound a little extreme to the average person, but it may not to people in the platinum industry. They know that platinum is finding more and more uses in our society, uses that most of us aren’t even aware of.

Platinum is silvery white metal, and, like gold, a pure element. South American Indians were using it a thousand years ago, but it was unknown to Europeans until Spanish Conquistadors ran across it in the late 1600s in the Choco region of what is today Colombia. They considered it a nuisance: it interfered with their gold mining. It was considered of so little value that forgers used it to adulterate Spanish gold coins.

However, scientists soon grew interested in platinum because of its unique properties. When it first arrived in Europe, nobody could manage to get it hot enough to melt (because its melting temperature, 1,7774 degrees, is much higher than gold’s), and almost nothing would corrode it. Once somebody did manage to melt it, in 1751, however, industrial uses were quickly found for it. Laboratory apparatus was often made from it because of its resistance to heat and corrosion, and in France by 1780, crucibles for melting glass in were made of platinum (and still are today).

Today, most of us think of platinum in terms of jewelry, and that, too, developed in the 1700s. In 1788, for instance, Francisco Alonso of Spain crafted a platinum chalice (weighing nearly two kilograms!) for Pope Pius VI.

In the 1800s, new refining techniques made platinum useful in ever more ways, from gun parts to batteries to a variety of chemical refining procedures (acid-making, for example). The discovery of new sources of platinum in Russia (which made the first platinum coins in 1822) helped spread platinum throughout society.

Platinum continued to be popular as jewelry in the early part of the 20th century; at the time of the Second World War it was declared to be a strategic metal, and as a result, stopped being used for a long time. Only recently has it begun to regain its pride of place in the jewelry market. Not only is it used to produce rings and other jewelry items itself, but it is combined with gold to make “white gold,” used not only by jewelers but also by dentists. From 1995 to 1996 alone, demand for platinum jewelry grew by 38 percent in the U.S. Recently, Mauro Adami of the Domo Adami fashion house wove together a wedding gown, estimated to be worth $1.5 million U.S., using microscopic platinum fibers threaded into a fabric.

The jewelry market, however, is just the tip of the iceberg as far as uses of platinum goes. Platinum is literally indispensable to our high-tech way of life. By one estimate, one of every five goods manufactured in the world today either contains or is produced using platinum.

The biggest use of all at the moment is for catalytic converters, which suck up about 40 percent of the platinum on the market every year. A catalyst is a substance that can speed a chemical reaction while remaining unaffected itself. In a catalytic converter, a car’s exhaust gases are passed through a honeycomb of small beads coated with platinum and palladium. When the converter is heated and extra air is pumped into it, the hydrocarbons and the carbon monoxide in the exhaust are converted into carbon dioxide and water, while, in a separate reaction, nitrogen oxide is converted into nitrogen, carbon dioxide and water. (The reason cars equipped with a catalytic converter must use unleaded gas is that leaded gas coats the platinum with lead, preventing it from doing its job.)

Platinum is used for many other purposes as well, however. For example, many computer hard disks are coated with an ultra-thin layer of platinum. Non-polluting fuel cells, which are being aggressively pursued by automobile manufacturers as the motive power of the future (and are already used on the space shuttle and as emergency power sources for hospitals and in remote locations), use platinum. Again, platinum serves as a catalyst, allowing a fuel cell to produce energy from a hydrogen-based fuel while producing only water in its exhaust.

Platinum also plays a vital role in sensor technology–tiny amounts of the metal are used in sensors that can detect hitherto undetectable levels of electrical currents or chemical reactions.

Platinum is more valuable than gold not only because of high demand, but also because it is very rare. The entire world’s supply is essentially drawn today from just two places: South Africa and Russia. Extracting it is difficult. For one thing, it is usually found in combination with other metals, and separating it from them is a long, involved process that can take up to six months.

Only around 130 tonnes of new platinum reaches the market each year, less than five percent the amount of gold that’s produced. In fact, all the platinum ever mined would fill a room measuring about eight metres on a side.

It’s no wonder that in Cardiff, they’re talking about sweeping the streets for it. Platinum is so valuable, you don’t want to let a speck escape.

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