Friday, March 30, 2007

Platinum Barrier to Fuel cells.

Platinum is a very rare metal. Since the amount of "new" platinum on the world market is around only 150 tonnes annually (about 1/50th of world gold production), and demand is already outstripping this supply, it is debatable whether enough of it might be provided to fabricate the putative fantastic number of fuel cells that will be necessary to "burn" hydrogen for the purpose of fuelling vehicles under the regime of the "Hydrogen Economy", and this may prove yet another nail in the coffin of this increasingly unlikely future scenario. Significant reserves for platinum production are highly localised, and over 90% of the world's production is concentrated in only two regions of South Africa and in Russia. Even in relatively rich ores, the proportion of platinum is very small. As a rough guide, the amount of platinum in these ores is around 3 parts per million, which means that one tonne of ore needs to be mined and processed, in order to provide 3 grams of highly purified platinum, which is about enough to make a small engagement ring.

It is pressure on curbing environmental emissions that is responsible for much of the increase in demand for platinum which is employed in catalytic converters, and takes around 41% of the total market, almost exactly the same quantity as is used to make jewelry. It might seem obvious to solve this problem by simply producing more platinum, but this is far easier suggested than accomplished, since platinum mining and production is attended with considerable difficulties. Most platinum mining is carried out underground, although some open-cast mining does exist. The actual mining of the raw ore is highly labour-intensive, and miners use hand-held pneumatic drills to bore holes into which sticks of explosives are placed, and the ore is blasted out before being drawn-up to the surface. The ore is then crushed and milled and then concentrated using "froth flotation" technology. The flotation-concentrate is then dried and smelted in an electric furnace at temperatures above 1,500 degrees C. Base metals, such as copper, nickel and cobalt are separated at another refinery and the residues in which the "Platinum Group Metals" (PGM) are concentrated are processed to separate the PGM from gold and silver.

This is the most difficult part of the process, involving a combination of solvent extraction and ion-exchange techniques, and the metals are finally extracted into "aqua regia" (or a mixture of concentrated hydrochloric acid and chlorine gas) ultimately obtaining gold, platinum and palladium. There are significant environmental impacts from platinum mining and production, which include groundwater pollution and the release of sulphur dioxide, ammonia, chlorine and hydrogen chloride into the atmosphere. However, the industry is beginning to address some of these problems. Nevertheless, 6 kilograms of carbon are emitted during the process per gramme of platinum recovered, which equates to about 300 - 600 kg for a contemporary fuel-cell powered car. It is also worth mentioning that currently, one such car costs around half-a-million dollars (US) to produce, although undoubtedly that price tag will fall appreciably if the technology becomes more widely adopted. The above figure for carbon emissions incurred during platinum manufacture for fuel cells assumes that 50 - 100 grammes of platinum are needed for an average fuel-cell powered car, but the current industry target is to achieve a loading of 15 g per 70 kW engine, while the US DOE target is closer to 12 g per 70 kW engine.

Assuming, for the sake of argument, that world production of platinum could be doubled (while acknowledging there is no certainty that it could) from 150 to 300 tonnes per year, thus providing an extra 150 tonnes to make fuel-cells from, simple arithmetic and the best possible scenario would suggest that 150 tonnes x 1000 kg x 1000 g/12 g = 12,500,000 such fuel cells might be fabricated each year. This of course must be compared with a world total of 700 million road vehicles. Certainly, platinum can be recycled to maintain the status quo number of cars, but it would take at least 700/12.5 = 56 years before all that fleet were replaced by hydrogen powered fuel cells, by which time the oil-age will essentially be long over.

Add-in the tremendous cost of building and supplying the hydrogen infrastructure, including the manufacture of hydrogen (which is not a fuel and must be synthesised from other raw materials), and the problem is enormous. Of course, energy must be provided to power the platinum production processes and to finally manufacture fuel cells, but to make hydrogen as well. So we need to agree, at the outset, as to which sources all this energy will come from. There will be only about half the world's present reserves of oil remaining in 15 years time (much of which is used as a chemical feedstock for industry apart from as a fuel), and we might by that stage have introduced 187.5 million fuel-cell based vehicles, which is only one fifth of the current oil-powered number of them. I suspect too, that trying to utilise the existing transportation infrastructure might be conceived as the better option over subscribing to a huge and untested new network, and may well take precedent over an expansion of the fuel cell/hydrogen industry essentially from scratch, especially in terms of the production and management of hydrogen itself.

Will we ever run out of platinum? I managed to find some figures suggesting that the world reserve of PGM is around 71,000 tonnes (close to the resource of 80,000 tonnes). Since the proportion of platinum to palladium (the main contenders) varies from place to place (i.e. it is about 2:1 in South Africa but 1:3 in Russia) I shall take a rough estimate that 50% of this is platinum. That gives us 35,500 x 1000 x 1000/12 = 3 billion cars worth! So, actually running out of platinum doesn't seem to be the problem, it is just providing all the energy for the isolation of the pure element, and to fabricate the fuel-cells ultimately, make the new cars, generate, store and transport the hydrogen etc., that is! However, even if we can get around all these problems and bring the technology on line, the total number of vehicles worldwide will likely be reduced to about one quarter of the current number at best, in 15 years, and using conventional fuel-cells, closer to 5 - 10%!

The more sensible option seems to be to generate biodiesel from algae (admittedly, also an untested technology on the very large scale), and burn that in efficient diesel engines, thus being able to exploit much of the existing transport infrastructure. It seems likely that there will be a cut in the level of transportation as the world oil production level falls, whatever alternatives we try to bring in its place, but just how much depends on our choice of technology and how quickly we act upon it.

Related Reading.
"U.S. Geological Survey, Mineral Commodity Summaries, January 2005 - Platinum-Group Metals."
"Platinum Today: Resources in South Africa."
"Department for Transport - Platinum and hydrogen for fuel cell vehicles."

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