We live on a planet with finite resources, and yet use them up with alacrity in the false assumption of limitless growth. I read a recent statistic that "if all the world's 500 million vehicles in use today were re-equipped with fuel cells, operating losses would mean that all the world's platinum would be exhausted within 15 years." In a previous posting, I estimated that there were probably around 35,500 tonnes of platinum available as a reserve on Earth, 90% of it in two mines in South Africa and most of the rest in Russia. Hence, each vehicle would account for 35,500 tonnes x 1000 kg/tonne x 1000 g/kg /500,000,000 = 71 grams of platinum. For 700 million of them, as I understood the figure to be, this amounts to 51 grammes each.
In my article "Platinum Barrier to Fuel Cells", I worked-out, assuming that pledged technology (here we go again!) would come to our rescue, that there is enough platinum at a putative 12 g per "highly improved" fuel cell to supply 3 billion cars, but the real problem is that only relatively limited quantities of platinum can be produced each year, and so other resources (principally oil) will have run-out long before we might replace our oil-fuelled fleet by fuel-cell driven cars. This ignores the likely prohibitive difficulty in inaugurating the infrastructure for the hydrogen to run them with. Either way platinum is a scarce and precious resource and cannot be counted upon to match current and continuing demands for it. Contemporary fuel-cells contain around 50 - 100 g of platinum each, which is close to the above estimates.
Currently, even in the absence of fuel-cells, around 40% of the world's platinum is used in catalytic-convertors (CC's) to keep levels of exhaust gases such as NOx down, which is coincidently the same amount as is used to make jewelry. It is fascinating that the "dust" and litter routinely swept off the streets may contain of the order of parts per million (ppm) of platinum, emitted into the air from the platinum-based catalysts that are the heart of CC's, similar to the 3 ppm typical of the ores in the South African platinum mines. It may therefore be feasible to "mine" the dust from road-sweeping machines to recover its platinum.
Platinum is only one of the elements likely to run-short in a few decades or so. Indium, used for solar cells and LCD's may run-out in 10 years, impending a further need to develop alternative photo-voltaic (PV) technology, beyond the difficulty in providing enough pure-silicon to fabricate silicon-based cells on the grand scale. Dye-cells (e.g. Gratzel-cells) begin to look particularly attractive, even if the "dyes" will be made from oil, emphasising the terrible waste of simply burning oil as a fuel, when we also need it as a chemical feedstock. In my opinion, it would be more to the point to preserve as much conventional crude oil as possible as a raw material for chemical manufacture, because what will our industries use otherwise once it has gone, or is absurdly too expensive to use?
Some salient points are made by the following list of elements, world total reserve of each, their time of exhaustion based on current rates of production and main uses for them:
Aluminium, 32,350 million tonnes, 1027 years (transport, electrical, consumer durables)
Arsenic, 1 million tonnes, 20 years (semiconductors, solar cells)
Antimony, 3.86 million tonnes, 30 years (some pharmaceuticals and catalysts)
Cadmium, 1.6 million tonnes, 70 years (Ni-Cd batteries)
Chromium, 779 million tonnes, 143 years (chrome plating)
Copper, 937 million tonnes, 61 years (wires, coins, plumbing)
Germanium, 500,000 tonnes (US reserve base), 5 years (semiconductors, solar cells)
Gold, 89,700 tonnes, 45 years (jewelry, "gold-teeth")
Hafnium, 1124 tonnes, 20 years? (computer chips, power stations)
Indium, 6000 tonnes, 13 years? (solar-cells and LCD's)
Lead, 144 million tonnes, 42 years (pipes and lead-acid batteries)
Nickel, 143 million tonnes, 90 years (batteries, turbine-blades)
Phosphorus, 49,750 million tonnes, 345 years ( fertilizer, animal feed)
Platinum/Rhodium, 79,840 tonnes, 360 years for Pt (jewellery, catalysts, fuel-cells, cat-convs.)
Selenium, 170,000 tonnes, 120 years (semiconductors, solar cells)
Silver, 569,000 tonnes, 29 years (jewellery, cat.-convs.)
Tantalum, 153,000 tonnes, 116 years, (cell-phones, camera-lenses)
Thallium, 650,000 tonnes, 65 years (High Temperature Superconductors, Organic Reagents)
Tin, 11.2 million tonnes, 40 years, (cans, solder)
Uranium, 3.3 million tonnes, 59 years (nuclear power stations and weapons)
Zinc, 460 million tonnes, 46 years (galvanizing).
These figures are based on known reserves and of course more might be found if it were explored for. However, new technologies are likely and the developing nations are aspiring to a "Western Lifestyle" so minerals are being exhausted at a relentlessly growing rate.
It is predicted that if new technologies do appear and with the growth in world population, some key resources will be used up quite rapidly, e.g.:
Antimony, 15 - 20 years.
Hafnium, 10 years.
Indium, 5 - 10 years.
Platinum, 15 years.
Silver, 15 - 20 years.
Tantalum, 20 - 30 years.
Uranium, 30 - 40 years.
Zinc, 20 - 30 years.
It is worth observing that the distribution of these minerals is of course uneven, as I noted above about platinum, and the US currently imports 90% of its "rare earth" metals from China. We know all too well also that most of the world's oil is in the Middle East. In concluding this posting I am left with a sense of living on borrowed-time.
(1) David Cohen, "Earth Audit", New Scientist, 26th May 2007, p. 35.