Wednesday, July 20, 2011

Peak Gold and Peak Platinum?

On the BBC News programme this morning ( I noted mention that there is thought to be enough recoverable gold to fill "three Olympic sized swimming pools"(OSSP) and enough platinum to occupy one such volume "up to your ankles". According to FINA (Fédération Internationale de Natation), the body recognised by the International Olympic Committee for administering international competition in the aquatic sports, an OSSP has at least a length of 50 m, a width of 25 m and a depth of 2 m, making a volume of 2,500 m^3.

Now, this does place a tangibly illustrative physical dimension on how much of these metals might be available.

In the case of gold, we may deduce that there are 3 x 2,500 m^3 x 19.3 t/m^3 = 144,750 tonnes recoverable.

In the case of platinum, the sum may run something like 2,500 m^3 x 21.45 t/m^3 x ("up to my ankles", say 4 inches, or 0.1 m/2 m) = 2681.25 tonnes recoverable.

The value for platinum shocks me, as I had heard there were maybe 36,000 tonnes recoverable, but I have found an interesting analysis ( which places the issues of resources and reserves into perspective. This report concludes there are "estimated proven and probable reserves of platinum at 203.3 million troy ounces, (6,323 tonnes)"... plus... " In addition to these reserves, inferred resources were estimated at 939 million troy ounces (29,206 tonnes) of platinum." So, taken together, this is about the amount I had understood existed.

However, the bulk of this is likely to be got at far reduced EROEI, and greater difficulty/cost, though a more valuable product will urge more assiduous efforts to produce it. If one does the sum in reverse, i.e. 2m x 6,363 t/(2,500 x 21.45) = 0.24 m, I deduce that the OSSP would be filled with platinum to about nine and a half inches up my leg, which is about half way up my calf, and well above my ankles.

But how much gold is there? According to the USGS ( there are 51,000 tonnes, which is more like one OSSP, rather than three. I have seen estimates that maybe up to half a million tonnes of gold might be recovered, but the quality of gold ore is falling. In 1960, one tonne of gold ore yielded 2.86 grams of gold, but by 2000 only 1.37 grams of gold were recovered per tonne. The most recent gold ore discoveries are yielding less than one gram per tonne. Thus, the situation is like oil, that most of the easily-had stuff has been had, and more energy and resources (reflected in the falling EROEI) must be expended to recover and process a poorer quality material.

In making Jewellery, the highly resistant nature of Gold and Platinum symbolises eternity, e.g. in wedding-rings. However, gold and the platinum group metals (PGM) have many important practical uses. Gold finds increasing application in the circuitry of computers, while platinum, rhodium, palladium and rhenium provide catalysts, e.g. in catalytic converters, fuel-cells, and the production of synthetic fertilizers. If the supply of these metals will fail demand for them, many central and projected technologies for communications, transport and food production must be re-thought.

Wednesday, July 06, 2011

Natural Limits to World Wind Energy?

The amount of energy available in the Earth system to be extracted by wind-turbines is limited, and if sufficient energy is removed the world climate will be affected. These striking conclusions follow from a recent analysis ( reported from the University of Jena in Germany. Humans use energy in total at a rate of 17 TW (terawatts), 87% of which is provided by fossil fuels. In the effort to mitigate carbon emissions and climate-change, sources of carbon-free renewable energy are sought, particularly wind-power. From a simple engineering perspective, the more wind-turbines are placed around the globe, the more energy can be extracted, with no particular effect on the overall energy of the atmospheric flow.

From the various simulations used it was inferred that between 18 - 68 TW of mechanical wind power can be extracted from the atmospheric boundary layer, taken over all non-glaciated land surfaces. While a single wind-turbine does not affect the global atmosphere, the installation of a large number of such devices will interfere with the atmospheric circulation and diminish the extraction efficiency on the large scale, since any extraction of momentum will act in competition with natural wind-power energy dissipation by turbulence in the boundary layer.

The amount of extractable energy evaluated using this "top-down" thermodynamic approach is significantly smaller than has been estimated using "bottom-up" engineering models based on wind turbine characteristics and wind velocity measurements which give values up to 1700 TW. If wind-energy were extracted on the scale of human demand for energy (17 TW), amounting to 50 -95% of the total energy available, significant climatic effects are predicted. These are a result of increased turbulence and entrainment of air at higher altitudes by the simulated turbines. At higher altitudes the air is potentially warmer and heats the air nearer to the surface by mixing with it. The warming effect is similar to that predicted from an elevation of the atmospheric CO2 concentration to 720 ppm.

While presently only 0.03 TW of energy was extracted from wind in 2008, and there is room for a considerable expansion of this technology with relatively insignificant effects on the climate, any future expansion on the global scale must take account that the potential for extraction of wind energy is finite according to the nature of the Earth system. It is thought too that as the atmospheric CO2 concentration increases, as it must with the continued burning of fossil fuels, the kinetic energy generation from the atmosphere will decrease thus further diminishing the amount of energy that may be sensibly extracted by wind-turbines on the very large scale.

Tuesday, July 05, 2011

UK Government Report Calls for “Strategic Metals” Plan.

Not only are supplies of oil and natural gas under imminent threat of failing to meet demand for them, but so is a whole range of precious metals, along with indium, gallium and germanium and other vital elements such as phosphorus and helium. A report [1] from the Science and Technology Committee, advised by the Royal Society of Chemistry [2], warns that if the U.K. does not secure supplies of strategic metals, its economic growth will be severely jeopardized. Of particular concern are indium, used in touch screens and liquid crystal displays, and rare earth elements (REEs) particularly neodymium and dysprosium, used to fabricate highly efficient magnets for electric cars and wind turbines. Platinum group metals are an issue too, used in catalytic converters and fuel cells.

As is true of oil and gas, and indeed world population, such resources are not evenly distributed around the globe, and for example 80% of available new platinum is extracted from just two mines in South Africa. 92% of the niobium used in the world (for superconducting magnets and highly heat-resisting superalloys e.g. in jet-engines and rocket subassemblies) is exported from Brazil, and 97% of REEs are presently supplied from China. In developing a low-carbon transport infrastructure, it is proposed that biofuels should be used principally for aviation where there is no practical alternative to liquid fuels. Thus, it is ventured, electric cars will become increasingly important in providing personalised transport while avoiding the use of petroleum or natural-gas based fuels. The knock-on effect is that new sources of lithium must be found along with the means to mine and process the metal, plus the inauguration of recycling technology for lithium.

One can immediately take issue with the practicalities of both arms of this scheme, however. Roughly one fifth of all fuel in the UK is used for aircraft, or around 13 million tonnes. At a yield of 952 L/ha and a density of 0.88 g/cm3, to produce this much biodiesel would take 15.5 million hectares of arable land, of which the UK has only 6.5 million hectares. Thus if we were to stop growing food crops entirely and just rapeseed, we could still only fuel 42% of our aviation fleet. It is obvious that just a few percent at best of our current number of planes can be kept in the air by means of biofuels. Clearly, the days of cheap air-travel are numbered and this may be one reason why the coalition government has scrapped plans to build the controversial and vexed third runway at Heathrow Airport.

Given the 30 million cars on the roads here currently fuelled by oil, the case for a wide-scale implementation of electric-cars might appear compelling. However, the lead-in time to make a dent in that number of vehicles and the 60 million tonnes of crude oil used for fuel would be decades at best, even if the necessary supplies of REEs, lithium and overall manufacturing capacity for them could be achieved. The most practical use for electricity is to power mass transportation, e.g. tramways and railway networks rather than individual vehicles.


(2) Davis, E. (2011) "Critical Thinking.”