Posted on: 3rd June 2013
June 8th is World Oceans Day, to celebrate the central role that the oceans play to our life on this planet. Among the list of reasons for celebrating the ocean provided on the Oceans Day website, there is a major future one that is missing – that of fuel tank for the future power stations.
Worldoceansday.org reminds us that the ocean generates most of the oxygen we breathe, helps feed us, regulates our climate, cleans the water we drink and offers us a “pharmacopoeia of potential medicines”. But the oceans also contain 425 parts per million of lithium and 160 parts per million deuterium – the raw materials for fusion (as tritium is produced from neutron bombardment of lithium). This amounts to hundreds of billions of tonnes of each ingredient; ingredients which have an extremely high yield of energy – more than a million times more energy per kilogram than coal. It is clear that in an energy landscape based on fusion, fuel supply would be the least of our worries.
However, is there any cause for concern that the extraction of these vital ingredients could endanger our oceans?
The separation of deuterium from its lighter isotope hydrogen-1 has previously resulted in nasty effluent. The process is tricky because the two isotopes are chemically almost identical. There is a slight difference in the boiling points of normal water (H20) and deuterium-containing “heavy water” (D20), but this can only be exploited once the heavy water is concentrated to around 20 percent. Conventionally this has been done using the Girdler-Sulphide process, based on chemical exchanges of the hydrogen isotopes between water and hydrogen sulphide (rotten-egg gas). Fortunately the use of this undesirable chemical is being superseded by a much cleaner process developed by the Atomic Energy of Canada Limited based on a platinum catalyst.
Lithium extraction is a simpler process, although expensive. Lithium production today mostly comes from terrestrial mines, although use of lithium for batteries may lead to us to turn to the oceans in the future. The current process for extracting lithium from water relies on the concentration of the lithium ions being increased through evaporation in pools, which can take up to a year. Then chemical processes are employed to systematically remove other chemicals, such as magnesium and then precipitate out lithium chloride, which can then be processed into lithium metal with electrolysis. Effectively this is purifying the water, but the drawback is that this takes a lot of energy. However, because fusion requires such small amounts of fuel – only a couple of grams at any time – the overall cost would barely impact on the cost of fusion.
There are only three facilities in the world currently producing lithium from salt water, so if large scale production were required one would imagine that the processes would be improved. For example Simbol Mining is exploring a cleaner and cheaper source of lithium, from brine in geothermal hotspots.
Other developments might also have large impacts on fusion’s fuel production processes, such as a move to hydrogen as a transport fuel, suggests CCFE’s David Ward. “It might be fun to have a fusion plant that generated electricity, hydrogen and desalinated water all at the same time. Whilst doing that, extracting a bit of deuterium as fuel would be very easy!”