lithium (Li) and the 'lithium problem'
A sample of lithium freshly cut.
Lithium was discovered by Johan A. Arfvedson in Stockholm in 1817. It was first isolated by W. T. Brande and Humphrey Davy in the nineteenth century, but was not commercially produced until 1923. Its name comes from the Greek lithos meaning 'stone.'
Sources of lithium
Some lithium is recovered from the mineral spodumene. Commercial quantities of spodumene are found in a special igneous rock deposits known as pegmatites. In pegmatites, the liquid rock (magma) cools so slowly that crystals have time to grow very large. The largest spodumene crystal ever found was in a pegmatite formation in South Dakota.
Most lithium is recovered from brine, or water with a high concentration of lithium carbonate. Brines trapped in the Earth's crust (called subsurface brines) are the major source material for lithium carbonate. These sources are less expensive to mine than from rock such as spodumene, petalite, and other lithium-bearing minerals.
Lithium is made by electrolysis of fused lithium chloride.
|Properties of lithium|
|relative atomic mass||6.941|
|atomic radius||152 pm|
|relative density||0.534 (at 20°C)|
|melting point||180.5°C; (357.0°F;)|
|boiling point||1,342°C; (2,448°F;)|
Uses of lithium
Lithium is used as a heat-transfer medium, because of its high specific heat, and in various alloys, ceramics, and optical forms of glass. Its two stable isotopes are the rarer 6Li, with three protons and three neutrons, and the more common 7Li, with three protons and four neutrons. 6Li is important in thermonuclear processes. Lithium stearate is an additive to lubricating greases.
The 'lithium problem'
Lithium is one of the few elements, along with hydrogen and helium, that were formed in the immediate aftermath of the Big Bang. The trouble is the amount of lithium observed in the universe is three to four times lower than what our physics of the Big Bang predicts. Several theories have been put forward to explain this discrepancy.
It may be that our understanding of what happened in the period immediately after the Big Bang is wrong or incomplete. For example, it's been suggested that dark matter may have played a role in depleting the cosmic supply of lithium right from the start. Another possibility is that there's some process going on in interstellar space, yet to be fathomed, which, over billions of years, has run down the lithium stock. Or it may be that the missing lithium is hiding deep within stars, having been processed and moved inward in some way not yet understood.
Unfortunately, a study published in 2012 has made the lithium problem even more acute because it predicts that some small black holes – those weighing in at about 5 solar masses – should act as lithium factories, so there should be even more of the stuff around than what we're seeing. In the accretion disk of such black holes, the study finds, the temperature should be just right to trigger nuclear fusion reactions that would produce large amounts of lithium – in total matching that supposed to have been manufactured shortly after the Big Bang.
Another piece of research, also published in 2012, looked at the lithium content of gas clouds in the Small Magellanic Cloud and again confirmed that we have a missing lithium problem. Although the gas has nearly as much lithium as Big Bang models they ought to contain very much more considering how much lithium has been manufactured inside stars since the Big Bang and then shot into space during supernova explosions.
1. Iocco, F. and Pato, M. "Lithium synthesis in microquasar accretion." Physical Review Letters, Vol. 109, July 13, 2012.
2. Howk, J. C., Lehner, N., Fields, B. D., and Mathews, G. J. "Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud." Nature, 489, 121–123 (2012).