Worldwide annual consumption of lithium grew from 15,100 tonnes in 2003 to 37,000 tonnes by 2012, a 145% increase; demand is expected to rise even further with the move towards sustainable power and electrical storage capacity increases.

Shenjun Qin of Hebei University of Engineering, in Handan, China, and colleagues point out that coal is a highly polluting energy source that is still widely used for electricity generation and other applications. They suggest that the recovery of valuable rare metals from coals or coal-processing byproducts could be a promising way to make the inevitable long-term use of this fossil fuel resource more economic, efficient and cleaner. Indeed, the extraction of lithium from coal would offer an ironic twist to its continued use.

The team explains that lithium has been found dispersed and even anomalously enriched in coal deposits, and is potentially extractable. Two analytical techniques—inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma as an excitation source (ICP-AES)—are widely used for assaying the chemical elements in coal and coal ash and either of these techniques could be used widely to optimize sources for lithium, or any given metal, for subsequent extraction.

The team has also reviewed two techniques for lithium extraction. The first, a patented technology for extracting both lithium and aluminum metals from coal ash involves sulfur sintering the ash and acid leaching the metal from the solution to obtain lithium carbonate in a yield of 95.6%; actual recovery of the metal is 60%. The second approach, alkali sintering, avoids the need for the sulfur step but has a lower yield at 85.3% and a recovery of 55%.

The investigation into lithium recovery from coal ash is still at a laboratory scale.

Resources

• Qin, S., Zhao, C., Li, Y. and Zhang, Y. (2015) “Review of coal as a promising source of lithium”, Int. J. Oil, Gas and Coal Technology, Vol. 9, No. 2, pp.215-229 doi: 10.1504/IJOGCT.2015.067490