Review of coal as a promising source of lithium

Coals are a major source of pollution in certain parts of the world due to mining, coal combustion, and disposal of fly ash. The recovery of valuable rare metals from coals or coal-processing byproducts is a promising way to utilise these traditional resources economically, efficiently and in an environmentally friendly way. Lithium, a highly interesting metal, has been found dispersed and even anomalously enriched in coal deposits, and is potentially extractable. This paper presents a review of geochemical investigations on Li-bearing coal and the technical development of Li extraction from coal. Based on available literature, inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma as an excitation source (ICP-AES) are regarded as the preferred methods of measuring Li concentration in coal and coal ash. Anomalous Li accumulations have been reported in coal deposits, especially in China. The limited studies on Li modes of occurrence and origins are discussed, and Li is shown to have an affinity mainly for clay minerals in coal, although further investigations are needed. Lithium is also found to be enriched in fly and bottom ashes during coal combustion. Finally, two successful Li recovery techniques from coal ash are presented.