A Review on the geochemical distribution of rare earth elements (REE) in coal, with a view on Iran's coal

In recent years, recovery of rare earth elements (REEs) from coal reserves as by products, in many countries has helped to alleviate the current raw material crisis. Due to the variety of research done in this field and the lack of a review article, doing this research is necessary. The purpose of this article is to review the geochemical distribution of rare earth elements in coal with an overview on Iranian coal. The results of this research show that the amount of heavy rare earth elements is usually higher than light coal rare earth elements than shales and chondrites. The proportion of Ce/Yb ratio in conventional shales is 4 to 6 and in coal and coal shales is about 7 to 8. Four sources for this enrichment have been proposed: 1. Organic origin, 2. Surface absorption by clay minerals in coal basins, 3. Mineral origin and 4. Sedimentation with organic matter during coal formation. Studies have also shown that the concentration of elements on the ash from coal combustion is much higher than coal itself. Extraction of these elements from the ash is easier than coal mining, which significantly reduces the environmental problems caused by the resulting ashes by combustion. The study of Alborz coal (Karmzad, Loshan, and Shahrood) and Central Iran (Tabas, Heshuni, Pabdana, Pudnee Springs, Hajdak) has shown that the grade of rare earth elements in Iranian coal is higher than the average grade of these elements in the upper crust and coal of the world such as China and America.