Extraction of rare earths from coal and coal by-products as a non-traditional source

Abstract

Rare earth elements (REEs) are one of the critical metals used for modern technological applications and green technologies. Due to growing demand and limited availability, there is a huge supply risk associated with REEs. The primary resources of rare earths in India are limited and associated with many processing challenges. In this scenario, it is important and timely to explore the non-traditional sources of rare earths to meet the domestic demand of country in the future. India is rich in coal deposits. The studies are very limited and there is scarcity of the research work carried out on the extraction of rare earths from Indian coal and coal by-products. Therefore, the objective of the present research article is to highlight the presence of REEs in Indian coal along with coal by-products. The objective is to identify the sweet pots of rare earths in coal and coal by-products. The concentration of total REEs is in the range of 150–200 ppm in coal samples. Furthermore, coal ash contains the concentration of total REEs which is more than 600 ppm in the samples of study area. It is aimed to review the several methods to recover rare earths that can be economically applied for the extraction of rare earths from coal and its by-products. Column leaching experiments achieve a 50% recovery rate of REEs from coal, while thermal treatment of coal enhances the recovery rate by one and a half times compared to untreated samples. Process optimization experiments demonstrate the superiority of the flocculator jar test apparatus, resulting in a significant increase in REE recovery (52% from coal samples). It was found that there is a huge work is still needed to be done for the development of an energy efficient and economical recovery of rare earths from coal and its by-products.