Characterization and leaching of rare earth elements from Indian coal ash

Abstract

Consumption of critical elements is increasing day by day with the advancement of modern science and technology. Many of the rare earth elements belongs to the class of critical elements and play a pivotal role in modern society. Neodymium (Nd), Europium (Eu), Terbium (Tb), Dysprosium (Dy), and Yttrium (Y) are considered as critical rare earth elements (CREE) for both the short and long term perspective. Lanthanum (La) and Cerium (Ce) are considered as near critical rare earths. Rare Earth Elements (REEs) are consumed in the high-tech industry for the manufacture of various consumer goods such as cell phones, computers, permanent magnets, catalysts, medical devices, etc. Extensive use of REEs is also seen in the manufacturing of wind turbines. To meet the demand in light of restricted distribution of these elements worldwide, it is necessary to recover critical elements from secondary resources. Coal ash is an abundant industrial byproduct of coal combustion due to its large-scale reserves and low cost for energy production. A few ventures have been reported to recover rare earth elements (REEs) from coal-related ash materials in recent years. Coal ash is a very good source for critical elements, as it contains valuable rare earth elements. In this work, a leaching study on two ash samples, formed by the combustion of carbonaceous coal is carried out. The coal samples were taken from the coal mines of eastern region, India. One ash sample contains around 500 ppm REEs, named as Low Total REEs Ash (LTRA) and the other contains around 1000 ppm REEs, named High Total REEs Ash (HTRA). The leaching study was carried out in presence of two different types of acid, i.e. nitric acid (mineral acid), acetic acid (monocarboxylic acid). The leaching efficiency was measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis of the leached solution. For both types of ash samples (LTRA and HTRA), REEs leaching efficiency was observed around 70% in nitric acid. In the case of organic acid i.e. acetic acid, around 30% REEs leaching efficiency was observed for Low Total REEs Ash sample. However, it is observed that, only 40-45% leaching efficiency was there for the High Total REE Ash sample in organic acid.