Measurements of lithium isotopic compositions in coal using MC-ICP-MS

Abstract

Lithium is a very important metal for energy production. Lithium isotopes can be used to trace the source of fossil fuels that contribute to atmospheric haze and examine the occurrence and concentration of lithium in coal deposits. In this study, a microwave digestion method for coal decomposition using HNO₃ + HF and H₃BO₃ acid systems was evaluated. The results demonstrated that coal was completely decomposed when these acids were used and the microwave program run in two steps. Three coal reference materials with different lithium concentrations (SARM18, SARM19 and SARM20) and four samples of Li-bearing coal from the Guanbanwusu Mine (China) were analyzed and the lithium isotopic composition was determined using MC-ICP-MS. Li isotope data were obtained with an intermediate precision better than ±0.30‰. The δ⁷Li values determined for SARM18, SARM19 and SARM20 were 1.35 ± 0.23‰, 2.16 ± 0.27‰ and 1.48 ± 0.17‰, respectively. The non-certified coal samples revealed a similar range in lithium isotopes (δ⁷Li = 6.02‰ to 6.77‰) suggesting limited lithium isotope fractionation in coal locally, which could be useful for tracing atmospheric haze and contaminated waters in the environment. The comprehensive data and procedures in this study can be considered as a reference for conducting Li isotope determination in coal.