A Novel Analytical Method Utilising an In-House PTFE Digester Using NH4HF2 and Dilute HCl for Total Dissolution of Pegmatite-Type Lithium Ores (α-Spodumene, Petalite and Lepidolite)

Abstract

A novel and highly efficient hot plate digestion method was developed utilising an in-house PTFE digester using a mixture of ammonium bi-fluoride (NH₄HF₂) and dilute HCl (1, 1) for the total dissolution of pegmatite-type lithium ore samples (spodumene, petalite and lepidolite) for the quantitative determination of Li, Nb, Ti, Rb, Cs and Be and other co-existing elements (Fe, Al, Mn, Na, K, Ca and Mg) by inductively coupled plasma-atomic emission spectrometry. The proposed method was carried out in three analytical steps for total dissolution of Li ore matrix. The first step involved complete decomposition of the sample matrix (using a 1:4 sample to NH₄HF₂ ratio), while evaporation of the silica matrix was carried out in the second step. The third step involved aqua regia treatment for conversion of insoluble fluorides to corresponding soluble forms to obtain particle-free and clear sample solutions. Critical analytical parameters related to hot plate digestion processes were optimised by a univariate approach to obtain quantitative recoveries (> 95%) for all of the selected analytes. The solid residues obtained at each step of sample preparation were characterised by XRD and EDS analysis. The method was validated through the analysis of three NBS reference materials (spodumene 181, petalite 182 and lepidolite) certified for Li mass fraction only. The other mass fractions listed are approximate/information values. The developed method was subsequently applied to multiple ore samples of different geological origins.