Exploring the potential of secondary resources: LA-ICP-MS for critical raw materials characterization

This study compares methodologies and provides insights on best approaches for quantifying EU-listed critical raw materials. Europe's strategy towards greater resilience involves valorization of secondary resources such as mine tailings or by-products of metallurgical production that are typically discarded as waste, despite containing valuable resources. Thus, identifying the best methods to determine elemental concentrations in various resources is crucial for evaluating their recovery, both environmentally and economically. Elemental content is usually determined using techniques such as inductively coupled plasma mass spectrometry (ICP-MS) by digesting solid samples into liquid solutions, although challenging for some refractory materials. Direct analysis of solids by laser ablation (LA)-ICP-MS is another alternative and can be used for both bulk analysis and spatially resolved mapping of critical elements throughout the supply value chain, from raw materials to refined products. Here, we compare ICP-MS/MS analysis on dissolved samples, obtained after microwave-assisted acid dissolution, with LA-ICP-MS analysis on solid samples for determining rare earth element (REE) compositions of manganese ores and slags. For LA-ICP-MS, we present two approaches, particularly useful in cases where dissolution proves challenging: (i) analysis of glass beads obtained through borate flux fusion of raw powders, and (ii) direct analysis on pelletized powders using a novel non-matrix matched calibration strategy. Each method's feasibility and strengths are considered for the specific chemical composition of the samples of interests. The study shows that different methods have advantages and disadvantages related to particle size distributions and preparation costs that need to be considered during characterization of secondary resources.