Development and application of an analysis method for the determination of rare earth elements in silicate-rich samples by NaO sintering and ICP-MS analysis.

The performance of a fast and simple analytical procedure for rare earth elements (REEs) quantification from secondary sources was investigated in the present work. Seven silicate-rich certified reference materials (CRMs) in the form of Andesite (JA-1), Basalt (JB-3), Rhyolite (JR-1, JR-2), Granite (JG-2), Granodiorite (JG-3), and Till (TILL-1), were used for the optimization and characterization of the analysis method. The optimized method was used in the analysis of nine mining wastes selected within the ENVIREE project, under the ERA-MIN Program of the 7th Framework, having as the main aim to ensure a policy securing long-term access of REEs secondary sources at reasonable costs. For silicate-rich samples efficient solid dissolution involves sintering with NaO at 460 °C and a sample to oxidizing reagent ratio of 1:6.5. Inductively coupled plasma-mass spectrometry (ICP-MS) was used in the quantification of the REEs with aerosol dilution of samples applied to minimize the salt effect on the plasma and interface regions. The work performed in the present study clearly shows that accurate reports on the REE concentrations from geological matrices also involves as mandatory the estimation of the overall uncertainty from various sources (sample preparation or analyte measurements). In the analysis of geological samples, the proposed analysis method has on average 23% of the overall uncertainty explained by the sample preparation and 77% accounted by the analysis steps. Moreover, the method described by effective, cheap, robust and safe attributes, can be recommended as an accessible alternative to the HF wet digestion method. Although from all the investigated tailings samples, only those from Sweden and Czech Republic can be regarded as potential secondary sources for REEs, investigation of other resources with interest at European level might bring a great benefit in the general attempt to develop an economically viable method for the production of rare earth elements.