Analysis of Niobium–Rare-Earth Ores by Inductively Coupled Plasma Mass Spectrometry

Resumo

To determine the composition of niobium–rare-earth ores by atomic emission spectrometry and inductively coupled plasma mass spectrometry, two procedures are developed for sample preparation based on autoclave decomposition and flux fusion. Autoclave decomposition is carried out in a mixture of HF and HNO₃ at a temperature of up to 220°C and a pressure of up to 160 atm using a developed system with resistive heating. Subsequent evaporation to dry salts ensures the removal of F^– ions and silicon as SiF₄. The residue is dissolved in a mixture of HCl and H₂O₂ at 160°C under elevated pressure. The resulting solutions (10% with respect to HCl with the addition of H₂O₂) are diluted before measurements. The dissolution process is monitored for each sample using stable highly enriched isotopes of ⁹¹Zr, ¹⁰⁰Mo, ¹⁴⁹Sm, and ¹⁷⁸Hf. The second procedure is based on fusing samples with a mixture of Na₂CO₃ and Na₂B₄O₇ at 1050°C in a muffle furnace and dissolving the resulting melt in a mixture of HCl and H₂O₂. The procedures were tested using the national (NFS-23) and foreign standard samples of composition (OREAS-462, 463, 464, 465, Australia) and real samples of niobium–rare-earth ores.