Determination of 18 Elements in Bauxite by Inductively Coupled Plasma Mass Spectrometry with Four-Acid Digestion

A method for simultaneous determination of lithium, scandium, niobium, and 15 rare earth elements (lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium) in bauxite by inductively coupled plasma mass spectrometry (ICP-MS) with four-acid digestion was proposed. 0.100 0 g of the powder sample was taken, placed into a 50 mL-polytetrafluoroethylene crucible and wetted with a small amount of water, and 5.0 mL of hydrochloric acid was added. The mixture was heated at 100 ℃ for 30 min on a controlled electric heating plate and cooled. 1.0 mL of 50% (volume fraction) sulfuric acid solution, 5.0 mL of nitric acid, and 5.0 mL of hydrofluoric acid were added. The mixture was heated at 100 ℃ for 3 h. After settling overnight, the solution was heated at 150 ℃ until the volume of the digestion solution was evaporated to 1-2 mL, and then the temperature was raised to 220 ℃ until the thick smoke was completely emitted. After cooling, 5 mL of the mixed solution of nitric acid and hydrochloric acid at a volume ratio of 1∶3 and 5 mL of water were added, and then the mixture was heated at 100 ℃ to disslove the salts and evaporate the solution to dryness. The process was repeated until the solution was clear, and it was cooled and made its volume up to 100 mL with 1 g·L⁻¹ tartaric acid solution. After settling overnight, 10 mL of the supernatant was taken, diluted to 50 mL with 0.3 mol·L⁻¹ nitric acid solution, mixd well online with 10 μg·L⁻¹¹⁰³Rh internal standard solution, and determined by ICP-MS. As shown by the results, linear relationships between the ratios of the corresponding signal intensity to the internal standard signal intensity and mass concentrations of elements were kept in definite ranges, with detection limits (3s) in the range of 0.006-0.040 mg·kg⁻¹. The bauxite samples (1^#, 2^#, and 3^#) were determined in parallel 11 times, respectively, with RSDs (n=11) of the determined values less than 6.0%. Test for recovery was made on blank reagent solution by standard addition method at 3 concentration levels, giving results in the range of 92.0%-108%.