Determination of Total Amounts and 7 Chemical Species of Rare Earth Elements in Ionic-Adsorption Rare Earth Ore by Inductively Coupled Plasma Mass Spectrometry with Continuous Extraction

A sample of an ionic-adsorption rare earth ore was collected, which was removed from impurities, naturally air-dried, ground, sieved and mixed. 1.000 g of the sample was taken, and the water-soluble state (F1), ion-exchange state (F2), carbonate-bound state (F3), humic acid-bound state (F4), iron-manganese oxide-bound state (F5), strong organic-bound state (F6) and residue state (F7) of rare earth elements in the sample were sequentially extracted with water, 1 mol·L^-1 magnesium chloride solution, 1 mol·L^-1 sodium acetate solution, 0.1 mol·L^-1 sodium pyrophosphate solution, a mixture of 0.25 mol·L^-1 hydroxylamine hydrochloride-0.25 mol·L^-1 hydrochloric acid, and a mixture of 0.02 mol·L^-1 nitric acid-30% (volume fraction) hydrogen peroxide-1.6 mol·L^-1 ammonium acetate-1.6 mol·L^-1 nitric acid. 7 species of each element and the total amounts of 15 rare earth elements in the sample were determined by inductively coupled plasma mass spectrometry (ICP-MS). Matrix matched mixed standard solution series, diluting the chemical specie extract solution 20 times (F1 twice) and ¹⁰³Rh-¹⁸⁵Re double internal standards were used to eliminate the influence of various extractants on the determination of rare earth elements. Detection limits (3s) of the 7 chemical species of each rare earth element were in the range of 0.001 1-0.75 mg·kg^-1, and RSDs (n=5) of each rare earth element chemical specie analysis results were in the range of 1.4%-11%. GBW 07158 was the quality control sample, and its determined value was basically consistent with the certified value. This method was applied to the analysis of actual ionic-adsorption rare earth ore samples, and it was shown that the total amounts of rare earth elements in the samples of this ionic-adsorption rare earth ore were 691-2 299 mg·kg^-1. Except for cerium, speciation of 14 rare earth elements, including yttrium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, were mainly in F2, accounting for 47.6% to 84.5% of the total amounts of rare earth elements. The chemical species of cerium mainly existed in F2, F5, F6 and F7. Recoveries of the total chemical species to the total amounts of rare earth elements were in the range of 95.7%-98.6%, indicating that this continuous extraction was suitable for the chemical specie analysis of rare earth elements in ionic-adsorption rare earth ore.