XIA Xiang, LU Haichuan, DING Yang, GONG Cang, LIU Tao, LIAO Xuanzhe
Accurate determination of trace element contents, including rare earths, in mudstone can be used to assess its potential as an energy resource, serving geological research and the strategic action for a new round of mineral exploration breakthroughs. In this paper, the mudstone sample was treated using an open acid digestion method with a five-acid system of nitric acid, hydrochloric acid, hydrofluoric acid, perchloric acid, and sulfuric acid. A mixed solution of hydrogen peroxide and aqua regia was added for extraction. Rh and Re were used as internal standards for correction. The method for the determination of 33 elements in mudstone including rare earths (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Be, Mn, Co, Ni, Cu, Zn, Rb, Sr, Mo, Tl, Pb, Bi, Th, U, Ti, Nb, and Ta) by inductively coupled plasma mass spectrometry (ICP-MS) was established. The results showed that the linear correlation coefficients of the calibration curves for 33 elements were all greater than 0.999 5. The limits of detection and limits of quantification in this method were 0.000 1-0.9 μg/g and 0.000 4-3.6 μg/g, respectively. GBW07104 and five mudstone samples collected from the Turpan-Hami Basin in Shanshan, Xinjiang, were selected. The contents of 33 elements including rare earths were determined according to the experimental method. The results showed that the relative standard deviations (RSD,n=12) of the measurement results for each element ranged from 0.16% to 9.9%, which could meet the requirement of RSD ≤ 10% specified in DZ/T 0011-2015. The certified reference materials of rock (GBW07103 and GBW07104) with similar compositions to the mudstone samples were selected. The contents of 33 elements including rare earths were determined according to the experimental method. The results showed that the measured values of each element were basically consistent with the certified values. The logarithmic differences (Δlg) ranged from 0.00 to 0.08, which could meet the requirement of Δlg≤ 0.11 specified in DZ/T 0011-2015. Two mudstone samples were measured according to the experimental method, and a certain amount of mixed standard solution was added to each sample to conduct the recovery experiments. The results showed that the spiked recoveries of 33 elements including rare earths in the mudstone samples ranged from 92% to 110%, which could meet the requirement of 90%-110% specified in DZ/T 0130-2006 Specification for Quality Management of Geological and Mineral Laboratory Testing.