Determination of Major Elements in Sepoilite by Inductively Coupled Plasma-Optical Emission Spectrometry with Opening Acid Dissolution

BACKGROUNDSepiolite is a widely used fibrous magnesium-rich silicate clay mineral. Sepiolite is mainly composed of silicon and magnesium, with minor aluminum, potassium, sodium and other impurities. Determination of the major element of sepiolite usually adopts the classical chemical analytical method. After the alkali melting treatment, the sample is determined by volumetric method, photometry and atomic absorption spectrometry, which is inefficient and time-consuming. Moreover, potassium and sodium cannot be simultaneously determined.

OBJECTIVESTo find an efficient method for the determination of seven major elements in sepiolite.

METHODSThe samples were digested by hydrofluoric acid, nitric acid, and perchloric acid. Contents of major elements such as Al₂O₃ were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The dosage of hydrofluoric acid was optimized. The analytical spectral lines were Al 396.153nm, Ti 334.940nm, K 766.490nm, Na 589.592nm, Ca 422.673nm, Mg 285.213nm and Fe 238.204nm, and elements were determined by axial observation. The content of magnesium in sepiolite was high, and there was a certain matrix effect during ICP-OES analysis. A series of high magnesium mixed standard solutions were prepared to match the matrix.

RESULTSThe linear correlation coefficient of the standard curve of each element was greater than 0.9990, the detection limits of the method were 0.53-3.25μg/g, the relative standard deviations (RSD, n=10) of the measured results were 0.66%-5.65%, and the recoveries of each element were 95.3%-108.5%.

CONCLUSIONSAcid dissolution is easy to operate compared with the alkali fusion method. The results are consistent with those obtained by classical chemical analytical methods and thus meet the analytical requirements of sepiolite samples.