Fractionation of W in the topsoil of a meadow soil above the oxidation zone of the W deposit: results of sequential extraction and LA-ICP-MS analysis of soil from the Grantcharitsa deposit, Bulgaria

A four-step sequential extraction procedure (SEP) was used to assess the distribution of W fractionation in the topsoil (0–20 cm) of the soil above the oxidation zone of the W deposit. Data on the extraction of W and other elements were obtained using LA-ICP-MS and SEM-EDX analyses of the dried, sieved and finely grinded original soil and residual samples after each step of the procedure. When processing LA-ICP-MS data, the SiO2 content of the original soil was used as an internal standard for all samples in the sequential extraction procedure. It was found that of the approximately 90 ppm of total W content in the soil, about 25% is associated with organic matter, 40% with amorphous hydrous Fe oxides (ferrihydrite), 25% with crystalline hydrous Fe oxides (goethite), and about 10% with residual material (scheelite, silicates).