Tungsten In California Soils and Sediments Affected by Mine Tailings.

This research addresses the occurrence, speciation, and distribution of tungsten in the vicinity of abandoned mines near Bishop, CA. Tungsten, most commonly found as tungstate (WO₄^2-), exists in mineral phases such as sheelite (CaWO₄), ferberite (FeWO₄), and huebernite (MnWO₄). Tungstate can also form adsorption complexes with the siloxane surface groups associated with phyllosilicates and the hydroxyl groups associated with the edges of inorganic minerals such as Fe-oxides and Al-oxides, and kaolinite.

A modified fractionation scheme was used to target specifically bound, sorbed, and mineral phases tungsten. Weakly adsorbed W was extracted by ammonium chloride followed by an ammonium fluoride (NH₄F) solution, which separates Al-W from Fe-W. Fe-W was extracted with NaOH and reductant-soluble W with citrate dithionite bicarbonate (CBD). Calcium-tungstate was extracted with H₂SO₄. Residual tungsten was extracted by a modified microwave acid digest.

The sequential extraction analysis found most of the tungsten in the soil and sediment was in a residual form. Fe-W and reductant-soluble-W represented about 20 % of the total W. XANES data indicate fully oxidized W(VI)-adsorbed complexes. The locations of the samples with the highest W concentrations were found in the active stream channel and stream terraces. The W appears to be transported away from the abandon mine spoils either as residual mineral forms or as W-adsorbed complexes.