Investigations of tungsten mobility in soil using column tests

The geochemistry of tungsten has recently gained attention in the scientific and regulatory communities. Tungsten has a complex geochemistry, existing in many environmental matrices as the soluble and mobile tungstate anion, as well as a series of ill-defined polymeric species. Previous work has shown that soluble tungsten leached from a metallic tungsten-spiked Grenada Loring soil will reach an equilibrium concentration >150 mg L−1, and the concentration is greatly influenced by co-occurring analytes in the matrix, such as calcium and phosphate. In the present work, the mobility of tungsten compounds was investigated in a model soil with a range of aqueous leach solutions using column experiments. The relative column leachate concentrations measured followed trends from previously reported tungstate and polytungstate partition coefficients determined in the model soil under identical aqueous matrix conditions. Neutral to alkaline conditions produced maximum effluent tungsten concentrations >40 mg L−1, whereas acid leach eluents produced concentrations in the <1–3 mg L−1 range. The change in leached tungsten speciation over time was also measured as monomeric and polymeric tungsten species have different sorptive behaviors.