Solubility, sorption, and soil respiration effects of tungsten and tungsten alloys

This laboratory study addresses issues related to the fate and transport of tungsten and tungsten oxides in the environment (soil-water). Tungsten dioxide and tungsten trioxide were dissolved in aqueous solutions whose pH had been adjusted from 4.0 to 11.0. For initial pH smaller than 10.0, dissolved tungsten concentration remained fairly constant at around 10.0 mg/L for WO₂ and increased from 0.3 mg/L to 2.0 mg/L for WO₃ with increasing values of initial pH. Large amounts of dissolved tungsten were found when tungsten powder or alloy pieces were exposed to aqueous solutions. The dissolution occurs along depletion in solution pH and dissolved oxygen concentration. Depending upon the alloying elements present, the final dissolved tungsten concentration varied from 70 to 475 mg/L. Reduction in pH, dissolved oxygen depletion, and high levels of dissolved tungsten may be of relevance to environmental forensics. In the presence of alloying elements such as iron, nickel, and cobalt, tungsten strongly sorbed to well-characterized model soils. Sorption of tungsten to illite and montmorillonite clays occurs with an increase in pH and appears to be nonreversible. This behavior may significantly retard tungsten mobility. The mixing of tungsten powder with soils at rates higher than 3% (w/w) resulted in acidification of the soil matrix and had a significant impact on soil microbial community as determined by soil respiration.