Characterization of tungsten distribution in tungsten-rich slag and sediment by leaching experiment

The adverse environmental effects of tungsten have been underestimated for a long time. Recent studies have demonstrated that dissolved tungstate is mobile in aqueous environments and exhibits severe toxicological impacts. If substantial tungsten slags were directly exposed, they would potentially pollute the surrounding waters and soils. The objective of this study was to investigate the pollution and ecological risks of tungsten-rich slags and sediments as a result of leaching. In this study, samples of tungsten-rich slags and sediments were collected from Chenzhou and Tengchong (China), with the highest tungsten concentration up to 378.1 mg/kg. To investigate the pollution and ecological risks of tungsten-rich slags and sediments as a result of leaching, sequential extraction procedures (SEP) and batch leaching experiments were conducted. According to the Tessier SEP results, the residual fraction accounted for more than 90% of the total tungsten in most samples, while the Wenzel SEP results showed over 52% of the hydrous oxides bound fraction except for the samples SP02 and ZN02. Thus, the Tessier SEP underestimated the proportions of the Fe and Al oxides bound fraction and the environmental risks of tungsten. In contrast, the Wenzel SEP was superior to the Tessier SEP in terms of extracting the amorphous hydrous oxides bound fraction and crystalline hydrous oxides bound fraction of tungsten due to the use of more suitable extraction reagents. The leaching experiments demonstrated the tungsten concentrations in the leachate samples were up to 105.6 µg/L. Notably, leaching of tungsten from the tungsten-rich slags and sediments under acid conditions was less effective than under alkaline conditions, which was attributed to the strong adsorption of tungsten onto Fe/Al (hydro)oxides under acid conditions.