Tungstate (VI) sorption on hematite: An in situ ATR-FTIR probe on the mechanism

Abstract

Owing to the suspected toxicity and carcinogenicity of tungstate (VI) oxyanions [i.e. mono tungstate and several polytungstate, generally represented by W (VI)], the environmental fate of W (VI) has been widely studied. Sorption is regarded as a major mechanism by which W (VI) species are retained in the solid/water interface. Iron (hydr)oxides have been considered important environmental sinks for W (VI) species. Here we report sorption mechanisms of W (VI) on a common iron oxide mineral-hematite under environmentally relevant solution properties using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic probes. Initial W (VI) loadings varied from 10 to 200 μM at fixed pH values ranged from 4.6 to 8.1. For pH envelop (pHs = 4.6, 5.0, 5.5, 6.0, 6.5, 7.5, and 8.1) experiments, fixed W (VI) concentrations (i.e. 10 & 200 μM) were used to understand the effects of pH. The results indicated that at acidic pH values (pH < 6.0) the sorbed polytungstate surface species are prominent at 200 μM initial W (VI) conc. The pH envelop experiments revealed that sorbed polytungstates can be present even at lower initial W (VI) conc. (i.e. 10 μM) at pH values <5.5. Overall, our in situ ATR-FTIR experiments indicated that W (VI) forms inner-sphere type bonds on hematite surface and the strength of the interaction increases with decreasing pH. In addition, initial W (VI) concentration affected the sorption mechanisms of W (VI) on hematite. Our study will aid the molecular level understanding of W (VI) retention on iron oxide surfaces.

Comparison of two sequential extraction procedures for tungsten fractionation in the tungsten mining soils

“…It has been reported that the oxides/hydroxides of Al, Fe and Mn in environmental solid samples are the main tungsten scavengers. [21][22][23] In principle, the reducible fraction could be split into three fractions: easily reducible fraction (Mn oxides); moderately reducible fraction (amorphous Fe oxides); and poorly-reducible fraction (crystalline Fe oxides). The relatively high concentration of Al and Fe in the study soil samples may lead to a high proportion of reducible components of tungsten.…”

Influence of phosphate on tungstate sorption on hematite: A macroscopic and spectroscopic evaluation of the mechanism

“…One possible fate of added W (VI) is sorption by soil minerals. Consequently, many studies evaluated the sorption mechanisms of W (VI) on various soil minerals (Gustafsson, 2003;Xu et al, 2006Xu et al, , 2009Lorenz, 2009;Lorenz et al, 2011;Kashiwabara et al, 2013;Davantes and Lefevre, 2015;Sun and Bostick, 2015;Hur and Reeder, 2016;Rakshit et al, 2017). In general, W (VI) displays a high affinity for iron-and aluminum hydr (oxide) minerals (Gustafsson, 2003;Xu et al, 2009;Hur and Reeder, 2016).…”

“…In general, W (VI) displays a high affinity for iron-and aluminum hydr (oxide) minerals (Gustafsson, 2003;Xu et al, 2009;Hur and Reeder, 2016). To support the findings in macroscopic sorption isotherm and envelope, researchers determined molecular level information on surface retention mechanism using EXAFS and in situ ATR-FTIR spectroscopic tools as well (Davantes and Lefevre, 2015;Hur and Reeder, 2016;Davantes et al, 2017;Rakshit et al, 2017). These spectroscopic measurements are very sensitive and resulted in the detailed information about surface complexes at environmental range of W (VI) conc (Hur and Reeder, 2016;Rakshit et al, 2017).…”

Biogeochemistry of trace elements in anaerobic digesters

“…The authors correlate the adsorption capacity of W forms with different inner-sphere complexation on the pyrite surface. Another study investigated the interaction of tungsten with hematite showing strong adsorption and, similarly to pyrite, increased adsorption capacity with decreasing pH (Rakshit et al, 2017). Tungstate was also shown to adsorb onto organically modified montmorillonite and the main sorption mechanisms involve chemisorption and ion exchange (Muir et al, 2017).…”