Tungstate (VI) sorption on hematite: An in situ ATR-FTIR probe on the mechanism.
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.
Department of Agricultural and Environmental Sciences, Tennessee State University, 3500 John A. Merritt Blvd., Nashville, TN 37209-1561, USA. Electronic address: srakshit@tnstate.edu.
Sudipta
S
Rakshit
Department of Agricultural and Environmental Sciences, Tennessee State University, 3500 John A. Merritt Blvd., Nashville, TN 37209-1561, USA.
Bryan
B
Sallman
PSL Research University, Chimie Paris Tech-CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France.
Athénais
A
Davantés
PSL Research University, Chimie Paris Tech-CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France.
Grégory
G
Lefèvre
D000327:Adsorption; D004785:Environmental Pollutants / Q000032:analysis / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008903:Minerals; D008956:Models, Chemical; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D017973:Tungsten Compounds / Q000032:analysis / Q000737:chemistry*
D004785:Environmental Pollutants; D005290:Ferric Compounds; D008903:Minerals; D012996:Solutions; D017973:Tungsten Compounds; C000499:ferric oxide; C045951:tungstate
Hematite; Infrared; Polytungstate; Sorption