Infrared Study of (Poly)tungstate Ions in Solution and Sorbed into Layered Double Hydroxides: Vibrational Calculations and In Situ Analysis

Abstract

In situ attenuated total reflection infrared spectroscopy (ATR-FTIR) was used to study the speciation of (poly)tungstate ions in solution and the sorption process into layered double hydroxides (LDHs). In the first section, the W(VI) speciation in solution was performed by comparison of thermodynamical calculations and infrared spectroscopy of solutions as a function of pH. Then, the exchange mechanism within LDHs was followed in real time with the in situ ATR technique and compared with batch experiments characterized by powder X-ray diffraction (PXRD), elemental analysis, and FTIR. Decomposition of the (W−O) stretching vibration bands, between 800 and 1000 cm −1 , has allowed the identification of the high affinity of LDHs for the polytungstate species, W 7 O 24 6− , despite the presence of carbonate ions and higher charged polytungstate ions in solution. This was confirmed by the DFT methods used to investigate the structure and the vibrational modes of this anion, and very good agreement with experimental spectra has been obtained. The affinity series W 7 O 24 6− > CO 3 2− > WO 4 2− > SO 4 2− has been directly deduced from those results.

Extraction of tungsten as polyoxometalate anion using a layered double hydroxide: Selectivity and regeneration

“…Several sets of polymeric species and associated formation constants can be found in literature 21 . We have previously found 12 that our experimental data are in agreement with the work by Cruywagen at al.…”

“…The experimental conditions and setup are similar to those described in our previous articles 12,20 .…”

“…The extraction of tungsten from aqueous solution remains a process to improve, by decreasing the cost or the environmental impact, or by extending the range of sources that can be treated. Even though the affinity of tungstate polyanions towards layered double hydroxides (LDH) is known 12 , to the best of our knowledge no study on the application of these solids has been performed to evaluate the use of LDH to extract tungsten from a solution, and to describe the extraction mechanism. LDHs are inorganic materials that consist of positively charged stacked layers with charge-balancing anions located in the interlayer regions.…”

Influence of Increasing Tungsten Concentrations and Soil Characteristics on Plant Uptake: Greenhouse Experiments with Zea mays

“…Although speciation of tungsten in soil is of great importance [9,58], especially for the polymerization phenomena [59,60], we decided to evaluate the trend of the tungsten uptake using a model as simple as possible. This approach of course can only be considered as a preliminary step in developing mechanistic models.…”

Effects of tungsten source and tartrate additive on the microstructure and photoluminescence of hydrothermally crystallized ZnWO4

“…Tungstate anions exhibit rich solution chemistry and, critically depending on pH of solution, may exist in one or more of the ionic forms of WO 10− in an aqueous solution [32]. It is known that monomeric WO 4 2− can be stabilized by raising the pH value of solution to ~ 6.2, and then becomes the prevailing one (> 99%) when the pH value is over 7.8 [33]. Considering that the hydrothermal synthesis of this work was performed under the same solution pH value (pH = 8), Zn 2+ content (3 mmol) and Zn to W molar ratio (1:1), it is reasonable to conclude that WO 4 2− is the dominant type of tungstate anions in the reaction system and the concentration of WO + is considerably complexing toward many types of metal ions [34,35] and the existence of Zn 2+ -NH 4 + and/or Zn 2+ -NH 3 complex species may be expected in the current reaction system, where NH 3 is generated through the equilibrium NH 4 + + OH − ⇄ NH 3 + H 2 O under pH = 8.…”