Adsorption, Desorption and Bioavailability of Tungstate in Mediterranean Soils

The adsorption and desorption process of the tungstate ion was studied in three soils characteristic of the Mediterranean area, with particularly reference to bioavailability pathways. In the three soils examined, the tungstate adsorption was described by a Langmuir-type equation, while the desorption process showed that not all the adsorbed tungstate was released, probably due to the formation of different bonds with the adsorbing soil surfaces. The pH was found to be the main soil property that regulates the adsorption/desorption: The maximum adsorption occurred in the soil with the acidic pH, and the maximum desorption in the most basic soil. In addition, the organic matter content played a fundamental role in the adsorption of tungstate by soils, being positively correlated with the maximum of adsorption. These results indicate that the lowest bioavailability should be expected in the acidic soil characterized by the highest adsorption capacity. This is confirmed by the trend of the maximum buffer capacity (MBC) of soils which is inversely related to bioavailability, and was the highest in the acidic soil and the lowest in the most basic soil. Our data could contribute in drafting environmental regulations for tungsten that are currently lacking for Mediterranean soils.

Transport and surface charge density of univalent ion of polyvinyl chloride-based barium tungstate ion-exchange composite membrane for industrial separation of waste water

In the present study, a polyvinyl chloride-based barium tungstate ion-exchange membrane was synthesized by sol–gel method. The structure of membrane was studied in terms of Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. X-ray diffraction analysis confirms crystalline form of the composite membrane without any other impurity. Scanning electron microscopy and Fourier transform infrared spectroscopy analysis show the uniform arrangement of particles in the membrane with crack-free surface structure and presence of different functional groups of the organic-inorganic materials. The electrochemical properties like surface charge density ( D), transport number and mobility ratio of the ion-exchange composite membrane were theoretically evaluated and compared with observed values using “Teorell, Meyers and Sievers” method. Transport number follows the order as KCl <NaCl < LiCl < NH4Cl, while the surface charge density showed reversed order. The results showed that the low concentration of electrolytes favors the high mobility of univalent cation in the present study. The above result proves the analytical utility of polyvinyl chloride-based barium tungstate ion-exchange membrane in environmental management.

Evaluation of photocatalytic and supercapacitor potential of nickel tungstate nanoparticles synthesized by electrochemical method

Nickel tungstate nanoparticles (NiWO4 NPs) that were synthesized by an electrochemical method under various reaction conditions, namely, different tungstate ion concentrations, voltages, temperatures, and stirring rates, were studied here.