Solution Thermodynamic Properties of {Tetrabutyl Ammonium Bromide:Glycerol} Hydrophilic DESs at T = 298.15–348.15 K and 0.1 MPa and an Approach over Solvent Extraction of Cr(VI) Using {Tetrabutyl Ammonium Bromide:Decanoic Acid/Oleic Acid} Hydrophobic DESs

This study focuses on determining a pseudo-binary mixture's volumetric properties between 298.15 and 348.15 K temperature over the whole mole fractions to understand the molecular interaction between aqueous chromium solution and hydrophilic deep eutectic solvents (DESs). The solution thermodynamic properties like the mixtures' excess molar volume, partial molar volume and excess partial molar volume of individual components in the solution, apparent molar volume, partial molar volume at infinite dilutions, and isobaric expansivity were determined. Characteristics like the existence of functional groups, thermal stability, phase transitions, and degree of acidity were investigated using Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and pH measurement of six prepared DESs. For the extraction process, the hydrophilic glycerol in the DES will be replaced by decanoic acid and oleic acid, which are hydrophobic. The hydrophobic DES (HDES)-based extraction process was conducted for three volume fractions under atmospheric conditions. HDESs were used to remove heavy metal ions (25, 50, 75, and 100 ppm) from the water stream. Notably, the extraction efficiency increased with the concentration of chromium(VI) ions. Even at a lower concentration, the extraction efficiency showed more than 94% for all HDESs. Before and after extraction, chromium(VI) concentrations were analyzed using inductively coupled plasma–optical emission spectroscopy.