Comparative Study of Lauric Acid and Lauryl Alcohol as Hydrogen Bond Donors in Hydrophobic Deep Eutectic Solvents and Their Diluted Systems for Platinum and Palladium Extraction

The development of greener solvent systems for platinum group metal extraction is important for sustainable hydrometallurgy. This study systematically investigated how hydrogen-bonding interactions in hydrophobic deep eutectic solvents (DESs) affect the extraction of platinum (Pt), palladium (Pd), iron (Fe), and copper (Cu). Trioctylphosphine oxide (TOPO) was combined with lauric acid (LauA) or lauryl alcohol (LauOH) to prepare DESs with different hydrogen-bonding strengths. LauA/TOPO exhibited strong hydrogen bonding, altering the extraction behavior compared to TOPO alone and enabling the selective extraction of Pt and Fe at higher acidity. In contrast, LauOH/TOPO showed similar extraction behavior to TOPO, facilitating Pt and Pd separation under milder conditions. Dilution with dodecane reduced the extraction efficiency due to increased activity of hydrogen bond donors. These findings demonstrate the critical role of intermolecular interactions in designing DES-based extraction systems for efficient and selective metal recovery.