Efficient extraction of platinum with benzo-18-crown-6 in a potassium halide based system

This research investigated the ability of benzo-18-crown-6 (B18C6) for selective extraction and the mechanism underlying its complexation with Pt(IV) ions within systems containing potassium halides (i.e., KX, where X represents Cl, Br, or I). To systematically explore the complexation of B18C6 with Pt(IV), the impacts of several parameters were assessed. These parameters included the concentration of KX, mole ratio of B18C6 to Pt(IV), acidity levels, and reaction time. The experiments revealed that under optimal conditions and in the presence of competing ions, the B18C6-KI system is capable of efficiently and selectively extracting platinum, achieving a Pt(IV) extraction efficiency of 99.8 %. Furthermore, the loaded organic phase can be efficiently stripped of platinum using a mixture of thiourea and hydrochloric acid. After seven cycles of extraction and stripping, the Pt(IV) extraction efficiency remained consistently high, approximately 91 %, demonstrating the outstanding reusability of B18C6 for extracting Pt(IV) from a halide leaching system. The findings obtained via Job's method, mass spectrometry, SEM-EDS, and ¹H NMR spectroscopy indicated that the primary complexation between B18C6 and Pt(IV) during the extraction process occurred at a 2:1 stoichiometric ratio. Density functional theory calculations revealed that B18C6 initially coordinates with KX, forming the B18C6-KX complex. This complex then associates with PtX₆^2- via anion exchange, resulting in the formation of the [B18C6-K]₂PtX₆ complex, thereby enabling efficient extraction of Pt(IV).