Selective diammonium reagents hosted on nanofibers for recovery of iridium from rhodium: Theoretical and experimental studies

Abstract

Quaternary diammonium-functionalized polyvinyl benzyl chloride nanofibers were done using different diamines such as ethylenediamine (EDA), tetramethylene diamine (TMDA), hexamethylenediamine (HMDA), octamethylenediamine (OMDA), 1,10-diaminodecane (DMDA) and 1,12-diaminododecane (DDMDA) with quaternization using methyl iodide, followed by conversion to a chloride form. These were called F-QUAT EDA, F-QUAT TMDA, F-QUAT HMDA, F-QUAT OMDA, F-QUAT DMDA and F-QUAT DDMDA, respectively. Materials characterization was supported using elemental analysis, FTIR, XPS, SEM-EDS, TG and BET analysis. Langmuir and Freundlich's models were applied to analyze the adsorption of [IrCl6]2− and [RhCl5(H2O)]2− onto the materials, and the Freundlich model was obeyed. The mass transfer kinetics were tested on the pseudo-first-order and pseudo-second-order equations, and the process obeyed the pseudo-second-order kinetics. Column studies for the sorption of [IrCl6]2− using the functional materials were carried out and the loading capacities were 5.98 mg/g, 7.95 mg/g, 15.23 mg/g, 21.71 mg/g, 32.94 mg/g and 9.70 mg/g for F-QUAT EDA, F-QUAT TMDA, F-QUAT HMDA, F-QUAT OMDA, F-QUAT DMDA and F-QUAT DDMDA, respectively. This was the order of an improvement in the methylene chain amongst the two ammonium groups up to ten carbons. Theoretically calculated electrostatic potential energies of the cations, dipole moments and solvation energies of the free cations and anions, energies for replacement of the chloride by [IrCl6]2−, and thermodynamic parameters for the formation of ion-pair complexes were used to explain this trend observed for the capacity of the functional reagents. The functional nanofibers displayed potential for use in selective recovery of iridium from rhodium.