Cadmium Removal from Wastewater Through Ligand Complexation

This study presents the development of ligands tailored for the selective removal ofinorganic cadmium from wastewater. Designed for integration into flow-through filtration systems, these ligands exhibit reversible cadmium binding, enabling targeted extraction, material regeneration, and metal recovery, addressing key challenges in sustainable water remediation. Five ligands were synthesized, isolated, and fully characterized, along with the first reports of four new crystal structures. A novel, safer synthetic route to dithiomorpholine derivatives was developed, avoiding the use of mustard gas or its derivatives and offering improved operational simplicity over existing methods, enhancing the accessibility and sustainability of dithiomorpholine synthesis. Additionally, two new cadmium complexes were synthesized and fully characterized for the first time. A novel 113Cd-NMR method was developed for direct analysis of cadmium species in extraction solutions, enabling detection at concentrations as low as 0.01 M. The approach allows direct structural characterization without requiring sample modification, with cadmium-ligand complexes showing consistent downfield shifts relative to a Cd(NO3)2 in CD3OD reference. This method provides in situ structural insights into cadmium-ligand coordination, offering a valuable complement to MS, XRD, and AAS in remediation research. Finally, the quantification of the obtained complexes using atomic absorption spectroscopy (AAS) demonstrated the ability of a dioxime-based ligand in removing consistently 10% of the cadmium load from aqueous solutions.