From waste to wealth: chelating polymeric membranes for precious palladium recovery from wastewater

In this study, we propose a polymeric membrane adsorber that exhibits high adsorption site density capable of selectively capturing palladium Pd ions, providing an effective substitution for palladium recovery from dilute solutions. The membranes are fabricated using polythiosemicarbazide (PTSC), a polymer known for its one chelating site per monomeric unit. Employing a phase inversion fabrication method, we create interconnected porous structures in the membranes, rendering them highly suitable for liquid phase applications with high flux rates. Our approach involves starting with PTSC, inherently containing the requisite adsorption sites, thereby negating the need for introducing external agents into the membrane matrix. As a result, the membrane adsorber overcomes the limitations of traditional adsorbents with low capacities. Mechanically stable PTSC membranes facilitate pressure-driven permeation processes, eliminating the diffusion constraints often associated with packed column adsorption methods. Batch adsorption experiments were conducted at room temperature under acidic conditions of 10% HCl and a maximum adsorption capacity of 1310 mg g⁻¹ was achieved for 1000 pm Pd solution. The developed membrane exhibited an outstanding capability for palladium adsorption, showcasing exceptional adsorption capacity. Impressively, the dynamic adsorption via filtration exhibits a selectivity of 90-96% in recovering palladium from 10 ppm solutions. Moreover, the elution of palladium from the membrane is efficiently accomplished using a thiourea solution of 0.1 M, allowing for the membrane's reuse over at least three cycles without any significant loss in performance. Additionally, the developed membranes exhibited high selectivity towards palladium over other metal ions such as copper, chromium and cadmium.