Removal of metal-cyanide complexes and recovery of Pt(II) and Pd(II) from wastewater using an alkali–tolerant metal-organic resin

Metal-cyanide complexes are hazardous and toxic pollutants that can accumulate in organisms, and their natural degradation is difficult. These complexes are primarily present in alkaline wastewater effluents, and an effective technique for their removal must be developed. Herein, we have successfully synthesized a novel quaternary ammonium-functionalized Zr4+ metal-organic resin (MOR) (H16[Zr6O16(MPATP)4]Cl8·xH2O, MPATP = 2-((1-methylpyridin-1-ium-2-ylmethyl)amino)-terephthalic acid), which we refer to as MOR-2-QAS. With alkali resistance, high surface area, and high anion exchange capacity, it acts by introducing positively charged pyridine into the organic ligand. The experimental results indicate that MOR-2-QAS becomes rapidly attached and efficiently removes Pt(CN)42−, Pd(CN)42−, Co(CN)63−, and Fe(CN)63−. Valuable metals (Pt(II) and Pd(II)) can be effectively recovered from the simulated wastewater containing four-component cyanide complexes via the two-step elution process. The recovery efficiency of Pt(II) and Pd(II) was higher than 90.0% after three adsorption-desorption cycles. The adsorption mechanism, which proceeded via ionic association (ion-exchange) and complied with the minimum surface charge density experiential principle, was confirmed using density functional theory. This study provides ideas for developing efficient and stable MORs to enable the simultaneous removal of multiple metal–cyanide complexes and recovery of valuable metals.