Selective recovery of Au(0) nanoparticles from solid wastes using dimercaptothiadiazole-functionalized UiO-66-NH2 and tin chloride.

Developing effective adsorbents for the recovery of noble metals from secondary resources is of considerable environmental significance. In this study, a metal-organic framework, UiO-66-2,5-dimercapto-1,3,4-thiadiazole (DMTD), was synthesized as a promising adsorbent for gold (Au) recovery from solid wastes. Initially, UiO-66-NH₂ was functionalized with four different thiadiazole derivatives, containing thiol, amine, and methyl functional groups at the 2' and 5' positions. Among these, DMTD was selected due to its superior sorption efficiency. The synthesized UiO-66-DMTD exhibited exceptional selectivity and sorption efficiency during repeated addition of spent adsorbent, even in the presence of competing ions, within a pH range of 1 to 6. Au(III) appears to interact with S = C, S-H, and N = C groups on thiadiazole through reductive chelation, resulting in 53% Au(0), 26% Au(I), and 21% Au(III), based on the X-ray photoelectron spectroscopy results. To obtain pure Au(0), tin chloride solution was reacted following the Au sorption by UiO-66-DMTD, and as a result, Au(0) nanoparticles with 200-500 nm size range were recovered. Overall, the consecutive reaction of the leaching solution with UiO-66-DMTD and tin chloride is an effective method for the selective recovery of Au(0) nanoparticles from secondary resources.