Silver recovery as Ag nanoparticles from ion-exchange regenerant solution using electrolysis.

Many silver (Ag) containing consumer-products (e.g. textiles) release Ag into the environment, posing ecotoxicological risks. Ag recovery mitigates environmental hazards, recycles Ag, and leads to sustainability. In the present work, Ag has been recovered as Ag nanoparticles from the spent solution (thiourea (TU) ~0.5 mol/L pH ~1.1-1.2, and Ag ~550 mg/L) obtained from the regeneration of an Ag-loaded resin using a simple undivided electrolytic cell. The reclaimed regenerant solution has been recycled and reused in a closed-loop scheme over multiple cycles. The process parameters, i.e., current (0.05 A) and stirring speed (600 r/min), have been optimized for Ag recovery of ~94% and TU loss of ~2%. The reclaimed regenerant solution has been shown to regenerate Ag-loaded resin samples with >90% regeneration efficiency over 4 cycles of consecutive extraction and regeneration. The recovered Ag nanoparticles are monodisperse, consistently spherical in shape, and have a mean diameter of ~6 nm with standard deviation of the Gaussian fit as ~2.66 nm.