The use of silver (Ag) in consumer products, as an anti-microbial agent, particularly on textiles, has been steadily rising. Ag-leaching during laundry and its subsequent discharge in the environment pose ecotoxicological risks. Therefore, Ag recovery is important from environmental and economic perspectives. Trace concentration of Ag+, high concentration of competing cations (Na+, Ca2+, Mg2+), and the complexity of the detergent matrix make the recovery challenging. The use of ion-exchange resin with thiol group offers a potential solution due to its high selectivity for silver. The present study utilizes a silver-selective cation-exchanger to remove Ag from laundry wastewater. Regeneration of the exhausted ion exchanger has been optimized with respect to the solution pH and thiourea (TU) concentration. Finally, Ag has been recovered as Ag0 nanoparticles and Ag2S (as nanoparticles and micro-sized powder) from the spent regenerant solution (TU: ~0.5 M, pH: ~1.1 – 1.2) using electrolytic and wet-chemistry techniques respectively. The recovered Ag0 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. The role of each detergent component in affecting Ag-speciation and the resin performance has been analyzed. Builders and bleaching agents are reported to negatively impact the resin performance. pH and co-cationic species (Ca2+) concentration are reported to be critical parameters for Ag recovery. The resin and the regenerant have been used in multiple cycles without compromising their performance.

Silver removal and recovery from laundry wastewater

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.