Silver recovery from greywater: Role of competing cations and regeneration

The use of silver in consumer products and its subsequent leaching in greywater show an increasing trend. Silver recovery is not only commercially lucrative but also an environmental necessity. Trace concentration of Ag+ and high concentration of other competing cations (Na+, Ca2+, Mg2+) in a typical laundry wash water makes the separation process challenging. The use of ion-exchange resin with thiol group in its chain offers a potential solution due to its high selectivity for silver. This work successfully recovers silver (>90%) as high purity grade Ag2S powder (>99%) from synthetic greywater solution using a commercially available resin, Ambersep GT74, in a fixed-bed column mode. The regeneration process in the work has been optimized with respect to the solution pH and thiourea concentration (0.5 M thiourea concentration at pH 1). The resin and the regenerant have been used in multiple cycles (4 times) without compromising on their performance. The study successfully demonstrates a closed-loop sustainable scheme by reusing and recycling all the raw materials to the point of exhaustion with no chemicals/toxic released into the environment.