Researchers at the University of Massachusetts are in a quest to recover silver from laundry wastewater and, according to a paper published today in ACS Sustainable Chemistry & Engineering, they have discovered how different variations in detergent chemistry impact the amount of metal they can get.
But Tabish Nawaz and Sukalyan Sengupta, the leaders of this project, are not trying to become a new type of miner. With their research, they want to figure out how to avoid silver nanoparticles from coming off clothing and ending up in the environment.
In recent years, Ag specks are being used by clothing manufacturers because they can kill odor-causing bacteria. However, as the garments are laundered, those elements are released. “Silver nanoparticles can be toxic to many aquatic organisms and can impact the effectiveness of bacterial processing in wastewater treatment plants,” a media statement by the American Chemical Society reads.
Thus, the scientists want to learn how to prevent the tiny bits of metal from coming off. By analyzing how they interact with individual detergent ingredients, they were able to discern that silver mainly exists as a positively charged ion and that this ion will interact with negatively charged ions in the detergent at different pH ranges.
This discovery set the foundation that allowed them to use an ion-exchange resin with different pH and ion concentrations which, at a specific point, was able to recover as much as 99 per cent of the silver.
The resin was tested with detergent components and reused over five cycles, and it maintained the ability to remove silver. Yet, the addition of products, such as bleaching and water-softening agents, negatively impacted the efficiency of the resin.
Even though it may look simple, the process was not easy. According to the scientists, low concentrations of silver in the water, high concentrations of competing ions and an uncertainty as to which exact forms of silver are present made this work very challenging.