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article imageMining for silver in your laundry wastewater

By Karen Graham     Dec 26, 2017 in Science
Silver nanoparticles are being used in clothing for their anti-odor abilities but some of this silver comes off when the clothes are laundered. The wastewater from this process could end up in the environment, having a detrimental effect.
Because silver nanoparticles are toxic to the marine environment, researchers have been trying to find a way to remove them. One group reports in ACS Sustainable Chemistry & Engineering that detergent chemistry plays a significant role in how much of this silver can be removed from laundry wastewater.
Tiny particles of silver are used in a wide variety of commercial products, primarily because of their antibacterial properties. But very little research has been done into their effects on human health until recently. Furthermore, studies are still being done on whether toxicity is the release of silver nanoparticles or the release of silver ions.
However, when presented with the possibility of nanoparticles on clothing being released during laundering, this opened up a whole new line of research. Human and solid waste has to be removed from the water and be treated before it is released into the environment.
But tiny particles, bacteria, and other chemicals invariably slip through this process and are dumped back into the environment. Researchers with the Civil and Environmental Engineering Department, University of Massachusetts Dartmouth, realized there had to be a way of removing the silver nanoparticles as an environmental necessity.
They were aware of several problems - One, they weren't absolutely certain if the silver was in the form of ions or nanoparticles. Two, the silver would be in low concentrations in the wastewater, along with high concentrations of competing ions. But the researchers realized the previous studies had not taken into consideration the role of detergent chemistry, which could interfere with ion-exchange selectivity. So that’s what they wanted to examine in the current report.
The researchers analyzed how silver interacts with individual detergent ingredients. The team found that silver mainly exists as a positively charged ion, and this form will interact with several detergent compounds under certain conditions. In other words, the positively-charged silver ions will react with negatively-charged detergent ions.
The researchers then used an ion-exchange resin, and this allowed them to remove as much as 99 percent of the silver, depending on the pH and competing ions. The team found the resin could be used over five washing cycles without losing its ability to remove silver ions. However, the use of water-softening and bleaching agents negatively impacted the resin.
Bottom line to all this? Why do we need silver in our clothing in the first place, especially if there is the possibility of it being toxic?
More about Silver, Nanoparticles, toxicity, antibacterial, detergent chemistry
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