Gold Binding and Removal by Sulfur-Based Cationic Polymers

Gold’s unique properties have made it highly desirable for currency, jewelry, and electronics. With our expanding electronics use and rapid turnover of devices, a significant amount of gold is thrown away as electronics waste. Recovering gold from this and other waste streams poses a challenge due to the diversity of components and a lack of safe and selective extraction materials. Sulfur is known to form strong bonds with gold. Additionally, it is inexpensive and abundant due to its large-scale production during petroleum refinement. Inverse vulcanization offers a simple, solvent-free method to repurpose surplus sulfur into high sulfur content polysulfides. Most of these polysulfides are insoluble and rely on an enhanced surface area to bind to heavy metals. Incorporating charged monomers allows soluble polysulfides to better interact with aqueous metal ions. Here, we have utilized inverse vulcanization to create four cationic polysulfides and characterized them using NMR, XRD, GPC, DSC, and TGA. The water solubility, metal binding capacity, and selectivity were analyzed. Additional testing revealed the role of the soluble, insoluble, and suspended portions in heavy metal binding. Varying the cationic monomers significantly impacted the physical properties, metal binding capacity, and selectivity. Enhanced solubility was not a key factor in improving selective gold binding and removal. Instead, the slightly soluble poly(S-vinylimidizole) provided the highest gold binding capacity of 1929 mg Au3+/g polymer while maintaining reasonable selectivity.