Separation of Gold from Other Noble Metals Using Acrylic-Acid-Based Cryogels.

The recovery of noble metals from industrial wastewater, printed circuit boards and end-of-life electronics is very important to ensure the availability of these non-renewable sources in the future. Metal recycling can be afforded through different solution-based methods including reductive precipitation, oxidative dissolution, solvent extraction, or adsorption. The latter is particularly appealing due to its simplicity and potential selectivity, which can be tailored by a wide range of materials. A significant challenge lies in the separation of gold from platinum group metals owing to their similar chemical properties. In this study, we demonstrate an easy method for the selective recovery of gold from mixed-metal solutions (including Pd, Pt, Ru, Rh, and Ir) exploiting adsorbent materials prepared by cryopolymerization of acrylic monomer solutions. These cryogels present an interconnected macroporous structure that enables fast swelling and a high water content across different pH values. They exhibit high selectivity even in the presence of metals like Pd and Pt, which are difficult to separate with other techniques in solution. The key advantages of this method include an easy synthesis and the direct use of industrial wastewater without the need for pH adjustment, the addition of reductants, or other pretreatment steps. Unlike other adsorbents, this separation method allows selective gold recovery without the need for special protocols or precise kinetic control, making it easier to scale up for industrial use.