Water purification is important for ensuring the supply of safe, clean water. Energy-efficient or energy-neutral water purification processes would be ideal for sustainability. Cyanide is a toxic chemical that needs to be removed from wastewater created by, e.g., gold extraction and electroplating. However, it is also a useful chemical feedstock for industry. Thus, an approach to removing cyanide from water that allows its recovery would be useful.

Ji-Woong Lee, University of Copenhagen, Denmark, and colleagues have developed a CO₂-mediated wastewater treatment process that can remove cyanide non-destructively. The team added 2-methoxybenzaldehyde to cyanide solutions under a CO₂ atmosphere at room temperature. In the presence of CO₂, the aldehyde quickly reacts with cyanide ions to give an insoluble cyanohydrin. This species can be removed via a simple filtration, thus providing purified water.

According to the researchers, CO₂ promotes the reaction between cyanide and the aldehyde and shifts the equilibrium towards the cyanohydrin. The team showed that the process can effectively remove up to 97 % of cyanide from water under practical conditions without any toxic oxidants or a need for membrane filtration.

• CO₂‐Mediated Non‐Destructive Cyanide Wastewater Treatment,
  Allan R. Petersen, Martin Juhl, Aleksa Petrovic, Ji-Woong Lee,
  Eur. J. Org. Chem. 2021.
  https://doi.org/10.1002/ejoc.202100997