Controlled Reaction-Diffusion Coupling for Critical Elements Separations

The surging demand of critical elements for use in green energy technologies has necessitated the development of new methods for obtaining these materials. Complex mixtures of various metals present in some industrial wastewaters represent a possible new source of important elements; however, extracting these elements is a complicated and environmentally challenging separation process. For example, while wastewater produced from battery and electronics recycling contains valuable lithium, manganese, cobalt, and nickel, methods will be needed to extract and separate these elements from the acidic, organic-containing waste stream. One possible method to overcome the technical challenges associated with adsorption and solvent separation techniques is selective precipitation using reaction-diffusion coupling, in which metal ions are precipitated during diffusion through a gel, separating products by their diffusion and reaction rates. In this work, we explore how selectivity can be improved by changing the diffusion rate and reaction time of the metal ions. A base gel was used for reaction-diffusion with sodium hydroxide added to initiate precipitation of the metal ions. The cross linking density of the gel was then varied to observe the role of gel mesh size on precipitate diffusion. We further explored using a diffusion cell and cross-flow cell along with a traditional microporous membrane to control the rate of rate of reaction, in an effort to develop a continuous separation process.Taken together, this work explores how reaction-diffusion can be used in novel ways to enhance critical metal separations.