(524b) Bipolar Membranes for pH Assisted Electrochemical Separations

Electrochemical separations are emerging as an enticing technology for selective ion separations in several applications important to global sustainability initiatives (e.g., securing critical minerals and materials for the clean energy transition and nutrient recovery from wastewater for curbing the deleterious environmental impacts from fertilizer runoff). In these applications, the feedstocks often contain competing ionic species at much higher concentrations than the desired ion of interest. There are numerous handles in electrochemical separations to achieve selective ion separations. They include electrode design, selective membranes, electrode potential, and electric field strength. Furthermore, adjustment of the solution pH combined with the said handles can amplify ion selectivity. This talk presents our work on bipolar membranes (BPMs) for in-situ pH adjustment of process streams to enable selective ion separations in capacitive deionization (CDI) platforms. The first part of the presentation covers copper and lithium recovery from model wastewater and geothermal brines, respectively. The operating parameters of BPM-CDI can influence the extent of pH adjustment and hence the ion removal rate and removal selectivity. The second part of the presentation covers phosphate removal from model wastewater streams. In both the first and second parts of the talk, we will discuss how selective electrodes and composite membranes work cooperatively with in-situ pH adjustment for selective ion separations. The talk will also include molecular dynamics (MD) simulations that further our understanding of ion partitioning behavior in membrane materials and unexpected changes in process stream pH behavior upon ion release after capture.