Influence of surfactants on selective mechanical separation of fine active materials used in high temperature electrolyzers contributing to circular economy†

Abstract

As one of the promising hydrogen production technologies, the development of water electrolysis systems including recycling of their functional components is actively investigated. However, the focus lies on energy and chemical intensive metallurgical operations and less on mechanical separation processes in most studies. Here, an innovative surfactant-based separation process (using CTAB and SDS) is investigated to contribute to developing a selective physical separation process for ultrafine particles used in high temperature water electrolyzers (composed of NiO, LSM, ZrO₂, and YSZ). Their different surface charge in alkaline solutions influences the adsorption of surfactants on particle surfaces as well as the modification of particulate wettability, which is a key separation feature. Through the observations of changes in surface charge and wetting behavior in the presence of surfactants, a feasibility of liquid–liquid particle separation (LLPS) is evaluated. The performance of LLPS with model particle mixtures shows the potential of selective separation with recovery of NiO in the organic phase, while the rest of the particles remain in the aqueous phase. Perovskite LSM is not considered in this system because it shows a high possibility of being recovered by magnetic separation. The proposed process can be further optimized by increasing the phase separation stages, and further research is needed on the NiO phase, which showed exceptional behavior in the presence of the surfactants.

Keywords: Fine particle separation; Solid oxide electrolyzer; Recycling; Particle surface modification.