The transition to sustainable energy systems demands efficient recycling methods for critical raw materials like lithium. In this study, we present a new class of pH- and light-switchable flotation collectors based on isomeric derivatives of the natural product Punicine, termed inverse Punicines. These amphoteric molecules were synthesized via a straightforward four-step route and structurally tuned for hydrophobization by alkylation. Their performance as collectors was evaluated in microflotation experiments of lithium aluminate (LiAlO₂) and silicate matrix minerals such as melilite and calcium silicate. Characterization techniques including ultraviolet-visible (UV-Vis), nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy as well as contact angle, zeta potential (ζ potential) and microflotation experiments revealed strong pH- and structure-dependent interactions with mineral surfaces. Notably, N-alkylated inverse Punicine derivatives showed high flotation yields for LiAlO₂ at pH of 11, with a derivative possessing a dodecyl group attached to the nitrogen as collector achieving up to 86% recovery (collector conc. 0.06 mmol/L). Preliminary separation tests showed Li upgrading from 5.27% to 6.95%. Radical formation and light-response behavior were confirmed by ESR and flotation tests under different illumination conditions. These results demonstrate the potential of inverse Punicines as tunable, sustainable flotation reagents for advanced lithium recycling from complex slag systems.

The pyridinium phenolate punicine is a switchable molecule from Punica granatum. Depending on the pH, punicine exists as a cation, neutral molecule, anion, or dianion. In addition, punicine reacts to light, under the influence of which it forms radical species. We report on three punicine derivatives that possess an adamantyl, 2-methylnonyl, or heptadecyl substituent and on their performance in the flotation of lithium aluminate, an engineered artificial mineral (EnAM) for the recycling of lithium, e.g., from lithium-ion batteries. By optimizing the parameters: pH and light conditions (daylight, darkness), recovery rates of 92% of LiAlO₂ are achieved. In all cases, the flotation of the gangue material gehlenite (Ca₂Al[AlSiO₇]) is suppressed. IR, the contact angle, zeta potential measurements, TG-MS, and PXRD confirm that the punicines interact with the surface of LiAlO₂, which is covered by LiAl₂(OH)₇ after contact to water, resulting in a hydrophobization of the particle. The plasma pretreatment of the lithium aluminate has a significant influence on the flotation results and increases the recovery rates of lithium aluminate in blank tests by 58%. The oxidative plasma leads to a partial dehydratisation of the LiAl₂(OH)₇ and thus to a hydrophobization of the particles, while a reductive plasma causes a more hydrophilic particle surface.