Recovery of lithium by ion-exchange in zeolitic materials

More than 70% of the global lithium resources are not solid minerals but dissolved salts within continental brines or geothermal waters. Critical issues in the exploitation of such deposit include low Li concentrations and high level of impurities that need to be discarded. One of the most important methods for Li acquisition from brines is ion-exchange. In this perspective, the use of zeolitic materials as ion-exchangers in lithium extractions can potentially represent a fast and cheap alternative to traditional methods. In ion-exchange processes, the anionic charge of the host structure is compensated by Li+ cations. Because of the high charge density, the Li+ cations can interact relatively strongly with the host framework and therefore significantly distort it. We examined this effect at the atomic scale and highlight the structural distortion upon Li-exchange in vanadosilicate zeotypes. Using X-ray diffraction, we were able to precisely locate the Li cations within the framework and characterize the structure. Differences in the position and bond energy of the cationic sites strongly affected the extent and kinetics of the cation exchange. Thus, we observe Li+ exclusion at specific exchange sites. This appears to be directly linked to the coordination requirements of the Li-cations with the framework oxygen atoms. Our findings might contribute to a rational design and functionalization of zeolitic material to efficiently extract lithium from brines.