Advances of materials for ion-selective membranes for extraction of Lithium ions out of saline water

Lithium plays a vital role not only in products used in daily life but also as an indispensable element for storage of acyclic occurring energy resources which is the case for a big part of renewable energies. Conventional primary resource extraction methods posing tremendous burdens on the environment and no industrially used process for lithium ions from secondary resources lead to a need for a both, economically and ecologically, sustainable method of Lithium extraction. Membrane processes playing a huge role for ion exchange in every living cell, could be the key to an environmentally friendly and cost-saving lithium extraction method from primary and secondary resources. This work represents different approaches regarding the material of membranes and focuses on metal organic frameworks (MOF) which have extremely ordered pores with a small pore size distribution. Additionally, those pores can be tuned and therefore represent a highly interesting material for a lithium-ion selective membrane. In this research, a layer of ZIF-8 was built on commercial membrane NF90 support by an easy fabrication method followed by a layer of ZIF-L. This results in an asymmetric pore structure which is crucial for enhancement of separation properties. Selectivity ratios of 1.52 and 1.09 were obtained for K+/Li+ and Na+/Li+, respectively. This work thus gives insight into the performance of different membrane materials for lithium-ion extraction out of saline water.