Al and F ions co-modified Li1.6Mn1.6O4 with obviously enhanced Li+ adsorption performances

Abstract

A surge of interest has been attracted by Li1.6Mn1.6O4-type adsorbent for collecting lithium resources from salt-lake brines due to its excellent selectivity, high theorical adsorption capacity up to 72. 3 mg g−1 and low cost. However, its large-scale practical application is limited because of its bone element Mn dissolution during the cycled desorption process. Herein, F and Al co-modifying technique, an efficient method for stabilizing its spinel structure or forming protective coating, was employed to improve the application performances of Li1.6Mn1.6O4-type adsorbent prepared by sol–gel method. Based on the various characterization results, the co-modification not only leads to the formation of fluoride-rich coating and the substitution of Mn3+ by Al3+, but also generates the active adsorbents with abundant nano-islands. DFT calculations revealed that the coating layer is indeed AlF3 rather than LiF. In addition, in-situ high-temperature XRD tests demonstrates that the co-modification can significantly enhance the heat resistance and structural stability of the material. As-prepared adsorbent exhibits greatly improved Li adsorption capacity (increased from 28.5 to 33.7 mg g−1), lower Mn loss rate (decreased from 2.1 to 1.8%), enhanced cycling stability and good adsorption selectivity in the Qarhan brine containing Na+, K+, Ca2+, Mg2+, which is very significant and important for effectively removing lithium from low-grade brines.