Al and Cr ions co-doped spinel manganese lithium ion-sieve with enhanced Li+ adsorption performance and structural stability

The Li1.6Mn1.6O4 driven lithium ion-sieve (LIS) is considered as a potential adsorbents for recovering Li+ ions from brines owing to their good theoretical adsorption performance and excellent adsorption selectivity. However, the poor cycle stability and the decrease of adsorption capacity resulting from the manganese dissolution loss limit its practical applications. In this work, to mitigate this issue, several novel Al and Cr co-doped manganese LISs were prepared by a facile hydrothermal synthesis method, followed by the acid treatment. The characterization results show that Al and Cr ions are uniformly doped into the spinel crystal structure of LIS, and the introduction of Al and Cr ions can cause the crystal shrinkage, decrease the Mn3+ content, and raise the mean valence of manganese in the co-doped samples, effectively improving their structural stability. Compared with un-doped ion-sieve H1.6Mn1.6O4, the optimal co-doped ion-sieve H1.6Mn1.54Al0.02Cr0.04O4 with 2% Al doping and 4% Cr doping possesses a higher lithium adsorption capacity, lower manganese dissolution loss, and stronger cyclic stability. Additionally, the H1.6Mn1.54Al0.02Cr0.04O4 possesses a high adsorption selectivity of Li + over Mg2+, Ca2+, K+ and Na+. Furthermore, the lithium adsorption is determined to be a chemical and monolayer adsorption process on the prepared LIS. The good lithium adsorption capacity and adsorption selectivity as well as the good recyclability make the prepared Al and Cr co-doped LIS a promising adsorbent for the efficient lithium recovery form brines.