Electrochemical behaviors of porous spherical spinel H1.6Mn1.6O4 with high Li+ adsorption capacity

A self-assembled spherical H1.6Mn1.6O4 adsorbent with surface porous and internal hollow structure was successfully synthesized. Due to the special surface porous and internal hollow structure, the adsorbent exposes channels and interfaces for ions migration and ad/desorption, and also provides sites for charge transfer. At an initial Li+ concentration of 400 mg/L, the spherical adsorbent adsorption capacity of lithium can efficiently reach an extreme 47.54 mg/g in 360 min (the traditional adsorption route is 44.36 mg/g at 2880 min) without alkaline assistance by applying the electrochemical adsorption technique. In the multiple MCl (M = Li, Na, K, Rb, Cs) solution with each metal ion molar concentration of 14.41 mmol/L, the adsorbent adsorption capacity keeps 89.71% of a single LiCl solution. After the 5th cycle, the adsorption capacity to lithium remains at 94.98% (the traditional adsorption route is 86.65%) of the initial adsorption value. According to the analysis of cyclic voltammetry (CV) curves, it is found that the key kinetic factor limiting the adsorption rate is that the ions migration rate cannot catch up with the electrons transfer rate during the adsorption process. Furthermore, the electric field self-promotes the pH of the solution, and the corresponding alkaline environment is favorable for the adsorption behaviors. In the actual salt lakes brine, the 1st electrochemical adsorption capacity of the adsorbent for lithium is 3.26 mmol/g (Salt lake B), and the 5th adsorption capacity is 83.74% of the 1st adsorption value.