Effects of dry processing on adsorption of uranium on Mg-Al layered double hydroxides and calcined layered double oxides

Mg-Al layered double hydroxides (LDH) (F-MgAl-LDHs and O-MgAl-LDHs) and Mg-Al layered double oxides (LDO) (F-MgAl-LDO and O-MgAl-LDO) nanosheets were prepared using a modified co-precipitation and oven/freeze dry route for adsorption of uranium. The freeze dry could evidently promote the adsorption ability. It’s resulted from larger specific surface (F-MgAl-LDO > F-MgAl-LDHs > O-MgAl-LDO > O-MgAl-LDHs) and pore size, as well as sufficient expose of vacant sites in the inner struture of F-MgAl-LDHs and F-MgAl-LDO. The pH, shaking time, initial uranium concentation and temperature influenced the adsorption capacity of F-MgAl-LDHs, O-MgAl-LDHs, F-MgAl-LDO and O-MgAl-LDO, while ionic strength exerted slightly little influence. Na2CO3 highlighted the best desorption effectivity, with desorption efficiency of 97.84% for F-MgAl-LDHs and 98.52% for F-MgAl-LDO, respectively. It is noteworthy that maximum adsorption capacity of F-MgAl-LDO reached 1099.93 mg/g, locating the top rank in the uranium-specific adsorbents. The adsorption conformed to the pseudo-second-order model, indicating chemical adsorption in nature. The thermodynamic was also investigated. The adsorption mechanism was determined that M-O and C-O bonds participated the complex process in the uranium adsorption. The study proposed the freeze dry as an efficient method to promote adsorbent performance.