The increased global demand for lithium is rapidly depleting the lithium ore reserves. Therefore, attention has turned to the recovery of lithium from aqueous solutions, such as lithium-containing brine. Compared with other methods of lithium recovery, adsorption is energy efficient and simple to implement, increasing demand for selective lithium adsorbents. In this study, a selective lithium-ion adsorbent, H4Ti5– xLa xO12, was synthesized via the sol–gel method, followed by heat treatment and acid washing. The effects of the temperature and degree of lanthanum doping ( x) on the crystalline phase, morphology, lithium-ion adsorption capacity, and lithium-ion selectivity of the ion sieve were investigated, and the optimal synthetic conditions were determined. We found that doping with La3+ cations ( x = 0.01) increased the lithium-ion adsorption capacity (23.96 mg g−1 at 25 °C at pH = 12; 8.2% higher than before doping), rate, and selectivity. In addition, the ion sieve could be used over multiple adsorption–desorption cycles with only a minor reduction in the lithium-ion adsorption capacity (22.88 mg g−1). Overall, these results suggest that doping with La3+ cations stabilized the H4Ti5– xLa xO12 crystal structure, alleviated particle agglomeration, expanded the lithium-ion channels, and decreased the resistance to lithium-ion migration, thus improving adsorption performance. The findings suggest that the proposed ion sieve has practical applications in the selective recovery of lithium from aqueous solutions containing a mixture of metal ions.

Removal of Cu2+ ions from contaminated water is an important but challenging task. This study reports the synthesis of a composite hydrogel from two natural polysaccharides, namely, sodium alginate and chitosan, using inexpensive kaolin as a raw material and polyacrylamide as a modifier. The hydrogel had a high adsorption capacity and selectivity for Cu2+. The composite hydrogel was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The pseudo-second-order kinetic model was the most suitable model for the kinetic results, and the Langmuir isotherm model was the most representative of the sorption system. The results revealed that the adsorption process was mainly controlled by chemisorption. The maximum adsorption capacity of the adsorbent was 106.4 mg·g−1. Therefore, this study presents a new perspective on the application of composite hydrogels as Cu2+ adsorbents.