Sodium alginate-crosslinked montmorillonite nanosheets hydrogel for efficient gallium recovery

An efficient adsorbent for Ga(III) recovery was developed by applying the geochemical principles of Ga mineralization, using Al-rich clay minerals with a natural affinity for Ga as the raw material. Sodium alginate (SA) facilitated the cross-linked assembly of montmorillonite nanosheets (MMTNS), forming a three-dimensional structured hydrogel. This was achieved through electrostatic interactions between -OH groups on the edges of MMTNS and -COO^- groups in SA, as well as the complexation of Ca²⁺ and -COO^- groups. The resulting hydrogel maintained a porous structure while preserving the layered arrangement of MMTNS, significantly enhancing the adsorption capacity for Ga(III). Thermodynamic analysis revealed that Ga(III) adsorption was both endothermic and spontaneous. The Elovich model indicated that heterogeneous chemisorption dominated the adsorption process. Ga(III) adsorption followed the Langmuir isotherm model, indicating that it was controlled by specific binding sites and occurred via uniform monolayer adsorption, with a maximum capacity of 85.95 mg/g. The adsorption mechanism involved ion exchange interactions, chelation of functional groups, and electrostatic interactions. After 4 cycles, the hydrogel retained an adsorption capacity of 65.4 mg/g. Additionally, the hydrogel demonstrated good selectivity for Ga(III) in a quaternary ion solution system. This hydrogel shows significant potential as a candidate for Ga(III) recovery.