Fabrication of alendronate doped sodium alginate composite hydrogel for enhanced adsorption of rare earth elements from wastewater

The rising demand for rare earth elements (REEs) in agriculture and industry highlights the risk of environmental contamination due to their inherent toxicity and potential for ecological accumulation. In this work, a simple and cost-effective alendronate modified sodium alginate composite hydrogel (SA@ANDS) was designed and successfully fabricated. Using the adsorption of REEs La (III) as a scenario, several parameters including pH, adsorbent dosage, time, initial concentration and temperature were systematically examined. Furthermore, isothermal adsorption was adopted to analyze the adsorption mechanism. The results revealed that the adsorption capacity of the adsorbent was 163.93 mg g⁻¹. Moreover, the density functional theory calculations revealed an adsorption energy of −9.54 eV, indicating SA@ANDS has a good affinity for La (III). Additionally, the SA@ANDS composite hydrogel showed good adsorption capacities of 169.49, 175.43 and 178. 57 mg g⁻¹ for Ce (III), Pr (III) and Sm (III), respectively. The comparative adsorption performance results demonstrated the SA@ANDS composite hydrogel exhibited a stronger binding affinity for La (III) compared to Al (III), Mg (II), Co (II), and Cd (II). The SA@ANDS composite hydrogel showed good recyclability for La (III) of 82.73 % after 5 cycles and was successfully applied for the extraction of La (III) from industrial wastewater.