Preparation of micron-sized alginate-based particles for rare earth adsorption

In this brief report, omitting the step of dissolving sodium alginate with water, directly mixing sodium alginate powder with calcium chloride powder sufficiently, and gelatinizing sodium alginate by the impregnation method improve the characteristics of sodium alginate gel which is in the form of jelly and has poor mechanical properties. In this paper, micron-sized gel particles were prepared by slow impregnation method using mixed powder of sodium alginate and calcium chloride. The preparation method is simple and low-cost, and can be used for the recovery of rare earth ions from aqueous solutions. The SAG-2 gel prepared at a mass ratio of sodium alginate to calcium chloride of 1:1 showed the best adsorption performance; the particle size varies from 50 to 200 µm. The adsorption capacities of SAG-2 for La(III), Ce(III), Pr(III), and Nd(III) were 334.1, 349.8, 360.1, and 364.5 mg g⁻¹ at pH = 5. The adsorption equilibrium was reached in 35 min. The kinetic study showed that the adsorption process was chemisorption and the adsorption isotherm was well fitted with the Freundlich model. The adsorption mechanism was explored using FTIR and XPS characterization, indicating that both -OH and -COOH functional groups were involved in adsorption. The desorption of rare earths by different eluents was explored and the recyclability of the adsorbent was examined.