<p>Effective separation and recovery of rare earth elements from industrial wastewater using eco-friendly adsorbents has been highly emphasized. A three-dimensional magnetic alginate biogel composite (Ca-SA@Fe₃O₄) was synthesized in the study, and its morphological structure and physicochemical characteristics were analyzed by multiple techniques. Critical preparing and adsorbing requirements, adsorption capacity, mechanism, and reusability of Ca-SA@Fe₃O₄ composite for La(III) ions from water were systematically investigated by serial experiments. The results show that the approximately 1.3-mm-diameter Ca-SA@Fe₃O₄ gel beads have a peculiar fully folded surface structure with many pores, good stability, and a sensitive magnetic response. La(III)-ion removal from water by the composite reachs 90.2% at pH 7.0, contact time of 20&#xa0;h, and 298&#xa0;K. The spontaneous adsorption kinetics and equilibrium data are conformed to the pseudo-second-order rate model and Langmuir isothermal model. The maximum adsorption capacity is up to 91.0&#xa0;mg/g at 298&#xa0;K. The ionic strength and commonly coexisting ions hardly interfere with the La(III) adsorption, apart from a minor influence of Ca²⁺ ions. Strong adsorption of La(III) ions by Ca-SA@Fe₃O₄ primarily involves complexation and micropore filling. Ca-SA@Fe₃O₄ macroparticles can be totally and fast recovered after adsorption by external magnetic field and regenerate with 0.05&#xa0;mol/L HCl and recycle at least four times. The remarkable adsorption efficiency, convenient separation, and environmental friendliness of Ca-SA@Fe₃O₄ composite make it a prospective biosorbent in recycling La(III) of La(III)-containing wastewater.</p>