A straightforward procedure was developed for the synthesis of surface-modified organicinorganic hybrid adsorbent materials derived from alginate. Sphere-shaped particles were produced by gravitational droplet coagulation and chemically modified by soaking in a solution of the silica precursor tetramethyl orthosilicate (TMOS) and the functionalized organosilane (3-mercaptopropyl) trimethoxysilane (MPTMS). Upon oxidation of the thiol groups by hydrogen peroxide, sulfonic acid groups were obtained, homogeneously distributed over the hybrid polymer matrix. Three different particle sizes (2.2, 2.8, and 3.5 mm in diameter) were made to evaluate differences in material properties and the corresponding adsorption behavior. The alginatesulfonatesilica (ASS) particles were characterized by Raman spectroscopy, optical microscopy, and scanning electron microscopy. The specific surface area, porosity, mechanical strength, and chemical composition were determined. Subsequently, the functionalized materials were examined for the recovery of indium from secondary resources. Adsorption of indium(III) was first investigated in batch mode from single-element solutions to evaluate adsorption parameters such as kinetics and adsorption capacity and from a binary metal solution of gallium(III) and indium(III) and a simulated leachate of a zinc refinery residue to investigate the selectivity. The adsorbent particles showed a high adsorption capacity and selectivity for indium(III). They showed hardly any affinity for the major elements in the leachate, such as cadmium(II) and zinc(II). By using the multifunctional spheres as the stationary phase in a gravitationally eluted chromatography column, it was shown that the valuable minor elements, indium(III) and gallium(III), could be separated from the major elements present in the feed solution.