<p>This work reports the fabrication of innovative alginate/treated diatomaceous earth (Alg/DE) hybrid hydrogel beads designed for the simultaneous removal of cationic and anionic dyes from wastewater. The novelty of this study lies in the immobilization of acid-treated diatomaceous earth within Al³⁺-cross-linked alginate network to produce mechanically stable, reusable, and eco-friendly adsorbents capable of dual-dye adsorption. The prepared beads were thoroughly characterized by SEM-EDX, XRD, FTIR, TGA, and BET, and their swelling behavior and surface charge properties were systematically investigated. The results confirmed the successful incorporation and uniform dispersion of DE within the matrix through hydrogen bonding and physical entrapment, leading to enhanced structural integrity and thermal stability. Compared to pristine beads, Alg/DE composites particularly those containing 10 wt%-DE exhibited significantly improved adsorption capacities for methylene blue (MB; 50.76&#xa0;mg&#xa0;g⁻¹) and direct red 16 (DR16; 31.35&#xa0;mg&#xa0;g⁻¹). Adsorption kinetics followed a pseudo-second-order model, while equilibrium data were well described by the Langmuir isotherm, indicating monolayer adsorption on homogeneous surfaces. The adsorption of MB/DR16 was attributed to mechanisms such as ion exchange, electrostatic interactions, hydrogen bonding, pore filling, and π–electron interactions. The main advantages of the developed materials include their low cost, biodegradability, high adsorption efficiency, pH-dependent selectivity toward cationic/anionic dyes, and good reusability over multiple cycles. However, excessive DE loading was found to reduce swelling and adsorption performance due to increased cross-linking density and particle aggregation, which represents a limitation of the system. Overall, Alg/DE hybrid hydrogels demonstrate strong potential as sustainable and effective adsorbents for wastewater decontamination.</p> Graphical Abstract <p></p>