Eco-Friendly Removal of Cationic and Anionic Textile Dyes Using a Low-Cost Natural Tunisian Chert: A Promising Solution for Wastewater Treatment

The discharge of synthetic dyes into aquatic ecosystems stands as a pointed environmental concern, with serious consequences affecting not only biodiversity and water quality but also human health. To address this challenge, this study introduces a natural Tunisian chert, a silica-rich sedimentary rock, as a promising, sustainable, and low-cost adsorbent for treating textile dye-polluted wastewater. For the first time, the adsorption capabilities of a Tunisian chert were systematically evaluated for both cationic (Methylene Blue; MB and Cationic Yellow 28; CY28) and anionic dyes (Eriochrome Black T; EBT). To assess the impacts of key operational parameters, such as pH (2–12), contact time (0–240 min), adsorbent dosage (0.02–0.25 g), and initial dye concentration (50–500 mg/L), batch mode adsorption trials were performed. The Langmuir isotherm model most accurately fits the adsorption data, yielding a maximum adsorption capacity of 138.88 mg/g for MB, 69.93 mg/g for CY28, and 119.04 mg/g for EBT, outperforming multiple conventional adsorbents. Kinetic modeling revealed that adsorption adhered to a pseudo-second-order model, with rapid equilibrium within 45–60 min, highlighting the efficiency of the Tunisian chert. Optimal dye removal was obtained at pH = 8 for cationic dyes and pH = 4 for EBT, driven by electrostatic interactions and surface charge dynamics. The current research work reveals that Tunisian chert is a low-cost and efficient adsorbent with a high potential serving for large-scale industrial applications in wastewater treatment. Using a locally abundant natural resource, this work provides a maintainable and economical approach for dye removal from polluted wastewater.