Experimental and modeling studies for the simultaneous removal anionic dyes in single and binary systems using activated clay

The treatment of dyes and pigments represents a significant environmental challenge worldwide. This study investigates the adsorption of Bemacid Blue (BB) and Congo Red (CR) using hydrochloric acid-activated bentonite clay treated at an 8 N concentration (B-8 N), in both single and binary dye systems. The adsorbent material was characterized by thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The processes of adsorption, desorption, and regeneration were examined. In binary systems at 55 °C, the adsorption capacity for CR (247.72 mg g⁻¹) exceeded that for BB (152 mg g⁻¹). The pseudo-second-order kinetic model, the Extended Sips and Extended Langmuir isotherms most accurately characterized the adsorption behavior of dyes in the binary system. Desorption with NaOH resulted in the release of 83.82% of CR and 55.23% of BB. The adsorbent maintained high performance over three successive regeneration cycles. Thermodynamic analysis confirmed that the binary adsorption process is spontaneous. The proposed adsorption mechanism suggests that electrostatic attraction and hydrogen bonding are the main interactions between the two dyes and the modified bentonite surface. This study underscores the potential of activated clay as a sustainable and highly efficient adsorbent for the removal of anionic dyes from industrial wastewater.