Comparative Evaluation of Regeneration Strategies for Rhodamine B Removal Using Raw Date Seeds: Insights into...

Rapid industrial development has led to a substantial increase in the discharge of dyestuffs into the environment, leading to severe environmental contamination. Elevated concentrations of dyes in aquatic systems have raised significant concerns due to their toxicity, persistence, and adverse ecological effects, thereby motivating extensive research into effective wastewater treatment strategies. Among the various remediation techniques, adsorption has gained considerable attention as an efficient, cost-effective, reusable adsorbent and environmentally friendly method for dye removal from aqueous media. This study investigates the adsorption mechanism of Rhodamine B (RhB) onto raw date seed as a low-cost biosorbent, with particular emphasis on surface interactions, kinetic behavior, and regeneration performance. Equilibrium isotherm analysis revealed that RhB adsorption proceeds on a heterogeneous surface via a predominantly multilayer mechanism, with the Freundlich and Dubinin-Radushkevich models providing the most accurate representation of the experimental data. Kinetic results showed excellent agreement with the pseudo-second-order model, indicating that surface interactions govern the rate-limiting step. Zeta potential analysis showed that the adsorbent surface becomes increasingly negatively charged, indicating that electrostatic interactions are a major contributing factor in the adsorption process. Accordingly, maximum RhB removal efficiency was achieved under pH:3, 1.0-g adsorbent, 303.0 K, and with 30.0 min contact time. Regeneration, SEM, and FTIR analyses revealed that adsorption-desorption performance strongly depends on the regeneration strategy, with the fourth regeneration method, which combined NaOH treatment with high-temperature drying at 120 °C, most effectively preserving surface morphology and pore accessibility. Furthermore, the RhB removal efficiencies obtained using the fourth regeneration method were 96.3 and 88.1% in the first and fourth cycles, respectively. Overall, the findings establish raw date seed as an efficient, regenerable, and mechanistically well-defined biosorbent for RhB removal from aqueous systems.