Optimization and modeling of adsorption of Congo Red and Rhodamine B dyes onto Carpobrotus edulis plant

This paper deals with the valorization of the native Carpobrotus edulis plant (C. edulis) as a bioadsorbent for the removal of toxic dyes such as Rhodamine B (RB) and Congo Red (CR). This plant was further characterized by BET, SEM, EDX, and FT-IR methods. The colorants were applied in a batch adsorption experiment that included measurements of adsorbent ratio, ionic strength, contact time, initial concentration, pH, and temperature. It was observed that for 100 mg/L initial dye concentration, 0.2 g of C. edulis showed maximum adsorption efficiency for RB (> 75%), while 0.4 g for CR (> 70%). For both dyes on the biomaterial tested, ionic strength and pH have no significant impact on the adsorption. Adsorption fits a pseudo-second order kinetic model and Langmuir isotherm. The optimum adsorbed amount of C. edulis was indicated at 56.18 and 19.84 mg/g for RB and CR, respectively. The results of the thermodynamic study show that the adsorption process of the dyes by the biomaterial is spontaneous and exothermic with a decrease in the randomness of the adsorption process. The results of the regeneration indicate that the bioadsorbent was efficiently recycled with 55.80% and 36.26% uptake for RB and CR dyes, respectively, after 3rd cycles of desorption-adsorption. Operational factors were studied using Taguchi's experimental design. Our experimental results confirm the importance of the influence of initial concentration, adsorbent ratio, and contact time on adsorption with maximum adsorption of RB and CR was found to be 76.06% and 68.18% dye, respectively.