Valorization of plant biomass by chemical pretreatment: Application to the removal of Rhodamine B and Congo Red dyes

Preparation, recovery, and regeneration of low-cost bioadsorbents are recognized as a sustainable solution for wastewater treatment. In this study, low-cost byproducts from Carpobrutus edulis plant were used as bioadsorbents for industrial dyes, Rhodamine B, and Congo Red from aqueous solutions. The adsorbents were obtained after chemical treatment of the plant by HCl (HMCE) and NaOH solutions (NMCE) and characterized by S-S, SEM, EDX, FT-IR, pH(Z), COD, and BOD5. The effect of adsorbent doses, contact time, solution pH, initial concentration, ionic strength, and temperature parameters, on adsorption efficiency, was studied. The results show that more than 70% of the organic matter (COD and BOD5) released into the aqueous solution by the biomaterial was reduced after chemical treatment. The kinetic data revealed that the adsorption of two dyes onto the bioadsorbents follows the pseudo-second-order model, and the equilibrium data correlated well with the Langmuir isotherm. The maximum adsorption capacities of RB and CR onto HMCE were 90.9 and 27.3 mg/g, while onto NMCE; it was 103.1 and 31.15 mg/g, respectively. The thermodynamic study indicates that, for both dyes, the adsorption process onto bioadsorbents was endothermic and spontaneous. The biomaterial could be used up to five adsorption-desorption cycles.