Biosorption of Acid Dye in Single and Multidye Systems onto Sawdust of Locust Bean (Parkia biglobosa) Tree

Abstract

Properties of raw sawdust of Parkia biglobosa, as a biosorbent for the removal of Acid Blue 161 dye in single, binary, and ternary dye systems with Rhodamine B and Methylene Blue dyes in aqueous solution, were investigated. The sawdust was characterized using Scanning Electron Microscopy, Fourier Transform Infrared spectrophotometry, X-ray diffraction, and pH point of zero charge. Batch adsorption experiments were carried out to determine the equilibrium characteristics, thermodynamics, and kinetics of the sorption processes. The data obtained were subjected to various isotherm and kinetics equations. The results showed that the adsorption processes were described by different isotherm models depending on the composition of the system; they were all spontaneous (ΔG ranges from −0.72 to −5.36 kJ/mol) and endothermic (range of ΔH is 11.37–26.31 kJ/mol) and with increased randomness with ΔS values of 55.55 and 98.78 J·mol/K for single and ternary systems, respectively. Pseudo-second-order kinetics model gave better fit for all the sorption systems studied irrespective of the differences in composition, with the initial and overall rate constants higher for the mixtures than for the single system (6.76 g·mg−1min−1). The presence of Rhodamine B and Methylene Blue had a synergetic effect on the maximum monolayer capacity of the adsorbent for Acid Blue 161 dye.