Competitive adsorption of Congo red by sawdust in the presence of reactive black 5 and the effect of ionic strength

ABSTRACT Industrial revolution has led to the release of contaminants into water bodies, with multiple pollutants often co-existing. This study investigates the competitive adsorption of Congo red and Reactive black 5 considering initial dye concentration, time, adsorbent dosage, solution pH and temperature. Furthermore, the effect of ionic strength (NaCl, BaCl2, Na2SO4, and CuSO4) on Congo red adsorption was also examined. The adsorbent was characterized using Fourier Transform Infrared Spectroscopy, Scanning Electron Microscope, and pH-point of zero charge. Result indicated that increasing initial dye concentration decreased the percentage removal of Congo red in both single and binary system, with the removal rate being lower in the binary system, suggesting competitive adsorption. Increasing adsorbent dosage and temperature led to increased percentage removal. The optimum pH of the adsorption process was noted at pH 5. BaCl2 and CuSO4 exhibited the most significant enhancing influence on Congo red adsorption. Equilibrium data was modelled using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models revealing a maximum monolayer adsorption capacity of 27.29 mg/g in the single system which reduces to 21.48 mg/g in the binary system indicating antagonistic effect of Reactive black 5 on Congo red adsorption. Thermodynamic studies revealed that the adsorption process was endothermic and spontaneous at higher temperature.