Competitive Adsorption of Congo red in Single and Binary Systems Using a Low-cost Adsorbent

Background. Sawdust from Parkia biglobosa was prepared as an adsorbent for the adsorption of dye from aqueous solution. Objectives. The ability of sawdust to adsorb Congo red in a single dye system and binary dye system was examined. Methods. Effects of several variables (pH, contact time, initial dye concentration and adsorbent dose) were investigated and optimum conditions were established. The equilibrium data were subjected to kinetic and isotherm models. Results. Equilibrium time was observed at 600 mins while the optimum dose was 0.2 g and there was an increase in adsorption at low pH. The equilibrium data fitted the Freundlich isotherm model in both systems (coefficient correlation (R2) > 0.9). Harkin-Jura was the worst-fitted (R2 < 0.8). The qm in the single system (21.65) was lower than in BDS (27.17; 34.01). The values of 1/n show the heterogeneity on the surface of sawdust which reduced in the BDS. The increase in qm in the binary system showed that the presence of another dye (Reactive black 5) had a synergistic effect on the adsorption of Congo red. The kinetics of the process followed the pseudo-second-order model both in the single system and one of the binary systems. The dynamics of the process showed that the single system was nonspontaneous at low temperatures, endothermic and increased randomness on the surface of the adsorbent, while in the binary system, the process was exothermic and had little affinity for the adsorbent. Conclusions. Sawdust from Parkia biglobosa is a potential adsorbent for removing Congo red dye from aqueous solution in single and binary systems.