The biosorption of Acid Red 337 and Acid Blue 324 on Enteromorpha prolifera: The application of nonlinear regression analysis to dye biosorption

The biosorption of Acid Red 337 and Acid Blue 324 from aqueous solution on Enteromorpha prolifera was investigated in a batch system. Optimum initial pH and temperature values for AB 324 and AR 337 dyes were found as 3.0 and 2.0, 25 and 30 °C, respectively and the optimum dye uptake amounts per unit mass were obtained at 0.5 g/l biosorbent concentration for both dyes. The Langmuir, Freundlich and Redlich-Peterson adsorption models were applied to experimental equilibrium data and the isotherm constants were calculated using Polymath 4.1 software. The monolayer covarage capacities of E. prolifera for AB 324 and AR 337 were obtained as 160.6 and 210.9 mg/g, respectively. It was observed that the biosorption data fitted well to Redlich-Peterson model than the other models. The external diffusion and intraparticle diffusion models were also applied to biosorption data of AR 337 and AB 324 and it was found that both the surface adsorption as well as intraparticle diffusion contribute to the actual adsorption process. The constants obtained from the pseudo-second order kinetic model at different temperatures were evaluated and the activation energies for the biosorption of AB 324 and AR 337 were found to be −31.5 and −19.87 kJ/mol, respectively. Thermodynamic parameters such as enthalpy, entropy and Gibb's free energy changes were also calculated and it was concluded that the biosorption of these acidic dyes on E. prolifera was exothermic in nature.