Calcined mussel shells as a new and eco-friendly biosorbent to remove textile dyes from aqueous solutions

• Calcined Mussels shells considered as new and eco-friendly biosorbent to remove dyes.
• Biosorption kinetics of Rhodamine B, Alizarin Red S and Orange II in a batch system was found to conform to pseudo-second order model.
• The biosorption equilibrium was well described by the Langmuir isotherm model.
• Thermodynamic studies indicated that biosorption process was spontaneous, endothermic for Alizarin Red S and Orange and physical reaction.
• Thermodynamic studies indicated that biosorption process was spontaneous, exothermic for Rhodamine B and chemical reaction.

Batch biosorption experiments were carried out for the removal of Rhodamine B, Alizarin Red S and Orange II as textile dyes from aqueous solutions by using the calcined mussel shells as a potential biosorbent. The effects of solution pH, biosorbent amount, dye concentration, temperature and contact time on the biosorption of the three dyes studied were investigated. The experimental results showed that maximum pH was about 9 for efficient biosorption of Rhodamine B and comprised between 4 and 6 for Alizarin Red S and Orange II. The equilibrium was attained for all dyes in 60 min. The biosorption of Rhodamine B was exothermic in nature (ΔH° = 25.65 kJ/mol), while the positive value of entropy 97.67 J/mol K indicated that the increasing randomness at the solid/liquid interface. The biosorption was endothermic (ΔH° = −13.67 kJ/mol and ΔH° = −18.87 kJ/mol) for Alizarin Red S and Orange II respectively. The negative values of entropy are −58.73 J/mol K and −47.77 J/mol K for Alizarin Red S and Orange II respectively suggesting that the biosorption onto CMS occur by a decreasing randomness at the solid/liquid interface. The experimental isotherm data were analyzed using Langmuir and Freundlich isotherm equations. The best fit was obtained by Langmuir model with maximum monolayer biosorption capacity of 45.67 mg/g for Rhodamine B, 39.65 mg/g for Alizarin Red S and 41.75 mg/g for Orange II. Biosorption kinetic data were properly fitted with the pseudo second order kinetic model.