Investigation of the sorption mechanisms of metal-complexed dye onto Posidonia oceanica (L.) fibres through kinetic modelling analysis

This research deals with the exploitation of highly available and renewable marine biomass, Posidonia oceanica (L.) fibres as low cost biosorbent for the removal of metal-complexed textile dyestuff from aqueous medium, and the investigation of the probably involved physiochemical mechanisms. Experiments were carried out in batch reactor. Firstly, the adsorption process was studied as a function of initial solution pH and contact time under different initial dye concentration. The results showed that the highest dye adsorption capacity was found at pH 2 under a constant temperature of 30 °C, and the equilibrium state was reached within 48 h of exposure time. Secondly, several adsorption kinetic models were applied to fit the experimental data, namely Lagergren irreversible first-order, Reversible first-order, Pseudo-second-order, Elovich, Ritchie and intraparticle diffusion models. The proposed explanations were deduced from the theoretical assumptions behind the most appropriate model(s), which could satisfactorily describe the present biosorption phenomenon. The interpretation of the related results have shown that, with R² of about 99%, the pseudo-second order model is the most suitable dynamic theory describing the biosorption of metal complex dye onto P. oceanica fibres, predicting therefore a chemisorption process.