Sorption dynamic investigation of chromium(VI) onto Posidonia oceanica fibres: Kinetic modelling using new generalized fractal equation

Abstract

This research deals with the utilization of highly available and renewable marine biomass, Posidonia oceanica (L.) fibres as low cost biosorbent for the removal of toxic hexavalent chromium from aqueous solutions and the investigation of the probably involved physiochemical mechanisms in such sorption system throughout a kinetic modelling study. Experiments were carried out in batch reactor. Firstly, the adsorption process was studied as a function of contact time under different initial chromium concentration and initial solution pH. The highest Cr(VI) adsorption capacity determined within the equilibrium time (3 h) was found at pH 2, under a constant temperature of 30 °C. Secondly, several adsorption kinetic models were applied to fit the experimental data, namely Lagergren irreversible first-order, reversible first-order, pseudo-second-order, Elovich and Brouers–Sotolongo models using both the linear and nonlinear regression analyses. 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, although some error estimation ambiguities, that the Brouers–Sotolongo “BS” model is the most suitable dynamic theory describing the biosorption of hexavalent chromium onto P. oceanica fibres, predicting therefore a chemisorption process and providing the time necessary to adsorbed half the maximum quantity ( τ 1/2), a convenient tool to measure the speed of the reaction.