Adsorption of Cu(II), Ni(II), Pb(II) and Cd(II) from Ternary Mixtures: Modelling Competitive Breakthrough Curves and Assessment of Sensitivity

This study describes the competitive sorption of Cu(II), Ni(II), Pb(II) and Cd(II) onto grape stalks wastes (GS) in ternary mixtures in a continuous bed up-flow system. The characteristic breakthrough profile was observed for just one of the metals while the other two suffered overshoots. The elution profile showed that (i) lead is not overshot in any mixture, (ii) copper overshoots when lead occurs in the ternary mixture, and (iii) cadmium and nickel exhibit intense overshoots when either lead or copper are present. A kinetic model based on the Homogeneous Surface Diffusion Model (HSDM) was developed to describe the sorption profile of each metal in the mixtures. To simulate the breakthrough curves, the Extended Langmuir Model (MEL) has been incorporated into the HSDM to describe the equilibrium. The values of the Langmuir affinity constant, b, were found to follow the next ranking: Pb (54.5 +/- 0.2) >> Cu (15.2 +/- 0.3) >> Cd (9.4 +/- 0.1) > Ni (8.1 +/- 0.2). These constants successfully explain the competence that leads to the observed overshoots in the mixtures. The model successfully fits metal sorption kinetics and elution profile in the mixtures. A study of the model sensitivity was carried out to know how the uncertainty in the experimental data and the model parameters affect the uncertainty in the output of the model. This analysis highlighted the relevance of good estimation of K (max) , b and eta besides the need of gathering high quality experimental data for an accurate determination of the model parameters.