Competitive Adsorption of Methylene Blue and Cu2+ onto Citric Acid Modified Pine Sawdust

Abstract

Pine sawdust modified with citric acid (CA‐PS) is used as an adsorbent for the removal of Cu2+ and methylene blue (MB) from the single and binary compound systems. The initial pH has a significant effect on Cu2+ adsorption, but a relatively little effect on MB adsorption. The kinetic and isotherm studies indicate that the pseudo‐second‐order model and the generalized model provide the best correlation of the experimental data in the single systems as well as in the binary systems. The adsorption capacities of CA‐PS from Generalized isotherm model are 0.23 mmol/g for Cu2+ and 0.25 mmol/g for MB, which are higher than that of B‐PS. In the binary systems, Cu2+ and MB exhibit competitive adsorption behaviors. The adsorption capacity of Cu2+ or MB is considerably reduced with an increase in the concentration of the other, and Cu2+ exhibits better competiveness than MB. However, the total adsorption capacity is higher compared with that in the single systems, which increases with an increase in the initial concentration of Cu2+ or MB and reaches a plateau value of 0.301 mmol/g.