Biosorption of Lead (II) and cadmium (II) ions from aqueous solution by buckwheat (Fagopyrum Esculentum) hulls biosorbent: kinetic, equilibrium and thermodynamic studies

In this study buckwheat hull was used as an efficient, cheap and environmentally safe for the removal of Pb(II) and Cd(II) from an aqueous solution through optimizing various experimental parameters such as temperature (25–50 °C), solution pH (2–6 for Pb(II) and 2–7 for Cd(II)), amount of buckwheat hulls (0.1–0.35 g), initial Pb(II) and Cd(II) concentration (5–400 mg L −1 ) and contact time (30–1440 min). SEM, FTIR, EDX, and pH pzc measurements were used to analyze buckwheat hulls before and after biosorption. Kinetic data fitted best to the pseudo-second-order model due to higher values of R 2 (R 2 Pb(II) = 0.999 and R 2 Cd(II) = 0.999). Equilibrium data matched the Langmuir model, yielding sorption capacities of 87.72 mg·g −1 for Pb(II) and 23.2 mg·g −1 for Cd(II), indicating monolayer adsorption. Analysis of thermodynamic parameters, revealed the non-spontaneous and exothermic characteristics of the removal of Pb(II) and Cd(II) by buckwheat hulls.