Comparative study on Pb(II), Cu(II), and Co(II) ions adsorption from aqueous solutions by arborvitae leaves

In this study, the pretreatment feasibility of fallen leaves for the removal of heavy metals in aquatic environments was evaluated. The arborvitae leaves were selected as representative and characterized by Brunauer-Emmett-Teller (BET) and FT-IR. BET analysis showed that the surface area of arborvitae leaves was 29.52m(2)/g with the pore diameter ranging from 2 to 50nm. Absorption bands in FT-IR were assigned to C-H, O-H, C-O, and C=O groups, which were the main sites for heavy metals adsorption. With the arborvitae leaves as a natural adsorbent, the removal of Pb(II), Cu(II), and Co(II) ions in the single and ternary component systems was studied by means of batch adsorption experiment. The results indicated that the adsorption amounts by arborvitae leaves increased sharply from 1.12 to 8.76mg/g for Pb(II), 0.49 to 3.87mg/g for Cu(II), and 0.44 to 2.28 for Co(II), respectively, with pH increasing from 1.79 to 4.26. The adsorption equilibrium was attained within 120min, and the adsorption affinity order of the three heavy metals was Pb>Cu>Co in both of the single and ternary systems. All equilibrium data of Pb(II), Cu(II), and Co(II) ions obtained fit perfectly with Langmuir isotherm model compared with Freundlich isotherm model. Compared with the results in the single system, the adsorption capacity of Pb(II), Cu(II), and Co(II) ions on arborvitae leaves decreased from 35.84 to 9.32mg/g, 7.94 to 3.07mg/g, and 6.78 to 1.54mg/g in the ternary systems, respectively. For the Dubinin-Kaganer-Radushkevich isotherm model, the sorption energy E-values for Pb(II), Cu(II), and Co(II) ions on arborvitae leaves were all below 8kJ/mol in the single and ternary metal solution systems, indicating that the adsorption mechanism could be explained as the physical adsorption.