Equilibrium and Kinetic Modeling of Pb(II) Biosorption by a Chemically Modified Orange Peel Containing Cyanex 272

Abstract

In this paper, a new kind of biosorbent containing the extractant Cyanex 272 was prepared by the method of solid−liquid grinding and found to be efficient in removing Pb(II) from aqueous solution. Orange peel (OP) biosorbents were characterized by SEM, FTIR, BET, and elemental analysis, which confirmed that carboxylic groups were introduced into the orange peel by chemical modification [citric acid (CO), saponification and citric acid (SCO)] and that Cyanex 272 was successfully immobilized on the orange peel (272OP, 272CO, and 272SCO). In addition, Cyanex 272 played an important role in the adsorption process, i.e., the maximum adsorption capacity (obtained from the Langmuir−Freundlich model) was improved, with the order of the adsorption capacities being 272SCO (1.30 mol·kg−1) > SCO (1.26 mol·kg−1) > 272CO (1.20 mol·kg−1) > 272OP (1.02 mol·kg−1) > CO (0.62 mol·kg−1), and the equilibrium time was shortened from 60 to 40 min for 272SCO. It was obvious that adsorption of Pb(II) strongly depends on pH, with the optimum pH range being 5.0−5.8 for all adsorbents, and the removal rate of Pb(II) by 272SCO could be as high as 100 %. The optimum solid/liquid ratio was 3.7 g·L−1 for an initial Pb(II) concentration of 0.002 mol·L−1. The kinetic equilibria could be explained as pseudo-second-order kinetic processes. The optimum desorption agent was found to be 0.1 mol·L−1 HCl. The adsorption capacity of 272SCO declined slightly after being recycled six times. After the sixth cycle, the adsorption rate of Pb(II) onto 272SCO was still 89.61 %.