Kinetics,equilibrium and thermodynamic study on removal of Cr(VI)from aqueous solutions using low-cost adsorbent Alligator weed

摘要

The removal of Cr(VI)from aqueous solutions using Alligator weed,a freshwater macrophyte,was investigated as a function of initial pH,contact time,reaction temperature and adsorbent concentration in batch studies.An initial solution pH of 1.0 was most favorable for Cr(VI)removal.The kinetic experimental data fitted the pseudo-second-order equation,Elovich equation and Langmuir-Hinshelwood equation very well.The adsorption of Cr(VI)onto Alligator weed conformed to the linear forms of the Langmuir,Freundlich and Temkin equations.The removal efficiencies increased with the increased adsorbent dose from 1 to 8 g/L and were 86.6,97.6 and 99.7% at the adsorbent dose of 8 g/L,solution pH 1.0 and temperatures of 30,40 and 50 °C,respectively.Thermodynamic parameters(activation enthalpy change,activation entropy change and activation free energy change)revealed that the adsorption of Cr(VI)onto Alligator weed is endothermic,non-spontaneous,with a decreased randomness in nature.