Abstract
The adsorption kinetics of natural commercial bentonite (NB) with respect to Cu (II) has been studied in order to consider its application to purify metal finishing wastewaters. The batch method has been employed, using metal concentrations in solution ranging from 40 to 2000 mg/l. We have investigated how solution pH, temperature, adsorbent amount, contact time, washing and calcinations of bentonite (the calcinations of bentonite at 700 C and washed bentonite termed by CB and WB, respectively) affect this process. Results of kinetic experiments showed that Cu (II) adsorption rate was fast, and more than 90% of Cu adsorption occurred within 5 min. Among the kinetic models tested, the adsorption kinetics was best described by the pseudo-second-order equation. The adsorption capacity of Cu (II) ions on NB has increased with increasing pH, adsorbent amount and temperature. The Langmuir adsorption isotherm properly describes the equilibrium adsorption and the maximum adsorption capacities of NB towards Cu (II) were determined to be 24.5, 35.5 and 39.3 mg/g at 293, 313, and 333 K, respectively. Values of Gibbs free Energy (Delta G degrees) ranging from -17.2, -18.56, and -19.9 kJ/mol suggest that the adsorption process is spontaneous and mainly governed by specific surface interaction mechanism. The values of standard enthalpy (Delta H degrees) and entropy (Delta S degrees) were 2.494 kJ/mol and 67.29 J/ (mol K), respectively. The adsorption capacity of washed bentonite sample (WB) was significantly higher than that of Natural bentonite sample (NB) and calcined bentonite sample (CB). Results of this study can be useful for future up-scaling in using this material as a low-cost adsorbent for the removal of Cu (II) from industrial wastewater.