Investigation of the efficiency of bentonite nanoclay as an adsorbent for removal of Cr and Co from aqueous solutions: Adsorption isotherm and kinetics studies

Introduction and Aims Nowadays, the presence of toxic heavy metals in the industrial, commercial, domestic and agricultural effluents is known as a major environmental concern. Since the adsorption process is one of the most effective methods for removing of metal ions from the environment, the current study was carried out to investigate the efficiency of bentonite nanoclay as an adsorbent for removal of Cr and Co from aqueous solutions.
Materials and Methods All stages of the experiment were performed under optimum conditions, using nanosized bentonite absorbent discontinuously. In this study, batch experiments were carried out as a function of solution pH, adsorbent dosage, initial concentration, and contact time. The equilibrium isotherms were characterized and kinetic models were tested. Also, to determine the adsorption rate constant of metals onto the adsorbent, experimental data were compared by pseudo-first-order and pseudo-second-order kinetic models and then were adjusted to Langmuir and Freundlich models. All statistical analyses were performed using the SPSS statistical package.
Results The results showed that by raising pH, the adsorption efficiency of Co and Cr from solution were increased and decreased respectively. The maximum adsorption capacity of Cr and Co was observed at pH 3 and 5 respectively after 30 minutes. Also, by increasing the adsorbent amount to 0.5 g and 2 g, adsorption efficiency increased and then there is no significant changes in removal efficiency were observed by increasing the adsorbent dosage. Moreover, under these conditions, the kinetics of the adsorption process followed pseudo-second-order and both Langmuir and Freundlich adsorption isotherms with a correlation coefficient greater than 0.90.
Conclusion Based on the results, it can be concluded that the bentonite nanoclay can be used for removal of metals ions from real samples.