The effects of cadmium on the adsorption of Cr (VI) by nano clay (Cloisite® Na+)

In recent years, concerns about the long-term effects of heavy metals as one of the main environmental pollutants has increased. These metals have adverse effects on human health, which include growth retardation, cancer, damage to the nervous and heart system. Mainly heavy metals discharge into environment from industrial and urban sewage. There are the different methods to reduce water pollution and removal of heavy metals from water.There are the different methods to reduce water pollution and removal of heavy metals from water that one of them is adsorption by using organic and inorganic absorbers. In this study, the use of nanoclay (Cloisite Na) for adsorption of chromium form Single- and two- component solution (competitive) was investigated.
this study was conducted in scale laboratory conditions and batch system by changing the factors that affect the absorption process such as pH (2-10), contact time (5-1440 minutes), adsorbent dose (1- 5 and 2 gr/L) and adsorbate concentration (1-100 mg/ L). Then in solution of single and two elements systems, experimental data were investigated with absorption isotherms of Freundlich, Langmuir and Sips.
Results showed that the optimum pH values for adsorption of chromium were 6 and 7 for single-element and two elements systems, respectively. Also, in single and two-element systems, the maximum removal efficiency was obtained (82% and 59.2%). Effect of contact time on the adsorption process showed that equilibrium time of removal of Cr (VI) by nanoclay (Cloisite Na) is 180 min in single element systems and 240 min in two-element systems. Optimum dosage of adsorbent for absorption of chromium ions from single and two element solution with a concentration of 10 ppm is 5 and 20 g/L, respectively. Comparison of the Freundlich, Langmuir and Sips isotherms showed that the Sips model for single element system was described data of adsorption better than other models with R2 (0.9977) and RMSE (0.1751). Also in two-element system, Freundlich model with R2 (0.9721) and RMSE (0.2831), is better fit with data of adsorption.
Due to the presence of heavy metals in various industries wastewater and their effects on adsorption of each other by the different adsorbent, it is necessary for getting real results in the process of adsorption Notice to this matter. The results of this study also showed that the absorption presses of chromium from solutions of single element or combination of elements with the same adsorbent are completely different.