Isotherm and selectivity study of Ni(II) removal using natural and acid-activated nanobentonites.

In this research, natural bentonite and its acid-activated forms were employed as adsorbents for the adsorption of Ni ions from wastewater. Natural bentonite was activated with 2 M sulfuric acid, 4.5 h and 95 °C (the best acid-activated sample with the highest adsorption capacity) and the other 6 M sulfuric acid, 7.5 h and 95 °C (the worst acid-activated sample with the lowest adsorption capacity). The adsorption of Ni was studied through experiments including equilibrium contact time and selectivity. The equilibrium contact time for bentonite was obtained at 180 min. The Ni separation process along with Zn selectivity studies was considered through adsorption experiments. The results showed that there was a maximum amount of Ni adsorption in the absence of Zn for all samples. The results showed the best fit is obtained with the pseudo-second-order kinetic model. Working out different bentonite types to determine the best kinetic models, we explored the Langmuir and Florry-Huggins models provided a good fit with experimental data for acid-activated bentonites and the best results from linear forms of the adsorption isotherm models for fitting the experimental data of natural bentonite are obtained for Langmuir, Temkin and Freundlich models.