In this research, natural bentonite and its acid-activated forms were employed as adsorbents for the adsorption of Ni2+ ions from wastewater. Natural bentonite was activated with 2M sulfuric acid, 4.5 h and 95 °C (the beast acid-activated sample with the highest adsorption capacity) and the other 6M sulfuric acid, 7.5 h and 95 °C (the worst acid-activated sample with the lowest adsorption capacity). The adsorption of Ni2+ was studied through experiments including equilibrium contact time and selectivity. The equilibrium time of contact for bentonite was obtained at 180 min. The Ni2+ separation process along with Zn2+ selectivity studies was considered through adsorption experiments. The results showed that there was a maximum amount of Ni2+ adsorption in the absence of Zn2+ 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 Langmuir, Temkin and Freundlich models.
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