Modeling of equilibrium isotherms and kinetic studies of Cr (VI) adsorption into natural and acid-activated clays

Smectite clay has great potential for the removal of heavy metal ions from aqueous solution. This work aims to develop inexpensive, highly available, effective metal ion adsorbents from clay minerals as alternatives to existing commercial adsorbents. In particular, natural clay was modified with sulfuric acid to yield excellent adsorbent material. The adsorptive interactions of Cr (VI) ions with natural clay and their acid-activated derivative in aqueous solution are investigated in this study. The adsorption experiments were carried out under batch process with Cr (VI) concentration, pH, time, and temperature as the variables. The adsorption was strongly dependent on pH of the solution. Adsorption was very fast at low coverage, and equilibrium was approached within 35 min. The kinetic data were analyzed using different kinetic models. It was shown that the adsorption of Cr (VI) ions could be described by a pseudo-second-order equation and Elovich model. The experimental data were also analyzed using two and three-parameter isotherm models of adsorption. Thermodynamic parameters such as AG, AH. and AS have been evaluated, and it has been found that the sorption process was spontaneous and exothermic. From all our data, we conclude that the treated clay by sulfuric acid investigated in this study showed good potential for Cr (VI) ions removal from aqueous solutions.