Low-cost adsorbents for a dye uptake from contaminated water modeling of adsorption isotherms: The Langmuir, Freundlich and Elovich models

The adsorption of organic molecule to clay minerals has been reported by several investigators. Bentonite, which is made homoionics by mono-, di- and trivalent cations was used to remove the dye, an organic molecule (Quinalizarin) used to dye cotton. Equilibrium data were obtained by the batch technique. The results show the largest adsorption capacity of the homoionic bentonite; the saturation level was reached, the high adsorption capacity (79 meq/100 g), close to the cation exchange capacity of the synthesized bentonite (89 meq/100 g), indicates a strong interaction between the dye molecule and the adsorbent. Adsorption onto the clay was essentially immediate and correlated with the cation exchange-capacity (CEC). The type of exchangeable cations indicate that adsorption was primarily to the negatively charged sites on the clay. The amount of the adsorbed color was found to be a function of the type of exchangeable cations; it drops off in the following order: Bent-Al3+ > bent-NH4+ > bent-Na+ > bent-Fe3+ > bent-Li+ > bent-Ca2+ > bent-Mg2+ > bent-K+. The Langmuir, Freundlich and Elovitch models were employed to examine the equilibrium adsorption data. In all cases, the results show that all adsorption systems could be adequately fitted by these three models. It is seen that the linear fit is fairly good for these three models, the correlation coefficients R2 was found to be equal to 0.9 in approximately all cases.