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The aim of the present work is to investigate the ability of commercial natural bentonite (untreated) (NB) to remove silver ions from aqueous solution. Specific surface area of the sample was determined as a result of N 2 adsorption-desorption at 77 K using BET method. X-ray powder diffraction (XRD) was used to characterize the (NB). Towards this aim, batch adsorption experiments were carried out and the effect of various parameters on this removal process has been investigated. The effects of pH, adsorption time, silver ion concentration, bentonite doses, Temperature and the NB treatment (calcinations and washing) on the adsorption process were examined. The optimum pH for adsorption was found to be 4-8. It was found that NB treatment has a substantial effect on the metal uptake. In adsorption studies, residual silver ions concentration reached equilibrium in a short duration of 15 min. The paper discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Adsorption of Ag + on NB appeared to follow Langmuir isotherm. Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. Additionally, a pseudo-second-order rate model was adopted to describe the kinetics of adsorption. In desorption experiment, an approximately (15%) desorption yield was obtained for silver ions.

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In this study, the adsorption behavior of natural bentonite with respect to Fe(III) and Ni(II) has been studied in order to consider its application to purity metal finishing wastewaters. During the adsorption process, batch technique is used, and the effects of pH, bentoite amount, temperature, heavy metal concentration, bentonite treatment (calcinations of natural bentonite at 700 C, washing by deionized water to remove the excess salt from bentonite surface), and agitation time on adsorption efficiency are studied. The washed and calcined bentonite samples were labeled by WB and CB, respectively. The pH-dependence of Fe(III) and Ni(II) sorption on the bentonite is significantly more noticeable, indicating a major contribution of surface complexation at the edge sites. It was determined that adsorption of Fe(III) and Ni(II) is well fitted by the second order reaction kinetic. Furthermore, the sorption rate of Fe(III) was higher than the sorption rate of Ni(II). Adsorption of Fe(III) and Ni(II) on NB appeared to follow Langmuir isotherm. In addition, calculated and experimental adsorbed amounts of Fe(III) by the unit NB mass are very higher than Ni(II). The paper also discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. Also the adsorption capacity of bentonite for Fe(III) Ni(II) and increases with increased bentonite dose. According to the equilibrium studies, the selectivity sequence can be given as Fe(III) > Ni(II). The adsorbed amount of Fe(III) and Ni(II) on washed bentonite (WB) were very higher compared to NB and CB. Our results show that bentonite could especially WB be considered as a potential adsorbent for Fe(III) and Ni(II) removal from aqueous solutions.

ABSTRACT:The adsorption of polymer on clay particles has great importance in many industrial applications. This work aimed to study the adsorption of anionic polymer, poly (4-sodium styrene sulfonate), on kaolinite clay surfaces. Three different Egyptian kaolinite clay samples were used. The kaolinite clays were saturated with sodium or calcium cation. It was found that the Freundlich isotherm is applicable for this polymer adsorption on kaolinite. The parameters of the Freundlich equation are very close, indicating a comparable nature for the binding behavior between the different samples of kaolinite and the adsorbed polymer.The adsorption process was examined at different pH values (3, 6, and 9 Ϯ 0.1) to cover the range below and above the point of zero charge of kaolinite surfaces. It was found that, below this point, the polymer adsorption increased, while above it the polymer adsorption decreased. The polymer adsorption on calcium kaolinite was higher than that of sodium kaolinite at the same pH value.