Humic substances and clay minerals have been studied intensively because of their strong complexation and adsorption capacities. In this work, adsorption of Ni2+ on Na-montmorillonite was studied using batch technique under ambient conditions. Effect of pH, ionic strength, solid content, humic acid (HA), fulvic acid (FA) and the addition sequences of fulvic acid/Ni2+/montmorillonite on Ni2+ adsorption was also investigated. The results indicate that adsorption of Ni2+ on montmorillonite are strongly dependent on pH and ionic strength. The adsorption of Ni2+ is mainly dominated by surface complexation and ion exchange. The adsorption–desorption hysteresis suggests that the adsorption of Ni2+ is irreversible. The thermodynamic parameters (ΔH, ΔS, and ΔG) are calculated from the temperature dependence, and the results suggest that the adsorption reaction is endothermic and spontaneous. The presence of FA and the addition sequences of FA/Ni2+/montmorillonite do not influence the adsorption of Ni2+ on FA bound montmorillonite hybrids. Montmorillonite is a suitable candidate for pre-concentration and solidification of Ni2+ from large volume of solutions.
"It is recognized that there is a lack of knowledge on metal ion desorption behavior from clay minerals. In general, desorption studies have been conducted using electrolyte solutions such as NaNO 3 , CaCl 2 , KCl and organic ligands (citrate, EDTA) as extractors (Özdemir and Yapar, 2009; Shirvani et al., 2006; Xu et al., 2008). Besides these aspects, most adsorption studies of metals onto clay minerals describe the results of batch type experiments that are commonly used to measure the adsorption of single or few metals at a time, generally at a concentration level of mg L "
[Show abstract][Hide abstract] ABSTRACT: Montmorillonite and vermiculite as solid phases for the preconcentration of trace elements in natural waters: Adsorption and desorption studies of As, An evaluation of the feasibility of vermiculite and K10 montmorillonite for use as adsorbent in the separation and/or preconcentration of elements prior to their determination was performed for As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sr, V and Zn. The adsorption of elements onto both clay minerals was studied using a multi-element solu-tion in trace concentrations by batch technique, and no stirring under ambient conditions. Effects of adsorbent concentration, pH and ionic strength were also investigated. The desorption process of the previously adsorbed elements onto clay minerals was studied using HCl and HNO 3 as extractors. In general, the adsorbents exhibited excellent sorption properties for most of the elements. The content of adsorption obtained was higher than 70% for almost all cases. On average, at low salt concentration (b 0.05 mol L −1) the sorption efficiency was only slight-ly higher in montmorillonite when compared to vermiculite, however the reverse is true at high salt concentra-tion. The adsorption of metal ions onto vermiculite and montmorillonite reduces with decreasing pH and increasing ionic strength. An opposite behavior was observed in the adsorption of oxi-anionic species of arsenic and vanadium. The results of desorption experiments indicated that a single extraction with 1.0 mol L −1 HNO 3 or HCl was sufficient for the recovery of most elements with an average desorption of 82% and 90% for K10 mont-morillonite and vermiculite, respectively.
"Similar fast equilibrium times were found for Sb(III) adsorption on goethite and Fe–Mn binary oxide (Watkins et al. 2006; Xu et al. 2011). The adsorption achieves equilibration in the first several hours, which indicates that chemical adsorption/surface complexation rather than physical adsorption is the main adsorption mechanism as suggested by Xu et al. (2008). It is well known that spectroscopic methods such as extend X-ray absorption fine structure (EXAFS) spectroscopy , Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) are the direct method to prove the binding forms between ions and minerals. "
[Show abstract][Hide abstract] ABSTRACT: Antimony (Sb) emissions to the environment are increasing, and there is a dearth of knowledge regarding Sb fate and behavior in natural systems. In natural systems, the presence of competitive anions may compete with Sb for adsorption sites on mineral surfaces, hence increasing its potential bioavailability. Accordingly, the adsorption of Sb(III) on kaolinite was investigated in the presence of competitive anions. Kinetic studies suggest that adsorption reaction of Sb(III) on kaolinite is rapid initially and becoming slow after 12 h both in binary Sb(III)–kaolinite system and in ternary Sb(III)-competitive anion–kaolinite system. The presence of PO43− has a much stronger and more obvious promotive effect on the adsorption of Sb(III) on kaolinite compared with the other two anions. The adsorption data of Sb(III) on kaolinite in the absence and presence of competitive anions at three temperatures were successfully modeled using Langmuir (r
2 > 0.95) and Freundlich (r
2 > 0.95) isotherms. Accompanied the adsorption of Sb(III) on kaolinite, significant oxidation of Sb(III) to Sb(V) had occurred under the experimental conditions used in this study. The presence of kaolinite which has a larger specific surface area could increase the contact area between the adsorbed Sb(III) and oxygen in the bulk solution, which promoted the oxidation rate of Sb(III) to Sb(V).
"Its chemical structure is composed of two fused silica tetrahedral sheets sandwiching an edge-shared octahedral sheet of either aluminum or magnesium hydroxide and an interlayer region containing Na þ or Ca 2þ . Montmorillonite is widely used in adsorption   , catalysis , composites    and nanocomposites    . "
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