Adsorption and desorption of Ni2+ on Na-montmorillonite: Effect of pH, ionic strength, fulvic acid, humic acid and addition sequences
ABSTRACT 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.
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ABSTRACT: Chitosan-montmorillonite is a modified montmorillonite in which the sodium ions in montmorillonite layers are replaced by biopolymeric chitosan. The effects of characteristics of chitosan (i.e. molecular weight and degree of deacetylation) and the chitosan/montmorillonite mass ratio on the properties of chitosan-montmorillonite were investigated. Thermogravimetric analysis, zeta potential and X-ray diffraction results confirmed intercalation of chitosan into montmorillonite layers. An interaction between chitosan and montmorillonite was revealed by FTIR and the zeta potential. The amount of chitosan intercalated into the montmorillonite layers depended on the characteristics of chitosan, with the largest amounts of intercalated chitosan achieved by addition of chitosan with a molecular weight of 71,000 g/mol or a degree of deacetylation of 80% at a fixed chitosan/montmorillonite mass ratio of 2:1. The resulting chitosan-montmorilllonite had good adsorbent properties, especially for adsorption of cationic dyes, and also inhibited E. coli by almost 100%. The chitosan-montmorillonite may be useful as a functional material for dye adsorption and antibacterial applications. © 2012 Chinese Materials Research Society.Progress in Natural Science 10/2012; 22(5):502-508. · 0.99 Impact Factor
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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.Applied Clay Science 07/2014; 99:289. · 2.34 Impact Factor
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ABSTRACT: This study’s main objective was the development of effective low-cost sorbents for the removal of heavy metal ions from aqueous solutions. The influence of different factors on the sorption capacity of ash and modified ash as low-cost sorbents obtained by different methods was investigated. The synthesis of new ash-based materials was carried out at ambient temperature (20°C), 70°C, and 90°C, respectively, in an alkaline medium with NaOH concentrations of 2 M and 5 M, respectively, corresponding to a mixture with solid/liquid ratios of 1: 3 and 1: 5, respectively. The prepared materials (sorbents) were characterised by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction, and BET surface measurement. Adsorption isotherms were determined using the batch equilibrium method. The results showed that these types of new materials displayed a good capacity to remove copper, nickel, and lead ions (29.97 mg of Cu2+ per g of sorbent, 303 mg of Ni2+ per g of sorbent, and 1111 mg of Pb2+ per g of sorbent) from aqueous solutions. The modified materials were prepared using an alkaline attack (a recognised method used in previous studies), but Romanian ash from a thermal power plant was studied for the above purpose for the first time. Hence, the factors which affect the sorption capacity of the prepared low-cost sorbents were determined and their behaviour was explained, taking into account the composition and structure of the new materials.