ABSTRACT:The adsorption performance of a low-cost adsorbent (IS), viz. an iron-containing waste sludge arising during a hot-dip galvanizing process, towards the removal of As(III) ions from synthetic aqueous solutions and natural underground water was examined. The adsorption process was best described by the pseudo-second-order kinetic equation. The equilibrium adsorption data were well described by the Langmuir model. The value of the dimensional separation factor, R L , indicated favourable adsorption. The maximum adsorption capacity of IS was 625 µg As(III)/g. The variation in the extent of adsorption with temperature was used to evaluate the thermodynamic parameters for the adsorption process. The values of ∆H 0 and ∆G 0 obtained demonstrated that the adsorption process was exothermic and spontaneous. The studied material exhibited an excellent As(III) ion adsorption performance from both synthetic solutions and a natural water sample. Moreover, no secondary contaminated substances arise if the exhausted adsorbent is recycled (e.g. in glass applications).

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In the present work a polymer with phosphonium pendant groups impregnated with crown ether (dibenzo-18-crown-6) and loaded with iron ions was investigated for arsenic removal through adsorption from aqueous solutions. The impregnated polymer was loaded with iron ions due to the high affinity of arsenic to it. The characterization of the surface modification of the obtained new adsorbent material was performed on the basis of energy dispersive X-ray analysis; scanning electron microscopy and Fourier transform infrared spectroscopy. The arsenic adsorption was investigated, including effect of pH, arsenic initial concentration, the shaking time and temperature. The effect of the pH was examined over the range 2-11. The adsorption of As(V) increases with pH increasing reaching a maximum at pH higher than 8. Equilibrium, kinetic and thermodynamic studies were carried out to study the adsorption performance of the obtained material in the removal process of arsenic from aqueous solutions. For the studied materials the equilibrium data closely fitted Langmuir model and was achieved a maximum adsorption capacity of 32.6 μg As(V)/g of material. The pseudo-second order kinetic model is suitable for describing the adsorption system. The obtained results show that the studied adsorbent can be used with efficiency in the arsenic removal from underground water even from low influent arsenic concentration solutions.

Due to the large amount of industrial activity during the last century, heavy metal contamination of the environment has become a serious problem. Therefore, it is important to develop new and efficient methods of heavy metals removal from aqueous solutions. In this respect, three phosphonate metal organic frameworks were obtained in our labs by the reaction of divalent inorganic salt (CoSO4·7H2O), phosphonic acid [phosphonoacetic (CP), N,N-bis(phosphonomethyl)glycine (Gly) and vinylphosphonic (VP)] in hydrothermal conditions. The synthesized compounds were characterized by FTIR, X-Ray crystallography scanning electron microscopy and thermogravimetric analysis. These materials were used in the removal process of lead ions from aqueous solutions in order to determine the possibilities of their use as adsorbent materials. The effect of pH, lead initial concentrations and contact time upon the adsorption properties were investigated. From the experimental data it can be observed that the Co-Gly material developed a higher adsorption capacity for lead metal ions than the Co-VP and Co-CP, increasing following Co-CP<Co-VP<Co-Gly trend.

The effects of the sorption of environmental applications by various source materials of natural organic matter, i.e., bone powder, was examined. Sorption capacities and subsequent rare earth element retention characteristics of all metals tested were markedly increased by ionic task-specific. In this study, the abilities of three models’ isotherms widely were used for the equilibrium sorption data: Langmuir, Freundlich and Redlich-Peterson. For all studied metal ions the maximum adsorption capacity is close to those experimentally determined. The characteristic parameters for each isotherm and related coefficients of determination have been determined. The experimental data achieved excellent fits within the following isotherms in the order: Langmuir > Redlich-Peterson > Freundlich, based on their coefficient of determination values. The bone powder has developed higher adsorption performance in the removal process of Nd(III), Eu(III), La(III) from aqueous solutions than in the case of the removal process of Cs(I), Sr(II) and Tl(I) from aqueous solutions. The described relationships provide direct experimental evidence that the sorption-desorption properties of bone powder are closely related to their degree of the type of the metal. The results suggest a potential for obtaining efficient and cost-effective engineered natural organic sorbents for environmental applications.

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In this paper, we studied the feasibility of using Fe III -loaded Amberlite XAD7 impregnated resin containing di(2-ethylhexyl) phosphoric acid (DEHPA) as adsorbents for the removal of As V from aqueous solution. The XAD7-DEHPA resins are obtained by the dry method (DM) and column method (CM) of impregnation, respectively. Equilibrium, kinetic, and thermodynamic studies are carried out to study the adsorption performance of both types of Fe-XAD7-DEHPA resins for the removal process of As V from aqueous solution. The effects of initial As V concentration, contact time, and temperature of the solution on the adsorption were studied. The Langmuir and DubininÀKaganerÀRadushkevich (DKR) isotherm models fit the equilibrium data better than Freundlich and Temkin isotherm models, which are used to describe the adsorption of As V onto Fe-XAD7-DEHPA resins. The pseudosecond-order model is suitable for describing the adsorption kinetics for As V removal from aqueous solutions onto Fe-XAD7-DEHPA resins. Thermodynamic parameters, such as the Gibbs energy (ΔG # ), enthalpy (ΔH # ), entropy (ΔS # ), and equilibrium constant of activation (K # ) are calculated. The adsorption capacities of the both studied materials are found to be almost the same. However, the Fe-XAD7-DEHPA obtained through the CM is the most advantageous as this is obtained in a shorter time than the resin obtained through the DM.