جستجوی مقالات مرتبط با کلیدواژه "جذب سطحی" در نشریات گروه "فیزیک"

In This study, an absorbent consisting of DEHPA impregnated onto Amberlite XAD-7 resin was prepared and used for the adsorption of Ce (ΙΙΙ) and La(ΙΙΙ) ions from aqueous solution. The absorbent (XAD-7 + DEHPA) was charaterized by SEM and FTIR analysis Techniques. Several influential variables such as, contact time, pH and  temperature were studied in batch mode of operation. Th results showed that the optimum adsorption condition  were acjieved at pH=6, optimum amount of absorbent and the equilibrium time equal to 0.6 gr and 180 min, respectively. According to the results the adsorption percentage of cerium and lanthanum ions onto the aforementioned resin were 99.99%, 78.76% respectively. Various isotherms models such as Langmuir, Freundlich, Temkin and Dubinin-Radushkevich were used in 25°C to analyze the equilibrium isotherm data and results showed that  Langmuir model had a better agreement with the experimental data. The maximum adsorption capacity of the resin  for cerium and Lanthanum ions were 8.28 mg.g-1, 5.52 mg.g-1 respectively. The kinetic data were fitted to pesudo- frist- order, pesudo-second-order and Intra particle diffusion models. Based on the results, the pesudo- frist- order model and Intra particle diffusion  model described the experimental data as well. Thermodynamic parameters of adsorption such as ΔHº, ΔS°, ΔG° were calcutated. Positive ΔHº and negative ΔG° were indicative of the endothermic and spontaneous nature of the adsorption. The  aforementioned resin shows the stability during the five cycles of adsorption-desorption and it’s  degradation was less than 3%

In this paper, the long-range Van Der Walls dispersion force correction (vdW-DF) for a combined system consisting of an Ag-chain adsorbed on a monolayer of graphene is studied. Calculations are based on density functional theory (DFT) performed by using various LDA, PBE and BLYP approximations. Since Ag chain is weakly adsorbed on graphene sheet, the Van Der Waals contribution to the total adsorption energy cannot be ignored. When applying this correction, the structural and electronic properties of the combined system such as adsorption energy, adsorption distance, and the Fermi level shift with respect to the Dirac point are significantly affected. The weak hybridization of the electronic states of silver and carbon at the interface gives rise to a small band gap opening at the Dirac point.

One of the byproducts of uranium enrichment industry is hydrogen fluoride gas. Due to the toxicity and corrosivity of the molecule, it has adverse effects on the environment and the process. Therefore, it must be removed by adsorption towers. The activated carbon is one of the proposed sorbent for the adsorption. Hydrogen fluoride adsorption equilibrium curve gives important information for designing the adsorption towers. In this article, the hydrogen fluoride adsorption and adsorption factors were determined experimentally, and four different types of carbon have been used. The operating pressure in all tests was less than 0 mbar. Comparison between the obtained experimental equilibrium curves shows that the first, second and fourth types of activated carbon are suitable for the adsorption of hydrogen fluoride. The experimental data were fitted using mathematical models of Longmuir, Freundlich, Toth and Henry. The results show that Toth mathematical model is more suitable than other models. Also, the absolute error were predicted by the model of Toth for the first, second and fourth types of the activated carbon were .9, 6.5 and percent, respectively.

This paper examines heavy metals removal from synthetics wastes by the use of natural and sulfuric acid-activated bentonite so that a cheap adsorbent can be attained for removing these metals from the wastes. Bentonite is a 2:1 layer aluminnisilicate whose dominant mineral is montmorillonite which is a nano-structure and nanoporous material. Montmorillonite affects all the properties of bentonite. In the next step, the effect of acid activation on the adsorption of both of lead (Pb) and thallium (Tl) is studied. In this research, after the mineralogical and chemical composition analyses by X-ray diffraction and fluorescence (XRD and XRF) methods, granulometric analysis is carried out on five samples namely, S2-RAW, S3-RAW, ES3-RAW, G1-RAW and GH1-RAW to remove the heavy metals such as Cr, Co, Cu, Fe, Pb, Tl, Ni, and Zn accompanying atomic absorption spectroscopy (AAS). Then, the effect of four factors including concentration, liquid to solid ratio (L/S), time, and activation temperature in acid activation process were studied. This process is done by a mineral acid, sulfuric acid, to promote the adsorbability of lead and thallium in both natural and activated types of ES3-RAW and GH1-RAW. In all case, due to the presence of dominant mineral of nano-montmorillonite and its unique structure, montmorillonite has a higher adsorbability in comparison with that of the other clay minerals.

Sodium fluoride is one of the most important adsorbents in enrichment facilities, where it is availabe in the form of powder and pellets. Linear and parabolic curve of the reaction between uranium hexafluoride and sodium fluoride, in the form of powder, in comparison with the parabolic curve of sodium fluoride in the form of pellets is shown that it is the best shape for the sodium fluoride adsorbents. But, it is impossible to determine these properties only by comparison of UF6 and NaF reaction kinetics and, selecting the shape and dimension requires the study of the effects of loading and pressure drop. In this paper, effects of adsorbents shape on pressure drop and capacity is studied. Based on these studies, it was realized that as the dimension of adsorbents decreases, the active surface area increases and cansequently, the final capacity of the adsorption decreases.

Ferric ions in dilute acidic leach liquor of uranium ore of Saghand were separated by anion exchange resins. In this research, a simulated solution similar to the actual leach liquor of Saghand was prepared. The simulated solution which was containing chloride and ferric ions, rare earth elements, and some other impurities was treated by different types of Dowex anion exchange resins for ferric ions removal. It appeared that hydrochloric acidic concentration, resin types and particle sizes have a great impact on ferric ions adsorption. Dowex 1X4 (200-400 mesh) has the best adsorption of 91% in simulated solution and 79% in actual leach liquor of uranium ore of Saghand respectively.

The adsorption behavior of natural vermiculite for cesium (137Cs), in radioactive aqueous waste, has been investigated. Our experiments, aimed at the study of the effect of some parameters such as residential time (for batch equilibrium), pH, temperature, and flow rate (for column tests) on the efficiency of adsorption operation. The adsorption experiments were performed using both static batch equilibration and flow-through tests. The maximum adsorption was observed in alkaline condition (0.01 mol L-1 NaOH solution), using 1gr of adsorbent for 100ml of radioactive liquid waste at 60ºC, in 24h of residential time for a batch experiment. Finally, with the result of the column experiments, the breaktrough isotherm has been drawn. The present work deals with a series of experiments to assess the potential of vermiculite for the removal of radio cesium from radioactive aqueous waste. The results of these investigations are expected to be valuable, in order to reach at a higher degree of radioactive waste decontamination.

Hydrated cerium (IV) dioxide has been synthesized by adding excess cerium sulphate to 4M ammonia solution at 250C and pH=12.5 with constant stirring. The properties of the compound were investigated by means of infrared and thermogravimetric techniques. The effect of temperature and pH on the adsorption of Ba and Sr ions and also the distribution coefficients of Cs and Eu at various pH values on cerium (IV) dioxide were considered. The distribution coefficient results showed that with the increase of pH of the media, the amount of adsorption of Ba and Sr cations on the surface of cerium (IV) dioxide increases, and this is due to their amphoteric nature of this oxide.

In this research, adsorption of molybdenum has been investigated by a new silica aerogel. This hydrophobic silica aerogel synthesized on the basis of TMOS (tetra methyl ortho silicate) precursor and in the presence of two co-precursors, tri fluoro propyl-tri methoxy silane and di-ethyl tri-methyl silyl phosphite. As the obtained results show, this aerogel is highly capable to uptake Mo in an optimum concentration of metal solution of about 10 ppm, the optimum pH about 4, contact time about 5 hours and the adsorbent dose about 3gr for 50ml of metal solution. The kinetics approaches show that the rate of this adsorption follows a first order reaction and the rate constant (Kad) is equal to 0.1248(h-1). The thermodynamic approaches have also been studied, and thereby the feasibility and the spontaneous nature of  Mo ions adsorption on aerogel have been demonstrated. A comparison between obtained results from silica aerogel and the activated carbon shows the more capability of the synthesized silica aerogel.