Evaluation of sorption of uranium onto metakaolin using X-ray photoelectron and Raman spectroscopies

Metakaolin prepared from a natural clay mineral ore of aluminium kaolinite is a promising low cost and high activity aluminosilicate material that has been investigated for studying the sorption behavior of uranium. Here, metakaolin was characterized using X-ray photoelectron spectroscopy (XPS) and the effects of pH, contact time and initial metal ion concentration on its sorption behavior were studied. The sorption process was found to initially be rapid (∼60% at time 0 min) but became slower with time; equilibrium was established within 24 h (∼80% sorption). The data were applied to study the kinetics of the sorption process. The Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms were used to describe partitioning behavior for the system at room temperature. The binding of metal ions was found to be pH dependent, with optimal sorption occurring at pH 5. The retained metal ions were eluted with 5 mL of 0.1 M HNO₃. Raman spectroscopy and XPS were used to evaluate the sorption mechanism of U(VI).     

Effect of surface modification of an engineered activated carbon on the sorption of 2,4-dichlorophenoxy acetic acid and benazolin from water

The performance of a conventional (F400) and a surface modified activated carbon (F400AN) has been investigated for the sorption of benazolin and 2,4-dichlorophenoxy acetic acid (2,4-D) from water. It was observed that the modified carbon, F400AN, which was obtained by annealing the conventional sample had a higher BET surface area (960 m2 g(-1) compared to 790 m2 g(-1)) and it had a higher proportion of micropores. This was attributed to the loss of oxygen containing functional groups during the thermal treatment. Zeta potential and pH titration measurements also showed that acidic functionality had been lost on the F400AN sample. The adsorption data were analysed and were fitted well using the Langmuir isotherm. The modified carbon marginally out-performed the conventional activated carbon for sorption of these two herbicides. Thermodynamic parameters (DeltaG0, DeltaH0, and DeltaS0) were determined and their values indicated that the sorption process was spontaneous and endothermic for both herbicides. A pseudo-second-order kinetic model was employed for analysing the kinetic data. It was concluded that the herbicide sorption process was controlled by a film diffusion mechanism.     

Kinetic models of sorption: a theoretical analysis

The kinetics of sorption from a solution onto an adsorbent has been explored theoretically. The general analytical solution was obtained for two cases. It has been shown that at high initial concentration of solute (sorbate) the general equation converts to a pseudo-first-order model and at lower initial concentration of solute it converts to a pseudo-second-order model. In other words, the sorption process obeys pseudo-first-order kinetics at high initial concentration of solute, while it obeys pseudo-second-order kinetics model at lower initial concentration of solute. The theoretical results (derived equations) show that the observed rate constants of pseudo-first-order and pseudo-second-order models are combinations of adsorption and desorption rate constants and also initial concentration of solute. The obtained theoretical equations are used to correlate experimental data for sorption kinetics of some solutes on various sorbents. The predictions of the theory are in excellent agreement with the experimental data.     

Effect of contact time,pH, humic acid and temperature on the sorption of radionuclide Am(III) onto attapulgite

Attapulgite has been applied in the sorption of metal and radionuclide ions since its discovery. Herein, radionuclide Am(III) sorption onto attapulgite was carried out at 25 °C in 0.01 mol/L NaNO₃ solutions. Effects of contact time, Am(III) initial concentration, pH, humic acid and temperature on Am(III) sorption onto attapulgite were investigated. The sorption of Am(III) increases with increasing contact time and reaches a maximum value within 24 h at different Am(III) initial concentration. The fast sorption velocity indicates that strong chemical sorption or strong surface complexation contributes to the sorption of Am(III) onto attapulgite under the experimental conditions. The experimental data can be described well by the pseudo-second-order rate model. The sorption of Am(III) onto attapulgite is strongly dependent on pH values and surface complexation is the main sorption mechanism. The presence of HA enhances the sorption of Am(III) onto attapulgite at pH < 8.5, whereas, at pH > 8.5, little effect of HA on Am(III) sorption is observed. The Langmuir, Freundlich and D-R models were used to simulate the sorption data at different pH values and the results indicated that Langmuir model simulates the experimental data better than Freundlich and D-R models. The thermodynamic parameters indicates that the sorption of Am(III) onto attapulgite is an endothermic and spontaneous process. The results suggest that the attapulgite is a suitable material as an adsorbent for preconcentration and immobilization of Am(III) from aqueous solutions.     

Sorption studies of europium on cerium phosphate using Box-Behnken design

Amorphous cerium phosphate was prepared and characterized. Three-level Box-Behnken design (BBD) was employed to analyze the effect of process variables such as initial pH (2–6), contact time (60–180 min), and sorbent amount (0.05–0.15 g) on the sorption capacity of europium. Analysis of variance (ANOVA) revealed that the main effect of initial pH and sorbent amount has a substantial impact on the sorption of Eu(III). Probability F-value (F = 3 × 10^-3) and correlation coefficient (R2 = 0.97) point out that the model is in good accordance with experimental data. The maximum sorption capacity of Eu(III) was found to be 42.14 mg g^-1 at initial pH 6, contact time of 180 min, and a sorbent amount of 0.05 g. Sorption isotherm data was well explained by the Langmuir model and monolayer Eu(III) sorption capacity was obtained as 30.40 mg g^-1. Kinetic data were well described by the pseudo-second-order model. Thermodynamic data suggested that the process is endothermic and spontaneous.     

Thermodynamics of Chromium(VI) Anionic Species Sorption onto Surfactant-Modified Montmorillonite Clay

Batch sorption experiments performed on Cr(VI) species sorption showed a significantly enhanced removal of inorganic hexavalent chromium anionic species from aqueous solution by montmorillonite clays modified with quaternary amine, hexadecyltrimethylammonium (HDTMA) bromide. Unmodified clay had no affinity for chromium(VI) species. The sorption of Cr(VI) species has been carried out as a function of pH, contact time, adsorbate concentration (4.14x10(-5) to 8.62x10(-3) M), and temperature (5-45 degrees C). The surfactant-modified clay surface was stable when exposed to extremes in pH. The optimum pH for maximum sorption of Cr(VI) species was found to be at pH 1 and was constant between pH 2 and pH 6. The sorption data obtained was well described by DKR and Langmuir sorption isotherms. Sorption energy (E) for (i) surfactant sorption by montmorillonite clay and (ii) sorption of chromium(VI) species by surfactant modified clay have been computed from the DKR equation. Sorption energy evaluated for the sorption of both surfactant and Cr(VI) species showed that an ion-exchange mechanism was operative. The mechanism of retention appears to be replacement of counterion of the surfactant by Cr(VI) anionic species. Adsorbent capacity for the sorption of Cr(VI) species has been evaluated from the Langmuir sorption isotherm data. Thermodynamic parameters (Delta H degrees, Delta S degrees and Delta G degrees ) for surfactant sorption on montmorillonite clay and Cr(VI) sorption by modified clay have been evaluated. The specific rate constant for sorption of Cr(VI) species on modified montmorillonite was rapid during the first 10 min and equilibrium was found to be attained within 30 min. The sorption of Cr(VI) species onto modified montmorillonite clay followed first-order rate kinetics. Copyright 2000 Academic Press.     

Removal of Fluorescein using different iron oxides as adsorbents: effect of pH

In this work the adsorption process of Fluorescein (dye with aril-methane group) as a function of pH on three different adsorbents: goethite, Co-goethite, and magnetite has been studied experimentally and theoretically. FTIR and Raman spectroscopy have been performed in an attempt to confirm the structure of surface complexes formed by sorption of the Fluorescein to different iron oxides. Typical anionic adsorption behaviour was observed for this dye onto goethite and Co-goethite whereas the adsorption level was practically constant in the range of pH studied when the adsorbent was magnetite. The diffuse layer model was employed to fit the experimental results. The surface complexes proposed from the adsorption data were in agreement with the patterns obtained from FTIR and Raman spectroscopy. The surface structure of the oxides affects the adsorption process and the final adsorbed amount at the equilibrium. Our model of diffuse double layer with the addendum of the effect of hydrophobic forces fits well the adsorption data of Fluorescein on iron oxides at different pH in the studied range. At lower pH electrostatic forces by ligand-exchange are predominant. In the range of pH 9-11 hydrophobic forces are managing the Fluorescein adsorption on the iron oxides, with the formation of outer-sphere complexes through van der Waals/hydrophobic forces. It is interesting that in the three iron oxides studied, the adsorbed amount in this range is similar.     

pH、富里酸和温度对铀酰在ZrP_2O_7上的吸附影响

采用质量滴定法和静态法分别研究了ZrP2O7的零电荷点(pHPZC)和铀酰离子在ZrP2O7上的吸附及解吸行为.铀酰离子在ZrP2O7上的吸附受体系pH、固液比、电解质种类及富里酸(FA)强烈影响,离子强度对铀酰离子在ZrP2O7上吸附的影响较小;随着固液比(m/V)和pH增大,吸附边界向左偏移;磷酸根与硫酸根对吸附有相反的影响;在低pH下,富里酸(FA)促进铀酰离子在ZrP2O7上吸附;柠檬酸根对吸附有非常大的影响;温度升高有利于吸附.采用Langmuir和Freundlich模型对吸附等温线进行拟合研究,表明Freundlich模型可以更好地拟合铀酰离子在ZrP2O7上的吸附.通过对热力学数据如(△H0,△S0和△G0)的计算可知吸附过程是自发和吸热过程.铀酰离子在ZrP2O7上吸附为不可逆吸附.     

Magnetic chitosan grafted with polymerized thiourea for remazol brilliant blue R recovery: Effects of uptake conditions

Magnetic chitosan was prepared by co-precipitation with polymeric Schiff’s base resulting from the reaction of thiourea with glutaraldehyde. This material has great potential as high-effective sorbent for Remazol Brilliant Blue R (RBBR): maximum sorption capacity reached 0.441?mmol?g^?1 at pH 1.6 and at 25°C. Kinetic plots, pH dependence, isotherm data, and influences of ionic strength were reported. The data from equilibrium sorption experiments are well fitted to the Langmuir isotherm and the pseudo-second-order sorption kinetics indicates that chemisorption controls the process. The distribution coefficient was calculated at different temperatures and the thermodynamic parameters have been calculated: the sorption reaction is endothermic, spontaneous, and increases the entropy of the system. Alkaline solution (0.5?M NaOH) was used for desorbing RBBR from loaded sorbent. The sorbent exhibited good regenerability over several repeated adsorption/desorption cycles.     

Preparation of TiO<Subscript>2</Subscript> nanoparticles by sonochemical method,isotherm, thermodynamic and kinetic studies on the sorption of strontium

The objective of this study is to evaluate the use of titanium dioxide nanoparticles which were prepared by novel sonochemical method as an ion exchange material for the removal of Sr from aqueous solution. The pH effect on the Sr²⁺ sorption was investigated. The data obtained have been correlated with Freundlich, Temkin and Dubinin–Radushkevich (D–R) isotherm models. Thermodynamic parameters fort he sorption system have been determined at four temperatures. Simple kinetic models have been applied to the rate and isotherm sorption data and the relevant kinetic parameters were determined from the graphical presentation of these models at 298°K. Results explained that the pseudo second-order sorption mechanism is predominant and the overall rate constant of sorption process appears to be controlled by chemical sorption process. The value of sorption energy E = 13 kJ/mol at 298°K and the value of Gibbs free energy ∆G° = 3,222 kJ/mol at 298°K prove that the sorption of strontium on titanium dioxide nanoparticles is an endothermic and non-spontaneous process.     

New anion-exchange solid-phase extraction support used for preconcentration and determination of lead in water samples by flame atomic absorption spectrometry

A new chelating resin was prepared by coupling Amberlite XAD-2 with Brilliant Green through an azo spacer. The resulting resin has been characterized by FTIR spectrometry, elemental analysis, and thermogravimetric analysis and studied for the preconcentration and determination of trace Pb(II) ions from solution samples. The anionic complex of Pb(II) and iodide was retained on the resin by the formation of an ion associate with Brilliant Green on Amberlite XAD-2 in weak acidic medium. The optimum pH value for sorption of the metal ion was 5.5. The sorption capacity of the functionalized resin is 53.8 mg/g. The chelating resin can be reused for 20 cycles of sorption-desorption without any significant change in sorption capacity. A recovery of 103% was obtained for the metal ion with 0.1 M EDTA as the eluting agent. Scatchard analysis revealed that the homogeneous binding sites were formed in the polymers. The resin was subjected to evaluation through batch binding and column chromatography of Pb(II). The equilibrium adsorption data of Pb(II) on modified resin were analyzed by Langmuir, Freundlich, and Temkin models. Based on equilibrium adsorption data, the Langmuir, Freundlich, and Temkin constants were determined to be 0.192, 13.189, and 3.418 at pH 5.5 and 25 degrees C. The method was applied for lead ion determination in tap water samples.     

Equilibrium, kinetics, mechanism, and process design for the sorption of methylene blue onto rice husk

Batch experiments were carried out for the sorption of methylene blue onto rice husk particles. The operating variables studied were initial solution pH, initial dye concentration, adsorbent concentration, and contact time. Equilibrium data were fitted to the Freundlich and Langmuir isotherm equations and the equilibrium data were found to be well represented by the Langmuir isotherm equation. The monolayer sorption capacity of rice husks for methylene blue sorption was found to be 40.5833 mg/g at room temperature (32 degrees C). The sorption was analyzed using pseudo-first-order and pseudo-second-order kinetic models and the sorption kinetics was found to follow a pseudo-second-order kinetic model. Also the applicability of pseudo second order in modeling the kinetic data was also discussed. The sorption process was found to be controlled by both surface and pore diffusion with surface diffusion at the earlier stages followed by pore diffusion at the later stages. The average external mass transfer coefficient and intraparticle diffusion coefficient was found to be 0.01133 min(-1) and 0.695358 mg/g min0.5. Analysis of sorption data using a Boyd plot confirms that external mass transfer is the rate limiting step in the sorption process. The effective diffusion coefficient, Di was calculated using the Boyd constant and was found to be 5.05 x 10(-04) cm2/s for an initial dye concentration of 50 mg/L. A single-stage batch-adsorber design of the adsorption of methylene blue onto rice husk has been studied based on the Langmuir isotherm equation.     

Amberlite XAD-4 functionalized with m-phenylendiamine: Synthesis, characterization and applications as extractant for preconcentration and determination of rhodium (III) in water samples by Inductive Couple Plasma Atomic Emission Spectroscopy (ICP-AES)

A new chelating resin is prepared by coupling Amberlite XAD-4 with metaphenylendiamine through an azo spacer, characterized (elemental analysis, IR and thermogravimetric analysis (TGA)) and studied for preconcentration Rh (III) using Inductive Couple Plasma Atomic Emission Spectroscopy (ICP-AES) for rhodium monitoring. The optimum pH value for sorption of the metal ion was 6.5 (recovery 100%). The sorption capacity was found 0.256 mmol g^− 1 of resin for Rh (III). The method has a detection limit and limit of quantification of 0.05 and 0.08 μg mL^− 1 at pH 6.5, respectively. The chelating resin can be reused for 10 cycles of sorption-desorption without any significant change in sorption capacity. A recovery of 100% was obtained for the metal ion with 1.5 M HCl as eluting agent. The equilibrium adsorption data of Rh (III) on modified resin were analyzed by Langmuir and Freundlich models. Adsorption data were modeled using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics equations. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy and entropy of adsorption. The positive value of the enthalpy change (2.48 kJ/mol) indicates that the adsorption is an endothermic process. The method was applied for rhodium ions determination from tap water sample.     

Some peculiarities in the specific adsorption of phosphate ions on hematite and gamma-Al2O3 as reflected by radiotracer studies

The specific adsorption of radiolabeled phosphate ions from perchlorate supporting electrolyte onto gamma-Al2O3 and hematite powder has been investigated. The pH dependence of the adsorption of phosphate species was compared with that of sulfate ions. It was demonstrated that in contrast to the behavior of sulfate ions the pH dependence of phosphate ions goes through a maximum. On the other hand, it was found that the reversible adsorption of phosphate ions is accompanied by the formation of strongly chemisorbed species. Results obtained from a study of the competitive adsorption of sulfate and phosphate ions at various pH values are reported and interpreted. An attempt is made to correlate the experimental findings with the models for anion adsorption reported in the literature.     

Mesoporous silica SBA-15 functionalized with phosphonate and amino groups for uranium uptake

Mesoporous silicas have a very attractive ability of sorption and enrichment of metal ions due to their huge surface area and facile functionalization by organic ligands.In this work,phosphonate-amino bifunctionalized mesoporous silica SBA-15(PA-SBA-15) as U(VI) sorbent was fabricated through post-grafting method.The obtained mesoporous silica was characterized by SEM,XRD,NMR and nitrogen sorption/desorption experiments,which revealed the existence of ordered mesoporous structure with uniform pore diameter and large surface area.The adsorptivity of PA-SBA-15 for U(VI) from aqueous solution was investigated using batch sorption technique under different experimental conditions.The preliminary results show that the U(VI) sorption by PA-SBA-15 is very quick with equilibrium time of less than 1 h,and the U(VI) uptake is as large as 373 mg/g at pH 5.5 under 95 ℃.The sorption isotherm has been successfully modeled by the Langmuir isotherm,suggesting a monolayer homogeneous sorption of U(VI) in PA-SBA-15.The sorption is pH-dependent due to the pH-dependent charge of sorbent in the aqueous solution.The thermodynamics research shows that the sorption is a feasible and endothermic process.Based on these results,PA-SBA-15 could be a promising solid phase sorbent for highly-efficient removal of U(VI) ions from waste water and enrichment of U(VI) from a solution at a very low level.     

Sorption of Am(III) on natural sediment: experiment and modeling

Release of long-lived radioactivity to the aquatic bodies from various nuclear fuel cycle related operations is of great environmental concern in view of their possible migration into biosphere. This migration is significantly influenced by various factors such as pH, complexing ions present in aquatic environment and sorption of species involving radionuclides on the sediments around the water bodies. ^241/243Am are two major radionuclides which can contribute a great deal to radioactivity for several thousand years. In the present study, ²⁴¹Am sorption on natural sediment collected from site near a nuclear installation in India, has been investigated under the varying conditions of pH (3–10) and ionic strength [I = 0.01–1 M (NaClO₄)]. The sorption of Am increased with pH of the aqueous medium [10% (pH 2) to ~100% (pH 10)], which was explained in terms of the increased negative surface charge on the sediment particles. There was marginal variation in Am(III) sorption with increased ionic strength (within error limits) of the aqueous medium suggesting inner-sphere complexation/sorption process. Sediment was characterized for its elemental composition and structural phases using Energy Dispersive X-Ray (SEM-EDX) and X-Ray Diffraction (XRD) techniques. Zeta-potential measurement at I = 0.1 M (NaClO₄) suggested that Point of Zero Charge (pH_PZC) was ~2, indicating the presence of silica as major component in the sediment. Kurabtov plot using sorption data as a function of pH at fixed I = 0.1 M (NaClO₄) indicated the presence of multiple Am(III) species present on the surface. Potentiometric titration of the suspension indicated the presence of mineral oxide like behavior and assuming a generic nature (≡XOH) for all types of surface sites, protonation–deprotonation constants and total number of sites have been obtained. The sorption data has been modeled using 2-pK Diffuse Double Layer Surface Complexation Model (DDL-SCM). ≡XOAm²⁺ has been identified as the main species responsible for the sorption profile.     

Removal of Thoron and Arsenazo III from radioactive liquid waste by sorption onto cetyltrimethylammonium-functionalized polyacrylonitrile

A surfactant-functionalized polyacrylonitrile (SFPAN) was synthesized in the present investigation via gamma radiation-induced polymerization and was applied for sorbing two hazardous organics, Thoron (TH) and Arsenazo III (ARIII), from radioactive liquid waste. Efficient removals were achieved for both organics over a wide range of pH. The sorption kinetic studies of TH and ARIII revealed that the equilibrium time is significantly dependent on the solution pH. Among the tested sorption kinetic models, the kinetic data of TH and ARIII fit well to the pseudo-second-order one. The sorption equilibrium data obtained for TH and ARIII were analyzed using Freundlich, Langmuir, Temkin and Dubinin–Radushkevich (D–R) isotherm models. The obtained results demonstrated that the equilibrium data are well described by Freundlich and D–R models. The calculated values of the sorption energy (E) and the Gibbs free energy change (ΔG ^o) suggested that the sorption process of TH and ARIII onto SFPAN is governed by physisorption. SFPAN was further tested for the uptake of the concerned organics from radioactive process wastewater. The obtained results suggest its applicability for the treatment of liquid organic radioactive wastes.     

Sorption of radiocobalt(II) from aqueous solutions to Na-attapulgite

The sorption of Co(II) on Na-attapulgite as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic acid (FA) and temperature under ambient conditions was studied. The kinetic of Co(II) sorption on Na-attapulgite was described well by pseudo-second-order model. The sorption of Co(II) on Na-attapulgite was strongly dependent on pH and ionic strength. The sorption of Co(II) was mainly dominated by outer-sphere surface complexation and/or ion exchange at low pH, whereas inner-sphere surface complexation or surface precipitation was the main sorption mechanism at high pH values. The presence of FA did not affect Co(II) sorption obviously at pH <7, and a negative effect was observed at pH >7. The Langmuir and Freundlich models were used to simulate the sorption data at different temperatures, and the results indicated that the Langmuir model simulated the data better than the Freundlich isotherm model. The thermodynamic parameters (∆G°, ∆S°, ∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Co(II) on Na-attapulgite was an endothermic and spontaneous process. The results suggest that the attapulgite sample is a suitable material in the preconcentration and solidification of radiocobalt from large volumes of aqueous solutions.     

Removal of malachite green from dye wastewater using mesoporous carbon adsorbent

Mesoporous carbon was synthesized for the removal of a cationic dye malachite green (MG) from aqueous solution. The studies were carried out under various experimental conditions such as contact time, dye concentration, adsorption dose and pH to assess the potentiality of mesoporous carbon for the removal of malachite green dye from wastewater. The sorption equilibrium was reached within 30 min. In order to determine the adsorption capacity, the sorption data were analyzed using linear form of Langmuir and Freundlich equation. Langmuir equation showed higher conformity than Freundlich equation. More than 99% removal of MG was reached at the optimum pH value of 8.5. From kinetic experiments, it was concluded that the sorption process followed the pseudo-first-order kinetic model. This study showed that mesoporous carbon can be recommended as an excellent adsorbent at high pH values.     

Investigation of the specific adsorption of sulfate ions on powdered TiO2

The specific adsorption of radiolabeled sulfate ions from perchlorate supporting electrolyte onto TiO2 powder (anatase) has been investigated. The pH and concentration dependence of the adsorption was determined. Langmuir-like adsorption behavior similar to that on other oxides was found. From the pH dependence it follows that the protonation of the surface should precede the specific anion adsorption. The results obtained are compared with those reported for TiO2 bulk electrodes.