Influence of contact time, pH, soil humic/fulvic acids, ionic strength and temperature on sorption of U(VI) onto MX-80 bentonite

The sorption of U(VI) from aqueous solution on MX-80 bentonite was studied as a function of contact time, pH, ionic strength, solid contents, humic acid (HA), fulvic acid (FA) and temperature under ambient conditions using batch technique. The results indicate that sorption of U(VI) on MX-80 bentonite is strongly dependent on pH and ionic strength. The removal of U(VI) to MX-80 bentonite is rather quick and the kinetic sorption data is simulated well by a pseudo-second-order rate equation. The presence of HA enhances the sorption of U(VI) on MX-80 bentonite obviously, but the influence of FA on U(VI) sorption is not obvious. The thermodynamic parameters (ΔH ⁰, ΔS ⁰, and ΔG ⁰) for the sorption of U(VI) calculated from temperature dependent sorption suggest that the sorption reaction is endothermic and spontaneous.     

Sorption of Th(IV) on MX-80 bentonite: effect of pH and modeling

MX-80 bentonite was characterized by XRD and FTIR in detail. The sorption of Th(IV) on MX-80 bentonite was studied as a function of pH and ionic strength in the presence and absence of humic acid/fulvic acid. The results indicate that the sorption of Th(IV) on MX-80 bentonite increases from 0 to 95% at pH range of 0–4, and then maintains high level with increasing pH values. The sorption of Th(IV) on bentonite decreases with increasing ionic strength. The diffusion layer model (DLM) is applied to simulate the sorption of Th(IV) with the aid of FITEQL 3.1 mode. The species of Th(IV) adsorbed on bare MX-80 bentonite are consisted of “strong” species o \textYOHTh^{4 +} \equiv {\text{YOHTh}}^{4 + } at low pH and “weak” species o \textXOTh(OH)₃ \equiv {\text{XOTh(OH)}}_{3} at pH > 4. On HA bound MX-80 bentonite, the species of Th(IV) adsorbed on HA-bentonite hybrids are mainly consisted of o \textYOThL₃ \equiv {\text{YOThL}}_{3} and o \textXOThL₁ \equiv {\text{XOThL}}_{1} at pH < 4, and o \textXOTh(OH)₃ \equiv {\text{XOTh(OH)}}_{3} at pH > 4. Similar species of Th(IV) adsorbed on FA bound MX-80 bentonite are observed as on FA bound MX-80 bentonite. The sorption isotherm is simulated by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models, respectively. The sorption mechanism of Th(IV) on MX-80 bentonite is discussed in detail.     

A comparative study of Pb<Superscript>2+</Superscript> sorption onto MX-80 bentonite,LA bentonite, γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and SiO<Subscript>2</Subscript>

Humic substances have attracted great interest in the investigation of metal ion behavior in the environment because of their special properties. Sorption and complexation of Pb²⁺ on MX-80 bentonite, LA bentonite, alumina and silica as a function of pH were studied in the presence and absence of fulvic acid (FA). The experiments were carried out in 0.01M and 0.001M NaNO₃ solutions under ambient conditions. The results indicate that sorption of Pb²⁺ on the solid samples is strongly dependent on pH and FA. The sorption of Pb²⁺ is not influenced drastically by ionic strength. The nature of minerals/oxides, nature of humic substances and the composition of the solution are important factors in the behavior of metal ions in the environment. The results also indicate that FA has a positive effect on Pb²⁺ sorption at low and a negative effect at high pH values, and the results are discussed in the comparative complexation between FA-Pb²⁺ and Pb²⁺-minerals.     

Sorption and diffusion of 90Sr2+in compacted bentonite investigated by a capillary method

Summary The effects of bentonite density and fulvic acid on the sorption and diffusion of ⁹⁰Sr²⁺in compacted bentonite were investigated by using a capillary method. The experiments were carried out at pH 7.0±0.1 in the presence of 0.01M NaClO₄. The results suggest that the sorption and diffusion of ⁹⁰Sr²⁺in compacted bentonite decreases with increasing the density of compacted bentonite. The presence of FA enhances the sorption of Sr²⁺, but reduces the diffusion of Sr²⁺in compacted bentonite. The porosity of the compacted bentonite plays an important role in the sorption and diffusion behavior of ⁹⁰Sr²⁺. Using the calculated effective diffusion coefficients the long-term relative concentration distribution of strontium was evaluated in compacted bentonite.     

Modeling of radionickel sorption on MX-80 bentonite as a function of pH and ionic strength

MX-80 bentonite was detected using acid-based titration, XRD and FTIR in detail. The sorption behavior of 63Ni(Ⅱ) from aqueous solution to MX-80 bentonite was investigated as a function of solid content, ionic strength and pH by using batch technique. The experimental data of 63Ni(Ⅱ) sorption on MX-80 bentonite was obtained using the diffuse layer model (DLM) with the aid of FITEQL 3.1 program. The results indicated that the sorption of 63Ni(Ⅱ) on MX-80 bentonite was mainly dominated by surface complexation...     

A thermodynamic surface model for caesium sorption on bentonite

Caesium sorption on Wyoming bentonite MX-80 has been studied in solutions of NaCl, KCl, MgCl₂, CaCl₂, NaNO₃ and Ca (NO₃)₂ of concentrations varying between 0.025 and 1 mol/L, as well as in a weakly saline (I=0.004 ml/L) and a strongly saline (I=0.46 mol/L) natural groundwater. These experiments have been used to derive a thermodynamic model for the interaction of caesium with the bentonite surface in accordance with a surface chemical model, including acid/base reactions developed recently for montmorillonite. The sorption behaviour of caesium on bentonite can be described, within the experimental and model uncertainties, in terms of a one-site ion exchange model. The ion exchange constant obtained for the reaction NaX+Cs⁺CsX+Na⁺ (where X represents the ion exchange sites on montmorillonite) is log₁₀K⁰_ex=1.6. Impurities in the bentonite, influencing the concentrations of competing cations, such as Na⁺, K⁺, Mg²⁺ and Ca²⁺, have a crucial impact on the sorption of caesium. This impact can be adequately quantified with the present model. The model predictions compare well with sorption data published in the open literature on both Wyoming bentonite MX-80 and other types of bentonite. Distribution coefficients from the literature obtained from both batch and diffusion experiments and varying over four orders of magnitude are reproduced and explained successfully by the model.     

Impact of environmental conditions on the sorption behavior of UO<Subscript>2</Subscript><Superscript>2+</Superscript> onto attapulgite studied by batch experiments

The sorption of UO₂ ²⁺ from aqueous solution on attapulgite was investigated as a function of contact time, solid content, pH, ionic strength, foreign ions, humic acid (HA), and fulvic acid (FA) under ambient conditions by using batch technique. The attapulgite sample was characterized by XRD and FTIR in detail. The results indicated that the sorption of UO₂ ²⁺ was strongly dependent on pH and ionic strength. The sorption of UO₂ ²⁺ on attapulgite increased quickly with rising pH at pH < 6.5, and decreased with increasing pH at pH > 6.5. The presence of HA or FA enhanced the sorption of UO₂ ²⁺ on attapulgite obviously at low pH because of the strong complexation of surface adsorbed HA/FA with UO₂ ²⁺ on attapulgite surface. Sorption of UO₂ ²⁺ on attapulgite was mainly dominated by ion-exchange or outer-sphere surface complexation at low pH values, but by inner-sphere surface complexation at high pH values. The results indicate that attapulgite is a very suitable adsorbent for the preconcentration and solidification of UO₂ ²⁺ from large volumes of aqueous solutions because of its negative surface charge and large surface areas.     

Effect of pH,ionic strength,fulvic acid and humic acid on sorption of Th(IV) on Na-rectorite

Sorption of Th(IV) on Na-rectorite as a function of pH, ionic strength, soil humic acid (HA) and fulvic acid (FA) are studied under ambient conditions by using a batch technique. The results indicate that the sorption of Th(IV) on Na-rectorite is not only dependent on medium pH values, but also dependent on medium ionic strength and humic substances. Surface complexation and cation competition exchange account for Th(IV) sorption on Na-rectorite. The sorption of Th(IV) on Na-rectorite decreases with the increase on the concentration of NaNO₃, Mg(NO₃)₂ and Ca(NO₃)₂, and increases with the increasing amount of HA/FA in the suspension/adsorbed on rectorite. Soil HA/FA enhances the sorption of Th(IV) on rectorite at medium pH<4 drastically, but the presence of FA reduces the sorption of Th(IV) at medium pH>6, and HA has no effect on Th(IV) sorption at medium pH>6. An interpretation for the results is attempted, considering the occurrence of different sorption mechanisms.     

Adsorption of nickel on synthetic hydroxyapatite from aqueous solutions

The sorption of nickel on synthetic hydroxyapatite was investigated using a batch method and radiotracer technique. The hydroxyapatite samples used in experiments were a commercial hydroxyapatite and hydroxyapatite of high crystallinity with Ca/P ratio of 1.563 and 1.688, respectively, prepared by a wet precipitation process. The sorption of nickel on hydroxyapatite was pH independent ranging from 4.5 to 6.5 as a result of buffering properties of hydroxyapatite. The adsorption of nickel was rapid and the percentage of Ni sorption on both samples of hydroxyapatite was >98 % during the first 15–30 min of the contact time for initial Ni²⁺ concentration of 1 × 10^?4 mol dm^?3. The experimental data for sorption of nickel have been interpreted in the term of Langmuir isotherm and the value of maximum sorption capacity of nickel on a commercial hydroxyapatite and hydroxyapatite prepared by wet precipitation process was calculated to be 0.184 and 0.247 mmol g^?1, respectively. The sorption of Ni²⁺ ions was performed by ion-exchange with Ca²⁺ cations on the crystal surface of hydroxyapatite under experimental conditions. The competition effect of Co²⁺ and Fe²⁺ towards Ni²⁺ sorption was stronger than that of Ca²⁺ ions. NH₄ ⁺ ions have no apparent effect on nickel sorption.     

Sorption of thorium(IV) from aqueous solutions by graphene oxide

Graphene oxide (GO) is one of the most important carbon nano-materials. In this paper, GO was synthesized from flake graphite and characterized by transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The sorption of Th(IV) on GO was investigated as a function of contact time, solid-to-liquid ratio, pH, ionic strength, and in the presence of fulvic acid (FA) and humic acid (HA) by batch experiments. The sorption percentage of Th(IV) on GO decreased with increasing ionic strength and decreasing solid-to-liquid ratio. The sorption edge of Th(IV) in the presence of FA/HA is much lower than that in the absence of FA/HA. Furthermore, the sorption processes of Th(IV) can be described by a pseudo-second order rate model. Based on the Langmuir model, the maximum sorption capacities (Cs_max) of Th(IV) were about 5.80 × 10^?4 mol/L. From thermodynamic investigation, sorption of Th(IV) on GO is spontaneous and endothermic in nature. The rapid sorption rate and high sorption capacity suggest that GO is a promising adsorbent for Th(IV).     

Sorption of nickel on chitosan

The sorption of nickel on chitosan was studied using batch method. As a tracer was used radioisotope ⁶³Ni. The effect of pH and contact time to reach sorption equilibrium was investigated. During the sorption of Ni²⁺ ions occur mostly to ion-exchange reactions on the surface of sorbent. The time to reach the sorption equilibrium of nickel on chitosan was 14 h. The percentage of sorption after 14 h achieved the value of 84 %. On the sorption of nickel used solutions with initial pH in the range from 3.9 to 8.1. In the monitored range of pH after 24 h of contact was the sorption of nickel on chitosan >97 %. The sorption of nickel was reduced by increasing concentrations of Ni²⁺ ions in the solution. The experimental data for sorption of nickel have been interpreted in the term of Langmuir isotherm and the value of maximum sorption capacity of nickel on chitosan was 2.71 × 10^?3 mol g^?1.     

A thermodynamic surface model for caesium sorption on bentonite

Caesium sorption on Wyoming bentonite MX-80 has been studied in solutions of NaCl, KCl, MgCl(2), CaCl(2), NaNO(3) and Ca (NO(3))(2) of concentrations varying between 0.025 and 1 mol/L, as well as in a weakly saline (I=0.004 ml/L) and a strongly saline (I=0.46 mol/L) natural groundwater. These experiments have been used to derive a thermodynamic model for the interaction of caesium with the bentonite surface in accordance with a surface chemical model, including acid/base reactions developed recently for montmorillonite. The sorption behaviour of caesium on bentonite can be described, within the experimental and model uncertainties, in terms of a one-site ion exchange model. The ion exchange constant obtained for the reaction NaX+Cs(+) left arrow over right arrow CsX+Na(+) (where X represents the ion exchange sites on montmorillonite) is log(10) K(0)(ex)=1.6. Impurities in the bentonite, influencing the concentrations of competing cations, such as Na(+), K(+), Mg(2+) and Ca(2+), have a crucial impact on the sorption of caesium. This impact can be adequately quantified with the present model. The model predictions compare well with sorption data published in the open literature on both Wyoming bentonite MX-80 and other types of bentonite. Distribution coefficients from the literature obtained from both batch and diffusion experiments and varying over four orders of magnitude are reproduced and explained successfully by the model.     

Comparison of Linear and Nonlinear Forms of Isotherm Models for Strontium Sorption on a Sodium Bentonite

Sorption on bentonite will play an important role in retarding the migration of radionuclides from a waste repository. Bentonite is characterized by low permeability, water swelling capability and excellent sorption potential for cationic radionuclides. To correctly assess the sorption potential of radionuclides on bentonite is essential for the development of predictive migration models. The sorption isotherm model is usually used to describe the sorption behavior and assess the sorption potential of radionuclides on bentonite. However, there are few studies to investigate the feasibility of isotherm models for the sorption of radionuclides on bentonite. Thus, in this study, we compared the goodness-of-fit of linear and nonlinear forms of two common isotherm models, Langmuir and Freundlich equations. The experimental sorption isotherms of strontium (Sr) on Wyoming bentonite, MX-80, were used for illustration. The results showed that the nonlinear forms of Langmuir and Freundlich isotherm models are more suitable for fitting the experimental sorption isotherms of Sr on MX-80 than are the linear forms. Thus, the nonlinear forms of isotherm models should be primarily adopted to fit experimental isotherms. On the other hand, we also found that the goodness-of-fit of Langmuir model is better than that of Freundlich model. Moreover, based on the theoretical assumptions of Langmuir isotherm model, the parameters M and K _L represent the sorption capacity and affinity, respectively. One can use the values of M and K _L , obtained from fitting the experimental isotherms, to assess the sorption potential of radionuclides in bentonite. Thus, we suggested that the Langmuir isotherm model is more useful for investigating the sorption behavior of radionuclides on bentonite.     

SYNTHESIS OF MACROPOROUS HUMIC ACID RESINS AND THEIR CHELATING PROPERTIES FOR HEAVY METAL IONS

Macroporous HA resins (HAR) can be prepared in pearl form by grafting HA onto crosslinked PS through azo or through ester and / or ether linkages. At pH 13 and the HA / PSNH_2 weight ratio 0.7—1.0, PSN_2~+-Cl~-couples with HA and results in the formation of a7o-type HA resin (HAR-A), which shows good adsorbility towards heavy metal ions. The Cu~(2+) sorption capacity of ester / ether type humic acid resin (HAR-E) is increased by lengthening the reaction time of HA and PSCH_2Cl. The structure of HAR is discussed on the basis of the IR spectra. The sorption capacity of HAR-A is 1.01 mmol / g for Cd~(2+) and 0.6—0.53 mmol/g for Ni~(2+), Mn~(2+), Cu~(2+), Co~(3+) and Zn~(2+). respectively. The calculated distribution coefficients of heavy metal ions on HAR-A can be arranged in the following order: Cu~(2+)(8.7×10~3)>Cd~(2+) (3.8×10~2)>Zn~(2+)(2.4×10~2)>Ni~(2+)(1.8×10~2)>Mn~(2+)(4.9×10). At pH 6.5, Cu~(2+), Cd~(2+), Ni~(2+), Mn~(2+) can be quantitatively adsorbed by HAR-A and completely eluted with 1N HNO_3. HAR-A can be regenerated and reused. Trace quantities of the above-mentioned heavy metal ions in four samples of the natural occurring water and one sample of the tap water were analyzed by using HAR-A.     

The effects of pH and ionic strength on fulvic acid uptake by chitosan hydrogel beads

The objective of this work is to investigate the effects of pH and ionic strength on the adsorption capacity for fulvic acid (FA) by chitosan hydrogel beads. The results indicated that the sorption amount increased with decreasing pH and increasing ionic strength concentration. The sorption isotherms were well described by using non-linear Langmuir, Freundlich and Redliche–Peterson equation. The adsorption kinetics of FA onto chitosan hydrogel beads could be described by pseudo-second-order rate model. The extent of FA removal in the presence of other ions decreases in the order Ca²⁺ > Mg²⁺ > Na⁺ ≈ K⁺ and Cl⁻ > NO₃⁻ > CO₃²⁻. FTIR along with XPS analyses revealed the amine groups on the beads were involved in the sorption of FA and the organic complex between the protonated amino groups and FA was formed after FA uptake. Sorption mechanisms including electrostatic interaction and surface complexation were found to be involved in the complex sorption of FA on the chitosan hydrogel beads.     

Sorption of Am<Superscript>3+</Superscript> cations on suspended silicate: Effects of pH,ionic strength,complexing anions,humic acid and metal ions

Sorption of tracer Am³⁺ to silicate particles was studied as a function of pcH (4 to 9) and of ionic strength [0.20M to 1.50M (NaClO₄)] at 298 K. The sorption increased with increased pcH from 4 to 6 above which saturation was observed. The insensitivity of Am³⁺ sorption to increased ionic strength indicates inner-sphere complexation with the surface silicate sites. The effects of different complexing anions such as carbonate, acetate, oxalate, phosphate, citrate, EDTA and humic acid, on Am³⁺ sorption were investigated. Synergistic enhancement in Am³⁺ sorption was observed in the presence of phosphate (4≤pcH≤7) and acetate (4≤pcH≤5) ligands at 0.20M NaClO₄. The presence of the other ligands inhibited Am³⁺ sorption in the order: EDTA > citrate > oxalate > carbonate. Am³⁺ sorption in the presence of HA (25.00 mg/l) increased in the pcH range of 4.0 to 5.5, then decreased. Increased ionic strength enhanced Am³⁺ sorption in the presence of 25.00 mg/l HA for 4≤pcH≤9. The sorption increased in the presence of a mixture of HA (25.00 mg/l) and phosphate (1.00·10⁻³M) as compared to that of HA (25.00 mg/l) alone. The presence of Fe³⁺ (1.00·10⁻⁴M) enhanced Am³⁺ sorption at pcH∼4 but suppressed it from pcH of 5 to 9; 1.00·10⁻⁴M of Ca²⁺ and of UO₂²⁺ ions had no effect on the sorption profile. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai -400 085, India.     

Polymer modified biomass of baker's yeast for treating simulated wastewater containing nickel and lead

Baker's yeast was cross‐linked by glutaraldehyde and then modified by grafting with poly(amic acid), which was prepared via reaction of pyromellitic dianhydride (PMDA) and arginine at 50°C. The morphology of the pristine, cross‐linked, and modified biomass was observed by microscope. The presence of poly(amic acid) on the biomass surface was verified by X‐ray photoelectron spectroscopy (XPS) analyses. Due to the high density of the functional groups on the modified biomass surface, the metal adsorption capacity for nickel and lead increased significantly, especially when the carboxylic acid groups were converted into carboxylate ions using NaOH. The adsorption process for nickel and lead adsorption followed the pseudo‐second‐order kinetics. The metal adsorption data were fitted with the Langmuir and Freundlich isotherms with the former having a better fit. Using the Langmuir adsorption isotherm, the maximum uptakes for nickel and lead were found to be 0.848 and 0.980 mmol g^?1 respectively which were about 15 and 11 times higher than the prisitine biomass. In the simulated wastewater containing 0.400 mmol l^?1 of Ni²⁺ and Pb²⁺, the metal adsorption capacity of Ni²⁺ and Pb²⁺ reached 0.365 mmol l^?1 and 0.390 mmol l^?1, respectively. The metal ions loaded biomass was regenerated using Ethylene Diamine Tetraacetic Acid (EDTA) solution and used repeatedly over four cycles with little loss of uptake capacity. Copyright © 2007 John Wiley & Sons, Ltd.     

Investigation of radionuclide <Superscript>63</Superscript>Ni(II) sorption on ZSM-5 zeolite

The sorption of ⁶³Ni(II) from aqueous solution using ZSM-5 zeolite was investigated by batch technique under ambient conditions. ZSM-5 zeolite was characterized by point of zero net proton charge (PZNPC) titration. The sorption was investigated as a function of shaking time, pH, ionic strength, foreign ions, humic acid (HA), fulvic acid (FA) and temperature. The results indicate that the sorption of ⁶³Ni(II) on ZSM-5 zeolite is strongly dependent on pH. The sorption is dependent on ionic strength at low pH, but independent of ionic strength at high pH values. The presence of HA/FA enhances ⁶³Ni(II) sorption at low pH values, whereas reduces ⁶³Ni(II) sorption at high pH values. The sorption isotherms are simulated by Langmuir model very well. The thermodynamic parameters (i.e., ∆H ⁰, ∆S ⁰ and ∆G ⁰) for the sorption of ⁶³Ni(II) are determined from the temperature dependent sorption isotherms at 293.15, 313.15 and 333.15 K, respectively, and the results indicate that the sorption process of ⁶³Ni(II) on ZSM-5 zeolite is spontaneous and endothermic.     

In situ Electrochemical Synthesis of a Composite Film Containing Nickel Hexacyanoferrate and Bentonite Clay for the Sensitive Determination of Acetaminophen and Dopamine

A composite film of nickel hexacyanoferrate (NiHCF) and bentonite (Bt) clay (abbreviated as NiHCF?Bt) is synthesized by an in situ electrochemical method. For this synthesis, nickel ions are immobilized on Bt clay by an ion‐exchange process, equilibrating Bt clay with nickel nitrate. On a glassy carbon electrode (GCE), the nickel ion‐exchanged Bt clay (Ni²⁺?Bt) is coated to get the modified electrode which is represented as GCE/Ni²⁺?Bt. The NiHCF?Bt composite film is prepared on the GCE surface using the GCE/Ni²⁺?Bt and scanning the electrode potentials between ?0.10 to 1.00 V continuously in an aqueous solution containing potassium hexacyanoferrate and potassium chloride. This NiHCF?Bt modified GCE (GCE/NiHCF?Bt) exhibits redox peaks due to the oxidation and reduction of the central metal ion, Fe²⁺. The electro‐generated Fe³⁺ present in the GCE/NiHCF?Bt, electrocatalytically oxidizes a range of drugs like acetaminophen (AC), dopamine (DA), and tyrosine (TY) at decreased overpotentials with high current. This property is advantageously used for the precise quantification of AC, DA, and TY. Sensitivity, limit of detection, and linear calibration range for the determination of AC are found to be 0.20 μA μM^?1 cm^?2, 1.5 μM, and 25.0–1000.0 μM, respectively. Further, the amount of AC present in pharmaceutical products is satisfactorily quantified which demonstrated the use of the NiHCF?Bt composite film in electroanalysis.     

Sorption characteristics of Am(III), Sr(II) and Cs(I) on bentonite and granite

The ability of the back-fill and the host rock materials to take up radioisotopes like ²⁴¹Am, ^85,89Sr and ¹³⁷Cs has been examined as a function of contact time, pH, amount of sorbent, sorbate concentration, and the presence of complementary cations. A batch technique using actual borehole water from the granite formation has been utilized. In general, the uptake of nuclides by bentonite is much higher than that with granite. The sorption order of nuclides on bentonite is Am>Cs>Sr. The presence of complementary cations, Na⁺, K⁺, Ca²⁺ and Mg²⁺ depresses the sorption of Cs and Sr on bentonite. The sorption data have been interpreted in terms of Freundlich and Langmuir isotherm equations. Utilizing the Langmuir isotherm equation, the monolayer capacity, V _m ,and the binding constant, K, have been evaluated. The change in free energy for the sorption of nuclides on bentonite has also been calculated.