Sorption of 63Ni(II) to montmorillonite as a function of pH, ionic strength, foreign ions and humic substances

Different kinds of clay minerals have been studied extensively in the removal of radionuclides from large volumes of aqueous solutions because of their high sorption capacity. Herein, the Na-montmorillonite was characterized by using XRD and FTIR in detail. The sorption of ⁶³Ni(II) from aqueous solution to montmorillonite as a function of pH, ionic strength, foreign ions, humic substances and temperature was studied by batch technique. The sorption of ⁶³Ni(II) on montmorillonite achieved equilibration quickly. The sorption of ⁶³Ni(II) to montmorillonite was strongly dependent on pH, and dependent on ionic strength at low pH and independent of ionic strength at high pH values. The sorption of ⁶³Ni(II) on montmorillonite was enhanced at low pH in the presence of humic acid (HA), while a negative effect of HA on ⁶³Ni(II) sorption was found at high pH values. At low pH values, the sorption of ⁶³Ni(II) was attributed to outer-sphere surface complexation or ion exchange, whereas the sorption was dominated by inner-sphere surface complexation at high pH values. The montmorillonite sample is a suitable material in the preconcentration of radionuclides from large volumes and the material can be used as backfill material in nuclear waste repository.     

Sorption and desorption of Co(II) on montmorillonite in presence and absence of fulvic acid

Sorption and desorption of Co(II) on montmorillonite under ambient conditions as a function of pH, ionic strength and fulvic acid are studied by batch technique. The results indicate that the sorption of Co(II) is dependent on pH, and ionic strength. The sorption-desorption hysteresis is found in the desorption tests. Surface complexation is considered as the main sorption mechanism of Co(II) on montmorillonite. The presence of fulvic acid (FA) enhances the sorption of Co(II) on montmorillonite. Montmorillonite is considered as a promising candidate for the solidification and pre-concentration of Co(II) from large volume of solutions.     

Sorption of Th(IV) from aqueous solution to GMZ bentonite: effect of pH, ionic strength, fulvic acid and electrolyte ions

Bentonite has been studied extensively because of its strong sorption and complexation ability. In this study, GMZ bentonite (China) was studied as a potential sorbent for the removal of Th(IV) from aqueous solutions. The results indicate that the sorption of Th(IV) is strongly dependent on pH and ionic strength at pH <5, and is independent of ionic strength at pH >5. Outer-sphere surface complexation or ion exchange in inter-layer sites of the montmorillonite fraction of the GMZ bentonite may be the main sorption mechanism of Th(IV) onto GMZ bentonite at low pH values, whereas the sorption of Th(IV) at pH >5 is mainly dominated by inner-sphere surface complexation or surface precipitation. The presence of soil fulvic acid has a positive influence on the sorption of Th(IV) on GMZ bentonite at pH <5. The competition between Th(IV) with aqueous or surface adsorbed cation ions (e.g., herein Li⁺, Na⁺ and K⁺) and surface functional groups of GMZ bentonite is important for Th(IV) sorption on GMZ bentonite. The results of high sorption of Th(IV) suggest that the GMZ bentonite is a suitable backfill material in nuclear waste management.     

Solution chemistry effects on sorption behavior of 109Cd(II) on Ca-montmorillonite

The sorption of radiocadmium on Ca-montmorillonite as a function of contact time, pH, ionic strength, foreign ions, humic acid (HA) and fulvic acid (FA) was studied using batch technique. The results demonstrated that the sorption of Cd(II) was dependent on ionic strength at pH < 9, and was independent of ionic strength at pH > 9. Outer-sphere surface complexation and/or ion exchange were the main mechanism of Cd(II) sorption on Ca-montmorillonite at low pH, whereas the sorption at high pH was mainly dominated via inner-sphere surface complexation. The sorption of Cd(II) on Ca-montmorillonite was dependent on foreign ions at low pH values, but was independent of foreign ions at high pH values. A positive effect of HA/FA on Cd(II) sorption was found at low pH values, whereas a negative effect was observed at high pH values. The thermodynamic parameters (i.e., ??H ⁰, ??S ⁰, ??G ⁰) were calculated from the temperature dependent sorption isotherms, and the results indicated that the sorption process of Cd(II) on Ca-montmorillonite was spontaneous and endothermic.     

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.     

Uptake properties of Eu(III) on Na-attapulgite as a function of pH, ionic strength and temperature

Herein, the sorption properties of Eu(III) on Na-attapulgite were performed by using batch sorption experiments under different experimental conditions, such as contact time, pH, ionic strength, humic acid and temperatures. The results indicated that the sorption of Eu(III) on Na-attapulgite was strongly dependent on pH and temperature. At low pH values, the sorption of Eu(III) was influenced by ionic strength, whereas the sorption was not affected by ionic strength at high pH values. The sorption of Eu(III) was mainly dominated by ion exchange or outer-sphere surface complexation at low pH values, and by inner-sphere surface complexation or surface precipitation at high pH values. The sorption of Eu(III) onto Na-attapulgite increased with increasing temperature. The Langmuir and Freundlich models were applied to simulate the sorption isotherms, and the results indicated that the Langmuir model simulated the sorption isotherms better than the Freundlich model. The thermodynamic parameters (∆G ^o, ∆S ^o, ∆H ^o) were calculated from the temperature dependent sorption isotherms at 293, 313 and 333 K, respectively, and the results indicated that the uptake of Eu(III) on Na-attapulgite was an endothermic and spontaneous process. The results of high Eu(III) sorption capacity on Na-attapulgite suggest that the attapulgite is a suitable material for the preconcentration and immobilization of Eu(III) ions from large volumes of aqueous solutions.     

Sorption mechanism of U(VI) on a reference montmorillonite: Binding to the internal and external surfaces

Batch type experiments of U(VI) sorption on a reference montmorillonite(SWy-2) were carried out over wide ranges of pH, ionic strength, and totalU(VI) concentration. The influences of these factors on the sorption behaviorof U(VI) were analyzed to gain a macroscopic understanding of the sorptionmechanism. The sorption of U(VI) on montmorillonite showed a distinct dependencyon ionic strength. When it was low (0.01 or 0.001M), almost all of the totalU(VI) was sorbed over the whole pH range studied, therefore, the dependencyon pH was not clear. But the sorption of U(VI) on montmorillonite showed asorption pH edge in the high ionic strength condition (0.1M), like those onother clay minerals, kaolinite and chlorite. A mechanistic model was establishedby considering the mineral structure of montmorillonite together with ourprevious EPR result, which successfully explained the U(VI) sorption on montmorilloniteover the whole range of experimental conditions. The model describes the U(VI)sorption on montmorillonite as simultaneous and competitive reactions of ionexchange and surface complexation, whose relative contribution to the totalsorption depends on pH and ionic strength. At low ionic strength and low pHconditions, ion exchange was the dominant mechanism for U(VI) sorption onmontmorillonite. At high ionic strength and high pH conditions, surface complexationwas the dominant     

Application of NKF-6 zeolite for the removal of U(VI) from aqueous solution

To better understand the application of NKF-6 zeolite as an adsorbent for the removal of U(VI) from radionuclides and heavy metal ions polluted water, herein, NKF-6 zeolite was employed to remove U(VI) at different experimental conditions. The influence of solid/liquid ratio, contact time, pH, ionic strength, humic substances and temperature on sorption of U(VI) to NKF-6 zeolite was investigated using batch technique under ambient conditions. The experimental results demonstrated that the sorption of U(VI) on NKF-6 zeolite was strongly dependent on pH. The sorption property of U(VI) was influenced by ionic strength at pH < 7.0, whereas was independent of ionic strength at pH > 7.0. The presence of fulvic acid or humic acid promoted the sorption of U(VI) on NKF-6 zeolite at low pH values while restrained the sorption at high pH values. The thermodynamic parameters (i.e., ΔS ⁰, ΔH ⁰, and ΔG ⁰) calculated from the temperature-dependent sorption isotherms demonstrated that the sorption process of U(VI) on NKF-6 zeolite was endothermic and spontaneous. At low pH values, the sorption of U(VI) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on NKF-6 zeolite surfaces, while inner-sphere surface complexation was the main sorption mechanism at high pH values. From the experimental results, one can conclude that NKF-6 zeolite can be used as a potential adsorbent for the preconcentration and solidification of U(VI) from large volumes of aqueous solutions.     

Sorption of uranyl ions on silica: Effects of contact time, pH, ionic strength, concentration and phosphate

The sorption of UO₂ ²⁺ and phosphate on silica were simultaneously studied. The effect of contact time between the solid phase and aqueous solution, pH and ionic strength on the UO₂ ²⁺ sorption in the absence and the presence of phosphate was investigated. The effect of contact time between the solid phase and aqueous solution, pH and ionic strength on the phosphate sorption was investigated too. The isotherms of UO₂ ²⁺ and phosphate sorption at different pH values were determined. It was found that as compared with the sorption in the absence of phosphate, the sorption of UO₂ ²⁺ on silica in the presence of phosphate is increased at low pH and decreased at high pH; the abruptly increased with increasing pH in the pH range 3-6; the sorption is gradually decreased with increasing pH in the pH range 2-12; the sorption insensitive and the sorption of phosphate is sensitive to ionic strength.     

Sorption of radiocobalt(II) onto Ca-montmorillonite: effect of contact time, solid content, pH, ionic strength and temperature

In this paper, the sorption of Co(II) from aqueous solution to Ca-montmorillonite was studied under ambient conditions by using batch technique. The effects of contact time, solid content, pH, ionic strength and temperature on the sorption of Co(II) to Ca-montmorillonite was also investigated. The results indicated that the sorption of Co(II) was strongly dependent on pH values. The sorption was dependent on ionic strength at low pH values, but independent of ionic strength at high pH values. Outer-sphere surface complexes were formed on the surface of Ca-montmorillonite at low pH values, whereas inner-sphere surface complexes were formed at high pH values. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms of Co(II) at three different temperatures. The thermodynamic parameters (ΔH ⁰, ΔS ⁰ and ΔG ⁰) were calculated from the temperature dependent sorption isotherms, and the results indicated that the sorption reaction of Co(II) to Ca-montmorillonite was an endothermic and spontaneous process. The high sorption capacity of Co(II) on Ca-montmorillonite suggests that the Ca-montmorillonite is a suitable material for the preconcentration and solidification of radiocobalt from aqueous solutions.     

Effect of pH,foreign ions and temperature on radionickel sorption onto bentonite from Inner Mongolia,China

The development of nuclear power releases large amounts of radionuclides into the natural environment. Herein, the sorption of radionuclide ⁶³Ni on bentonite from Gaomiaozi county (Inner Mongolia, China) at different experimental conditions such as pH, contact time, ionic strength, foreign cations and anions, and temperatures were investigated by using batch technique. The results indicated that the sorption of ⁶³Ni on the bentonite was quickly at first contact time and then increased slowly with increasing contact time. The sorption of ⁶³Ni was strongly dependent on ionic strength at low pH values and independent of ionic strength at high pH values. The sorption of ⁶³Ni on bentonite was mainly dominated by outer-sphere surface complexation or ion exchange at low pH values, whereas inner-sphere surface complexation was the main sorption mechanism at high pH values. The Langmuir, Freundlich, and D–R models were applied to simulate the sorption isotherms of ⁶³Ni at three different temperatures, and the thermodynamic parameters (i.e., ΔH°, ΔS° and ΔG°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of ⁶³Ni on bentonite was an endothermic and spontaneous process. Experimental results indicate that the bentonite is a suitable material for the preconcentration and solidification of ⁶³Ni from large volume of solutions in radionickel pollution cleanup.     

Sorption/desorption of radionickel on/from Na-montmorillonite: kinetic and thermodynamic studies

In this work, Na-montmorillonite was used as a novel adsorbent for the sorption of Ni(II) from aqueous solutions. The sorption and desorption of Ni(II) on Na-montmorillonite was investigated as the function of pH, ionic strength, Ni(II) concentrations and temperature. The results indicated that the sorption of Ni(II) on Na-montmorillonite was strongly dependent on pH, ionic strength and temperature. The sorption of Ni(II) increases slowly from 22.1 to 51.4% at pH range 2–6.5, abruptly at pH 6.5–9, and at last maintains high level with increasing pH at pH > 9 in 0.1 mol/L NaNO₃ solutions. The Ni(II) kinetic sorption on Na-montmorillonite was fitted by the pseudo-second-order model better than by the pseudo-first-order model and the experimental data implies that Ni(II) sorption on montmorillonite were mainly controlled by the film diffusion mechanism. The Langmuir, Freundlich and D–R models were used to simulate the sorption data at three different temperatures (298.15, 318.15 and 338.15 K) and the results indicated that Langmuir model simulates the experimental data better than Freundlich and D–R models. The sorption–desorption isotherm of Ni(II) on montmorillonite suggested that the sorption is irreversible. The irreversible sorption of Ni(II) on montmorillonite indicates that montmorillonite can be used to pre-concentration and solidification of Ni(II) from large volumes of solution and to storage Ni(II) ions stably.     

Eu(Ⅲ)在蒙脱石上的吸附及碳酸根和磷酸根对其吸附的影响

锕系核素在处置库围岩和缓冲回填材料中的吸附和迁移参数是处置库安全评价的重要数据模块之一，而Eu(Ⅲ)由于其与三价锕系元素An(Ⅲ)相似的离子半径和化学性质常被用于模拟三价锕系元素的化学行为。本文通过批式吸附实验研究了固液比、接触时间、离子强度、pH、碳酸根及磷酸根等对Eu(Ⅲ)在蒙脱石上吸附的影响，重点关注了吸附机理和表面种态。研究结果表明，低pH时Eu(Ⅲ)在蒙脱石上的吸附方式为外层配位吸附，近中性时为内层配位吸附，高pH时则以表面沉淀的方式被吸附。离子强度的增大对Eu(Ⅲ)在低pH时的吸附产生抑制作用。低pH时碳酸根对Eu(Ⅲ)吸附的影响不明显，但在高pH时其会改变Eu(Ⅲ)的表面吸附种态。尽管磷酸根本身的吸附非常弱，但磷酸根会显著增强Eu(Ⅲ)的吸附。X射线光电子能谱结果和磷酸根吸附实验说明Eu(Ⅲ)在蒙脱石表面上形成了EuPO₄沉淀。本工作研究了蒙脱石/Eu(Ⅲ)二元体系和蒙脱石/Eu(Ⅲ)/阴离子三元体系的吸附行为，并用光谱技术探究了其吸附种态，为理解三价锕系核素在蒙脱石上的吸附行为提供了重要参考。     

Interaction of U(VI) with Na-attapulgite in the presence and absence of humic acid as a function of pH, ionic strength and temperature

The interaction of U(VI) with Na-attapulgite was studied by using batch technique at different experimental conditions. The effect of contact time, solid content, pH, ionic strength and temperature on the sorption of U(VI) onto Na-attapulgite in the presence and absence of humic acid was also investigated. The results showed that the sorption of U(VI) on Na-attapulgite achieved sorption equilibrium quickly. Sorption of U(VI) on Na-attapulgite increased quickly with increasing pH at pH < 6.5, and then decreased with pH increasing at pH > 6.5. The sorption curves were shifted to left in low NaClO₄ solutions as compared those in high NaClO₄ solutions. The sorption was strongly dependent on pH and ionic strength. The sorption was dominated by ion exchange or outer-sphere surface complexation at low pH values, and by inner-sphere surface complexation or surface precipitation at high pH values. The thermodynamic parameters (i.e., ΔH ⁰, ΔS ⁰, and ΔG ⁰) for the sorption of U(VI) were calculated from the temperature dependent sorption isotherms, and the results suggested that the sorption reaction was an endothermic and spontaneous process. The Na-attapulgite is a suitable material in the removal and preconcentration of U(VI) from large volumes of aqueous solutions in nuclear waste management.     

Sorption and desorption of Eu(III) on alumina

Summary Effects of ionic strength and of fulvic acid on the sorption of Eu(III) on alumina were investigated by using a batch technique. The experiments were carried out at T=25±1 °C, pH 4-6 and in the presence of 1M NaCl. The results indicate that sorption isotherms of Eu(III) are linear at low pH values. The sorption-desorption of Eu(III) on alumina at pH 4.4 is reversible, but a sorption-desorption hysteresis is found at pH 5.0. Fulvic acid has an obvious positive effect on the sorption of Eu(III) on alumina at low pH values. The migration of Eu(III) in alumina was studied by using column experiments and ^152+154Eu(III) radiotracer at pH 3.8. For column experiments, Eu(III) sorbed on alumina can be desorbed completely from the solid surface at low pH values. The findings are relevant to the evaluation of lanthanide and actinide ions in the environment.     

Removal of Co(II) from aqueous solution by using hydroxyapatite

Herein, hydroxyapatite (HAP) was prepared by aqueous precipitation technique and was characterized by using FT-IR and XRD to determine its chemical functional groups and micro-structure. The removal of cobalt from aqueous solution to HAP was studied by batch technique as a function of various environmental parameters such as contact time, pH, ionic strength, foreign ions, fulvic acid (FA), and temperature under ambient conditions. The results indicated that the sorption of Co(II) on HAP was strongly dependent on pH and ionic strength. The presence of FA enhanced the sorption of Co(II) on HAP at low pH, whereas reduced Co(II) sorption on HAP at high pH. The Langmuir, Freundlich and D-R models were used to simulate the sorption isotherms at three different temperatures of 303.15, 323.15 and 343.15 K. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent sorption isotherms indicated that the sorption process of Co(II) on HAP was spontaneous and endothermic. The sorption of Co(II) was dominated by outer-sphere surface complexation and ion exchange at low pH, whereas inner-sphere surface complexation or surface precipitation was the main sorption mechanism at high pH values. The results suggest that the HAP is a suitable material in the preconcentration and solidification of Co(II) from large volumes of aqueous solutions.     

Sorption behavior of selenide on montmorillonite

Batch sorption experiments were performed to investigate the sorption mechanism of Se on montmorillonite under reducing conditions in deep geological environments. Based on E_h–pH diagrams and ultraviolet–visible spectra, Se was dissolved as selenide (Se(–II)) anions under the experimental conditions. The distribution coefficients (K_d; m³ kg^?1) of Se(–II) indicated ionic strength independence and slight pH dependence. The K_d values of Se(–II) were higher than those of Se(IV), which also exists as an anionic species. X-ray absorption near edge spectroscopy showed that the oxidation state of Se-sorbed on montmorillonite was zero even though selenide remained in the solution. These results suggest that Se(–II) was oxidized and precipitated on the montmorillonite surface. Therefore, it is implied that a redox reaction on the montmorillonite surface contributed to high K_d values for Se(–II).

     

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.     

Sorption Studies of Cobalt(II) on Colloidal Hematite Using Potentiometry and Radioactive Tracer Technique

The sorption of Co(II) on colloidal hematite was studied as a function of pH, ionic strength, and Co(II) concentration. Two different techniques were used, yielding two different sets of information: (i) potentiometric titrations that provide information on the number of protons released as a function of pH owing to the sorption of Co(II) and (ii) measurement of the amount of cobalt sorbed on the surface as a function of pH using a radioactive tracer, (60)Co. At low Co(II) concentrations (10(-8) M), the sorption was found to be independent of ionic strength but there seems to be a weak ionic strength dependence at higher Co(II) concentrations (10(-4) M). The adsorption edge moved to higher pH with increasing Co(II) concentration. For the high Co(II) concentration, the number of protons released per cobalt sorbed increased from zero to approximately 1.5. The basic charging properties of hematite were modeled with four different surface complexation models. The 1-pK Basic Stern Model (BSM), with binding of electrolyte ions to the Stern plane, seems to be the most reasonable model if the ambition is to describe experimental data at different ionic strengths. The sorption of cobalt was modeled with the 1-pK BSM. By introducing a low concentration of high affinity surface sites for cobalt sorption it was possible to model the sorption in very wide cobalt concentrations, ranging from 10(-8) M to 10(-4) M. Copyright 2000 Academic Press.     

Impact of environmental conditions on the removal of Ni(II) from aqueous solution to bentonite/iron oxide magnetic composites

The sorption of radionuclide ⁶³Ni(II) on bentonite/iron oxide magnetic composites was investigated by batch technique under ambient conditions. The effect of contact time, solid content, pH, coexistent electrolyte ions, fulvic acid, and temperature on Ni(II) sorption to bentonite/iron oxide magnetic composites was examined. The results demonstrated that the sorption of Ni(II) was strongly dependent on pH and ionic strength at pH <8.0, and was independent of pH and ionic strength at high pH values. The sorption of Ni(II) was dominated by outer-sphere surface complexation or ion exchange at low pH, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The experimental data were well fitted by Langmuir model. The thermodynamic parameters (∆G°, ∆S°, ∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Ni(II) on bentonite/iron oxide magnetic composites was an endothermic and spontaneous processes. The results show that bentonite/iron oxide magnetic composites are promising magnetic materials for the preconcentration and separation of radionickel from aqueous solutions in environmental pollution.