Interaction of radionickel with diatomite as a function of pH, ionic strength and temperature

Sequestration of Ni(II) on diatomite as a function of reaction time, pH, ionic strength, foreign ions and temperature were investigated by batch sorption technique. The results indicated that the sorption of Ni(II) on diatomite was quickly in the first contact time of 2 h and then slowly with increasing contact time. The interaction of Ni(II) with diatomite was strongly pH- and ionic strength-dependent at low pH values (i.e., which was dominated by ion exchange or outer-sphere surface complexation), while the pH-dependent and ionic strength-independent sorption at high pH suggested that inner-sphere or multinuclear surface complexation was the main sorption mechanism. With increasing temperature, the sorption of Ni(II) on diatomite increased and the experimental data were well fitted by Langmuir model. The sorption samples at pH 6.8 and 10.0 were also characterized by XPS spectroscopy, and the results suggested that Si atoms also participated in Ni(II) sorption on diatomite. The results are important to evaluate the physicochemical behavior of Ni(II) and other similar radionuclides and heavy metal ions in the environment.     

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.     

Sorption study of radionickel on attapulgite as a function of pH, ionic strength and temperature

Sorption of radionickel on attapulgite is studied as a function of contact time, ionic strength, pH and temperature. The results indicate that the sorption of Ni(II) on attapulgite is strongly ionic strength-dependent at pH <8, and independent of ionic strength at pH >8. Outer-sphere surface complexation or ion exchange contributes to Ni(II) sorption on attapulgite at pH <8, whereas the sorption of Ni(II) is mainly dominated by inner-sphere surface complexation at pH >8. The sorption of Ni(II) on attapulgite increases with increasing temperature, and the thermodynamic parameters (??H ⁰, ??G ⁰ and ??S ⁰) calculated from the temperature dependent sorption isotherms suggest that the sorption of Ni(II) on attapulgite is a spontaneous and endothermic process. The high sorption capacity of attapulgite suggests that attapulgite is a suitable material for the preconcentration and solidification of radionickel from large volumes of aqueous solutions.     

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.     

Impact of environmental conditions on sorption of <Superscript>210</Superscript>Pb(II) to NKF-5 zeolite

The sorption of Pb(II) from aqueous solution using NKF-5 zeolite was investigated by batch technique under ambient conditions. The NKF-5 zeolite sample was characterized by using FTIR and X-ray powder diffraction in detail. The sorption of Pb(II) was investigated as a function of pH, ionic strength, foreign ions, and humic substances. The results indicated that the sorption of Pb(II) on NKF-5 zeolite was strongly dependent on pH. The sorption was dependent on ionic strength at low pH, but independent of ionic strength at high pH. At low pH, the sorption of Pb(II) was dominated by outer-sphere surface complexation and ion exchange with H⁺ on NKF-5 zeolite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. From the experimental results, one can conclude that NKF-5 zeolite has good potentialities for cost-effective preconcentration of Pb(II) from large volumes of aqueous solutions.     

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 60Co(II) binding to TiO2 by batch technique, surface complexation model and DFT calculations

The interaction between radionuclides and solid/water interfaces is important to understand the physicochemical processes of radionuclides in the natural environment.Herein,the interaction of 60Co(Ⅱ) with TiO 2 in aqueous solution as a function of pH and ionic strength was studied by using batch technique combined with surface complexation model and density functional theory(DFT) calculations.The batch experimental results showed that the adsorption of 60Co(Ⅱ) was dependent on pH and independent of ionic strength,indicating the formation of inner-sphere surface complexes on TiO 2 surfaces.The results of surface complexation models and DFT calculations indicated that the surface species of 60Co(Ⅱ) adsorbed on TiO 2 followed the trend:B structure(i.e.,60Co(Ⅱ) was linked to one bridge oxygen site) was the dominant surface species at low pH,and TT structure(i.e.,60Co(Ⅱ) was linked to two terminal oxygen sites) became the important surface complex at neutral and alkaline pH values.These results demonstrated that a multi-technique approach could lead to definitive information on the structures of adsorbed 60Co(Ⅱ) at the molecular level at the TiO 2 /water interfaces,as well as realistic models to rationalize and accurately evaluate the macroscopic manifestations of radionuclide adsorption phenomena.     

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...     

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 of radiocobalt(II) onto MWCNTs: effects of solid content, contact time, pH, ionic strength, humic acid and temperature

Multiwalled carbon nanotubes (MWCNTs) have attracted intense multidisciplinary study because of their special physicochemical properties. In this paper, the effect of solid content, contact time, pH, temperature and humic acid on radionuclide (⁶⁰Co(II)) on MWCNTs was studied by using batch technique. The results indicate that the sorption of Co(II) on MWCNTs can achieve sorption equilibration in short time and the kinetic sorption can be described by pseudo-second-order model well. The sorption of Co(II) on MWCNTs is strongly dependent on pH and independent of ionic strength, suggesting that the sorption of Co(II) on MWCNTs is mainly dominated by inner-sphere surface complexation rather than by outer-sphere surface complexation or ion exchange. The thermodynamic parameters calculated from the temperature-dependent sorption isotherms indicate that the sorption of Co(II) on MWCNTs was an endothermic and spontaneous process. The results of high sorption capacity of Co(II) suggest that MWCNTs can be used as efficient materials for the preconcentration of radiocobalt from large volumes of aqueous solutions in radionuclide polluted water.     

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.     

Removal of radiocobalt ions from aqueous solutions by natural halloysite nanotubes

In this study, natural halloysite nanotubes (HNTs) were applied to remove radiocobalt from wastewaters under various environmental parameters such as contact time, pH, ionic strength, foreign ions and temperature by using batch technique. The results indicated that the sorption of Co(II) on HNTs was dependent on ionic strength at pH < 8.5 and independent of ionic strength at pH > 8.5. Langmuir and Freundlich models were applied to simulate the sorption isotherms of Co(II) at three different temperatures of 293, 313 and 333 K. Langmuir model fitted the sorption isotherms of Co(II) on HNTs better than Freundlich model. The thermodynamic parameters (ΔG ⁰, ΔS ⁰ and ΔH ⁰) calculated from the temperature-dependent sorption isotherms manifested that the sorption of Co(II) on HNTs was an endothermic and spontaneous process. The sorption of Co(II) was dominated by outer-sphere surface complexation or ion exchange at low pH, whereas inner-sphere surface complexation or precipitation was the main sorption mechanism at high pH. The experimental results show that HNTs have good potentialities for cost-effective disposal of cobalt-bearing wastewaters.     

Study of <Superscript>63</Superscript>Ni(II) sorption on CMC-bound bentonite from aqueous solutions

Bentonite was investigated to remove Ni(II) from aqueous solutions because of its strong sorption ability. Herein, bentonite was modified with sodium carboxymethylcellulose (CMC) and used as an adsorbent to remove Ni(II) from aqueous solutions. The results indicated that CMC-bentonite had higher sorption capacity than bare bentonite in the sorption of Ni(II) from aqueous solutions. Sorption of Ni(II) on CMC-bentonite was mainly dominated by ion exchange or outer-sphere surface complexation at low pH values, but by inner-sphere surface complexation or surface precipitation at high pH values. The thermodynamic data calculated from temperature dependent sorption isotherms indicated that the sorption of Ni(II) to CMC-bentonite hybrids was an spontaneous process and enhanced with increasing temperature.     

Removal of U(VI) from aqueous solutions by using attapulgite/iron oxide magnetic nanocomposites

The attapulgite/iron oxide magnetic nanocomposites were prepared by coprecipitation method and characterized by scanning electron microscopy, X-ray diffraction, vibrating sample magnetometer and Fourier transform infrared sorption spectroscopy. The results of characterization showed that iron oxides were successfully deposited on the surfaces of attapulgite. The prepared magnetic nanocomposites were applied to remove radionuclide U(VI) ions from aqueous solutions by using batch technique and magnetic separation method. The results showed that the sorption of U(VI) on attapulgite/iron oxide magnetic composites was strongly dependent on ionic strength and pH at low pH values, and was independent of ionic strength at high pH values. The interaction of U(VI) with the magnetic nanocomposites was mainly dominated by outer-sphere surface complexation or ion exchange at low pH values, and was controlled by inner-sphere surface complexation or multinuclear surface complexation at high pH values. With increasing temperature, the sorption of U(VI) on attapulgite/iron oxide magnetic composites increased and the thermodynamic parameters calculated from the temperature dependent sorption isotherms suggested that the sorption of U(VI) on the magnetic nanocomposites was a spontaneous and endothermic process. The high sorption capacity and easy magnetic separation of the attapulgite/iron oxide magnetic composites make the material as suitable sorbent in nuclear waste management.     

Impact of environmental conditions on the sorption behavior of radionuclide 63Ni(II) onto hierarchically structured γ-MnO2

A novel hierarchically structured γ-MnO₂ has been synthesized using a simple chemical reaction between MnSO₄ and KMnO₄ in aqueous solution without using any templates, surfactants, catalysts, calcination and hydrothermal processes. As an example of potential applications, hierarchically structured γ-MnO₂ was used as adsorbent in radionuclide ⁶³Ni(II) treatment, and showed an excellent ability. The effects of pH, ionic strength, temperature, humic acid (HA) and fulvic acid (FA) on the sorption of radionuclide ⁶³Ni(II) to hierarchically structured γ-MnO₂ have been investigated by using batch techniques. The results indicated that the sorption of ⁶³Ni(II) on γ-MnO₂ is obviously dependent on pH values but independent of ionic strength. The presence of HA/FA strongly enhances the sorption of ⁶³Ni(II) on γ-MnO₂ at low pH values, whereas reduces ⁶³Ni(II) sorption at high pH values. The sorption of ⁶³Ni(II) on γ-MnO₂ is attributed to inner-sphere surface complexation rather than outer-sphere surface complexation or ion exchange. The thermodynamic parameters (ΔH ⁰, ΔS ⁰, ΔG ⁰) are also calculated from the temperature dependent sorption isotherms, and the results suggest that the sorption of ⁶³Ni(II) on γ-MnO₂ is a spontaneous and endothermic process.     

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.     

Sorption behavior of hydroxyapatite for 109Cd(II) as a function of environmental conditions

In this work, hydroxyapatite (HAP) was prepared by aqueous precipitation technique and was characterized by using FT-IR to determine its chemical functional groups. A series of batch experiments were carried out to investigate the effect of various environmental factors such as contact time, pH, ionic strength, foreign ions, fulvic acid (FA) and temperature on the sorption behavior of HAP towards radionuclide ¹⁰⁹Cd(II). The results indicated that the sorption of ¹⁰⁹Cd(II) on HAP was strongly dependent on pH and ionic strength. A positive effect of FA on ¹⁰⁹Cd(II) sorption was found at pH <7.0, whereas a negative effect was observed at pH >7.0. The Langmuir, Freundlich and D-R models were used to simulate the sorption isotherms at three different temperatures of 298.15, 323.15 and 343.15 K. The thermodynamic parameters (ΔH⁰, ΔS⁰ and ΔG⁰) calculated from the temperature dependent sorption isotherms indicated that the sorption process of ¹⁰⁹Cd(II) on HAP was spontaneous and endothermic. At low pH, the sorption of ¹⁰⁹Cd(II) was dominated by outer-sphere surface complexation and ion exchange on HAP surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. From the experimental results, it is possible to conclude that HAP has good potentialities for cost-effective treatments of ¹⁰⁹Cd(II)-contaminated wastewaters.     

Effect of pH,ionic strength,foreign ions,humic acid and temperature on sorption of radionuclide <Superscript>60</Superscript>Co(II) on illite

In this article, a series of batch experiments were carried out to investigate the effect of various environmental factors such as contact time, solid content, pH, ionic strength, foreign ions, temperature and coexisting humic acid on the sorption behavior radionuclide ⁶⁰Co(II) on illite. The results indicated that the sorption of Co(II) was strongly dependent on pH, ionic strength and temperature. At low pH, the sorption was dominated by outer-sphere surface complexation and ion exchange on illite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The Langmuir, Freundlich and Dubinin-Radushkevich (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 data (∆G ⁰, ∆S ⁰, ∆H ⁰) were calculated from the temperature dependent sorption isotherms and the results suggested that the sorption process of Co(II) on illite was an endothermic and spontaneous process. The sorption test revealed that the illite can be as a cost-effective adsorbent suitable for pre-concentration of Co(II) from large volumes of aqueous solutions.     

Effect of humic acid on nickel(ii) sorption to Ca-montmorillonite by batch and EXAFS techniques study

The influence of humic acid (HA) on Ni(ii) sorption to Ca-montmorillonite was examined by using a combination of batch sorption experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy technique. The sorption of Ni(ii) on HA-montmorillonite hybrids is strongly dependent on pH and temperature. At low pH, the sorption of Ni(ii) is mainly dominated by Ni-HA-montmorillonite and outer-sphere surface complexation. The EXAFS results indicate that the first coordination shell of Ni(ii) consists of ～6 O atoms at the interatomic distances of ～2.04 ? in an octahedral structure. At high pH, binary Ni-montmorillonite surface complexation is the dominant sorption mechanism. EXAFS analysis indicates the formation of mononuclear complexes located at the edges of Ca-montmorillonite platelets at pH 7.5, while a Ni-Al layered double hydroxide (LDH) phase at the Ca-montmorillonite surface formed with pH 8.5. At pH 10.0, the dissolved HA-Ni(ii) complexation inhibits the precipitation of Ni hydroxide, and Ni-Al LDH phase forms. The rise of temperature increases the sorption capacity of Ni(ii), and promotes Ni-Al LDH phase formation and the growth of crystallites. The results are important to evaluate the physicochemical behavior of Ni(ii) in the natural environment.     

Investigation of radionuclide 63Ni(II) sequestration mechanisms on mordenite by batch and EXAFS spectroscopy study

The sorption behavior and microscopic sequestration mechanisms of radionuclide 63Ni(II) on mordenite as a function of aging time,ionic strength,initial 63Ni(Ⅱ) concentrations,solid content and coexistent electrolyte ions were investigated by the com-bination of batch and EXAFS techniques.Macroscopic experiment results show that the sorption of 63Ni(Ⅱ) is dependent on ionic strength at pH<7,and independent of ionic strength at pH>7.The sorption percentage of 63Ni(Ⅱ) on mordenite increases with increasing solid content,while the sorption capacity decreases as solid content increases.The presence of different elec-trolyte ions can enhance or inhibit the sorption of Ni(II) on mordenite in various degrees.EXAFS analysis results of the sam-ples under three different ionic strengths suggest that the retained 63Ni(Ⅱ) in these samples exists in an octahedral environment with six water ligands.In the initial period of rapid uptake,the sorption of 63Ni(Ⅱ) is dominated by the formation of in-ner-sphere surface complexes.As aging time increases,63Ni(Ⅱ) sequestration behavior tends to be mainly controlled by the formation of Ni phyllosilicate co-precipitates and/or Ni(OH)2(s) precipitates.Results for the second shell fit of the sample pre-pared at an initial 63Ni(Ⅱ) concentration of 100 mg/L indicate the possible formation of Ni polynuclear surface complexes.Both the macroscopic sorption data and the molecular level evidence of 63Ni(Ⅱ) surface speciation at the mordenite/water in-terfaces should be factored into better predictions of the mobility and bioavailability of 63Ni(Ⅱ) in environment mediums.