The influence of pH on diffusion of 75Se(IV) in Beishan granite

The through-diffusion method and batch sorption experiments were used to explore the influence of pH on the diffusion behavior of ⁷⁵Se(IV) in matrix Beishan granite (BsG). In the pH range of 2.0–8.5, the D_e values of ⁷⁵Se(IV) in BsG decreased first and then increased with pH increasing, while the changing trend of K_d was nearly opposite. It was speculated that the influence of pH on the diffusion of ⁷⁵Se(IV) in BsG was due to the joint effects of different species distribution of Se, change in surface charge of BsG and change in ionic strength at various pH values.

     

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.     

Adsorption and Structural Properties of Montmorillonite Pillared by Cr(III) and Cr(III)–Cu(II) Hydroxocomplexes

The sorption and structural parameters and thermal stability of montmorillonite pillared by Cr(III) polyhydroxocomplexes and heteronuclear Cr(III)–Cu(II) polyhydroxocomplexes were investigated. It was shown that the introduction of intercalating Cr(III) and Cr(III)–Cu(II) agents into the montmorillonite increased the value of the first basal reflection (d ₀₀₁) up to 1.85 nm in the first case and up to 1.98 nm, in the second. The dependence of the values of d ₀₀₁and specific surface area on the OH^–/Cr³⁺ratio was found, which is retained during the calcination of the samples up to 500–800°C. The sorption ability of the prepared samples with respect to acetone, ethanol, benzene, toluene, and water was investigated.     

Comparative study on sorption of individual and coupling cesium and selenium on mudrock

This study focused on sorption mechanism of Cs and Se in mudrock by batch techniques. Batch kinetics tests have been conducted with carriers 10^{− 4}M CsCl and SeO₂ by using individual and coupling radiotracers of ¹³⁷Cs and ⁷⁵Se. The distribution coefficients (K _d ) of Cs in synthetic groundwater (GW) and seawater (SW) showed that there is no interference between individual and coupling value (13 and 6 ml/g). Moreover, individual and coupling K _d ) (80 and 40 ml/g) of Se in GW and SW are in agreement with Cs. It is quite clear that the sorption mechanisms of Cs and Se on mudrock are independent and different by using radiotracer’s technique.     

Impact of environmental conditions on the sorption behavior of radionuclide <Superscript>60</Superscript>Co(II) on MnO<Subscript>2</Subscript>

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The removal of ⁶⁰Co(II) from wastewaters by MnO₂ was studied as a function of various environmental parameters such as shaking time, pH, ionic strength, foreign ions, and humic substances under ambient conditions. The results indicated that the sorption of ⁶⁰Co(II) on MnO₂ was strongly dependent on pH and ionic strength. At low pH, the sorption of ⁶⁰Co(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on MnO₂ surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of HA/FA enhances ⁶⁰Co(II) sorption at low pH values, whereas reduces ⁶⁰Co(II) sorption at high pH values. The Langmuir and Freundlich models were used to simulate the sorption isotherms of ⁶⁰Co(II) at three different temperatures of 298.15, 318.15 and 338.15 K. The thermodynamic parameters (ΔH ⁰, ΔS ⁰ and ΔG ⁰) calculated from the temperature dependent sorption isotherms indicated that the sorption process of ⁶⁰Co(II) on MnO₂ was endothermic and spontaneous.     

Diffusion of cesium and selenium in crushed mudrock

In this study, the diffusion behavior of cesium and selenium with 10⁻⁴M concentration in mudrock was studied by trough-diffusion tests and summarized in order to provide confidence on long-term performance assessment of nuclear waste repositories. The diffusion process of Cs and Se reached equilibrium after 60 and 500 days, respectively. Besides, it also displays that the distribution coefficients (K _d ) of Se in through-diffusion tests is higher than that of Cs in agreement with that obtained from the batch method. The K _d value (15.14±1.99 mL/g) of Cs by diffusion techniques is equivalent to that of batch method (15.10±0.40 mL/g) because sorption of Cs was assumed to fast sorption step. However, the K _d value of Se (137.58±12.20 mL/g) derived from the diffusion technique is higher than that from batch tests (76.72±2.96) and showed an obvious variation with K _d of Cs. The difference of K _d between diffusion and batch methods resulted from the fact that 14 days were not long enough to reach equilibrium or stable state in the batch method.     

Sorption of144Ce(III) and147Pm(III) on hydrated iron sesquioxide

The sorption of¹⁴⁴Ce(III) and of¹⁴⁷Pm(III) on hydrated iron sesquioxide suspension and the sorption of¹⁴⁴Ce(III) on hydrated iron sesquioxide in a laboratory column were studied. The dependence of the sorption on pH and time, the sorption isotherm, the temperature-dependence of sorption, and the effects of ionic strength on sorption and desorption were determined under static conditions. The maximum sorptions of¹⁴⁴Ce(III) and¹⁴⁷Pm(III) were reached at pH=7.4 (K_d=8.9·10⁵) and pH=9.1 (K_d=6.2·10⁵), respectively.     

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.     

A review on distribution coefficient (Kd) of some selected radionuclides in soil/sediment over the last three decades

This review paper presents the different methods to estimate K_d and subsequent compiles of the K_d data on U, Ra, Th, ¹³⁷Cs and ⁶⁰Co in soil/sediment under various aquatic medium based on the extensive literature survey over the last 3-decades (1990–2019). The estimated K_d values show a very wide range and make more difficult to derive generic value. The finding suggests that K_d values are to be estimated for site-specific conditions while assessing the radionuclide transport modeling and risk analysis around the nuclear facilities. Review includes research papers, reports, reviewed papers, dissertations, published compilations and other technical documents.

     

Plutonium-239 sorption and transport on/in unsaturated sediments: comparison of batch and column experiments for determining sorption coefficients

Sorption (distribution) coefficients of plutonium were most often derived by static batch experiments. However, it is not clear how unsaturated flow conditions including moisture content and pore water velocity change the sorption coefficients. Transport experiments of plutonium through the unsaturated sediments packed into the columns were then performed in order to determine the sorption coefficients (column-K _ds). Static batch experiments were also conducted to obtain batch-K _ds and then compare the differences between batch-K _ds and column-K _ds. The results show that unsaturated flow conditions had no significant effect on column-K _ds, and the average column-K _d value was 1.74 ± 0.02 m³/kg. By comparison, batch-K _d values spanned several orders of magnitude, regardless of the specified liquid–solid conditions. Moreover, the batch-K _d (22.7 m³/kg) at the standard L/S (4 mL/g) recommended by ASTM D 4319 was over an order of magnitude larger than the average column-K _d.     

Sorption of hafnium on hydrous titanium oxide using radiotracer technique

The sorption of hafnium on hydrous titanium oxide (TiO₂·1.94 H₂O) has been studied in detail. Maximum sorption of hafnium can be achieved from a pH 7 buffer solution containing boric acid and sodium hydroxide using 50 mg of the oxide after 30 minutes shaking. The value ofk _d, the rate constant of intraparticle transport for hafnium sorption, from 0.01M hydrochloric and perchloric acid and pH 7 buffer solutions has been found to be 17 mmole·g^–1·min^–2. The kinetics of hafnium sorption follows Lagergren equation in 0.01M HCl solution only. The values of the overall rate constantK=6.33·10^–2 min^–1 and of the rate constant for sorptionk ₁=6.32·10^–2 min^–1 and desorptionk ₂=2.28·10^–5 min^–1 have been evaluated using linear regression analysis. The value of correlation factor() is 0.9824. The influence of hafnium concentration on its sorption has been examined from 4.55·10^–5 to 9.01·10^–4 M from pH 7 buffer solution. The sorption data followed only the Langmuir sorption isotherm. The saturation capacity of 9.52 mmole·g^–1 and of a constant related to sorption energy have been estimated to be 2917 dm³·mole^–1. Among all the additional anions and cations tested only citrate ions reduce the sorption significantly. Under optimal experimental conditions selected for hafnium sorption, As(III), Sn(V), Co(II), Se(IV) and Eu(III) have shown higher sorption whereas Mn(II), Ag(I) and Sc(III) are sorbed to a lesser extent. It can be concluded that a titanium oxide bed can be used for the preconcentration and removal of hafnium and other metal ions showing higher sorption from their very dilute solutions. The oxide can also be employed for the decontamination of radioactive liquid waste and for pollution abatement studies.     

Sorption of Cs(I) and Sr(II) on a mixture of bentonite and magnetite using SCM + IExM: A parametric study

Summary The sorption of Cs(I) and Sr(II) on bentonite and magnetite was experimentally studied and numerically simulated using surface complexation (SCM) and ion-exchange (IExM) models. The empirical system consisted of: (1) synthetic granitic water with a given ionic strength (0.1 or 0.01 NaNO₃), (2) radionuclides studied (10^-6M CsCl or SrCl₂ ^. 6H₂O spiked with ¹³⁷Cs or ⁸⁵Sr), and (3) bentonite pre-treated with the aim to remove carbonates, and magnetite as a representative of steel canister corrosion products. The parametric study covered, e.g., the influence of pH, bentonite to magnetite ratio and volume-liquid ratio on the values of selectivity coefficients and K_d.     

Sorption behavior of Co(II) on γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the presence of humic acid

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The extent of sorption of divalent metal cations is controlled by a number of factors including cosorbing or complexing. In this work, the effects of pH, humic acid HA/Co(II) addition orders, ionic strength, concentration of HA, and foreign cations on the Co(II) sorption on γ-Al₂O₃ in the presence of HA were investigated. The sorption isotherms of Co(II) on γ-Al₂O₃ in the absence and presence HA were also studied and described by using S-type sorption model. The experimental results showed that the Co(II) sorption is strongly dependent on the pH values, concentration of HA, but independent of HA/Co(II) addition orders, ionic strength, and foreign cations in the presence of HA under our experimental conditions. The results also indicated that HA enhanced the Co(II) sorption at low pH, but reduced the Co(II) sorption at high pH. It was hypothesized that the significantly positive influence of HA at low pH on the Co(II) sorption on γ-Al₂O₃ was attributed to strong surface binding of HA on γ-Al₂O₃ and subsequently the formation of ternary surface complexes such as ≡S-OOC-R-(COO⁻) _x Co^2−x . Chemi-complexation may be the main mechanism of the Co(II) sorption on γ-Al₂O₃ in the presence of HA.     

Preliminary selection of clay minerals for the removal of pharmaceuticals,bisphenol A and triclosan in acidic and neutral aqueous solutions

Pharmaceuticals, personal care products and endocrine disruptors demonstrate huge potential to cause adverse ecological health effects at very low concentration in aquatic environment. There is a need to improve current purification technologies used in sewage and drinking-water treatment plants. This article aims at providing new insights into the recent development of natural and modified clay-based sorbents for the removal of aqueous contaminants such as pharmaceuticals and personal care products. The removal of six widely used pharmaceuticals: ibuprofen, diclofenac, ketoprofen, carbamazepine, as well as endocrine disrupting chemicals – bisphenol A and a bactericidal agent, triclosan – was examined by sorption onto eight adsorbents. Sorption was performed using natural and modified clay minerals – montmorillonite (Mt), vermiculite (VER), bentonite (B), kaolinite (K), commercial acid activated montmorillonites K10 and K30, and two carbonaceous-mineral nanocomposites, MtG5%T, BAlG3%C. This study showed that among the tested natural clays, vermiculite is the most promising sorbent for the removal of pharmaceuticals in purification processes. Among the modified clay minerals, the best results were achieved for carbonaceous bentonite and two acid activated montmorillonites K10 and K30. However, the removal of acidic pharmaceuticals on montomorillonite K10 and carbonaceous bentonite was strongly dependent on the pH value. In the case of vermiculite and acid-modified montmorillonite K30, the sorption of the selected compounds was not significantly affected by pH, which is crucial in wastewater treatment. The sorption constant divided by the specific surface area (K_d/A) is proposed to assess whether the surface area or chemical properties of the materials control the sorption process. K_d/A values were relatively high in the case of vermiculite, so it should be noticed that individual and specific surface properties of vermiculite were of crucial importance for sorption.     

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 selenite onto chlorite considering mineral dissolution

In this study we investigated the sorption of selenite (SeO₃ ^2?) onto chlorite as a function of Se(IV) concentration, pH, and ionic strength. The sorption isotherm of Se(IV) onto chlorite was successfully presented by both the Langmuir isotherm and Tempkin equation although the Langmuir isotherm is somewhat better than the Tempkin equation. The sorption of Se(IV) onto chlorite was maintained to be constant at an acidic pH region, while the sorption decreased with an increasing pH at neutral and alkaline pH regions. However, the Se(IV) sorption onto chlorite was independent of the ionic strength of NaClO₄ solution. The amount of Se(IV) sorbed onto chlorite was significantly low compared to those of iron oxides such as apatite, goethite, hematite, and magnetite because of the lower content of Fe. We also investigated the effect of Fe(II) ions dissolved from chlorite on the Se(IV) sorption as a function of contact time. The chemical oxidation states of selenium sorbed onto chlorite surface were identified using X-ray absorption near edge structure (XANES) at the Pohang synchrotron light source. The amount of Fe(II) dissolved was increased by the contact time of 28 days but decreased after 28–56 days although the amount of dissolved Fe(II) ions was significantly small. This decrease of the dissolved Fe(II) may be due to the formation of Fe-oxyhydroxides such as ferrihydrite. The results of XANES measurements also showed that the Se(IV) sorbed onto chlorite was not reduced into Se(0) or Se(-II) even in the presence of Fe(II) ions in the solution because of the low Fe content of the chlorite although the mechanism was not clearly understood.     

Sorption of radioactive strontium on a silica-titania mixed hydrous oxide gel

A silica-titania (Si–Ti) mixed hydroxide gel with Ti to Si mole ratio of 11 was prepared. Studies on the sorption of radiostrontium from alkaline solutions having various concentrations of sodium were carried out with Si–Ti. The distribution coefficient (K _d) of strontium decreased with increasing concentrations of sodium from 0.1 to 4.0 mol·dm^–3. The plot of logK _d versus log [Na⁺] gave a slope of –0.55 as against the theoretical value of –2.0. This suggests that some other paths in addition to the simple stoichiometric ion exchange is also existing for sorption. From pH titrations the pH_pzc of Si–Ti was found to be 4.22 coinciding nearly with the pH sorption edge. An attempt was made to correlate the sorption results with the surface characteristics of the sorbent. It was found that sorption is favored when the surface of the sorbent transforms into an anionic form. Sharp increase in the sorption of strontium was observed when the equilibrium pH was between 7 and 10. This behavior could be attributed to the abrupt increase in net negative charge on the surface of the sorbent.     

Influence of pH,humic acid,ionic strength,foreign ions,and temperature on <Superscript>60</Superscript>Co(II) sorption onto γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The sorption of ⁶⁰Co(II) on γ-Al₂O₃ was conducted under various conditions, i.e., contact time, adsorbent content, pH, ionic strength, foreign ions, humic acid (HA), and temperature. Results of sorption data analysis indicated that the sorption of ⁶⁰Co(II) on γ-Al₂O₃ was strongly dependent on pH and ionic strength. At low pH the sorption was dominated by outer-sphere surface complexation or ion exchange, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of different cation ions influenced ⁶⁰Co(II) sorption, while the presence of different anion ions had no obvious influences on ⁶⁰Co(II) sorption. The presence of HA decreased the sorption of ⁶⁰Co(II) on γ-Al₂O₃. The sorption isotherms were simulated well with the Langmuir model. The thermodynamic parameters (ΔH ⁰ , ΔS ⁰ and ΔG ⁰ ) calculated from the temperature-dependent sorption isotherms indicated that the sorption of ⁶⁰Co(II) on γ-Al₂O₃ was an endothermic and spontaneous process. Experimental results indicated that the low cost material was a suitable material in the preconcentration of ⁶⁰Co(II) from large volumes of aqueous solutions.     

Effect of pH, ionic strength, foreign ions, fulvic acid and temperature on 109Cd(II) sorption to γ-Al2O3

The sorption of Cd(II) from aqueous solution on γ-Al₂O₃ was investigated under ambient conditions. Experiments were carried out as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic acid and temperature. The results indicated that the sorption of Cd(II) was strongly dependent on pH and ionic strength. At low pH, the sorption of Cd(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on γ-Al₂O₃ 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. The thermodynamic data (ΔG ⁰, ΔS ⁰, ΔH ⁰) calculated from the temperature dependent sorption isotherms suggested that the sorption of Cd(II) on γ-Al₂O₃ was an spontaneous and endothermic process.     

The distribution coefficient of60Co in sediments from the Solway Firth, UK

The behaviour of⁶⁰Co in sea water and sediments typical of the Solway Firth has been investigated. The distribution coefficient,K _d, of⁶⁰Co²⁺ in sediments was determined using the batch sorption method and theK _d variation with aqueous phase composition, sediment type and pH has been studied. Adsorption of⁶⁰Co by sediments was found to be highest in de-ionised water and lower in NaCl solution (31 salinity). Adsorption was lowest in natural sea water, where theK _d range was 2,270 to 2,750. Variation ofK _d with sediment grain size was observed. It was shown that⁶⁰Co adsorption was strongly dependent on pH in de-ionised water, with less variation in NaCl solution. Variance of⁶⁰CoK _d values were lowest in sea water in the range pH 5–8 indicating a more conservative behaviour of⁶⁰Co than previously recognised. Hence⁶⁰Co dispersion will be predominantly govemed by tidal behaviour.