Effects of pH,ionic strength,temperature, and humic acid on Eu(III) sorption onto iron oxides

Effects of pH, Eu(III) concentration, ionic strength, temperature and humic acid (HA) on Eu(III) sorption to iron oxides were investigated in detail. The sorption of Eu(III) to iron oxides was significantly dependent on pH and weakly dependent on ionic strength, and higher temperature was gainful to Eu(III) sorption. In the presence of HA, Eu(III) sorption was enhanced significantly at low pH; whilst obvious negative effect was observed in higher pH range. Below 12 mg/L HA, HA could obviously enhanced Eu(III) sorption to iron oxides, nevertheless Eu(III) sorption decreased steeply with increasing HA while HA exceeded 12 mg/L. The results were helpful for understanding radionuclides behaviors in natural environment.     

Effect of humic acid, pH and ionic strength on the sorption of Eu(III) on red earth and its solid component

Sorption and desorption of radioeuropium on red earth and its solid components to remove organic matter was studied at pH 5.3±0.1 and 4.5±0.1, and in 0.01M and 0.001M NaClO₄ solutions, respectively. Eu(III) sorption showed strong pH and humic acid concentration dependency, and NaClO₄ concentration independency. The sorption increased with increasing pH and amount of HA adsorbed on red earth. The sorption of Eu(III) on red earth was mainly dominated by surface complexation. Humic acid and high pH had a great tendency to immobilize the movement of Eu(III) in red earth. Sorption-desorption hysteresis of Eu(III) on red earth indicated that the sorption was irreversible.     

The sorption of Eu(III) on calcareous soil: effects of pH,ionic strength,temperature, foreign ions and humic acid

The sorption of Eu(III) on calcareous soil as a function of pH, humic acid (HA), temperature and foreign ions was investigated under ambient conditions. Eu(III) sorption on soil was strongly pH dependent in the observed pH range. The effect of ionic strength was significant at pH < 7, and not obvious at pH > 8. The type of salt cation used had no visible influence on Eu(III) uptake on soil, however at low pH values, the influence of anions was following the order: Cl⁻ ≈ NO₃ ⁻ > ClO₄ ⁻. In the presence of HA, the sorption edge obviously shifted about two pH units to the lower pH, whilst in range of pH 6–7, the sorption of Eu(III) decreased with increasing pH because a considerable amount of Eu(III) was present as humate complexes in aqueous phase, then increased again at pH > 11. The results indicated that the sorption of Eu(III) on soil mainly formed outer-sphere complexes and/or ion exchange below pH ~7; whereas inner-sphere complexes and precipitation of Eu(OH)₃(s) may play main role above pH ~8.     

Adsorption of Am(III) on red earth and natural hematite

Summary The Am(III) adsorption isotherms on natural hematite, on a red earth and on three kinds of treated red earth samples were determined and compared. The treatment was performed to remove iron oxides, organic matter (OM) and both. The batch technique and aqueous Am(III) solutions with molarities less than 3 ^. 10^-9 mol/l were used. A very high adsorbability of Am(III) on hematite was found, and in order to decrease the adsorption percentage, stable Eu³⁺ as a hold back carrier was added to the aqueous solution. All the isotherms were found to be linear. The strong effects of pH, ionic strength and fulvic acid (FA) on the Am(III) adsorption on natural hematite were demonstrated. A positive contribution of OM and an unexpectedly high negative influence of iron oxides on the Am(III) adsorption by the untreated red earth were found too. The average distribution coefficients of Am(III) adsorption on natural hematite, on red earth and on three kinds of treated red earth samples were determined, respectively, from these linear isotherms. The very high adsorbability of Am(III) on hematite and the very strong negative influence of iron oxides on the Am(III) adsorption on untreated red earth were distinctly demonstrated as well. It appears that the adsorbability of composed natural materials cannot be predicted from the adsorbabilities of each of the mineral components alone, due to possible interactions between the mineral components and the different characteristics of the composite.     

Sorption of Eu(III) onto Gaomiaozi bentonite by batch technique as a function of pH, ionic strength, and humic acid

The bentonite from Gaomiaozi county (Inner Mongolia, China) (denoted as GMZ bentonite) was characterized by X-ray powder diffraction and Fourier transform infrared spectroscopy. The effect of pH, contact time, ionic strength, humic acid (HA) and Eu(III) concentrations on Eu(III) sorption to the GMZ bentonite was studied by batch technique under ambient conditions. The sorption of Eu(III) on GMZ bentonite was strongly dependent on pH and independent of ionic strength. The sorption of Eu(III) on GMZ bentonite was mainly dominated by surface complexation rather than by ion exchange. The presence of HA enhanced Eu(III) sorption at low pH values, but decreased Eu(III) sorption at high pH values. The enhanced sorption of Eu(III) on GMZ bentonite at low pH was attributed to the strong complexation of Eu(III) with surface adsorbed HA on GMZ bentonite and the reduced sorption of Eu(III) at high pH was attributed to the formation of soluble HA–Eu complexes in aqueous solution. The strong sorption of Eu(III) on GMZ bentonite suggested that the GMZ bentonite could be used as the backfill material in nuclear waste disposal.     

Sorption of radioeuropium onto attapulgite: effect of experimental conditions

Batch sorption experiments were performed to remove Eu(III) ions from aqueous solutions by using attapulgite under ambient conditions. Different experimental conditions, such as contact time, solid content, foreign ions, pH, ionic strength, fulvic acid and temperature, have been investigated to study their effect on the sorption property. The results indicated that the sorption of Eu(III) onto attapulgite was strongly dependent on pH, ionic strength and temperature. The sorption increased from about 8.9 to 90% at pH ranging from 2 to 6 in 0.01 mol/L NaNO₃ solution. The Eu(III) kinetic sorption on attapulgite was fitted by the pseudo-second-order model better than by the pseudo-first-order model. The sorption of Eu(III) onto attapulgite increased with increasing temperature and decreasing ionic strength. The Langmuir and Freundlich models were used to simulate the sorption isotherms, and the results indicated that the Freundlich model simulated the data better than the Langmuir model. The thermodynamic parameters (∆G ^o, ∆S ^o, ∆H ^o) were determined from the temperature dependent isotherms at 298.15, 318.15 and 338.15 K, and the results indicated that the sorption reaction was an endothermic and spontaneous process. The results suggest that the attapulgite is a suitable material as an adsorbent for preconcentration and immobilization of Eu(III) from aqueous solutions.     

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.     

The influence of humic acid on the pH-dependent sorption of americium(III) onto kaolinite

This work investigates the sorption of americium [Am(III)] onto kaolinite and the influence of humic acid (HA) as a function of pH (3–11). It has been studied by batch experiments (V/m = 250:1 mL/g, C _Am(III) = 1 × 10⁻⁵ mol/L, C _HA = 50 mg/L). Results showed that the Am(III) sorption onto the kaolinite in the absence of HA was typical, showing increases with pH and a distinct adsorption edge at pH 3–5. However in the presence of HA, Am sorption to kaolinite was significantly affected. HA was shown to enhance Am sorption in the acidic pH range (pH 3–4) due to the formation of additional binding sites for Am coming from HA adsorbed onto kaolinite surface, but reduce Am sorption in the intermediate and high pH above 6 due to the formation of aqueous Am-humate complexes. The results on the ternary interaction of kaolinite–Am–HA are compared with those on the binary system of kaolinite–HA and kaolinite–Am and adsorption mechanism with pH are discussed. Effect of different molecular weight of HA, with three HA fractions separated by ultrafiltration techniques, on the Am sorption to kaolinite were also studied. The results showed that the enhancement of the sorption of Am onto kaolinite at the acidic pH conditions (pH 3–4) was higher with HA fractions of higher molecular weight. Also, the Am sorption over a pH range from 6 to 10 decreased with decreasing molecular weight of HA.     

Effect of pH, ionic strength, foreign ions and temperatures on the sorption of Eu(III) on attapulgite-iron oxide magnetic composites

In this paper, the attapulgite-iron oxide magnetic composites were synthesized by coprecipitation method and were characterized by SEM, XRD and FTIR in detail. The characterization results indicated that the iron oxide was successfully formed on the surface of attapulgite. The prepared attapulgite-iron oxide magnetic composites were applied as adsorbents to remove Eu(III) from aqueous solutions by using batch sorption experiments under different experimental conditions. The sorption properties of Eu(III) on bare attapulgite were also performed as comparison. The results indicated that the sorption of Eu(III) on attapulgite-iron oxide magnetic composites was strongly dependent on pH and temperature. The attapulgite-iron oxide magnetic composites can be separated from aqueous solutions using magnetic separation method in large scale. At low pH values, the sorption of Eu(III) was influenced by ionic strength and pH obviously, while the sorption of Eu(III) was not affected by ionic strength at high pH values. The sorption of Eu(III) was dominated by ion exchange or outer-sphere surface complexation at low pH values, and mainly by inner-sphere surface complexation at high pH values. The thermodynamic parameters (i.e., ?G ^°, ?S ^°, ?H ^°) calculated from the temperature dependent sorption isotherms indicated that the sorption of Eu(III) on attapulgite-iron oxide magnetic composites was an endothermic and spontaneous process. Although the sorption capacities of Eu(III) on attapulgite-iron oxide magnetic composites were a little lower than those of Eu(III) on bare attapulgite, the magnetic separation in large scale is suitable for the application of the magnetic composites in the preconcentration of Eu(III) from large volumes of aqueous solutions in possible real applications.     

Sorption and desorption of radioselenium on red earth and its solid components

The effect of organic matter and iron oxides as solid components of the red earth on the retention of SeO₃ has been investigated by a batch technique and selective extraction method. The sorption and desorption isotherms of SeO₃ on the untreated red earth and the three treated soils were determined at 20°C, pH 6.8 or 7.2 and in the presence of 0.01M CaCl₂. It was found that the sorption-desorption hysteresis for untreated an treated soils is obvious and the clays play an important role in the sorption-desorption hysteresis, and that the retention of SeO₃ on red earth is attributed to the iron oxides to a great extent.     

pH and concentration dependence of luminescent characteristics in glass-encapsulated Eu-complex

In order to improve the stability of red phosphor with efficient and high color-purity characteristics under ultraviolet excitation, we encapsulated Eu(TTA)₃phen(tris(2-thenoyltrifluoroacetonato)(1,10-phenanthroline)europium(III)) by sol–gel derived silica glasses and studied their photoluminescence (PL) characteristics. The dependence of pH values in the starting solution revealed that the process condition should be within the modest region with the optimum pH value around 6–7. The PL intensity increased with increasing the concentration of Eu(TTA)₃phen initially, then it showed saturating tendency above 0.6 mol%. An improvement of reliability by the glass encapsulation was exemplified by monitoring the long-term PL intensity under constant UV irradiation. We consider that the glass network carefully prepared by sol–gel process is effective for preventing free oxygen and water from attacking Eu(TTA)₃phen molecule without loss of PL output.     

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.     

Analytical characterization of a silica gel sorbent with thioetheric sites

The sorption behavior of a newly synthesized silica gel sorbent with thioetheric sites (STS) towards microgram levels of Au(III), Pt(IV) and Pd(II) was studied. Au(III) is quantitatively (>95%) sorbed in the pH region of 1–9. The sorption of Pt(IV) starts at pH 1 and does not exceed 25% in the entire pH region examined. The sorption of Pd(II) starts at pH 7 and reaches 80% at pH 9. The sorption of Au(III) on STS at pH 1 is not affected by milligram amounts of Ni(II), Zn(II), Fe(III), Cu(II), Pb(II), Cd(II) or Co(II). Au(III) is quantitatively eluted with a 5% aqueous solution of thiourea. The adsorption capacity of STS towards Au(III) is 195 mg g⁻¹. The detection limit (DL) of Au(III) (3σ, n = 9) is 25 ng mL⁻¹. The RSD at a level of 10 × DL is about 2%. Solid-phase extraction of trace amounts of Au(III) on the STS sorbent, followed by its flame AAS determination in the eluate was applied to the determination of gold in geological samples. The results obtained for the gold content in the samples were in good agreement with those of the ICP-AES analysis.     

Effects of nitrate,fulvate, phosphate,phthalate, salicylate and catechol on the sorption of uranyl onto SiO<Subscript>2</Subscript>: a comparative study

We have performed a large number of batch sorption experiments of uranyl onto SiO₂ and examined the effects of nitrate or ionic strength, phosphate, fulvic acid(FA), phthalic acid (PH), salicylic acid (SA), and catechol (CA) on the uranyl sorption onto SiO₂. Three sorption edges and three sorption isotherms at ionic strengths 0.05, 0.1, and 0.5 mol/L KNO₃ were used to investigate the effect of ionic strength or nitrate on the sorption and the Langmuir, Freundlich, and Dubinin-Radushkevich models are used to simulate the sorption isotherms, respectively. Five sorption edges in the presence of phosphate, FA, PH, SA, and CA were compared with that in the absence of complexing ligand. The results suggest that the effect of complexation of uranyl with nitrate on the uranyl sorption can be negligible and the sorption can be described Freundlich and D-R model very well. The positive effect of phosphate on the uranyl sorption was found, though the extent of effect was decreased with increasing pH. The positive effect and the negative effect of FA on the uranyl sorption were found at low pH and high pH ranges, respectively. The sorption edge of uranyl sorption remained unaffected in the presence of PH in the pH 2–10. In the presence of SA, the no effect and the negative effect on the uranyl sorption were, respectively, found at low pH and high pH ranges. The negative effect of CA on the uranyl sorption was found in the pH 2–10.     

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

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

Sorption of Eu(III) on GMZ bentonite in the absence/presence of humic acid studied by batch and XAFS techniques

Bentonite has been extensively studied because of its strong sorption ability and low permeability. In this work, the Na-bentonite from Gaomiaozi County (China) has been characterized by XRD, FTIR and acid-base titration. The sorption of Eu(III) on Na-bentonite in the absence/presence of humic acid (HA) was studied at T = 25 ± 2 °C and in 0.01 mol/L NaClO₄ solution. The effects of pH, HA, contact time and initial Eu(III) concentrations were also investigated. The results indicate that the sorption of Eu(III) on Na-bentonite was dependent on pH values. The presence of HA had little effect on Eu(III) sorption at low pH values, but decreased Eu(III) sorption at high pH values. X-ray absorption fine structure spectroscopy (XAFS) was applied to characterize the local structural environment of the adsorbed Eu(III) on bare Na-bentonite and HA-bentonite hybrids. The results indicate that Eu(III) was bound to O atoms at a distance of about 2.39 Å at pH 4.15. The results are crucial for the evaluation of the sorption and migration of other trivalent lanthanides and actinides in bentonite as backfill materials.     

Insights into sorption species of Eu(III) on γ-Al2O3 and bentonite under different pH: Studies at macro- and micro-scales

The sorption species of Eu(III) on γ-Al₂O₃ and bentonite was investigated by batch, surface complexation model (SCM), and X-ray absorption spectroscopy (XAS). The results showed that sorption edges of Eu(III) on γ-Al₂O₃ and bentonite were as expected shifted forward high pH with the increasing in Eu(III) concentration, and sorption of Eu(III) was strongly dependent on pH. In γ-Al₂O₃ system, sorption of Eu(III) was decreased above pH 8.5 at low concentration of Eu(III) because of water soluble carbonate species of Eu(III), however the decline did not appear at high concentration of Eu(III) possibly due to a offset effect of surface precipitation. Actually, the sorption species of Eu(III) on bentonite mainly referred to at least four kinds of species including ion exchange (>X₃Eu⁰) at low pH, inner-sphere complexes (>AlOEu²⁺ and >SiOEu²⁺) at neutral condition, and hydrolysis species (>SiOEu(OH) ₂ ⁰ ) at alkaline condition. Linear combination fitting (LCF) in k space testified that hydrolysis of Eu(OH)₃(s) and oxide of Eu₂O₃ species were major for Eu(III) sorption on γ-Al₂O₃, whereas Eu³⁺(aq) and hydrolysis species comprised sorption species on bentonite. Extended X-ray absorption fine structure (EXAFS) analysis further confirmed the prediction from SCM and LCF. In addition, the typical shells of Eu–Al in R range of 3.0–3.4 Å and Eu–Si at ~4.0 Å were found in radial structure functions, which was possibly identified to edge-shared bidentate of Eu(III) on Al₂O₃ and bentonite.     

Arsenic sorption by modified clinoptilolite–heulandite rich tuffs

Recent works show that modified natural zeolites improve the remotion of anionic or non-polar organic pollutants from water. In this work the arsenic sorption from aqueous solutions onto clinoptilolite–heulandite rich tuffs modified with lanthanum, hexadecyltrimethylammonium or iron was investigated considering the arsenic chemical species and the pH of the arsenic solutions. Clinoptilolite–heulandite rich tuffs were characterized by scanning electron microscopy and X-ray diffraction analysis. The elemental composition of the zeolitic samples was also determined. According to the Langmuir isotherm model the arsenic (V) sorption capacity of the zeolites was 75.4 μg As/g at pH 3, 3.9 μg As/g at pH 5 and 53.6 μg As/g at pH 6, for the lanthanum, HDTMA and iron modified clinoptilolite–heulandite rich tuff from Chihuahua (México), respectively. In general, the results suggested that the arsenic retention depends on the precedence of zeolitic material, the nature of arsenic chemical species, pH as well as the characteristics of modified natural zeolites. In this work the arsenic adsorption mechanisms are also discussed.     

Adsorptive Voltammetric Studies on the Cerium(III)–Alizarin Complexon Complex at a Carbon Paste Electrode

A novel procedure was developed for the determination of trace cerium on the basis of anodic adsorption voltammetry of the Ce(III)–alizarin complexon (ALC) complex at a carbon paste electrode (CPE). The procedure is convenient to determine cerium individually in the presence of other rare earths because there is a 100 mV difference between the peak potentials of Ce(III)–ALC and other rare earth(III)–ALC complexes in a supporting electrolyte of 0.08 M HAc–NaAc and 0.012 M potassium biphthalate (pH 4.7) when performing linear-scanning from −0.2 to 0.8 V (vs. SCE) at 100 mV/s. The second-order derivative peak currents are directly proportional to the Ce(III) concentration over a range of 6.0 × 10⁻⁹–3.0 × 10⁻⁷ M. The detection limit is as low as 2.0 × 10⁻⁹ M (S/N = 3) for a 120 s preconcentration. An RSD of 3.5% was obtained for 15 determinations of Ce(III) at a concentration of 4.0 × 10⁻⁸ M on the same CPE surface. The method was applied successfully to the determination of cerium in samples of rare earth nodular graphite cast iron.     

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.