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.     

Mercury(II) Biosorption Using <Emphasis Type="Italic">Lessonia</Emphasis> sp. Kelp

Lessonia nigrescens and Lessonia trabeculata kelps have been tested for the sorption of mercury from aqueous solutions. A pretreatment (using CaCl₂) allowed stabilizing the biomass that was very efficient for removing Hg(II) at pH 6–7. Sorption isotherms were described by the Langmuir equation with sorption capacities close to 240–270 mg Hg g⁻¹ at pH 6. The temperature had a negligible effect on the distribution of the metal at equilibrium. The presence of chloride anions had a more marked limiting impact than sulfate and nitrate anions. The uptake kinetics were modeled using the pseudo-second-order equation that fitted better experimental data than the pseudo-first-order equation. The particle size hardly influenced sorption isotherms and uptake kinetics, indicating that sorption occurs in the whole mass of the biosorbent and that intraparticle mass transfer resistance was not the limiting rate. Varying the sorbent dosage and the initial metal concentration influenced the equilibrium, but the kinetic parameters were not drastically modified. Metal can be eluted with hydrochloric acid, citric acid, or acidic KI solutions.     

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

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

Reaction of lead ions with hydroxylapatite granules

In the effort to improve the performance of hydroxylapatite (HA) in removing lead ions from aqueous solutions, millimeter-sized granules with 50 % porosity were synthesized. Such HA particles, after drying at 100°C, or heating at 800°C or 1100°C, exhibited the specific surface areas of 50 m² g⁻¹, 25 m² g⁻¹, and 5 m² g⁻¹, respectively. It was found that heavy metal sorption capacity of HAs can be related to their surface area. Non-calcined granules were difficult to handle and easy to crush. Hardened granules showed heavy metal absorption on their outer surfaces. Absorption capacity of sintered HA particles towards lead was lower but adsorbed lead ions were spread inside the porous structure of HA granules more evenly. Under flow conditions, lead ions were captured by HA at a rate of 0.5 mg g⁻¹ min⁻¹. Small lead phosphate aggregates were released from the HA sorbent together with calcium ions. Size of the aggregates depended on the lead concentration and ranged from 1–50 μm in diameter; the aggregates could be removed by ultrafiltration. Results show that porous hardened HA granules can be used as an efficient phosphate source for the immobilization of lead ions from aqueous media. Organic ligands tend to interfere with the water purification procedure.     

Sorption of cesium from water solutions on potassium nickel hexacyanoferrate-modified <Emphasis Type="Italic">Agaricus bisporus</Emphasis> mushroom biomass

In order to gain biosorbent that would have the ability to bind cesium ions from water solution effectively, potassium nickel hexacyanoferrate(II) (KNiFC) was incorporated into the mushroom biomass of Agaricus bisporus. Cesium sorption by KNIFC-modified A. bisporus biosorbent was observed in batch system, using radiotracer technique using ¹³⁷Cs radioisotope. Kinetic study showed that the cesium sorption was quite rapid and sorption equilibrium was attained within 1 h. Sorption kinetics of cesium was well described by pseudo-second order kinetics. Sorption equilibrium was the best described by Freundlich isotherm and the distribution coefficient was at interval 7,662–159 cm³ g⁻¹. Cesium sorption depended on initial pH of solution. Cesium sorption was very low at pH₀ 1.0–3.0. At initial pH 11.0, maximum sorption of cesium was found. Negative effect of monovalent (K⁺, Na⁺, NH₄ ⁺) and divalent (Ca²⁺, Mg²⁺) cations on cesium sorption was observed. Desorption experiments showed that 0.1 M potassium chloride is the most suitable desorption agent but the complete desorption of cesium ions from KNiFC-modifed biosorbent was not achieved.     

The Enthalpy and Kinetics of Sorption on VION Fibrous Chemisorbents

The enthalpy and kinetics of interaction of acids and alkalis with VION KN-1 and VION AN-1 weakly ionized fibrous chemisorbents were determined by the calorimetric and sorption techniques. The interaction of the chemisorbents, no matter what their initial form, with acids and alkalis was exothermic, and the maximum thermal effect was attained within the initial period of 10–20 min. The sorption of Cu²⁺, Co²⁺, Ni²⁺, Zn²⁺, and Cd²⁺ by the salt (Na) form of the cation exchanger was endothermic, and the enthalpy of the process depended on the nature of metal cations and their concentration in solution. Original Russian Text ? V.D. Kopylova, O.M. Zverev, A.V. Astapov, Yu.S. Peregudov, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 4, pp. 739–744.     

Investigation of the Cr(VI) removal from aqueous solutions by stabilized iron-nanoparticles using 51Cr-tracer

Stabilized iron-nanoparticles were used for the Cr(VI)-removal from acidic and neutral aqueous solutions (pH 1, 3, 5 and 7). The chromium interaction with the iron-nanoparticles was studied by a batch technique under different experimental conditions (e.g. pH, temperature, contact time, solid to liquid ratio) using ⁵¹Cr as radiotracer and gamma-ray spectroscopy. The results showed that the Cr-removal was fast and the interaction kinetics could be described by a pseudo-second order rate equation. The maximum Cr-removal was observed from solutions of initial pH 3. The sorption showed a positive temperature and solid to liquid ratio dependence. The experimental results were modeled using the Langmuir, Freundlich and Dubinin–Radushkevich isotherm equations and compared with literature data obtained using other sorbents. X-ray photoelectron spectroscopy (XPS) measurements were performed in order to obtain information about the mechanism of the Cr-removal by the iron-nanoparticles. It was demonstrated that the dominated process based on the Cr(VI) reduction followed by the simultaneous oxidation of iron.     

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.     

The determination of arsenic and selenium in standard reference materials using sector field ICP-MS in high resolution mode

Sector field ICP-MS was used to analyse As and Se in a range of standard reference materials (NIST 1643d Water, NIST 1573a Tomato Leaves, NIST 1566a Oyster Tissue, NIST 2704 Buffalo River Sediment and Bio-Rad Reference Urine Level 2). A spectral resolution of m/Δm = 7500 enabled ⁷⁵As and ⁷⁷Se to be separated from problematic ArCl interferences. Following microwave acid digestion, solid samples were typically diluted 1 + 99 prior to analysis, while the urine sample was diluted 1 + 9. The water sample was analysed undiluted and diluted 1 + 9. Despite near baseline spectral separation, ⁷⁵As and ⁷⁷Se were still found to be influenced by ArCl at high Cl concentrations, the effect being most pronounced for ⁷⁷Se. When necessary ⁸²Se was also monitored to determine the accuracy of the ⁷⁷Se results. Detection limits (LOD, based on 3σ of 10 replicates) for ⁷⁵As, ⁷⁷Se and ⁸²Se in ultra-pure water, 1% (w/w) HNO₃ and 1% (w/w) HCl were ∼ 0.1, ∼ 0.2 and ∼ 0.5 ng g^–1, respectively. Although signal intensities when using high resolution were ∼ 1% of that found when using low resolution mode (m/Δm = 300), measured As concentrations and certified values were found to agree to within ± 11% for all samples analysed. The concentration of Se in NIST 1566a Oyster Tissue, NIST 2704 Buffalo River Sediment and Bio-Rad Reference Urine were found to be in agreement with certified values to within ± 15– 20%, as measured by ⁷⁷Se. However, closer agreement (± 5%) was found when these samples were analysed using ⁸²Se. The Se concentration in NIST 1643d Water was found to agree to within ± 5% of the certified value (depending on dilution factor). Due to the low concentration of Se in NIST 1573a Tomato Leaves, quantitation was not possible (below LOQ, 10σ). As a consequence of the lower ion transmission when using resolution 7500, analytical precisions were found to be elevated over that normally observed using low resolution mode, typically ± 5–20% (depending on analyte concentration and isotopic abundance). Received: 28 December 1998 / Accepted: 9 February 1999     

Ion exchange and solvent extraction of the thiourea complex cation of technetium-99 from mineral acid solutions

Sorption of macroamounts of the technetium thiourea complex cation by a cation exchange resin was studied in HNO₃ and HClO₄ solutions as a function of the concentration and reaction time for pertechnetate with thiourea. The distribution ratio reaches the value of 10³ and may be even higher (>10⁴) when sorption proceeds from a solution of the solid complex in dilute perchloric acid. The complex cation is extracted from 0.25–1M HNO₃ with solutions of the bis(1,2-dicarbollyl)cobalt(III) anion in nitrobenzene—chloroform (1:1), log D=2.75−2.95 being obtained. The preconcentration and separation of technetium on cation exchangers from dilute mineral acids would seem to be one field of application.     

Effects of glucose,glutamine, and malate on the metabolism of spodoptera frugiperda clone 9 (sf9) cells

Optimal design and operation of bioreactors for insect cell culture is facilitated by functional relations providing quantitative information on cellular metabolite consumption kinetics, as well as on the specific cell growth rates (μ_G). Initial specific consumption rates of glucose, malate, and oxygen, and associated changes in μ_G, were measured forSpodoptera frugiperda clone 9 (Sf9) cells grown in batch suspension culture in medium containing 7–35 mM glucose, 0–16 mM malate, and 4–16 mM glutamine. The initial specific glucose consumption rate (q _G ) could be described by a modified Michaelis-Menten equation treating malate as a “competitive” inhibitorK ₁ = 6.5 mM) and glutamine as a “noncompetitive” inhibitorK _I = 14 mM) ofq _G , with aK _m of 7.1 mM for glucose. All three carbon sources were found to increase μ_G in a saturable manner, and a modified Monod equation was employed to describe this relationship (μ_Gmax = 0.047 h^-1). The initial specific oxygen consumption rate (q_O2) in Sf9 cells could be related to μ_G by the maintenance energy model, and it was calculated that, under typical culture conditions, about 15–20% of the cellular energy demand comes from functions not related to growth. Fitted parameters in mathematical expression for μg: K₄, Monod constant for glucose (mM); K₅, modified Monod constant for malate (mM); K₆, Monod constant for glutamine (mM); m_o2, specific consumption rate of oxygen by the cells under zero-growth conditions (nmol/cell/h); q_F, initial specific fumarate production rate (nmol/cell/ h);q _G , initial specific glucose consumption rate (nmol/cell/h); q_Gmax, maximum initial specific glucose consumption rate (nmol/cell/h);q _M , initial specific malate consumption rate (nmol/cell/h); q_o2, initial specific oxygen consumption rate (nmol/cell/h); Y_o2, cell yield on oxygen (cells/nmol); μ, initial specific cell growth rate (h^-1); μ_g, initial specific cell growth rate (h^-1); μG_max, maximum initial specific cell growth rate (h^-1).     

Spectral distribution of the radiochemiluminescence from gamma-irradiated humic acid

This study was conducted to investigate radiochemiluminescence (RCL) spectra (340–650 nm), kinetics and absorption spectra of humic acids (HA) after their exposure of γ-radiation (absorbed doses of 1–10 kGy, ⁶⁰Co) in model systems. The kinetics and spectral distribution of RCL were measured using the single photon counting method (SPC) and cut-off filters. Absorption spectra (range 240–800 nm) of irradiated solutions indicated that post-radiative degradation/polymerization processes take place in the HA changing their macromolecule or properties. The intensity of the delayed RCL was nonlinearly and suggested that complex radical formation mechanisms were still involved in the post-radiative reactions.     

Sorption of aliphatic alcohols, acetates, and their mixtures by corn starch cryotextures depending on concentrations of sorbates and starch in initial sols

The sorption of a mixture ofn-hexanol,n-octanol, andn-hexyl andn-octyl acetates from aqueous solutions by corn starch cryotextures was studied using capillary gas chromatography at different initial concentrations of the sorbates (1–25 mmol L⁻¹) and corn starch (2–6%). The amounts of compounds sorbed by cryotextures are proportional to the increase in their concentration in the initial sol and the length of the alkyl substituent. Linear equations describing the concentration dependence were proposed. The sorption ofn-hexanol from a mixture of substances containingn-octanol increases as compared to that from the individual alcohol. It was shown that the degree of sorption of aroma by cryotextures was independent of the content of starch in the initial sol. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1496–1501, August, 1999.     

A high efficient sorption of U(VI) from aqueous solution using amino-functionalized SBA-15

Uranium is one of the most hazardous heavy metal due to its long half-life radioactivity, high toxicity and mobility as aqueous uranyl ion (UO₂ ²⁺) under ordinary environmental conditions. Herein, amino functionalized SBA-15 (APSS) was developed as a rapid and efficient sorbent for removal of U(VI) from the environment. The APSS sample was synthesized by grafting method and was characterized by SEM, NMR, SAXS, and N₂ sorption/desorption isothermal experiments. The sorption of U(VI) by APSS was investigated under different conditions of pH, contact time, initial U(VI) concentration, ionic strength and solid–liquid ratio. The results show that the sorption of U(VI) by APSS is strongly dependent on pH but independent of ionic strength and solid–liquid ratios (m/V). The sorption is ultrafast with an equilibrium time of less than 30 min, and the sorption capacity is as large as 409 mg/g at pH 5.3 ± 0.1. Besides, the U(VI) sorption by APSS from extremely diluted solution and the desorption of U(VI) from APSS were also studied. It is found that 100 mg of APSS can almost completely remove the U(VI) ions from 4 L aqueous solution with the U(VI) concentration as low as 4.2 ppb and the sorbed U(VI) can be completely desorbed by 0.1 mol/L nitric acid. The results strongly reveal the high performance of the APSS material in the removal and preconcentration of U(VI) from the aqueous solution.     

GC–ICP–MS determination of dimethylselenide in human breath after ingestion of <Superscript>77</Superscript>Se-enriched selenite: monitoring of in-vivo methylation of selenium

The amount of volatile dimethylselenide (DMSe) in breath has been monitored after ingestion of sub-toxic amounts of selenium (300 μg ⁷⁷Se, as selenite) by a healthy male volunteer. The breath samples were collected in Tedlar bags every hour in the first 12 h and then at longer intervals for the next 10 days. The samples were subjected to speciation analysis for volatile selenium compounds by use of cryotrapping–cryofocussing–GC–ICP–MS. Simultaneously, all urine was collected and subjected to total selenium determination by use of ICP–MS. By monitoring m/z 82 and 77, background or dietary selenium and selenium from the administered selenite were simultaneously determined in the urine and in the breath—dietary selenium only was measured by monitoring m/z 82 whereas the amount of spiked ⁷⁷Se (99.1% [enriched spike]) and naturally occurring selenium (7.6% [natural abundance]) were measured by monitoring m/z 77. Quantification of DMSe was performed by using DMSe gas samples prepared in Tedlar bags (linear range 10–300 pg, R ²=0.996, detection limit of Se as DMSe was 10 pg Se, or 0.02 ng L⁻¹, when 0.5 L gas was collected). Dimethylselenide was the only selenium species detected in breath samples before and after the ingestion of ⁷⁷Se-enriched selenite. Additional DM⁷⁷Se was identified as early as 15 min after ingestion of the isotopically-labelled selenite. Although the maximum concentration of ⁷⁷Se in DMSe was recorded 90 min after ingestion, the natural isotope ratio for selenium in DMSe (77/82) was not reached after 20 days. The concentration of DMSe correlated with the total Se concentration in the urine during the experiment (R ²=0.80). Furthermore, the sub-toxic dose of 300 μg selenium led to a significant increase of DMSe and renal excretion of background selenium, confirming that selenium ingested as selenite is homeostatically controlled by excretion. The maximum concentration of DMSe resulting from the spiked selenite was 1.4 ng Se L⁻¹ whereas the dietary background level was less than 0.4 ng Se L⁻¹. Overall excretion as DMSe was calculated to be 11.2% from the ingested selenite within the first 10 days whereas urinary excretion accounts for nearly 18.5%.     

Powerful preconcentration method for capillary electrophoresis and its application to analysis of ultratrace amounts of polycyclic aromatic hydrocarbons

For environmental analyses, a high-performance and powerful preconcentration system exceeding 1×10⁷-fold was developed that was composed of a blue cotton method (solid extraction method)/homogeneous liquid–liquid extraction method/on-line concentration method for capillary electrophoresis (CE). This system was named the “triplex concentration system” and it was achieved by finding a new phase-separation phenomenon (homogeneous liquid–liquid extraction) from a water-miscible organic solvent. Parts per trillion levels of polycyclic aromatic hydrocarbons (PAHs) were used as model analytical targets in this study. With the proposed method, 20-L levels of environmental water could be preconcentrated up to 1×10⁷-fold within a maximum of 1 h. The parts per trillion levels of PAHs were easily determined even using UV/CE, which has a serious sensitivity problem, and the detection limit of benzo[a]pyrene was 3.60 ppt. This system was also used as a practical monitoring method for the Miyata River (in Japan).     

Sorption of aliphatic alcohols from aqueous solutions by starch cryotextures

Capillary GLC was applied to study the sorption ofn-butanol,n-hexanol,n-octanol, and linalood from aqueous solutions by com starch cryotextures. The concentrations of alcohols in aqueous solutions were varied from 0.5 to 15 mmol L⁻¹. The sorption of alcohols by crytotextures formed of sols containing these alcohols and the coefficients of their. distribution depend on the initial concentration and structure of the alcohols.n-Butanol is not sorbed by the corn starch cryotextures over the range of 0.5–80 mmol L⁻¹. The sorption of other alcohols increases with increasing length of the alkyl substituent and the concentration of the alcohol. The highest sorption capacity of the cryotexture (88%) was observed forn-octanol. The sorption of linalool decreases due to the double bonds and branching in its molecules. Translated fromIzestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 734–737, April, 1999.     

Impact of environmental conditions on the sorption behavior of Co(II) on Na-rectorite studied by batch experiments

The sorption of Co(II) from aqueous solution on Na-rectorite 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 Co(II) was strongly dependent on pH. 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 Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms at three different temperatures. 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 Na-rectorite was spontaneous and endothermic. Experimental results indicate that Na-rectorite is a suitable adsorbent for preconcentration and solidification of Co(II) from large volumes of aqueous solutions.     

Determination of ultra-trace amounts of inorganic selenium species in natural water by ion chromatography-inductively coupled plasma-mass spectrometry coupled with nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> solid phase extraction

This work presents a nano-Al₂O₃ solid phase extraction technique for the determination of ultra-trace amounts of inorganic selenium species in aqueous systems using ion chromatography inductively coupled plasma-mass spectrometry (IC-ICP-MS). In this experiment, the inorganic selenium species were successfully extracted on a nano-Al₂O₃ solid phase column and then quantitative eluted with a 100 mmol L⁻¹ NaOH solution. Extraction conditions such as solvent identity, solvent concentration, solvent volume, solvent pH and salt addition were optimized. Under the optimum extraction conditions (elute solvent: 100 mmol L⁻¹ NaOH, solvent volume: 4 mL, pH: 7.0), low detection limits (Se (IV): 6 ng L⁻¹, Se (VI): 11 ng L⁻¹; RSD<5.0%) and good linear range (0.5–100 ng mL⁻¹, R² > 0.999) were obtained for all of the analytes. Good spiked recoveries over the range of 80–98% were obtained by applying the proposed method on real environmental water samples. These results indicated that this method is very sensitive and reliable when monitoring trace levels of inorganic selenium species in aqueous samples.