Study of sorption processes of strontium on the synthetic hydroxyapatite

The sorption of strontium on synthetic hydroxyapatite was investigated using batch method and radiotracer technique. The hydroxyapatite samples were prepared by a wet precipitation process followed by calcination of calcium phosphate that precipitated from aqueous solution. Also, commercial hydroxyapatites were used. The sorption of strontium on hydroxyapatite depended on the method of preparation and it was pH independent ranging from 4 to 9 as a result of buffering properties of hydroxyapatite. The distribution coefficient K _d was significantly decreased with increasing concentration of Sr²⁺ and Ca²⁺ ions in solution with concentration above 1 × 10⁻³ mol dm⁻³. The percentage strontium sorption for commercial and by wet method prepared hydroxyapatite was in the range of 83–96%, while calcined hydroxyapatite was ranging from 10 to 30%. The experimental data for sorption of strontium have been interpreted in the term of Langmuir isotherm. The sorption of Sr²⁺ ions was performed by ion-exchange with Ca²⁺ cations on the crystal surface of hydroxyapatite. Although calcined hydroxyapatite is successfully used as biomaterial for hard tissues repair, it is not used for the treatment of liquid wastes.     

Competitive sorption between glyphosate and inorganic phosphate on clay minerals and low organic matter soils

Inorganic phosphate may influence the adsorption of glyphosate to soilsurface sites. It has been postulated that glyphosate sorption is dominatedby the phosphoric acid moiety, therefore, inorganic phosphate could competewith glyphosate for surface sorption sites. We examine sorption of glyphosatein low organic carbon systems where clay minerals dominate the available adsorptionsites using ³²P-labeled phosphate and ¹⁴C-labeled glyphosateto track sorption. We found glyphosate sorption strongly dependent on phosphateadditions. Isotherms were generally of the L type, which is consistent witha limited number of surface sites. Most sorption on whole soils could be accountedfor by sorption observed on model clays of the same mineral type as foundin the soils.     

Sorption of neptunyl(V) cations on suspended silicate: Effects of pH, ionic strength, complexing anions, humic acid, and metal ions

Sorption of NpO₂ ⁺ on silicate (10.00 g/l) particles dispersed in sodium perchlorate media was studied as a function of pcH and ionic strength at 298 K. The sorption increased with increased pcH in the range of ∼6.5 to 9.2, above which saturation was observed. An increase in ionic strength from 0.20M to 1.00M (NaClO₄), increased the NpO₂ ⁺ sorption, which then decreased at 1.50M (NaClO₄) for 7<pcH<8.5. The effects of different types of ligands on the sorption of NpO₂ ⁺ to suspended silicate were investigated. The types of ligands included: (i) inorganic anions (fluoride, carbonate, phosphate (ii) N-donors (ethylenediamine, 1,10 phenanthroline (iii) carboxylic acids (oxalic acid, citric acid, iminodiacetic acid, ethylenediaminetetraacetic acid) and (iv) humic acid. A synergistic enhancement in sorption to the suspended silicate was observed for phosphate, oxalate, ethylenediaminetetraacetic acid, ethylenediamine, 1,10 phenanthroline (5<pcH<8) and humic acid (6.5<pcH<8.8). This behavior was attributed to the formation of ternary NpO₂ ⁺/silicate/ligand complexes. The effects of Ca(II) (1.00·10⁻³M) and Eu(III) (1.00·10⁻⁴ and 1.00·10⁻³M) ions on NpO₂ ⁺ sorption to suspended silicate were also investigated. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India.     

Application of co-electroosmotic capillary electrophoresis for the determination of inorganic anions and carboxylic acids in soil and plant extract with direct UV detection

Summary Indirect UV detection in capillary zone electrophoresis (CZE) is frequently used for the determination of inorganic anions and carboxylic acids. However, there are few reports on direct UV detection of these solutes in real samples. This paper describes the use of direct UV detection of inorganic anions and organic acids in environmental samples using co-electroosmotic capillary zone electrophoresis (co-CZE) at 185 nm. The best separation and detection of the solutes was achieved using a fused silica capillary with an electrolyte containing 25 mM phosphate, 0.5 mM tetradecyltrimethylammonium bromide (TTAB) and 15% acetonitrile (v/v) at pH 6.0. Four common inorganic anions (Cl⁻, NO₂ ⁻, NO₃ ⁻ and SO₄ ²⁻) and 11 organic acids (oxalic, formic, fumaric, tartaric, malonic, malic, citric, succinic, maleic, acetic, and lactic acid), were determined simultaneously in 15 min. Linear calibration plots for the test solutes were obtained in the range 0.02–0.5 mM with detection limits ranging from 1–9 μM depending on the analyte. The proposed method was successfully used to determine inorganic anions and carboxylic acids in soil and plant tissue extracts with direct injection of the sample.     

Sorption of Am<Superscript>3+</Superscript> cations on suspended silicate: Effects of pH,ionic strength,complexing anions,humic acid and metal ions

Sorption of tracer Am³⁺ to silicate particles was studied as a function of pcH (4 to 9) and of ionic strength [0.20M to 1.50M (NaClO₄)] at 298 K. The sorption increased with increased pcH from 4 to 6 above which saturation was observed. The insensitivity of Am³⁺ sorption to increased ionic strength indicates inner-sphere complexation with the surface silicate sites. The effects of different complexing anions such as carbonate, acetate, oxalate, phosphate, citrate, EDTA and humic acid, on Am³⁺ sorption were investigated. Synergistic enhancement in Am³⁺ sorption was observed in the presence of phosphate (4≤pcH≤7) and acetate (4≤pcH≤5) ligands at 0.20M NaClO₄. The presence of the other ligands inhibited Am³⁺ sorption in the order: EDTA > citrate > oxalate > carbonate. Am³⁺ sorption in the presence of HA (25.00 mg/l) increased in the pcH range of 4.0 to 5.5, then decreased. Increased ionic strength enhanced Am³⁺ sorption in the presence of 25.00 mg/l HA for 4≤pcH≤9. The sorption increased in the presence of a mixture of HA (25.00 mg/l) and phosphate (1.00·10⁻³M) as compared to that of HA (25.00 mg/l) alone. The presence of Fe³⁺ (1.00·10⁻⁴M) enhanced Am³⁺ sorption at pcH∼4 but suppressed it from pcH of 5 to 9; 1.00·10⁻⁴M of Ca²⁺ and of UO₂²⁺ ions had no effect on the sorption profile. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai -400 085, India.     

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

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

Effects of phosphate and Cr3+ on the sorption and transport of uranium(VI) on a silica column

Six column experiments were performed and seven breakthrough curves (BTCs) and seven displacement (desorption) curves (DPCs) of phosphate and U(VI) were obtained, which demonstrated the effects of phosphate and Cr³⁺ on the sorption and transport of U(VI) on a silica column at pH 3 and uranium concentration 10⁻⁵–10⁻⁶ mol/L of the influent. It was found that in the presence of phosphate sorbed preliminarily on the silica column, the amount of U(VI) sorbed on this column is significantly increased owing to the interaction of U(VI) with phosphate sorbed as compared with that in the absence of phosphate, and the breakthrough and the mean residence time of U(VI) on this column are similar to those in the absence of phosphate. While the effect of simultaneous injection of Cr³⁺ on the retardation of U(VI) on the silica column, the maximum concentration of BTC and the amount of U(VI) sorbed was found to be insignificant. Transport and sorption studies of U(VI) are important, since all uranium isotopes are radioactive, there is a need to understand the potential for migration away from radioactive waste storage and mill tailing sites.     

Plant Growth Promotion by an Extracellular HAP-Phytase of a Thermophilic Mold <Emphasis Type="Italic">Sporotrichum thermophile</Emphasis>

Phytase of the thermophilic mold Sporotrichum thermophile Apinis hydrolyzed and liberated inorganic phosphate from Ca⁺², Mg⁺², and Co⁺² phytates more efficiently than those of Al³⁺, Fe²⁺, Fe³⁺, and Zn²⁺. The hydrolysis rate was higher at 60 °C as compared to 26 °C. Among all the organic acids tested, citrate was more effective in enhancing solubilization of insoluble phytate salts by phytase than others. The dry weight and inorganic phosphate contents of the wheat plants were high when supplemented with phytase or fungal spores. The plants provided with 5 mg phytate per plant exhibited enhanced growth and inorganic phosphate. With increase in the dosage of phytase, there was increase in growth and inorganic phosphate of plants, the highest being at 20 U per plant. The compost made employing the combined native microflora of the wheat straw and S. thermophile promoted growth of the plants. The plant-growth-promoting effect was also higher with the compost made using S. thermophile than that from only the native microflora.     

A microtiter plate assay for the detection of inhibitors of the Na +, K + -ATpase

A rapid microtiter plate assay for the detection of inhibitors of the Na⁺, K⁺-ATPase has been developed. The assay is based on the measurement of inorganic phosphate released from the substrate, ATP, and has been designed to be carried out in the individual wells of a microtiter plate. Since the production of inorganic phosphate is determined colorimetrically, multiple samples can be tested simultaneously using a microtiter plate reader. This microtiter plate assay is particularly useful for screening large numbers of samples, such as microbial culture supernatants.     

Preparation of zirconium phosphate on support material and its application for the sorption of some radioions

Several sorbents were prepared by precipitating zirconium phosphate on activated carbon support material. The main parameters of the chemical procedure were optimized in order to obtain the highest decontamination factors which can be achieved in the case of Cs⁺, Sr²⁺ and I⁻ ions. For the characterization of the sorbents, sorption isotherms and capacity data were determined. The reproducibility of the preparation is about 10%.     

Effect of pH,fulvic acid and temperature on sorption of Th(IV) on zirconium oxophosphate

Sorption of Th(IV) on Zr₂O(PO₄)₂ as a function of contact time, reaction temperature, pH, ionic strength and solid-to-liquid ratio (m/V) is studied under ambient condition by using batch technique. Effects of fulvic acid (FA), phosphate, sulfate and citrate on Th(IV) sorption are investigated in detail. A pseudo-second-order rate equation is used to simulate the kinetic sorption. The removal of Th(IV) increases with increasing pH and hardly depends on ionic strength. Sorption of Th(IV) increases with increasing m/V and reaction temperature. The presence of FA and phosphate enhances the sorption of Th(IV) on Zr₂O(PO₄)₂ while sulfate and citrate decrease the sorption. The Langmuir and Freundlich models are used to simulate the sorption isotherm of Th(IV) on Zr₂O(PO₄)₂ at different temperatures. The thermodynamic data (i.e., ∆H ⁰, ∆S ⁰, ∆G ⁰) are calculated from temperature dependent sorption isotherms. The results suggest that the sorption process of Th(IV) on Zr₂O(PO₄)₂ is spontaneous and endothermic.     

Kinetic regularities of micellar catalysis in the dephosphorylation with peroxide anion

The acid-base equilibrium of hydrogen peroxide in water solutions of cetyltrimethylammonium bromideand the reactivity of hydroxide and peroxide anions with respect to 4-nitrophenyl diethyl phosphate were investigated. In the micelles the acid ionization constant of the hydrogen peroxide increased three-fold. The application of the pseudophase distribution model under the conditions of competitive sorption of HO⁻ and HOO⁻ anions with the micelles of cetyltrimethylammonium bromide to the estimation of the main kinetic parameters of the micellar process was tested.     

Sorption of Th(IV) ions onto TiO2: Effects of contact time, ionic strength, thorium concentration and phosphate

Summary The sorption of Th(IV) onto TiO₂ was studied by the batch technique as a function of pH and ionic strength at moderate concentration (10^-4-10^-5 mol/l) and in the presence and absence of phosphate. It was found that the sorption rate of Th(IV) was relatively slow, the sorption percent was abruptly increased from pH 2 to 4, and the sorption was decreased with increasing ionic strength as a whole. In the concentration range of Th(IV) from trace concentration to 1.4 ^. 10^-4 mol/l and in the absence of phosphate, the sorption isotherms were roughly fitted the Freundlich equation at different ionic strengths and approximately constant pH. These sorption characteristics of Th(IV) onto TiO₂ were compared with those of uranyl on the same sorbent. In addition, the positive effect of phosphate on the sorption of Th(IV) onto TiO₂ was demonstrated obviously and can be attributed to strong surface binding of phosphate, and the subsequent formation of ternary surface complexes of Th(IV). The difference between the sorption characteristics of Th(IV) ions and uranyl ions onto TiO₂ is discussed.     

Sorption of mercury on chemically synthesized polyaniline

Summary Sorption of inorganic mercury (Hg²⁺) and methyl mercury, on chemically synthesized polyaniline, in 0.1-10N HCl solutions has been studied. Hg²⁺ is strongly sorbed at low acidities and the extent of sorption decreases with increase in acidity. The sorption of methyl mercury is very low in the HCl concentration range studied. Sorption of Hg²⁺ on polyaniline in 0.1-10N LiCl and H₂SO₄ solutions has also been studied. The analysis of the data indicates that the sorption of Hg²⁺ depends on the degree of protonation of polyaniline and the nature of mercury(II) chloride complexes in solution. X-ray photoelectron spectroscopy analysis (XPS) of polyaniline sorbed with mercury show that mercury is bound as Hg²⁺. Sorbed mercury is quantitatively eluted from polyaniline with 0.5N HNO₃. Polyaniline can be used for separation and pre-concentration of inorganic mercury from aqueous samples.     

Characterization of Lactose Powder Surfaces by Isothermal Microcalorimetry

Several lactose samples containing various amounts of amorphicity were studied with an isothermal microcalorimetric technique, which allow to detect the heat and the quantity of water sorption simultaneously. As interaction with vapor is characteristic of different surfaces, the samples were easy to be discriminated from each other by studying sorption behavior. With the crystalline lactose samples, the amount of sorbed water was too minor to be detected reliably with the technique, but differences were found when the energy values (J g⁻¹) were compared. In the future work, the measurement set-up will be improved so that sorption rates less than 0.1 nmol s⁻¹ can be measured repeatably and reliably. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sorption of 60Co on a synthetic titanosilicate analogue of the mineral penkvilksite-2O and antimonysilicate

The ability of two different types of synthetic inorganic ion-exchangers to sorb radioactive cobalt-60 using a batch-type method was studied. The two materials examined were the analogue of the natural titanosilicate penkvilksite-2O (AM-3) and a synthetic antimonysilicate. Ion-exchange experiments were performed with solutions labelled with radioactive cobalt (⁶⁰Co). The sorption of ⁶⁰Co onto the two samples materials were compared in terms of distribution coefficient (K _d), sorption percentage and cobalt quantity removed in mg per gram weight of the material. Several parameters were investigated viz. contact time, cobalt concentration, and sorbent concentration. It was found that the batch factor and cobalt concentration had a significant influence on the sorption of cobalt onto both of the materials. This was associated with the difference in pH generated by suspensions of the materials in water which was alkaline for the penkvilksite-2O analogue, and acid for the synthetic antimonysilicate.     

Potentiometric detection of monovalent anions separated by ion chromatography using all solid-state contact PVC matrix membrane electrode

Summary An all solid-state contact tubular PVC-matrix membrane electrode has been applied for potentiometric detection of inorganic and organic monovalent anions using phosphate and hydrogen phosphate eluents at low concentrations. This is a “monovalent detection method” as the selectivity of the electrode towards monovalent anions results in some other anions being undetected unless the concentration of those other anions is higher than 10⁻³ mol dm⁻³ in the sample solution injected. It takes only eight minutes to complete the separation with a good resolution. Theoretical and practical considerations are discussed, and in particular, sensitivity, linearity, detection limit and dynamic behaviour are presented. The use of an all solid-state contact bromide-selective electrode as a detector offers so far the best simultaneous sensitivity toward all anions when compared with other detection methods. Determination of Cl⁻ and NO₃ ⁻ ions in river, rain and drinking water samples without any further sample preconcentration has been successfully achieved. The detection limit is sub-ppb for most of anions in a 20 μL injection volume.     

Contribution to the study of the sorption of radionuclides on hydrated oxides

The mechanism of¹⁰⁶Ru(III),¹⁰⁶RuNO(II),¹⁴⁴Ce(III),¹⁴⁷Pm(III),⁸⁵Sr(II),¹³¹I⁻,³⁵SO ₄ ²⁻ , and H₂ ³²PO ₄ ²⁻ radionuclide sorption on hydrated ferrous, ferric, aluminium and chromic hydrated oxides was studied. The dependence of sorption on the pH has shown that in a certain range of pH values it is the ion exchange of the radionuclide for a proton or a hydroxyl group of the oxide that probably plays a decisive role in the sorption process. The sorption depends considerably on the pH in the whole range of studied, but its decrease with cations in alkaline media and its increase with I⁻ ion in acidic media does not agree with the above sorption mechanism. Similarly, the course of the dependence of sorption on the sorbent concentration does not indicate ion exchange to be the only mechanis, but it indicates a more complicated sorption process. Probably the sorption of colloidal forms of the radionuclides proceeds, too.     

Sorption and desorption of 125I-, 137Cs+, 85Sr2+ and 152,154Eu3+ on disturbed soils under dynamic flow and static batch conditions

Sorption of radionuclides on homogenized soils (under 2.5 mm grain size) from synthetic groundwater of 8·10⁻³M ionic strength and pH 8.5 has been studied under dynamic (flow) and static (batch) conditions. The corresponding water-soluble compounds, as carriers in the 10⁻⁶ mol/dm³ concentration, were added into the SGW prior to the experiments. Soil samples were taken from several locations around the environment of the High Level Waste Storage Facility at Nuclear Research Institute Řež plc in 5–100 cm depth. The dynamic experiments were carried out in columns made of PP+PE injection syringes of 17.8 cm length and 2.1 cm in diameter. A multi-head peristaltic pump was used for pumping the water upward through the columns at a seepage velocity of about 0.06 cm/min in average. The radioactive nuclides were added into the water stream individually in a form of a short pulse in 0.1 cm³ of demineralized water. Dynamic desorption experiments were performed with the same experimental arrangement using a mixture of 10⁻²N H₂SO₄ and 10⁻²N HNO₃ in a volume ratio of 2: 1. Retardation, distribution and hydrodynamic dispersion coefficients during transport of radionuclides were determined by the evaluation of the integral form of a simple advection-dispersion equation, used for fitting experimental data and modeling the theoretical sorption breakthrough and desorption displacement curves. The static experiments were realized in 100 cm³ plastic bottles stirring 5 g of soil samples with SGW occasionally in a soil to SGW ratio of 1: 10 (m/V). Kinetic parameters including equilibrium sorption activity, activity transfer rate constants and sorption half-times were also determined. The results of dynamic experiments were compared with static sorption experiments.     

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.