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Journal of Radioanalytical and Nuclear Chemistry
Authors: Concetta De Stefano, Antonio Gianguzza, Alberto Pettignano, Daniela Piazzese, and Silvio Sammartano

Abstract  

Stability data on the formation of dioxouranium(VI) species with polyacrylic (PAA) and fulvic acids (FA) are reported with the aim to define quantitatively the sequestering capacity of these high molecular weight synthetic and naturally occurring ligands toward uranium(VI), in aqueous solution. Investigations were carried out at t = 25 °C in NaCl medium at different ionic strengths and in absence of supporting electrolyte for uranyl–fulvate (

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–FA) and uranyl–polyacrylate (
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–PAA, PAA MW 2 kDa) systems, respectively. The experimental data are consistent with the following speciation models for the two systems investigated: (i) UO2(FA1), UO2(FA1)(FA2), UO2(FA1)(FA2)(H) for
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–fulvate (where FA1 and FA2 represent the carboxylic and phenolic fractions, respectively, both present in the structure of FA), and (ii) UO2(PAA), UO2(PAA)(OH), (UO2)2(PAA)(OH)2 for
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–polyacrylate. By using the stability data obtained for all the complex species formed, the uranium(VI) sequestration by PAA and FA was expressed by the pL50 parameter [i.e. the −log(total ligand concentration) necessary to bind 50% of uranyl ion] at different pH values. A comparison between pL50 values of FA and PAA and some low molecular weight carboxylic ligands toward uranyl ion is also given.

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Journal of Thermal Analysis and Calorimetry
Authors: Jiří Kučerík, Petra Bursáková, Alena Průšová, Lucie Grebíková, and Gabriele Ellen Schaumann

) are fulvic acids (FA) and humic acids (HA); FA are fractions of NOM soluble at all pH values, while HA are soluble only in alkaline solutions [ 2 ]. Hydration is the crucial factor playing role in biological function of molecules in both living

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Abstract  

Five column experiments have been carried out to investigate the effect of flow rate on the breakthrough curves (BTCs) of phosphate, fulvic acid, and uranium(VI) onto a silica column. Both BTCs of phosphate and fulvic acid, and three BTCs of uranium(VI) in the presence and absence of phosphate or fulvic acid at high flow rate published in the previous paper [<cite>1</cite>] were compared with corresponding initial parts of BTCs at low flow rate in this paper. Each BTC in this paper was expressed as both C/Co–t and C/Co–V/Vo plots, where C and Co are the concentrations in the influent and the effluent respectively, t and V are the time and the effluent volume from the start of injection of pulse solution respectively, Vo is the pore volume of the SiO2 column. Based on the experimental results and the relationship among V, t, and flow rate F, it was found that there are advantages to using C/Co–V/Vo plot as BTC to study the effect of flow rate. Based on these comparisons of C/Co–V/Vo plots at different flow rates and the theoretical analysis from the Bohart–Adams sorption model, it was found that the right shift (increase in V/Vo of breakthrough), the left shift (decrease in V/Vo of breakthrough), and the non-shift (non-change in V/Vo of breakthrough) of initial parts of BTCs with increasing flow rate are certain to occur instead of only left shift and that three different trends of shifts can be mainly attributed to different rate-controlling mechanisms of sorption process.

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Abstract  

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.

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Abstract  

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.

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. Res. Bull. 124 1995 Nand Ram, Raman, K. V. (1981): Characterization of humic and fulvic acids extracted from different

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Abstract  

Complexation of trivalent europium by a well characterized soil fulvic acid was investigated by equilibrium dialysis titration method ([FA]=24 mg·dm–3, [Eu]t=9.0·10–7–3.5·10–6 mol·dm–3, pH 6.0). The concentrations of the fulvate bound and free europium were measured radiometrically using152Eu as a tracer. The experimental results were evaluated using a bimodal normal distribution model and a plot with two overlapping normal distributions was obtained which gave two means logKI=7.0, I=1.1; µII=4.9, II=0.5) values for binding of europium by two classes of sites in fulvic acid. A multiligand model was assumed for fulvic acid, based upon the Eu(III) luminescence studies (7F0 5D0 excitation) on many organic acids as model ligands.

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Abstract  

Sorption and desorption of Co(II) on montmorillonite under ambient conditions as a function of pH, ionic strength and fulvic acid are studied by batch technique. The results indicate that the sorption of Co(II) is dependent on pH, and ionic strength. The sorption-desorption hysteresis is found in the desorption tests. Surface complexation is considered as the main sorption mechanism of Co(II) on montmorillonite. The presence of fulvic acid (FA) enhances the sorption of Co(II) on montmorillonite. Montmorillonite is considered as a promising candidate for the solidification and pre-concentration of Co(II) from large volume of solutions.

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Summary  

Sorption and desorption of radiostrontium on the red earth and its solid components in the presence and absence of fulvic acid were investigated by a batch technique under ambient conditions at pH 5.3±0.1 and T = 25±2 °C. The organic matter in the red earth is a significant trap of 90Sr2+ and the presence of fulvic acid enhances the sorption of 90Sr2+ on the red earth at pH 5.3. It was found that all the sorption and desorption isotherms are linear and the sorption of 90Sr2+ on the red earth can be described by a reversible sorption process and the sorption mechanism is mainly ion-exchange. The effect of ionic strength on 90Sr2+ sorption was also investigated.

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Abstract  

The effect of pH and fulvic acid on the sorption of Sr on bentonite was investigated by using batch experiments. The sorption and desorption isotherms of Sr on bentonite were determined at room temperature, at pH 6.0±0.2 and in presence of 0.1M NaCl. It was found that the sorption of Sr is independent at pH<8, and then increases slightly with increasing pH. Fulvic acid increases the sorption of Sr significantly on bentonite at low pH, but decreases the sorption of Sr at pH>8. The sorption of Sr on bentonite can be described by a reversible sorption process and the sorption mechanism consists mainly of ion exchange.

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