Search Results
Abstract
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.
Abstract
The sorption of UO2 2+ from aqueous solution on attapulgite was investigated as a function of contact time, solid content, pH, ionic strength, foreign ions, humic acid (HA), and fulvic acid (FA) under ambient conditions by using batch technique. The attapulgite sample was characterized by XRD and FTIR in detail. The results indicated that the sorption of UO2 2+ was strongly dependent on pH and ionic strength. The sorption of UO2 2+ on attapulgite increased quickly with rising pH at pH < 6.5, and decreased with increasing pH at pH > 6.5. The presence of HA or FA enhanced the sorption of UO2 2+ on attapulgite obviously at low pH because of the strong complexation of surface adsorbed HA/FA with UO2 2+ on attapulgite surface. Sorption of UO2 2+ on attapulgite was mainly dominated by ion-exchange or outer-sphere surface complexation at low pH values, but by inner-sphere surface complexation at high pH values. The results indicate that attapulgite is a very suitable adsorbent for the preconcentration and solidification of UO2 2+ from large volumes of aqueous solutions because of its negative surface charge and large surface areas.
Abstract
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.
Abstract
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.
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.
Abstract
Sorption of U(VI) from aqueous solution to Na-attapulgite was investigated at different experimental chemistry conditions by using batch technique. The attapulgite sample was characterized by FTIR and XRD. Sorption of U(VI) on attapulgite was strongly dependent on pH and ionic strength. The sorption of U(VI) on attapulgite increased quickly with rising pH at pH < 6, and decreased with increasing pH at pH > 7. The presence of humic acid (HA) enhanced the sorption of U(VI) on attapulgite obviously at low pH because of the strong complexation of surface adsorbed HA with U(VI) on attapulgite surface. Sorption of U(VI) on attapulgite was mainly dominated by ion exchange and/or outer-sphere surface complexation at low pH values, whereas the sorption was attributed to the inner-sphere surface complexation or precipitation at high pH values. The sorption increased with increasing temperature and the thermodynamic parameters calculated from the temperature dependent sorption isotherms suggested that the sorption of U(VI) on attapulgite was a spontaneous and endothermic process. The results indicate that attapulgite is a very suitable material for the preconcentration of U(VI) ions from large volumes of aqueous solutions.
Abstract
The history of sorption and ion-exchange processes starts with the use of natural materials which properties were discovered coincidentally and ends with the age of polymer and anorganic—or synthetic sorbents specifically made for a particular project. Its objectives are focused on sorption of anthropogenic radionuclides originating from nuclear power plant operations (fission, activation, corrosion products and transuranium elements) on bentonites, zeolites, hydroxyapatites, magnetic sorbent, ferrocyanides, and silica sorbent. Bentonites from Slovak deposits should be used as part of multi-barrier system in deep geological repository for spent nuclear fuel and high level radioactive waste. Zeolites are used as molecular sieves, catalysts, ion-exchangers, sorbents, water softeners, in wastewater treatment, in chemistry industry, buildings. Hydroxyapatite is a suitable sorbent for heavy metals and radionuclides due to its low water solubility, high stability under reducing and oxidizing conditions, high specific surface area and good buffering properties. The leaching wastes from the Sereď hydrometallurgical plant represent a large stock of inexpensive, ready-to-use magnetic sorbent for the decontamination of soil or sediments in their common suspensions, followed by the magnetic separation and sorbent recycling. Insoluble ferrocyanides of nickel are highly selective sorbents for heavy alkali metals ions, and therefore can be used to separate cesium from liquid radioactve waste. Silica sorbents modified with imidazole can be used for the separation of cobalt ions from aqueous solution.
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.
. Sorption studies of Zn(II) and Cu(II) onto vegetal compost used on reactive mixtures for in situ treatment of acid mine drainage, Water Research , Vol. 39, No. 13, 2005, pp. 2827–2838. Ayora C
Abstract
Distribution coefficients (K d), apparent diffusion coefficients (D a) and retardation factor (Rf) in this work obtained by batch and through-diffusion experiments have been performed, respectively. The accumulative concentration method developed by Crank (The mathematics of diffusion, <cite>12</cite>) was applied to realize apparent and effective diffusion coefficient (D a and D e) of Se. Besides, a non-reactive radionuclide, HTO, was initially conducted in through-diffusion experiment for assessing the ability of radionuclide retardation. The distribution coefficients (K d) obtained by batch tests in 14 days under aerobic and anaerobic systems were 6.98 ± 0.35 and 5.21 ± 0.25 mL/g. Moreover, Rfcal and K d cal of Se obtained from accumulative concentration’s method in through-diffusion test showed an obvious discrepancy with the increase of length/diameter (L/D) ratio. However, it presented an agreement of RfH/Se and K d H/Se in a various L/D ratio by comparison of apparent diffusion coefficient’s (D a) between HTO and Se. It appears that the RfH/Se and K d H/Se obtained from the through-diffusion experiments are lower than those derived from the batch experiments. Therefore, it demonstrates that reliable Rf and K d of Se by through-diffusion experiments could be achieved at a non-reactive radiotracer (HTO) prior to tests and will be more confident in long-term performance assessment of disposal repository.
