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.     

Sorption, desorption and extraction of cadmium from some arable and forest soils

Summary The behavior of cadmium labeled with ¹⁰⁹Cd in different depth horizons of arable and forest soils were studied under static (batch) conditions in three interconnected processes, which consist of sorption, desorption and extraction. In the sorption, Cd²⁺ was applied in the aqueous calcium nitrate solution. Both untreated soils and peroxide treated soils were used in order to remove organic matter from some of the soil samples used in parallel. The influence of the V/m ratio on the sorption coefficients was investigated in preliminary experiments with untreated soils. Contrary to the usually short-term sorption, a long-term sorption of cadmium was investigated in untreated and treated soil horizons, which lasted more than fortnight. Kinetic studies of sorption were carried out and cadmium concentration dependence in aqueous phase of the second order kinetic constants was observed. For evaluation of sorption and desorption processes Freundlich isotherms were used. It was found that the Freundlich adsorption intensity coefficient is more time dependent than the absorption capacity coefficient, and the sorption itself consists of rapid and slow processes according to the soil constituents. Desorption and extraction processes revealed the possibility of cadmium recovery from various soil horizons. Based on the obtained results two- or three-stage theory of cadmium retention in soils was proposed. Some new insight into the role of organic matter in the sorption/desorption process of cadmium is also presented.     

Removal of toxic metals from wastewater by Brazilian natural scolecite

The cation-exchange capacity of Brazilian natural zeolite, identified as scolecite, was studied with the aim of evaluating its applications in wastewater control. We investigated the process of sorption of chromium(III), nickel(II), cadmium(II), and manganese(II) in synthetic aqueous effluents, including sorption isotherms of single-metal solutions at 298, 313, and 333 K, by batch experiments, and the influence of pH on the process. The results have demonstrated that removal of metals from specific metal solutions is best described by a Freundlich isotherm, in which the values obtained for the Kf constants were in the following order: Cr > Mn > Cd > Ni. A Lagergren pseudo-second-order was the model that best described the sorption mechanism. The retention of metals was shown to be a function of the pH; the maximum binding capacity occurring at pH values around 6.0. Thermodynamic data indicate the spontaneity of the endothermic cation-exchange process. The values of Delta G0 suggest the following selectivity series at 298 K: Ni > Cr > Cd > Mn. The desorption process reaches equilibrium during the first 60 min of binding, suggesting that the mechanism involves specific sites located in the external surface of the scolecite.     

Purification of waste waters containing 60Co2+, 115mCd2+ and 203Hg2+ radioactive ions by ETS-4 titanosilicate

Summary The sorption of ⁶⁰Co²⁺, ^115mCd²⁺ and ²⁰³Hg²⁺ from diluted solutions (as analogues for radioactive waste waters) on ETS-4 microporous titanosilicate was studied at 277, 293, 313 and 333 K by measuring the sorption kinetics using a batch-method. The sorption of these radiocations was compared by means of the distribution coefficient and of the sorption capacity. The maximum sorption capacities follow the order: ²⁰³Hg²⁺>^115mCd²⁺3⁶⁰Co²⁺. The thermodynamic functions of the sorption processes have been estimated. The increase of the absolute value of DG° with increasing temperatures shows that higher temperatures favor ionic exchange.     

Inorganic particulates in removal of toxic heavy metal ions

Adsorption behavior of zinc, cadmium and mercury ions on hydrous titanium oxide in aqueous solution has been studied as a function of concentration of the metal ion (10⁻²−10⁻⁷M), temperature (303–333 K) and pH 3–10 by applying radiotracer technique. The kinetics of adsorption follows the first order rate law and agrees well with the classical Freundlich isotherm. The removal was found to increase with increasing pH but was suppressed in the presence of EDTA. The overall process is endothermic and irreversible in nature. Part VII. Efficient removal of cadmium ions from aqueous solutions by hydrous manganese oxideS. P. Mishra, D. Tiwary, Radiochim. Acta, 80 (1998) 213.     

Investigation of solution chemistry effects on sorption behavior of radionuclide <Superscript>64</Superscript>Cu(II) on illite

In this work, a series of batch experiments were carried out to investigate the effect of various environmental factors such as contact time, pH, ionic strength, coexisting electrolyte ions, humic substances and temperature on the sorption behavior of illite towards ⁶⁴Cu(II). The results indicated that ⁶⁴Cu(II) sorption on illite achieved equilibrium quickly. The pH- and ionic strength-dependent sorption suggested that ⁶⁴Cu(II) sorption on illite was dominated by ion exchange or outer-sphere surface complexation at pH < 7, whereas the pH-dependent and ionic strength-independent sorption indicated that the sorption process was mainly attributed to inner-sphere surface complexation at pH > 7. A positive effect of humic substances on ⁶⁴Cu(II) sorption was found at pH < 6.5, whereas a negative effect was observed at pH > 6.5. The Langmuir and Freundlich models were used to simulate the sorption isotherms of ⁶⁴Cu(II) at three different temperatures of 293, 313, and 333 K. The thermodynamic parameters (ΔH ⁰, ΔS ⁰, and ΔG ⁰) of ⁶⁴Cu(II) sorption on illite were calculated from the temperature dependent sorption isotherms, and the results indicated that the sorption of ⁶⁴Cu(II) on illite was endothermic and spontaneous. From the experimental results, it is possible to conclude that illite has good potentialities for cost-effective treatments of ⁶⁴Cu(II)-contaminated wastewaters.     

Removal of Zn(II) from aqueous solution by natural halloysite nanotubes

Clay minerals have been widely used in wastewater disposal due to their strong sorption and complexation ability towards various environmental pollutants. In this study, the removal of Zn(II) from aqueous solution by natural halloysite nanotubes (HNTs) was studied as a function of various solution chemistry conditions such as contact time, pH, ionic strength, coexisting electrolyte ions and temperature under ambient conditions. The results indicated that the removal of Zn(II) by HNTs was strongly dependent on pH and ionic strength. Langmuir and Freundlich models were used to simulate the sorption isotherms of Zn(II) at three different temperatures of 293, 313 and 333 K. The thermodynamic parameters (ΔH ⁰, ΔS ⁰ and ΔG ⁰) calculated from the temperature dependent sorption isotherms indicated that the removal process of Zn(II) by HNTs was endothermic and spontaneous. At low pH, the removal of Zn(II) was dominated by outer-sphere surface complexation and/or cation exchange with Na⁺/H⁺ on HNT surfaces, whereas inner-sphere surface complexation was the main removal mechanism at high pH. From the experimental results, one can conclude that HNTs may have a good potentiality for the disposal of Zn(II)-bearing wastewaters.     

Kinetic and thermodynamic aspects of U(VI) and Th(IV) sorption on a zeolitic volcanic tuff

Summary The sorption behavior of U(VI) and Th(IV) from simulated waste solutions on a zeolitic volcanic tuff from Nereju (Vrancea, Romania) has been studied in the absence of the ionic competition as a function of contact time, radioactive ions concentration, temperature and pH using a batch mode technique. The effect of the above-mentioned parameters on the sorption efficiency was discussed. The apparent thermodynamic parameters of the sorption of uranium and thorium onto the considered volcanic tuff were calculated, showing that the process is endothermic and higher temperatures favor the sorption process.     

Influence of synthesis method of nano-hydroxyapatite-based materials on cadmium sorption processes

Hydroxyapatite is a member of apatite mineral family, with a high stability and flexibility of the apatitic structure, which allows the substitution of Ca²⁺ from its structure with other metals. This makes it an ideal material for the disposal of long-term contaminants because of its high sorption capacity for heavy metals. The synthesis parameters variation to obtain materials with specific physical–chemical properties in function of the application field is a necessary step in process optimization. The goal of this paper was to prepare hydroxyapatite-based materials with increased sorption capacity for cadmium retaining from aqueous solutions. The materials were characterized with X-ray diffractometer, transmission electron microscopy and the average particle size was also determined. The influence of synthesis method (co-precipitation and sol–gel), silica/silicon doping, granulometry, initial cadmium concentration and temperature was studied. pH and calcium ion concentration were monitored during sorption and compared to values obtained during dissolution. The kinetic data were fitted to pseudo-first order, pseudo-second order and intraparticle diffusion models. The sorption process follows pseudo-second-order kinetics with a contribution of intraparticle diffusion. The sol–gel prepared materials follow a different reaction mechanism than those prepared by co-precipitation method.     

Sorption studies of strontium on hydrous zirconium dioxide

Summary Hydrous zirconium dioxide was prepared to study the sorption behavior and the removal of strontium from radioactive waste solutions. The hydrous zirconium dioxide were identified and characterized. The parameters affecting the strontium adsorption were investigated. Sorption data have been interpreted in terms of Langmuir equations. Thermodynamic parameters for the sorption system have been determined at 303, 313, 323 and 333 K temperatures. The values ofDH°=102.30 kJ/mol andDG°=-26.03 kJ/mol at 313 K prove that the sorption of strontium on hydrous zirconium oxide is an endothermic and a spontaneous process.     

Separation of no-carrier-added radioactive scandium from neutron irradiated titanium

In this work, sorption of Ni(II) from aqueous solution to goethite as a function of various water quality parameters and temperature was investigated. The results indicated that the pseudo-second-order rate equation fitted the kinetic sorption well. The sorption of Ni(II) to goethite was strongly dependent on pH and ionic strength. A positive effect of HA/FA on Ni(II) sorption was found at pH < 8.0, whereas a negative effect was observed at pH > 8.0. The Langmuir, Freundlich, and D-R models were applied to simulate the sorption isotherms at three different temperatures of 293.15 K, 313.15 K and 333.15 K. The thermodynamic parameters (ΔH ⁰, ΔS ⁰ and ΔG ⁰) were calculated from the temperature dependent sorption, and the results indicated that the sorption was endothermic and spontaneous. At low pH, the sorption of Ni(II) was dominated by outer-sphere surface complexation or ion exchange with Na⁺/H⁺ on goethite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH.     

Removal of Mn(II) and Cd(II) from wastewaters by natural and modified clays

The adsorption capacities of commercial and Brazilian natural clays were evaluated to test their applications in wastewater control. We investigated the process of sorption of manganese(II) and cadmium(II) present in synthetic aqueous effluents, by calculating the adsorption isotherms at 298 K using batch experiments. The influence of temperature and pH on the adsorption process was also studied. Adsorption of metals was best described by a Langmuir isotherm, with values of Q ₀ parameter, which is related to the sorption capacity, corresponding to 6.3 mg g^{− 1} for K-10/Cd(II), 4.8 mg g^{− 1} for K-10/Mn(II), 11.2 mg g^{− 1} for NT-25/Cd(II) and 6.0 mg g^{− 1} for NT-25/Mn(II). We observed two distinct adsorption mechanisms that may influence adsorption. At the first 5 min of interaction, a cation exchange mechanism that takes place at exchange sites located on (001) basal planes is predominant. This process is inhibited by low pH values. After this first and fast step, a second sorption mechanism can be related to formation of inner-sphere surface complexes, which is formed at edges of the clay. The rate constants and the initial sorption rates correlate positively with temperature in all studied systems, denoting the predominance of a physisorption process. The addition of complexing agents that are incorporated within the K10 structure, enhance metal uptake by the adsorbent. The results have shown that both Cd(II) and Mn(II) were totally retained from a 50 mg L^{− 1} solution when K10 grafted with ammonium pyrrolidinedithiocarbamate (APDC) was used as adsorbent.     

Effect of pH,ionic strength,foreign ions,humic acid and temperature on sorption of radionuclide <Superscript>60</Superscript>Co(II) on illite

In this article, a series of batch experiments were carried out to investigate the effect of various environmental factors such as contact time, solid content, pH, ionic strength, foreign ions, temperature and coexisting humic acid on the sorption behavior radionuclide ⁶⁰Co(II) on illite. The results indicated that the sorption of Co(II) was strongly dependent on pH, ionic strength and temperature. At low pH, the sorption was dominated by outer-sphere surface complexation and ion exchange on illite 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 of 303.15, 323.15 and 343.15 K. 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 illite was an endothermic and spontaneous process. The sorption test revealed that the illite can be as a cost-effective adsorbent suitable for pre-concentration of Co(II) from large volumes of aqueous solutions.     

Effect of temperature on the adsorption of phosphatidylcholine by silicon-containing materials with various degrees of order

Features of the adsorption of phosphatidylcholine (PCh) by inorganic silicon-containing materials with various degrees of order (MCM-41, MMC-1, and silica gel) from solutions in hexane under equilibrium conditions in the temperature range of 283–323 K are considered. It is found that the adsorption of the phospholipid within the C _e = (0.6–4.0) × 10^–4 mmol/dm³ range of concentrations on the investigated materials is characterized by monomolecular absorption. Differential thermodynamic characteristics (ΔG, ΔH, and ΔS) of the sorption of PCh by silicon-containing materials with various degrees of order in the temperature range of 283–323 K are considered. An increase in the affinity of silicon-containing materials toward the phospholipid upon an increase in the temperature of the sorption process is observed.

     

Effect of Temperature on Cd2+ Sorption by Mixed Oxides of Iron and Silicon

The current study focuses on the synthesis and sorption properties of two mixed oxides of iron and silicon prepared by physical mixing (M₁) and sequential precipitation methods (M₂). Both the mixed oxides were synthesized from equimolar ratios of Fe(OH)₃ and SiO₂ and characterized for surface area, EDX, XRD and PZC. The surface area, micropore volume and average pore width of the oxide M₁ were higher as compared to the oxide M₂. However, potentiometric titrations revealed that mixed oxide synthesized by this method had a very high capacity towards Cd²⁺ ions as compared to the mixed oxide M₁. Sorption of Cd²⁺ ions at pH 5 on mixed oxide, M₂ was found to increase with temperature in the range 288 to 318 K. Langmuir equation was found applicable to the sorption data with R²>0.99. Entropy (ΔS^?), enthalpy (ΔH^?) and free energy changes (ΔG^?) were calculated which revealed the process to be endothermic and spontaneous in nature.     

Sorption Mechanism of Cadmium from Aqueous Solution on Iron Sulphide

The characterization and adsorption studies of Cd²⁺ on FeS were performed. Adsorption of Cd²⁺ from aqueous solutions on synthetic iron sulphide (FeS) was investigated as a function of pH (5–7) and temperature (303–323 K). It was found that the iron sulphide (FeS) had adsorptive properties comparable with those of other adsorbents reported in the literature. The sorption of Cd²⁺ was observed to increase with the increase in pH but not strongly sensitive to temperature. The adsorption data fitted both the Kurbatov and Langmuir adsorption models. In addition, ΔG^? values were calculated from the values of the binding constant, which showed that the cadmium adsorption process was spontaneous in nature.     

Radiochemical study of Co2+ sorption on chlorite and kaolinite

In this work, the sorption behavior of Co(II) ions on natural chlorite and kaolinite as a function of time, concentration and temperature was studied.⁶⁰Co radiotracer method and the batch technique were used. The kinetic results indicated that about one day of contact time was enough to achieve equilibrium. The sorption process was described by Freundlich type isotherms. Sorption of Co(II) ions on both clays was found to be endothermic with ΔH ⁰ (kJ/mol) and ΔS ⁰ (kJ/mol·K) being 33 and 0.14 for kaolinite and 17 and 0.102 for chlorite, respectively. The magnitudes of the corresponding ΔG ⁰ values suggest that sorption occur mainly via an ion exchange mechanism on both clays.     

Self-discharge behavior of LaNi5-based hydrogen storage electrodes in different electrolytes

Nickel–metal hydride (Ni–MH) batteries using hydrogen storage alloys as negative electrode materials have been developed and commercialized because of their high energy density, high rate capability and long cycle life, without causing environmental pollution (Song et al. J Alloys Comp 298:254, 2000; Jang et al. J Alloys Comp 268:290, 1998). However, the self-discharge rate is relatively higher than that of the Ni–Cd batteries, which would certainly be disadvantageous in practical applications. The capacity loss of a battery during storage is often related to self-discharge in the cells. Self-discharge takes place from a highly charged state of a cell to a lower state of charge (SOC) and is typically caused by the highly oxidizing or reducing characteristic of one or both of the electrodes in the cell. This self-discharge behavior may be affected by various factors such as gases, impurities, temperature, type of alloy electrode, electrolytes, or charge/discharge methods. The loss of capacity can be permanent or recoverable, depending on the nature of the mechanism (chemical or electrochemical) and aging condition. In this paper, the effects of electrolyte composition and temperature on self-discharge behavior of LaNi₅-based hydrogen storage alloy electrodes for Ni–MH batteries have been investigated. It was found that both reversible and irreversible capacity loss of MH electrode tested at 333 K were higher than that at 298 K. When tested at 298 K and 333 K, reversible capacity loss was mainly affected by the electrolyte, while the irreversible capacity loss was not affected. The dissolution of Al from the electrode can be reduced more effectively in an electrolyte with Al addition, compared with that in normal electrolyte. This resulted in a lower reversible capacity loss for the electrode exposed in the Al³⁺-rich electrolyte. SEM analysis has shown that some needle shape and hexagonal corrosion products were formed on the surface of the alloy electrodes, especially after storage at high temperature.     

Sorption characteristics of Am(III), Sr(II) and Cs(I) on bentonite and granite

The ability of the back-fill and the host rock materials to take up radioisotopes like ²⁴¹Am, ^85,89Sr and ¹³⁷Cs has been examined as a function of contact time, pH, amount of sorbent, sorbate concentration, and the presence of complementary cations. A batch technique using actual borehole water from the granite formation has been utilized. In general, the uptake of nuclides by bentonite is much higher than that with granite. The sorption order of nuclides on bentonite is Am>Cs>Sr. The presence of complementary cations, Na⁺, K⁺, Ca²⁺ and Mg²⁺ depresses the sorption of Cs and Sr on bentonite. The sorption data have been interpreted in terms of Freundlich and Langmuir isotherm equations. Utilizing the Langmuir isotherm equation, the monolayer capacity, V _m ,and the binding constant, K, have been evaluated. The change in free energy for the sorption of nuclides on bentonite has also been calculated.     

Investigation of radionuclide <Superscript>63</Superscript>Ni(II) sorption on ZSM-5 zeolite

The sorption of ⁶³Ni(II) from aqueous solution using ZSM-5 zeolite was investigated by batch technique under ambient conditions. ZSM-5 zeolite was characterized by point of zero net proton charge (PZNPC) titration. The sorption was investigated as a function of shaking time, pH, ionic strength, foreign ions, humic acid (HA), fulvic acid (FA) and temperature. The results indicate that the sorption of ⁶³Ni(II) on ZSM-5 zeolite is strongly dependent on pH. The sorption is dependent on ionic strength at low pH, but independent of ionic strength at high pH values. The presence of HA/FA enhances ⁶³Ni(II) sorption at low pH values, whereas reduces ⁶³Ni(II) sorption at high pH values. The sorption isotherms are simulated by Langmuir model very well. The thermodynamic parameters (i.e., ∆H ⁰, ∆S ⁰ and ∆G ⁰) for the sorption of ⁶³Ni(II) are determined from the temperature dependent sorption isotherms at 293.15, 313.15 and 333.15 K, respectively, and the results indicate that the sorption process of ⁶³Ni(II) on ZSM-5 zeolite is spontaneous and endothermic.