A comparative study on the sorption and desorption of Hg,Th and U on clay

The sorption and desorption of uranium, thorium and mercury on a western Anatolian montmorillonite, obtained from the deposit located in Kula, were studied by application of a batch technique. The clay used is a tertiary clay originally found in a rather large geological formation of west Anatolia. It is nearly pure montmorillonite. Its cation exchange capacity (CEC) determination was performed for ammonium acetate by the Mehlich procedure. The mean CEC was found to be 83 meq/100 g, which, taking into account that CEC determinations were carried out on unfractionated material, is in good agreement with previously reported data. The concentration ranges were between 70–1500 ppm for mercury and 100–2000 ppm for thorium and uranium. The relative importance of test parameters, e.g., pH, clay particle size, groundwater composition, contact time and solid/water ratio, which determine the distribution coefficients was studied. The sorption coefficients varied between 2.7–6.4 ml/g for U, 0.22–1.59 ml/g for Th and 152.4–427.2 ml/g for Hg. The differences of distribution coefficients are discussed. The data could be fitted to Freundlich and Langmuir isotherms. The quantities of the sorbed and desorbed Th were much lower than its theoretical CEC's. This attitude was attributed to the blocking of montmorillonite by cation islands sorbed in the interlayer. Hg is sorbed most strongly. The experimental results indicate that the montmorillonites studied should be effective components of the buffer and backfill material and lead to eventual immobilization of these elements, which are environmentally dangerous.     

Application of simplified desorption method to study on sorption of americium(III) on bentonite

To elucidate the sorption behavior of americium(III) on bentonite, which is a mixture of montmorillonite clay, quartz and other minerals, simplified desorption experiments were applied to the solid phases collected after the sorption experiments. The sorption–desorption behavior was examined in the final pH range from 2 to 8. The desorption experiments revealed that most of the Am was sorbed on the montmorillonite moiety of the bentonite. The sorption of Am on montmorillonite was divided into two types: one was the “exchangeable” sorption, in which the sorbed Am was desorbed with a 1 M KCl aqueous solution, and the rest was the “unexchangeable” sorption. The exchangeable sorption was ion exchange of mostly Am³⁺. The unexchangeable sorption was the strong sorption of Am hydroxides. An accessory iron mineral, pyrite, might be involved in the Am sorption on bentonite at neutral pH.     

Sorption mechanism of U(VI) on a reference montmorillonite: Binding to the internal and external surfaces

Batch type experiments of U(VI) sorption on a reference montmorillonite(SWy-2) were carried out over wide ranges of pH, ionic strength, and totalU(VI) concentration. The influences of these factors on the sorption behaviorof U(VI) were analyzed to gain a macroscopic understanding of the sorptionmechanism. The sorption of U(VI) on montmorillonite showed a distinct dependencyon ionic strength. When it was low (0.01 or 0.001M), almost all of the totalU(VI) was sorbed over the whole pH range studied, therefore, the dependencyon pH was not clear. But the sorption of U(VI) on montmorillonite showed asorption pH edge in the high ionic strength condition (0.1M), like those onother clay minerals, kaolinite and chlorite. A mechanistic model was establishedby considering the mineral structure of montmorillonite together with ourprevious EPR result, which successfully explained the U(VI) sorption on montmorilloniteover the whole range of experimental conditions. The model describes the U(VI)sorption on montmorillonite as simultaneous and competitive reactions of ionexchange and surface complexation, whose relative contribution to the totalsorption depends on pH and ionic strength. At low ionic strength and low pHconditions, ion exchange was the dominant mechanism for U(VI) sorption onmontmorillonite. At high ionic strength and high pH conditions, surface complexationwas the dominant     

Sorption of 63Ni(II) to montmorillonite as a function of pH, ionic strength, foreign ions and humic substances

Different kinds of clay minerals have been studied extensively in the removal of radionuclides from large volumes of aqueous solutions because of their high sorption capacity. Herein, the Na-montmorillonite was characterized by using XRD and FTIR in detail. The sorption of ⁶³Ni(II) from aqueous solution to montmorillonite as a function of pH, ionic strength, foreign ions, humic substances and temperature was studied by batch technique. The sorption of ⁶³Ni(II) on montmorillonite achieved equilibration quickly. The sorption of ⁶³Ni(II) to montmorillonite was strongly dependent on pH, and dependent on ionic strength at low pH and independent of ionic strength at high pH values. The sorption of ⁶³Ni(II) on montmorillonite was enhanced at low pH in the presence of humic acid (HA), while a negative effect of HA on ⁶³Ni(II) sorption was found at high pH values. At low pH values, the sorption of ⁶³Ni(II) was attributed to outer-sphere surface complexation or ion exchange, whereas the sorption was dominated by inner-sphere surface complexation at high pH values. The montmorillonite sample is a suitable material in the preconcentration of radionuclides from large volumes and the material can be used as backfill material in nuclear waste repository.     

Removal of diphenhydramine from water by swelling clay minerals

Frequent detection of pharmaceuticals in surface water and wastewater attracted renewed attention on studying interactions between pharmaceuticals and sludge or biosolids generated from wastewater treatment. Less attention was focused on studying interactions between pharmaceuticals and clay minerals, important soil and sediment components. This research targeted on investigating interactions between diphenhydramine (DPH), an important antihistamine drug, and a montmorillonite, a swelling clay, in aqueous solution. Stoichiometric desorption of exchangeable cations accompanying DPH adsorption confirmed that cation exchange was the most important mechanism of DPH uptake by the swelling clay. When the solution pH was below the pK(a) of DPH, its adsorption on the swelling clay was less affected by pH. Increasing solution pH above the pK(a) value resulted in a decrease in DPH adsorption by the clay. An increase in d(001) spacing at a high DPH loading level suggested interlayer adsorption, thus, intercalation of DPH. The results from this study showed that swelling clays are a good environmental sink for weak acidic drugs like DPH. In addition, the large cation exchange capacity and surface area make the clay a good candidate to remove cationic pharmaceuticals from the effluent of wastewater treatment facilities.     

Adsorption isotherms of homologous alkyldimethylbenzylammonium bromides on sodium montmorillonite

The adsorption of homologous alkyldimethylbenzylammonium bromides, [C(6)H(5)CH(2)N(CH(3))(2)R]Br, on sodium montmorillonite from aqueous NaCl solutions at room temperature has been studied. R stands for the methyl-, butyl-, hexyl-, octyl-, decyl-, and dodecyl-group, and the corresponding ammonium cations will be denoted as C1+, C4+, C6+, C8+, C10+, and C12+, respectively. C1+, the reference cation, attains the plateau region of adsorption at a level close to the cation exchange capacity (CEC) of the clay. The chain-length dependence on adsorptivity of the homologous cations exhibits an unexpected peculiarity. In the case of short-chain homologues of C1+ their adsorption onto sodium montmorillonite decreases in the order C1+>C4+>C6+. This behavior is due, presumably, to the growing steric hindrances at the surface of clay, which occur because of the limited area available for the bulky organic cations at the exchange sites. These limitations appear to be out-balanced in the case of higher homologues for which the increasingly growing hydrophobic effects lead to the expected sequence of adsorptivity of the cations, i.e., C1+相似文献   

Mobility of 137Cs Related to Speciation Studies in Contaminated Soils of the Chernobyl Area

Chernobyl derived ¹³⁷Cs present in upper soil layers can still remain available to cation exchange and hence to downward migration. More than its physico-chemical deposit forms (fuel particles and/or condensed aerosols), radiocesium mobility is influenced by soil properties. Although all the soils studied contain illitic clay minerals, different ¹³⁷Cs fixation levels were observed due to: (1) the reactivity state of sorption sites with a low radiocesium content in soil, and (2) the presence, or absence, of organic matter complexes inhibiting cation sorption on clays.     

Thermodynamics of Chromium(VI) Anionic Species Sorption onto Surfactant-Modified Montmorillonite Clay

Batch sorption experiments performed on Cr(VI) species sorption showed a significantly enhanced removal of inorganic hexavalent chromium anionic species from aqueous solution by montmorillonite clays modified with quaternary amine, hexadecyltrimethylammonium (HDTMA) bromide. Unmodified clay had no affinity for chromium(VI) species. The sorption of Cr(VI) species has been carried out as a function of pH, contact time, adsorbate concentration (4.14x10(-5) to 8.62x10(-3) M), and temperature (5-45 degrees C). The surfactant-modified clay surface was stable when exposed to extremes in pH. The optimum pH for maximum sorption of Cr(VI) species was found to be at pH 1 and was constant between pH 2 and pH 6. The sorption data obtained was well described by DKR and Langmuir sorption isotherms. Sorption energy (E) for (i) surfactant sorption by montmorillonite clay and (ii) sorption of chromium(VI) species by surfactant modified clay have been computed from the DKR equation. Sorption energy evaluated for the sorption of both surfactant and Cr(VI) species showed that an ion-exchange mechanism was operative. The mechanism of retention appears to be replacement of counterion of the surfactant by Cr(VI) anionic species. Adsorbent capacity for the sorption of Cr(VI) species has been evaluated from the Langmuir sorption isotherm data. Thermodynamic parameters (Delta H degrees, Delta S degrees and Delta G degrees ) for surfactant sorption on montmorillonite clay and Cr(VI) sorption by modified clay have been evaluated. The specific rate constant for sorption of Cr(VI) species on modified montmorillonite was rapid during the first 10 min and equilibrium was found to be attained within 30 min. The sorption of Cr(VI) species onto modified montmorillonite clay followed first-order rate kinetics. Copyright 2000 Academic Press.     

Study of uranium sorption and desorption on some Turkish clays

The sorption and desorption of uranium on two different clay samples which are obtained from the deposit located in Turgutlu and Kula have been studied by application of a batch technique. The two types of clay materials are Ca-montmorillonite. The uranium concentration range was between 200–3000 ppm. Experimental procedures are outlined and results for uranium contacted with montmorillonite are reported and discussed. The sorption/desorption isotherms were reversible and non-linear for this concentration range. The relative importance of test parameters e.g., pH, clay particle size, temperature, ground water composition, contact — time, solid/water ratio which require definition in order to arrive at meaningful distribution coefficients were carried out. The sorption coefficients varied between 0.65–1.45 and 0.45–1.14 for Kula clay and for Turgutlu clay, respectively. The data could be fitted to Freundlich and Langmuir isotherms. The quantity of the sorbed and desorbed uranium ions was much lower than its theoretical CEC's. This was attributed to a blocking of montmorillonite's CEC by uranium islands sorbed in interlayer. The results have shown that the test parameters can have a marked effect on sorption and the present work provides further evidence of the need to take account of the presence of such materials in safety assessment modeling.     

Effect of pH and ionic strength on U(IV) sorption to oxidized multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWCNTs) have attracted multidisciplinary study because of their unique physicochemical properties. Herein, the sorption of U(VI) from aqueous solution to oxidized MWCNTs was investigated as a function of contact time, pH and ionic strength. The results indicate that U(VI) sorption on oxidized MWCNTs is strongly dependent on pH and ionic strength. The sorption of U(VI) is mainly dominated by surface complexation and cation exchange. The sorption of U(VI) on oxidized MWCNTs is quickly to achieve the sorption equilibrium. The sorption capacity calculated from sorption isotherms suggests that oxidized MWCNTs are suitable material in the preconcentration and solidification of U(VI) from large volumes of aqueous solutions.     

Modification of the structure of natural bentonite and study on the sorption of Cs+

Natural bentonite clay was treated in order to remove impurities to increase the cation exchange capacity of the montmorillonite and to obtain a more effective radioactive cesium sorption. It was found that the treatment of the clay determines the amount of sorbed cesium. On the other hand it was shown that montmorillonites may retain cesium through several mechanisms which provide strongly retained cations occupying cationic sites into the clay structure or sorbed cesium which may be lost by purification treatments.     

Formability and properties of self-standing clay film by montmorillonite with different interlayer cations

Influences of exchangeable interlayer cations were investigated on self-standing film formability, film morphology, and properties of the clay films such as flexibility and gas barrier property. Ion-exchanged montmorillonite samples were prepared by a cation exchange from naturally bearing cation, mostly Na⁺, to Li⁺, Mg²⁺, Ca²⁺, Al³⁺, and Fe^{2+, 3+}. Self-standing films were prepared from aqueous colloidal dispersions of these montmorillonite samples with no additives. The montmorillonite samples with monovalent or divalent cation formed flat self-standing films while the Al-montmorillonite sample produced a distorted film. The Fe-montmorillonite sample formed many separated reddish-brown rod-shaped pieces. Clay film microstructures were different with interlayer cations. The films with monovalent interlayer cations were constructed by the stacking of units with delicately waved thin clay sheets in the whole film, but other films show different morphologies between the upper side and lower side; the upper side is laminated with thin sheets; the lower side is laminated with large thick sheets.The self-standing films’ flexibility and gas barrier property differed according to the interlayer cations. These properties were good in cases of samples with monovalent cations. The innumerable short wave and sheet thinness are considered to foster good flexibility and gas barrier properties. The differences in film formability and properties of the films are attributable to different swellability among samples with different interlayer cations. The montmorillonite samples with monovalent cations swell sufficiently by water, but those with polyvalent cations swell poorly. In the latter case, clay crystals aggregate in water, then the aggregate grows into large particles, creating a film with large particles.     

Cation and anion exchange on clay modified electrodes

Carbon paste electrodes modified with clay minerals were used for the study of ion-exchange properties of these clay minerals. Cation exchange of Cu(II) was studied by the dependence on the pH, ionic strength and the form of the minerals. The highest anionic exchange of Hg(II) acetates and chlorides was found on montmorillonites. Anionic exchange of Au(III) chloro complexes was found on montmorillonite, but their sorption is strongly influenced by other anions such as chlorides and thiocyanates. The results found are important with regard to the study of the anion-exchange properties of clay minerals. Received: 2 December 1999 / Accepted: 2 March 2000     

Adsorption and Interactions of Methyl Green with Montmorillonite and Sepiolite

The divalent organic cation, methyl green (MG), undergoes a slow transformation (6 h) to a monovalent cation, carbinol (MGOH(+)) upon dilution of its solution (10 mM), or in a buffer at neutral pH. Adsorption isotherms of MG on montmorillonite were determined by two procedures, both of which yield a final pH of suspensions between 7 to 7.4. When the amounts of MG in suspension were lower than the cation-exchange capacity (CEC) of the clay (0.8 mol(c)/kg clay), no measurable amount of MG remained in solution. The maximal amounts of MGOH(+) adsorbed were larger than those of MG(2+), being 1.15 and 0.75 mol MG/kg clay, respectively, corresponding to 140% of the CEC in the first case. On a charge basis the adsorption of added MG(2+) amounts to 185% of the CEC, which raises the possibility that a certain fraction of MG(2+) transformed into the monovalent form during the incubation period, since other divalent organic cations previously studied only adsorbed up to the CEC (paraquat), or slightly above it (diquat). Adsorption of MG on sepiolite (CEC=0.15 mol(c)/kg) further emphasizes the two patterns of its adsorption. The maximal adsorbed amounts of MG(2+) and MGOH(+) were 0.09 and 0.30 mol/kg clay, respectively. X-ray diffraction measurements gave lower values for the basal spacings for montmorillonite-MG(+) than for MGOH(+), suggesting that MG(2+) binds two clay platelets together, as in the case of other divalent cations. A competition for adsorption between MG and the monovalent organic cation, acriflavin (AF), gave lower adsorbed amounts of AF when competing with MG(+), which is interpreted to be due to the smaller basal spacing in this case, which partially inhibits the entry of AF molecules into the interlammelar space. Spectra of montmorillonite-MG particles in the visible range exhibited significant differences between clay-MG and clay-carbinol. Copyright 2000 Academic Press.     

Surface and bulk sorption of uranium(VI) onto granite rock

Surface and bulk sorption of U(VI) onto granite rock with different types of surfaces were carried out and the results were compared for the different surfaces such as crushed granite, machined core granite, and core granite with fractured surface. The sorption behavior of U(VI) dependent on surface types was investigated and discussed for contacting time, pH, constituent minerals, and surface area. Results from the sorption experiments were also compared each other in order to analyze the differences in sorption behaviors of U(VI) and to correlate the surface sorption coefficient K_a and the bulk sorption coefficient K_d. The effect of contact time and pH on the sorption of U(VI) onto fractured surfaces was larger than that onto the machined fresh surfaces but smaller than that onto the crushed surfaces. As expected, it was noticed that the surface sorption coefficients of U(VI) for the natural fracture surfaces were greater than those of the machined fresh surfaces due to the higher content of secondary minerals such as calcite and chlorite which acted as stronger sorbents. It is presumed that there are many micro-fractures or micro-pores available for the uranium sorption on the granite surfaces, even on the machined fresh surfaces, and there can be an intrinsic difference between the surface and the bulk sorption due to the different types of surfaces.     

Sorption of uranium(VI) from aqueous solution onto magnesium silicate hollow spheres

The sorption of uranium(VI) from aqueous solutions was investigated using synthesized magnesium silicate hollow spheres as a novel adsorbent. Batch experiments were conducted to study the effects of initial pH, amount of adsorbent, contact time and initial U(VI) concentrations on uranium sorption efficiency. The desorbing of U(VI) and the effect of coexisting ions were also investigated. Kinetic studies showed that the sorption followed a pseudo-second-order kinetic model. The Langmuir sorption isotherm model correlates well with the uranium sorption equilibrium data for the concentration range of 25–400 mg/L. The maximum uranium sorption capacity onto magnesium silicate hollow spheres was estimated to be about 107 mg/g under the experimental conditions. Desorption of uranium was achieved using inorganic acid as the desorbing agent. The practical utility of magnesium silicate hollow spheres for U(VI) uptake was investigated with high salt concentration of intercrystalline brine. This work suggests that magnesium silicate hollow spheres can be used as a highly efficient adsorbent for removal of uranium from aqueous solutions.     

一种二价季铵盐在粘土矿物上的吸附

研究了一种不显著降低界面张力的二价季铵盐化合物(MD膜驱剂)在粘土矿物上的吸附. 选取蒙脱土(Su-M)和膨润土(B)两种粘土矿物作为研究对象，其阳离子交换容量(CEC)分别为0.44和0.88 mmol•g^-1. 研究结果表明，MD膜驱剂在低的加入浓度下，MD膜驱剂分子在两种粘土矿物上能全部被吸附，此外，其在Su-M上的饱和吸附量达到100% CECSu-M，而在B上仅为77%CECB. MD膜驱剂只能吸附在粘土矿物的负电荷点上，而不能吸附在单元层外表面的Si-OH中性点上. XRD数据显示，随MD膜驱剂添加浓度的增大，两种粘土矿物的干态层间距略有减小，并根据分子的理论空间尺寸，认为MD膜驱剂在粘土层间只能以单层平卧方式排列.     

Interactions in clay/electrolyte systems

The sorption of cesium and cobalt on kaolinite and montmorillonite were followed by radiotracer method. The sorption of cesium can be described by a Freundlich isotherm. Cobalt sorption on clays equilibrated in cesium chloride solutions significantly differs for kaolinite and montmorillonite due to their differences in sites available for cation sorption and changes in solution chemistry.Heterogeneous exchange of cesium ions between clay and the surrounding electrolyte was performed in order to obtain information about clay/electrolyte systems equilibration. An interplay of different processes included in the attainment of true chemical equilibria of clay/electrolyte systems are responsible for the change of clay surface properties and total exchange capacity.     

Light scattering studies on Ficoll PM70 solutions reveal two distinct diffusive modes

Enrofloxacin (ENR) occurs widely in natural waters because of its extensive use as a veterinary chemotherapeutic agent. To improve our understanding of the interaction of this emerging contaminant with soils and sediments, sorption of ENR on homoionic smectites and kaolinite was studied as a function of pH, ionic strength, exchangeable cations, and humic acid concentration. Batch experiments and in situ ATR-FTIR analysis suggested multiple sorption mechanisms. Cation exchange was a major contributor to the sorption of cationic ENR species on smectite. The decreased ENR sorption with increasing ionic strength indicated the formation of outer-sphere complexes. Exchangeable cations significantly influenced the sorption capacity, and the observed order was Cs相似文献