Study of phosphate species of chernozem and sand soils by heterogeneous isotope exchange with 32P radioactive tracer

Weakly and tightly sorbed phosphate species on chernozem and humus sand are investigated by radioactive tracer method using ³²P. The comparison of the heterogeneous isotope exchange of ³²P-labeled phosphate of non-radioactively incubated soils and desorption of ³²P-labeled phosphate of radioactively incubated soils shows the transformation of weakly sorbed species to tightly sorbed ones. The quantity of weakly sorbed phosphorus and the steady state phosphorus exchange rate between soil and soil solution, transformation half-life of weakly to tightly sorbed phosphate are calculated.

Study of fast and slow consecutive processes by heterogeneous isotope exchange using P-32 radiotracer

The sorption of phosphate on soils is studied by radioisotopic tracer method. Two consecutive processes with rather different rates were differentiated: namely the heterogeneous isotope exchange between the phosphate in the soil solution and the weakly sorbed phosphate (fast reaction), and the transformation of weakly sorbed phosphate to tightly sorbed phosphate (slow reaction). In this paper, it is shown how the rate constants of these two processes can be determined by a radiotracer with a relatively short half-life.

Application of Modified Bentonites for Arsenite (III) Removal from Drinking Water

Four modified bentonites (La(III), Ce(III), Y(III), Fe(III)) were prepared by ion exchange process to remove arsenite (III) ions from water. The modified bentonites were examined with X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD). The rare earth (REE) and Fe(III) ion content in bentonite was higher than the CEC values obtained by ammonium acetate method related to trivalent ions (2.7 x 10-4 mol g-1). The kinetics, equilibrium time, sorption isotherms and desorption experiments were examined. Lanthanum, yttrium and cerium bentonite can bind similar amount of arsenite(III) ions. Iron-bentonite cannot bind significant amounts of arsenite ions. The active sites and the solubilities of the sorption complex were determined. Arsenite (III) ions sorb in the interlayer space as REEAsO3. The solubility of the arsenite complex was two orders of magnitude smaller than that of the phosphate complex. After desorption the eluted amount of arsenite (III) was 55 % related to the sorbed amount of arsenite. The d(001) basal spacing of modified bentonites and that of after sorption and desorption was measured. After the sorption of arsenite ion on lanthanum bentonite, the d(001) basal spacing of montmorillonite was decreased and after desorption an increase in d(001) basal spacing was observed again. Modified bentonites can be used for removing arsenic ions from water.

Use of La-, Ce-, Y-, Fe- bentonites for Removing Phosphate Ions from Aqueous Media

Clays play an important role in the environment. By removing cations and anions either through ion exchange, adsorption and precipitation, or all these combined, they can act as natural decontaminating agents of numerous pollutants. In this study, four modified bentonites (La-, Ce-, Y-, Fe-bentonite) were prepared and characterized, and their phosphate sorption capabilities were measured in batch experiments. Equilibrium times were also examined. The activation energy of the sorption process was calculated. The La- , Ce- and Y-bentonite can bind similar amount of phosphate ions, while iron-bentonite can bind only half of it compared to La-, Ce- and Y-bentonite.

CD95 expression in white blood cells of malnourished infants during hospitalization and catch-up growth

Malnutrition continues to be a major health burden in developing countries. Flow cytometric estimation of the apoptotic marker CD95 in peripheral neutrophils, lymphocytes and monocytes was done for 18 infants with non-oedematous protein energy malnutrition (PEM) and 12 oedematous ones, on hospital admission and after supervised nutritional rehabilitation, and compared with 12 matched controls. CD95 counts in the 3 types of white blood cells were significantly higher in PEM infants and showed improvement after nutritional rehabilitation yet not reaching the control values. Enhanced apoptosis in the leukocytes of peripheral blood of PEM patients may be a marker of increased infection and immune disturbances. This derangement reverses upon proper nutritional rehabilitation.

Study of pH-dependent charges of soils by surface acid–base properties

The pH-dependent charges of Hungarian soils have been studied via surface acid-base properties. The intrinsic stability constants of protonation and deprotonation processes, as well as the concentration of surface sites, have been determined by surface complexation modeling. The protonation and deprotonation constants have been nearly the same for most soils. There is a relation between the concentration of surface sites and composition, expect for the freshly deposited soils with high primary silicate content. The results show that the concentrations of silanol and aluminol sites are different for each soil, the intrinsic stability constants of protonation and deprotonation processes, however, are nearly the same within experimental error. This can only be explained if these stability constants are real thermodynamic equilibrium constants. The fact that these constants are nearly the same supports the conclusion that we succeeded in excluding all processes that would disturb the measurements. The parameters characteristic of the edge sites of the soils are of two types: (a) the parameters depending on the quality and composition of the soils, (i.e.), the concentration of surface sites; (b) the parameters depending on the thermodynamically well-defined acid-base processes, independent of soil composition.

Acid–base properties of bentonite rocks with different origins

Five bentonite samples (35-47% montmorillonite) from a Sarmatian sediment series with bentonite sites around Sajóbábony (Hungary) is studied. Some of these samples were tuffogenic bentonite (sedimentary), the others were bentonitized tuff with volcano sedimentary origin. The acid-base properties of the edge sites were studied by potentiometric titrations and surface complexation modeling. It was found that the number and the ratio of silanol and aluminol sites as well as the intrinsic stability constants are different for the sedimentary bentonite and bentonitized tuff. The characteristic properties of the edges sites depend on the origins. The acid-base properties are compared to other commercial and standard bentonites.

The effect of mineral composition on the sorption of cesium ions on geological formations

The sorption of cesium-137 on rock samples, mainly on clay rocks, is determined as a function of the mineral composition of the rocks. A relation between the mineral groups (tectosilicates, phyllosilicates, clay minerals, carbonates) and their cesium sorption properties is shown. A linear model is constructed by which the distribution coefficients of the different minerals can be calculated from the mineral composition and the net distribution coefficient of the rock. On the basis of the distribution coefficients of the minerals the cesium sorption properties of other rocks can be predicted.

Study of the change in the properties of Mn–bentonite by aging

In this paper the structure and properties of fresh manganese(II)-bentonite was compared with that of an old substance. It was concluded that the oxidation state of Mn changed. This did not cause many changes in the scanning electron microscope (SEM) and in the X-ray diffraction (XRD) studies; caused minor changes in the Mn concentration (determined by XRF) and thermoanalytical and electron spectroscopy analysis (ESCA). The change in the oxidation state of manganese was indicated by the colors of the samples, the difference in the surface sites, titration curves, redox potentials, adsorption, and catalytic activity of the fresh and the old Mn-bentonite. Potentiometric titration data were evaluated by a surface complexation model using the FITEQL3.2 computer program. Stability constants of edge charge reactions and the number of aluminol, silanol, and edge sites were calculated. Potentiometric titration data of commercial and freshly made MnO2 were also evaluated; the calculated constants and site numbers were compared with that of found in literature. Catalytic and adsorption activity of the samples were also investigated. It was found that fresh Mn-bentonite does not adsorb valine, while the old one and MnO2 does. Fresh Mn-bentonite does not catalyze the decomposition of H2O2, while the old one, as well as MnO2 does.

Physical and chemical formations of lead contaminants in clay and sediment

A possible sink for divalent lead in the environment is clays such as montmorillonite that have cation exchange capacities. To assess the reaction, a calcium-montmorillonite was mixed with lead perchlorate solutions of varying concentrations and at various pH's. The recovered solids were studied by a variety of techniques (X-ray photoelectron and infrared spectroscopy, scanning electron microscopy, and atomic force microscopy) to determine what, if any, alterations occurred. The ion exchange of lead for calcium reduced the hydrated water in the clay, and evidence for proton-lead ion exchange at the edges of the sheets was observed. Evidence for a second, unexpected, reaction was also observed. Small spots (0.2 to 1 microm) of lead enrichment were observed on the surface of clay particles. They were also observed on clays recovered from the sediment of a Hungarian lake. The results show that lead ions are adsorbed onto montmorillonite by two processes: cation exchange and nano- and microparticle production. Cation exchange leads to the even distribution of the ions, while the production of spots causes the enrichment of lead ions. The production of these particles is not expected from the thermodynamic properties of the solution and cannot be observed in the absence of clay.