J. Mizera

Sorption of metal ions on lignite and the derived humic substances.

The study presents results of sorption of metal ions (Pb2+, Zn2+, Cu2+, and Cd2+) onto lignite mined in South Moravia, Czech Republic, and solid humic substances (humin and humic acid) derived from it. The efficiency of these sorbents has been studied as a function of contact time, solution pH, and metal concentration. The sorption efficiencies were higher for humin and lower for humic acid samples than for the original lignite. With its high sorption capacities of several mmol/g, particularly for Pb2+ and Cd2+, the South Moravian lignite can provide a cheap source material for preparation of sorbents utilizable in removal of toxic metals from wastewaters.

Chemical composition of plant silica phytoliths

Silica phytoliths are a subgroup of biogenic opal. Silica phytoliths are formed in many plant species and remain preserved in soil and sediments after plant decay. The chemical composition of fossil phytoliths may reveal ancient plant taxa, soil composition and climate. However, actually detailed knowledge on silica phytolith composition is scarce. Here we present result of instrumental neutron activation analysis of barley awns, stems and leaves, and barley phytoliths. The elements of interest were Na, Mg, Al, Si, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Zn, As, Br, Rb, Sb, Cs, Ba, La, Ce, Sm, Eu, Tb, Dy, Yb, Hf, Ta, W, Th, and U. We compared three phytolith extraction methods: dry ashing, acid digestion, and acid digestion followed by incineration. We found that sole acid digestion is inefficient to remove organic matter. By contrast both dry ashing and acid digestion followed by incineration are suitable for phytolith analysis. Comparison of phytoliths with their source plant material shows that phytoliths are enriched in terrigenous elements such as Al, Sc, Ti, V, Cs, Fe, rare earth elements, and depleted in the major inorganic constituents of plants such as K, Ca, Mg, Mn, Cl and Br.

Modeling of metal-humate complexation based on the mean molecular weight and charge of humic substances: Application to Eu(III) humate complexes using ion exchange

A general model, the so called Mean Molecular Weight Model (MMWM), of complexation of metal cations (Mez+) with macromolecular polyanions of humic acid (HAp-) is proposed. The model is based on the results of previous studies of the electrophoretic mobility of humate complexes and assumes that the complexation proceeds by consecutive neutralization of the dissociated carboxyl groups of the central polyanion HAp- with Mez+ cations. It reflects the macromolecular character of humic acid, applies molar concentrations of reacting components with equations for stability constants and incorporates also the mean charge of humic macromolecules. The model has been verified with experimental data obtained in the study of complexation of Eu(III) with Aldrich humic acid using ion exchange (Amberlite IR-120), over a broad range of [Eu] to [HA] ratio, at pH 4 and 7.

Geochemical characterization of impact glasses from the Zhamanshin crater by various modes of activation analysis. Remarks on genesis of irghizites

A large set of impact glasses from the Zhamanshin crater in Kazakhstan was analyzed by various modes of instrumental neutron activation analysis, supplemented by instrumental photon activation analysis and prompt gamma-ray activation analysis. Results of the determination of more than forty major and trace elements have shown that the analyzed set of homogeneous, tektite-like impact glasses with size of several centimeters and of various forms could be divided into two geochemically different groups. The lustrous, silica rich (acidic) glasses with high Ni content have been classified conventionally as irghizites. The dull, silica poor (basic) glasses with very low Ni content should not be confused with the large, heterogeneous impactite forms—zhamanshinites, but considered as a separate type of impact glass. Within both primary groups, further division has been suggested based on lower contents of Ni in an irghizite subgroup, and evidence of mixing of source materials for both primary groups in a part of the basic glasses. Based on the contents of Ni, Cr, Mn, Fe and Co, an ordinary chondrite impactor has been suggested with its contribution to the irghizite matter ranging between 4 and 21%. Possible source materials and impact processes leading to irghizite formation have been outlined.

Radiotracer study of sorption of europium on Gorleben sand from aqueous solutions containing humic substances

The sorption of trace europium, as a trivalent actinide homologue, was studied in the system Gorleben sand - aqueous solution with the aim to elucidate its mechanism. Radiotracer method (152/154Eu) and batch experiments were used. Simultaneously, the distribution of humic substances present in, or added to the system was measured. The evaluation of the sorption was complicated by the adsorption of Eu on the walls of polyethylene vials used for the experiments, which was rather high and had to be taken into consideration. It has been found that Eu sorption on Gorleben sand increases from pH 2 to pH 5-7 and then it decreases. The decrease is due to the complexation of Eu with humic substances leached from Gorleben sand at pH >7. The position of the sorption maximum depends on the composition of the solution and on the liquid-to-solid ratio. It is shifted to lower pH values in the presence of added humic acid (HA), which enhances Eu sorption at low pH values and suppresses it at pH values higher than 5. The regions of the enhancing/suppressing effects coincide with the high/low adsorption of HA on Gorleben sand, respectively. The increasing ionic strength (from 0.01 to 0.1) and europium concentration (3.4.10-8 to 9.3.10-7 mol/l) suppress the relative sorption (expressed in %) at low pH values and enhance it at pH>6-8. Addition of carbonates (5.10-3 mol/l) supports Eu sorption at pH>7.5 so that no decrease with pH is observed till pH 9. Alkaline leaching of the sand significantly changes most of the effects found. These results were qualitatively interpreted and conclusions were drawn on the mechanism of the sorption.

Radiotracer study of the electrophoretic behavior of Eu and its complexes with humic acid

The interaction of Eu with purified/protonized Aldrich humic acid (HA) was studied by the free liquid/moving boundary electrophoresis used in combination with the radiotracer method. Introductory experiments were carried out to test electrophoretic behavior of Eu in HA-free solutions, and to determine mobility of Eu3+ cation. To get the data for evaluation of parameters describing Eu binding to HA, titrations of HA (10 mg/L) with Eu were performed batchwise in the range 3.4×10-8-1.7-3 M of Eu total concentration at pH 3, 4, 5 and 6, and 0.01 M ionic strength (NaClO4). In each batch, the degree of Eu complexation with HA was determined from 152Eu electrophoretic mobilities in the cathodic direction. The experimental data were fitted with a discrete site model (Scatchard plot-like model) with two types of carboxylic sites. An additional information on the charge characteristics of the Eu-HA complexes has been obtained from the 152Eu anodic mobilities.

Application of radiotracer techniques to a kinetic study of the interaction of Eu with humic acid

Experimental methods based on the radiotracer technique have been designed to study kinetic aspects of the interaction of humic substances (HS) with metal ions. The rate of dissociation of Eu-HS complexes was observed via the rate of the isotope exchange in the system 152Eu - stable Eu - humic acid (HA) determined by the diaphragm method. The rate of exchange was found to be enhanced by decreasing pH value, increasing ionic strength and increasing degree of loading of HA with Eu, and was described with a simple 1-component kinetic model (mono-exponential decay function). Additional information on the kinetics has been derived from the electrophoretic mobilities of Eu depending on metal loading of HA and pH, determined by the free liquid/moving boundary electrophoresis with radiometric and spectrophotometric detection of the electromigration of the Eu/Eu-HA complex.

17th Radiochemical conference: RadChem 2014 Mariánské Lázně, 11–16th May 2014

The 17th Radiochemical Conference—RadChem 2014, was held in the Casino conference centre in Marianske Lazně, Czech Republic, on the 11–16th May 2014. As usual in its more recent history, the conference was coorganized by the Department of Nuclear Chemistry, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague (DNC FNSPE CTU), Czech Chemical Society, and Ioannes Marcus Marci Spectroscopic Society. Together with the ‘‘International Conference on Nuclearand Radiochemistry (NRC)’’ series, the RadChem series form the pillars of the pan-European conference series organised on behalf of the Division of Nuclear and Radiochemistry of the European Association for Chemical and Molecular Sciences (DNRC EuCheMS). Traditionally, RadChem 2014 was organised in cooperation with the International Atomic Energy Agency (IAEA) and was sponsored by the International Union of Pure and Applied Chemistry (IUPAC). Over its 50? years long tradition, the conference has gained a good reputation among the researchers in the field of nuclearand radiochemistry as a platform for the presentations of research results and for the discussions about current issues. It offers a great opportunity to establish new contacts with local and foreign colleagues, especially for young researchers and students.

Radiotracer study of the kinetics of complexation and decomplexation of Eu(III) with humic acid using ion exchange

The kinetics of complexation (C) and decomplexation (D) reactions between Eu(III) and Aldrich humic acid (HA) was investigated as a function of pH (pH 4, 5, 6, 7 and 8) in the system Eu(III) - HA - Amberlite IR-120(Na) (I = 0.1). The derivation of the kinetic differential equations was based on the reactions of Eu3+ with, so called, strong (HAS) and weak (HAW) carboxylic groups of HA formulated in accordance with the new complexation model.1 The differential equations determining d[EuaHAS]/dt and d[EubHAW]/dt have the classical form applicable for reversible reactions where the forward reaction is the C-reaction and the reverse one is the D-reaction. Kinetic model used for the evaluation of experimental data includes these differential equations and the film diffusion model of sorption of Eu3+ on Amberlite IR-120(Na).

Neutron and photon activation analyses in geochemical characterization of Libyan Desert Glass

Geochemical characterization of nine samples of Libyan Desert Glass (LDG) based on assay of more than forty elements by instrumental neutron and photon activation analyses has pointed to quartz sand cemented by aluminosilicates and Fe, Ti oxides as LDG parent materials. Contamination by extraterrestrial material has not been evidenced in studied LDG samples, but depletion of volatile elements indicating their evaporation during the impact process was noticed. Authors support the common concept of LDG formation by an impact into Cretaceous Nubian sandstones, derived from Proterozoic crystalline basement and possibly weathered and redeposited from alluvial or shallow water marine environments.