Thermal analysis was carried out on peat and its residues after successive separation of water-soluble substances (6.8%), bitumens (3.9%), hemicellulose (5.9%), humic acids (33.4%) and cellulose (21.5%). The primary peat gives two exothermal effects, at 290° and at 275°. After humic acid and cellulose separation, respectively, the second effect decreases and then disappears completely.
Authors:Jiří Kučerík, Petra Bursáková, Alena Průšová, Lucie Grebíková, and Gabriele Ellen Schaumann
) are fulvic acids (FA) and humicacids (HA); FA are fractions of NOM soluble at all pH values, while HA are soluble only in alkaline solutions [ 2 ].
Hydration is the crucial factor playing role in biological function of molecules in both living
The complexation of the uranyl ion with humic acid is investigated. The humic acid ligand concentration is described as the
concentration of reactive humic acid molecules based on the number of humic acid molecules, taking protonation of functional
groups into account. Excess amounts of U(VI) are used and the concentration of the humic acid complex is determined by the
solubility enhancement over the solid phase. pH is varied between 7.5 to 7.9 in 0.1M NaClO4 under normal atmosphere and room temperature. The solubility of U(VI) in absence of humic acid is determined over amorphous
solid phase between pH 4.45 and 8.62. With humic acid, only a limited range of data can be used for the determination of the
complexation constant because of flocculation or sorption of the humic acid upon progressive complexation. Analysis of the
complex formation dependency with pH shows that the dominant uranyl species in the concerned pH range are UO2(OH)+ and (UO2)3(OH)5+. The complexation constant is evaluated for the humate interaction with the to UO2(OH)+ ion. The stability constant is found to be logβ = 6.94±0.3 l/mol. The humate complexation constant of the uranyl mono-hydroxo species thus is significantly higher than that
of the nonhydrolyzed uranyl ion (6.2 l/mol). Published data on the Cm3+, CmOH2+ and Cm(OH)2+ humate complexation are reevaluated by the present approach. The higher stability of the hydrolysis complex is also found
for Cm(III) humate complexation.
The contamination of potable water aquifers by heavy metals is one of the most severe environmental threats. For the transport of heavy metals from various types of contaminated sites into the ground water and also into surface water aquifers, humic substances (HS) are recognized to be of main importance. Dissolved in natural waters humic substances are readily complexed with a variety of metal ions. Therefore, humic substances are of cardinal importance for the migration and, consequently, the pollution of ground waters with heavy metals. Our paper presents the results of a comprehensive comparison of several isolated humic acids of soils of different origin (different geochemical milieu) and their metal complexes. Two polluted sites in Germany, which differ in their geochemical milieu (pH-value) were selected. The aim of our experiments was to describe the properties of terrestrial humic substances depending on their origin and genesis as well as the effects of the transport of humic substance-bound metals into the water-unsaturated soil zone. After determination of heavy metals in the soils by photon activation analysis the activated soil was used as an inherent tracer in batch experiments with the isolated humic acid. After adsorption of the loaded humic acid on an XAD-8 resin column, the partition of metals mobilized by humic acids could be quantified. There are correlations of the formation of metal-humic complexes with the soil pedogenes, with the pH-value as well as with the humic acid concentration.
Humic acids and associated radionuclides were extracted from several soil samples with a significant organic matter content, such as peaty soils and forest soil layers. Extractions were made using two alkaline solutions (Na4P2O7 0.1 mol·1–1 and NaOH 0.1 mol·1–1 under N2). The humic acid content in the extract was determined by the capillary zone electrophoresis technique (CZE) and associated radiocaseium was determined by gamma spectrometry. After analizing a large number of samples and studying the relationship between humic acid and organic matter content it was possible to conclude that the CZE technique may be a good alternative to classical techniques in humic acid determinations, with NaOH extractions leading to higher results than Na4P2O7. Furthermore, the quantification of the radiocaseium desorbed by applying different extractant reagents (NaOH, Na4P2O7, NH4AcO and CaCl2) showed that there may be some organic matter-radionuclide interations, other than those originated by humic acids. which may govern radionuclide retention in soils with a high content of organic matter.
Authors:K. Štamberg, P. Beneš, J. Mizera, J. Dolanský, D. Vopálka, and K. Chalupská
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.
Authors:H. Bowen, E. Page, I. Valente, and R. Wade
Radio-tracer experiments have shown that antimony, mercury and zinc interact to form complexes with humic and/or fulvic acids,
whose molar masses can be estimated by gel chromatography. Sb(III) and (V) humates are stable in the pH range 7–11, but are
largely dissociated below pH 4; humic acid does not reduce Sb(V) to Sb(III) in solution. Mercury forms a strong complex with
humic+fulvic acids. Zinc forms complexes with both humic acids and glycine, and the humic acid complex has similar elution
behaviour on dextran gel to a fraction from river water equilibrated with65Zn. At least one other form of zinc, in addition to Zn2+, occurs in this river.
Humin is separated from a soil sample and characterized by elemental analysis, IR and potentiometric titration. These investigations
indicated that humin displayed similar characteristics as humic acid. The sorption behavior of137Cs,90Sr and153Gd with humin was investigated from aqueous solution. The results indicated that the sorption process follows the order: Gd3+≫Sr2+>Cs+. It was time dependent and increased with pH. The sorption in the presence of humic acid or EDTA showed that both form a
metal-ligand complex and consequently decrease the % uptake.
Envestigations on the behaviour of the defect centres in calcites by means of electron spin resonance spectroscopy /ESR/ have shown the occurrence of important interferences, which may have an impact on age determinations. These effects are produced by humic acids, sunlight exposure, grinding, instability of paramagnetic centres, measurement conditions, and possible pretreatment of the sample. The consequence of these interferences are discussed.
Authors:A. A. Helal, Aly A. Helal, N. Z. Salim, and S. M. Khalifa
In a previous paper we studied the interaction of the radionuclides 110mAg, 60Co and 65Zn with peat humin. These nuclides are among the fission or corrosion products in nuclear reactors. The aim of this paper
is to study the effect of certain ligands, which are present in the environment, such as humic acid, fulvic acid, EDTA and
urea, on the sorption of these radionuclides by humin. The obtained results indicated that urea has no effect on the sorption
of Co and Zn by humin, and only a little in case of Ag. However, the presence of the other ligands (humic acid, fulvic acid
or EDTA) leads to different decreases in the sorption of the three nuclides by humin. The results are interpreted in the light
of the complex formation between ligands and the metal cations and of the strength of binding of these cations to the humin
sorbent. The release of Ag+in the presence of different ligands was found to follow the order: humic acid>EDTA>fulvic acid>urea. In the case of both
Co2+and Zn2+, the sequence is changed to be: EDTA>humic acid>fulvic acid>urea, with a higher release in the case of Zn2+. The results showed that cobalt is bound more strongly to humin than silver and zinc. The sulphur content of the humic fractions
plays a significant role in the competition for silver and zinc.