It was found that some trivalent cations form precipitates with humic acid at pH 4.2. The precipitates contain less metal
cations than suggested by the neutralization-charge model for soluble complexes based on the available anionic sites. It is
suggested that cations, which can form inner-sphere complexes, may precipitate before they are completely neutralized, while
those that do not form complexes precipitate only after complete neutralization.
The effect of some environmental ligands and certain fertilizers on the complexation of strontium with humic acid wasinvestigated
colorimetrically and radiometrically. The results indicate that Na2-EDTA, Na3-citrate and NaCl compete to complex strontium in solution with the sequence: chloride < citrate < EDTA while Na3-phosphate has the reverse behavior. In the case of nitrogen containing fertilizers, the results show that urea, Mg-ammonium
nitrate and ammonium nitrate increase the availability of strontium to plants and microorganisms.
In this study, the sorption behavior of two important contaminants, phenol and radioactive cesium (137Cs), onto surfactant modified insolubilized humic acid (SMIA) were investigated as a function of time, sorbate concentration
utilizing the radiotracer method and UV–Vis spectroscopy. Phenol sorption process was well described by both Freundlich and
Tempkin type isotherms, and cesium sorption was described by Freundlich and Dubinin–Radushkevich isotherms. It was found that
SMIA adsorbs both cations and phenolic substances. Kinetic studies indicated that adsorption behavior of phenol obey the pseudo
second order rate law. FTIR spectroscopic technique was used to understand the structural changes during modification process
Commercial humic acid (HA) was anchored onto silica gel (SiAPTS) previously modified with 3-aminopropyltrimethoxysilane (APTS).
HA was anchored onto SiAPTS through two routes: adsorption and covalent chemical immobilization onto the surface. The adsorption
occurred by adding SiAPTS to HA in an aqueous solution, producing SiHA1, while chemical immobilization was performed by reacting
HA suspended in N,N-dimethylformamide with SiAPTS, to yield SiHA2. The infrared spectra confirm HA immobilization using both
procedures and the termogravimetric results showed that the anchored compounds have significantly thermal stability increased.
While natural HA presents a thermal stability up to 200C, the anchored compound presents a thermal stability near to 750C.
Authors:S. Kumar, N. Rawat, B. Tomar, V. Manchanda, and S. Ramanathan
Sorption of technetium on hematite colloids, at varying pH (3–10), has been studied in absence and presence of humic acid
using 95mTc-96Tc radiotracers. Technetium was found to be weakly sorbed on hematite at lower pH (<5) values, while no sorption was observed
at higher pH values. Humic acid was found to have no effect on the sorption of technetium on hematite under aerobic conditions,
while at lower pH values small reduction was observed which was attributed to the reduced zeta potential of the hematite colloids
owing to the strong sorption of humic acid.
Authors:S. Mortazavi, Gh. Asgari, S. Hashemian, and G. Moussavi
Catalytic ozonation has recently been used as a new means of contaminant removal from water and wastewater. In this study, bone charcoal (BC), a new catalyst prepared under laboratory conditions, was used to catalyze the ozonation
of humic substances (HS) in aqueous solutions. The catalytic effect of bone charcoal and the relevant parameters of this ozonation
process (solution pH, temperature, scavenger effect, humic acids concentration and BC dosage) were investigated. In the catalytic
ozonation experiments, the degradation kinetics was investigated. The reaction rate and the rate constant were determined.
The results showed that using a BC catalyst in the ozonation of HS produced a 1.43- and 1.56-fold increase in reaction rates
compared to the sole ozonation processes (SOP) under acidic and alkaline conditions, respectively. Furthermore, the applicability
of heterogeneous catalytic ozonation with bone charcoal (HCOBC) to humic acid degradation was evaluated by performing comparisons
with H2O2, O3, O3/H2O2 and O3/H2O2/BC processes. With the use of the Arrhenius equation, the activation energy (Ea) was calculated to be 10 kJ mol−1. The results also showed that under the different temperatures, the reaction of the catalytic ozonation of HS was defined
as diffusion controlled in accordance with the activation energy. These findings suggest that the HCOBC can be applied as
an efficient and feasible method for the removal of HS from water.
The complexation of Eu3+ and Am3+ ions with the humic acids has been investigated at various pH (4.0, 4.5, 5.0, 5.4) in 0.1M NaClO4 solution using solvent extraction technique. Two humic acids are used in this study: humic acid extracted from the soil of Taejon on the Okchon Basin of Korea (TJHA) and commercially available one from Aldrich Chemical Co. (AHA). The total carboxylate group concentrations were determined to be 3.58 meq/g and 4.59 meq/g for Taejon and Aldrich humic acids, respectively. The conditional stability constants (log
1 and log
2), dependent on the pH of the solution, of the complexes of Eu3+ and Am3+ ions with the humic acids have been determined at the ionic medium of 0.1M NaClO4. The values of stability constants with the degree of ionization of TJHA for Eu and Am complexes are quite well agreed with those of Lake Bradford humic acid (LBHA), indicating that structural characteristics of TJHA and LBHA may be quite similar to one another.
Effects of pH, Eu(III) concentration, ionic strength, temperature and humic acid (HA) on Eu(III) sorption to iron oxides were
investigated in detail. The sorption of Eu(III) to iron oxides was significantly dependent on pH and weakly dependent on ionic
strength, and higher temperature was gainful to Eu(III) sorption. In the presence of HA, Eu(III) sorption was enhanced significantly
at low pH; whilst obvious negative effect was observed in higher pH range. Below 12 mg/L HA, HA could obviously enhanced Eu(III)
sorption to iron oxides, nevertheless Eu(III) sorption decreased steeply with increasing HA while HA exceeded 12 mg/L. The
results were helpful for understanding radionuclides behaviors in natural environment.
Authors:T. Sakuragi, S. Sawa, S. Sato, T. Kozaki, T. Mitsugashira, M. Hara, and Y. Suzuki
In the wide pH range of 4 to 10, distribution ratios of Am(III)-humate species to free Am(III) ions (DAmHA = [Am(III)HA]/[Am(III)]free) were determined at 10 ppm (4.7 . 10-5 eq/dm3) of humic acid and 0.1M NaClO4 by a cation-exchange equilibrium method under N2 atmosphere. The DAmHA was insensitive to an increase in pH (logDAmHA ≈ 2.6-2.8), which indicates the formation of mixed hydroxo-humate complexes. The present DAmHA value is larger than the estimated value from available stability constants for ternary complexations by spectroscopic analysis (1.4-2.1) and is markedly smaller than that of Eu(III) obtained by the dialysis method (3.7-8.0) reported in the literatures. The DAmHA obtained in the present study is widely applicable to estimate the actinide(III) and lanthanide(III) sorption on minerals in the presence of humic and fulvic acids.
The interaction of UO22+ with various humic acids (HA's) has been studied by capillary zone electrophoresis (CZE). The experiments were done in 10 mM acetate buffer with pH 3.3 and 4.0, to avoid hydrolysis of uranium. It was found that in slightly acidic media and low HA concentration (<3 mM), two complexes with uranium(VI) are formed by fast kinetics and uranyl migrates as cationic species. Electrophoretic mobilities are decreasing with the increasing HA/uranium ratio and a low soluble neutral compound is also formed. In addition, it was found that at HA concentrations higher than 3 mM negatively charged species are formed. Similar results were obtained for HA's of different origin (soil, peat, coal derived, IHSS standards). Conditional stability constants of the complexes UO22+-HA for Fluka I HA, were estimated to be log
1 = 4.18±0.06 and log
2 = 7.28±0.18.