Clay Humic Acid Research Articles

Interaction kinetics and accessibility of sulfadiazine in model clay-humic acid suspension: Electron spin resonance investigations with nitroxide spin label

The characterization of the interaction of sulfonamides with soil is of particular interest in environmental risk and persistence assessment. In the present work electron spin resonance spectroscopy (ESR) was used to investigate the interaction kinetics of spin labelled sulfadiazine (SL-SDZ) with model clay-humic acid suspensions. The ESR spectra showed that SL-SDZ incubated with Leonardite humic acid (LHA) and Ca-hectorite as model clay was immobilized due to covalent binding of its aniline moiety to LHA. From the immobilization kinetics measured over a period of 1200 h a pseudo-first order reaction with a time constant of 82.6 ± 25.0 h of covalent binding was determined. Additionally, SL-SDZ was strongly sorbed by LHA immediately after incubation but not durably sequestered. Compared to incubation without Ca-hectorite the covalent binding kinetics of SL-SDZ as well as its strong sorption were retarded.

Desorption of arsenic from clay and humic acid-coated clay by dissolved phosphate and silicate

Arsenic (As) contaminated aquifers contain iron minerals and clays that strongly bind As at their surfaces. It was suggested that As mobilization is driven by natural organic matter (including fulvic acids (FA) and humic acids (HA)) present in the aquifers either via providing reducing equivalents for reductive dissolution of Fe(III) (hydr)oxides or via competitive desorption of As from the mineral surfaces. In the present study we quantified sorption of As(III) and As(V) to Ca 2+-homoionized illite (IL) and to kaolinite (Kao) as well as to HA-coated clays, i.e., illite–HA (IL–HA) and kaolinite–HA (Kao–HA) at neutral pH. Clay–HA complexes sorbed 28–50% more As than clay-only systems upon addition of 100 μM As(III)/As(V) to 0.5 g of clay or HA–clay with Ca 2+ probably playing an important role for HA binding to the clay surface and As binding to the HA. When comparing sorption of As(V) and As(III) to clay and HA–clay complexes, As(V) sorption was generally higher by 15–32% than sorption of As(III) to the same complexes. IL and IL–HA sorbed 11–28% and 6–11% more As compared to Kao and Kao–HA, respectively. In a second step, we then followed desorption of As from Kao, Kao–HA, IL and IL–HA by 100 and 500 μM phosphate or silicate both at high (0.41–0.77 μmol As/g clay), and low (0.04 to 0.05 μmol As/g clay) As loadings. Phosphate desorbed As to a larger extent than silicate regardless of the amount of As loaded to clay minerals, both in the presence and absence of HA, and both for illite and kaolinite. At high loadings of As, the desorption of both redox species of As from clay–HA complexes by phosphate/silicate ranged from 32 to 72% compared to 2–54% in clay only systems meaning that As was desorbed to a larger extent from HA-coated clays compared to clay only systems. When comparing As(III) desorption by phosphate/silicate to As(V) desorption in high As-loading systems, there was no clear trend for which As species is desorbed to a higher extent in the four clay systems meaning that both As species behave similarly regarding desorption from clay surfaces by phosphate/silicate. Similarly, no significant differences were found in high As-loading systems in the amount of As desorbed by phosphate/silicate when comparing Kao vs. IL and Kao–HA vs IL–HA systems meaning that both clay types behave similarly regarding desorption of As by phosphate/silicate. At low As loadings, up to 80% of As was desorbed by phosphate and silicate with no noticeable differences being observed between different As species, different types of clay, clay vs clay–HA or the type of desorbant (phosphate and silicate). The results of this study showed that HA sorption to Ca 2+-homoionized clay minerals can increase As binding to the clay although the As sorbed to the clay–HA is also released to a greater extent by competing ions such as phosphate and silicate. Desorption of As depended on the initial loadings of As onto the clay/clay–HA. Based on our results, the effect of humic substances on sorption of As and on desorption of As by phosphate and silicate has to be considered in order to fully understand and evaluate the environmental behavior of As in natural environments.

Surface binding site analysis of Ca2+-homoionized clay–humic acid complexes

Clay-humic substance complexes play a major role in controlling the mobility of toxic metals in contaminated soils. However, our understanding of the underlying mechanisms is limited. Binding site analysis of clay and clay-mineral-humic composites, in this study, revealed an enhanced surface reactivity for the clay surface by the sorbed humic substances. Kaolinite and illite had three binding sites with pK(a) values ranging from ∼4.5 to 9.6 at Ca(2+) concentrations of 0.01 and 0.1 M respectively. In the presence of peat humic acid (PHA), four or five binding sites were observed for humics sorbed kaolinite surface at Ca(2+) concentrations of 0.01 and 0.1 M respectively. pK(a) values ranged from ∼4.4 to 9.6 for humic acid concentration of 0.01 and 0.1 mg/mL. For illite, four or five binding sites were found with pK(a)s ranging from ∼4.1 to 9.4. From zeta potential measurements of PHA-kaolinite or PHA-illite suspensions, the already negative potential decreased by 30 mV from pH 4 to 7, and by 10 mV for pH values greater than 7. For illite the initial negative surface potential decreased by 15 mV up to a pH of 9. Above this pH, the potential decrease diminished to 2 or 5 mV. These changes in surface potential confirm the adsorption of PHA to the clay mineral surface. FTIR measurements of clay samples were able to identify the kaolinite and illite phases. In addition, FTIR absorption bands found in the range of 1950-1800 cm(-1), suggest the interaction of PHA with kaolinite and illite surfaces. The results of this study indicate that the sorption of humic substances increases the availability of clay surface functional groups for deprotonation and potential sorption of toxic metal cations.

Stability constants of U(VI) and U(IV)-humic acid complexes

Conditional stability constants have been determined for U(IV) and U(VI) Boom Clay humic acid (BCHA) and Aldrich humic acid (AHA) complexes, under anaerobic and carbonate free conditions. The constants are needed for nuclear waste repository performance assessment purposes. The U(IV) constants were obtained by developing an approach based on the solubility product of amorphous U(OH)4. The U(VI) constants were obtained by applying the Schubert ion-exchange approach.

Flow cytometry discrimination between bacteria and clay–humic acid particles during growth-linked biodegradation of phenanthrene by Pseudomonas aeruginosa 19SJ

Methods that quickly assess microbial density and aggregation in soil and sediments are needed in environmental microbiology. We report a flow cytometry method that uses the green and orange emission of the fluorochrome SYTO-13 to discriminate between bacteria and clay–humic acid particles. This approach distinguishes single or clustered bacteria, and clusters of bacteria and abiotic particles during the growth of the biosurfactant-producing strain Pseudomonas aeruginosa 19SJ on solid phenanthrene in the presence of humic acid–clay complexes.

Flow cytometry discrimination between bacteria and clay–humic acid particles during growth-linked biodegradation of phenanthrene by Pseudomonas aeruginosa 19SJ

Abstract Methods that quickly assess microbial density and aggregation in soil and sediments are needed in environmental microbiology. We report a flow cytometry method that uses the green and orange emission of the fluorochrome SYTO-13 to discriminate between bacteria and clay-humic acid particles. This approach distinguishes single or clustered bacteria, and clusters of bacteria and abiotic particles during the growth of the biosurfactant-producing strain Pseudomonas aeruginosa 19SJ on solid phenanthrene in the presence of humic acid-clay complexes.

Land‐use effects on the composition of organic matter in particle‐size separates of soils: II. CPMAS and solution 13C NMR analysis

SummarySoils from A horizons of Eutrochrepts under spruce forest (Sf), mixed deciduous forest (Df), permanent grassland (Gp), and arable rotation (Ar) were fractionated into clay‐ (<2 μm), silt‐(2–20 μm) and sand‐ (20–2000 μm) sized separates. 13C NMR spectroscopy was used to compare SOM composition across size separates and between land‐use regimes.CPMAS 13C NMR spectroscopy showed that the intensity of signals assigned to carbohydrates (representing most O‐alkyl C) and lignin (phenolic and methoxyl C) declined with decreasing particle size. Concurrently, alkyl C and C‐substitution of aromatic C increased in the order sand, silt, clay. The amount of alkyl C correlated well with microbial resynthesis of carbohydrates. Solution 13C NMR spectra suggested that humic acids (HA) extracted from the size separates were richer in carboxyl C and aromatic C than the bulk size separates. Also HA reflected increasing percentage of alkyl C with decreasing particle size. O‐alkyl C were lower in silt HA than in clay HA whereas aromatic C tended to peak in silt HA. These results suggested that sand‐sized separates were enriched in plant residues (primary resources) whereas clay‐sized separates were dominated by products of microbial resynthesis (secondary resources). Silt was rich in selectively preserved and microbially transformed primary resources. 13C NMR spectroscopy showed only small differences in SOM composition between land‐use regimes, except that silt and silt HA from Ar were richer in aromatic C than those from the other plots. But enrichment factors (E= content in fraction/content in whole soil) revealed differences in the distribution of C species across the size separates. Relatively high Earomatic (0.9) and Eo‐alkyl (1.0) for sand from Gp indicated high amounts of plant residues, probably due to intense rhizodeposition and to occlusion of plant debris within aggregates. Low Earomatic (0.3) and Eo‐alkyl (0.3) for sand from Ar suggested depletion of primary resources, which could be attributed to disintegration of soil aggregates upon cultivation. A pronounced enrichment of alkyl C in Ar clay‐sized separates (Ealkyl= 3.1) suggested large amounts of microbial carbon. Microbial products attached to clay surfaces by a variety of physico‐chemical bondings appeared more stable against mineralization induced by cultivation than plant residues sequestered in aggregates.

Caesium sorption—desorption in clay—humic acid systems

SUMMARYSoaking for 7 d with 0.05 M NaCl resulted in less caesium being sorbed by bentonite and kaolinite, but more by illite, compared to soaking for 2 d prior to addition of Cs. Overall the amount of Cs sorbed by the three clays was in the order bentonite > illite > kaolinite. Addition of humic acid to the clays depressed the sorption of Cs by all three clays, with illite showing the greatest effect. Desorption of added Cs was not totally reversible. The presence of humic acid resulted in an enhanced desorption of Cs from bentonite and to a lesser extent kaolinite. This enhanced desorption in the presence of humic acid was not seen for illite. The order of Cs retention following desorption for both clay and clay/ humic‐acid mixtures was illite > bentonite > kaolinite. A single Kd value could not describe the whole isotherm, but individual values were calculated at different Cs concentrations to cover the range of the isotherm. Kd values for desorption were higher than the corresponding Kd for sorption. For both sorption and desorption, the presence of humic acid resulted in lower Kd values than in its absence.

Behaviour of trace cadmium in boom clay reducing sediment I. Complexation with in situ dissolved humic acids

Boom clay is a reducing clay layer that contains 1.5% pyrite, 1% CaCO 3, 1.2% organic carbon and about 50% clay. Trace Cd conditional complexation constants were determined from Cd and organic matter distribution measurements at different solid/liquid ratios under in situ reducing conditions of solid- and liquid-phase composition. Cadmium forms 1:1 complexes with boom clay humic acids. The conditional complexation constant of trace Cd with boom clay humic acids under in situ solution conditions (pH 9, E h = −250 mV) is log K 1 = 7.5. Conditional complexation constants decrease by about 0.15 log K 1 units for each 10-fold increase in Cd loading in the range 10 −6 to 10 −10 eq. Cd/g organic matter. Cadmium-organic matter complexes were predicted to dominate the speciation of Cd in the in situ solution phase (pH 9, CO 3 = 0.015 M, 100 ppm DOM).

SOME ASPECTS OF CLAY-HUMUS COMPLEXATION

The influence of exchangeable cations on montmorillonite, illite, and kaolinite and of lattice charge of montmorillonite on clay-humic acid complexation were studied with complexes which were subjected to drying. The amounts of humic acid (HA) nonextractable by water from the complexes (termed “fixed” humic acid) were determined. The fixation of HA by montmorillonite followed the order Li+

Adsorption mechanisms of nicotine on humic acid and clay humic acid complex

AbstractThe adsorption isotherm of nicotine on humic acid ‐ surface was found to be multiphase according to the applied concentrations of nicotine. Each phase was characterized by its own change in free energy and represented a mechanism of interaction. At low concentrations, the isotherm showed a H‐curve of high affinity between both reactants as a result of protonation of the pyrrolidine nitrogen atom of nicotine, the second phase was that of flat adsorption in which the nitrogen atoms of nicotine acted as electron donor. The third phase was that of the rearrangement of the nicotine from flat to side adsorption on the humic surface, after which the phase of multilayer formation followed. The adsorption on the surface of the humic acid‐clay complex showed no distinct phases but an isotherm looks like the L‐type, although it could not verify Langmuir's equation. Probably the isotherm was the resultant of two mechanisms one due to the adsorption of the humic acid part and the other due to the clay part in the complex. Comparison of the constants of Freundlich's equation showed that the capacity of the adsorption humic surface was greater than that of the complex.

Migration studies of radionuclides in boom clay

Sorption results obtained with Boom clay for Am, Pu, Eu, Tc and Np under near in-situ conditions are presented, and the significance of K d values in Boom clay is discussed. Clay humic acids are shown to be a controlling factor in the sorption of Am, Eu, Np. Results with Tc and Pu are different and need further examination. Experiments to determine the mobility of light molecular weight organic material in compacted Boom clay is discussed.

Surface Characteristics of Kaolinitic Clays and Clay-Humic Acid Complexes by Potentiometric and Conductometric Titrations

AbstractAcid and non-acid forms of kaolinite clays were found by potentiometric and conductometric titrations to possess a weak acid species, the concentration of which was increased by acidic preparation conditions and by the presence of soil organic matter bound to the clay. A stronger acid species was also found in untreated and in organic-free, HCl-treated samples (washed free of excess acid). The end points for organic-free and/or ion-exchanged samples were used to predict the end points for untreated samples. A surface-chemical model involving MOH2+, MOH, and MO− species (where M = Al and/or Fe) was fitted to the titration data and to the cation-exchange capacities. MOH2+ is the stronger acid and MOH the weaker acid; exchange of Na+ counterions by H+ converts MO−Na+ sites to MOH sites. Humic acid was probably complexed or chelated to some hydroxylated Al/Fe sites through COOH and phenolic OH groups. The COOH groups contributed supplementary stronger acid species which were not exchangeable, whereas the OH groups contributed supplementary weaker acid species and also increased the CEC relative to that for organic-free samples.

Electrical Conductivity and the Surface Characteristics of Kaolinitic Clays and Clay-Humic Acid Complexes

AbstractThe conductivites of the Na and H ion-exchanged forms of kaolinitic clay rejects from sand-washing operations, both purified and as found naturally as a complex with soil organic matter, were examined. The two Na-clays showed linear conductivity-concentration characteristics, each having two regions with different slopes intersecting at ∼3.3% by weight of clay, which probably reflect a structural change from sol to gel. In the gel region, only the Na-counterions conducted, the reduction in conductivity with concentration being due to a smaller proportion of these ions in the Gouy layer and/or a decrease in their mobilities. In the sol, an additional, concentration-dependent conductivity arose from the electrophoretic motion of clusters of clay particles which gradually broke down on dilution. The two acid clays showed curved conductivity-concentration characteristics consistent with a weak acid dissociation equilibrium; the pKa values of 6.37 to 6.56 are close to those determined independently from titration with alkali. A stronger acid species detected in the titrations was not seen in the conductivity. The MOH2+/MOH/MO− model of the clay-surface species and one set of the predicted concentrations of each species (see preceding paper) are consistent with the observed conductivities. The MOH2+ species probably bridged the edges and faces of clay particles so that the H atoms were identical, but became different when alkali was added.

The effect of pH on the retention of Cu, Pb, Zu and Cd by clay-humic acid mixtures

The amount of metal ion sorbed by the solids increased with increasing pH over the range 3 to 6, and with mixtures of clay-cellulose or illite-humic acid the uptake corresponded to the direct addition of individual substrate adsorption values. When the humic acid samples were admixed with Na+-form kaolinite or montmorillonite, there was some reduction in adsorption, attributable to component interactions, and this effect was most marked in the presence of Cu and Zn ions.