Humic Acid Colloids Research Articles

Influence of heteroaggregation processes between intrinsic colloids and carrier colloids on cerium(III) mobility through fractured carbonate rocks

Colloid facilitated transport of radionuclides has been implicated as a major transport vector for leaked nuclear waste in the subsurface. Sorption of radionuclides onto mobile carrier colloids such as bentonite and humic acid often accelerates their transport through saturated rock fractures. Here, we employ column studies to investigate the impact of intrinsic, bentonite and humic acid colloids on the transport and recovery of Ce(III) through a fractured chalk core. Ce(III) recovery where either bentonite or humic colloids were added was 7.7–26.9% Ce for all experiments. Greater Ce(III) recovery was observed when both types of carrier colloids were present (25.4–37.4%). When only bentonite colloids were present, Ce(III) appeared to be fractionated between chemical sorption to the bentonite colloid surfaces and heteroaggregation of bentonite colloids with intrinsic carbonate colloids, precipitated naturally in solution. However, scanning electron microscope (SEM) images and colloid stability experiments reveal that in suspensions of humic acid colloids, colloid-facilitated Ce(III) migration results only from the latter attachment mechanism rather than from chemical sorption. This observed heteroaggregation of different colloid types may be an important factor to consider when predicting potential mobility of leaked radionuclides from geological repositories for spent fuel located in carbonate rocks.

Particle phase distribution of polycyclic aromatic hydrocarbons in stormwater — Using humic acid and iron nano-sized colloids as test particles

The distribution of polycyclic aromatic hydrocarbons (PAHs) in different particulate fractions in stormwater: Total, Particulate, Filtrated, Colloidal and Dissolved fractions, were examined and compared to synthetic suspensions of humic acid colloids and iron nano-sized particles. The distribution of low-molecular weight PAHs (LMW PAHs), middle-molecular weight PAHs (MMW PAHs) and high-molecular weight PAHs (HMW PAHs) among the fractions was also evaluated. The results from the synthetic suspensions showed that the highest concentrations of the PAHs were found in the Filtrated fractions and, surprisingly, high loads were found in the Dissolved fractions. The PAHs identified in stormwater in the Particulate fractions and Dissolved fractions follow their hydrophobic properties. In most samples >50% of the HMW PAHs were found in the Particulate fractions, while the LMW and MMW PAHs were found to a higher extent in the Filtrated fractions. The highest concentrations of PAHs were present in the stormwater with the highest total suspended solids (TSS); the relative amount of the HMW PAHs was highest in the Particulate fractions (particles>0.7μm). The highest concentration of PAHs in the Colloidal fraction was found in the sample with occurrence of small nano-sized particles (<10nm). The results show the importance of developing technologies that both can manage particulate matter and effectively remove PAHs present in the Colloidal and Dissolved fractions in stormwater.

Unravelling the fate of arsenic during re-oxidation of reduced wetland waters: Experimental constraints and environmental consequences

The presence of arsenic(As)-bearing Fe(III) oxyhydroxides in wetland zones may threat water quality due to the reduction processes that affect these zones. These processes have indeed the potential of releasing As into the soil solutions, and ultimately into the nearby river network, being given the hydrological connectivity that exists between wetlands and rivers. The effective transport of the released As into the river network is however dependent on the behaviour of As during the re-oxidation process that will occur at the wetland-river boundary, which could immobilize the released As into neo-formed Fe(III) oxyhydroxides. One of the key questions is, however, which is the impact of the organic-rich nature of wetland waters on this neoformation, which could instead favour the development of highly mobile As-bearing, organomineral colloids. In this study, we evaluated this possibility by carrying out oxidation experiments on humic acid (HA)- and As(III)/Fe(II)-rich waters. The ultrafiltration results showed that the presence of organic molecules during Fe oxidation events played a major role in the hydrolysis reaction of Fe oxyhydroxides. When Fe microparticles were formed in the absence of HA, the occurrence of HA during Fe oxidation events promoted the formation of amorphous nanosize Fe phase diffusely embedded within the organic matrix. These mixed Fe–HA colloids constrained the fate and distribution of As. These results were confirmed by nanoSIMS images that showed As sorption onto and within Fe microparticles (>0.2μm) in the absence of HA. By contrast, with HA, results showed preferential incorporation of As in the bulk of Fe–HA colloids (<0.2μm) during their formation rather than surface adsorption onto these colloids.

Removal of dissolved humic acid from water by coagulation method using polyaluminum chloride (PAC) with calcium carbonate as neutralizer and coagulant aid

Coagulation experiments were performed to find out the optimum coagulant and alkaline chemical for the removal of humic acid (HA) from environmental water. This research clearly indicates the effectiveness of coagulation method using polyaluminum chloride (PAC) with calcium carbonate as neutralizer and coagulant aid to remove HA. The removal of HA was evaluated from absorbance at 260nm and concentration of dissolved organic carbon (DOC). The highest removal ratio was found to be 96.6% for the absorbance of HA and 91.6% for DOC concentration when 30mg/L of PAC with calcium carbonate (CaCO3) was used as an alkaline reagent. In this method, the sludge volume (SV) was reduced about half compared with the PAC method using NaOH as neutralizer. Ca2+ which is derived from CaCO3 makes HA colloid size bigger and easier to form flocks because of the compression in the electrical double layer (EDL) between HA colloids. The adsorption of HA onto porous CaCO3 particles also plays an important role. The experiments conducted with sample water collected from Sebangau River, Indonesia consists of 33.4mg/L of DOC and was found to have a removal efficiency of 86.5%, whereby the final concentration of DOC was 4.5mg/L. These results suggested that CaCO3 requires a lesser amount of coagulants and also shortens the settling time. This proposed technique provides a more effective and conventional removal method for HA by coagulation–precipitation processes.

Influence of Humic Acid Colloid on Adsorption of DDT in the Riverbed Sediments

Influence of Humic Acid Colloid on Adsorption of DDT in the Riverbed Sediments

Influence of Humic Acid Colloid on Adsorption of Oxytetracycline in Sediment

Influence of Humic Acid Colloid on Adsorption of Oxytetracycline in Sediment

Impact of Interactions between Natural Organic Matter and Metal Oxides on the Desorption Kinetics of Uranium from Heterogeneous Colloidal Suspensions

Colloids play an important role in governing the transport of radionuclides in geologic environments. As naturally occurring colloidal suspensions are compositionally heterogeneous, the subsurface fate of radionuclides may be sensitive to interactions among different kinds of colloids. Therefore, we investigated the adsorption equilibrium and desorption kinetics of uranium (U(VI)) in experiments conducted with compositionally homogeneous suspensions of colloidal SiO(2), ZnO, hydrous ferric oxide (HFO) or humic acids (HAs) as well as heterogeneous suspensions consisting of a colloidal metal oxide and HA. We found that interactions between HAs and ZnO or HFO greatly inhibited the sorption of U onto colloids in the heterogeneous suspensions. HA-ZnO interactions enhanced the desorption of U from the heterogeneous colloidal suspensions, while the association between HA and SiO(2) or HFO inhibited U desorption. Molecular-level characterizations reveal that HFO interacted with HAs by electrostatic interactions, association with aliphatic/aromatic carbon and inner-sphere complexation with carboxyl functional groups, while SiO(2) and ZnO mainly associated with HAs by weak interactions (e.g., van der Waals interactions). The present findings indicate that interactions between HA and metal-oxide colloids can substantially influence the desorption of U(VI) from these particles, thereby potentially affecting the mobility of this radionuclide in groundwater.

Coupling of arsenic mobility to sulfur transformations during microbial sulfate reduction in the presence and absence of humic acid

Microbial sulfate reduction is an important terminal electron accepting process in arsenic-contaminated subsurface environments. Humic acids are ubiquitous in such environments, yet their impact on arsenic mobility under sulfate-reducing conditions is poorly understood. In this study, we examined the effects of microbial sulfate reduction and humic acid on arsenic mobilization via a series of advective-flow column experiments. The initial solid-phase in these experiments comprised quartz sand that was coated with As(III)-sorbed goethite (α-FeOOH). The effect of humic acid was assessed by comparing columns that received artificial groundwater in which humic acid was either absent or present at 100mgL−1, whilst the effect of microbial sulfate reduction was investigated by comparing columns that were inoculated with the sulfate-reducer Desulfovibrio vulgaris (ATCC strain 7757) versus abiotic control columns. The presence of high concentrations of humic acid alone did not enhance the overall extent of arsenic release from either the abiotic or the inoculated (sulfate reducing) columns. This is consistent with similar arsenic concentrations in porewaters filtered to both <0.45μm and <3kDa, demonstrating that aqueous arsenic did not form mobile colloidal humic acid complexes. In contrast, microbial sulfate reduction was found to mobilize substantial levels of arsenic relative to those observed in the corresponding abiotic control columns. Iron and sulfur K-edge X-ray absorption spectroscopy (XAS) showed that reaction between goethite and microbially-produced sulfide lead to accumulation of mackinawite (FeS) and elemental S. Microbial sulfate reduction also caused important changes in arsenic speciation, especially the formation of aqueous dithioarsenate and monothioarsenate. However, arsenic K-edge XAS showed that arsenic sulfide mineral phases (orpiment and realgar) did not form during the 60day advective-flow experiment. The formation of poorly-sorbing thioarsenate species appeared to contribute to the observed enhancement of arsenic mobilization from the inoculated columns. Dithioarsenate and monothioarsenate were relatively stable, and were found to make up>40% of aqueous arsenic even at very low porewater sulfide concentrations (i.e. <10μmolL−1). Accordingly, the formation, stability and sorption–desorption of thioarsenate species need to be considered when evaluating and predicting subsurface arsenic mobility.

Diffusion of U(VI) in Opalinus Clay: Influence of temperature and humic acid

The diffusion of U(VI) (c0=1×10−6mol/L) in compacted Opalinus Clay from the Mont Terri underground laboratory, Switzerland, was studied in the absence and presence of humic acid (10mg/L) at two different temperatures (25°C, 60°C) under anaerobic conditions. As background electrolyte synthetic Opalinus Clay pore water (pH 7.6, I=0.36mol/L) was used. The diffusion-accessible porosity, ε, was determined for each Opalinus Clay bore core sample by through-diffusion experiments with tritiated water (HTO) before the U(VI) diffusion experiments were carried out. The values for the effective diffusion and distribution coefficients De and Kd obtained for U(VI) and humic acid at 25°C as well as at 60°C showed that humic acid has no significant influence on the U(VI) diffusion. The diffusion profiles of humic acid in Opalinus Clay at 25 and 60°C indicate the contributions of two different humic acid particle size fractions (<1kDa and 10–100kDa). The small-sized humic acid fraction diffused through the whole Opalinus Clay samples at both temperatures within the 3 month duration of the U(VI) diffusion experiments. At 60°C, diffusion profiles of two different U(VI) species were observed. In a separate experiment the U(VI) speciation in the source reservoir solution at 60°C was analyzed by laser-induced fluorescence spectroscopy, photon correlation spectroscopy and scanning electron microscopy with an energy dispersive X-ray detector. The two diffusion profiles could be attributed to an unknown colloidal and a known aquatic U(VI) species (Ca2UO2(CO3)3(aq)). The diffusion results showed that the interaction of U(VI) and of the large-sized humic acid colloid fraction with the clay is stronger at 60°C. An increase of Kd from 0.025±0.003m3/kg at 25°C to 0.25±0.05m3/kg for U(VI)colloidal at 60°C was determined. In addition, the value for De of U(VI) increased with increasing temperature. Using the De values at 25 and 60°C, a preliminary activation energy for the diffusion of U(VI) through Opalinus Clay of 10kJ/mol was calculated. The observed increased Kd and De values for U(VI)aqueous at 60°C compensated each other to almost equal values of the apparent diffusion coefficient Da at 25 and 60°C. Hence, an elevated temperature of 60°C does not impact the migration of U(VI) through OPA significantly.

Layer-by-layer self-assembly of multilayer films based on humic acid

Multilayer films consisting of negatively charged humic acid and positively charged polyelectrolyte have been fabricated on various substrates using the layer-by-layer self-assembly technique. The thickness (linearly increasing with the square root of NaCl concentration) and refractive index of the films determined by ellipsometry can be regulated by ionic strength through adjusting the coiling of the polyelectrolyte chains for assembly. The cone-shaped features on surface obtained by atomic force microscope are derived from the negatively charged colloidal humic acid binding with polyelectrolyte cation. The smooth features are corresponding to the dissociated humic acid with carboxylate ion (―COO −) electrostatically attracted on polyelectrolyte cation. These results are verified by Fourier transform infrared spectra. The linear dependence of the peak current on the square root of the scan rate revealed by the cyclic voltammetry indicates that the redox process at the electrode surface is diffusion-limited and the charge transport does not involve the film itself.

Application of different types of resins in the radiometric determination of uranium in waters

The aim of this study is to compare different resins regarding their separation and pre-concentration efficiency for uranium from aqueous solutions and its subsequent radiometric determination by liquid scintillation counting (LSC). The different types of the investigated resins include: (a) a pure cation-exchange resin (Dowex Marathon C), (b) a complex forming resin (Chelex 100) and (c) an impregnated resin (5% diethylene glycol succinate on Chromosorb W-H). The radiometric measurements were performed after mixing of the pre-concentrated aqueous phase with the liquid scintillation cocktail. The effect of experimental conditions such as pH, salinity (e.g. [NaCl]) and the presence of other chemical species (e.g. Ca2+ and Fe3+ ions or humic acid and silica colloids) on the separation recovery have been investigated at constant uranium/radioactivity concentration. According to the experimental results the maximum chemical recovery differs significantly from one resin to another as a function of either, pH or the other chemical parameters. The optimum pH is found to be 8, 4 and 8 for Marathon C, Chelex-100 and diethylene glycol succinate, respectively. On the other hand, generally Ca2+ and Fe3+ ions as well as the presence of colloidal species in solution (even at low concentrations) result in a significant decrease of the chemical recovery of uranium, particularly for Marathon C and the diethylene glycol succinate impregnated resins. Generally, among the studied resins Chelex 100 was superior regarding chemical recovery, selectivity, regeneration and reuse.

Thorium determination in water samples by liquid scintillation counting after its separation by cloud point extraction

The aim of this study is the separation and pre-concentration of thorium from aqueous solutions by cloud point extraction (CPE) and its the radiometric determination by liquid scintillation counting (LSC). For CPE, tributyl phosphate (TBP) was used as the complexing agent and (1,1,3,3-Tetramethylbutyl)phenyl-polyethylene glycol (Triton X-114) as the surfactant. The radiometric measurements were performed after phase separation by mixing of the surfactant phase with the liquid scintillation cocktail. The effect of experimental conditions such as pH, ionic strength (e.g. [NaCl]) and the presence of other chemical species (e.g. Ca2+ and Fe3+ ions, and humic acid colloids) on the CPE separation recovery have been investigated at constant reactant ratio (m(TBP)/m(Triton) = 0.1). According to the experimental results the maximum chemical recovery is (60 ± 5)% at pH 3. Regarding the other parameters, generally Ca2+ and Fe3+ ions as well as the presence of colloidal species in solution (even at low concentrations) results in significant decrease of the chemical recovery of uranium. On the other hand increasing NaCl concentration leads to enhancement of chemical recovery. Generally, the method could be applied successfully for the radiometric determination of thorium in water solutions with relatively increased thorium content.

STXM and LSLM investigation of Eu(III) induced humic acid colloid aggregation

Humic acids (HA) are potentially important in binding traces of actinides or lanthanides, thus affecting their transport in aquatic systems. Eu(III) induced HA colloid aggregation has been investigated by a combination of Scanning Transmission X-ray Microscopy (STXM) and Laser Scanning Luminescence Microscopy (LSLM). Both methods reveal the same aggregate morphology – optically dense zones embedded in a matrix of less dense material observed by STXM correspond to areas with increased Eu(III) luminescence yield in the LSLM micrographs. From these comparative measurements we infer the enrichment of Eu(III) cations in the optically dense zones. These areas also exhibit a C 1s-NEXAFS signature strongly differing from the signal extracted from the less dense areas. Spectral filtering of Eu(III) luminescence lines corresponding to valence transitions affected by organic acid complexation indicates that Eu(III) cations are more strongly bound in the dense zones.

Effects of feed water temperature on separation performance and organic fouling of brackish water RO membranes

Data are presented from a series of laboratory experiments designed to evaluate separation performance and humic acid fouling for two RO membranes treating brackish water at temperatures of 15, 25, and 35°C. A model is proposed that considers changes only to solute and solvent properties. Model results and experimental data confirm that solute concentration polarization decreases, while water permeability and salt permeability increase with temperature. Overall, higher feed water temperature reduces energy consumption and observed salt rejection to a greater extent than that predicted by the model, which suggests that RO transport models must be developed for predicting changes in solution and membrane properties. At all temperatures, salt rejection increases after introduction of humic acid, probably due to membrane modification and sealing of thin film defects. Humic acid colloidal size decreases with increasing temperature. At higher temperatures, humic acid rejection is lower (as measured by TOC) due to changes in the membrane structure and in the fraction of dissolved TOC. Flux decline is much more severe at 15°C, but practically identical at 25 and 35°C. The mass of humic acid accumulated on the membranes is essentially the same at all temperatures, but specific cake resistance increases as temperature decreases; hence, specific cake resistance increases with increasing humic acid colloid size. These results have important implications for engineering efforts to mitigate membrane fouling and reduce energy consumption in brackish water desalination.

Interaction of trace elements in acid mine drainage solution with humic acid

The release of metal ions from a coal mining tailing area, Lamphun, Northern Thailand, is studied by leaching tests. Considerable amounts of Mn, Fe, Al, Ni and Co are dissolved in both simulated rain water (pH 4) and 10 mg L −1 humic acid (HA) solution (Aldrich humic acid, pH 7). Due to the presence of oxidizing pyrite and sulfide minerals, the pH in both leachates decreases down to ∼3 combined with high sulfate concentrations typical to acid mine drainage (AMD) water composition. Interaction of the acidic leachates upon mixing with ground- and surface water containing natural organic matter is simulated by subsequent dilution (1:100; 1:200; 1:300; 1:500) with a 10 mg L −1 HA solution (ionic strength: 10 −3 mol L −1). Combining asymmetric flow field-flow fractionation (AsFlFFF) with UV/Vis and ICP-MS detection allows for the investigation of metal ion interaction with HA colloid and colloid size evolution. Formation of colloid aggregates is observed by filtration and AsFlFFF depending on the degree of the dilution. While the average HA size is initially found to be ⩽ 2 nm , metal–HA complexes are always found to be larger. Such observation is attributed to a metal induced HA agglomeration, which is found even at low coverage of HA functional groups with metal ions. Increasing the metal ion to HA ratio, the HA bound metal ions and the HA entities are growing in size from <3 to >450 nm. At high metal ion to HA ratios, precipitation of FeOOH phases and HA agglomeration due to colloid charge neutralization by complete saturation of HA complexing sites are responsible for the fact that most of Fe and Al precipitate and are found in a size fraction > 450 nm . In the more diluted solutions, HA is more relevant as a carrier for metal ion mobilization.

Study of exchangeable metal on colloidal humic acids and particulate matter by coupling ultrafiltration and isotopic tracers: Application to natural waters

A new method is proposed to characterize the complexation properties of colloids and metal–colloid interactions in natural waters. Based on the association of ultrafiltration with isotopic tracing, this method could quantify the pool of elements in an exchangeable position and also address the kinetic aspects of these exchanges. Basically, it consists of the comparison of isotopic compositions between the bulk sample and a succession of filtrates through time. Exchanges between colloidal humic acids (HA) and metals were first characterized, before applying such manipulations on natural waters. A few elements, representative of a wide range of complexation properties, were chosen: Cu, Zn, Cd, Pb, Sr, Nd, Ni, Th and U. In the case of humic acids, very small (less than 10% of isotopes), but significant isotopic shifts were observed compared to the isotopic equilibrium. It means that more than 90% of the isotopes were exchanged just after addition of isotopic tracers. Experiments on natural organic-rich waters (Mengong and Nyong streams) indicate isotopic composition variations close to those of humic acids. On the contrary, ultrafiltration performed on the total Sanaga River water (including suspended matter “SM”) shows an important isotopic shift between the filtered and unfiltered solutions. It means that in the case of the Sanaga River, a significant part of the chemical elements did not exchange.

In situ AFM study of sorbed humic acid colloids at different pH

Humic acid colloids adsorbed on the basal plane of cleaved muscovite are investigated under in situ conditions by non-contact mode atomic force microscopy (AFM) in liquid (also called fluid tapping-mode AFM). Structures are found to be of nanometer scale, consisting of flat particles (8–13 nm in diameter), aggregates of particles (20–100 nm), chain-like assemblies, networks and torus-like structures. In contrast to former investigations colloids are investigated in aquatic solution and structures are not influenced by sample preparation. Nanostructure, surface coverage and particle sizes are found to depend on solution pH. Humic colloids can be distinguished from surface roughness and background noise by image processing. Furthermore, an approach to quantify the surface coverage is discussed. Therefore, non-contact mode AFM in liquid is shown to be a powerful method to study the interaction of colloids at solid–liquid interfaces.

Humic substances and associated small molecules from peats in balneology

The therapeutic effect of peat has been known for a long time. The application of peat to medicine is mainly in the recouperation to working capability of a patient after illness or an operation, in rheumatism and in special cases for gynaecology. Furthermore bactericidic, fungistatic, anti-viral and perhaps also cacinostatic effects have been observed. Knowledge of these effects are, at present, mostly empirical. To elucidate the mechanism of action, several natural scientists and medical research workers co-ordinated their efforts. The differences in conditions for the formation of low-bog and raised-bog peat cause differences in the composition of their constituents. The separation of the different fractions of peat using conventional methods is described. The bitumen and humic acids fractions are the most therapeutically interesting. Substances in the bitumen fraction, such as sterins and hormones, and precursors of humic acids such as lignin degradation products, are of physiological interest for their variety of biochemical reactions. The high molecular weight, spherical, colloidal humic acids are important for the transport of heat from a peat-slurry bath, into the nucleus of the body of the patient.

Competitive actinide interactions in colloidal humic acid-mineral oxide systems

The adsorption behavior of americium, thorium, neptunium, and plutonium was investigated in multicomponent systems containing γ y-alumina or amorphous silica as model inorganic particles and polydispersed humic acid (HA) colloids isolated from an organic-rich clay formation. The sorption selectivity of the actinide ions on bare mineral oxide particles can be explained on the basis of the hard-soft Lewis acid-base behavior

The Importance of Organic Compounds on the Modbilization and Bioassimilation of Thorium in the Morro do Ferro Environment

AbstractData are presented on the role of naturally occurring and synthetic organic compounds in the mobilization and bicassimilation of Th-232. The study is taking place in the state of Minas Gerais, Brazil, in and around an exposod and deeply weathered are body (the Morro do Ferro) estimated to contain 30,000 tonnes of Th and &gt; 100,000 tonnes of the light rare earth elements. Indigenous plants collected from the are body surface are shown to contain high concentrations in the range of 20–1,000 μg/g ash of Th-232. Prcliminary estimates of Th-232 concentration factors range between 10−5 and 10−3 and are comparable with those reported for plutonium. Leaching studies using different chelating agents indicate that the release of Th-232 from. weathered soil and are as well as plant uptake are directly related to complex stability. Preliminary results of speciation studies using ultrafiltration techniques indicate that for water which has percolated through the are body, most of the dissolved Th-232 is associated with colloidal humic acids of molecular weight &gt; 300,000.