Colloid Sorption Research Articles

Addressing Challenges of Membrane Clogging in AF4-UV-ICPMS Analysis for Size Determination of Trace Elements in Acidic, Organic-Rich Peat Bog Waters.

The analysis of colloid-associated trace elements (TEs) in acidic, organic-rich waters (pH 3.8-5.8) using AF4-UV-ICPMS often necessitates the use of neutral or weakly alkaline carriers (pH 7-8.6). Employing acidic mobile phases has been deemed impractical due to the substantial sorption of colloids onto a 0.3 kDa polyethersulfone (PES) membrane and greatly reduced separation performance. This has greatly restricted the determination of potentially bioavailable forms of TEs (i.e., < 1 kDa) in acidic, organic-rich waters. To address this issue, porewaters from Sphagnum moss and peat were investigated. Membrane clogging was more pronounced in peat porewaters, where a higher deposition rate of dissolved organic matter onto the membrane was observed compared to that in moss waters. This adsorption is driven by membrane-colloid interactions, with colloids in peat porewaters exhibiting weaker electrostatic repulsion due to their higher positive ζ-potentials. Considering the actual pore size and clogging tolerance of the membrane, it is advisable to employ a 5 kDa PES membrane for peat porewaters, while a 1 kDa PES membrane suits moss waters better. Employing the optimal method enables the separation of TEs within the 0.5-20 kDa size range. Operating within a metal-free, ultraclean laboratory, TEs are detectable at the ng·L-1 level. By enabling precise and accurate separation of dissolved TEs into their size species in these peat bog waters at an appropriate pH, this method addresses diverse size profiles. This information is crucial for comprehending the chemical forms, transformations, mobility, and potential bioavailability of TEs in peat bogs.

Natural mineral colloids facilitated transport of EE2 in saturated porous media: Effects of humic acid and conjugate form

Steroid estrogens have posed significant ecological risks to aquatic organisms due to their potent endocrine-disrupting effects. The role of natural mineral colloids in facilitating the transport of hydrophobic organic pollutants in the environment has been confirmed, but the control mechanisms of colloids on 17α-Ethinylestradiol (EE2) migration in the subsurface environment are often still not well understood. This study combined the batch sorption equilibrium experiments and dynamic transport simulations to reveal the interface interactions and co-transport characteristics between illite colloids and EE2 at both macroscopic and microscopic levels. The existing form changes of EE2 and the influence of coexisting humic acid (HA) during transport in porous media were also specifically investigated. The batch experiments demonstrated that the primary mechanisms governing EE2 sorption onto illite colloids involved surface sorption and hydrogen bonding. The coexistence of HA could load onto the surface of illite colloids, thereby enhancing the colloidal sorption capacity for EE2. Transport experiments demonstrated that the migratory ability of EE2 in silty clay was limited, but illite colloids could significantly promote its penetration, with the peak penetration content (Ct/C0) increasing from 0.64 to 0.77. In the absence of HA, EE2 primarily transported in a dissolved form, accounting for 62.86% of the total concentrations. When HA concentrations were increased to 10 mg/L and 20 mg/L, the proportion of colloidal conjugate EE2 in the effluents reached 52.13% and 54.49%, respectively. The enhanced transport of EE2 by HA was primarily attributed to the improved migration ability of illite colloids and the increased proportion of illite-EE2 conjugate, resulting in a maximum Ct/C0 value of 0.94. The validity of these results was further confirmed by employing calculations based on the Derjaguin–Landau–Verwey–Overbeek and Colloidal Filtration Theory. This study provides new insights of understanding the transport of EE2 in subsurface environment.

Perspectives of coagulation/flocculation for the removal of pharmaceuticals from domestic wastewater: A critical view at experimental procedures

Literature frequently reports that colloids in aqueous matrices sorb a large fraction of pharmaceuticals. Since coagulation/flocculation removes colloids, it is expected that coagulation/flocculation in principle should be useful in concentrating pharmaceuticals in wastewater treatment, which would facilitate the treatment of these refractory compounds. In our present work, we researched the potential of coagulation/flocculation for removing pharmaceuticals from raw sewage. Results from jar tests showed that pharmaceuticals are hardly removed from sewage with coagulation/flocculation. To investigate the discrepancy between reported colloidal sorption and the lack of removal when removing colloids, we tested a commonly applied experimental setup, which makes use of ultra-filtration (UF), for determining the colloidal sorption of pharmaceuticals. The UF method under research was compared with an assessment making use of flocculation. Both methods, UF and flocculation, showed similar removal of colloids. However, during UF, the retention of pharmaceuticals reached values up to 93 ± 4 %. In contrast, when removing the colloids with flocculation, no pharmaceutical removal was observed. These results confirm that it is very likely to introduce an analysis bias in using UF membranes in the determination of colloidal sorption of pharmaceuticals. In fact, results predict an over-estimation caused by a direct retention of pharmaceuticals without any binding to colloidal matter. Overall results of the current work show that pharmaceuticals hardly sorb to colloids and herewith the absence of removal of pharmaceuticals during coagulation/flocculation is explained.

Geochemistry of Suspended Particulate Matter in the Marginal Filter of the Pregolya River (Baltic Sea)

The article discusses the results of studying the marginal filter of the Pregolya River in different seasons. Three transformation stages of dispersed sedimentary material are distinguished: gravitational, colloidal–sorption, and biogenic. Study of the chemical composition of suspended particulate matter at all marginal filter stages showed variation in the composition of suspension-forming elements, as well as strong enrichment of suspended particulate matter in a number of trace elements, which can be explained by pollution. Matrix correlation analysis of chemical element concentrations revealed strong links between elements.

Investigation into bentonite colloid sorption behavior of cesium using batch tests

In this study, we characterized the physical properties of bentonite colloids, conducted stability tests, and examined the effects of the colloids on the sorption of radionuclides in groundwater (Cs-137). The resulting data provides a valuable reference for safety assessments of final disposal sites for spent nuclear fuel and high-level radwaste. Our results demonstrate that Cs-137 is easily adsorbed by bentonite colloids. Adsorption capacity of colloidal solutions was shown to be greater than that of colloidal gel type, and the adsorption rate decreases with an increase in ionic strength in a groundwater environment.

Karakter dan Potensi Inokulum Bakteri Fosfat dalam Melepaskan Fosfor

Soil bacteria group which can release soil P-adsorbed is phosphate bacteria (PB). PB can release soil P-adsorbed through: 1) acidification, 2) chelating 3) ligand exchange 4) mineralization and 5) compete colloid sorption site. PB have a potential to release soil P-adsorbed. This study was aimed to determining the character and PB inoculant potential in soil P-adsorbed release. The results of BLASTn PB showed that isolate 1 was Pseudomonas trivialis , isolate 5 was Pseudomonas putida and isolate 9 was Pseudomonas fluorescens . Based on the growth curve on day 5 th (the end log. phase) population of Pseudomonas trivialis was 10 10 CFU/mL, Pseudomonas putida was 10 14 CFU/mL and Pseudomonas fluorescens was 10 17 CFU/mL. Storage inoculant PB population decrease 97-84 % and 80-65 % PB lowering capabilities.

Site-Specific Retention of Colloids at Rough Rock Surfaces

The spatial deposition of polystyrene latex colloids (d = 1 μm) at rough mineral and rock surfaces was investigated quantitatively as a function of Eu(III) concentration. Granodiorite samples from Grimsel test site (GTS), Switzerland, were used as collector surfaces for sorption experiments. At a scan area of 300 × 300 μm(2), the surface roughness (rms roughness, Rq) range was 100-2000 nm, including roughness contribution from asperities of several tens of nanometers in height to the sample topography. Although, an increase in both roughness and [Eu(III)] resulted in enhanced colloid deposition on granodiorite surfaces, surface roughness governs colloid deposition mainly at low Eu(III) concentrations (≤5 × 10(-7) M). Highest deposition efficiency on granodiorite has been found at walls of intergranular pores at surface sections with roughness Rq = 500-2000 nm. An about 2 orders of magnitude lower colloid deposition has been observed at granodiorite sections with low surface roughness (Rq < 500 nm), such as large and smooth feldspar or quartz crystal surface sections as well as intragranular pores. The site-specific deposition of colloids at intergranular pores is induced by small scale protrusions (mean height = 0.5 ± 0.3 μm). These protrusions diminish locally the overall DLVO interaction energy at the interface. The protrusions prevent further rolling over the surface by increasing the hydrodynamic drag required for detachment. Moreover, colloid sorption is favored at surface sections with high density of small protrusions (density (D) = 2.6 ± 0.55 μm(-1), asperity diameter (φ) = 0.6 ± 0.2 μm, height (h) = 0.4 ± 0.1 μm) in contrast to surface sections with larger asperities and lower asperity density (D = 1.2 ± 0.6 μm(-1), φ = 1.4 ± 0.4 μm, h = 0.6 ± 0.2 μm). The study elucidates the importance to include surface roughness parameters into predictive colloid-borne contaminant migration calculations.

Sorption of Pu(IV) in the polymeric colloidal form on rock typical of Mayak Production Association area

Sorption of colloids of polymeric Pu from simulated groundwater on a rock typical of Mayak Production Association area was studied. In 20 days, polymeric Pu with the particle size exceeding 220 nm is 99% sorbed by the rock with the distribution coefficient K d = 1880. Desorption performed for 5 days allows no more than 40% of the sorbed Pu to be transferred into the solution, even with such strong complexing agents as 0.05 M hydroxyethylidenediphosphonic acid in 0.1 M HNO3 and 0.1 M Tamm solution.

Water‐column concentrations and partitioning of polybrominated diphenyl ethers in the New York/New Jersey Harbor, USA

AbstractDespite the emerging concern regarding polybrominated diphenyl ethers (BDEs), very few measurements of BDE concentrations in ambient water have been published. In the present study, BDEs were measured in water samples from the New York/New Jersey Harbor (USA). Samples were taken in Raritan Bay west of Sandy Hook during four intensive sampling campaigns in 2000 and 2001. Congeners 17, 47, 99, 100, 153, 154, 183, and 209 were detected. Total BDE (σBDE) concentrations (average ± standard deviation) were 175 ± 75 ng/g in the particle phase and 110 ± 72 pg/L in the apparent dissolved phase. The deca‐congener, BDE 209, constituted 85 and 9% of σBDEs in the particle and apparent dissolved phases, respectively. The σBDE levels are significantly higher than those measured in Lake Ontario, USA, and in The Netherlands, but they are similar to concentrations measured in Lake Michigan and San Francisco Bay (both USA). Calculated values of the organic carbon‐water partition coefficient (KOC) were strongly correlated with literature values of the octanol‐water partition coefficient (KOW). The data suggest that sorption of BDEs to colloids is important in this system, although quantifying the extent of colloid sorption is difficult.

WATER COLUMN CONCENTRATIONS AND PARTITIONING OF POLYBROMINATED DIPHENYL ETHERS IN THE NEW YORK/NEW JERSEY HARBOR, USA

Despite the emerging concern regarding polybrominated diphenyl ethers (BDEs), very few measurements of BDE concentrations in ambient water have been published. In the present study, BDEs were measured in water samples from the New York/New Jersey Harbor (USA). Samples were taken in Raritan Bay west of Sandy Hook during four intensive sampling campaigns in 2000 and 2001. Congeners 17, 47, 99, 100, 153, 154, 183, and 209 were detected. Total BDE (SigmaBDE) concentrations (average +/- standard deviation) were 175 +/- 75 ng/g in the particle phase and 110 +/- 72 pg/L in the apparent dissolved phase. The deca-congener, BDE 209, constituted 85 and 9% of SigmaBDEs in the particle and apparent dissolved phases, respectively. The SigmaBDE levels are significantly higher than those measured in Lake Ontario, USA, and in The Netherlands, but they are similar to concentrations measured in Lake Michigan and San Francisco Bay (both USA). Calculated values of the organic carbon-water partition coefficient (K(OC)) were strongly correlated with literature values of the octanol-water partition coefficient (K(OW)). The data suggest that sorption of BDEs to colloids is important in this system, although quantifying the extent of colloid sorption is difficult.

Pore-Scale Visualization of Colloid Transport and Retention in Partly Saturated Porous Media

In unsaturated porous media, sorption of colloids at the air–water (AW) interface is accepted as a mechanism for controlling colloid retention and mobilization. However, limited actual pore-scale observations of colloid attachment to the AW interface have been made. To further investigate these processes, a real-time pore-scale visualization method was developed. The method builds on the light transmission technique for fingered flow studies in packed-sand infiltration chambers and combines it with high-resolution, electro-optical hardware and public domain imaging software. Infiltration and drainage of suspensions of hydrophilic negatively charged carboxylated latex microspheres provides compelling visual evidence that colloid retention in sandy porous media occurs via trapping in the thin film of water where the AW interface and the solid interface meet, the air–water–solid (AWS) interface. With this modified theory of trapped colloids at the AWS interface, we are able to explain the apparent discrepancy between previous experimental evidence of hydrophilic colloids seemingly partitioning to the AW interface and more recent findings that suggest this type of colloid does not adsorb at the AW interface.

Pore‐Scale Visualization of Colloid Transport and Retention in Partly Saturated Porous Media

In unsaturated porous media, sorption of colloids at the air–water (AW) interface is accepted as a mechanism for controlling colloid retention and mobilization. However, limited actual pore‐scale observations of colloid attachment to the AW interface have been made. To further investigate these processes, a real‐time pore‐scale visualization method was developed. The method builds on the light transmission technique for fingered flow studies in packed‐sand infiltration chambers and combines it with high‐resolution, electro‐optical hardware and public domain imaging software. Infiltration and drainage of suspensions of hydrophilic negatively charged carboxylated latex microspheres provides compelling visual evidence that colloid retention in sandy porous media occurs via trapping in the thin film of water where the AW interface and the solid interface meet, the air–water–solid (AWS) interface. With this modified theory of trapped colloids at the AWS interface, we are able to explain the apparent discrepancy between previous experimental evidence of hydrophilic colloids seemingly partitioning to the AW interface and more recent findings that suggest this type of colloid does not adsorb at the AW interface.

Evidence for the interaction of technetium colloids with humic substances by X-ray absorption spectroscopy.

Spectroscopic extended X-ray absorption fine structure (EXAFS) evidence was obtained on the chemical environment of 99Tc(IV) atoms formed upon introduction of TcO4- into four types of laboratory-scale synthetic and natural systems which mimic in situ natural reducing conditions in humic-rich geochemical environments: (a) magnetite/pyrite in synthetic groundwater in the absence of humic substances (HSs), (b) magnetite/pyrite in natural Gorleben groundwater in the presence of HSs, (c) Boom clay sediment mixed with synthetic groundwater, and (d) Gorleben sand mixed with natural Gorleben groundwater. The investigated systems obey to pH 8-9 conditions, and all measured samples show similar EXAFS spectra for Tc, which could be fitted by a hydrated TcO2 x xH2O phase. The results are interpreted as follows: upon introduction of high concentrations (millimolar to micromolar) of TcO4-to chemically reducing environments, small Tc(IV) oxidic polymers are formed, which either may aggregate into larger units (colloids) and finally precipitate or may interact in their polymeric form with (dissolved and immobile) humic substances. This latter type of interaction--Tc(IV) colloid sorption onto HSs--differs significantly from the generally accepted metal--humate complexation and therefore offers new views on the possible reaction pathways of metals and radionuclides in humic-rich environments.

Partitioning of Clay Colloids at Air–Water Interfaces

Colloid sorption onto air–water interfaces in a variety of natural environments has been previously recognized, but better quantification and understanding is still needed. Affinities of clay colloids for the air–water interface were measured using a bubble-column method and reported as partition coefficients (K). Four types of dilute clay suspensions were measured in NaCl solutions under varying pH and ionic strength conditions: kaolinite KGa-1, illite IMt-2, montmorillonite SWy-2, and bentonite. The K values of three types of polystyrene latex particles with different surface-charge properties were also measured for comparison. Kaolinite exhibited extremely high affinity to the air–water interface at pH values below 7. Illite has lower affinity to air–water interfaces than kaolinite, but has similar pH dependence. Na-montmorillonite and bentonite clay were found excluded from the air–water interface at any given pH and ionic strength. Positively and negatively charged latex particles exhibited sorption and exclusion, respectively, at the air–water interface. These results show the importance of electrostatic interactions between the air–water interface and colloids, especially the influence of pH-dependent edge charges, and influence of particle shape.

Colloidal Particles at Solid–Liquid Interfaces: Mechanisms of Desorption Kinetics

We study the sorption of colloids on equally charged surfaces. Our focus is on the time scale from hours to weeks, where adsorption is not an irreversible process but interplays with (spontaneous) desorption. Using model calculations, we show how the desorption kinetics is influenced by readsorption, a potential barrier, a secondary potential minimum, local variation of the potential, and bond aging. In the experimental part we present results ofin situobservation of the sorption kinetics of polystyrene latex particles onto a glass surface. Combining the evanescent field method with video microscopy, we were able to identify the particle arrival and departure times individually and therefrom determine the adhesion time distribution function. The nonexponentiality of this function can be explained by a gamma distribution of the potential depth at the binding sites as well as by logarithmic bond aging.

Atrazine Adsorption by Soil Colloids and Co‐Transport through Subsurface Environments

AbstractThis study evaluated the potential of water‐dispersible soil colloids with diverse physicochemical and mineralogical characteristics to adsorb and mediate the transport of atrazine through macropores of intact soil columns. The soil columns were taken from the upper solum of an Alfisol (Maury) and a Mollisol (Loradale) in the Bluegrass region of Kentucky. Six different colloid suspensions mixed with atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] were introduced at a constant flux into the undisturbed soil columns. The eluents were collected and analyzed periodically for colloid and herbicide concentrations. Colloid recovery in the eluents ranged from 45 to 90%. The presence of colloids enhanced the transport of atrazine by 2 to 18%, depending on colloid type and mobility. Colloids with higher pH, total exchangeable bases (TEB), cation‐exchange capacity (CEC), organic carbon (OC), surface area (SA), and electrophoretic mobility (EM), showed greater mobility, greater affinity for atrazine, and greater potential to co‐transport atrazine. In contrast, increased levels of kaolinite, Fe, and Al inhibited atrazine adsorption and transport. Soil columns with higher hydraulic conductivity, well‐developed macropore system, and lower surface reactivity (Maury) also transported more atrazine. In spite of the increased transportability of atrazine by the presence of soil colloids, the colloid‐bound herbicide fraction contributed ≤1% to the observed increase. This suggests that matrix‐surface‐site exclusion and blocking mechanisms induced by the presence of colloids are more important than colloid sorption in promoting atrazine mobility in subsurface soil environments.

Modeling Colloid Transport in Unsaturated Porous Media and Validation with Laboratory Column Data

Colloidal particles can act as carriers to enhance the transport of contaminants in porous media by reducing retardation effects. When colloids are present, especially in the vadose zone, the system can be treated as consisting of four phases: an aqueous phase, the stationary soild matrix phase, a carrier (colloidal particles) phase, and a stagnant air phase. In the work reported a mathematical model based on mass balance equations was developed to describe the transport and fate of colloids in an unsaturated porous medium. Colloidal particles can sorb onto the air‐water interface as well as to the solid matrix surfaces. Colloid/matrix mass transfer rate is represented by first‐order kinetics, while the colloid/air‐water interface mass transfer mechanism is formulated by second‐order kinetics. The model was applied to simulate the migration of colloids through an unsaturated finite column. Numerical solutions were obtained to provide estimates of colloidal concentrations. A sensitivity analysis of the transport model was utilized to assess the effect of several parameters on model behavior. The aqueous phase colloid concentration is quite sensitive to changes in the rate coefficient of colloidal deposition on the solid matrix. However, the colloidal capture on the air‐water interface is affected by the fraction of air‐water interface available for particle deposition as well as by the rate coefficient of colloidal capture on the air‐water interface, k3. As k3 increases, the available sorption site reduces quickly. Furthermore, increasing colloidal sorption capacity significantly retards the colloidal migration. The model results match successfully with experimental data of Wan and Wilson [1994a] and Wan et al. [1994]. A comparison between the breakthrough curves of hydrophobic and hydrophilic colloids suggests that the hydrophobic colloids have less affinity for both solid matrix and the air‐water interface. Experimental data and model results show that the presence of the air‐water interface retards the colloid transport very significantly. Finally, the proposed model is extended to simulate the colloid transport under transient water flow conditions. Simulations show that aqueous phase colloid concentration varies along the column following a trend similar to the saturation profile for both hydrophobic and hydrophilic colloids. However, the migration profile of hydrophilic colloid suspension is faster than the hydrophobic one.

Transport of hydrophobic organics by colloids through porous media 1. Experimental results

The transport of two hydrophobic organic compounds (HOCs), namely, phenanthrene and pyrene, through model porous media (glass microsphere and quartz sand) in the presence of a homogenous colloid (polystyrene latex) was studied. The sorption and desorption of colloids were dependent on the pH and ionic strenght of the porewater. The sorption of colloids was only partially reversible even after modifying the aqueous solution chemistry, viz. the ionic strength and pH. The organic sorption on the porous media was directly related to the behavior of colloids. In the absence of an electrolyte, the HOCs showed an early brakthrough in the presence of the colloids compared to that without colloids. At higher ionic strength, the colloids were deposited on the porous medium. Owing to their high sorbed mass on the colloids, the HOCs remained on the porous material, thus decreasing their mobility in the column. Mobile colloids in porewater have been shown to impact the transport of HOCs through porous media.

Colloid transport in unsaturated porous media

This paper explores the significance of the gas‐water interface on colloid sorption and transport. Three types of common saturation conditions were simulated in packed sand columns: (1) a completely water‐saturated condition, (2) gas bubbles trapped by capillary forces as a nonwetting residual phase (15% gas), and (3) gas present as a continuous phase (46% gas), or in other words, a vadose zone situation. Different saturations provided different interfacial conditions. Two types of polystyrene latex particles (0.2 μm), hydrophilic and hydrophobic, were used in each of the three saturations. Relative surface hydrophobicity of latex particles was characterized by contact angle measurements. Each experiment was repeated five times. A total of 30 columns with good reproducible packing and gas content gave reproducible particle breakthrough curves. The retention of both hydrophilic and hydrophobic colloids increased with gas content of the porous medium. Colloids preferentially sorbed onto the gas‐water interface relative to the matrix surface. The degree of sorption increased with the increase of colloid surface hydrophobicity. The results validate and quantify direct microscopic scale visualization observations made in two‐dimensional pore network glass micromodels (Wan and Wilson, 1994). These findings suggest an additional mechanism for filtration and for particulate transport in the subsurface environment, whenever more than one fluid phase is present. The results also give clear evidence that the presence of inadvertently trapped residual gas could help explain the discrepancy between water‐saturated laboratory column experiments and related theory.

Mechanisms of colloid sorption on mineral surfaces: a RBS study

A novel experimental approach is presented to assess the mechanisms of colloid sorption. In this technique, centimetre-sized sections of individual minerals (silica, muscovite) were contacted with aqueous solutions containing colloidal particles. After mineral/solution separation, the solid surface was analysed by Rutherford backscattering spectrometry (RBS). Information on the amount and depth distribution of retained colloids was obtained. This versatile technique provides insight into the mechanisms of retention and the identification of controlling properties (charge and size of colloids, surface state of minerals).