Colloidal Water Research Articles

Zirconia colloid analysis by single particle inductively coupled plasma–mass spectrometry

Single particle analysis of zirconia colloids in water has been performed by inductively coupled plasma–mass spectrometry (ICP–MS). The transient signal induced by the flash of ions due to the ionisation of a zirconia colloidal particle in the plasma torch can be detected and measured for selected zirconium ion masses by the mass spectrometer. The intensity of the MS signal is recorded in time scan. The peaks recorded are analysed as a function of the particle size, and the fraction of the studied element or isotope in the colloid phase. The frequency of the flashes is directly proportional to the concentration of particles in the colloidal suspension. After developing the theoretical aspect on detection, composition and intensity of ion flashes generated by colloid ionisation in the plasma torch, tests were performed on model zirconia colloids and on silica colloids coated with zirconia. This feasibility study also describes the experimental conditions and the choice of isotopes to detect zirconia colloids in a single particle analysis mode.

Assessment of the use of industrial by-products to remediate a copper- and arsenic-contaminated soil.

Two water treatment sludges (WTS-A, WTS-B), two red muds (RM), and red gypsum (RG), all rich in iron oxy-hydroxides, were added to a soil highly polluted with As and Cu at 2% (w/w) to reduce metal bioavailability. Because the amendments increased soil pH to approximately 6, a lime treatment to the same pH and an unamended treatment were included for comparison. All the amendments had significant positive effects on the soil microbial biomass and growth of ryegrass (Lolium multiflorum Lam. cv. Avance), but only WTS-A improved lettuce (Lactuca sativa L. cv. Tom Thumb) growth. The mineralization of added ammonium nitrogen was not significantly affected by the treatments, while a physiologically based extraction test (PBET) showed that bioaccessibility of As was low (< 5%) and decreased only in the WTS-A treatment. Concentrations of As in soil pore water and extractable As only decreased in the WTS and RG treatments. In contrast, Cu concentrations in soil pore water and extractable Cu decreased in all treatments, by more than 84% in the WTS, RM, and RG treatments. Non-isotopically exchangeable As and Cu were present in colloids in the soil pore water. Untreated soil had < 4% isotopically exchangeable As and this decreased by approximately 50%, with WTS, RM, and RG. The labile Cu pool represented a large proportion (34%) of the total Cu pool, and the isotopically exchangeable and soluble Cu were strongly correlated with soil pH. Acidification of the treated soils showed that the labile As and Cu both increased in the treated soils compared with untreated soils. The significance of the treatment effects on soil fertility and potential off-site transport of As and Cu to ground water are discussed.

Phenol nitration upon oxidation of nitrite by Mn(III,IV) (hydr)oxides

An interesting aspect of the chemistry of nitrite is the possibility for this compound to interact with other environmental factors and many oxidising species, which results in the oxidation of nitrite to nitrogen dioxide. This is a potentially interesting process that can lead to the formation of nitroaromatic compounds in the environment. In previous papers we have shown that nitrite can interact with dissolved Fe(III) and nitrate under irradiation, Fenton and heterogeneous photo-Fenton reagents, and semiconductor oxides such as TiO 2, α-Fe 2O 3, and β-FeOOH under irradiation. This paper reports on the interaction between nitrite/nitrous acid and the Mn(III,IV) (hydr)oxides β-MnO 2 and γ-MnOOH, both in neutral solution under irradiation and in acidic conditions in the dark. β-MnO 2 and γ-MnOOH originate from the oxidation of Mn(II) and play a key role in the redox cycling of manganese in the environment. These Mn(III,IV) (hydr)oxides show some photocatalytic activity, and they can act as thermal oxidants at acidic pH. The photoinduced oxidation of nitrite and the thermal oxidation of nitrous acid by Mn(III,IV) (hydr)oxides yield nitrogen dioxide and lead to the formation of nitrophenols in the presence of phenol. These processes can take place at the water–sediment or water–colloid interface in natural waters and on the surface of atmospheric particulate. Furthermore, the phenol/γ-MnOOH/HNO 2 system in dark acidic solution is an interesting model due to the formation of phenoxyl radical upon phenol monoelectronic oxidation by γ-MnOOH. The kinetics of nitrophenol generation under such conditions indicates that phenol nitration is unlikely to take place upon reaction between phenoxyl and NO 2 and suggests a solution to a literature debate on the subject.

Phase diagram of aggregation of oppositely charged colloids in salty water.

Aggregation of two oppositely charged colloids in salty water is studied. We focus on the role of Coulomb interaction in strongly asymmetric systems in which the charge and size of one colloid is much larger than the other one. In the solution, each large colloid (macroion) attracts a certain number of oppositely charged small colloids (Z-ion) to form a complex. If the concentration ratio of the two colloids is such that complexes are not strongly charged, they condense in a macroscopic aggregate. As a result, the phase diagram in a plane of concentrations of two colloids consists of an aggregation domain sandwiched between two domains of stable solutions of complexes. The aggregation domain has a central part of total aggregation and two wings corresponding to partial aggregation. A quantitative theory of the phase diagram in the presence of monovalent salt is developed. It is shown that as the Debye-Hückel screening radius r(s) decreases, the aggregation domain grows, but the relative size of the partial aggregation domains becomes much smaller. As an important application of the theory, we consider solutions of long double-helix DNA with strongly charged positive spheres (artificial chromatin). We also consider implications of our theory for in vitro experiments with the natural chromatin. Finally, the effect of different shapes of macroions on the phase diagram is discussed.

Structural Properties of Nonionic Cyclodextrin Colloids in Water

The amphiphilic character in water of a novel class of chemically modified cyclodextrins has been investigated by means of small-angle X-ray scattering and light scattering. The introduction ofhydrophilic oligo(ethylene glycol) onto the secondary side of heptakis[6-alkylthio-6-deoxy-2-oligo(ethylene glycol)]-beta-cyclodextrins produces an enhanced water solubility of these molecules. Shape and dimensions of the generated micellar aggregates, analyzed in terms of a suitable core-shell model, remain stable in the wide concentration range explored. The highly associative behavior of these macromolecules is evidenced by the very low value of the critical micelle concentration (cmc), which is about 2 orders of magnitude smaller than the cmc usually obtained for traditional surfactant. Despite the complex geometry of this novel macromolecule, shape and dimensions of generated micellar aggregates can be properly described according to the thermodynamic approaches generally used for amphiphilic molecules and block copolymers. Results show how the modulation of hydrophobic and hydrophilic components sensitively influence the structural features of the generated aggregates thus offering the possibility to control molecular organization in a manner similar to that for traditional colloids. For all the classes of the investigated systems, the small micelles have been found in equilibrium with polydisperse large aggregates of entangled micelles. These novel nonionic colloidal systems combine inclusion and transport properties of host macrocycles, such as cyclodextrin, together with the increased stability of colloidal aggregates, and may be of interest for their potential application as innovative drug delivery systems.

Iron (III)-silica interactions in aqueous solution: insights from X-ray absorption fine structure spectroscopy

The influence of aqueous silica on the hydrolysis of iron(III) nitrate and chloride salts in dilute aqueous solutions ( m Fe ∼ 0.01 mol/kg) was studied at ambient temperature using X-ray absorption fine structure (XAFS) spectroscopy at the Fe K-edge. Results show that in Si-free iron nitrate and chloride solutions at acid pH (pH < 2.5), Fe is hexa-coordinated with 6 oxygens of H 2O- and/or OH-groups in the first coordination sphere of the metal, at an Fe-O distance of 2.00 ± 0.01 Å. With increasing pH (2.7 < pH < 13), these groups are rapidly replaced by bridging hydroxyls (-OH-) or oxygens (-O-), and polymerized Fe hydroxide complexes form via Fe-(O/OH)-Fe bonds. In these polymers, the first atomic shell of iron represents a distorted octahedron with six O/OH groups and Fe-O distances ranging from 1.92 to 2.07 Å. The Fe octahedra are linked together by their edges (Fe-Fe distance 2.92–3.12 Å) and corners (Fe-Fe distance ∼3.47 ± 0.03 Å). The Fe-Fe coordination numbers ( N edge = 1–2; N corner = 0.5–0.7) are consistent with the dominant presence of iron dimers, trimers and tetramers at pH 2.5 to 2.9, and of higher-polymerized species at pH > 3. At pH > 2.5 in the presence of aqueous silica, important changes in Fe(III) hydrolysis are detected. In 0.05- m Si solutions (pH ∼ 2.7–3.0), the corner linkages between Fe octahedra in the polymeric complexes disappear, and the Fe-Fe distances corresponding to the edge linkages slightly increase (Fe-Fe edge ∼ 3.12–3.14 Å). The presence of 1 to 2 silicons at 3.18 ± 0.03 Å is detected in the second atomic shell around iron. At basic pH (∼12.7), similar structural changes are observed for the iron second shell. The Fe-Si and Fe-Fe distances and coordination numbers derived in this study are consistent with (1) Fe-Si complex stoichiometries Fe 2Si 1-2 and Fe 3Si 2-3 at pH < 3; (2) structures composed of Fe-Fe dimers and trimers sharing one or two edges of FeO 6-octahedra; and (3) silicon tetrahedra linked to two neighboring Fe octahedra via corners. At higher Si concentration (0.16 m, polymerized silica solution) and pH ∼ 3, the signal of the Fe second shell vanishes indicating the destruction of the Fe-Fe bonds and the formation of different Fe-Si linkages. Moreover, ∼20 mol.% of Fe is found to be tetrahedrally coordinated with oxygens in the first coordination shell ( R Fe-O = 1.84 Å). This new finding implies that Fe may partially substitute for Si in the tetrahedral network of the silica polymers in Si-rich solutions. The results of this study demonstrate that aqueous silica can significantly inhibit iron polymerization and solid-phase formation, and thus increase the stability and mobility of Fe(III) in natural waters. The silica “poisoning” of the free corner sites of iron-hydroxide colloids should reduce the adsorption and incorporation of trace elements by these colloids in Si-rich natural waters.

Forces between colloid particles in natural waters.

The origin and nature of interparticle forces acting on colloid surfaces in natural waters has been examined using an atomic force microscope. Natural colloids were represented by a surface film of iron oxide precipitated onto spherical SiO2 particles, and the effects of adsorbed natural organic matter (NOM), solution pH, and ionic composition on the force-separation curves were investigated. NOM from both riverine and marine environments was strongly adsorbed to the iron oxide surface. Under conditions of low ionic strength, the interparticle forces were dominated by electrostatic repulsion arising from negative functional groups on the NOM, except at very small separations (<10 nm) where repulsive forces arising from steric interference of the NOM molecules were also present. At high ionic strength (e.g., seawater) or low pH, the electrostatic forces were largely absent, allowing steric repulsion forces to dominate. In addition, adhesive bridging between surfaces by adsorbed NOM was observed, creating a strong energy barrier to spontaneous disaggregation of colloid aggregates. Our results demonstrate that adsorbed NOM dominates the surface forces and thus stability with respect to aggregation of natural water colloids.

Colloid analysis by single particle inductively coupled plasma-mass spectroscopy: a feasibility study

The feasibility of single particle analysis of colloids in water has been studied by inductively coupled plasma-mass spectroscopy (ICP-MS). The transient signal induced by the flash of ions due to the ionisation of a colloidal particle in the plasma torch can be detected and measured for a selected ion mass by the mass spectrometer. The intensity of the MS signal is recorded in time scan, and the peaks recorded are analysed as a function of the particle size and the fraction of the studied element in the colloid phase. The frequency of the flashes is directly proportional to the concentration of particles in the colloidal suspension. After developing the theory on detection, composition and intensity of ion flashes generated by colloid ionisation in the plasma torch, tests were performed on model colloids (rutile, alumina, goethite) and on a natural clay (montmorillonite). This feasibility study also describes the experimental conditions and the choice of isotopes to detect natural colloids in a single particle analysis mode.

Laser induced morphology change of silver colloids: formation of nano-size wires

We have performed laser irradiation at 355 nm onto spherical silver colloids in pure water, which were prepared by laser ablation of silver plate in pure water. In addition to size-reduced particles due to fragmentation, we have found that nano-size wire structures were formed in solution for the first time. The width of the wires was in the 10–100 nm range, and the length of long wires was more than 1 μm. Electron diffraction patterns revealed that these wires were composed of pure silver. It was suggested that the wires were formed via fusion of particles photo-thermally melted by laser irradiation.

Tomographic studies of nontronite particles in aqueous media

X-ray microscopy allows the direct visualization of soil colloids in water. In combination with tomographic techniques it is possible to visualize the three dimensional distribution of the linear absorption coefficient of soil colloids and to investigate the surface amount and spatial arrangement of the particles. First experiments of Nontronite particles from the XM-1 are presented.

Scavenging and immobilization of trace contaminants by colloids in the waters of abandoned ore mines

The occurrence of mine water colloids mainly results from the formation of oxyhydroxides and hydroxysulfates of Fe(III) and Al. In acid rock drainage solutions As and Pb are strongly associated with the colloids. In the near-neutral bulk waters of mines, as for instance in adit waters, trace elements such as As, Pb, Cu and the rare earth elements are sorbed. These trace contaminants can be scavenged by the colloids in the near-neutral mine waters and can be immobilized due to colloid coagulation and aggregate precipitation (‘natural attenuation’). In the pH range of 4–6, a pH range that must be passed through during the flooding of a mine, also U(VI) is adsorbed to the colloids and can be temporarily immobilized by precipitating colloids. The latter can result in a delay of the uranium release of a uranium mine and thus in a flattening and broadening of the uranium concentration profiles during the mine's ‘first flush’.

Use of single particle counters for the determination of the number and size distribution of colloids in natural surface waters

Abstract Particle size distribution (PSD) is a fundamental physical property, which should be measured to understand the role of the colloids in the biogeochemical cycle of aquatic contaminants. The single particle counter (SPC) is an instrument designed to precisely determine sub-micron PSD. The advantages of this system are: to give an absolute colloid number concentration, to measure without bias highly polydispersed samples, to avoid artefacts resulting from sample pre-concentration, to be transportable, allowing on-site measurements. This study presents the results of the methodological work done on our SPC, a 2-counter (one monitor and spectrometer) based system including a precision pump for sample injection and dilution. This system is able to count and size colloids from 50 nm to 2 μm into 19 size classes. Calibration work was performed with standard latex beads and natural samples from various surface waters. The quantification limit on the colloid number concentration for the smallest (50–100 nm), the medium (400–500 nm) and the largest (>2 μm) size classes are 1.0×104, 1.1×102 and 18 ml−1, respectively. Instrument saturation occurs at 8×108 ml−1 for the 50–100 size class, and at 2×103 ml−1 for medium and highest size classes. The relative repeatability varies between 7 and 29% for the different size classes in a synthetic, polydispersed sample reproducing typical environmental colloid concentration. These values are not significantly different from the with-in replicates variability. The verification of the factory calibration shows that measured concentrations are between 27 and 106% of the nominal concentration of standards. In conclusion, the presented SPC system gives reliable results of colloid number concentration and size distribution in a wide range of natural surface waters and offers new opportunities for on-site studies.

Interplay between slow interfacial water diffusion and colloid dynamics: A way to probe colloidal transitions.

ABSTRACTParticle fluctuations in colloidal suspensions are generally considered to be much slower than the embedded fluid dynamics. It was recently proposed that the fluid self-diffusion nearby an interface follows Lévy statistics, extending the time domain of the fluid dynamics towards the low frequency range. It is then possible to probe colloidal particle motion and especially its evolution during a phase transition looking at the slow dynamics of the fluid molecule close to an particle surface. Using field cycling NMR relaxometry, we show how the slow and confined water dynamics at proximity of a colloidal surface provide an original way to follow the glass transition of a colloidal system made of plate-like Laponite particles, a synthetic clay. The interplay between fluid Levy dynamics and particle jamming is discussed. An analytical model involving correlated elementary water time steps on the colloidal interface is proposed and critically compared to our experimental data. The method permits probing of colloidal motions and especially their evolution during a phase transition in a new way. This method can be extended to other systems including mineral lyotropic liquid crystals and biological molecular structures.

Colloid mobilization and transport within unsaturated porous media under transient‐flow conditions

Contaminant‐scavenging colloids are mobilized in the vadose zone during infiltration events, characterized by transient flow regimes. In the research reported here we develop a mathematical model in order to investigate the influences of flow transients on colloid mobilization in unsaturated media. The model solves coupled equations for unsteady pore water flow, colloid release, advective‐dispersive colloid transport, and redeposition of pore water colloids. The immobile‐phase colloid population is discretized into a series of compartments, each of which are assigned a value of critical moisture content (Θcr) according to a piecewise linear density function. A compartment is activated when the model‐calculated moisture content exceeds the Θcr for the compartment, whereupon colloids are released at a rate proportional to the product of the pore water velocity and the colloid concentration within the compartment. We fit solutions of the model equations to data on the mobilization and transport of silica colloids within columns of unsaturated quartz sand. The model accurately reproduces measured pulse‐type colloid releases induced by successive step‐change increases in flow rate and moisture content. This work illuminates the important role of flow transients in colloid mobilization and, through the derivation of a model that couples pore water flow characteristics with colloid mass transfer kinetics, provides a means for quantifying the phenomenon.

Laser induced breakdown detection for the assessment of colloid mediated radionuclide migration

Colloids play an important role in the transport of pollutants in the environment. Harmful substances can undergo transport over large distances if bound to colloids in aqueous surrounding. One important example is the migration of Pu(IV) at unexpectedly high rates over several miles at a Nevada nuclear detonation test site. For long term safety assessments of radioactive waste repositories, it is hence crucial to know about the amount, size distribution and chemical composition of colloids in the ground water. Standard methods (e.g. light scattering) can be applied for high concentrations and large sizes of particles. Colloids smaller than 50 nm, however, are detected with very low efficiency. Laser induced breakdown detection (LIBD) can fill this gap. A new instrumentation is presented, which as compared to previous instruments, opens up a much wider operational dynamic range, now covering three orders of magnitude in size (5–1000 nm) and seven orders of magnitude in particle concentration (1 ppt – several ppm). The technique is based on plasma formation on colloidal particles inside the focus of a pulsed laser. The plasma plume is detected by three-dimensional optical observations and by means of its shock wave with a piezo-detector. For mathematical modelling, detailed knowledge on the photon fluence distribution in the focal region is indispensable. For the first time a true Gaussian TEM00 mode has been achieved in the focus of a LIBD apparatus and great care has been taken to guarantee long-term stability of the optical parameters. Automated control of the laser pulse energy and beam shape is introduced to allow routine reproducible measurement. The apparatus combines acoustic detection with three-dimensional optical monitoring of the focal region with two CCD cameras placed perpendicular to each other in order to gain additional size information. The breakdown events are systematically characterized with respect to the number density and size of aquatic colloids as a function of the laser pulse energy. Whereas the threshold energy (irradiance) only depends on the colloid size, the breakdown probability at higher pulse energies is a direct function of the number density of colloids. A correlation of the two facts allows the speciation of the colloidal size distribution.

Natural Waters and Water Technology, EuroConference on Colloids in Natural Waters

Natural Waters and Water Technology, EuroConference on Colloids in Natural Waters

Evaluation and optimization of two complementary cross-flow ultrafiltration systems toward isolation of coastal surface water colloids.

While colloidal phases in natural waters are important to the speciation and bioavailability of trace metals and organic compounds, accurate isolation of these submicron entities from their lower molecular-weight counterparts has proved challenging. Here, both laboratory and field experiments have been conducted to constrain integrity aspects of two different cross-flow filtration (CFF) systems. We tested both a commonly applied 5000 cm2 CFF system (Pellicon2, Millipore; manufacturer-specified 1 and 3 kDa cutoff) and a less studied mini-CFF system with a 50 cm2 membrane area (Pellicon Lab Scale XL, Millipore; with 5, 10, 100, and 1000 kDa cutoff). A natural water matrix amended with a series of fluorescently tagged colloidal probes was employed to demonstrate that a cross-flow ratio (CFR; retentate-to-permeate flux) > 15 was required for both of these systems to obtain high recoveries of colloids. Contrary to previous calibrations of CFF, also at colloid concentrations characteristic of natural waters, the established retention profiles for the colloid probes on these systems, when operated under CFR > 15, affirmed the manufacturer-specified cutoff values (in parentheses): 2.4 kDa (1 kDa), 3.3 kDa (3 kDa), 6.1 kDa (5 kDa) and 8.7 kD (10 kDa). A concentration factor (cf) > 10 was found necessary for the reliable determination of the colloidal pool of several elements in the surface waters of the open Baltic Sea. Application of CFR > 15 and cf > 10 returned recoveries around 100% for the studied organic carbon, Ca, Mo, Fe, Cu, and Ni on both systems. Furthermore, the trend of colloid association for the transition elements in the offshore Baltic surface waters followed expectations from their Irving-Williams series of coordination chemistry.

Selective collection of inorganic iron(III) colloids in water with oxine-impregnated water-in-oil emulsion

An oxine-impregnated emulsion was prepared by dissolving 100 mg of oxine and 0.3 ml of non-ionic surfactant (Span-80) in 10 ml of toluene and mixing with 3 ml of 1 mol l −1 hydrochloric acid by sonication (20 kHz). The water-in-oil emulsion was injected into 50 ml of water sample (containing iron(III) at the ppb level, pH 4–7) and dispersed by stirring for 10 min as numerous small globules (0.1–0.5 mm in diameter). The iron diffused through the toluene layer into the small droplets of hydrochloric acid. The emulsion was separated by flotation and heated to segregate the aqueous (hydrochloric acid) and organic (toluene) phases. The iron in the aqueous phase was determined by graphite-furnace atomic absorption spectrometry (GFAAS). Hydrated iron(III) oxide having particle sizes of larger than 1 μm did not penetrate into the emulsion. Other iron species which were not incorporated into the emulsion include humic complexes and hybrid particles of hydrated iron(III) oxide and humic substances. This discrimination can be attributed to the surfactant layer at the oil–water interfaces and gentle stirring of the solution. The conventional liquid–liquid extraction, however, did not offer such a selectivity, because all iron(III) species were simultaneously extracted into the organic phase with vigorous shaking. The unique property of the emulsion method has been applied to the separation and determination of inorganic dissolved iron species in river water.

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.

Natural Ground Water Colloids From the USGS J-13 Well in Nye County, NV: a Study Using SAXS and TEM

We report results from ultra small angle x-ray scattering (USAXS) and transmission electron microscopy (TEM) of dilute silicate colloids that occur naturally in groundwater from the USGS J-13 well, located near the Yucca Mountain Site in Nevada. We also examined a separate sample of this groundwater that had been treated by heating to 90 degrees C in contact with crushed Topopah Spring Tuff from the Yucca Mountain. The USAXS measurements were done at the UNICAT undulator beamline at the Advanced Photon Source at the Argonne National Laboratory. Power-law plots (scattering intensity verses momentum transfer) were fitted to the USAXS data. Colloids in the untreated J-13 groundwater were shown to have a fractal dimension of nearly 3, whereas colloids in the treated groundwater (“EJ-13”) have a dimensionality of approximately 2.4 over a length scale of approximately 3 to 300 nm. Similar power-law plots with dimension 3 characterized concurrent SAXS measurements from aqueous suspensions of Na-montmorillonite and NIST Brick Clay (NBS-67). We attribute these results to the sheet silicate layered structure of the clay colloids present in J-13 well water, montmorillonite, and “brick clay” systems. The differences between EJ-13 and as-received J-13 are perhaps owing to exchange of calcium for sodium with the tuff. Radionuclide incorporation into, adsorption onto, or ion exchange with existing groundwater colloids may promote colloidal transport of radionuclides in groundwater. Such radionuclide-bearing colloids could thereby increase the concentrations of actinides in groundwater and enhance migration into human-accessible aquifers. Our results demonstrate the first application of USAXS to study the physical nature of such groundwater colloids, and represent perhaps one of the most dilute systems ever studied by small angle scatering.