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PubMed2003

Preliminary 3-D site-scale studies of radioactive colloid transport in the unsaturated zone at Yucca Mountain, Nevada.

The U.S. Department of Energy (DOE) is actively investigating the technical feasibility of permanent disposal of high-level nuclear waste in a repository to be situated in the unsaturated zone (UZ) at Yucca Mountain (YM), Nevada. In this study we investigate, by means of numerical simulation, the transport of radioactive colloids under ambient conditions from the potential repository horizon to the water table. The site hydrology and the effects of the spatial distribution of hydraulic and transport properties in the Yucca Mountain subsurface are considered. The study of migration and retardation of colloids accounts for the complex processes in the unsaturated zone of Yucca Mountain, and includes advection, diffusion, hydrodynamic dispersion, kinetic colloid filtration, colloid straining, and radioactive decay. The results of the study indicate that the most important factors affecting colloid transport are the subsurface geology and site hydrology, i.e., the presence of faults (they dominate and control transport), fractures (the main migration pathways), and the relative distribution of zeolitic and vitric tuffs. The transport of colloids is strongly influenced by their size (as it affects diffusion into the matrix, straining at hydrogeologic unit interfaces, and transport velocity) and by the parameters of the kinetic-filtration model used for the simulations. Arrival times at the water table decrease with an increasing colloid size because of smaller diffusion, increased straining, and higher transport velocities. The importance of diffusion as a retardation mechanism increases with a decreasing colloid size, but appears to be minimal in large colloids.

Colloids↗
PubMed2001

Migration of radionuclides in porous rock in the presence of colloids: effects of kinetic interactions.

This work investigates the colloid-facilitated migration of radionuclides with radioactive decay in porous media. The sorption processes for radionuclides with both the solid matrix and colloids are treated as equilibrium or nonequilibrium. An analytical solution is obtained from a simplified linear equilibrium interaction mechanism. In addition, the adsorption processes for radionuclides with colloids and porous rock can be assumed as nonequilibrium and modeled by the linear kinetic adsorption. The numerical method is employed to solve the coupled colloid and radionuclide transport equations under nonequilibrium sorption assumption. Moreover, the reaction rates of the adsorption processes for radionuclides with the solid matrix and colloids affect the transport characteristics of radionuclides. The fast reaction rate of radionuclides with colloids causes a higher concentration of radionuclides adsorbed on colloids in a dispersed phase and enlarges acceleration caused by colloids. However, the fast reaction rate for radionuclides with solid matrix increases the retardation effect caused by the solid matrix. This work developed a predictive model for the transport of colloid-facilitated radionuclides in porous medium and to assess the importance of various phenomenological coefficients, particularly parameters for the adsorption interactions.

Adsorption↗
PubMed2004

Stream-subsurface exchange of zinc in the presence of silica and kaolinite colloids.

The mobility of sorbing contaminants in surface waters often depends strongly on associations with sediments, including both fine suspended particles and stationary bed sediments. Hydrodynamic flow coupling causes an exchange of dissolved and suspended substances between streams and underlying pore waters (hyporheic exchange). As a result, the fate of many pollutants is expected to be greatly influenced bythe flux of colloids and contaminants across the stream-subsurface interface and the interactions of both types of substances with the bed sediments. Herein, we present experimental results on the stream-subsurface exchange of zinc in the presence of colloidal silica and kaolinite in a laboratory flume. We also apply a process-based theoretical model to predict the coupled transport of colloids and reactive solutes. Model input parameters were obtained using independent batch and column experiments. Zinc immobilization in the bed was found to be significantly greater in the presence of kaolinite than in the presence of colloidal silica. Model predictions indicated that there were two distinct reasons for the greater zinc immobilization in the presence of kaolinite: zinc sorbed more strongly to kaolinite than to silica, and kaolinite particles also deposited more readily in the streambed than did silica colloids. Model simulations were found to be highly dependent on the colloid size distribution. When the colloids had a bimodal distribution, colloidal-phase contaminant transport occurred primarily on the finer fraction, but bulk colloid deposition was dominated by removal of the coarser fraction.

Adsorption↗
PubMed2005

Colloid facilitated transport of strongly sorbing contaminants in natural porous media: mathematical modeling and laboratory column experiments.

Mobile colloidal particles may act as carriers of strongly sorbing contaminants in subsurface materials. Such colloid-facilitated transport can be induced by changes in salinity, similar to freshwater intrusion to a contaminated aquifer saturated with saltwater, or groundwater penetration into a contaminated site saturated with a dumpsite leachate. This process is studied for noncalcareous soil material with laboratory column experiments with sodium and calcium as major cations and with lead as a strongly sorbing model contaminant. The measured breakthrough curves of these elements were described with a mathematical transport model, which invokes release and deposition kinetics of the colloids, together with adsorption and desorption of the relevant ions to the solid matrix as well as to the suspended colloids. In particular, the specific coupling between colloid and solute transport is considered. The crux of a successful description of such colloidal transport processes is to capture the inhibition of the particle release by adsorbed divalent ions properly and explicitly to considerthe dependence of colloid release on the solution chemistry and the chemical conditions at the solid-liquid interface. Experiments and modeling address colloid-facilitated transport of lead out of a contaminated zone and through a noncontaminated zone, including effects of flow velocity and length of the noncontaminated zone. We finally show that colloid-facilitated transport can be suppressed by the injection of a suitably chosen solution of a calcium salt.

Adsorption↗
PubMed2006

Experimental and numerical iInvestigations of effects of silica colloids on transport of strontium in saturated sand columns.

Transport experiments with strontium were conducted using saturated sand columns in the presence and absence of silica colloids, and numerical modeling was performed with modeling results compared to experimental data. The experiments were aimed at testing the hypothesis that under certain chemical conditions colloids act as movement-retarding agents and yield a larger effective retardation factor for the migrating contaminant. Four individual experiments were conducted to identify conditions where the mobility of silica colloids is increased or decreased, and a similar set was conducted for strontium transport in the absence of colloids. Mobility of colloids was found to increase with decreasing ionic strength and increasing pH, with the ionic strength having the more significant impact. The reverse effect was obtained for strontium. Based on these results, two additional experiments were conducted where both colloids and strontium were injected at the column inlet. Results showed that under certain conditions of ionic strength and pH (I = 3.0 x 10(-2) M and pH = 4-5.4) colloids retarded the movement of strontium. The retardation effect was obtained in two experiments under slightly modified conditions, which confirms the role of colloids as retarding agents. Afinite difference numerical model was used to (a) simulate mobile breakthrough curves and compare to experimental data and (b) estimate the model parameters describing cotransport of strontium and colloids. The model accurately predicted arrival time and the overall shape of the breakthrough curves.

Colloids↗
PubMed1998

Serum albumin and colloid osmotic pressure in survivors and nonsurvivors of prolonged critical illness.

We retrospectively compared the changes in serum albumin concentration and colloid osmotic pressure between survivors and nonsurvivors of prolonged (> or = 7 days) critical illness over a 2-year period from 1 July 1995. All patients had serum albumin measured daily, and colloid osmotic pressure measured 5 days a week, throughout their ICU admission. They received crystalloid and colloid infusions as well as parenteral or enteral feeding. Infusions of albumin were not used to treat hypoalbuminaemia. One hundred and forty-five patients were included, 66 nonsurvivors and 79 survivors. Nonsurvivors were significantly older than survivors [mean (95% CI): 58 (3.8) and 49 (4.1) years, respectively] and had a greater risk of death [mean (95% CI): 0.44 (0.06) and 0.28 (0.05); p < 0.05]. There was no significant difference in gender, APACHE II score [mean (95% CI): 22 (2.7) (nonsurvivors); 18 (2.3) (survivors)] or length of stay [median (interquartile range): 14 (9-27) days (nonsurvivors); 15 (9-26) days (survivors)]. There was no difference between the two groups in the absolute minimum serum albumin concentrations reached, the time to reach that minimum or the minimum in the first 7 days. However, nonsurvivors had a significantly lower mean serum albumin concentration: [mean (95% CI): 15.7 (5.1) g.l-1 compared with 18.3 (4.6) g.l-1 in survivors; p < 0.05]. They also had a lower recovery mean (the weighted mean after the minimum value): [mean (95% CI): 13.3 (5.1) g.l-1 (nonsurvivors) and 18.6 (5.3) g.l-1 (survivors); p < 0.01]. Analysis of colloid osmotic pressure results showed no difference between the groups in mean, minimum or recovery mean. Regression analysis of mean colloid osmotic pressure and albumin revealed that albumin only contributed 17% of the colloid osmotic pressure in these patients. The similar decrease in albumin in nonsurvivors and survivors may reflect the acute inflammatory response and/or haemodilution. However, survivors showed an ability to increase serum albumin concentrations, possibly owing to resumption of synthesis. The colloid osmotic pressure varied little between or within either group of patients, possibly because of the use of artificial colloids. There was no relationship between death and colloid osmotic pressure.

Adult↗
PubMed2001

Dermal injection of radioactive colloid is superior to peritumoral injection for breast cancer sentinel lymph node biopsy: results of a multiinstitutional study.

OBJECTIVE: To determine the optimal radioactive colloid injection technique for sentinel lymph node (SLN) biopsy for breast cancer. SUMMARY BACKGROUND DATA: The optimal radioactive colloid injection technique for breast cancer SLN biopsy has not yet been defined. Peritumoral injection of radioactive colloid has been used in most studies. Although dermal injection of radioactive colloid has been proposed, no published data exist to establish the false-negative rate associated with this technique. METHODS: The University of Louisville Breast Cancer Sentinel Lymph Node Study is a multiinstitutional study involving 229 surgeons. Patients with clinical stage T1-2, N0 breast cancer were eligible for the study. All patients underwent SLN biopsy, followed by level I/II axillary dissection. Peritumoral, subdermal, or dermal injection of radioactive colloid was performed at the discretion of the operating surgeon. Peritumoral injection of isosulfan blue dye was performed concomitantly in most patients. The SLN identification rates and false-negative rates were compared. The ratios of the transcutaneous and ex vivo radioactive SLN count to the final background count were calculated as a measure of the relative degree of radioactivity of the nodes. One-way analysis of variance and chi-square tests were used for statistical analysis. RESULTS: A total of 2,206 patients were enrolled. Peritumoral, subdermal, or dermal injection of radioactive colloid was performed in 1,074, 297, and 511 patients, respectively. Most of the patients (94%) who underwent radioactive colloid injection also received peritumoral blue dye injection. The SLN identification rate was improved by the use of dermal injection compared with subdermal or peritumoral injection of radioactive colloid. The false-negative rates were 9.5%, 7.8%, and 6.5% (not significant) for peritumoral, subdermal, and dermal injection techniques, respectively. The relative degree of radioactivity of the SLN was five- to sevenfold higher with the dermal injection technique compared with peritumoral injection. CONCLUSIONS: Dermal injection of radioactive colloid significantly improves the SLN identification rate compared with peritumoral or subdermal injection. The false-negative rate is also minimized by the use of dermal injection. Dermal injection also is associated with SLNs that are five- to sevenfold more radioactive than with peritumoral injection, which simplifies SLN localization and may shorten the learning curve.

Breast Neoplasms↗
PubMed1990

Investigation of factors affecting adhesion of 99Tcm labelled colloids to glass vials.

Factors which may possibly influence the adhesion of 99Tcm labelled colloid to glass vials were investigated. Of five colloids studied, two protein-free tin colloids were affected most by the problem, some 12-18% being lost by adhesion to the glass vial when the colloid was left resting on the bench, or 60-87% when it was rotated for a period of 4 h. The proportion of activity which adhered to the vial was dependent on the time the product had been contained within it, whether on the bench or rotated. Two of the colloids, both of which contained protein, were affected only slightly by the problem, one being a tin colloid and the other a sulphur colloid. An antimony sulphide colloid, which contained no added protein, was virtually unaffected by the problem. The degree of adhesion was not related to the pH of the product, nor to the temperature at which the product was stored, nor to the tendency of the colloid particles to grow in size upon vigorous agitation.

Colloids↗
PubMed2005

Impact of colloid response on survival after preoperative radiotherapy in locally advanced rectal carcinoma.

Neoadjuvant therapy for rectal carcinoma modifies morphology and natural history of the tumor. Colloid response defined by predominant colloid changes with or without residual tumor cells is a form of tumor response whose impact on survival is unknown. This study evaluated influence of tumor histologic response, especially of colloid response, on survival in patients treated by long-course preoperative radiotherapy for rectal cancer. In 200 patients with uT3-T4 or N1 rectal carcinomas, influence of type of surgery, dose of radiotherapy, residual tumor size, surface tumor aspect, tumor response (downstaging vs. colloid or no response), tumor grade, vascular and neural invasion, circumferential margin, and postoperative chemotherapy on 5-year overall and disease-free survival were studied by univariate and multivariate analyses. A colloid response was observed in 20% of the cases. Tumor response, circumferential margin, and vascular invasion were independently associated with the disease-free survival. Patients with downstaging had a better disease-free survival than patients without response (80% vs. 54%), whereas those with colloid response had an intermediate survival (64%). After colloid response, the rate of recurrence was similar to patients with downstaging for local recurrence (0%-3%) and to those with no response for distant recurrence (28%). After preoperative radiotherapy for rectal cancer, survival and type of recurrence are influenced by the tumor response. The intermediate natural history of patients with colloid response suggests taking colloid response into account in postoperative tumor staging to optimize adjuvant therapy.

Adenocarcinoma, Mucinous↗
PubMed2006

Sampling silica and ferrihydrite colloids with fiberglass wicks under unsaturated conditions.

The suitability of passive capillary samplers (PCAPS) for collection of representative colloid samples under partially saturated conditions was evaluated by investigating the transport of negatively and positively charged colloids in fiberglass wicks. A synthetic pore water solution was used to suspend silica microspheres (330 nm in diameter) and ferrihydrite (172 nm in diameter) for transport experiments on fiberglass wicks. Breakthrough curves were collected for three unsaturated flow rates with silica microspheres and one unsaturated flow rate with ferrihydrite colloids. A moisture characteristic curve, relating tensiometer measurements of matric potential to moisture content, was developed for the fiberglass wick. Results indicate that retention of the silica and the ferrihydrite on the wick occurred; that is, the wicks did not facilitate quantitative sampling of the colloids. For silica microspheres, 90% of the colloids were transmitted through the wicks. For ferrihydrite, 80 to 90% of the colloids were transmitted. The mechanisms responsible for the retention of the colloids on the fiberglass wicks appeared to be physicochemical attachment and not thin-film, triple-phase entrapment, or mechanical straining. Visualization of pathways by iron staining indicates that flow is preferential at the center of twisted bundles of filaments. Although axial preferential flow in PCAPS may enhance their hydraulic suitability for sampling mobile colloids, we conclude that without specific preparation to reduce attachment or retention, fiberglass wicks should only be used for qualitative sampling of pore water colloids.

Colloids↗
PubMed2004

Organic colloids and their influence on low-pressure membrane filtration.

Wastewater treatment by low-pressure membrane filtration (MF and UF) is affected to a large extent by macromolecules and colloids. In order to investigate the influence of organic colloids on the membrane filtration process, colloids were isolated from a wastewater treatment plant effluent using a rotary-evaporation pre-concentration step followed by dialysis. Stirred cell tests were carried out using redissolved colloids, with and without additional glass fiber filtration. After constant pressure membrane filtration of 190 L/m2, the initial flux had declined by 50% for colloids > 6-8 kD (glass fiber filtered) with a hydrophilic MF membrane and for colloids > 12-14 kD (glass fiber filtered) with a hydrophobic MF membrane. For the non-filtered colloidal solutions, the flux decline was even steeper with the flux being below 10% of the initial flux after 190 L/m2 were passed through the membranes. As with larger particles, colloids form a filtration cake layer on top of the membrane surface when used as isolates without prior filtration. This filtration cake is easily removed during backwashing. However, polysaccharides as a macromolecular component of the colloid isolate cause severe fouling by the formation of a gel layer on the membrane surface that is difficult to remove completely.

Colloids↗
PubMed1983

Crystalloid versus colloid for fluid resuscitation of hypovolemic patients.

The choice of the initial asanguinous fluid--either crystalloid or colloid--used for the resuscitation of the hypovolemic patient remains controversial. Colloid supporters argue for the careful preservation of the plasma colloid osmotic pressure (PCOP) to protect the lung from pulmonary edema. A careful analysis of the Starling microvascular forces operative at the pulmonary capillary makes such an effect unlikely. In fact, the lung is relatively immune to hemodilution and any decrease in PCOP is roughly one fourth as important as increases in hydrostatic pressure in causing increased fluid exchange. A critical review of the experimental and clinical studies comparing crystalloid versus colloid resuscitation essentially shows no physiologic difference in the two solutions. Using the thermal-green dye technique of extra-vascular lung water (EVLW) measurement in twenty crystalloid resuscitated trauma (n = 10) and burn (n = 10) patients, we have specifically evaluated the pulmonary effects of profound depression of PCOP and a negative PCOP - PAWP gradient (a shorthand form of the Starling equation argued to predict the presence of pulmonary edema if + 4 mm Hg or less). Average resuscitative fluid volumes during the first two hospital days were: 31.8 litres of crystalloid and no colloid for each burn patient; and 18.5 liters of crystalloid, 21 units of blood and 1 liter of colloid (as fresh frozen plasma) for each trauma patient. EVLW remained in the normal range of 7.0 +/- 1.0 ml/kg during the first five hospital days for all patients despite profound decrease in PCOP (less than 15 mm Hg) and a low or negative PCOP - PAWP gradient. Crystalloid resuscitation clearly is not harmful to the lung and it is equally as effective as colloid resuscitation. Crystalloid is markedly less expensive than colloid and, given the greater cost of colloid without evident benefit, one wonders how their further use can be justified.

Animals↗
PubMed2002

Mesoscopic dispersion of colloidal agglomerate in a complex fluid modelled by a hybrid fluid-particle model.

The dispersion of the agglomerating fluid process involving colloids has been investigated at the mesoscale level by a discrete particle approach--the hybrid fluid-particle model (FPM). Dynamical processes occurring in the granulation of colloidal agglomerate in solvents are severely influenced by coupling between the dispersed microstructures and the global flow. On the mesoscale this coupling is further exacerbated by thermal fluctuations, particle-particle interactions between colloidal beds, and hydrodynamic interactions between colloidal beds and the solvent. Using the method of FPM, we have tackled the problem of dispersion of a colloidal slab being accelerated in a long box filled with a fluid. Our results show that the average size of the agglomerated fragments decreases with increasing shearing rate gamma, according to the power law A x gamma(k), where k is around 2. For larger values of gamma, the mean size of the agglomerate S(avg) increases slowly with gamma from the collisions between the aggregates and the longitudinal stretching induced by the flow. The proportionality constant A increases exponentially with the scaling factor of the attractive forces acting between the colloidal particles. The value of A shows a rather weak dependence on the solvent viscosity. But A increases proportionally with the scaling factor of the colloid-solvent dissipative interactions. Similar type of dependence can be found for the mixing induced by Rayleigh-Taylor instabilities involving the colloidal agglomerate and the solvent. Three types of fragmentation structures can be identified, which are called rupture, erosion, and shatter. They generate very complex structures with multiresolution character. The aggregation of colloidal beds is formed by the collisions between aggregates, which are influenced by the flow or by the cohesive forces for small dispersion energies. These results may be applied to enhance our understanding concerning the nonlinear complex interaction occurring in mesoscopic flows such as blood flow in small vessels.

Journal Article↗
PubMed2005

Quantifying the effect of ionic strength on colloidal fouling potential in membrane filtration.

Ultrafiltration experiments were conducted to study the fouling potential of colloidal suspensions under different ionic strengths and colloid concentrations. A linear relationship was found relating the colloidal fouling potential to the logarithm of the Debye-Huckel parameter, a characteristic for electrical double layers of colloids. This finding provided a useful quantitative linkage between the colloidal fouling potential and the water chemistry. Considering the linear dependence of colloidal fouling potential on the colloid concentration, a bilinear model was proposed to explain the coupling effects of colloid concentration and ionic strength of the suspension on the fouling potential. The model predictions of fouling potential were found to fit accurately with experimentally determined fouling potential values. Further analysis of the model showed that ionic strength can significantly affect colloidal fouling, for example, a 10-fold increase in ionic strength from 0.001 to 0.01 M for a given feed concentration has the same membrane fouling effect as doubling the feed concentration. The model allows for a quick and reliable assessment of fouling potential without even performing any experiments. This could then be used to design the membrane process or pretreatment stages required to mitigate membrane fouling.

Journal Article↗
PubMed2006

Model analysis of the colloid and radionuclide retardation experiment at the Grimsel Test Site.

The colloid and radionuclide retardation experiments performed at NAGRA's Grimsel Test Site in Switzerland are part of an international collaboration program designed to collect in situ data on the impacts of colloids on radionuclide transport. In this work, breakthrough behaviors of trivalent americium (i.e., 241Am and 243Am) both in the absence and presence of bentonite colloids are analyzed with COLFRAC--a code that models colloid-facilitated solute transport in discretely-fractured, porous media. Model fits to the experimental results indicate that Am sorbed onto mobile colloids, which enhance Am transport relative to a non-sorbing tracer, 131I. Modelling results suggest that Am is kinetically sorbed onto both naturally occurring and exogenous bentonite colloids. Results also indicate that desorption of Am from colloids is slow with respect to the duration of the experiment. In addition, early colloid breakthrough compared to a conservative tracer suggests the effects of hydrodynamic chromatography. Overall, Am breakthrough curves suggest enhanced mobility due to co-transport with both naturally occurring and bentonite colloids.

Journal Article↗
PubMed2003

Depletion-induced phase separation in colloid-polymer mixtures.

Phase separation can be induced in a colloidal dispersion by adding non-adsorbing polymers. Depletion of polymer around the colloidal particles induces an effective attraction, leading to demixing at sufficient polymer concentration. This communication reviews theoretical and experimental work carried out on the polymer-mediated attraction between spherical colloids and the resulting phase separation of the polymer-colloid mixture. Theoretical studies have mainly focused on the limits where polymers are small or large as compared to the colloidal size. Recently, however, theories are being developed that cover a wider colloid-polymer size ratio range. In practical systems, size polydispersity and polyelectrolytes (instead of neutral polymers) and/or charges on the colloidal surfaces play a role in polymer-colloid mixtures. The limited amount of theoretical work performed on this is also discussed. Finally, an overview is given on experimental investigations with respect to phase behavior and results obtained with techniques enabling measurement of the depletion-induced interaction potential, the structure factor, the depletion layer thickness and the interfacial tension between the demixed phases of a colloid-polymer mixture.

Journal Article↗
PubMed2006

Microwave-assisted self-organization of colloidal particles in confining aqueous droplets.

Monodisperse aqueous emulsion droplets encapsulating colloidal particles were produced in the oil phase, and controlled microwave irradiation of the aqueous drop phase created spherical colloidal crystals by so-called evaporation-induced self-organization of the colloidal particles. Unlike usual colloidal crystals, colloidal crystals in spherical symmetry (or photonic balls) possessed photonic band gaps for the normal incident light independent of the position all over the spherical surface. While the consolidation of colloidal particles in emulsion droplets in an oven took several hours, the present microwave-assisted evaporation could reduce the time for complete evaporation to a few tens of minutes. Under the microwave irradiation, the aqueous phase in emulsions was superheated selectively and the evaporation rate of water could be controlled easily by adjusting the microwave intensity. The result showed that the packing quality of colloidal crystals obtained by the microwave-assisted self-organization was good enough to show photonic band gap characteristics. The reflectance of our photonic balls responded precisely to any change in physical properties including the size of colloidal particles, refractive index mismatch, and angle of the incident beam. In particular, for polymeric particles, the photonic band gap could be tuned by the intensity of microwave irradiation, and the reflection color was red-shifted with stronger microwave irradiation. Finally, for better photonic band gap properties, inverted photonic balls were prepared by using the spherical colloidal crystals as sacrificial templates.

Journal Article↗
PubMed2006

Formation of aquatic Th(IV) colloids and stabilization by interaction with Cm(III)/Eu(III).

The present investigation is to ascertain under what conditions actinide ions undergo aggregation via oxo-bridging to form stable colloidal species. Eu and Th are taken for this purpose as trivalent and tetravalent actinide homologue ions, respectively. For verification of the effects of impurities in chemicals on the actinide colloid generation, pH is adjusted either by a conventional acid-base titration or by coulometry without addition of NaOH. The colloid generation is monitored by highly sensitive laser-induced breakdown detection in varying pH from 3 to 7, first in dilute Eu and Th solutions separately and then in a mixture of both, all in 0.5 M HCl/NaCl. The formation of stable colloids is observed particularly in a mixed solution of Eu and Th, suggesting that aggregation via mutual oxo-bridging of trivalent and tetravalent metal ions results in surface polarization, leading to stable hydrophilic particles of 20-30 nm in diameter. When Eu is replaced by Cm in the mixed solution in favor of the high fluorescence intensity of the latter, the chemical speciation is determined on colloid-borne Cm by time-resolved laser fluorescence spectroscopy. Two different colloid-borne Cm species, oxo-bridged with Th, are identified: a minor amount at 598.0 nm (denoted as Cm-Th(1)) and a major amount at 604.8 nm (Cm-Th(2)). The former is found as a transitional state, which converts to the latter with increasing pH and prevails at pH > 5.5. Both colloid-borne species (Cm-Th) are distinctively different from hydrolyzed Cm or its carbonate complexes with respect to their fluorescence peak positions and lifetimes. In conclusion, a mixed oxo-bridging of trivalent and tetravalent actinides elicits the generation of stable colloids, whereas individual ions in their pure state form colloids under oversaturation at near neutral pH only as a transitional state for precipitation.

Journal Article↗