Colloids concentration

In a study of the bioaccumulation of metals as colloid complexes and free ions by the marine brown shrimp, Penaeus aztecus [29] the colloids were isolated and concentrated from water obtained from Dickinson Bayou, an inlet of Galveston Bay, Texas, using various filtration and ultrafiltration systems equipped with a spiral-wound 1 kDa cutoff cartridge. The total colloidal organic carbon in the concentrate was found to be 78 lmgdm 3. The shrimps were exposed to metals (Mn, Fe, Co, Zn, Cd, Ag, Sn, Ba and Hg) as radiolabelled colloid complexes, and free-ionic radiotracers using ultrafiltered seawater without radiotracers as controls. The experiments were designed so that the animals were exposed to environmentally realistic metal and colloid concentrations. 

This simple relationship allows us to express all the thermodynamic variables in terms of our colloid concentration. The Helmholtz free energy per unit volume depends upon concentration of the colloidal particles rather than the size of the system so these are useful thermodynamic properties. If we use a bar to symbolise the extensive properties per unit volume we obtain... 

Once reaching a water system, the components of a crude oil or a petroleum hydrocarbon are truly dissolved at a molecular level or apparently soluble at a colloidal level when droplets characterized by radii of tens to hundreds of microns are formed. The apparent solubility of polycyclic aromatic hydrocarbons from oil in an aquatic system is reported by Sterling et al. (2003), who consider that the colloidal concentration of a given hydrocarbon contaminant in aqueous phase, C, is described by the equation... 

Andrade, E.M. Molina, F.V. Gordillo, G.J. Posadas, D. (1994a) Adhesion of colloidal hematite onto metallic surfaces. II. Influence of electrode potential, pH, ionic strength, colloid concentration, and nature of the electrolyte on the adhesion on mercury. J. Colloid Interface Sci. 165 459-466... 

A major outcome of the abovementioned studies is the importance of pH and notably of the salinity of the groundwater controlling colloid concentrations and, consequently, the relevance of colloids for radionuclide transport. The pH-dependent colloid stability varies considerably for different colloid types. Experimental data for the relationship of the stability ratio W... 

Fig. 5. Colloid concentrations determined under in situ conditions at the Aspo hard rock laboratory, Sweden. Analysis of colloids has been performed on line by (a) using a mobile laser-induced breakdown detection (LIBD) arrangement, and (b) DOC analysis of collected samples in the laboratory (Hauser et al. 2003). Bars in the upper diagram represent colloid concentration ranges detected during the campaign. Colloid concentrations and DOC are plotted against salinity expressed as the groundwater CP concentration (lower x-axis) and ionic strength (upper x-axis).

Colloid concentrations drop to almost zero at I>0.2mol/L. The same trend is found for humic/fulvic acids represented in Fig. 5b as dissolved organic carbon (DOC). The studies, however, also make clear that the variation of the chemical conditions with the creation of oxidizing conditions by, for example, radiolysis may temporarily generate high colloid populations even under conditions of high ionic strength. 

An increase in colloid concentration requires increased Al(III) dosages to obtain comparable values of relative colloid stability... 

Colloid concentrations in the eluent were determined with a Bio-Tek multichannel (optical densitometer with fiber-optics technology Bio-Tek Instruments, Winooski, VT) microplate reader, precalibrated with known concentrations of each colloid at 540 nm. Total metal concentration in the eluents was allocated to solution phase and colloidal phase (colloid-bound contaminant). The eluent samples were centrifuged for 30 min at 3500 rpm (x 2750 g) to separate the soluble contaminant fraction from the colloid-bound contaminant fraction. The absence of colloidal material in the supernatant solution was verified by filtration through a 0.2-pm membrane filter. The soluble metal (Cu, Zn, Pb) fractions were analyzed by atomic absorption (concentrations >0.5 mg/H) or inductively coupled plasma (ICP) spectrometry (concentrations <0.5 mg/H). The colloid fraction was extracted with 1 M HNO3-HCI [32] solution and analyzed with the same methodology used for the soluble fraction. The results for the duplicate soil monoliths and for the two soils were combined for practical purposes, because the reproducibility between soil monoliths was within 15%. 

The leaching solutions/suspensions were applied to the top of each monolith through a continuous step input of 2.2 cm/h-1 controlled with a peristaltic pump. This rate was tested in earlier experiments and found to provide consistent freeflow conditions without ponding on the top of the monoliths. All input mixtures were allowed to equilibrate for 24 h before application. For -10 days, eluents were monitored with respect to volume, colloid, and metal concentration. BTCs were constructed based on reduced metal and colloid concentrations (C/CG) and pore volumes. 

In many instances, researchers have simply used a UV/Vis spectrophotometer to estimate the colloid concentration, rather than a dedicated turbidimeter. For dilute suspensions, a linear relationship... 

The high concentrations of numerous chemicals in urban media contribute to complex chemical interactions and transformations within urban chemical mixtures. One example of this complexity is chemical speciation and distribution in stormwater, which affects bioavailability, toxicity and fate. High particle and colloidal concentrations suggest that many compounds in stormwater are not bioavailable, although the extent to which bioavailability is reduced depends on location. 

Primary charges—Charges that colloids concentrate at their immediate snrfaces. Rapid or flash mix—Process of rapidly mixing the coagnlant in the volume of... 

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