Decontamination of oil-polluted soil by cloud point extraction

An extraction procedure based on cloud point phase separation of nonionic surfactants was used to remove oil contamination from soils. The detergent employed was Triton X-114, and its clouding behavior was monitored by means of a fluorescence probe. Changes in the I (1)I (3) ratio of pyrene indicated gradual dehydration of the detergent micelles upon heating. The rate of phase separation, and the volume and water content of the micellar phase were determined. In the practical clean-up, 85-98% of the oil present in the soil was found to enter the micellar phase of the separated washing liquid. A 15-min washing time with 3-5% detergent was found to be sufficient for this degree of contaminant removal from soil containing 0.009-0.017% oil, using a liquid:solid ratio of 5:2. The extraction efficiency decreased with increasing carbon content of the soil. The process holds promise for large-scale treatment of oil-polluted soils.     

The role of selected cations in the formation of pseudomicelles in aqueous humic acid

The fluorescence intensity enhancement of a pyrene probe in aqueous humic acid solutions was assessed in terms of added lanthanide and thorium cations. Among the trivalent ions it was found that size played a role, with the small Lu(3+) ion producing the greatest increase in pyrene emission. This was attributed to its superior ability to cause pseudomicellization in the humic acid polymer. Slow kinetic effects were observed, leading to substantial fluorescence enhancement over a period of 7 h. This was ascribed to a continuous aggregation process in aqueous humic acid, leading to ever more viscous microenvironments for the probe molecule.     

ENERGY TRANSFER IN TRITON X-405 MICELLES: THE EFFECTS OF TEMPERATURE AND BRIJ 35

–Energy transfer from the phenyl groups of micellar Triton X-405 (TX-405) to solubilized pyrene molecules has been measured at a range of temperatures and in the presence of different polyoxyethylene 23 lauryl ether (Brij 35) concentrations. Increases in temperature lead to elimination of water from the outer, wet, micelle layer and an inward movement of associated pyrene. The addition of Brij also leads to a reduction in polarity of the microenvironment of pyrene. However, sensitization is observed even at high Brij concentrations. The donor/acceptor separation caused by the introduction of Brij proceeds slowly, continuing for several minutes after its addition to micellar TX-405.     

Dynamic conductivity measurements in humic and fulvic acid solutions

Conductivity changes of dilute aqueous humic and fulvic acids solutions were monitored after the addition of small quantities of Cu, Cd, Pb, and Zn. The solutions were stirred at a constant and reproducible rate, and measurements proceeded until stable conductivities were attained. The values were compared to KCl reference solutions treated in an identical manner, and the results showed that the humic materials significantly reduced metal ion mobilities. Pb and Cu were affected more than Cd and Zn, and especially Zn regained a significant portion of its mobility upon dispersal. Cu, in contrast, was strongly and irreversibly retarded in all cases. It was inferred that Zn underwent transient electrostatic interactions with humics at high local concentration, while associations between Cu and humics were rapid and permanent. Different humic materials showed these effects to different extents. Raising the temperature from 20 to 60 °C did not, as expected, lead to higher relative conductivities in metal-humate solutions, but showed enhanced retardation of the cations. It was noted that temperature induced aggregation (clouding) of humic solutions increased the effective sizes of the metal-humate complexes, reducing their mobilities in aqueous solution.     

Functional group analysis of Suwannee River fulvic acid with reactive fluorescent probes

The reactive functional group content of Suwannee River fulvic acid (SRFA) was determined by reaction with fluorescent probes. Reaction with a triflate (R-SO₂CF₃) provided the total reactive group content in SRFA, and pyrene butanoic acid was used to determine the hydroxyl and amino groups. After purification of the product, standard addition analysis was used for quantification. The total reactive site content of SRFA was found to be 13.9 mmol/g, of which 57% were carboxylic acids, and 43% hydroxyl and amino groups. These values compare well with those obtained by other methods.     

Precapacitive processes in single potential-step chronoamperometry

Extremely short-lived anodic currents were observed in the early parts of the transient response following the application of a cathodic potential step to a mercury working electrode. It is proposed that this phenomenon is due to the existence of a brief precapacitive period, which precedes full development of the double-layer charging current, and which allows momentary reaction (reduction) of species present at the electrode surface. The observed anodic currents are explained in terms of a re-oxidation of such "resident" species that were reduced during this precapacitive period. The subsequent capacitive surge produced by the charging of the electrical double layer leads to an anodic shift of the electrode potential that can be sufficient for the re-oxidation of the precapacitive amalgam. The anodic peak is linearly related to depolarizer concentration and varies with supporting electrolyte concentration, ion mobility and potential step size. Cathodic preconcentration of the depolarizer enhances the effect.     

Conductometric characterization of dissolved humic materials

Conductometric replacement titrations of humic and fulvic acids dissolved in a slight excess of hydroxide were carried out with standard acid. The slope of the titration curve corresponding to the protonation of humate/fulvate was related to the electrophoretic mobility of the polyanions or aggregates, and hence to their dimensions. Promising qualitative agreement was found between sizes of a number of these species and their conductance slopes. Both the separation of humic fractions and size reduction by photolysis and sonication led to the anticipated decrease in slope. The slight reduction in slope observed during the course of the titration was tentatively ascribed to contraction of the expanded (drained) humic aggregates.     

Dynamic light scattering measurements of particle size development in aqueous humic materials

Dynamic light scattering (DLS) has been used to monitor changes in aggregate sizes of aqueous humic materials as a function of solution properties. Humic and fulvic acids were dissolved at relatively low concentrations (15-30 mg L(-1)) in solutions of different temperature, cation and ethanol content, and pH. The results could be explained in terms of intramolecular contraction and intermolecular aggregation of humic polymers. The former were prevalent in soil humic acids, and less so in aquatic humic acids and fulvic acids. Increasing the temperature of humic solutions generally led to an increase in particle sizes, which was ascribed to an effect akin to surfactant clouding. The addition of cations led to either contraction or expansion, depending on the charge and concentration of the ion, and the nature of the humic material. Reducing the pH initially caused contraction, followed by growth and precipitation in more highly acidic media.     

Assessment of inner filter effect corrections in fluorimetry

Summary The inner filter effect (IFE) in fluorescence spectroscopy is not easily distinguished from dynamic and static quenching phenomena, since IFE rarely occurs without quenching. IFE corrections may be subject to under-or over-compensation effects that are difficult to assess accurately. To evaluate existing IFE correction procedures, it is proposed that the linearity of resulting Stern-Volmer plots and the relative change of their slopes with temperature be adopted as criteria. Three correction methods are assayed in this manner, and the equation described by Gauthier et al. is found to produce the best results.