Batch and stop-flow column experiments were performed to estimate persulfate decomposition kinetic parameters in the presence of seven well-characterized aquifer materials. Push-pull tests were conducted in a sandy aquifer to represent persulfate decomposition under in situ conditions. The decomposition of persulfate followed a first-order rate law for all aquifer materials investigated. Reaction rate coefficients (k(obs)) increased by an order of magnitude when persulfate concentration was reduced from 20 g/L to 1 g/L, due to ionic strength effects. The column experiments yielded higher k(obs) than batch experiments due to the lower oxidant to solids mass ratio. The kinetic model developed from the batch test data was able to reproduce the observed persulfate temporal profiles from the push-pull tests. The estimated k(obs) indicate that unactivated persulfate is a persistent oxidant for the range of aquifer materials explored with half-lives ranging from 2 to 600 d.

Although thermogravimetric analysis (TGA) is a widely accepted technique for assessing coal combustion, conflicting trends have often been reported when relating apparent TGA reactivities to pulverized fuel (PF) burner conditions. Therefore, this paper compares the reactivity of chars generated in a drop tube furnace (DTF) to those from TGA. The implications of devolatilization temperature, heating rate and residence time are considered. For the smaller particle size ranges of the bituminous coal investigated (ATC), optimized devolatilization procedures were used to generate corresponding TGA burnout rates between the two char types. However, with fractions of >75 μm, the DTF chars showed an increased burnout propensity when moving from combustion regime II to combustion regime III. Scanning electron microscope (SEM) images and internal surface areas indicate that this is because of incompatible char morphologies. Thus, while chars produced under the conditions of TGA pyrolysis strongly resemble raw coal and display an undeveloped pore network; the DTF chars are highly porous, extensively swollen and possess considerably larger internal surface areas. Subsequently, char burnout variability was quantified, with the reactivity distribution for the DTF samples found to be up to an order of magnitude more significant than for the TGA chars. This is attributed to a fluctuating devolatilization environment on the DTF. Finally, a TGA study observed a robust particle size based compensation effect for the TGA chars, with the relative reaction rates and activation energies demonstrating the presence of internal diffusion control. However this phenomenon was partly alleviated for the DTF chars, since their higher porosities reduce mass transfer restrictions. Moreover, it should be realized that DTF char fractions of <38 μm, including those required to ensure true intrinsic control under the investigated burnout conditions, cannot be produced directly. This is because of bridging and sloughing in the DTF's screw-feeder. Instead, such samples must be created by grinding larger particles, which destroys the char's existing porosity.

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Diesel fuel distilled from crude oil should contain no greater than trace amounts of sodium. However, fuel specifications do not include sodium; there is a limit of five parts per million for the amount of sodium plus potassium in fatty acid methyl esters (FAME) used as biodiesel. Sodium compounds are often used as the catalyst for the esterification process for producing FAME and sodium hydroxide is now commonly used in the refining process to produce ultra-low sulphur diesel (ULSD) fuel from crude oil. Good housekeeping should ensure that sodium is not present in the finished fuel. A finished fuel should not only be free of sodium but should also contain a diesel fuel additive package to ensures the fuel meets the quality standards introduced to provide reliable operation, along with the longevity of the fuel supply infrastructure and the diesel engines that ultimately burn this fuel. There has recently been an upsurge in reported field problems due to fouling of the fuel injection system in modern diesel engines. This can take the form of deposits in the fuel filters or within the fuel injectors themselves. Recent work proposed a mechanism whereby sodium contaminated fuel can undergo adverse reactions between the sodium compounds and fuel additives leading to the formation of material that can impede the operation of diesel fuel injectors. This paper presents new work carried out to enhance the understanding of this mechanism and demonstrates that the fate of any sodium contaminant is highly dependent on (i) the fuel additives present in the fuel (ii) the amount of water in the system, (iii) potentially the intensity of fuel/water mixing and (iv) the identity of the sodium salt involved in the reaction. This can lead to sodium accumulating in the water bottoms, forming sodium compounds that go on to plug fuel filters or which may cause injector fouling. The data found may explain the variation in engine test data regarding sodium induced fouling reported in the recent literature.

The carbon isotopic composition (•8C and •4C) of the inorganic carbon dissolved in the waters of a small, largely unconfined aquifer in unconsolidated sediments on the Canadian Shield has been investigated. Three principal carbon sources are recognized: soil COa, rock carbonate, and biogenic CO:. The average •8C value of the soil COa is close to -21.0 4-1.5%, and present-day '4C activities of the soil COa vary between 130 and 162% modern •4C. Very minor amounts (< 1.0%) of carbonate minerals (6'aC = -0.6%o) are present within the aquifer and react with this soil CO: to produce a dissolved inorganic carbon (DIC) with 'aC activities which are as much as 50% below the initial activities of the soil COa. The third carbon source, a biogenic CO:, could be detected only indirectly, and its presence is primarily deduced from the occurrence of methane in the deeper parts of these aquifers. The large isotope fractionation which occurs during bacterial coproduction of CO: with this methane results, however, in a •aC-rich CO•. and thus a DIC with high •'aC values. Values of •'•C as high as +11%o have been measured in groundwaters on the Canadian Shield. Since the origin of the destroyed organic matter is not yet known, no assessment of the importance of this CO: for the •aC contents of the DIC is possible. models which are based on utilization of these ions as indicators for such processes. A Fortran IV computer program attached to the water analyses treatment program (WATEQF) by Plumruer et al. [1976] has been presented by Reardon and Fritz [1978]. This program considers corrections based on initial versus final carbonate, simple carbonate, dissolution carbonate plus gypsum dissolution with and without ion exchange processes, and dissolution-precipitation processes as they may occur during the incongruent dissolution of dolomites. Chemical and isotope analyses are compared to model calculations for both chemistry and carbon 13. 1059 1971)', Vienna, 1969-1971. Kiiley, R. W. D., Carbon geochemistry of an unconfined aquifer-lake system on the Canadian Shield, M.Sc. thesis, Univ. of Waterloo, Waterloo, Ont., 1977. McNaughton, D. M., A hydrogeological, geochemical and isotopic study of an uncontaminated flow system, Perch Lake Basin, Ontario, M.Sc. thesis, Univ. of Waterloo, Waterloo, Ont., 1975. Mock, W. G., The dissolution-exchange model for dating groundwater with carbon-14, Interpretation of Environmental Isotope and Hydrochemical Data in Groundwater Hydrology, STI Publ. 429, pp. 213-225, lnt. At. Energy Agency, Vienna, 1976. Park, R., and S. Epstein, Carbon isotope fractionation during photosynthesis, Geochim. Cosmochim. Acta, 21, 110-126, 1960. Parsons, P. J., Movement of radioactive wastes through soils, l, Soil and groundwater investigations in lower Perch Lake basin, Rep. AECL 1038, At. Energy of Can. Ltd., Chalk River, Ont., 1960. Reardon, E. J., and P. Fritz, Computer modelling of groundwater and •4C isotope compositions, J. Hydrol., 36, 201-224, 1978. Rightmire, C. T., and B. B. Hanshaw, Relationship between the carb...