Effects of particle size on properties and thermal inertization of bottom ashes (MSW of Turin’s incinerator)
Caterina CavigliaGiorgia ConfalonieriIngrid CorazzariEnrico DestefanisGiuseppe MandroneLinda PasteroRenato BoeroAlessandrο Pavese
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Abstract This paper addresses the nature of incongruent dissolution of calcite in glacial settings using an experimental approach. Various CaCO 3 samples were comminuted using two contrasting techniques (dry machine-milling, and hand-grinding of an ice-water mixture) and dissolved to calcite saturation in both high-pCO 2 (10 −2 atm) and low-pCO 2 (10 −3.5 = atmospheric) conditions. Ion yields of Ca, Mg and Sr were determined at the end of the experiments. Leachates displayed enhancement of Mg/Ca and Sr/Ca by a factor of 1.3–8.3 compared with bulk solid carbonate. Lower Mg/Ca and Sr/Ca ratios under higher-pCO 2 conditions reflect the percentage dissolution of the carbonate, not the pCO 2 per se. The experimental results imply that reported natural incongruent dissolution is readily reproducible in the laboratory and is primarily dependent on the water/rock ratio. Quantitative analysis of new and previous results suggests that the effect relates to the most reactive 0.15–0.25% of the sample, equating volumetrically to the outer few lattice layers, and it is interpreted as an anomalous leaching behaviour of calcite surfaces freshly exposed by crushing. This phenomenon could serve as an index of the relative efficiencies of fragmenting and dissolutional processes in glacial environments.
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Re-examination of an experimental determination of the dissolution rate of reagent-grade calcite in seawater shows that the original conclusion of rate law with 4.5-order dependence on undersaturation was very sensitive to uncertainties in the saturation state of the seawater with respect to calcite,ΩC. In particular, use of an erroneously high value of the calcite stoichiometric solubility product generated correspondingly low values of the saturation state. Extrapolation of the experimental measurements to a rate of zero dissolution indicates that the calcite solubility was about 20% lower than that used in the original study, similar to more recent estimates. If the lower solubity is used for recalulation of the experimental saturation states, the dissolution rate Rd,C (% day−1) is adequately described by the rate experssion: Rd, C = 38(1−omega;C)1 In situ measurements of pH in the pore waters of calcite-rich sea floor sediments are more consistent with first-order kinetics than with 4.5-order kinetics. Interpretation of pore water pH data using the 4.5-order rate expression requires dissolution rate constants that are different by at least two orders of magnitude and stoichiometric calcite solubility products that are different by several percent between two otherwise similar sites. Application of the first-order dissolution reduces the variability in the rate constant to less than one order of magnitude, and all in situ observations are consistent with a single estimate of calcite solubility. First-order kinetics do not reduce the discrepancy between the laboratory determined rate constants and those based on pore water measurements. Dissolution rate constants constrained by the in situ pH measurements are at least two orders of magnitude less than the laboratory results.
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Solubility equilibrium
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Magnesite
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In situ electrode measurements of porewater oxygen and pH from four sites on the Ceara Rise in the western Tropical Atlantic unequivocally demonstrate that calcite dissolution driven by metabolic CO2 produced within the sediments is a significant part of the diagenesis of sedimentary calcite, dissolving at least 20% of the calcite rain to the seafloor. The first ever in situ absorbance-based measurements of porewater CO2(aq) support the dissolution estimates based on models of the observed pH distributions and are incompatible with scenarios excluding metabolic CO2-driven dissolution. Our dissolution estimates are consistent with those estimated by an independent study of porewater calcium and alkalinity profiles (Martin and Sayles, 1996) at this location. The consistency of these disparate porewater measurements and our ability to interpret them with simple models of respiration and dissolution implies that no special mechanism is required to describe this process. The calcite dissolution rate constant in the sediments of the deepest station in this study is significantly higher than determined by in situ studies at other locations; values approach those determined by early laboratory measurements. The dissolution rate constant here must be at least two orders of magnitude higher than for calcite in sediments on the Ontong-Java Plateau, based on in situ electrode-measurements there (Hales and Emerson, 1996). The calcite solubility consistent with these data is not compatible with that consistent with the Ontong-Java data. The reason for this difference is currently unresolved, but may be due to the high order of the empirical dissolution rate law assumed in this study.
Alkalinity
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ABSTRACT Cultures of known species of fungi placed on crystals of Iceland spar calcite resulted in extensive dissolution of the calcite. This organically mediated dissolution produced large patches of spiky calcite within a period of 253 days. The dissolution of the calcite occurred via surface-reaction-controlled kinetic processes that were mediated by the fungi. This occurred despite the lack of vast quantities of fluids undersaturated with respect to calcite. Locally, at least 10 µm of calcite was removed from the original crystal surface.
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Seafloor Spreading
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