Sulphate depletion

In some systems, chemical reduction of the sediment leads to sulphide production, and capture of Fe with loss of Mn. However, in sulphate depleted systems, there is insufficient sulphide, and Fe is also lost. 

Acid ferric- sulphate (Streicher) test n 50wt.% H2SO4 -1-25 g/l ferric sulphate 120 h exposure to boiling solution Mass loss per unit area -1- 0-7 to -1- 0-9 1. Chromium-depleted areas 2. <7-phase in some alloys... 

Acid copper sulphate test t 16 wt.% H2SO4 -1-100 g/l CuSO, (-1- metallic copper) 72 h exposure to boiling solution 1. Appearance of sample upon bending 2. Electrical resistivity change 3. Change in tensile properties -1- 0-30 to -1- 0-58 Chromium-depleted area... 

Analysis of the dynamics of SCR catalysts is also very important. It has been shown that surface heterogeneity must be considered to describe transient kinetics of NH3 adsorption-desorption and that the rate of NO conversion does not depend on the ammonia surface coverage above a critical value [79], There is probably a reservoir of adsorbed species which may migrate during the catalytic reaction to the active vanadium sites. It was also noted in these studies that ammonia desorption is a much slower process than ammonia adsorption, the rate of the latter being comparable to that of the surface reaction. In the S02 oxidation on the same catalysts, it was also noted in transient experiments [80] that the build up/depletion of sulphates at the catalyst surface is rate controlling in S02 oxidation. 

Figure 7.10 Metabolism of paracetamol. With therapeutic doses, paracetamol is metabolised to the glucuronide and sulphate conjugates. With higher doses these pathways become saturated and metabolism proceeds via die P-450-mediated route, with the formation of the toxic metabolite benzoquinone. This is normally metabolised by conjugation with glutathione. When glutathione is depleted benzoquinone is free to interact with cellular macromolecules, leading to cellular damage.

PM 10 concentrations and constituents appear systematically higher at urban sites. Urban increments have been measured for most chemical constituents. Nearby (anthropogenic) sources and reduced dispersion in the urbanised areas are the main determining factors here. The observed increment for SIA is caused by more nitrate and sulphate. It is explained by depletion of chloride stabilising part of the nitrate and sulphate in the coarse mode. The question then arises how to assign the coarse mode nitrate (and sulphate) in the mass closure exercise as they replace the chloride. 

The reason why SIA is higher in urban areas is less obvious as these are secondary aerosols. The observed increment is predominantly caused by more nitrate and sulphate. The reaction of nitric acid and sulphuric acid with the sea-salt aerosol in a marine urbanised environment follows an irreversible reaction scheme. In essence, the chloride depletion stabilises part of the nitrate and sulphate in the coarse mode and may partly explain part of the observed increment. However, it also raises the question how to assign the coarse mode nitrate in the mass closure. The sea salt and nitrate contributions cannot simply be added any more as nitrate replaces chloride. Reduction of NOx emissions may cause a reduction of coarse mode nitrate, which is partly compensated by the fact that chloride is not lost anymore. A reduction would yield a net result of ((N03-C1)/N03 = (62-35)/62=) 27/62 times the nitrate reduction (where the numbers are molar weights of the respective components), and this factor could be used to scale back the coarse nitrate fraction in the chemical mass balance. A similar reasoning may be valid for the anthropogenic sulphate in the coarse fraction. Corrections like these are uncommon in current mass closure studies, and consequences will have to be explored in more detail. 

See Rosing, M.T., 1999, 13C-depleted carbon microparticles in >3700-Ma sea-floor sedimentary rocks from West Greenland, Science 283 674-676 Shen, Y., Buick, R., and Canfield, D.E., 2001, Isotopic evidence for microbial sulphate reduction in the early Archaean era, Nature 410 77-81 and Shidlowski, M.A., 1988, A 3800-million-year isotopic record of life from carbon in sedimentary rocks, Nature 333 313-318. 

In a preliminary experiment, weanling male Wistar rats were depleted of zinc by feeding a low zinc basal diet (0.6 yg/g zinc) for two weeks and then repleted by adding 12 yg/g zinc as zinc sulphate. The analysis of the zinc content of the different tissues at weekly intervals for four weeks revealed that the body weight and the total femur zinc were the parameters of choice because the responses were linear with duration of feeding. Moreover, the relative errors of the slopes of the regression lines were minimal (5). The results of this experiment also showed that since depletion did not reduce the variability in these parameters, it was not essential for the assay. 

Glutathione depletion can occur in malnourished people and alcoholics. The dominant metabolic pathway in neonates and children is sulphate conjugation. Glucuronide conjugation matures more slowly (the urinary glucuronide to sulphate ratio increases throughout childhood from 0.4 in neonates to 2 in adults) [7]. 

Figure 6.3 shows a mass balance model for sulphur speciations. Once other more thermodynamically amenable electron acceptors have been depleted, sulphate is used by sulphate reducing bacteria, such as Desulfovibrio sp. This occurs until the sulphate concentration falls to a point where it is outcompeted for the organic substrate by methanogenic bacteria. The sulphide produced by sulphate reduction is then removed or recycled by different processes depending on the environment of deposition. 

W14. Weismann, K., Intravenous zinc sulphate therapy in zinc-depleted patients. Der-matologica 159, 171-175 (1979). 

Eogenetic magnesite cement in sandstones is relatively rare because its formation requires pore waters to be enriched in Mg " " and depleted in Ca " ", S04 and Cl". These conditions may occur in arid climates in which marine pore waters evaporate and become successively saturated with respect to calcium carbonates, calcium sulphates and halite, such as in sabkha settings (Kinsman, 1969 Morad et al., 1995). Continental brines enriched in Mg + are also suitable for the formation of eogenetic magnesite due to the low sulphate and chloride ion concentrations. Most recent magnesite cements form in the fine-grained sediments of alkaline/saline lakes (Last, 1992 Warren, 1990) and, less commonly, in freshwater lacustrine sediments (Zachmann, 1989). 

Several concretions in the Pliocene, Mamoso-arenacea and Loiano formations possess calculated or whole-rock 6 C values more C depleted than -10%o. These have higher IGV values than other cemented samples (e.g. 31% for more C-depleted carbon samples vs. 14% for more C-enriched carbon samples in the Loiano), which indicates that they were cemented at shallower depths than most samples. But these earlier-phase concretions still formed after significant compaction had occurred, which would also be below the depth of sulphate survival. Mass balance calculations indicate that from 20 to 30% of the carbon in these more C-depleted cements must have been derived from the oxidation of methane, assuming that methanic carbon has a 6 C composition of at least -40%o (Curtis, 1977). 

Sulphate reduction becomes important when nitrate is depleted its products are carbon dioxide, water and hydrogen sulphide (Box 3.10). Sulphate reducers (e.g. Desulfo vibrio, Desuifolomaculum, Desulfobacter,... 

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