Calcium carbonate, reduction concentrations

Two of the study systems, Lake Michigan and Pond 3513, exhibit cyclic behavior in their concentrations of Pu(V) (Figure 2 and 3). The cycle in Lake Michigan seems to be closely coupled with the formation in the summer and dissolution in the winter of calcium carbonate and silica particles, which are related to primary production cycles in the lake(25). The experimental knowledge that both Pu(IV) and Pu(V) adsorb on calcium carbonate precipitates(20) confirms the importance of carbonate formation in the reduction of plutonium concentrations in late summer. Whether oxidation-reduction is important in this process has not been determined. 

In a review of the course and mechanism of the catalytic decomposition of ammonium perchlorate, the considerable effects of metal oxides in reducing the explosion temperature of the salt are described [1], Solymosi s previous work had shown reductions from 440° to about 270° by dichromium trioxide, to 260° by 10 mol% of cadmium oxide and to 200°C by 0.2% of zinc oxide. The effect of various concentrations of copper chromite , copper oxide, iron oxide and potassium permanganate on the catalysed combustion of the propellant salt was studied [2], Similar studies on the effects of compounds of 11 metals and potassium dichromate in particular, have been reported [3], Presence of calcium carbonate or calcium oxide has a stabilising effect on the salt, either alone or in admixture with polystyrene [4],... 

All these results are related to observations and measurements in the field as well as from oxalotrophic bacterial cultures in the laboratory (Braissant et al, 2004). There is no theoretical model available to explain the oxalate-carbonate transformation and its consequences on the soil solution properties, i.e. alkalinization facilitating precipitation of calcium carbonate (CaCOs) and CO2 release into the atmosphere. This kind of model should be able to explain the process of oxido-reduction reactions, pH regulation and the evolution of the various phase concentrations involved in the system, i.e. oxalate, carbonate, water and CO2. This is the aim of the next section. 

Janes, Neumann and Sethna ° reviewed the general subject of solid lubricant composites in polymers and metals. They pointed out that the reduction in mechanical properties with higher concentrations of solid lubricant can be offset by the use of fibre reinforcement. Glass fibre is probably the most commonly used reinforcing fibre, with carbon fibre as a second choice. Metal and ceramic fibres have been used experimentally to reinforce polymers, but have not apparently been used commercially. To some extent powders such as bronze, lead, silica, alumina, titanium oxide or calcium carbonate can be used to improve compressive modulus, hardness and wear rate. 

Walter and co-workers (Walter and Burton, 1990 Walter et al., 1993 Ku et al., 1999) have made extensive efforts to demonstrate the importance of dissolution of calcium carbonate in shallow-water carbonate sediments. Up to — 50% carbonate dissolution can be driven by the sulfate reduction-sulfide oxidation process. In calcium carbonate-rich sediments there is often a lack of reactive iron to produce iron sulfide minerals. The sulfide that is produced by sulfate reduction can only be buried in dissolved form in pore waters, oxidized, or can diffuse out of the sediments. In most carbonate-rich sediments the oxidative process strongly dominates the fate of sulfide. Figure 6 (Walter et al., 1993) shows the strong relationship that generally occurs in the carbonate muds of Florida Bay between total carbon dioxide, excess dissolved calcium (calcium at a concentration above that predicted from salinity), and the amount of sulfate that has been reduced. It is noteworthy that the burrowed banks show much more extensive increase in calcium than the other mud banks. This is in good agreement with the observations of Aller and Rude (1988) that in Long Island Sound siliciclas-tic sediments an increased bioturbation leads to increased sulfide oxidation and carbonate dissolution. 

Attempts by Smith and ToUens " to oxidize n-fructose with bromine by the method of Clowes and Tollens were unsuccessful a double compound of D-fructose and calcium bromide was obtained. No yield of this product was given. The reaction mixture of D-fructose, calcium carbonate, water and bromine was shaken until all the bromine had dissolved, after which the double compound was separated from the concentrated solution. The calcium bromide was formed from the interaction of calcium carbonate with hydrogen bromide in the reaction solution. The hydrogen bromide could be formed in two ways by the hydrolysis of bromine in water (reaction 1, page 134) or by the reduction of bromine during the oxidation of D-fructose. The former is the more probable explanation, but a blank run without the ketose was not attempted. 

Phase 3 exhibits a far-reaching emptying of the carbonate buffer in the slag. This is correlated with low pH-values, buffered by the still-present oxides and silicates. Compared to phase 2, elevated trace metal concentrations can be expected. Temporal development of alkalinities in several examples from Swiss MSWI incineration landfills (Baccini et al. 1993) indicate the expected sequence of depletion of individual buffer substances. In the young deposit there are still calcium hydroxide and other effective bases, but these components are depleted in the older deposits. In the medium-age deposits ( 10 years old), there is a typical reduction of the calcium silicate and bicarbonate, whereas calcium carbonate is not changed to any great extent. 

When sulfate reduction occurs, sulhde can react with iron to form pyrite. This decreases the amount of phosphorus that is bound with iron and results in more available phosphorus. Inorganic phosphorus retention is regulated by pH, Eh, phosphate concentration (there is a limited amount of substrate for adsorption), concentrations of Ee, Al, and calcium carbonate, and temperature. 

But the major reduction of heat is accomplished by evaporation. As we evaporate and concentrate cooling water, dissolved minerals soon would reach levels at which scale deposits would form, in the absence of corrective measures. Calcium carbonate scale control is a major concern. 

The next approach to scale control was reduction of potential calcium carbonate by acidification of makeup water. Sulfuric acid is added to reduce alkalinity and convert most of the calcium bicarbonate to calcium sulfate. Calcium sulfate is soluble up to about 1,700 parts per million in cooling waters at ordinary temperatures, whereas calcium carbonate solubility is less than 30 ppm. So by slightly acidifying makeup water we greatly reduce tendency for calcium carbonate deposition. The calcium sulfate level in concentrated cooling water is controlled by bleed-off adjustment—manually or automatically. 

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