Metal carbonates solution equilibria

Eq. (4e)] is not reduced by metal-ammonia solutions so that the existence of this equilibrium cannot lead to further reduction of the saturated ketonic product only protonation on carbon can result in further reduction (see page 39). 

Figure 12.4. Stability lines for various metal-carbonate or metal-hydroxide species in solution as a function of pCC>2- The data were generated employing MINTEQ2A by assuming equilibrium with metal-carbonate solids without allowing formation of metal-hydroxide solids (from Evangelou, 1997, unpublished data, with permission).

A long time contact of the dissolved fraction with particulate matter can produce changes in the distribution of chemical forms of heavy metals in solution. Any change in the equilibrium conditions after collection can promote or remove dissolved metals (54) or desorption of adsorbed metals operated by particulate. Biological activity involves photosynthesis and respiration which will change the carbon dioxide content of the water and its pH. All the equilibrium reactions affected by pH will be altered, e.g., the reactions of precipitation, complexation and redox involving heavy metals. 

Group 4 transition aza-metal-diene complexes have received considerable attention because of their unique M-N and M-C bonding properties and their high reactivity toward a broad range of electrophiles and unsaturated hydrocarbons. Reduction of CpTiCl3 with magnesium in THF in the presence of the appropriate 1-aza-l,3-diene affords the 1-aza-l,3-diene titanium complexes CpTiCl[N(R)CH=C(Me)CH(Ph)] (Scheme 217). Spectroscopic data indicate that the aza-diene ligands adopt a cis-supine conformation in the case of the Buc derivative a solution equilibrium with the /)nw-disposition is observed. The chemical shifts of the terminal carbon atoms of the aza-diene... 

The three Salem samples show increased leaching rates as a function of increased acidity, but not the rate values predicted by simple chemical stoichiometry. A pH decrease from 5.6 to 4.0 is a 39.8x increase in acidity, while a change from 4.0 to 3.0 is a 10x acidity increase. The observed changes were factors of 2.88x and 1.58x, respectively. These discrepancies can be attributed to the complex equilibrium interactions involved in the solubilities of the metal carbonates. These two solubility equilibria are further complicated by the two acid equilibria for the carbonic acid/bicarbon-ate/carbonate system in addition to the equilibrium solubility of congas in water. The solution of these simultaneous equilibria processes to determine the relationship between carbonate solubility and acid concentration is a non-trivial one (sixth degree in concentration). This solubility problem has been approached from several different viewpoints (31-35), the most convenient being a graphical solution of the solubility as a function of initial solution and final solution pH. From this method, it can be theoreti-... 

As seen, the studies of CO3- dissociation under non-equilibrium conditions are connected with the solubility of the C02 formed in ionic melts. The greater the solubility value, the higher the degree of holding C02 by the ionic solvent that retarded the decomposition of carbonate solutions. To obtain some information on the solubility of carbon dioxide in molten alkali metal halides over a wide temperature range we shall consider the following works. 

To determine the solubilities of alkaline-earth carbonates in molten KCl-NaCl we used the calibration-like method [350], which consisted in the addition of weights of the substance studied to the solvent with subsequent measurement of the equilibrium e.m.f. Let us consider the applicability of such a technique to our case. The increase in the total initial concentration of alkaline-earth metal carbonate in the solution leads to the growth of ion concentrations on the right-hand side of equation (3.7.66) quite naturally, their product should also increase. Under the constant pressure of C02 (1 atm) the concentration of carbonate ion is proportional to that of O2- according to the simple relationship... 

As is well known, alkaline-earth metal-oxides possess a limited solubility in molten chlorides at 1000 K. In the saturated solutions of these oxides equilibrium (3.6.1) takes place. Therefore, there are two simultaneous reactions in the carbonate solutions, namely, equations (3.6.1) and (3.7.66), which may result in the precipitation of a solid phase. For equation (3.6.1) all we have said above for the carbonate remains true, i.e. the plateau (Fig. 3.7.23, sections 1-3) may also be a result of alkaline-earth metal-oxide precipitation. 

The previous systems for the recovery of metal ions have been primarily concerned with solutions containing only one metal ion. With mixed metal ion solutions there are thermodynamic and kinetic limitations which can effect the selectivity of the system and the final metal deposit. With some mixed metal ion solutions the difference in equilibrium potentials for the reactions can indicate that selective electrodeposition is probable, e.g. with solutions of zinc or cadmium and copper in dilute sulphuric acid solutions as used in fluidised bed electrolysis. Another example is the use of a flow-by carbon felt electrode in the extraction of Cu, Pb and Hg in a batch recirculating reactor [27]. The felt was of fibre diameter 1.1 x 10 m, with a porosity of 0.91 and a specific area of 2200 m By fixing the... 

Ferri D, Grenthe I and Salvatore F 1983 Studies on metal carbonate equilibriums. 7. reduction of the tris (carbonato) dioxouranate (vi) ion, uo2 (co3) 34-, in carbonate solutions. Inorganic Chemistry 22(21), 3162-3165. 

Chemical condensation This occurs when soluble corrosion products or atmospheric contaminants are present on the metal surface. When the humidity exceeds that in equilibrium with a saturated solution of the soluble species, a solution, initially saturated, is formed until equilibrium is established with the ambient humidity. The contaminants have already been detailed and of the corrosion products, obviously sulphates, chlorides and carbonates are most important in this context. However, in some cases there is a lack of reliable data on the vapour pressure exerted by saturated solutions of likely corrosion products. The useful data was summarised in Table 2.7. 

Two other methods of monitoring impurity levels in loop or reactor systems are based on the equilibration of metals with the solution of the nonmetal in sodium. Oxygen may be evaluated by the vanadium wire equilibrium method " and carbon by the use of stainless steel or nickel equilibration. Neither of these methods gives continuous monitoring of the impurity, but each is employed in a regular sampling system. 

Coprecipitation is a partitioning process whereby toxic heavy metals precipitate from the aqueous phase even if the equilibrium solubility has not been exceeded. This process occurs when heavy metals are incorporated into the structure of silicon, aluminum, and iron oxides when these latter compounds precipitate out of solution. Iron hydroxide collects more toxic heavy metals (chromium, nickel, arsenic, selenium, cadmium, and thorium) during precipitation than aluminum hydroxide.38 Coprecipitation is considered to effectively remove trace amounts of lead and chromium from solution in injected wastes at New Johnsonville, Tennessee.39 Coprecipitation with carbonate minerals may be an important mechanism for dealing with cobalt, lead, zinc, and cadmium. 

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