Carbonate dissolution/solubility

Another interesting result of carbon dioxide solubility in water is that it constitutes the basis for the phenomenon of spontaneous and violent liberation of dissolved C02 to the atmosphere in a stratified lake, as in the case of Lake Nyos in Cameroon mentioned above (see Section 6.1.3). When dissolved C02 seeps from a hydrothermal vent into a stratified lake, the pressure and low temperature favor the dissolution and saturation in the lower strata of the lake. Because of its high solubility, more than five volumes of C02 can dissolve in one volume of water. As for any other gas, however, its solubility depends on temperature and pressure, making the... 

The fundamental parameter in all models for calcium carbonate dissolution in the deep sea is the saturation state of pore waters. In order to determine the samration state, not only must the composition of the pore waters be known, but also the solubility of the calcium carbonate. Therefore, many studies of carbonate chemistry in deep-sea sediment pore waters have focused on the apparent solubility behavior of carbonates in these sediments. 

Figure 2 Rate of carbonate dissolution from deep-sea sediment versus (1 — O). SoUd Une from Hales and Emerson (1996), dotted line from Keir (1980), dashed line from Atlantic Ocean, and dotted and dashed line from Pacific Ocean sediment results of Morse (1978). Note that Hales and Emerson (1996) used a different calcite solubility product.

Dissolution of carbonates can only occur if the solution is undersaturated with regard to the solid carbonate. The solubility equilibrium of carbonates and especially of calcite has been discussed extensively in Chapters 4 and 7. 

Addition or removal of CO2 in an aqueous environment is regulated by life processes, primarily by respiration and photosynthesis. Respiration increases the amount of CO2, causing a drop in pH and CO3 concentration and therefore a higher solubility of CaCOs, thus promoting carbonate dissolution. Photosynthesis decreases the amount of CO2 in waters causing an increase in pH and COl" concentration (and therefore a lower solubility of CaC03) and thus promotes carbonate precipitation. 

Murray RW, Leinen M, Isem AR (1993) Biogenic flux of A1 in the central equatorial Pacific Ocean Evidence for increased productivity during glacial periods. Paleoceanogr 8 651-670 Murray RW, Knowlton C, Leinen M, Mix AC, Polski CH (2000) Export production and carbonate dissolution in the central equatorial Pacific Ocean over the past 1 Ma. Paleoceanogr 15 570-592 Nancollas GH, Amjad Z, Koutsoukas P (1979) Calcium phosphates-speciation, solubility, and kinetic considerations. Am Chem Soc Symp Ser 93 475-497... 

In theory, the lysocline records the sedimentary expression of the saturation horizon, that is the depth-dependent transition from waters oversaturated to waters undersaturated with respect to carbonate solubility (Figure 4). The lysocline thus marks the top of a depth zone, bounded at the bottom by the CCD, over which the bulk of carbonate dissolution in the ocean is expected to occur in response to saturation state-driven chemistry. The thickness of this sublysocline zone, as indicated by the vertical separation between the lysocline and CCD, is variable and is governed by the rate of carbonate supply, the actual dissolution gradient, and... 

The corrosion film of basic zinc carbonate is soluble in clean rain. The dissolution depends on the residence time of rain on the galvanized steel surface. 

For cathode materials, stmctural strength, low dissolution rates in molten electrolyte and good electrical conductivity are required. Nickel oxide is used as the cathode material due to its structural strength and limited solubility in carbonates. Dissolution of nickel ions may occm- leading to formation of Ni ions in the electrolyte. Furthermore, the Ni ion may move towards the anode and be precipitated out. The precipitation of Ni may cause an internal short-circuit of the cell and hence loss of power. At high CO2 pressure, the following reaction may take place ... 

Compounds which dissolve in concentrated sulphuric acid may be further subdivided into those which are soluble in syrupy phosphoric acid (A) and those which are insoluble in this solvent (B) in general, dissolution takes place without the production of appreciable heat or colour. Those in class A include alcohols, esters, aldehydes, methyl ketones and cyclic ketones provided that they contain less than nine carbon atoms. The solubility limit is somewhat lower than this for ethers thus re-propyl ether dissolves in 85 per cent, phosphoric acid but re-butyl ether and anisole do not. Ethyl benzoate and ethyl malonate are insoluble. 

Sucralfate. Sucralfate [54182-58-0] (Carafate) (6) is a white amorphous powder soluble in dilute hydrochloric acid and sodium hydroxide. It is practically insoluble in water, ethanol, and carbon tetrachloride. Dissolution of aluminum occurs at pH <3. It may be prepared by the method described in Reference 7. 

For some non-ferrous metals (copper, lead, nickel) the attack by sulphuric acid is probably direct with the formation of sulphates. Lead sulphate is barely soluble and gives good protection. Nickel and copper sulphates are deliquescent but are gradually converted (if not leached away) into insoluble basic sulphates, e.g. Cu Cu(OH)2)3SO4, and the metals are thus protected after a period of active corrosion. For zinc and cadmium the sulphur acids probably act by dissolution of the protective basic carbonate film. This reforms, consuming metal in the process, redissolves, and so on. Zinc and cadmium sulphates are formed in polluted winter conditions whereas in the purer atmospheres of the summer the corrosion products include considerable amounts of oxide and basic carbonate. ... 

Up to this point, we have focused on aqueous equilibria involving proton transfer. Now we apply the same principles to the equilibrium that exists between a solid salt and its dissolved ions in a saturated solution. We can use the equilibrium constant for the dissolution of a substance to predict the solubility of a salt and to control precipitate formation. These methods are used in the laboratory to separate and analyze mixtures of salts. They also have important practical applications in municipal wastewater treatment, the extraction of minerals from seawater, the formation and loss of bones and teeth, and the global carbon cycle. 

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