Carbon dioxide oversaturation

Carbon dioxide oversaturation is important only in fresh water. Not a single example of oversaturation with C02 has been reported from the sea, presumably a result of an efficient buffering system. In the ocean, the partial pressure of C02 varies within a narrow range, from 1.7 x 10-4 near the surface to 9.9 x 10 4 at 5000 m depth. In enclosed seas, the range is wider. For example, in the Black Sea these values are 3-3.9 x 10"4 in near-surface water and 20-25.8 x 10-4 in deep water (Alekin, 1966). 

In this connection equilibrium and aggressive carbon dioxide are distinguished. Equilibrium carbon dioxide is its concentration, at which water is saturated with calcite and the dissolution process is absent. At degassing, the solution loses CO and becomes oversaturated with calcite. Then part of calcite precipitates. Contrary to that, excess of CO facilitates the dissolution of additional portions of calcite, and that is why it is called aggressive carbon dioxide. 

Another way is fast removal of carbon dioxide, e.g., by bubbling inert gas through the melt, this favors high oversaturation providing faster crystallization processes as compared with the first case. The obtained oxide crystals will possess smaller sizes that result in formation of fine size mixtures, which can be used for subsequent thermal treatment. And the fourth stage consists of separation of the oxide crystals from melts, which can be done using different ways, which in essence are not so difficult to be specially discussed here. 

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