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The temperature at which limestone yields calcium oxide is usually given as 825 °C, but stating an absolute threshold is misleading. Calcium carbonate exists in equilibrium with calcium oxide and carbon dioxide at any temperature. At each temperature there is a partial pressure of carbon
When seawater is undersaturated, meaning the concentration of calcium and carbonate ions is below the saturation point, it becomes challenging for marine calcifiers to build and maintain their skeletal structures, as the equilibrium conditions favor dissolution of calcium carbonate. [6]
CaCO 3 can also be dissolved through metabolic dissolution (i.e. can be used as food and excreted) and thus deep ocean sediments have very little calcium carbonate. [16] The precipitation and burial of calcium carbonate in the ocean removes particulate inorganic carbon from the ocean and ultimately forms limestone. [16]
When water that contains dissolved calcium carbonate is warmed, CO 2 leaves the water as gas, this reduces the amount involved in the reaction causing the equilibrium of bicarbonate and carbonate to re-balance to the right, increasing the concentration of dissolved carbonate.
The root of the word calcination refers to its most prominent use, which is to remove carbon from limestone (calcium carbonate) through combustion to yield calcium oxide (quicklime). This calcination reaction is CaCO 3 (s) → CaO(s) + CO 2 (g). Calcium oxide is a crucial ingredient in modern cement, and is also used as a chemical flux in smelting.
It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. In 1936, Wilfred Langelier developed a method for predicting the pH at which water is saturated in calcium carbonate (called pH s). [26] The LSI is expressed as the difference between the actual system pH and the saturation pH: [27]
Calcium carbonate is more soluble at lower temperatures and at higher pressures. It is also more soluble if the concentration of dissolved CO 2 is higher. Adding a reactant to the above chemical equation pushes the equilibrium towards the right producing more products: Ca 2+ and HCO 3 − , and consuming more reactants CO 2 and calcium ...
Calcium carbonate is also excreted at high rates during osmoregulation by fish, and can form in whiting events. [37] While this form of carbon is not directly taken from the atmospheric budget, it is formed from dissolved forms of carbonate which are in equilibrium with CO 2 and then responsible for removing this carbon via sequestration. [38]