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Carbonatation is a slow process that occurs in concrete where lime (CaO, or Ca(OH) 2 ) in the cement reacts with carbon dioxide (CO 2) from the air and forms calcium carbonate. The water in the pores of Portland cement concrete is normally alkaline with a pH in the range of 12.5 to 13.5.
As lime in the form of limewater is added to raw water, the pH is raised and the equilibrium of carbonate species in the water is shifted. Dissolved carbon dioxide (CO 2) is changed into bicarbonate (HCO − 3) and then carbonate (CO 2-3). This action causes calcium carbonate to precipitate due to exceeding the solubility product.
Rain water contains dissolved carbon dioxide taken from the atmosphere. Some of the dissolved carbon dioxide reacts with the water to form carbonic acid, which remains in solution. Minerals containing calcium and magnesium form soluble bicarbonates when exposed to carbonic acid. Water containing these minerals is known as "hard water".
Calcium hydroxide is modestly soluble in water, as seen for many dihydroxides. Its solubility increases from 0.66 g/L at 100 °C to 1.89 g/L at 0 °C. [8] Its solubility product K sp of 5.02 × 10 −6 at 25 °C, [1] its dissociation in water is large enough that its solutions are basic according to the following dissolution reaction:
Soda lime canister used in anaesthetic machines to act as a carbon dioxide scrubber. Soda lime, a mixture of sodium hydroxide (NaOH) and calcium oxide (CaO), is used in granular form within recirculating breathing environments like general anesthesia and its breathing circuit, submarines, rebreathers, and hyperbaric chambers and underwater habitats.
Carbon dioxide (CO 2) from air (~ 412 ppm vol.) and bicarbonate (HCO − 3) or carbonate (CO 2− 3) anions dissolved in water react with the calcium hydroxide (Ca(OH) 2, portlandite) produced by Portland cement hydration in concrete to form calcium carbonate (CaCO 3) while releasing a water molecule in the following reaction: CO 2 + Ca(OH) 2 ...
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The lime industry is a significant carbon dioxide emitter. The manufacture of one tonne of calcium oxide involves decomposing calcium carbonate, with the formation of 785 kg of CO 2 in some applications, such as when used as mortar; this CO 2 is later re-absorbed as the mortar goes off.