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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.
The following chart shows the solubility of various ionic compounds in water at 1 atm pressure and room temperature (approx. 25 °C, 298.15 K). "Soluble" means the ionic compound doesn't precipitate, while "slightly soluble" and "insoluble" mean that a solid will precipitate; "slightly soluble" compounds like calcium sulfate may require heat to precipitate.
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:
CaO + H 2 O → Ca(OH) 2 Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O. In a laboratory, calcium carbonate can easily be crystallized from calcium chloride (CaCl 2), by placing an aqueous solution of CaCl 2 in a desiccator alongside ammonium carbonate [NH 4] 2 CO 3. [10] In the desiccator, ammonium carbonate is exposed to air and decomposes into ammonia ...
The less soluble Mg(OH) 2 precipitates because of the common ion effect due to the OH − added by the dissolution of Ca(OH) 2: [7] Mg 2+ + Ca(OH) 2 → Mg(OH) 2 + Ca 2+ For seawater brines, precipitating agents other than Ca(OH) 2 can be utilized, each with their own nuances: Use of Ca(OH) 2 can yield CaSO 4 or CaCO 3, which reduces the final ...
In other term, the C-S-H or the serpentine are less rich in Ca and Mg respectively. This is why the reaction leads to the elimination of the excess of portlandite (Ca(OH) 2 ) and brucite (Mg(OH) 2 ), respectively, out of the silicate system, giving rise to the crystallization of both hydroxides as separate phases.
Both reactions share in common the continuous regeneration of the sodium hydroxide (NaOH) after the reaction of soluble sodium carbonate or sodium silicate with calcium hydroxide, Ca(OH) 2. However, impure dolomitic aggregates also often contain clay impurities, and small amounts of pyrite (FeS 2) and organic matter. The alkali-carbonate ...
Burning (calcination) of calcium carbonate in a lime kiln above 900 °C (1,650 °F) [4] converts it into the highly caustic material burnt lime, unslaked lime or quicklime (calcium oxide) and, through subsequent addition of water, into the less caustic (but still strongly alkaline) slaked lime or hydrated lime (calcium hydroxide, Ca(OH) 2), the ...