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Solutions containing magnesium sulfate are generally more aggressive, for the same concentration. This is because magnesium also takes part in the reactions, replacing calcium in the solid phases with the formation of brucite (magnesium hydroxide) and magnesium silicate hydrates. The displaced calcium precipitates mainly as gypsum.
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO 4 ·2H 2 O. [4] It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster , drywall and blackboard or sidewalk chalk .
2)) present in the hardened cement paste to give gypsum: H 2 SO 4 + Ca(OH) 2 → CaSO 4 · 2H 2 O. When concrete is carbonated by atmospheric carbon dioxide (CO 2), or if limestone aggregates are used in concrete, H 2 SO 4 reacts with calcite (CaCO 3) and water to also form gypsum while releasing CO 2 back to the atmosphere: H 2 SO 4 + CaCO 3 ...
To better understand the conversion process of hydroxide anions in oxide and water, it is necessary to consider the autoprotolysis of the hydroxyl anions; it implies a proton exchange between two OH −, like in a classical acid–base reaction: + → + or also, 2 OH − → O 2− + H 2 O
Chemical pulping involves dissolving lignin in order to extract the cellulose from the wood fiber. The different processes of chemical pulping include the Kraft process, which uses caustic soda and sodium sulfide and is the most common; alternatively, the use of sulfurous acid is known as the sulfite process, the neutral sulfite semichemical is treated as a third process separate from sulfite ...
Magnesium hydroxide is an inorganic compound with the chemical formula Mg(OH) 2. It occurs in nature as the mineral brucite. It is a white solid with low solubility in water (K sp = 5.61 × 10 −12). [5] Magnesium hydroxide is a common component of antacids, such as milk of magnesia.
Calcined gypsum is an alternative material in industrial plasters and mortars. Cement, cement kiln dust, fly ash, and lime kiln dust are potential substitutes for some construction uses of lime. Magnesium hydroxide is a substitute for lime in pH control, and magnesium oxide is a substitute for dolomitic lime as a flux in steelmaking. [28]
Alternatively, gypsum (calcium sulfate, CaSO 4 · 2 H 2 O) can also be applied as a source of Ca 2+ ions to replace the sodium at the exchange complex. [9] Gypsum also reacts with sodium carbonate to convert into sodium sulphate which is a neutral salt and does not contribute to high pH.