Caustic-calcined magnesia

Excludes caustic-calcined magnesia used in tiie production of lefiactory magnesia. 

Accurate Chinese production figures are difficult to obtain however, it is estimated that the total production capacity of magnesia in China is about 2.7 Mt per annum. This comprises of 1.8 Mt of dead-burned magnesia and 900,000 tonnes of caustic-calcined magnesia. The purity of the magnesite ranges from 91 to 98% loss-free MgO content. 

A typical temperature profile for calcining magnesite to produce caustic-calcined magnesia in a MHF is shown in Figure 5.2. 

Caustic-calcine magnesias are calcined below 900°C and are characterized by moderate to high chemical reactivities. They are readily soluble in dilute acids and hydrate rapidly in cold water. They also slowly react with atmospheric moisture and carbon dioxide to form the basic carbonate, 5MgO 4C02 xH20. Common test methods for determining the reactivity... 

Magnesium oxide has very limited solubility in water. However, an accurate determination is complicated by trace quantities of dissolved carbon dioxide in the water and the purity of the sample, where the presence of lime can introduce error. Another complicating factor is the source of the periclase and what heat treatment it had received. All these factors influence the rate at which equilibrium is reached in solution and hence solubility. Many solubility measurements have been made that have produced a wide variation in results. The most accurate determination to date has produced a result of 8.6 mg/L at 30°C. Caustic-calcined magnesia readily hydrates to the hydroxide on exposure to moisture. 

The purer grades of seawater magnesia have proved more difficult to densify during calcination owing to the lower concentration of mineralizing impurities. To overcome this difficulty, high-pressure pelletization of caustic-calcined magnesia is used. It has been demonstrated that there is an optimum calcination temperature for maximum fired density after... 

Magnesia, caustic-calcined Magnesia clinker Magnesia, dead-burned Magnesia, fused Magnesia oxide fume... 

The product obtained is called caustic-calcined magnesia (CCM), also called natural magnesia. The purity of CCM ranges usually between 75 and 96 wt.% MgO, with most of the impurities (e.g., Fe 03, AI3O3, SiOj, etc.) coming from the raw material used. 

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