Magnesia dead burned

In the early days of the Dow Chemical process for producing magnesium metal, tonnes of Oyster shells were used as a source of pure calcium carbonate for the preparation of magnesia from seawater. 

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Dead-burned magnesia, characterized by large crystaUite size and very low chemical reactivity, is resistant to the basic slags employed in the metals refining industry. It reacts very slowly with strong acids, and does not readily hydrate or react with carbon dioxide unless finely pulverized. 

Table 20. Purity of Dead-Burned Magnesia from Various Processes ...

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. 

The production of chemical-grade magnesia or light-burned MgO requires careful control of the calcination temperature to achieve the required specific surface area of the finished product. A furnace well suited to this requirement is the multiple-hearths Herreshoff-type. For the production of dead-burned magnesia typically shaft or rotary kilns are employed. See Chapter 5 for furnaces used in MgO production. 

Dead-burned magnesia is used almost exclusively for refractory applications, primarily in brick and basic granular refractories. The essential qualities of dead-burned magnesite that make it suitable for refractory applications are that it has a very high melting point (2800°C), it does not oxidize, and it has excellent resistance to attack by iron oxide, alkalis, and... 

In general the properties of particular dead-burned magnesia will depend largely on the amount and distribution of the impurities present. Table 9.3 displays the effect of the CaO/Si02 ratio in the magnesia on the mineral phases formed and their melting temperatures. 

A basic oxygen furnace is shown in Fig. 27.2 and a cross-section is given in Fig. 27.3. The furnace is lined with dead-burned magnesia refractory impregnated with carbon, lypically the charge consists of molten iron at about 1250 °C (80 %), scrap iron (18 %), plate iron (1 %) and iron ore (1 %). Varying the amount of... 

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

Dead burned magnesia with chromite Fused magnesia Magnesia-carbon bricks... 

Magnesite China, Russia, Slovakia, Turkey, and Spain 19,000,000 Caustic magnesia 200 Dead burned magnesia 400 Electrofused magnesia 600... 

BRITE. Basic Research in Industrial Technologies in Europe/European Research on Advanced Materials - a European Community programme of research including advanced ceramics. Britmag. Trade-name dead-burned magnesia made by the seawater process... 

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