Production of Dead-Burned Magnesia

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 

The Chemistry and Technology of Magnesia, by Mark A. Shand Copyright 2006 John Wiley Sons, Inc. 

AxiaLTC ircu inferential Timing Mechanisms Compaction Forces up to 900 tons 

The high boron content of seawater-grade magnesia (which can be as high as 0.3%), even if it is present in a few tenths of a percent, can be detrimental to the hot strength of magnesia refractories and markedly affect their service performance under extreme conditions (Davies and Havranek, 1965 Taylor et al., 1969). 

TABLE 9.1 Effect of Firing Temerature on the Densification, Crystal Size, and Hydration Tendency of 0.2% B203 Containing Magnesia Grain 

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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. 

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. 

Calcination temperature is very important in the production process and dictates the particle size, purity and reactivity of the product. A dead-burned, sintered dense microcrystaUine product is obtained at calcination temperature of 1,400 to 1,700°C. A caustic-burned product is obtained when magnesium carbonate or hydroxide is calcined at 600 to 700°C. A hght grade (specific gravity 2.9) highly reactive caustic-hurned magnesia that contains some moisture and carbon dioxide is obtained at about 600°C. A denser form from... 

Dead-burned magnesias can be used as aggregates as well as matrices for refractory products. Table 1 (15) shows the brand name, country of origin, chemical composition, and bulk density for a number of selected commercial dead-burned magnesias from naturally occurring sources, while Table 2 (16) exhibits the same information for several selected dead-burned synthetic and fused magnesias. 

It is also used as a reducing agent in the production of pure uranium and other metals from their salts. The hydroxide (milk of magnesia), chloride, sulfate (Epsom salts), and citrate are used in medicine. Dead-burned magnesite is employed for refractory purposes such as brick and liners in furnaces and converters. 

The various spinels can be produced in three ways for use in refractory products. In all cases, the starting raw materials for their manufacture involve a specific mixture of magnesia (calcined or dead-burned) and alumina... 

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