Slags normalized compositions

Bowen [2J (pp. 167-8) has stated that metallurgical slags have occasionally proved toxic to plants but the normal composition of slags does not indicate the presence of any element at levels which would be likely to produce phyto-toxic effects at appropriate levels of application. 

In the blast furnace reduction slag-making materials are also added together with a small amount of iron, the function of which is to reduce any sulphide which remains, to the product of the roasting operation to produce a sinter. The sinter is then reduced with coke in a vertical shaft blast furnace in which air is blown tluough tuyeres at the bottom of tire shaft. The temperature in the heartlr where metal is produced must be controlled to avoid the vaporization of any zinc oxide in the sinter. The products of tlris process are normally quite complex, and can be separated into four phases. Typical compositions of these are shown in Table 13.1. 

The compositions of the slags from these viscosity tests are listed in Table II. (The compositional data are normalized to 100% the median closure on raw analytical data was 94.2%.) Also included are several other parameters that traditionally have been employed to characterize coal-ash slags. It should be emphasized that, unless otherwise noted, all calculations discussed herein were based on slag composition data (as opposed to ash composition data). This was done primarily for two reasons ... 

As a consequence of their variation in chemical composition, the toxicological properties of MMMF vary over a big range. Their carcinogenic potency increases in the series normal glass wool < rock wool < slag wool < ceramic fibers < asbestos. 

Montmorillonite may or may not break down (dissociate) into its constituent parts when coal is burned if it does dissociate, then, upon cooling, it may recombine with other elements or minerals to form mineral deposits on the inside surfaces of furnaces and boilers. This process (slagging or fouling) produces barriers to heat exchange in the affected equipment, which can substantially reduce its efficiency and require costly repairs. Illite, however, with its simpler composition, does not canse snch problems under normal furnace operating conditions. Where these two clay minerals and others occur, their relative abundances, relationships to other minerals, and exact compositions are snbjects for continued research in coal quality. 

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