The Conventional Slag Fuming Furnace

The first commercial installation of the standard slag fuming furnace was at the Asarco, East Helena lead smelter in Montana in 1927, and this furnace design has subsequently been applied at a number of other major lead smelters. Copper smelter slags rich in zinc are also processed in conventional slag turners such as at Boliden s Ronnskar smelter in Sweden, and at the Hin Flon smelter of Hudson Bay Mining and Smelting Company. 

A typical furnace has cross-sectional dimensions of 2.4 m wide by 6.4 m long and 6.4 m high. The walls are made of rows of water jackets, with three rows each of seven jackets making up each long side for the typical size. The floor is also made up of water-cooled panels. There are three tuyeres in each lower jacket, giving 21 tuyeres per side. Furnaces may vary in size by varying the number of side waU panels, but the width is usually constant and dictated by the depth of penetration of the blast from the tuyeres into the melt (Hancock, Hart and Pelton, 1970 Ashman et al, 2000). 

The water-cooled panels or jackets freeze a protective layer of slag on their iimer surface, which can be studded to assist in adherence of slag. This form of containment rather than refractories has been chosen because of the aggressive conditions and the high turbulence and abrasive nature of the bath, and has been highly successful with jacket life extending well over ten years and up to 20 years. 

The price of this form of containment is the additional fuel required to compensate for the relatively high heat loss throngh the jackets to maintain the protective slag layer. Water is circulated through the 

ZnO reduction, acting as a buffer that limits the initial rate of zinc reduction. Because of this effect close control of the heating cycle of a batch fuming process to minimise magnetite formation is an important issue. 

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As an alternative to the conventional slag fuming furnace, a top submerged lance slag bath reactor may be used for zinc fuming. In this process fuel as gas, oil or pulverised coal is injected with oxygen... 

For a reactor containing 1 m slag depth, the slag contained is approximately 3 t/m of cross-section and the zinc depletion rate is thus of the order of 0.121 of zinc fumed per hour per square metre of furnace cross-section. This represents a crude indication of reactor capacity only, as gas flow rates are also a major determining parameter and can differ significantly from the conventional slag fumer in relation to bath cross-sectional area. 

An important development in concrete mix design has been the addition of so-called supplementary cementitious materials. Two classifications apply to these compoimds Pozzolans, such as fly ash and silica fume, react with the cement hydration products, notably calcium hydroxide hydraulic materials, such as granulated blast furnace slag, undergo direct hydration reactions. As these materials are of lower cost than conventional cement and essentially represent environmental waste products, there are obvious incentives for blending them in concrete mixes. As pointed out by Hansson, these materials can improve the strength and durability of concrete, with the important proviso that the concrete is cured adequately. 

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