The newly developed technology makes use of the high-intensity process of carbon-thermic reduction in the slag foam bath mode. The proposed electric-furnace processing of zinc-containing oxide materials has high parameters of electricity utilization, is environmentally clean, and releases a minimal amount of tail gases carrying zinc sublimates. It is also characterized by a high specific duty (at the level of autogenous processes), a high product purity, and the possibility of using a broad spectrum of carbon materials, including coal, as reducing agents. The products are demetallized slag, zinc sublimates, suitable for preparing zinc oxide pigment or metallic zinc, and iron in the form of pig iron or steel.

The technology is based on producing a slag foam layer in an electric furnace; in this layer, particles of the carbon reducing agent and carbonized iron mix, and this considerably intensifies the process of carbon-thermic reduction. The foamy slag layer is produced not by forced blowing but by the generated gaseous products of the reaction of oxide reduction under the slag layer. The high adsorption and heat-insulating properties of the slag foam rule out any release of dust and reduce heat losses; the latter, in turn, assures a long service life of the furnace lining and low power expenditures on smelting. The low heat conduction of the foamy slag layer enables a relatively low temperature of the slag (1200 to 1300°С) to be maintained at a considerable overheating of the metal layer on the furnace bottom (1400 to 1650°С). This makes it possible to produce and easily tap iron or steel.

Thanks to the selective reduction of zinc and iron oxides, the process can be used to produce zinc sublimates only - without any substantial reduction of the iron oxides. Because the foamy layer is formed without blowing, the amount of escaping gases is minimal, and the zinc sublimates can be efficiently collected.

What with the absence of dust formation or spraying, the primary materials used in the process and serving as the reducing agent as well can be in the pulverized form, and zinc sublimates of a high degree of purity can be prepared. The technology of smelting in a foamy slag layer achieves an extraction of zinc to a residual content of 0.01 to 0.05 mass % in the slag, with an efficiency 3 to 5 times greater than in conventional electric smelting (see Figure); electricity consumption is at the same time slashed by 35 to 45%. Low energy consumption makes the technology efficient in both big and small furnaces (0.5 to 1 ton capacity).

The technology can be used for directly producing iron from ores and concentrates, for comprehensively processing ores, slags, slurries, etc., and for deactivating toxic wastes with the extraction of nonferrous metals and iron.

The technology has been tested in an enlarged laboratory-scale electric furnace (100 kW power) in processing zinc-containing copper-production slag, nickel-production slag, and iron-ore concentrate for the direct preparation of iron.

Zinc content (mass %) in an oxide slag melt as a function of time (min.) in carbon-thermic reduction.

1. conventional reduction smelting;

2. reduction smelting in the foamy slag mode.

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