Arc Fuming process for smelting and reduction

This slag fuming process can be used for melting and reduction of various types of raw materials. The process has so far been applied to recover zinc oxide from steel plant dust in a plant with the capacity 40 000 ton of dust per year.

Energy for smelting and reduction is transferred to the slag with gas (normally air) that is heated in plasma generators. To get a reducing gas a fuel like LNG, oil etc is added to the hot air before it enters the slag bath. The required degree of oxidisation is easy to control with the air/fuel ratio.

The smelting operation has few limitations in terms of particle size, moisture content in raw material or chemical composition. The feed preparation is simple and consists of mixing dust with slag additives and, for reduction, coal, coke breeze, pet-coke etc. to a pre-decided mixture with suitable moisture content.

The smelting and fuming furnace is charged with pre-mixed material by a system of feeding bin and conveyer belts. The feed drops directly from the belt into the furnace and the foaming slag bath.

The steel plant dust melts in the turbulent liquid slag bath. Reduction gas and solid reduction agents added to the feed material will reduce metal oxides. Zinc oxide is reduced to metallic gaseous zinc that leaves the slag bath with the reduction gas. Iron oxide is reduced to FeO that forms a slag mainly containing iron oxide, silica and lime. The gas mixture is after-burned by addition of compressed air just above the slag bath. The zinc vapour is converted into zinc oxide dust while carbon monoxide and hydrogen are oxidized into carbon dioxide and steam. The small zinc oxide particles are carried by the off-gas through a gas cooling system and are collected in a bag filter. The slag that remains in the furnace is tapped intermittently.