High Intensity Fuming Processes

A number of variants of this approach have been proposed and evalnated bnt there are no fnll-scale commercial operations solely for the purpose of zinc recovery. Two processes closest to commercial development for zinc applications are the Horsehead Flame Reactor and the Contop Hame Cyclone Reactor. 

Raw fume may be washed with water to remove halides. To prevent loss of zinc and other metals into the wash solution it is usual to use sodium carbonate solution for fume washing. This converts soluble zinc and other metal chlorides and fluorides to sodium chloride or fluoride and insoluble metal carbonates which are retained with the fume. Wash solutions are generally maintained at a pH of 9.0 to 9.2. Alternatively the fume can be first washed with water and the resulting solution treated with sodium carbonate or caustic soda to precipitate zinc (Chabot and James, 2000). 

Halides may be removed by heating the fume in a gas or oil fired rotary kiln to around 1200°C with a residence time of more than 12 honrs. This can remove over 90 per cent of the chlorine content and 

In general halogen removal improves with higher firing and exit temperatures. 

Rotary kilns used for de-halogenation require a capacity of the order of 0.6 m per tonne of raw fume processed per day, and typical kilns are of the order of 2.0 to 2.5 m OD and 20 to 30 m in length. Kiln slope is around 4° and refractory lining is typically 150 to 250 mm thick. Examples of commercial 

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