Selective recovery of metals

Metal oxides, like baghouse dust from electric arc steelmaking or secondary materials such as complex slag are fed into a slag bath where the reactions take place.

A reducing agent, for example coal, is fed into the slag. Due to the excellent mixing produced by the plasma heated gas, the different metal oxides are reduced according to the equilibrium determined by slag temperature and oxygen potential.

The slag temperature is controlled by the plasma power and the oxygen potential by the coal feed rate. The accurate controllability of the process makes it possible to reduce zinc and lead oxides from EAF (electric arc furnace) baghouse dust to metal while keeping the iron as oxide in the slag. Metals with a high vapour pressure such as lead and zinc will leave the furnace as metal vapour. The off-gas exits the furnace at about 1300°C and has to be cooled and cleaned to separate the metals and metal oxides from the fuel gas.

With high contents of volatile metals a condenser can be used to recover these metals from the gas. With lower contents it might be more convenient to burn the flue gas and thereby oxidize the metals, which then are collected in a bagfilter.