The Waelz Kiln is the dominant technology accounting for 80% of total crude zinc oxides production worldwide from EAF dust sources. In the Waelz process EAF steel dust is mixed with solid reducing agent and lime or silica, pelletized and then it is fed to the kiln and heated to reaction temperature to volatilize the non-ferrous metals like zinc and lead, while ferrous oxides are also reduced. The main components of the Waelz oxides are volatilized oxides of non-ferrous metals (Zn,Pb, Cd, etc.) and also halogens (mainly chlorides), alkaline metals (Na, K), and some sulphur oxide.

Nowadays, the major part of Waelz oxide is used by primary zinc smelters to produce electrolytic zinc. Because halogens content in the Waelz oxide have a detrimental effect in zinc electro-winning, the zinc smelters normally request a concentration of each CI and F not higher than 0.1%which requires a washing step. Nonetheless, the ratio of washed crude zinc oxides blended with sulphide concentrates that can be fed to the roaster is usually not higher than 10%. The direct feeding of washed Waelz oxide to the leaching is hardly applied.

Kiln Technical Details: