Transformational roasting in the treatment of metallurgical wastes

Abstract

The development of the concept of transformational roasting, or roasting with the addition of a solid reagent to produce a desirable mineralogical change in the starting material, is discussed. Preliminary results from the transformational roasting of several samples of metallurgical waste, including zinc ferrite residue, electric arc furnace dust and matte electrorefining residue, with Na₂CO₃ are also presented. This research shows that transformational roasting of these materials with Na₂CO₃ can effectively increase the solubility of valuable elements, such as Zn, Cu or Ni, produce a differential solubility between valuable and harmful elements (e.g. between Zn and Cr or between S or As and Cu or Ni) by using different leaching reagents, or control the emission of volatile elements during roasting (e.g. S and As). The addition of secondary additives during roasting with Na₂CO₃, in turn, allows for improved control over the solubility of a major impurity (e.g. Fe).