Development of a combined solid and liquid wastes treatment integrated into a high purity ZnO hydrometallurgical production process from Waelz oxide

- Novel process developed to treat residual heavy metals from secondary zinc recycling.
- Ammonia removal from hydrometallurgical exhausted liquors to be reused.
- Improvement to increase the sustainability of the zinc and steelmaking industries
- The study of benefits obtained combining the solid and the liquid wastes treatment.

Electric Arc Furnace Dust (EAFD) is an important hazardous waste from the steel production industry, due to its heavy metals content. It is recycled through a pyrometallurgical process to generate a Zn and Pb concentrate called Waelz oxide. This concentrate can be processed hydrometallurgically in order to obtain high purity ZnO. But this hydrometallurgical process also generates as wastes different solid residues with high content of heavy metals and a liquid waste stream with significant concentrations of ammonia and heavy metals. This is why the objective of this work is to design a process that can simultaneously treat these solid and liquid wastes. In the developed process, an alkaline solution is used to leach solid residues so as to produce an inert final waste. After filtration, the leaching liquor is mixed with the liquid waste in order to increase its pH and to enhance the ammonia evaporation by air stripping. This stripped stream can be recycled to the leaching stage of the Waelz oxide treatment process. Furthermore, the ammonia stripping precipitates the dissolved heavy metals as a zinc concentrate that can be commercialized as a raw material for the metallic zinc production industry. Therefore, the developed process reduces by more than half the wastes generation, increases the Zn recycling yield > 5% and recovers > 75% of the needed ammonia for the fresh leaching liquor.