Thermo-environmental evaluation of a modified Waelz process for hazardous waste treatment

Abstract

Electric arc furnace dust is a waste by-product of electric arc furnaces in steel production. This material is hazardous to the environment due to the presence of metals, such as chromium, lead, and cadmium; in addition to these, there is zinc in its composition. One of the main ways of recovering zinc from the electric arc furnace dust is carried out in rotary kilns called Waelz kilns. This work aims to develop a model of a Waelz kiln and evaluate the impact of processing sludge from an industrial effluent treatment plant as a feed along with electric arc furnace dust, with and without the inclusion of a drying system for the sludge and a thermal integration system with the Waelz slag. The model, validated against industrial data plant, revealed an optimum operational point, resulting in a zinc recovery of 98.3 %, which is equivalent to an increase in the production by 6.2 %. The scenario with direct sludge feed into the kiln resulted in a maximum zinc recovery rate of 89 %. The results from the sludge drying scenario imply a zinc recovery of 94 % and represent a viable alternative for reducing the amount of solid waste generated in the zinc production plants that use the Waelz kiln by 1100 t/year per tonne of sludge treated. Furthermore, it also increased zinc production to 1300 t/year.