Behavior of zinc, iron and calcium from electric arc furnace (EAF) dust in hydrometallurgical processing in sulfuric acid solutions: Thermodynamic and kinetic aspects

• Different behaviors of Zn, Fe and Ca in sulfuric acid solutions were demonstrated.
• Leaching mechanisms of Zn, Fe and Ca were determined from shape of kinetic curves.
• Ca in solution is given by limited solubility and not by experimental conditions.
• Pilot-scale process for processing EAF dust is designed on the basis of the results.

This work is focused on the behavior of zinc, iron and calcium during leaching EAF dust in sulfuric acid solutions. The influences of leaching time, temperature, sulfuric acid concentration and L:S (Liquid:Solid) ratio on the extraction of zinc, iron and calcium were studied. The leaching experiments were preceded by a thermodynamic study consisting of calculations of ΔG0 and E–pH diagrams of the Zn–Fe–Ca–S–H2O system. A thorough characterization of the input sample of EAF dust was performed. The highest zinc extraction, 87%, was achieved by using 1 M H2SO4 at the temperature of 80 °C and L:S ratio 50. From the perspective of a selective leaching of zinc, where no iron is passing into the solution, concentration 0.1 M H2SO4 at L:S ratio = 50 and 0.25 M H2SO4 at L:S ratios = 20 and 10 can be considered as optimal concentrations. The calculated values of the activation energy confirmed different mechanisms of leaching zinc, iron and calcium. The rate limiting step in the case of zinc and calcium is represented by a rate of diffusion, while in the case of iron it is a rate of chemical reaction.