Utilisation of residues of nickel production in EAF steelmaking route

A stock of over 100 Mt of residues (colas or tailings) from metallurgical production of nickel exists presently in Cuba with concentrations of around 0.4 wt% Ni, 42 wt% Fe and 2.0 wt% Cr. The annual production of colas in year 2005 will be about 10 Mt/year. The aim of this study is to develop a sustainable recycling concept in EAF steelmaking route for utilizing a part of those residues, thus reducing impact on the environment and recycling valuable materials. Experiments have been carried out in suitably equipped 50 kg lab-scale electric induction furnace by adding, inserting or injecting of tailings at 1 600°C with or without reducing agents (e.g. coal) to study recovery of the metals contained to the steel melt. The experiments were carried out under equilibrium, quasi-equilibrium and non-equilibrium conditions. Thermodynamical calculations at RWTH lab-scale conditions had shown nearly complete reducibility of the compounds NiO, Fe₃O₄and Cr₂O₃from the colas. The experimental conditions have confirmed this, resulting in about 90% recovery of Ni, 80% of Cr and 99% of Fe. Industrial tests at Antillana de Acero in Cuba in a 1.5 ton EAF with the injection of tailings in combination with coal have presented around 75% of recovery of chromium, 100% of nickel and 85% of iron.