Cinética de digestão alcalina da franklinita presente na lama fina de aciaria LD

Abstract

The present study aimed to evaluate the kinetic aspects of the thermal digestion of franklinite contained in the fine fraction of basic oxygen furnace (BOF) sludge, in the presence of NaOH. This was done in order to remove the zinc contained in the waste to be reused in the steelmaking production. A zinc content of 2.4% was found in the studied sludge, from which 70% occurs as franklinite, a spinel phase that is refractory to alkaline leaching. Therefore, a digestion step with NaOH is necessary in order to convert franklinite into soluble species in the NaOH solutions and, this way, recover iron species with initial content of around 60%. It was observed that the digestion reaction stabilizes after 15-25min, being favored at intermediate temperatures (300-400oC) and disfavored above this range. Analysis of X-Ray Diffraction and Mössbauer spectroscopy were not conclusive to identify properly the participating reacting species. Kinetic studies revealed that the reaction is controlled by nucleation and growth. Data fitted into Avrami-Erofeevs model and the calculated activation energy of the reaction was found to be 5.38 kcal/mol.