Application of stepwise isothermal analysis method in the kinetic study of reduction of basic oxygen furnace dust Eduardo Junca • Thomaz Augusto Guisard Restivo • Denise Crocce Romano Espinosa • Jorge Alberto Soares Teno ´rio Received: 14 July 2014 / Accepted: 23 January 2015 Ó Akade ´miai Kiado ´, Budapest, Hungary 2015 Abstract Basic oxygen furnace (BOF) dust is a by-product of steel plants that is rich in iron oxide. Reduction of this by- product may provide reutilization alternatives in steel indus- try. In this context, kinetic study was conducted using BOF dust pellets applying the forced stepwise isothermal analysis method. This work examines the reduction of BOF dust pellets using a mixture between hydrogen and carbon monoxide. Mass loss of 26 % was obtained after reduction of the BOF. Carbon oxide present in the reducing gas led to the formation of a carbon layer around the pellet between 550 and 650 °C. At higher temperatures, from 700 to 850 °C, it was observed that reduction was controlled by porous diffusion. In the range 900–1,000 °C, the control mechanism was determined as re- active species diffusion through metallic alloy lattice in in- dividual particles. Keywords Thermogravimetry  Kinetic analysis  Solid–gas reaction  By-product of steel-making Introduction Steel is produced basically by two routes. The first route is carried out in blast furnace and basic oxygen furnace (BOF), where the blast furnace produces pig iron and BOF is responsible to refine it in steel. The second route employs the electric arc furnace, where the raw material used is often steel scrap. However, BOF process is re- sponsible for 60 % of total iron produced worldwide. In this process, it is generated typically 10–20 kg of dust by ton of iron [1, 2]. In Brazil, during 2013, the production of crude steel was 34.1 million tons. In this way, it is possible to estimate a generation around 340 ktons of dust from BOF [3–5]. This dust is composed basically of iron, calcium, magnesium, silicon, zinc and lead [6, 7]. Meanwhile, the main element is iron. This element may be found as hematite, magnetite and wustite phases [8]. In this way, this dust has potential to be reused in the own steel plants as a source of iron. However, studies should be performed to improve it. Kinetic investigation is an important tool for determin- ing the reaction and the kinetic parameters, such as acti- vation energy, pre-exponential coefficient and reaction order. In addition, based on the results, the mechanisms that are involved in a reaction, including the control mechanisms, can be identified. The activation energy is the most studied parameter in a kinetic investigation. The concept of energy activation according to Atkins and De Paula [9] is the minimum ki- netic energy that the reagent needs to have in order to form the product. Soresen [10, 11] described an interesting method for kinetic investigation known as stepwise isothermal analysis (SIA). In this technique, the user stipulates the range of reaction rate establishing maximum and minimum values for reaction rate [12]. Once a heating rate has been estab- lished, as soon as the reaction rate reaches a programmed maximum value, the system commands the onset of an isotherm. With the progress of the reaction, the reaction E. Junca (&)  T. A. G. Restivo Department of Metallurgical and Materials Engineering, University of Sa ˜o Paulo, Av. Prof. Mello Moraes 2463, Sa ˜o Paulo, SP 05508-900, Brazil e-mail: eduardojunca@gmail.com T. A. G. Restivo University of Sorocaba, Rod. Raposo Tavares km 92,5, Sorocaba 18023-000, Brazil D. C. R. Espinosa  J. A. S. Teno ´rio Department of Chemical Engineering, University of Sa ˜o Paulo, Av. Prof. Lineu Prestes, 580, Sa ˜o Paulo, SP 05424-970, Brazil 123 J Therm Anal Calorim DOI 10.1007/s10973-015-4491-6