Carbothermic Reduction of Brazilian Linz–Donawitz (LD) Steel Sludges

Abstract

Carbothermic reduction was conducted using coarse (sample A) and fine (sample B) Brazilian Linz–Donawitz (LD) steel sludges and a sample of Peruvian anthracitic metallurgical coke (AMC) at 82.5% of fixed carbon. Specimens of 1 g of sample A and sample B preliminarily mixed with AMC at Fe/C: 1/2 were weighted. Sample A/AMC and sample B/AMC, reduction time and reduction temperature were identified as factors or independent variables. Conversions (α) or % reduction were selected as dependent variables. The values of weight ratios for sample A/AMC and sample B/AMC (3/7 and 7/3, respectively), reduction temperatures of 600 and 900 °C and reduction times lapses of 30 and 60 min, corresponding to their minimum as well as their maximum level of fluctuation respectively, were carried out via two design of experiments based in the factorial method 2³; one for each sample (A and B); using a Brazilian statistics software called COLMEIA—Snedecor algorithm F in order to evaluate the effects simple, double and multiple of factors over the conversions (α) or % Reduction. Carbothermic reduction tests were performed at the optimal weight ratio (sample A/AMC: 3/7 and sample B/AMC: 3/7), reduction temperatures: 600, 700, 800 and 900 °C and reduction times: 20, 30, 40, 50 and 60 min in order to estimate k-specific reaction rate constant, E_a-apparent activation energy and the A-Arrhenius pre-exponential frequency factor. The kinetic models that better fitted to the conversions (α) of both samples (A and B) were: boundary chemical reaction model for spherical symmetry (BCRM-ss): $1-{\left(1-\mathrm{\alpha }\right)}^{1/3}=\mathrm{kt}$ and the model of simple exponential continuous reaction (MSECR): $-\mathrm{ln}\left(1-\mathrm{\alpha }\right)=\mathrm{kt}$. The kinetic parameters obtained were: (1) sample A: E_a = 7. 45 − 8.08 kJ/mol and A = 0.009 − 0.032 Hz for a linear correlation between 0.8241 and 0.8276 and (2) sample B: E_a = 19.36 − 21.94 kJ/mol and A = 0.05 − 0.21 Hz for a linear correlation between 0.9758 and 0.9777.