Intensification of the Oxidation of Lignite and Coal by an Activating Additive of Fe(NO3)2

Resumo

The oxidation of lignite and bituminous coal modified with an activating additive of Fe(NO₃)₂ (5 wt %) was investigated. Iron nitrate was applied by incipient wetness impregnation with the preliminary dissolution of Fe(NO₃)₂ in a water–alcohol solution with the volume ratio C₂H₅OH : H₂O = 50 : 50. The reactivity of the samples was studied by thermogravimetric analysis in the oxidation mode at a heating rate of 2.5 K/min in a temperature range of 25–600°C at atmospheric pressure. It was established that the use of the activating additive decreased the initial temperature of intense oxidation (Δt_i = 77°C) and shifted the overall process to the low-temperature region. The qualitative analysis of the gas-phase products of bituminous coal oxidation was performed by mass spectrometry, and it was found that a decrease in the initial temperature of the release of volatile compounds was associated with the decomposition of iron nitrate. The activation energies of oxidation processes in the presence of iron nitrate were calculated using the Coats–Redfern method. A maximum decrease in E_a (from 74.0 to 64.4 kJ/mol) was observed in a modified sample of bituminous coal. A possible mechanism of the action of iron nitrate, which leads to the activation of the oxidation processes of the test coals, is discussed.