Demineralisation of lignites by single and successive pretreatment☆

In this study, two Turkish lignites (Bolu-Mengen, Kütahya-Tunçbilek) were treated under atmospheric and reflux conditions with 10–30% NaOH, 10% HCl and 10% H2SO4 solutions, singly and/or successive treatments to determine the effects of this treatment on the mineral matter and acidic functional groups. Characterisation of the treated and untreated samples was by Fourier transform infrared spectroscopy. The process of successive pretreatment was found to be more effective than single steps in terms of demineralisation and removal of carboxylate structures. During NaOH treatment, the first of successive steps, salts soluble in acid but not in water were determined. In successive demineralisation steps with 30% NaOH and 10% HCl, a low level of 3.3% ash was obtained for the Tunçbilek lignite. In addition, during the pretreatment, most of the Ca and K were exchanged with Na.