Effects of treatments on the mineral matter and acidic functional group contents of Turkish lignites

Abstract

Six Turkish lignites were treated with solutions of HCl or EtONa at ambient temperature or at 150°C. The proximate analysis, forms of sulfur, acidic functional groups and calcium contents of the raw and treated lignites were determined. The solutions after treatment were analysed for calcium. The effects of the treatment on certain structural components of the lignites varied from one lignitie to another. HCl treatment was effective in ash reduction and in the transformation of carboxylate species to carboxylic acids, but not in desulfurization. The ash reduction was accompanied by an increase in combustible sulfur. EtONa treatment was effective in desulfurization but not in ash reduction or in the removal of chelate- or salt-forming cations. The results suggested that this treatment promoted selective cleavage of certain chemical bonds, such as ester, ether or carbon-sulfur bonds, resulting in an increase in acidic functional groups of the lignites, desulfurization and partial dissolution. FT-i.r. spectroscopy and X-ray diffractometry provided some additional evidence regarding the changes in lignite structure due to the treatments.