Speciation of selected trace and major elements in lignite used in "Nikola Tesla A" power plant (Obrenovac, Serbia)

Abstract

Four samples of milled lignite used in the "Nikola Tesla A" power plant, located in Obrenovac near Belgrade, were subjected to a five-step sequential extraction, comprising of the following phases: distilled water, 1 M ammonium acetate, 0.2 M ammonium oxalate/0.2 M oxalic acid, acidic solution of H2O2 and a 6 M solution of HCl. The concentrations of the different elements obtained in the extractions were statistically analysed. The majority of the examined elements were found to be most probably associated with inorganic fractions of lignite, only aluminum, silicon, chromium and arsenic have a larger extractable organic/sulfide fraction than an extractable inorganic fraction. Alumosilicates of magnesium (carriers of arsenic, zinc, lead, copper and chromium), silicates of potassium (scavengers of lead and nickel), mixed aluminates of iron and magnesium (carriers of arsenic, zinc, copper and chromium) and compounds of iron that do not contain aluminum and magnesium (scavengers of manganese) were dissolved in the fifth phase of the sequential extraction. Copper is a substrate of alumosilicates of potassium and magnesium, while zinc and chromium are substrates of compounds of iron leached in the third phase of the sequential extraction. Interphase correlation revealed that the adsorbed and ion-exchangeable fractions of most of the examined elements do not exhibit preferential binding to the components of the inorganic matrix of lignite ash.