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, 1M ammonium acetate, 0.2M ammonium oxalate/0.2M oxalic acid, acidic solution of H2O2and a 6M solution of HCl. The concentrations of the different elements obtained in the extractions were statistically analyzed. 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.

Četiri uzorka mlevenog lignita korišćenog u Termoelektrani "Nikola Tesla A" u Obrenovcu u Beograda su podvrgnuta sekvencijalnoj ekstrakcija koja se sastojala od pet faza: u prvoj je korišćena destilovana voda, u drugoj 1M amonijum-acetat, u trećoj 0,2M amonijum-oksalat i 0,2M oksalna kiselina, u četvrtoj kiseo rastvor H2O2 i u petoj 6M rastvor HCl. Dobijene koncentracije izabranih elemenata su statistički analizirane, kako bi se utvrdile veze između različitih elemenata. Najveći deo ispitivanih elemenata je uglavnom asociran sa ekstrahovanom neorganskom fazom uglja, samo aluminijum silicijum, hrom i arsen imaju unutar ekstraktibilnog dela elemenata veću organsku/sulfidnu frakciju od neorganske. Od jedinjenja rastvornih u petoj fazi ekstrakcije uglja, alumosilikati magnezijuma su nosilac arsena, cinka olova, bakra i hroma, silikati kalijuma nosilac olova i nikla, mešoviti aluminati gvožđa i magnezijuma nosilac arsena, cinka, bakra i hroma, a jedinjenja gvožđa koja nisu povezana sa aluminatima ni magnezijumom nosilac mangana. U trećoj fazi ekstrakcije uglja se rastvaraju alumosilikati kalijuma i magnezijuma asocirani sa bakrom, dok su jedinjenja gvožđa rastvorna u trećoj fazi ekstrakcije asocirana sa cinkom i hromom. Interfazna korelaciona analiza je pokazala da se adsorbovana i jonoizmenjiva frakcija većine ispitivanih elemenata ne vezuje preferencijalno za delove neorganske matrice čestica pepela.