Isotopic composition of lead in Czech coals

The content and isotopic compositions of lead (Pb) were studied on selected coal samples from the Czech Republic. Simultaneously, the forms of bonding of Pb in coal were studied using sequential extraction (1M ammonium acetate, 3 M HCl, 48% HF and 2 M HNO3). Lead in most samples of bituminous and brown coal is mobilized by 3 M HCl, while sulphides are already oxidized in the studied samples at the beginning of the extraction (1 M ammonium acetate). Thus, Pb could be bonded in carbonates and oxides and also to sulphides present in the coal. Following decomposition of the sulphides, Pb is adsorbed on the remainder of the solid phase and is released only in the acidic medium of the second extraction solution (i.e. 3 M HCl).Bituminous coal contains an average of 33 mg/kg Pb, while brown coal contains an average of 8.9 mg/kg Pb. The 206Pb/207Pb ratio varies in the range 1.167–1.234 for bituminous and 1.172–1.24 for brown coal. No inverse proportionality of the Pb content and the 206Pb/207Pb ratio was observed in the studied samples and, thus, the Pb content in most samples is a result of the combination of lithogenic and ore Pb. Only several samples with high uranium contents exhibited a highly radiogenic 206Pb/207Pb ratio (> 1.3). It was not possible to demonstrate any statistical dependence between the operational defined speciation of Pb, the mineralogical composition and the Pb isotopic composition.