RESEARCH ARTICLE Potentially toxic elements in fly ash dependently of applied technology of hard coal combustion Danuta Smolka-Danielowska 1 & Dorota Fiedor 1 Received: 13 March 2018 /Accepted: 13 June 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Coal combustion is one of the most significant anthropogenic sources of thallium in the environment. This study presents the results of determination of thallium and some toxic elements (Pb, Cd, As, Ni, Zn, and Cu) concentration in fly ash produced in the coal combustion in conventional furnaces (pulverized coal furnace and grate furnace), in a fluidized-bed furnace with circulation bed, and in a home furnace. The high content of thallium was determined in ash produced in the grate furnace (on average 10.7 mg/kg) and fluidized-bed furnace with circulation bed (6.6 mg/kg). The average content of Tl in the fly ash of the pulverized coal furnace and in the home furnace is 1.7 and 2.4 mg/kg, respectively. There was a strong relationship between the occurrence of Tl and As, Cd, Pb, Cu, and Zn in ash from grate and pulverized coal furnace. Keywords Thallium . Coal combustion . Trace elements . Environment pollution Introduction Thallium compounds (III) have the similar toxicity as mercury compounds (II) and less-toxic thallium compounds (I) are about 10 times more toxic than lead compounds (II). According to Ensafi and Rezaei (1998), the lower valence status is more toxic and the trivalent status is generally less reactive. Thallium compounds have a variety of bioavailabil- ity and toxic properties, so the speciation of thallium is very important in the environment (López Antón et al. 2015). Thallium is characterized by high toxicity. It exhibits muta- genic, carcinogenic, and teratogenic effects. In nature, thallium is mainly found in sulfide minerals (Duffy and Van Loon 2007; Lukaszewski et al. 2010). Concentration of thallium in galena (PbS) may be 1.4– 20 mg/kg; in sphalerite (ZnS), 8–45 mg/kg; in pyrite (FeS 2 ), 5–23 mg/kg; and in chalcopyrite (CuFeS 2 ), up to 5% (Lis et al. 2003; Muszyńska et al. 2015). The main anthropogenic sources of thallium are emission from coal combustion, min- ing processing of iron ores and non-ferrous metals, cement production, and solid waste disposal (Hršak et al. 2003; Peter and Viraraghavan 2005; Lukaszewski et al. 2010). Thallium content in hard coal is 0.5–3 mg/kg (Lin and Nriagu 1998; López Antón et al. 2015). According to Jinghai and Chang (2016), the concentration of thallium in coal, ash, soil, and sediment was between 0.07 and 0.2 mg/kg. In the combustion process, thallium tends to concentrate in the finest ash fraction, which may contain from 29 to 76 mg/ kg of this element (López Antón et al. 2015). Thallium tends to concentrate in the smaller size ash fractions (Natush et al. 1974; ATSDR 1991). About 40% of Tl was distributed in the gas phase and 60% in the fly ash (López Antón et al. 2013). The speciation of thallium in fly ash is unknown, but it is a critically important determinant of its leaching behavior (Testoff 2013). In cement kiln dust, the thallium content can be up to 400 mg/kg (42–2380 mg/kg) (Zhang et al. 2004; Xiao et al. 2004; Kabata-Pendias and Szteke 2012). The annual emission of thallium from the power plants in the world is about 700 μg/m 3 and from the cement plant almost 2500 μg/m 3 (López Antón et al. 2015). In Poland, about 38 million tons of hard coal is burned annually, of which over 26% in individual home furnaces (GUS 2015). Power plants equipped with pulverized coal, grate, and fluidized-bed furnaces have dust extraction systems (e.g., electrostatic precipitators, multicyclones). The fly ashes Responsible editor: Philippe Garrigues * Danuta Smolka-Danielowska danuta.smolka-danielowska@us.edu.pl 1 Department of Geochemistry, Mineralogy and Petrography, Faculty of Earth Sciences, University of Silesia, Będzińska Str. 60, 41-200 Sosnowiec, Poland Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-2548-3