## 3 Results
### The Form of Occurrence of Elements in Fuels  
3.2.1. Waste Paper and Cardboard  
The high fibre plant material content and low ash content of the waste paper are interesting in terms of its further energy use. Corrugated cardboard contains up to 95% of organic matter, while printing paper contains 70-100% of organic matter and 0-30% of inorganic matter. The chemical composition of the paper depends on the type or grade of the paper. Paper is a heterogeneous mixture of fibre plant material--mostly cellulose, hemicellulose and, in smaller quantities, lignin or various compounds of lignin (Na-ligate) and inorganic compounds (filler). The fibre in newsprint is composed of 45.6% cellulose, 31.3% hemicellulose, and 23.1% lignin [36]. In paper production, to improve surface characteristics of paper, the following chemical compounds are used as precipitators and stabilizers: aluminium sulphate, aluminium chloride hydroxide, aluminium formate, aluminium nitrate, and sodium aluminium components [37]. A significant component of the paper is coating pigments (4%) and chemical additives (3-8%), whose use depends on the grade of the paper [38]. Printing is also the source of trace elements in waste paper. The main components of the inks are colouring substances (5-30%), binders (15-50%), solvents (15-65%), and additives (1-10%). Lead compounds PbCrO\({}_{4}\), PbSO\({}_{4}\), and PbO are used to produce yellow and green dyes and pigments [39]. Lead is also part of white ink. The main component of cyan in the colour printing processes is copper (II) phthalocyanine blue (C\({}_{32}\)H\({}_{16}\)CuN\({}_{8}\)). Nickel occurs as part of multiple colourants [40]. The content of major elements and selected trace elements in CB is shown in Table 4. The source of the major inorganic elements in the waste paper is the filler used. By concentration, major elements form the series Ca > Si > Al > Fe = K = S > Ti, while the order of trace elements is Mn >> Zn > Cu > Pb > Ni = Cr. The high Ca content is related to the use of calcium carbonate or calcium sulfate as a filler (0-25%) in the production of paper [41]. Silicates may also be used as a filler--clay, talk and oxides (titanium oxide). Mn is a biogenic element derived from wood biomass that occurs in wood and wood biomass at a concentration of 430 mg/kg [43]. As a filler and for enhancement of coating, Zn is used in the form of ZnO, ZnS, and lithophone (a blend of BaSO\({}_{4}\) with ZnS) in the production of cardboard products [42], which explains the highest levels of Zn in PB compared to WM and CB. Manganese is present in biomass as an essential element [44]. During repeated recycling of waste paper, there is a further increase in the concentration of Mn, but also of other elements Zn, Ni, Cu ([PERSON] et al., 2021), which probably explains the higher levels than Elmas and Cmar [37] reported for the cardboard used in the food industry, where the content of selected trace elements is capped by the \"Packaging Waste Directive 2018/852/EU\" [45]. \begin{table}
\begin{tabular}{l c c c c c c c c c c c c c c c} \hline \hline  & **Al** & **Si** & **Ca** & **Fe** & **Ti** & **P** & **S** & **k** & **Cl** & **Mn** & **Cr** & **Ni** & **Cu** & **Zn** & **Pb** & **As** \\ \cline{2-13}
**Waste Paper** & & & & & **\%** & & & & & & & & & **mgkg** & & \\ \hline PB & 0.67 & 1.76 & 7.85 & 0.23 & 0.11 & 0.12 & 0.21 & 0.22 & 263.6 & 520 & 7 & 9 & 54 & 95 & 25 & 3 \\ WOP & 0.036 & & 8.30 & 0.37 & & & & & & & & & & 14 & \\ Card board & **0.034-114** & & & & & & & & & & & 0.5-6.2 & 0.9-4.9 & 0.2-167 & 1.4-61.3 & 1.4-12.8 \\ Paper & **0.03-114** & & & & & & & & & & & 0.5-2.7 & 3.3 & 0.5-17.3 & 3.0-10.1 & 1.4-12.8 \\ Paperboard & **0.14-0.56** & & & & & & & & & & 0.9-27.0 & 0.9-2.5 & 0.9-49.7 & 1.4-7.4 & 1.5-11.1 \\ Corrugated board & **0.12-0.40** & & & & & & & & & 1.3-6.2 & 25.4-4.9 & 0.2-166.6 & 14.0-61.3 & 1.4-12.8 \\ \hline \hline \end{tabular}  
* [PERSON] et al. [41]; *
* [PERSON] [42]; **
* [PERSON] and [PERSON] [37] WOP—Waste office paper.  
\end{table}