# Effect of Particle Size on Composet Analysis by Portable X-ray Fluorescence
## 3 Results and Discussion
### Influence of the Particle Size on the Elemental Concentration Determined by pXRF Fractions  
The concentrations of several elements in the different particle size fractions (after milling them) of the three composts are shown in Figure 1. As can be seen in the figure, important variations were found for all of the elements between the different size fractions. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & **Certified** & **Average** & **Recovery,** & **Minimum** & **Maximum** & **Average** \\  & **Value,** & **Value,** & **\%** & **Recovery,** & **\%** & **RD 1, \%** \\  & **mg kg\({}^{-1}\)** & **mg kg\({}^{-1}\)** & & **\%** & **\%** & **\%** & **\%** \\ \hline Ag & 15 & 19.8 & 131.8 & 86.3 & 178.6 & 32.9 \\ As & 76 & 78.2 & 102.9 & 73.8 & 131.7 & 11.8 \\ Ba & 990 & 837 & 84.5 & 78.2 & 91.8 & 15.5 \\ Cd & \textless{}10 & 15.3 & - & 75.0 \({}^{2}\) & 149.8 \({}^{2}\) & 37.6 \({}^{2}\) \\ Cr & 49.6 & 53.7 & 108.3 & 73.1 & 151.1 & 19.1 \\ Cu & 236 & 222 & 93.9 & 75.8 & 105.8 & 6.6 \\ Mn & 1038 & 843 & 81.2 & 74.9 & 93.4 & 18.8 \\ Ni & 48.8 & 63.6 & 130.4 & 77.0 & 170.3 & 33.3 \\ Pb & 808 & 812 & 100.6 & 96.1 & 104.8 & 1.8 \\ Rb & 149 & 135 & 90.5 & 86.5 & 94.2 & 9.5 \\ S & 970 & 1117 & 115.2 & 77.4 & 156.5 & 18.3 \\ Sb & 107 & 98.9 & 92.4 & 83.4 & 110.0 & 8.6 \\ Sr & 144 & 142.2 & 98.8 & 92.8 & 103.1 & 1.8 \\ Th & 14.2 & 15.7 & 110.3 & 74.4 & 142.2 & 34.7 \\ Ti & 1798 & 1360 & 75.6 & 65.8 & 83.3 & 24.4 \\ Zn & 760 & 713 & 93.9 & 87.3 & 99.5 & 6.1 \\ K \(\times 10^{-3}\) & 41.5 & 37.1 & 89.3 & 76.6 & 95.4 & 10.7 \\ \({}^{3}\) Fe \(\times 10^{-3}\) & 18.4 & 18.4 & 99.8 & 97.5 & 103.0 & 5.0 \\ \({}^{3}\) Ca \(\times 10^{-3}\) & 6.00 & 5.62 & 93.6 & 87.8 & 96.9 & 10.0 \\ \({}^{3}\) Si \(\times 10^{-3}\) & 343 & 279 & 81.4 & 73.6 & 93.4 & 21.8 \\ \hline \hline \end{tabular} \({}^{\dagger}\) Average value of the absolute relative deviations; \({}^{2}\) relative deviations calculated in relation to the average value; \({}^{3}\) for these elements, measurements were conducted in the precalibrated mining mode; for the rest of the elements, the measurements were performed with the precalibrated soil method.  
\end{table} 
Table 3: Performance of the instrument: variations in daily measurements (N = 21) of the certified reference material sediment SdAR-M2. As a rule of thumb, the concentrations of the elements included in Figure 1 were higher in the finer fractions, with the exception of K, Cu, and S in the alperujo compost. The most remarkable differences were in the MSW compost in which the concentrations of Zn, Cu, Pb, and S almost doubled in the finer fraction (<0.5 mm) compared to the coarse fractions (2-5 and >5 mm). In this compost, the concentrations of Fe and K were also higher in the fine fractions, although the differences were less significant. These results are in agreement with previous studies [8; 9] carried out on MSW comp  
Figure 1: Concentrations of various elements in the ground granulometric fractions of the sludge compost, MSW compost, and alperujo compost. Bars with the same lower letter do not differ statistically according to [PERSON]’s test (\(p<0.05\)). In the sewage compost, higher concentrations of Zn, Pb, Fe, and S were observed as the fraction was finer, although the differences were less notable than in the MSW compost. In the alperujo compost, higher concentrations of Zn and Fe were observed in the finer fraction (<0.5 mm) and a higher concentration of K in the coarser fractions, greater than 0.5 mm. The reasons that justify these variations may be different and specific for each compost depending on its origin and nature. It is a known fact that in soils, the concentrations of trace elements increase as the particle size decreases, which is associated with the adsorption of these elements by the clays [22; 23]. In addition, in compost, finer fractions have been shown to accumulate heavy metals [9; 10]. In previous studies, the size fractionation highlighted Cd, Cu, Zn, and Pb accumulation in the fine-sized fractions, while Cr and Ni accumulated in the coarsest [24].