## 3 Results
### Mineralogical Analysis of Soil Samples
#### 3.3.2 X-ray Diffraction Spectra Analyses  
Figure 3 shows the XRD patterns of different particle size fractions. In the bulk soil samples, quartz, muscovite, dolomite, kaolinite, calcite, albite, and orthoclase were present. Through semi-quantitative calculation of the mineral components using Topas (Table 5), it was found that they varied greatly across particle size fractions, whereas they varied little across samples. Quartz existed in all fractions, but the distributions were uneven, accounting for 11.82% in clay in sample A and 11.56% in sample B, but exceeding 20% in the other fractions, especially sand, where its content exceeded 35%. Since quartz is the most stable primary mineral with strong weathering resistance [40], it is mainly found in sand and silt.  
Muscovite was the second most abundant mineral in the bulk soil after quartz, whereby it was also found in all particle size fractions, primarily concentrated in silt and fine sand, where its content was approximately 30%. It was also the main mineral in clay, with a content of 21.11%, but its content in coarse sand was only 12.74%. Dolomite was the third most abundant mineral in the bulk soil. It was distributed across all particle size fractions, but not uniformly, with high content in the coarse fractions and low content in the fine fractions. In both coarse sand and fine sand, the content of dolomite accounted for about one-fourth of the mineral composition, whereas its content in clay and silt was notably lower at 1.05% and 2.34%, respectively.  
Kaolinite is a layered silicate clay mineral, which was found in clay, silt, and fine sand, but no characteristic peak of kaolinite was identified in coarse sand. Its content accounted for 62.52% and 32.97% in clay and silt, respectively. The distribution of kaolinite was clearly enriched in the fine fractions, conforming to the general distribution law of secondary clay minerals [40]. The content of calcite decreased rapidly with particle size, accounting for 24.21% of coarse sand, whereas its content in other particle size fractions was lower than 8%. The contents of albite and orthoclase were low, and their characteristic peaks were not found in clay.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Sample** & **Fractions** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **CaO** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **K\({}_{2}\)O** & **P\({}_{2}\)O\({}_{5}\)** & **L.O.Ia** \\ \hline \multirow{6}{*}{A} & Bulk Soil & 48.19 & 15.08 & 10.08 & 5.31 & 2.48 & 1.97 & 0.23 & 14.99 \\  & Clay & 46.09 & 22.17 & 2.65 & 8.94 & 2.34 & 2.69 & 0.21 & 13.33 \\  & Silt & 49.03 & 18.19 & 5.78 & 6.84 & 2.14 & 2.45 & 0.21 & 13.9 \\  & Fine Sand & 50.14 & 14.09 & 10.1 & 4.87 & 2.96 & 1.82 & 0.26 & 13.97 \\  & Coarse Sand & 36.85 & 8.94 & 24.33 & 2.65 & 3.25 & 1.31 & 0.2 & 20.98 \\ \hline \multirow{6}{*}{B} & Bulk Soil & 48.92 & 14.87 & 10.65 & 5.21 & 2.55 & 2.12 & 0.24 & 15.32 \\  & Clay & 46.31 & 22.52 & 2.55 & 9.06 & 2.44 & 2.63 & 0.22 & 13.15 \\ \cline{1-1}  & Silt & 48.65 & 18.04 & 5.66 & 6.75 & 2.13 & 2.54 & 0.22 & 13.87 \\ \cline{1-1}  & Fine Sand & 50.22 & 14.18 & 11.21 & 4.98 & 3.18 & 1.78 & 0.26 & 14.09 \\ \cline{1-1}  & Coarse Sand & 36.98 & 9.03 & 24.23 & 2.47 & 3.28 & 1.32 & 0.21 & 20.88 \\ \hline \hline \end{tabular}  
* LO.Ia: loss on ignition; the amount that the sample lost on ignition at 2000 \({}^{\circ}\)C, usually including H\({}_{2}\)O and CO\({}_{2}\).  
\end{table}
Table 4: Chemical composition of different particle-size fractions (%).