## 3 Results  
### Solid-Liquid Partition Experiment  
In this experiment, the aqueous and non-aqueous liquids were not separated; as such, the amount of hexadecane retrieved from the liquid phase accounts for the dissolved and NAPL forms of this compound. Considering the physical-chemical properties of hexadecane, i.e., low water solubility (9.0 \(\times\) 10\({}^{-4}\) mg/L at 20 \({}^{\circ}\)C), low vapour pressure (1.9 \(\times\) 10\({}^{-1}\) Pa at 20 \({}^{\circ}\)C) and predicted log Kow = 8.6 and Koc = 2.9 \(\times\) 10\({}^{3}\) L/kg [48], adsorption to the organic carbon in soil can be mainly expected to occur.  
The mass of hexadecane recovered from the solid and liquid (aqueous and non-aqueous) phases, relatively to the different amounts added, are shown in supplementary material (Figure S1). More than 61% of the hexadecane added was retrieved from the solid phase, while only 1 to 4% was quantified in the liquid phase (Table 4), showing that this compound mostly adsorbed soil particles for all the concentrations tested. Total hexadecane recovery, calculated by the sum of the mass obtained from both solid and liquid phases, ranged from 64% to 109% (Table 4).  
In Figure 2, the distribution of hexadecane concentration between solid and liquid matrices is presented, highlighting once more the tendency of hexadecane for partitioning into the soil. The experimental results were adjusted to a Freundlich isotherm (Equation (2)) [49]. This equation is used here to describe the distribution of hexadecane in the soil (solid phase) versus in the liquid (aqueous and non- aqueous) phase. In this experiment,  
\[S=K_{f}C^{\frac{1}{h}} \tag{2}\]  
where \(S\) is the hexadecane concentration adsorbed on the solid phase (g/kg), \(C\) is the remained hexadecane concentration in the liquid (aqueous and non- aqueous phase) (g/L) and \(K_{f}\) and n are constants, specific for the adsorbate and adsorbent at a given temperature. The obtained parameters were: \(K_{f}\) = 0.004355 L/kg and \(n\) = 0.6712, with a \(R^{2}\) of 0.97. This correlation coefficient is satisfactory, suggesting that the Freundlich model can adequately describe hexadecane sorption characteristics.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Mass Added (mg)** & **Recovery from Solid Phase (\%)** & **Recovery from Liquid Phase (\%)** & **Total Recovery (\%)** \\ \hline
2.5 & 77.5 \(\pm\) 28.0 & 1.6 \(\pm\) 0.4 & 79.1 \(\pm\) 28.0 \\
5 & 107.6 \(\pm\) 0.7 & 1.3 \(\pm\) 0.8 & 108.9 \(\pm\) 1.0 \\
10 & 71.7 \(\pm\) 2.8 & 4.2 \(\pm\) 0.4 & 75.9 \(\pm\) 2.8 \\
25 & 61.1 \(\pm\) 2.0 & 2.7 \(\pm\) 0.4 & 63.9 \(\pm\) 2.0 \\
50 & 69.6 \(\pm\) 5.2 & 2.4 \(\pm\) 0.2 & 71.9 \(\pm\) 5.2 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Hexadecane recovery (%) from the solid and liquid phases and total recovery in the partition experiments.  
The ratio between the concentration of hexadecane adsorbed in soil and remaining in the liquid phase increases with the increase of hexadecane concentration, resulting in a convex curve (Figure 2). Therefore, for higher initial hexadecane concentrations, this compound will tend to adsorb more in soil and remain less in the liquid phase. This can possibly relate to the fact that at higher hexadecane concentrations, the surface of the soil particles may become covered by this compound, which potentially facilitates additional adsorption. Since in Figure 2 a plateau was not reached, the sorption capacity of the soil was not limited under the range of concentrations studied.