## 3 Results and Discussions  
### Physical-Chemical Monitoring  
Figure 1 shows the results of the EC monitoring in the batches with CS and SS soils for all of the L/S ratios. In all experiments EC reached asymptotical equilibrium values at the end of the monitoring period (48 h). All of the soluble salts passed in the water phase in a relatively small amount of time, which is typical of sandy materials characterized by large pore throats [26; 27]. Graphene showed lower values of EC for almost every treatment and L/S ratio. This was possibly due to the capability of Graphene to incorporate solute complexes and large dissolved ions within its honeycomb lattice [28]. Graphene's EC values were very close to Control and to Zeolites' EC values for L/S = 5, and L/S = 10. Biochar showed the highest value of EC for all L/S ratios, according to [PERSON] et al. [29] and [PERSON] et al. [12], mainly due to the dissolution of carbonates formed during the combustion process. Figure 2 shows the results of EC variations in response to the increasing L/S ratios. To directly compare the results with L/S = 1, the EC values measured in the batches with L/S > 1 were multiplied by factor 2, 5, and 10, respectively. It can be noticed that EC logarithmically increased in the CS and SS Control, reaching an asymptotic value of 500 uS/cm at L/S 10. This occurred since the larger amount of liquid phase respect to solid phase allowed a complete dissolution of precipitated salts, witnessing an availability control mechanism [16]. Biochar and Compost batches released more ions in solution respect to the Control since they release soluble nutrients such as N, P, and K [12], as witnessed by their statistically different values from the Control for all L/S ratios. This was not the case for Graphene and Zeolites CS batches at L/S = 5 and L/S = 10, which were statistically different from the Control only for CS L/S = 10. EC lowering respect to the Control was likely due to ions and complexes incorporation and sorption onto Zeolites nanotubes [30] and due to sorption and lattice incorporation for Graphene [28]. In general, EC values increased with the increase of L/S ratios, meaning that the dissolution in batches was dependent on L/S ratio. Therefore, if the aim of the experiment is to delineate the maximum amount of soluble salts released, a high L/S ratio must be employed. Additionally, SS characteristics were completely different than CS characteristics (Table 1), but the effect of the L/S ratio used was similar for both soils. This implies that the effect of L/S ratio is independent on the type of solid matrix for sandy soils. Figure 1: EC trends in SSE batches experiments with CS (**left panels**) and SS (**right panels**) for different L/S ratios. Error bars denote standard deviation calculated on three replicas. Figure 2: EC values variation in SSE batches with CS (**left panels**) and SS (**right panels**) soils versus L/S ratios at the end of the monitoring period. Error bars denote standard deviation calculated on three replicates, while lines are the best fit natural logarithmic curves. Different letters indicate statistically different means at 0.05 confidence. Figure 3 shows the results of pH monitoring in the batches with CS and SS soils for all L/S ratios. As for EC, the pH reached asymptotical equilibrium values at the end of the monitoring period. pH values in CS batches were generally higher than in SS ones, Due to their higher content of carbonates. Graphene showed pH values similar to Control and Zeolites ones, lower than Biochar and higher than Compost for both soils at all L/S ratios. This means that Graphene addition did not result in natural soil pH changes. Compost showed the lowest values of pH for all L/S ratios due to the release of Fulvic and Humic acids [31] in both CS and SS soils. Biochar showed the highest values of pH for all L/S ratios reaching the maximum value (12) in L/S = 1 for CS batches and in L/S = 2 for SS batches (10.8).