## 3 Results
### XRD Analyses  
After the neutralization trials had been performed, all the sediments were extracted from the beakers as explained in Section 2.3. The solid residues obtained when using such a method were analyzed using XRD to analyze their composition. Only the trial derived by the usage of a combination of CaO and HNO3 could not provide analyzable sediments. In fact, the residues precipitated as a hydrated salt that formed a paste rather than a powder.  
The XRD spectra of the two trials using CaO are shown in Figure 7. All the main peaks found in the trials using a 0.25 g addition of CaO, are identified in the 0.5 g trial too. In the trial using a 0.25 g addition of CaO, the analysis of the spectrum yielded a partial match  
Figure 5: Neutralization trials of a 0.1 M solution of HCl performed with 0.5 g and 0.25 g of pure CaO.  
Figure 6: Neutralization trials of the 0.1 M HCl and HNO3 acid solutions performed with 1 g of slag samples S1 and O1 (left and O2 and S2 (right).  
with sinjarite, whose chemical formula is CaCl\({}_{2}\).2(H\({}_{2}\)O). Therefore, CaCl\({}_{2}\) is believed to precipitate during the evaporation phase of the liquid phase in a multiple hydrated form having chemical formula CaCl\({}_{2}\).nH\({}_{2}\)O. This is in compliance with the results obtained in previous study, which used sulfuric acid instead, precipitating CaSO\({}_{4}\) in several hydrated forms [9] In the 0.5 g trial, there are also peaks belonging to at least another phase.  
Also, the reaction products obtained during the neutralization trials performed with slag and HCl were extracted from the beakers to determine their compositions. The 11 samples were analyzed using XRD and the spectra are showed in Figure 8. The spectra were grouped based on slag type, to determine the differences in compositions. In all four cases, all the spectra of the reaction products were different when a different quantity of reactant was used. In fact, when the XRD spectra produced by trials with the same slag, but different weights of slag are compared to each other, the peaks positions are the same. However, both relative and absolute intensities are different. This means that the phases in the samples are the same, but their ratio differs, when a different weight of slag is used.  
Figure 7: XRD spectra of the residues extracted after the neutralization trials of a 0.1 M HCl solution performed with 0.25 g and 0.5 g of CaO. The peaks related with the phase CaCl\({}_{2}\)-nH\({}_{2}\)O are highlighted by dots at their respective peaks.  
There are some similarities across spectra produced by different slags. In fact, the results that were obtained for the trials performed with additions of 1 g of O1, 1 g of S1 and 1 g of O2 seems comparable. Moreover, the spectra produced by those trials are also similar to the one obtained after the trial using a 0.25 g addition of CaO. To facilitate the comparison, the intensities of these 4 spectra have been normalized to a 100% value, as shown in Figure 9. As is it possible to notice, all the main peaks of reaction products obtained after the neutralization made using 0.25 g additions of CaO are present in the spectra of the residues obtained with the slag samples. For slag samples O1 and S1 almost the entire spectra can be described by the CaCl\({}_{2}\) nH\({}_{2}\)O peaks. On the other hand, when looking at the spectrum obtained by the reaction products made by slag O2, the match is only partial, and at least another phase in present. In addition, the peaks corresponding to CaCl\({}_{2}\) nH\({}_{2}\)O seem to decrease in intensity in favor of other phases, either when the initial weight of slag used for neutralization was reduced or increased. It should be pointed out that slag S2 was not grouped with the others, because the XRD spectra produced (as shown in Figure 8) were clearly different from the other reaction products obtained.  
Figure 8: XRD spectra of the residues extracted after the neutralization trials of a 0.1 M HCl solution performed with 0.5 g, 1.0 g and 2.0 g of the slag samples.