# Understanding Oxygen Concentrator Failures in Low Resource Settings: The Role of Dust and Humidity
## 3 Results and Discussion
As explained in Section 2.2, particular attention was given to the eventual detection of Zr, Ti, and Mn, whose occurrence in African dust elevates them as key indicators of dust on the zeolite samples. The WDXRF analysis revealed the presence of only a very small amount of Zr, Ti, and Mn (approximately 30-300 ppm) in all the samples, including the C-X zeolite. Thus, the outcome did not evidence the presence of  
Figure 2: XRD patterns for the E-1, E-2, U-1, U-2, SA, and C-X zeolite samples. Moreover, a focus on the shift in the FAU framework peaks of the SA sample is provided. dust. It should be noted that Fe is present even in the sample of C-X, so this cannot be due to the presence of dust and must be a contaminant in all the samples. The presence of Fe, as well as K and Ca, in 13X zeolite was also reported in the literature by other works [36; 37]. The zeolite characterization was completed by the results obtained from the BET analysis, which are reported in Table 2 along with the Si/Al ratio. The values of the BET surface area and the microporous volume for FAU-LSX zeolites are fully consistent with those reported in the literature [38; 39; 40]. The decrease in both the BET surface area and the microporous volume for sample C-X is likely attributed to the presence of a significant amount of monovalent K\({}^{+}\) ions (>1.5% wt), which are larger in size compared to Na\({}^{+}\) ions [39]. Such a result is completely in line with the literature evidence [41; 42; 43]. Figure 4: The weight percentage (wt%) of Mg, Fe, Ca, and K in the zeolite samples is presented based on the country in which they were employed. Figure 3: The values of Si/Al and Al/Na (mol/mol) determined by WDXRF for each sample, highlighting their region of provenance. The TGA measurements are shown in Figure 5. It can be observed that the profile of the mass loss as a function of temperature for samples U-1 and U-2, as well as samples E-1 and E-2, does not exhibit a significant variation (Figure 5a,b). To enhance clarity in presenting all the curves together, E-1 and U-1 are not included in Figure 5c,d. The latter illustrates the first-order derivative of the mass variation over the duration of the TGA test (DTG) and is used to visualize the temperature at which the maximum mass loss rate occurs. This temperature, together with the total percentage of mass loss (\(\alpha\)%), which was calculated as the ratio between the total mass loss during the test (\(M_{I}-M_{F}\)) and the sample mass at the beginning of the test (\(M_{I}\)) (see Equation (1)), is reported in Table 3.  
\[\alpha\%=\frac{M_{I}-M_{F}}{M_{I}}\times 100 \tag{1}\]  
\(M_{F}\) represents the sample mass at the end of the test. Moreover, in Table 3, the total adsorbed amount (\(q_{I}\)) on the zeolites is also included, calculated as shown in Equation (2):  
\[q_{I}=\frac{M_{I}-M_{F}}{M_{F}} \tag{2}\]  
Table 3 indicates that the maximum mass loss rate occurs within the temperature range of 130-160 \({}^{\circ}\)C. Notably, the temperature increase correlates with both the mass loss percentage and a corresponding rise in the adsorbed quantity. Furthermore, the observed temperature range suggests that water is the primary compound released during the zeolite heating process. This hypothesis finds confirmation in the mass spectrometry (MS) results presented in Figure 6, which illustrates the first-order derivative of the mass variation over the duration of the TGA test (DTG) plots against MS curves, with the water mass-charge ratio (m/z) set at 18. Notably, Figure 6 highlights a peak in the water content corresponding to the DTG minimum, indicating water as the primary component contributing to the sample's mass loss. Conversely, other MS curves corresponding to different m/z ratios did not exhibit similar behavior, further affirming water as the predominant component within the zeolite matrix of the sample.