# Physical-Chemical and Thermal Properties of Clays from Porto Santo Island, Portugal
## 5 Conclusions  
The residual soil samples from Porto Santo Island are composed of smectite, feldspars (K-feldspars and Ca/Na plagioclases), Fe-oxides/hydroxides (magnetite/maghemite and hematite), calcite and opal, with a CIA that varies from 49.29% to 70.33%. From the seven residual soil samples studied, one sample (36A) is composed mainly of smectite (82%), has a pH of 9.6, an EC of 772 \(\upmu\)S/cm and a CEC of 86.8 \(\mathrm{m}\mathrm{e}\mathrm{q}\mathrm{/}\mathrm{1}\mathrm{0}\mathrm{g}\). This sample also presents the highest CIA (70.33%) and has an SSA of 89 \(\mathrm{m}^{2}\mathrm{/}\mathrm{g}\) and 67% of silt plus clay grain size particles. The thermal properties are also good for use in pelotherapy, with the specific heat capacity of 0.9 J/g\({}^{\circ}\)C and the cooling kinetics of 19 min; however, measurement of moisture content should be considered. Moreover, in Sample 36A, the concentrations of PTEs (As, Cd, Co, Cr, Hg, Mn, Ni, Pb, Sb and V) did not meet the requirements for cosmetic and pharmaceutical purposes, and their dermal bioaccessibility should be assessed in future studies. Furthermore, it is proposed to enlarge the sampling in this bentonite deposit, the rheological characterization and the maturation process of the residual soils.  
Conceptualization, A.V., P.C.S.C. and F.R.; Methodology, A.V., P.C.S.C. and F.R.; Validation, F.R.; Formal analysis, A.V., P.C.S.C. and F.R.; Investigation, A.V., P.C.S.C. and F.R.; Resources, P.C.S.C. and F.R.; Data curation, A.V., P.C.S.C. and F.R.; Writing--original draft, A.V., P.C.S.C. and F.R.; Writing--review & editing, P.C.S.C. and F.R.; Visualization, P.C.S.C.; Supervision, F.R.; Project administration, F.R.; Funding acquisition, F.R. All authors have read and agreed to the published version of the manuscript. This work was funded by the Fundacao para a Ciencia e Tecnologia (FCT), through national funds, by the projects UIDB/04035/2020--GeoBioTec-GeoBioSciences, GeoTechnologies and GeoEngineering, funded by FCT, FEDER funds through the Operational Program Competitiveness Factors--COMPETE.  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
We are grateful to [PERSON] for the XRD data and [PERSON] for the XRF, SEM and grain size distribution data. As well as [PERSON] from the Department of Chemistry for specific heat data and [PERSON] from the Department of Materials and Ceramic Engineering for specific surface area data, all from the University of Aveiro. We thank the anonymous reviewers for their careful reading of our manuscript and valuable suggestions that helped improve it.  
The authors declare that they have no competing financial interests or personal relationships that may have influenced the work reported in this study.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Specific Heat Capacity** & **Cooling Kinetics** \\  & **(/g\({}^{\circ}\)C)** & **(min)** \\ \hline
5 & 0.6 & 14.5 \\
14 & 0.7 & 15.5 \\
14A & 0.8 & 18.0 \\
15A & 0.8 & 16.5 \\
26 & 0.9 & 15.5 \\
36A & 0.9 & 19.0 \\
119 & 0.8 & 17.0 \\ Pelotherapy \({}^{\ast}\) & 0.5 & - \\ Pelotherapy \({}^{\ast\ast}\) & - & \(\sim\)20.0 \\ \hline \hline \end{tabular} \({}^{\ast}\)In pelotherapy applications, in [PERSON] et al. [35] ** [PERSON] et al. [2]; - not defined.  
\end{table}
Table 7: Thermal results of residual soil samples from Porto Santo Island as well as theoretical values for pelotherapy applications.