# Mineral Powder Extraction by the Natural Drying of Water from the Public Springs in Borsec
## 4 Discussion
The water evaporation increases the solution concentration that facilitates the anion and cation interactions such as the following:  
\[\ce{Ca2+}{(aq)}+\ce{CO3-}{(aq)}\rightarrow\ce{CaCO3-}{(s)}\downarrow \tag{1}\]  
\[\ce{Ca2+}{(aq)}+\ce{Mg2+}{(aq)}+2\ce{CO3-}{(aq)}\rightarrow\ce{CaMg(CO3)2-}{( s)}\downarrow \tag{2}\]  
\[\ce{2 Na+}{(aq)}+\ce{CO3-}{(aq)}\rightarrow\ce{Na2 CO3-}{(s)}\downarrow \tag{3}\]  
\[\ce{Na+}{(aq)}+\ce{Cl-}{(aq)}\rightarrow\ce{NaCl}{(s)}\downarrow \tag{4}\]  
The increasing concentration gradient leads to the formation of the supersaturated solution which facilitates the precipitation of solid salt germs via homogeneous crystallization [22,23]. Literature data show that there is a competition between homogeneous and heterogeneous germination of the calcite from the hard waters during the softening process [23]. The heterogeneous crystallization presumes the pre-existence of fine small solid microscopic particles that ensure an optimal site for crystal growth from a supersaturatedsolution. In our specific case, there would be some soil particles such as quartz, kaolinite, chlorite, or pyroxenes. These solid mineral inclusions would be detected by the XRD investigation and observed at the POM inspection during the early stage of crystallization. The obtained results on our samples did not evidence any soil particle inclusion. This fact is confirmed by the zero turbidity measured in the water samples after the complete evaporation of the CO\({}_{2}\) bubbles. The crystals' growth is stimulated by continuous water evaporation facilitating solid material deposition onto the homogeneous germination centers. This leads to the formation of well-individualized crystals of fine micro-sizes around 5-20 \(\upmu\)m at the early stage of crystallization, a fact evidenced by POM investigation. Calcite crystals are more numerous and have a predominantly pseudo-hexagonal habit (rare rhombic crystals are observed) while aragonite has predominantly rhombic crystals, a fact being in good agreement with SEM observations in the literature [24]. It is obvious that the rich dolomite reported for the geological layers within both aquifers is the main source of the Mg\({}^{2+}\) ions in the mineral waters. Literature data clearly show that the reaction (2) did not form dolomite because of its lack of crystalline order among the magnesium and calcium crystallographic planes [25; 26; 27]. Thus, the magnesium ions randomly replace calcium ions within the calcite structure becoming pseudo-dolomite (e.g., rich magnesium calcite), a fact in good agreement with our XRD data. One of the most relevant peaks of pseudo-dolomite occurs at 29.72\({}^{\circ}\) instead of at 29.17\({}^{\circ}\) becoming a shoulder of the most representative calcite peak. The relevant peaks for pseudo-dolomite were found according to the powder diffraction file PDF 89-1305. The pseudo-dolomite germs precipitate due to the combined actions of Ca\({}^{2+}\) and Mg\({}^{2+}\) ions reacting with the carbonate ions, and the columnar crystals appear shortly after the development of the calcite and aragonite crystals. The EDS spectra in Figure 6 show a lower amount of Mg than would have been normal for dolomite, the stoichiometry being altered by the random placement of the Mg\({}^{2+}\) ions within the formed crystals, which is consistent with the data reported for pseudo-dolomite [28]. It was observed that concentrated brine with Ca\({}^{2+}\) and Mg\({}^{2+}\) injected with a fine bubble CO\({}_{2}\) flow induces the reactive crystallization of ordered dolomite at room temperature [29]. However, it requires a micro-controlled process where the fine gas bubbles induce partial re-crystallization over the growing crystals, allowing for the addition of ordered Mg and Ca layers. This is not our case when the CO\({}_{2}\) bubbles have randomly emanated from the mineral water, having less ability for modeling crystal growth. Thus, the pseudo-dolomite is formed, a fact confirmed by the elemental observations which agree with the XRD data.