*3.1.1 Bentonite before ion exchange experiments*

Bentonite is a rock composed essentially of minerals from the group of smectites, regardless of any genetic connotation. Additionally, it has the ability to inflate and increase its volume by weight several times on contact with water, to form thixotropic gels when added in small quantities. Finally, it can be said that its main interchangeable cations are Na<sup>+</sup> , Ca2+, K+ , Mg2+, Li+ , and H+ .

**Table 2** shows the results obtained by ICP and FRX of the elements contained in the bentonite studied, of which silicon, aluminum, iron, sodium, and potassium are present in the majority among others.

Likewise, in **Figure 1**, the mineral species identified by X-ray diffraction are observed, in which the presence of majority of mineral phases, such as quartz,


#### **Table 2.**

*Chemical composition of natural bentonite.*

**Figure 1.** *X-ray diffractogram of bentonite.*

anorthoclase, orthoclase, albite, and berlinite, can be seen, as well as sodium silicoaluminates (paragonite and gmelinite).

On the other hand, **Figure 2** shows an image of a bentonite particle at −400 mesh, analyzed by SEM-EDS, where the semiquantitative and point composition can be observed, showing the presence of elements such as silicon, aluminum, sodium, magnesium, potassium, and iron, which are characteristic in the bentonite (**Figure 2a**); likewise, the bentonite particle is shown in detail, having a lot of porosity, which is essentially one of the most important physical characteristics for the ion exchange that could be carried out, besides the particle size, offering a large surface and contact area, **Figure 2b**.
