Bentonites in Southern Spain. Characterization and Applications

Abstract

The objective of this work was to investigate and demonstrate the pozzolanic properties of the bentonites found at the San José–Los Escullos deposit, located in the southeast of the Iberian Peninsula, to be used in the manufacturing of more durable and environmentally compatible pozzolanic cements, mortars and concretes. These bentonites are mainly composed of smectites, with montmorillonite as the main clay mineral. They were formed by the hydrothermal alteration of tuffs, volcanic glasses, dacites, rhyolites and andesites. For this research, samples were taken from outcrops on the south, north and west side of the San José–Los Escullos deposit, and in the Los Trancos deposit located 19.3 km to the northeast. All samples consisted of bentonites, except for a zeolite sample taken from the northern flank of the San José–Los Escullos deposit, which was used to contrast and compare the behaviour of bentonite in some of the analyses that were done. An investigation of the mineralogical, petrological, chemical and thermogravimetric characteristics of the samples was carried out using various methods, such as XRD, OA (Oriented aggregates), TGA, XRF, SEM and thin section petrography (TSP). In addition, a chemical analysis of pozzolanicity (CAP) was done at 8 and 15 days to determine the pozzolanic capacity of the samples. XRD, XRF, SEM and TSP studies showed that these bentonites have a complex mineralogical constitution, composed mainly of smectites of the montmorillonite variety, as well as halloysite, illite, vermiculite, biotite, muscovite, kaolinite, chlorite, mordenite, feldspar, pyroxene, amphibole, calcite, volcanic glass and quartz. Thermogravimetric analysis (TGA) established the thermal stability of the bentonites studied at above 800 °C. Chemical analysis of pozzolanicity (CAP) confirmed the pozzolanic character of the bentonites, exhibited in their reactive behaviour with Ca(OH)2. The pozzolanic reactivity increased significantly from 8 to 15 days. These results show that the materials studied can be used as quality pozzolans for the manufacture of pozzolanic cements, mortars and concretes.

Mineralogical and Physico-Chemical Characterization of the Oraşu-Nou (Romania) Bentonite Resources

“…Similar bentonite resources can be found in the Carpathian area such as those from the Hliník nad Hronom deposit in Slovakia [7], but also in the world in Spain and in Turkey [8,14].…”

“…In contact with water, it can reversibly swell up to 15 times of its original volume, forming gelatinous colloidal suspensions or plastic films [6]. Subordinate minerals can be cristobalite, tridymite, feldspar, halloysite, kaolinite [7,8]. The various forms of silica present in the bentonite deposits can be opal, cristobalite and quartz.…”

Volcanic Ash from the Island of La Palma, Spain: An Experimental Study to Establish Their Properties as Pozzolans

“…As already mentioned above, the chemical composition of the VA agrees with a natural pozzolan, given the high values of the SiO 2 and Al 2 O 3 phases, as well as the relative balance between the alkaline compounds (Na 2 O y K 2 O) and alkaline earth (CaO and MgO). This kind of composition favors pozzolanic reactivity between these compounds-this fact has been mentioned in the works of some researchers [34,42,43].…”

“…The contents of Fe 2 O 3 y MgO indicate a composition of mostly ferromagnesian, preferably basaltic, while CaO and Na 2 O construe a chalcoalkaline chemism of the samples. However, one aspect to highlight is the low or almost zero value of the loss on ignition (LOI), which accentuates the differences between the pozzolans of zeolitic [42] and bentonite origin [43]. This kind of composition, mostly silica, aluminium, iron, calcium, and magnesium, indicates the presence of typical volcanic ash minerals such as albite, hematite, magnetite, anorthite, augite, diopside, and quartz (the existence of an amorphous phase should also be considered) [19,41].…”

Altered Volcanic Tuffs from Los Frailes Caldera. A Study of Their Pozzolanic Properties

“…As stated above, the altered volcanic tuffs are host rocks of zeolitic mineralisation within the Los Frailes caldera, so their proximity favours a diffusive interaction between both geological formations. Thus, the TFF-01 and TFF-03 samples, closer to the points of highest zeolite concentration, have more silica, alumina, sodium oxide and potassium oxide and a greater loss on ignition (LOI) than the TFF-2, located in a more distal position and more affected by the smectisation process; therefore, in its chemical composition, magnesium oxide and iron contents stand out [52].…”