Spanish Bentonites: A Review and New Data on Their Geology, Mineralogy, and Crystal Chemistry

Abstract

A review and a synthesis of the geological, mineralogical, and crystal chemical data available in the literature on active Spanish bentonitic exploitations were done, and at the same time, new data are provided from a set of representative samples from these deposits. They were located in three different areas with different geological origins: (1) Miocene sedimentary deposits from the Tajo Basin (Madrid–Toledo provinces) in the center of the Iberian Peninsula, where bentonites appear in two different units named for their colors (Green Clays and Pink Clays); (2) samples from Tamame de Sayago (Zamora province) originating from the hydrothermal alteration of granitic Variscan rocks; and 3) Miocene deposits originating from the hydrothermal alteration of volcanic or subvolcanic rocks from the Cabo de Gata volcanic area (Almería Province) in the southern part of Spain, where the three main deposits (Cortijo de Archidona, Los Trancos, and Morrón de Mateo) were studied. The bentonites from the Tajo Basin were formed mainly by trioctahedral smectites, and there were significant mineralogical differences between the Green and Pink Clays, both in terms of the contents of impurities and in terms of smectite crystallochemistry and crystallinity. The smectites from Tamame de Sayago were dioctahedral (montmorillonite–beidellite series), and they appeared with kaolinite, quartz, and mica in all possible proportions, from almost pure bentonite to kaolin. Finally, the compositions of the bentonites from the three studied deposits in Cabo de Gata were quite similar, and zeolites and plagioclases were the main impurities. The structural formulae of the smectites from Cortijo de Archidona and Los Trancos showed a continuous compositional variation in beidellite–montmorillonite, while in Morrón de Mateo, the smectites were mainly montmorillonite, although there was continuous compositional variation from Al montmorillonites to Fe–Mg-rich saponites. The variation in the smectite composition is due to the intrusion of a volcanic dome, which brings new fluids that alter the initial composition of the smectites.

Bentonites in Southern Spain. Characterization and Applications

“…The bentonisation and zeolitisation process in the south and southeast of Spain was practically ubiquitous, as has been stated by Martín-Vivaldi [30]; Leone et al [26]; Linares [31]; Delgado and Reyes [32]; García-Romero et al [33]; and Martínez et al [34]. Samples BFO-01 and BLT-01 lie to the west and south of the San José-Los Escullos deposit, respectively.…”

“…The high SiO 2 contents indicate a marked presence of mordenite in paragenesis with smectite which concurs with what was established by Costafreda [24]; this fact has been proven by comparing the ZFN-01 sample (67.04% SiO 2 ), from the San José-Los Escullos deposit, with BLT-01 (47.26% SiO 2 ), from the Los Trancos deposit. García-Romero et al [33] calculated the SiO 2 (51.25-53.47%) content in the Los Trancos bentonites, and found it to be slightly higher than the values obtained in this research; however, their calculations are similar for the Al 2 O 3 (17.01-17.75%), the MgO (4.56-4.87%), the Na 2 O (0.51-1.07%), the K 2 O (0.14-0.43%), the CaO (1.05-1.32%) and the Fe 2 O 3 (2.21-2.41%) (Table 2). The CaO content in the samples from the San José-Los Escullos deposit is discrete and homogeneous with respect to Na 2 O and K 2 O (Figure 9a), emphasising its alkaline character.…”

“…Chemical composition (wt% oxides) of bentonites from the Los Trancos deposit, by García-Romero et al[33].…”

Mineral Inactivation of Zinc in Polluted Soil—Sustainability of Zeolite, Bentonite and Blends

“…Natural, as well as synthetic zeolites, strongly bind trace metals and this process appears much more competitive compared to plant roots [13]. Bentonites consist of at least 75% montmorillonite as a component of smectite [14], and is also characterized by developed sorption and retention properties of pollutants in soils [15][16][17]. The incorporation into soils of both minerals may alter their pH, inducing a decrease of trace metals activity-Zn among others.…”

The Occurrence of Authigenic Clay Minerals in Alkaline-Saline Lakes, Pantanal Wetland (Nhecolândia Region, Brazil)

“…Regarding the smectite minerals, depending on the concentration of the solution and the amount of detrital material available, dioctahedral or trioctahedral minerals are favored [7,8]. Dioctahedral smectites are mainly formed through transformation of detrital material and they are associated with environments rich in Al 3+ and Fe 3+ , while trioctahedral smectites are formed by precipitation from aqueous solutions, associated with Mg 2+ [7,9,10].…”