Spanish palygorskites: geological setting, mineralogical, textural and crystal-chemical characterization

Abstract

A representative group of palygorskites from the six most important Spanish deposits and six other occurrences were studied comparing their mineralogy, textural features, crystal-chemistry, and surface properties. These palygorskites have different geological origin: (1) sedimentary in large Tertiary continental basins, (2) hydrothermally altered volcanic rocks in the southern Spanish Peninsula, also Tertiary in age; and (3) fault-hosted pure palygorskites. The most common impurities are quartz and carbonates, both calcite and dolomite, but also feldspar, illite, smectite, and sepiolite have been identified. The structural formulae obtained show great variability between samples, as well as with respect to the theoretical formula for palygorskite, as they range from magnesian to aluminous palygorskites. The most common fibre length ranges between 1 and 10 mm but the palygorskites of hydrothermal origin are much longer, with lengths over 10 mm. The shorter fibres give rise to tightened textures, while longer fibres usually generate more open textures. These properties, along with the degree of compaction, condition the porosity of the sample, which in turn influences its surface properties. The specific surface areas obtained range between 30 m 2 g À1 and 263 m 2 g À1 , depending on the impurities content and on the texture and crystal-chemistry; the highest values correspond to Mg-rich palygorskite.

Adsorption Behavior of Acid-Treated Brazilian Palygorskite for Cationic and Anionic Dyes Removal from the Water

“…X-ray diffraction (XRD) patterns of the raw and acid-treated (2, 4, and 6 mol/L) Brazilian palygorskite are illustrated in Figure 1. Palygorskite (ICCD 21-0958) and quartz (ICCD 46-1045) phases were identified in the raw and acid-activated clays, as observed in other studies [58][59][60]. Câmara et al and Suarez et al [39,58] reported that the palygorskite can be classified into three types: Type I has similar Al and Mg contents and negligible isomorphic substitutions (d200 < 6.35 Å); Type II is rich in Al contents and has a dioctahedral character, and this is the most commonly found type (6.35 < d200 < 6.46 Å); and Type III is rich in Mg contents and has a trioctahedral character (d200 > 6.46 Å).…”

Investigation into Brazilian Palygorskite for Its Potential Use as Pharmaceutical Excipient: Perspectives and Applications

“…Moreover, their macroscopic similarities undeniable. The crystals shown in Figure 5 occur as thin, elongated fibers of varying lengths, r domly distributed in different ways: isolated, grouped in a few units parallel to each ot or forming massive bundles from the agglomerated structures [65,66]. Pharmasorb ® loidal fibers were shorter than in the raw palygorskite, which corroborates the data sho in Table 2.…”

New Environmentally-Friendly and Sustainable Materials

“…The contact angle results for the investigated materials are shown in Figure 10. The contact angle, in addition to enabling the assessment of the hydrophilicity or hydrophobicity of a material [38,58,59], also allows the assessment of surface energy [60], which is an important parameter during the production of compatible bioblends. Figure 10 shows the acquired data for the contact angle, where PLA displayed a value of 63 .…”