Structural Fluorine in Sepiolite

Abstract

Abstract--Sepiolite from Vallecas-Vichlvaro, Spain, contains 1.3% fluorine. Laser microprobe mass spectrometry of this sepiolite suggests the presence of fragments of (SiO2),OMgF and (SiO~),OMgOH, which are typical of the sepiolite structure. During thermal dehydroxylation, the fluorine in this sepiolite is removed simultaneously with OH groups at about 750~ Nuclear magnetic resonance spectroscopy (NMR) of ~gF indicates that the fluorine is located in the interior of the sepiolite structure, probably substituting for OH groups, and is homogeneously distributed. In the Vallecas-Vic~lvaro sepiolite, about one of every four OH groups bound to Mg 2 § is substituted by fluorine. The kinetics of extraction of Mg 2+ and F-ions by acid treatment (1 N HC1) shows a more rapid extraction of Mg 2 § with a monotonous decrease of the Mg/F ratio as the extent of extraction increases. These results support the internal location of the fluorine, as suggested by the NMR data.

Porous poly(vinyl alcohol)/sepiolite bone scaffolds: Preparation, structure and mechanical properties

“…It has also been used in conjunction with PVA to form hydrogel fibres where the degree of swelling can be easily controlled by the degree of crosslinking [30]. [30][31][32]. It is composed of blocks, which are characterized by a sandwich structure of a central magnesium octahedral sheet between two silica tetrahedral sheets, forming a capillary network of parallel channels [31][32][33].…”

“…[30][31][32]. It is composed of blocks, which are characterized by a sandwich structure of a central magnesium octahedral sheet between two silica tetrahedral sheets, forming a capillary network of parallel channels [31][32][33]. Sepiolite features a large specific surface area in the region of 140 -320m 2 /g [31,34], and its interactions with polymer(s) not only take place on the external surface, due to the significant number of silanol (Si-OH) groups but by penetration into the structural channels of sepiolite fibre blocks [35,36].…”

19F MAS-NMR Study of Structural Fluorine in Some Natural and Synthetic 2:1 Layer Silicates

“…The substitution of fluorine atoms for hydroxyl groups has been studied by various methods, namely by ~H and 19F broad-band nuclear magnetic resonance (Sanz and Stone, 1979;Santaren et al, 1990). Sanz and Stone…”

Principal component analysis of fluoride geochemistry of groundwater in Shanxi and Inner Mongolia, China

“…Chemically, F − and OH − are negatively charged and possess similar ionic radii, 1.33 Å for F − and 1.40 Å for OH − (Chidambaram et al, 2003;Jacks et al, 2005;Santaren et al, 1990). Therefore, OH − can replace the exchangeable F − from F-bearing minerals and enhance the F − concentration in groundwater (Dar et al, 2011;Guo et al, 2007).…”