M. Suárez Barrios

Acid activation of a palygorskite with HCl : development of physico-chemical, textural and surface properties

Abstract A palygorskite from Bercimuel (Segovia, Spain) was treated with 1.0, 3.0, 5.0 and 7.0 N solutions of HCI for 1 hour under reflux. The solids obtained were characterized by XRD, FT-IR spectroscopy, thermal analyses, TEM and nitrogen adsorption-desorption isotherms at 77 K. The acid treatment runs with the removal of the octahedral cations—Mg(II), Al(III) —and the formation of amorphous silica from the tetrahedral sheet. An important increase in the specific surface area was observed during treatment, reaching a maximum of 286 m2/g in the sample treated with 5.0 N HCI. The silica obtained after the treatments maintains the fibrous morphology of natural palygorskite. No creation of microporosity is observed during the treatment.

CHARACTERISTICS OF A Mg-PALYGORSKITE IN MIOCENE ROCKS, MADRID BASIN (SPAIN)

Palygorskite in Miocene mudstones, palustrine limestones and calcretes from the Esquivias locality (Madrid Basin, Spain) has been analyzed by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and analytical electron microscopy to determine its characteristics and chemical composition. Other palygorskites from the literature are used as references. The mean structural formula obtained from the analysis of isolated particles is (Si7.87Al0.13)O20(

ACID ACTIVATION OF A FERROUS SAPONITE (GRIFFITHITE): PHYSICO-CHEMICAL CHARACTERIZATION AND SURFACE AREA OF THE PRODUCTS OBTAINED

({\rm{A}}{{\rm{l}}_{1.04}}{\rm{Fe}}_{0.20}^{3 + }{\rm{M}}{{\rm{g}}_{3.11}}{\square _{0.65}})

Textural and structural modifications of saponite from Cerro del Aguila by acid treatment

(Al1.04Fe0.203+Mg3.11□0.65))(OH)2(OH2)4(Ca0.02K0.05Na0.08). This palygorskite has the largest Mg content reported in the literature, and it seems that, chemically, it fills the ‘compositional gap’ existing between sepiolite and palygorskite. Infrared spectroscopy reveals the absence of trioctahedral Mg and therefore the possibility of the existence of magnesic clusters in the ribbons is discounted. An homogeneous distribution of the octahedral cations (Al, Fe3+ and Mg) along the ribbons is proposed.

Electron microscopic study of the illite-smectite transformation in the bentonites from Cerro del Aguila (Toledo, Spain)

A ferrous saponite (griffithite) from Griffith Park (California, USA) was treated with solutions of HC1 (0.62, 1.25 and 2.5% by weight) at 25~ for 2, 6, 24 and 48 hours. The resulting solids were characterized by XRD, FT-IR spectroscopy, thermal analyses, SEM, TEM and nitrogen adsorption iso- therms at 77 K, showing the destruction of silicate structure by the treatments. The free silica generated by these treatments was digested and determined in all samples. Several samples had specific surface areas up to 250 m2/g, with maximum values which are 10 times higher than the surface area of natural saponite (35 m2/g). A sudden decrease in specific surface areas was observed when free silica was digested, which indicates that free silica makes a very important contribution to the surface area of leached samples.A ferrous saponite (griffithite) from Griffith Park (California, USA) was treated with solutions of HCl (0.62, 1.25 and 2.5% by weight) at 25°C for 2, 6, 24 and 48 hours. The resulting solids were characterized by XRD, FT-IR spectroscopy, thermal analyses, SEM, TEM and nitrogen adsorption isotherms at 77 K, showing the destruction of silicate structure by the treatments. The free silica generated by these treatments was digested and determined in all samples. Several samples had specific surface areas up to 250 m2/g, with maximum values which are 10 times higher than the surface area of natural saponite (35 m2/g). A sudden decrease in specific surface areas was observed when free silica was digested, which indicates that free silica makes a very important contribution to the surface area of leached samples.

Costras carbonatadas en la sucesión aluvial distal eocena de la Formación Hamada de Boudenib II al sur del Alto Atlas (Marruecos)

Abstract The physicochemical properties of clays can be modified by acid treatment with inorganic acids. This treatment is usually referred to as ‘acid activation’ , because it increases the specific surface area and the number of active sites of the solids. In the present study, the acid activation of saponite from Cerro del Aguila (Madrid, Spain) with HCl solutions was measured. Illite, quartz and small amounts of feldspar were found as impurities in the raw saponite. Acid treatments were carried out with different concentrations of HCl solutions. The samples obtained were characterized by mineralogical and chemical analyses, XRD, FT-IR spectroscopy, N2 adsorption-desorption isotherms and TEM. The acid attack, under the conditions employed, produced a progressive destruction of the structure of saponite by partial dissolution of the octahedral Mg(II) cations. Amorphous silica coming from the tetrahedral sheet of saponite was generated. The specific surface area of the most intensely treated sample (2.5% for 24 h) was doubled with respect to that of natural saponite. This increase in the surface area is due to the increase in both the external and internal surface areas.