ABSTRACT Bentonite as a raw material is an economical alternative to produce desiccants. The literature indicates that it is a good water adsorbent in relation to the desiccants commonly used in industry (silica gel, molecular sieve). In this sense, it is a valid alternative and an economic option since the clay is a natural compound, which makes it environmentally friendly. In this way, it is possible to protect products from moisture with the addi-tional advantage that its desiccant capacity remains practically constant after successive cycles of adsorption - regeneration, using low temperatures (100°C) for the latter process. Considering the interest of increasing the exploitation of bentonite in Argentina, previous studies evaluated its retention capacity, using, among others, a Patagonian bentonite. The adsorption of water vapor is affected by the concentration of the smectite clay mineral, the relative humidity, the drying of the samples, and the type of interlaminar cation of the smectite. In the present work it is determined that there is an increase of adsorption in relation to the starting material after the addition of increasing concentrations of Ca by ion exchange. In these samples the adsorption is carried out mainly by the hydrated ion present in the interlaminar space. Also, the desiccant materials benton-ite-Ca showed structural and textural differences in relation to natural bentonite.

RESUMEN La bentonita como materia prima constituye una alternativa económica para la producción de desecantes. La literatura indica que es un buen adsorbente de agua en relación a los desecantes comúnmente usados en la industria (sílica gel, tamiz molecular). En este sentido, constituye una alternativa válida y una opción económica ya que la arcilla es un compuesto natural, lo cual hace que sea amigable con el medio ambiente. De este modo, se consigue proteger productos de la humedad con la ventaja adicional de que su capacidad desecante se mantiene prácticamente constante luego de sucesivos ciclos de adsorción – regeneración, utilizándose baja temperatura (100°C) para este último proceso. Teniendo en cuenta el interés en aumentar la explotación de bentonita en Argentina, en estudios previos se evaluó su capacidad de retención, utilizando entre otras, una bentonita de la Patagonia. La adsorción de vapor de agua es afectada por la concentración del mineral de arcilla esmectita, la humedad relativa, el secado de las muestras y el tipo de catión interlaminar de la esmectita. En el presente trabajo se determinó que existe un incremento de adsorción en relación al material de partida luego del agregado de concentraciones crecientes de Ca por la vía intercambio iónico. En estas muestras la adsorción se lleva a cabo principalmente por el ión hidratado presente en el espacio interlaminar. Asimismo, los materiales desecantes bentonita-Ca mostraron diferencias estructurales y texturales en relación a la bentonita natural.

Glass compositions were carefully prepared, using natural quartz and potassium feldspar as a part of the starting raw materials. The solids were prepared so as to have theoretical stoichiometric leucite and 45S5 Bioglass in different L/Bg weight ratios between 0.43 - 1.00. Novel bioactive glass - ceramics, containing leucite, sodium calcium silicate and silicorhenanite, confirmed by XRD and FTIR, were obtained. Bioactivity tests were carried out on powdered and sintered disks forms. The immersion time was up to 25 days. Apatite formation on powders was studied by FTIR, and XRD and SEM were used to study bioactivity on disks. The materials developed an apatite layer on their surfaces within 6 days of immersion in simulated body fluid. The glass - ceramic with L/Bg ratio = 0.43 presented an apatite layer on all its surface, not so for the samples with 0.66 and 1.00 ratios, on which such layer was peeled off in most part of their surfaces.

Due to increase water pollution by organic compound derived from hydrocarbons such as toluene, several alternative technologies for remediation of polluted water have been originated. In this work natural bentonites were modified with cetyltrimethylammonium (CTMA+) for obtaining organophilic bentonites. The obtained CTMA-bentonites would be suitable for use as adsorbents of toluene present in water. The influence of structural characteristics of CTMA-bentonites on their adsorption capacity was studied. It was shown that adsorption of toluene depended on homogeneous interlayer space associated with arrangements of CTMA+ paraffin-monolayer and bilayer models, accompanied by a high degree ordering of the carbon chain of organic cation in both arrangements. However, packing density would not have an evident influence on the retention capacity of these materials. The solids obtained were characterized by chemical analysis, X-ray diffractions and infrared spectroscopy. Toluene adsorption was measured by UV-visible spectrophotometer. Adsorption capacity was studied by determining adsorption isotherms and adsorption coefficient calculation. The adsorption isotherms were straight-line indicating a partition phenomenon of toluene between the aqueous and organic phase present in organophilic bentonites.

The retentions of Zn, Cd and Pb cations by one treated bentonite up to 750 °C were analyzed. The retentions were evaluated by using mono-and poly-solute aqueous solutions of such cations. The adsorptions were carried out in batch system at room temperature. The solid/liquid ratio was 2% wt.v-1. The solids were characterized by X-ray diffraction, thermal and chemical analyses. The Zn cation from mono- or polysolute-solutions was retained in higher amount than Cd and Pb cations in similar solution types by bentonite. The retentions were effective up to 450 °C calcined bentonite, after that, the retention capacity decreased in concordance with dehydroxylation of the structure of clay minerals.

The adsorption of Cd ions from solution by a tuffaceous material (in natural and after clay concentration) from Neuquén Province, Argentine was tested. The solid was used as collected and after being concentrated in the clay fraction. The chemical analysis was performed by Plasma Couple Inductively and the mineralogical composition was identified by X-ray diffraction. The adsorption isotherms were carried out by using concentrations of Cd solutions in the range of 100 to 1000 ppm. The solid/liquid ratio was 2 % w/v and the contact time was 24 hours. The amount of metal ion retained was obtained by difference between the initial concentration and supernatant concentration after contacting metal ions solution with the solid. The metal concentrations were determined by atomic absorption spectrometry. The main mineralogical components of the sample were smectite/illite (clay minerals), quartz and feldspar. The purification of the tuffaceous material in clay minerals increased the adsorption capacity from 15.75 to 22.86 mg·g-1.

Se estudia la adsorción de iones de cadmio en solución por un mineral tobáceo, procedente de la Provincia de Neuquén, Argentina, utilizado en forma natural y luego de concentrado en fracción arcilla. El análisis químico fue efectuado por Plasma Acoplado Inductivamente y la composición mineralógica fue identificada por Difracción de Rayos X. La isoterma de adsorción fue obtenida usando cadmio en solución en el rango de concentración de 100 a 1000 ppm. El ensayo experimental se llevó a cabo con una relación sólido/liquido de 2 % p/v y tiempo de contacto de 24 horas. La retención de cadmio se determinó por diferencia entre la concentración inicial y la concentración luego del contacto con el sólido, lectura efectuada por espectrometría de absorción atómica. La mayor proporción de fracción arcillosa (esmectita e illita) lograda por la purificación, permitió reducir el contenido de cuarzo y feldespato y aumentar la capacidad de adsorción de 15.75 a 22.86 mg·g-1.

Titanium in hosted by a clay matrix has important applications in a variety of catalysts. However, there is insufficient information about of textural and structural characteristics of the titanium in matrix clay at room temperature and after thermal treatment. In this study, titanium in host matrix clay was obtained by treating montmorillonite clay minerals with different OH-Ti solutions. The titanium-solutions containing partially hydrolyzed titanium were obtained using a TiCl4 solution with and without the addition of glycerol. The amount of Ti added to the solid was 20 mmol Ti per gram of clay. Thermal treatments were carried out at 500 and 1,000 °C in an air atmosphere. The solids were characterized by X ray diffraction, thermal analyses, infrared spectroscopy, N2 adsorption-desorption isotherms. The products presented different structural and textural characteristics and, after calcination at 1,000 °C, anatase and rutile in different proportions were present in the samples.

A natural bentonite sample from Argentina was activated by sulfuric acid in different concentrations (20 and 40 wt%) and different contact time (120 and 210 min), at the same temperature (90 °C) . The ratio of the mass of clay to the volume of acid solution was 1:10 (w/v). These materials were tested to verify its bleaching (decolorization) capacity of soybean oil, which was compared to a standard commercial bleaching material Fulmont Premiere. Differential thermal analysis and thermogravimetric techniques, infrared spectrometry and chemical analysis showed that the acid activation modified the clay material structural properties. Bleaching capacity was found to be dependent on the acid concentration and treatment time used. The activated Argentine material showed superior bleaching performance compared to the commercial clay used by vegetable oil refiners.