Recently, we have reported the production of a microporous high purity silica powder from the acid leaching of glasses with average pore size around 2.5nm and specific surface area of 420m2/g (BET). The employed glasses derived from the melting of two types of waste from the industrial processing of Brazilian oil shale (retorted oil shale and the top fraction of the intermediate layer of Irati Formation). Depending on the proportion of the two wastes employed in the formulation of the glasses, either a silica gel or a powdered one is obtained, after leaching. The acid leaching of those glasses with hydrochloric acid, at 90 °C, was used to produce powdered microporous silica. In the present work it is studied the effect of aging time and temperature on the morphology and structure of the obtained powdered silica. Aging studies were performed in two different media, an acidic (hydrochloric acid) and a basic one (ammonium hydroxide) for different periods of time and temperatures. XRD, SEM/EDX, TEM, specific surface area measurements and DTA/TGA were used to characterize these materials. The results have shown a decrease of specific surface area with increasing time and temperature. Apparently, this behavior may be associated with dissolution and re-precipitation mechanisms.
ABSTRACT:The production of Brazilian shale oil gives rise to 6600 ton/day of a solid waste of retorted shale, and larger amounts of dolomitic waste rock are generated during mining. Two vitreous materials were obtained through the melting of different proportions of these two wastes. By leaching these materials with hydrochloric acid at 90°C, two different kinds of silicas (powder and gel, both amorphous) with specific surface areas reaching up to ϳ 420 m 2 /g were generated. These silicas were further modified through an Ostwald-ripening type of treatment in ammonium hydroxide solution at 80°C. The process eliminated almost completely the deleterious micropores. The obtained silicas were evaluated as reinforcing fillers for SBR-1502. The employment of one of the modified silicas gave rise to a composite with better mechanical properties than those displayed by the one with untreated silica. Scanning electronic microscopic observation disclosed the existence of great morphological differences between these silicas. Apparently, the aging treatment gave rise to the production of better anchoring sites for the elastomer molecules. NMR studies also showed the reduction of the silanol content of the treated silica. The fracture surface of the composite disclosed a good wetting of this silica by the elastomeric matrix.
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