Physical properties and Na-activation of Egyptian bentonitic clays for appraisal of industrial applications

Abstract Selected physical properties of bentonitic clays in the north Western Desert, Egypt were investigated to assess their potential use in industrial applications. Assessment tests included specific surface area (SSA), swelling index (SI), green (GCS) and dry (DCS) compressive strengths, rheological properties, and filtrate volume. The impact of Na-activation on swelling index and rheological properties was also considered. SSA, SI after Na-activation, GCS, and rheological properties were highly correlated with smectite content and a modified AgTU-CEC. Mineral impurities greatly influenced the physical properties. Quartz and feldspars reduced the rheological properties and increased the water loss. Halite and colloidal iron oxides increased swelling index and enhanced rheological properties. DCS was greatly influenced by the percentage of added water and kaolinite abundance. Na-activation improved the swelling index and rheological properties of halite-poor samples. The swelling index of Na-activated samples was a useful tool for determining the quality and grade of bentonitic clays. The suitability of the Egyptian bentonitic clays for drilling mud and bonding of foundry sands was determined by comparing the results with a standard bentonite and published industrial specifications. Egyptian bentonitic clays showed comparable compressive strengths with Wyoming Na-bentonite (SWy-1) by adding 8 and 10 wt.% clay to sand molds and can be used for most metal-type castings. Egyptian bentonitic clays with a high swelling index and low quartz and feldspar content, produced comparable rheological properties with the Wyoming Na-bentonite and met international drilling mud specifications. However, the filtrate volume measurements indicated that the samples require additional modifications to reduce water loss. Many desirable bentonitic clay properties were reduced by large quantities of kaolinite.