Vermiculite surface coating

Roth et al. (1969) have demonstrated that clay vermiculites commonly have a surface coating of positively charged Fe203 (approximately 10% A1203 is also present) which causes a decrease in C.E.C. This material can be removed (deferration) by reducing free Fe2 03 with Na2 S04 in the presence of Na citrate and NaHC03. 

The relative mildew growth on polymer and on paint samples exposed to Aurobasldlum pullulans was also studied using the "Zabel Test." In this procedure, veneer strips of southern yellow pine and bass wood are sterilized, cooled, and painted (2 coats with 24 hrs. drying time). After 2-3 days the strips were soaked In distilled water, sterilized at 100 C and placed vertically In 16-ounce French square bottles containing 20 gm. of vermiculite. A mlcronutrlent enriched nutrient media was then poured Into the vermiculite (100 ml per bottle). After sterilization at 121 the painted strips were positioned so that the bottom of the painted zone was 0.5 cm above the vermiculite surface. The specimens were Inoculated with a spore suspension of Aureobasldlum pullulans (16624) by pipette. Incubated two months at 28 , and then rated visually with a 20x binocular. In the weathered series, the specimens were exposed four days In an Atlas Weather 0 Meter (UV and water spray). Representative results are summarized In Table 13. 

Short-range-ordered or noncrystalline Al precipitation products are ubiquitous in soil environments (Parfitt, 1980 Kampf et al., 2000). They dominate the chemical reactions in soils because of their extremely small particle sizes and highly reactive surfaces. In pure form they are not stable, but in the presence of chelating anions they may remain unchanged indefinitely. Short-range-ordered Al precipitates and soluble OH-Al species often coat crystalline minerals in soils or may be interlayered into the interlamellar spaces of vermiculites or smectites, altering the surface properties of these phyllosificates. OH-Al interlayered vermiculites and smectites are particularly abundant in Ultisols and Alfisols (Bamhisel and Bertsch, 1989). 

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