Vermiculite, expanded

Vermiculites are formed by the decomposition of mica. They contain layers of water and magnesium ions in place the potassium ions. When heated to 800°C-1100°C, vermiculite expands because of the conversion of the water to gas. The expanded vermiculite has a low thermal conductivity and density, and is used as a thermal and sound barrier as well as an aggregate in lightweight concrete. It is also used as a moisture-retaining soil conditioner in planting. 

Light-weight concrete Sand and gravel concrete Mineral wool insulation Expanded vermiculite insulation Expanded vermiculite concrete... 

Properties Platelet-type crystalline structure. High porosity, high void volume to surface area ratio, low density, large range of particle size. Insoluble in water and organic solvents soluble in hot concentrated sulfuric acid. Water vapor adsorption capacity of expanded vermiculite less than 1%, liquid adsorption dependent on conditions and particle size, ranges 200-500%. Noncombustible. 

The results for the adsorption of crude oil on columns, and the BET surface area for the studied samples are summarized in Table 8.1. The adsorption factor (AF) is defined here as (oil mass)/(vermiculite mass). For both, expanded and FIV samples, the adsorption studies were performed at two different mass values 2.0 and 4.0 g. However, it was found that the AF values were not affected by the used vermicuHte mass. Adsorption experiments were also performed for hydrated (not expanded) vermiculite samples, and it was observed that the AF for these sample is very low (0.3). All adsorption experiments were performed in triplicate, and it was verified that the results are reproducible. 

In insulating refractory concretes the conventional aggregates are replaced by lightweight heat-resistant aggregates such as expanded vermiculite, expanded perlite, expanded chamotte, or pumice. These concretes are widely used to limit the heat losses of industrial kilns and high-temperature installations. 

Matrix-dispersed fertilisers have also been produced commercially. Expanded vermiculite, perlite, various gels, polymers and waxes have all been used as dispersing media. Granular fertilisers and soil conditioners can be produced from peat and water-soluble phosphates [36]. 

South Africa was the leading producer of vermiculite, followed by the United States and China. When finely ground vermiculite is quickly heated to 300 degrees Celsius in a furnace, water vapor escapes as steam, the mineral becomes porous and expands to about twenty times its original volume. Like the heat-treated perlite, expanded vermiculite is extremely fight. Vermiculite furnaces are often used to heat perlite, as both are frequently sold together. 

Carbon nanotubes (CNTs) have a unique one-dimensional stmcture, laige specific surface area, and are oleophilie and hydrophobic [64]. As filter materials, CNTs exhibit seleetive separation eharacteristics for different solutions [65, 66]. The CNTs directly synthesized on the surface of expanded vermiculite eould signifieantly improve the oil sorption capaeity by forming a hydrophobie surface [67],... 

AlSi)40io] (0H)2 4H2O, a type of hydrated biotite mica. Vermiculite expands at heating to 650-1,000 °C up to 18-25 times. Before expansion, the density is 2.4— 2.7 g/sm after expansion, the density is 0.15-0.3 g/sm. The blowup (thermal expansion) of vermiculite is usually performed in fluidized bed furnaces. The expanded vermiculite has a low thermal conductivity and is a good heat insulation material. 

Vermiculate-based heat insulation materials may be made with firing and without firing. The first step in processing is refining and expansion (blowup). In fired processing, the expanded vermiculite is mixed with clay and shaped in blocks by pressing and then fired in a tunnel kiln up to 900-1,000 °C. Fired materials do not contain water and do not absorb water from the atmosphere the safe service temperature of fired vermiculite blocks is superior to the safe service temperature of unfired ones. 

Other uses-Expanded vermiculite is used as an absorbent for industrial spill containment and cleanup, in groimd form as an alternative to asbestos for brake linings, in refi actoiy mold releases, and as a water filtration medium in aquaculture. Unexpanded vermicuHte is used to cover molten metal prior to casting, where the heat of the metal expands the mineral into an insulating l er. 

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