|
Vermiculite is a natural, non toxic mineral which expands with the application of heat. The expansion process is called exfoliation and it is routinely accomplished in purpose-designed commercial furnaces. Vermiculite is formed by hydration of certain basaltic minerals, and is often found in association with asbestos. The mineral was extracted during the 1960s in Libby, Montana, under the commercial name Zonolite (the Zonolite brand was acquired by the W.R. Grace Company in 1963*). Mining operations on the Libby site stopped in 1990 in response to asbestos contamination. The United States government estimates that it is used in more than 35 million homes. World production of vermiculite in the year 2000 exceeded 500 kilotons (metric). Major producers of vermiculite include China, South Africa, Australia, Zimbabwe, and the United States.
Structure Vermiculite is a 2:1 clay, meaning it has 2 tetrahedral sheets for every one octahedral sheet. It has a medium shrink-swell capacity and is considered a limited-expansion clay. Vermiculite has a high cation exchange capacity at 100-150 meq/100g. Vermiculite clays are weathered micas in which the K+ ions between the molecular sheets are replaced by Mg2+ and Fe2+ cations. Commercial uses Commercial manufacture of exfoliated vermiculite While the main exporter of the vermiculite ore is South Africa, exfoliators can be found in many industrialised nations. Most import the ore from South Africa. While some exfoliators focus on only a few of the possible applications, others can provide vermiculite products for all its applications. It is common for vermiculite exfoliators to also exfoliate perlite, as both are often sold together. To set up a new exfoliation process, it is possible to find expert consultants to advise in the design and construction of the desired facilities. Vermiculite exfoliators have a truly international trade association called The Vermiculite Association *, to represent the industry's interests and to exchange information. Many of its members also maintain memberships in The Perlite Institute*. Fireproofing For many years, since the advent of the asbestos removal business, before which nearly everyone sold asbestos-based spray fireproofing, vendors could be cleanly categorised into users of MMMF (man-made-mineral-fibres), which included both rockwool and ceramic fibres, and cementitious sprays, whereby the binder was typically portland cement and the lightweight aggregate inside the plaster was vermiculite. For many years, makers of the cementitious products would point out the ill health effects that are possible from overexposure and lack of proper industrial hygiene procedures when working with MMMF. Vendors of the MMMF products would point out the possibility of asbestos contamination, particularly with US mined vermiculite ore. Ironically, both sides were defending against lawsuits in the asbestos litigation and eventually stopped pointing out these particular weak spots about one another, which makes sense, since most affected manufacturers are still in receivership as a means of dealing with the results of the asbestos litigation. One large British manufacturer of asbestos products even had to totally discontinue selling anything to North America directly, having to rely on surrogate trading companies for sales to that continent now. See also | ||||||||
|
| |||||||||
 |
|
| |