Vermiculite is a hydrous, silicate mineral that is classified as a phyllosilicate and
that expands greatly when heated. Exfoliation occurs when the mineral is heated sufficiently,
and the effect is routinely produced in commercial furnaces. Vermiculite is formed by weathering
or hydrothermal alteration of biotite or phlogopite. Large commercial vermiculite mines currently
exist in Russia, South Africa, China, and Brazil.
Occurrence Vermiculite was first described in 1824 for
an occurrence in Millbury, Massachusetts, USA. Its name is from Latin vermiculare, to
breed worms, for the manner in which it exfoliates when heated.
It typically occurs as an alteration product at the contact between felsic and mafic or
ultramafic rocks such as pyroxenites and dunites. It also occurs in carbonatites and metamorphosed
magnesium rich limestone. Associated mineral phases include: corundum, apatite, serpentine
and talc. It occurs interlayered with chlorite, biotite and phlogopite.
Structure Vermiculite is a 2:1 clay, meaning it has
2 tetrahedral sheets for every one octahedral sheet. It is a limited expansion clay with
a medium shrink-swell capacity. Vermiculite has a high cation exchange capacity at 100-150
meq/100 g. Vermiculite clays are weathered micas in which the potassium ions between
the molecular sheets are replaced by magnesium and iron ions.
Commercial uses Moulded shapes: this process involves mixing
exfoliated vermiculite with inorganic bonding agents such as sodium silicate and potassium
to produce an 'earth damp' mixture. This material is then hydraulically pressed into shape in
a mould, and then heat cured at temperatures up to 180 °C for up to 24 hours depending
upon the thickness of the moulded part. Such parts can withstand service temperatures of
up to 1150 °C and are often used in the aluminium smelting industry as back-up insulation
behind the carbon cathode in the potcells which contain the molten mixture of cryolite
and alumina. The moulded shapes and boards are used in:
Open fireplaces High-temperature or refractory insulation
Acoustic panels Fireproofing of structural steel and pipes
Calcium silicate boards: exfoliated vermiculite is added to a calcium silicate slurry, this
is then dewatered by pressing or by using one of the FourdrinerHatschek processes to
form a flat board which is then heat cured under pressure for periods up to 24 hours.
Brake linings: finer grades of exfoliated vermiculite are being used in brake linings
primarily for the automotive market. The properties of vermiculite that make it an appropriate
choice for use in brake linings include its thermal resistance, ease of addition to other
raw materials to achieve a homogenous mix and its shape and surface characteristics
Roof and floor screeds and insulating concretes: exfoliated vermiculite can be added at site
to Portland cement and other aggregates, rheological aids and water to produce roof and floor concrete
screeds or lightweight concrete which have the benefit of being lightweight and insulating.
In many cases vermiculite based roof screeds are often used in conjunction with other insulation
materials such as polystyrene board to form a total roofing system. A bituminous binder
can also be used with exfoliated vermiculite can to produce a dry, lightweight roof screed
which has the advantages of low thermal conductivity, low moisture content and ease of placement
by pouring from the bag and then tamping. Soilless growing media: exfoliated vermiculite
is combined with other materials such as peat or composted pine bark compost to produce
soilless growing media for the professional horticulturalist and for the home gardener.
These mixes promote faster root growth and gives quick anchorage to young roots. The
mixture helps retain air, plant food and moisture, releasing them as the plant requires them.
These mixes were pioneered by Boodley and Sheldrake
Seed germination: either used alone or mixed with soil or peat, vermiculite is used to
germinate seeds. Very little watering is required. When vermiculite is used alone, seedlings
should be fed with a weak fertilizer solution when the first true leaves appear. A tablespoon
of soluble fertilizer per one imperial gallon of water is the recommended mix
Storing bulbs and root crops: pour vermiculite around bulbs placed in container. If clumps
are dug, allow to dry for a few hours in the sun and then place in cartons or bushel baskets
and cover with vermiculite. The absorptive power of vermiculite acts as a regulator that
prevents mildew and moisture fluctuation during the storage period. It will not absorb moisture
from the inside of stored tubers, but it does take up free water from the outside, preventing
storage rot. As a soil conditioner: Where the native soil
is heavy or sticky, gentle mixing of vermiculite up to one-half the volume of the soil is recommended.
This creates air channels and allows the soil mix to breathe. Mixing vermiculite in flower
and vegetable gardens or in potted plants will provide the necessary air to maintain
vigorous plant growth. Where soils are sandy, mixing of vermiculite into the soil will allow
the soil to hold water and air needed for growth.
As loose-fill insulation: Exfoliated vermiculite treated with a water repellent is used to
fill the pores and cavities of masonry construction and hollow blockwork to enhance fire ratings,
insulation and acoustic performance. Coarse grades of exfoliated vermiculite can be used
to insulate lofts and attics. Exfoliated vermiculite has the benefit of being easy to use with
application consisting of pouring the vermiculite between the joists and then leveling
Refractory/Insulation gunning and castable mixes: exfoliated vermiculite can be combined
with high alumina cements and other aggregates such as expanded shale, clay and slate to
produce refractory/insulation concretes and mortars. In the early days of their uses these
products were batched at or very close to the place of installation, this continues
to be the case in some limited circumstances, however more and more use is being made of
pre-batched proprietary mixes. Mixes containing vermiculite are used in areas where strength
and corrosion/abrasion resistance are of secondary importance, the most important factor being
the insulation performance of the in place refractory lining. These mixes find their
uses in such areas in industries including iron/steel, cement and hydrocarbon processing
As a constituent of a coating: vermiculite dispersions are typically either chemically
or physically very finely delaminated vermiculite in a fluid medium. These dispersions can be
used to make vermiculite 'paper' sheet by simply pouring them on to a piece of smooth
low surface energy plastic and allowing to dry, the resulting sheet can then be peeled
off the plastic.Typical end uses for vermiculite dispersions include in high temperature coatings
or binders for construction materials, gaskets, specialty papers/textiles, oxidation resistant
coating on carbon based composites, and as barrier coatings for films.
As a packing material, valued for its high absorbency
Waste treatment: the cation exchange capacity of vermiculite allows it to be used in fluid
purification processes for waste water, chemical processing and the pollution control of air
in mines and gases in industrial processes. In addition to its ion exchange properties
exfoliated vermiculite will retain liquids within the inter-laminar voids of the individual
particles as well as between the particles themselves.
As a substrate for various animals and/or incubation of eggs
As a lightweight aggregate for plaster, proprietary concrete compounds, firestop mortar and cementitious
spray fireproofing: Exfoliated vermiculite is used in both hand and spray applied general
building plasters to improve coverage, ease of handling, adhesion to a wide variety of
substrates, fire resistance, and resistance to chippingshrinkage.
As an additive to fireproof wallboard As a component of the interior fill for firestop
pillows, along with graphite As a carrier for dry handling and slow release
of agricultural chemicals As a growing medium for hydroponics.
As a hot topping: both exfoliated and crude vermiculite have been used for hot topping
in the steel industry. When poured onto molten metal crude vermiculite exfoliates immediately
and forms an insulating layer allowing the material to be transported to the next production
process without losing too much heat. Used to permit slow cooling of hot pieces
in glassblowing, lampwork, steelwork, and glass beadmaking
Used in in-ground swimming pools to provide a smooth pool base: Finer grades of exfoliated
vermiculite plus Portland cement may be combined either on site or a factory premix to provide
a base for swimming pool vinyl liners. These mixes are either pumped into place using a
rotor stator pump or hand poured. Used in commercial hand warmers
Used as a sterile medium for the incubation of reptile eggs
Light-weight insulative concrete Used in AGA cookers as insulation
Used in explosives storage as a blast mitigant Used to absorb hazardous liquids for solid
disposal Used in gas fireplaces to simulate embers
Used as part of a substrate for fungi cultivation Commercial manufacture of exfoliated vermiculite
In 2005, South Africa was the top producer of vermiculite with about 40% world share
followed by the USA and China, reports the British Geological Survey.
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
exfoliate perlite also, as both are often sold together. For those who want 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 an 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 While spray-applied asbestos-containing fireproofing
and girder insulation is still widely found in old construction, in some parts of the
world it is still being used. Recent improvements of these sprays replace asbestos with aggregates
of MMMF including rockwool and ceramic fibres. The cementitious versions of these fireproofing
sprays contain Portland cement and lightweight aggregates of the plaster vermiculite. Vermiculite
ore, particularly that ore extracted from the Libby Mine in Libby, Montana, U.S.A. may
contain asbestos. The U.S. EPA advises that vermiculite from the Libby Mine should be
considered to be contaminated with asbestos. Since the Libby mine has been closed since
1990, currently produced ores are considered safer because they have lower asbestos content.
Danger of exposure to asbestos in these spray-applied materials is greatly increased by not following
proper industrial hygiene procedures and by not following abatement regulations.
Asbestos contamination Although not all vermiculite contains asbestos,
some products were made with vermiculite that contained asbestos until the early 1990s.
Vermiculite mines throughout the world are now regularly tested for it and are supposed
to sell products that contain no asbestos. The former vermiculite mine in Libby, Montana,
did have tremolite asbestos as well as winchite and richterite — in fact, it was formed
underground through essentially the same geologic processes as the contaminants.
Pure vermiculite does not contain asbestos and is non-toxic. Impure vermiculite may contain,
apart from asbestos, also minor diopside or remnants of the precursor minerals biotite
or phlogopite. Controversy over health risks
The largest and oldest vermiculite mine in the United States was started in the 1920s,
at Libby, Montana, and the vermiculite was sold under the commercial name Zonolite. The
Zonolite brand and the mine was acquired by the W.R. Grace Company in 1963. Mining operations
at the Libby site stopped in 1990 in response to asbestos contamination. While in operation,
the Libby mine may have produced 80% of the world's supply of vermiculite.
The United States government estimates that vermiculite was used in more than 35 million
homes, but does not recommend its removal. Nevertheless, homes or structures containing
vermiculite or vermiculite insulation dating from before the mid 1990s—and especially
those known to contain the "Zonolite" brand—may contain asbestos, and therefore may be a health
concern. An article published in the Salt Lake Tribune
on December 3, 2006, reported that vermiculite and Zonolite had been found to contain asbestos,
which had led to cancers such as those found in asbestos-related cases. The article stated
that there had been a "cover-up" by W.R. Grace Company and others regarding the health risks
associated with vermiculite and that several sites in the Salt Lake Valley had been remediated
by the EPA when they were shown to be contaminated with asbestos. W.R. Grace Company has vigorously
denied these charges. The vermiculite deposit at the mine in Libby,
Montana, was heavily contaminated with asbestos. Numerous people were knowingly exposed to
the harmful dust of vermiculite that contained asbestos. Unfortunately, the mine had been
operating since the 1920s, and environmental and industrial controls were virtually non-existent
until the mine was purchased by the W.R. Grace Company in 1963. Yet, knowing the human health
risks, the mining company still continued to operate there until 1990. Consequently,
many of the former miners and residents of Libby have been affected and continue to suffer
health problems. Over 400 people in the town have died from asbestos-related disease due
to contamination from vermiculite mining from nearby Zonolite Mountain, where soil samples
were found to be loaded with fibrous tremolite, and countless others there who insulated their
homes with Zonolite have succumbed to asbestos-related diseases, most of whom never were employed
in environments where asbestos was an issue. After a 1999 Seattle Post-Intelligencer story
claimed that asbestos-related disease was common in the town, the EPA, in response to
political pressure, made cleanup of the site a priority and called Libby the worst case
of community-wide exposure to a toxic substance in U.S. history. The EPA has spent $120 million
in Superfund money on cleanup. In October 2006, W.R. Grace Company tried to appeal the
fines levied on them from the EPA, but the Supreme Court rejected the appeal. The United
States government is also pursuing criminal charges against several former executives
and managers of the mine for allegedly disregarding and covering up health risks to employees.
They are also accused of obstructing the government's cleanup efforts and wire fraud. To date, according
to the indictment, approximately 1,200 residents of the Libby area have been identified as
suffering from some kind of asbestos-related abnormality. Jury selection was to have been
completed in February 2009. The case ended in acquittals on May 8, 2009. On June 17,
2009, the EPA issued a public health emergency in and near Libby, thereby allowing federal
agencies to provide funding for health care, and for removal of contaminated insulation
from affected homes. See also
Passive fire protection Fireproofing
Firestop Asbestos
Perlite Sodium silicate
Plaster List of minerals
Square foot gardening References
External links The Vermiculite Association
Cornell Boodley and Sheldrake [1] US Geological Survey Vermiculite Section
Environmental Working Group United States Environmental Protection Agency
The Perlite Association [2] Petition for writ of certiorari to U.S. Supreme
Court U.S. EPA: Additional Frequent Questions on
Vermiculite Promat High Temperature Insulation