Chemical Properties
off-white powder
Brand name
Vanclay (Vanderbilt).
General Description
Odorless white to yellowish or grayish powder. Contains mainly the clay mineral KAOLINite (Al2O3 SiO2)2 H2O)2), a hydrous aluminosilicate. KAOLINite has mp 740-1785°C and density: 2.65 g cm-3. KAOLINe is insoluble in water but darkens and develops a earthy odor when wet.
Reactivity Profile
KAOLIN is stable and chemically unreactive under ordinary conditions.
Hazard
Respirable fraction; questionable carcinogen.
Description
Kaolin or china clay is a naturally occurring, almost white, hydrated aluminum silicate. This material does not exhibit a high degree of slip. Kaolin boasts good absorbency, is dense, and is sometimes used to reduce the bulk densities in loose powder products. It provides a matte surface effect, which can slightly reduce sheen left by some talc products.
Physical properties
Sericite is a mineral similar to white mica in shape and composition. It has a very fine grain size and a silky shine. This material is soft and smooth and has a slippery feel on the skin. Sericite may be coated with silicone and other treatments for enhanced water repellency and skin adhesion.
Occurrence
Kaolin is a naturally occurring clay that is treated for impurities.
Indications
Kaolin is a naturally occurring hydrated
aluminum silicate that is prepared for medicinal
use as a very finely divided powder. The rationale behind
its use in acute nonspecific diarrhea stems from its
ability to adsorb some of the bacterial toxins that often
cause the condition.
Preparation
The extraction of KAOLIN (china clay) from its deposits is usually performed in three steps: open-pit mining, mineral processing and beneficiation, and drying.
Open-pit operations require the removal of ground overlying the clay (i.e., overburden). The
exposed clay is then mined by a hydraulic mining process, that is, a high-pressure water jet
from a water cannon called a monitor erodes the faces of the pit. This liberates from the
quarry face the china clay, together with sand and mica. The slurry formed flows to the lowest part of the pit or sink, where it is pumped by centrifugal pumps to classifiers, where
coarse silica sand is removed. The silica sand is later reused for landscape rehabilitation. The
remaining suspension of clay is transported by underground pipeline to the mineral-processing and beneficiation plant, where a series of gravity separation techniques are used to
remove particulate materials such as quartz, mica, and feldspars. Sometimes the purified
clay slurry undergoes an additional chemical bleaching process that greatly improves its
whiteness. The refined clay suspension is then filtrated, and the filtration cake with a moisture content of about 25 wt.% passes through a thermal drier fired by natural gas to yield
a final product with 10 wt.% moisture. The end product is normally sold in pelletized form
with a pellet size ranging from 6 to 12 mm.
Production Methods
Kaolin is a hydrated aluminum silicate obtained by mining naturally
occurring mineral deposits. Large deposits are found in Georgia,
USA and in Cornwall, England.
Mined kaolin is powdered and freed of coarse, gritty particles
either by elutriation or by screening. Impurities such as ferric oxide,
calcium carbonate, and magnesium carbonate are removed with an
electromagnet and by treatment with hydrochloric acid and/or
sulfuric acids.
World Health Organization (WHO)
Kaolin, a hydrated aluminium silicate, is an absorbent and has
been used to treat diarrhoea because of its ability to bind and inactivate bacterial
toxins. However, it has been shown to induce only a slight change in stool
consistency and there is no evidence that it can reduce the duration or the severity
of diarrhoeal disease. It does not reduce fluid and electrolyte losses. It cannot be
recommended in the treatment of diarrhoea.
Pharmaceutical Applications
Kaolin is a naturally occurring mineral used in oral and topical
pharmaceutical formulations.
In oral medicines, kaolin has been used as a diluent in tablet and
capsule formulations; it has also been used as a suspending vehicle.
In topical preparations, sterilized kaolin has been used in poultices
and as a dusting powder. Therapeutically, kaolin has been used in
oral antidiarrheal preparations.
Industrial uses
The name kaolin comes from the two Chinese words kao-ling, meaning high ridge, and was originally a local term used to describe the region from which the clay was obtained. Kaolin (Al2O32SiO22 H2O) usually contains less than 2% alkalies and smaller quantities of iron, lime, magnesia, and titanium. Because of its purity, kaolin has a high fusion point and is the most refractory of all clays. Lone kaolins are widely used in casting sanitaryware, ceramics, and refractories.
Georgia china clay is one of the most uniform kaolins to be found. Generally speaking, there are two types of Georgia-sourced kaolin, both of which are widely used for casting and other processes. One type imparts unusually high strength and plasticity, and is used for both casting and jiggering where a high degree of workability is required. The other type typically is a fractionated, controlled particle size clay that also behaves well in casting, dries uniformly, and reduces cracking of ware.
Mechanism of action
For crop protection it mainly has a non-toxic mode of action, acting via its physical properties. It may also interfere with feeding behaviour and egg-laying. For animal health it can bind toxins, bacteria, and excess water in the gut. It adheres to the gastrointestinal mucosa, forming a protective coating that helps prevent the absorption of harmful substances.
Side effects
It is almost harmless and is effective
in many cases of diarrhea if taken in large enough
doses (2–10 g initially, followed by the same amount after
every bowel movement). The adsorbents are generally
safe, but they may interfere with the absorption of
some drugs from the GI tract.
Safety
Kaolin is used in oral and topical pharmaceutical formulations and
is generally regarded as an essentially nontoxic and nonirritant
material.
Oral doses of about 2–6 g of kaolin every 4 hours have been
administered in the treatment of diarrhea.
Veterinary Drugs and Treatments
Although its efficacy is in question, kaolin/pectin is used primarily
in veterinary medicine as an oral anti-diarrheal agent. It has also
been used as an adsorbent agent following the ingestion
of certain
toxins. Administration may be difficult due to the large volumes
that may be necessary
to give orally.
Source
Premier-quality deposits of kaolin such as those mined in Cornwall in the United Kingdom, Georgia and the Carolinas in the southe astern United States, and the Amazon Basin of Brazil.
Other suppliers of quality kaolin include France, Germany, the Czech Republic, Malaysia, and Australia.
storage
Kaolin is a stable material. Since it is a naturally occurring material,
kaolin is commonly contaminated with microorganisms such as
Bacillus anthracis, Clostridium tetani, and Clostridium welchii.
However, kaolin may be sterilized by heating at a temperature
greater than 160°C for not less than 1 hour. When moistened with
water, kaolin darkens and becomes plastic.
Kaolin should be stored in a well-closed container in a cool, dry
place.
Incompatibilities
The adsorbent properties of kaolin may influence the absorption of
other orally administered drugs. Drugs reportedly affected by
kaolin include amoxicillin; ampicillin;cimetidine; digoxin;
lincomycin; phenytoin; and tetracycline. Warfarin absorption by
rat intestine in vitro was reported not to be affected by kaolin.
With clindamycin, the rate (but not the amount) of absorption was
affected by kaolin.
Toxics Screening Level
The initial threshold screening level (ITSL) for kaolin is 20 μg/m3 based
on an 8-hour averaging time.
Regulatory Status
Accepted in Europe as a food additive in certain applications.
Included in the FDA Inactive Ingredients Database (oral capsules,
powders, syrups, and tablets; topical preparations). Included in
nonparenteral medicines licensed in the UK.
Pesticide Type
Insecticide; Veterinary substance
