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Kaolin is a potassium silicate with kaolinite as the
main constituent. Its first occurrence is dated at about
70 million years ago. Kaolin is the result mainly of
alterations to granite and feldspar caused by weathering.
Dependent on its intended use,
we make a distinction in the technical field between
raw kaolin and calcined kaolin.
Raw kaolin is used in the paper industry,
for example, as well as in the manufacture of chinaware
and engineering ceramics, etc. The kaolin must be cleaned
prior to being processed. To this end, the product is
washed in agitators and hydrocyclones, to free it from
contaminants such as quartz and undecomposed feldspars.
The raw kaolin is used predominantly in the form of
a slurry.
Some applications call for the product to be in dry
condition, meaning that it either has to be subsequently
dried or completely dry-processed from the word go.
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Water is extracted from the kaolin by thermal treatment in shaft
or tube kilns, whereby the kaolinite is heated to just below
its melting temperature – and is then known exclusively
as calcined kaolin. Different combustion temperatures
result in different properties, for example, high-calcined kaolin
is used mainly in the ceramics industry, whereas low-calcined
kaolin is used as a filler.
Because in contrast to raw kaolin,
the primary particle is no longer present in calcined kaolin,
it must be ground.
Systems combining, for example, ball mills and downstream classifiers
are designed and delivered by Alpine to match the problem specification
and final application.
The system example shows an actual system that was designed
and delivered for the quartz-free processing of calcined kaolin.
The specifications were as follows:
Product: calcined kaolin
Feed size: < 10 mm
Required end-product fineness: 97% < 15 µm
Processing: without iron contamination
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Legend
1 = Feed bin
2 = Proportioning belt weigher
3 = Metal separator
4 = Grinding additives
5 = Super Orion Ball Mill
6 = Sieving machine for Al2O3 fragments
7 = Turboplex Ultrafine Classifier ATP
8 = Rotary valve
9 = Automatic reverse jet filter
10 = Flap valve
11 = Fan with silencer
12 = End-product silo with activated discharge
13 = Control cabinet
A = Feed product
B = Grinding pearl fragments
C = End product
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The system operates in suction mode. To improve the flow behaviour
of the circuit material, a liquid grinding aid is added to the
feed product.
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