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Showing posts with label Raw Material. Show all posts
Showing posts with label Raw Material. Show all posts

Characteristics of China Clay Required for Ceramic and Other Industries

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9-Feb-2010

China clay is used as an important raw material for a number of industries. The most important is the ceramic industry where it is used for the manufacture of earthware, fine china, tiles etc. and also in other industries such as paper, textile, rubber, pharmaceutical, leather, paint, plastics, petroleum, cosmetic etc. Use of China Clay as Raw Material in the Production of Refractory Insulation Bricks has been discussed in a separate post.

India has extensive deposits of all varieties of china clays most of which after mining and processing, get consumed by the various domestic industries while around 20% - 30% of its total annual production are exported to other countries. The chemical compositions, other properties, uses, and occurrences of Indian china clays have been discussed in detail in a separate article
Indian China Clays - Properties, Occurrences and Uses
As we know that the specific requirements of china clays for different industries are different. Here in this article we present the important characteristics [see the Table below] of china clay required for ceramic industry (IS: 2840 - 1993) -

Characteristics
Requirements
Type - I (unwashed)
Type - II (washed)
Grade 1
Grade 2
Grade 3
Grit content / Fineness               (+45 micron IS sieve, max%)
2
3
4
1
Particle size distribution (%)
(a) Coarser than 25 micron (max)
(b) Coarser than 10 micron (max)
(c) Finer than 2 micron (max)

3
10
70

6
12
65

9
15
45

1
5
75
Plasticity (by hand feel)
Very
Good
Fair
Very good
Water of plasticity (max %)
30
32
34
28
Attenberg Number (min)
18
15
12
20
Al2O3 % (min)
28
25
20
28
Fe2O3 % (max)
1.5
2.0
2.0
1.5
TiO2 % (max)
1.5
2.0
2.0
1.5
(Fe2O3 + TiO2) % (max)
2.75
3.5
3.75
2.5
LOI % (max) [dried at 110OC]
10.5
9.5
9.0
11.0
Shrinkage, linear % (max)          [dried at 110OC]
6
7
8
6
Water absorption % (max)        [after firing at 1350OC]
3
5
9
2
Colour after firing at 1350OC
Creamish white
Pale to dull cream
Light gray
White pale cream without specks
MOR (MPa) [at 110OC] (min)
3.5
3.0
2.5
4.0
        
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Beneficiation of China Clay

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8-Feb-2010

Major Impurities in China Clay are quartz, mica, feldspar and iron oxide minerals. China clay is an important raw material for many industries like rubber, textile, paper, pharmaceutical, cosmetic, paint, and refractory besides ceramic industry. For any value-added application, the run-of-mines (ROM) clay is to be processed to remove or reduce the ancillary mineral impurities associated with the same. Beneficiation helps to achieve required particle size and size distribution and also to attain other physical and optical properties for the clay. [Refer to the article Improvement in the Quality of Indian China Clay after Various Treatments]. The different processes generally employed for beneficiation of china clays are:

1. Size separation through levigation technique;
Refractory Lining | Installation: China clay lump image2. Hydrocycloning by wet route;
3. Magnetic separation by high intensity magnetic separator (HIMS);
4. Froth flotation;
5. Deflocculation;
6. Chemical treatments like Acid Leaching and Bleaching.
7. Drying
8. Micronizing
9. Air-classification and Surface treatment.
Refractory Lining | Installation: China clay after beneficiation image
The ‘Levigation’ process by which the washing is done, involves passing the clay slurry through a series of troughs or channels with different slopes. This process aids in the settling of grit and other heavy mineral while floating of light fractions like mica. Settling of finest quality takes place in the final tank. This beneficiated clay is then dried and marketed to different industries as per the required specification and grading. 

‘Micronizing’ includes Test for physical properties like Bulk density, Oil absorption, Whiteness, and Particle - size distribution analysis etc. Sometimes, Surface Treatment is also done for testing of hydrophobicity, oil absorption and uniformity of coating.   
Mining and beneficiating activities often occur in a single location. De-colorization of clay is also attempted for certain clays which are coloured due to the presence of iron and titanium oxides. This is important since colour after firing is an important characteristic criterion of the china clay which is required for Ceramic Industry and some times in refractory industry too.
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