Ball clays are kaolinitic sedimentary clays that commonly consist of 20–80% kaolinite, 10–25% mica and 6–65% quartz, along with small amounts of organic matter (such as lignite) and trace amounts of other minerals such as pyrite and siderite.

They are a common raw material for various types of ceramics, where their primary roles are to impart unfired strength, plasticity or to aid rheological stability during the shaping processes.[1] Most ball clays impart colours ranging from buff to cream to off-white when fired in an oxidising atmosphere.[2][3]

The name "ball clay" is derived from the form of the extracted material when dug by spade as cubes, which then became rounded during subsequent transport, in Dorset and Devon, England during the early days of the industry during the 18th century.[4][3]

In 2008, UK production of ball clay was reported to be worth £82 million, with sanitaryware manufacturers being the largest single group of end users, representing 40% by volume.[5]

Locations

A ball clay mine in the UK

They are relatively scarce deposits due to the combination of geological factors needed for their formation and preservation.[6] Commercial extraction of ball clays is undertaken across the world, including:[7]

Production output

Global production of ball clay by country for 2002-2003 was estimated to be:[2]

Country 1,000 tonnes
South Africa 10
Africa - total 10
China 2,000
Malaysia 600
Indonesia 500
Thailand 300
Vietnam 200
India 150
Asia - total 3,750
Ukraine 3,500
Germany 3,000
Spain 1,200
United Kingdom 1,000
Turkey 550
Czech Republic 400
France 400
Italy 100
Poland 50
Europe - total 10,200
United States 1,200
North America - total 1,200
Australia 80
Oceania - total 80
Brazil 250
Argentia 50
Chile 5
South America - total 350
Global - total 15,385

Typical properties

Some selected typical properties of various UK ball clays are:[2]

Product name Hycast Rapide Sanblend 75 Slurry Prestige BLU Prestige TA Hyplas 71 Hymod Excelsior Hymod Blue
Source Bovey Bovey Bovey Petrockstow Petrockstow Wareham Warehan
Producing company Imerys WBB WBB WBB Imerys Imerys Imerys
Residue, wt% <125 µm 2.0 0.1 0.2 0.5 1.0 0.3 0.1
% <2 µm 70 78 82 77 57 92 89
% <1 µm 60 65 - - 50 87 79
% <0.5 µm 45 - - - 40 80 65
SiO2, % 55.0 53.7 54.0 60.5 69.0 49.0 53.0
Al2O3, % 29.0 28.9 31.2 25.8 20.0 35.0 31.0
Fe2O3, % 1.1 1.2 1.0 1.9 0.9 1.6 1.4
TiO2, % 1.1 1.1 1.2 1.5 1.7 1.3 1.0
CaO, % 0.2 - - - 0.1 0.3 0.3
MgO, % 0.3 - - - 0.4 0.3 0.5
K2O, % 1.6 2.5 3.0 2.9 1.9 1.2 3.2
Na2O, % 0.2 - - - 0.4 0.2 0.4
Carbon, % 2.0 2.5 0.2 0.6 0.1 0.3 0.4
LOI, % 12.0 12.0 9.0 8.0 5.4 12.0 9.2

History in the UK

The ceramic use of ball clays in Britain dates back to at least the Roman era. More recent trade began when a clay was needed to make tobacco pipes in the 16th and 17th century.[8] In 1771 Josiah Wedgwood signed a contract for 1,400 tons a year of ball clay with Thomas Hyde of Purbeck, enabling the production of thinner-walled ceramics.[9]

See also

References

  1. ^ 'Ceramic Raw Materials' 2nd edition. W.E. Worrall. Pergamon Press, 1982
  2. ^ a b c 'Industrial Minerals & Rocks - Commodities, Markets And Uses' J. E. Kogel. Society For Mining, Metallurgy And Exploration, 2006
  3. ^ a b "What is ball clay?". Industrial Minerals Association - North America. Archived from the original on 23 September 2009. Retrieved 5 August 2008.
  4. ^ ’Ball Clay Basics’ P. S. Powell. Ceram. Eng. Sci. Proc., 16 [3] 200-206, 1995. Pg. 200
  5. ^ ‘Ball Clay’ Mineral Plannng Factsheet. British Geological Surkey. 2008.
  6. ^ Highley, David; Bloodworth, Andrew; Bate, Richard (2006). "Ball Clay - Mineral Planning Factsheet" (pdf file). British Geological Survey. Retrieved 5 August 2008.
  7. ^ ’The Constitution, Evaluation And Ceramic Properties Of Ball Clays’ I. R. Wilson. Cerâmica vol.44 no.287-288 São Paulo May/June/July/Aug. 1998
  8. ^ "The Widespread Use of Ball Clay". Introduction to Ball Clays. The Ball Clay Heritage Society. Archived from the original on 6 October 2008. Retrieved 5 August 2008.
  9. ^ "History of Ball Clay - Swanage Railway". The Purbeck Mineral & Mining Museum. Archived from the original on 14 May 2008. Retrieved 5 August 2008.
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