CASE STUDY: Halloysite Clay
Halloysite clay is unique in two ways. It is the whitest clay in the world, and it is the only industrial mineral produced in New Zealand which is almost totally exported.
The New Zealand halloysites mined in Northland are processed to produce the whitest clay in the world. Halloysite clay is used to produce the highest quality porcelain and bone china. The world's leading porcelain and bone china manufacturers use halloysite from New Zealand.
Halloysite clays are currently mined in Northland at two sites: Matauri Bay and Mahimahi.
Imerys Tableware New Zealand Ltd. (formerly New Zealand China Clays Ltd) operate this halloysite clay deposit at Matauri Bay in Northland.
The unique and exceptionally white primary clay deposits at MatauriBay formed from the alteration of volcanic rocks. The feldspar minerals in the parent rhyolite have been broken down by low temperature hydrothermal alteration to form halloysite. The rhyolitic rocks came up through a weakness in the earth's crust as part of the Parahaki volcanic series. Weathering over millions of years has 'rotted' the rocks into clay minerals and residual silica. because the iron levels are very low the clay is exceptionally white - the whitest clay in the world.
Halloysite is 50% silica and 50% clay. Al2Si2O5(OH)42H2O+SiO2
The world's leading porcelain and bone china manufacturers use halloysite from Imerys Tableware New Zealand Ltd.
About 80,000 cubic metres of the raw clay are mined each year by Imerys Tableware New Zealand Ltd. The clay is excavated and transported to the treatment facility. At the present rate of production the current site has another 40 years of production.
The halloysite clay passes through a mill into a sandgrinder, then through a surge tank and into a centrifuge. After passing through a series of mixing tanks it is fed to a filter press. It is then dried and packaged ready for export. The finished clay products are containerised and transported to Auckland for shipping to markets overseas. The halloysite beneficiation process removes most of the silica from the clay. This coarse fraction silica sand is sold in New Zealand for concreting, plastering, and recently as sand for golf course bunkers. Both the clay and silica are very abrasive and result in high wear rates on machinery.
Clay products are exported to 24 countries for tableware manufacture, including porcelain, bone china and fine china. Some of Imerys Tableware New Zealand's better known customers are Noritake (Japan), Duraline (England), Haeng Nam (Korea), Tatung (Taiwan), Monno (Bangladesh), Limoges (France), and Lladro (Spain). In addition the clay produces exceptionally tough hotelware.
Pierre Balmain by Yamaka
The fineness of particle size enables halloysite clays to be used extensively as suspension agents in glaze preparations. The purity of the clay and the low iron and titania content produce exceptional whiteness and translucency to ceramic ware.
A small but increasing amount is used for hi-tech ceramic applications. Honeycomb catalyst support units are used in the exhaust systems of motor vehicles to clean up exhaust gases. Molecular sieves (synthetic Zeolites) are used in a wide range of applications including separation of liquids and gaseous mixtures, water purification, and in refining industries.
Waste water and silica are drained into purpose built ponds which provide a breeding ground for birds. The ponded areas are later drained and regrassed. At Mahimahi 6,600 trees have been planted.
Waste water containing clay from the mining operation collects in shallow ponds. These are rehabilitated in stages. A rehabilitated area can be seen in the foreground just behind the clay stockpile.
This information was prepared with the help of Imerys Tableware New Zealand Ltd. (formerly New Zealand China Clays Ltd).
For further information visit the Imerys Tableware New Zealand Ltd. website: www.imerys-tableware.com
[case study: limestone]
[case study: halloysite]