WHAT IS KAOLIN?
Kaolin or china clay is a commercial clay composed principally of the hydrated aluminosilicate clay mineral kaolinite. The commercial value of kaolin is based on the mineral’s whiteness and its fine, controllable particle size. Particle size affects fluidity, strength, plasticity, colour, abrasiveness and ease of dispersion. Other important properties include its flat particle shape, its soft and non-abrasive texture and its chemical inertness. The kaolinite content of processed kaolin varies, but is generally in the range of 75 to 94%. Kaolins from different deposits in the UK and from different parts of the world have markedly different properties and the range of minerals associated with kaolin influence its suitability for different applications.
The UK is a leading world producer and exporter of china clay and ball clay. Both minerals have a very limited geographical occurrence and their importance has been recognised by the establishment of Mineral Consultation Areas designed to ensure that these valuable minerals are not unnecessarily sterilised by other forms of development.
Kaolin production is confined to the primary deposits within the granites of South-West England, Hensbarrow (St Austell) in Cornwall and Dartmoor (Lee Moor) in Devon. Kaolin is Britain’s most important mineral export after hydrocarbons. In 2002 some 88% of total sales, valued at about £187 million were exported, making a considerable positive contribution to the balance of payments. There are no significant imports.
Kaolin is extracted from the ground by surface working (open cast method). It is tradtionally liberated from its host rock by powerful water jets (monitors) and the resultant slurry undergoes settlement and separation to remove the quartz, mica and unaltered feldspar. The clay is improved through bleaching, grinding, magneting and blending before being dried (and in some cases, calcined) and dispatched. The bulk of production is exported by sea (around 77%), with the remainder by rail (13%) and road (10%).
Kaolin has a range of industrial applications grouped into three main market areas: – Paper, ceramics and specialty minerals. Paper accounts for the majority of sales at around 70% of total sales. It is used in two distinct ways, as a filler between the paper fibres, to improve printing quality and as a coating, to enhance the surface properties of the paper.
Ceramics is the second most important sector, accounting for some 22% of total sales. It is used for the manufacture of sanitaryware, tableware, tiles, electrical porcelain and glazes. Fired brightness, strength and (in sanitaryware) rheological properties are the key parameters for these ceramic whitewares It is also used in refractories where it is of value for its high alumina content. Specialty applications include paint, rubber, plastics, adhesives and sealants and pharmaceuticals, where it is mainly used as a filler.
RESTORATION AND WASTE DISPOSAL
Kaolin production requires a large amount of waste to be removed. This consists of unkaolinized granite, sand and mica. Each tonne of kaolin recovered typically produces up to 9 tonnes of waste. Total industry arisings amount to 22 million tonnes a year. Currently some 2.5 million tonnes of waste sand and crushed rock are sold as aggregates, providing an alternative to primary aggregates.
The remaining waste has to be backfilled into disused pits or tipped on the surface. Backfilling is the preferred option and has been undertaken where possible over the last 30 years in over 40 pits. This process is planned to continue with backfilling accounting for around 30% of future waste mineral disposal.
The industry in Cornwall was a partner of the Cornish Heathland Project having created some 750 hectares of heathland. This is the largest heathland recreation project in Western Europe, contributing some 12.5% to the UK’s Biodiversity Action Plan for heathland recreation.
In addition the industry is planting some 340 hectares of broadleaf woodland, restoring some 325 hectares of existing broadleaf woodland and converting around 115 hectares of non-native tree belts to native broadleaf species.
It has also provided the land for the China Clay Trails Project leading to the creation of a network of paths for walkers, cyclists and horse riders around the St Austell china clay area. These trails link with the ‘Cornish Way’ section of the National Cycle Network.
The industry and the mineral planning authority in Cornwall have devised a Tipping and Restoration Strategy addressing the problems of mineral waste disposal and the rehabilitation of tips and are currently working to its recommendations.