China clay, also known as kaolin, is a naturally occurring mineral composed primarily of hydrated aluminum silicates. It is typically found in the form of white or near-white clay deposits. Calcined China clay, on the other hand, is China clay that has been subjected to a high-temperature process called calcination, which alters its properties.
Composition:
- China Clay: Naturally occurring hydrated aluminum silicate, primarily composed of kaolinite.
- Calcined China Clay: The same mineral composition as China clay, but with altered physical and chemical properties due to calcination.
Properties:
- China Clay: Soft, white, or near-white clay with good plasticity, low shrinkage, and excellent whiteness. It is commonly used in its raw form in various industries.
- Calcined China Clay: After calcination, the clay becomes more refractory, less plastic, and gains increased brightness and opacity. It may also exhibit altered particle size distribution and surface area.
Uses:
- China Clay: Widely used in ceramics, paper, rubber, paints, coatings, plastics, and pharmaceuticals for its properties like whiteness, plasticity, and inertness.
- Calcined China Clay: Often used as a filler or extender in various applications where improved brightness, opacity, and reinforcement properties are required. Commonly utilized in ceramics, paints, coatings, rubber, plastics, and catalysts.
Manufacturing Process:
- China Clay:
- Mining: China clay is typically mined from naturally occurring deposits using various methods like open-pit mining or underground mining.
- Beneficiation: The mined clay undergoes beneficiation processes to remove impurities and improve its quality.
- Processing: The processed clay may be further refined, dried, and micronized before being used in various industries.
- Calcined China Clay:
- Calcination: China clay is subjected to high temperatures (typically between 800°C to 1000°C) in a calcination process, often in rotary kilns or fluidized bed calciners.
- Transformation: During calcination, the clay undergoes physical and chemical changes, including the removal of water and organic matter, crystalline reordering, and the formation of meta-kaolin.
- Cooling and Grinding: The calcined material is cooled and then ground to the desired particle size distribution, often through processes like milling or pulverizing.
- Packaging: The Calcined China Clay is then packaged and distributed for various industrial applications.
- Calcination: China clay is subjected to high temperatures (typically between 800°C to 1000°C) in a calcination process, often in rotary kilns or fluidized bed calciners.
In summary, while China clay and calcined China clay share the same mineral composition, their properties and use differ significantly due to the calcination process. Calcined China clay offers enhanced properties such as improved brightness, opacity, and refractoriness, making it suitable for specific applications where these characteristics are desired.