ANS:A - hammer mills

Size reduction of asbestos and mica is typically done by hammer mills. Here's why:

1. Hammer Mills:
   • Hammer mills are machines that use rotating hammers or bars to impact and crush materials into smaller particles.
   • They are versatile and can handle a wide range of materials, including brittle and fibrous materials like asbestos and mica.
   • The hammers or bars inside the mill rotate at high speed and strike the material, breaking it apart.
2. Suitability for Asbestos and Mica:
   • Asbestos: Asbestos fibers are fibrous and brittle, requiring a method that can break them into smaller, manageable sizes without excessive fiber damage.
   • Mica: Mica is a mineral with layered structure and can be brittle. Hammer mills can effectively break down mica into smaller particles suitable for various applications.
3. Other Options:
   • Rod Mills: Rod mills are typically used for coarser grinding and are more suitable for minerals that require finer grinding.
   • Gyratory Crushers: These are used for primary crushing of large materials and are less suitable for the delicate nature of asbestos and mica.
   • Crushing Rolls: Also known as roll crushers, these are used for secondary and tertiary crushing of softer materials, and may not provide the impact force needed for efficient size reduction of asbestos and mica.