JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year MINERAL PROCESSING Previous Question Paper (March - 2022 - R18)

Mineral processing involves the physical separation of valuable minerals from gangue. The main steps are:

1. Comminution (Crushing and Grinding): Reduces the ore size to liberate valuable minerals from the gangue matrix. This is essential for subsequent separation processes.
2. Classification: Separates particles based on size or settling velocity, typically using screens or hydrocyclones, to ensure optimal feed size for downstream units.
3. Concentration: The core step where minerals are separated from gangue using physical or physicochemical properties such as density (gravity separation), magnetic susceptibility, or surface chemistry (flotation).
4. Dewatering: Involves thickening and filtration to remove water from the concentrate and tailings, facilitating transport and disposal.

Rod and tube mills are tumbling mills used for fine grinding. A Rod Mill consists of a cylindrical shell partially filled with long steel rods that span the length of the mill. As the shell rotates, the rods cascade and cataract, providing line contact grinding, which produces a uniform product size and prevents over-grinding. It is typically used for intermediate grinding.

A Tube Mill is a long cylindrical mill where the length is significantly greater than the diameter (often 3 to 5 times). It is filled with grinding media like steel balls or pebbles. Due to its length, it provides a high residence time, making it ideal for fine grinding or pulverizing materials to a very small particle size. The material travels through the length of the mill, undergoing progressive size reduction.

Sketch description: The mill is a horizontal rotating cylinder supported on trunnions. Feed enters through a hollow trunnion at one end, and the product discharges through a trunnion or peripheral ports at the other. The interior contains grinding media (rods or balls) that are lifted by the shell rotation and drop to crush the ore by impact and attrition.