JNTU B.Tech II Year MINERAL PROCESSING Previous Question Paper (September - 2021 - R18)

Mineral processing, also known as ore dressing, is the practice of separating valuable minerals from their associated gangue minerals based on physical and surface chemical properties. The process is generally divided into four primary stages: liberation, concentration, dewatering, and disposal.

1. Comminution (Liberation): This stage involves size reduction through crushing and grinding to break the ore into smaller particles, ensuring that valuable minerals are physically separated from the gangue. It typically involves primary crushing (jaw or gyratory crushers), secondary crushing (cone crushers), and grinding (ball or rod mills).

2. Classification: Following comminution, particles are sorted by size using screens or hydrocyclones. This ensures that only particles within the optimal size range for downstream separation proceed to the concentration stage, while oversized material is returned for further grinding.

3. Concentration: This is the core stage where the valuable minerals are separated from the gangue. Common methods include gravity separation (using jigs or shaking tables), magnetic separation, electrostatic separation, and froth flotation. The product is divided into two streams: the concentrate (high-grade valuable mineral) and the tailings (waste material).

4. Dewatering: The final stage involves removing water from the concentrate and tailings to facilitate transport and storage. This is achieved through thickening, filtration, and thermal drying.

Flow Sheet Representation:

The tailings generated during concentration are sent to a tailings dam for safe disposal, while the overflow from classification is recycled back to the grinding circuit to maintain efficiency.

A Blake Jaw Crusher is a double-toggle machine characterized by a fixed jaw and a swinging jaw pivoted at the top. The primary components include the frame, fixed jaw plate, swinging jaw plate, pitman, toggle plates, eccentric shaft, and flywheel.

The operation of a Blake Jaw Crusher is influenced by several critical factors:

• Eccentric Shaft Speed: Increasing the speed improves capacity but can lead to excessive vibration and wear. If the speed is too high, the material may not have sufficient time to drop through the discharge opening, leading to choking.
• Toggle Angle: The angle of the toggle plates determines the mechanical advantage and the stroke length. A larger angle increases the crushing force but reduces the stroke, impacting the throughput.
• Setting (Closed Side Setting): This is the minimum distance between the jaw plates at the bottom. It directly dictates the maximum size of the product. A smaller setting results in a finer product but reduces total capacity.
• Feed Characteristics: The hardness, abrasiveness, and moisture content of the ore affect the wear rate of the jaw plates and the power consumption. Sticky or high-moisture ores can cause bridging or clogging in the crushing chamber.
• Nip Angle: This is the angle between the fixed and swinging jaw plates. It must be small enough (typically 15-25 degrees) to prevent the ore from slipping upward (spitting) during the crushing stroke.
• Stroke Length: The amplitude of the swinging jaw motion affects the reduction ratio. A larger stroke is beneficial for harder materials but increases the stress on the machine frame and toggle mechanism.