JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III MINERAL PROCESS ENGINEERING Previous Question Paper (February/March - 2022 - R16)

Crushing and grinding are the primary unit operations in mineral processing designed to reduce the particle size of run-of-mine ore to liberate valuable minerals from the gangue. The process relies on the application of mechanical stress to overcome the internal cohesive forces of the material.

The theory of size reduction is governed by three fundamental laws that relate the energy input (E) to the change in particle size:

1. Rittinger's Law: Proposes that the energy required for size reduction is directly proportional to the new surface area created. It is most applicable to fine grinding where surface area generation is the dominant factor. The formula is
   E = K_R (1/d_2 - 1/d_1)
2. Kick's Law: Assumes that the energy required is proportional to the reduction ratio of the particles. This law is generally more accurate for coarse crushing operations where the energy is consumed primarily in elastic deformation. The formula is
   E = K_K ln(d_1/d_2)
3. Bond's Law: Acts as an intermediate theory, stating that the energy is proportional to the square root of the change in particle size. It introduces the Work Index (Wi), which represents the energy required to reduce a material from infinite size to 100 microns. The formula is
   E = 10 W_i (1/sqrt(d_2) - 1/sqrt(d_1))

Crushing typically involves compressive forces in machines like jaw or gyratory crushers, while grinding utilizes a combination of impact and attrition forces within tumbling mills (ball or rod mills). The efficiency of these processes is limited by the physical properties of the ore, such as hardness, toughness, and cleavage, as well as the moisture content and the feed size distribution.

Mineral processing is the art and science of treating run-of-mine ores to separate valuable minerals from gangue (waste) material by utilizing the physical and surface-chemical properties of the minerals without changing their chemical identity.

The primary objectives of mineral processing are:

• Liberation: Breaking the ore to detach valuable mineral grains from the gangue matrix.
• Separation: Concentrating the valuable minerals into a product (concentrate) while rejecting the unwanted material (tailings).
• Upgrading: Increasing the grade of the valuable mineral to meet the requirements of downstream metallurgical processes like smelting or refining.
• Economic Viability: Reducing the volume of material to be transported and processed, thereby lowering overall production costs.

The advantages of mineral processing include:

• Cost Efficiency: By rejecting waste at the mine site, transportation and energy costs for subsequent smelting or chemical extraction are significantly reduced.
• Resource Conservation: It allows for the exploitation of low-grade ore deposits that would otherwise be considered uneconomical.
• Environmental Management: Proper processing allows for better control of tailings and waste disposal, facilitating the recovery of secondary minerals or by-products.
• Process Optimization: Providing a consistent, high-grade feed to metallurgical plants ensures stable and efficient operation of furnaces and chemical reactors.