Model Answer
0 min readIntroduction
Mineral processing is a crucial step in the extractive metallurgy industry, aimed at separating valuable minerals from their gangue (unwanted material). Gravity concentration is one of the oldest and most widely used methods for achieving this separation, exploiting differences in specific gravity between minerals. The Wilfley Table, invented by A.M. Wilfley in 1906, is a sophisticated gravity concentration device that significantly improved upon earlier table designs. It remains a vital tool in the processing of various ores, particularly those containing fine particles, and is known for its efficiency and adaptability.
Principle of Operation: Gravity Concentration
The Wilfley Table operates on the principle of gravity concentration, which relies on the difference in specific gravity between valuable minerals and the waste gangue material. When a mixture of minerals and gangue is subjected to a pulsating motion in a flowing medium (usually water), the heavier minerals tend to settle more rapidly and are retained on the table, while the lighter gangue material is washed away. This separation is enhanced by riffles (raised bars) on the table surface, which trap the heavier minerals.
Construction of the Wilfley Table
The Wilfley Table is a rectangular table with a slightly inclined deck. Its key components include:
- Deck: The inclined surface where separation occurs. It’s typically made of steel and covered with riffles.
- Riffles: These are raised bars running across the deck, perpendicular to the direction of travel. They trap the heavier minerals. Riffles can be of various designs – square, triangular, or saw-tooth – depending on the mineral characteristics.
- Feed Box: Located at the higher end of the table, it distributes the slurry (mixture of mineral particles and water) evenly across the deck.
- Water Jackets: These surround the deck and provide a constant flow of water, which helps in washing away the lighter gangue.
- Eccentric and Cam Mechanism: This mechanism produces a pulsating motion to the table, enhancing the stratification of particles based on density. The eccentricity controls the stroke length and frequency of the pulsation.
- Discharge Ports: Located at the lower end of the table, these ports allow for the separate discharge of the concentrated mineral product and the tailings (waste material).
- Tilting Mechanism: Allows for adjustment of the table’s inclination, influencing the speed of particle travel and separation efficiency.
Working of the Wilfley Table
The process involves the following steps:
- Feeding: The slurry is fed onto the deck through the feed box.
- Stratification: The pulsating motion and the flowing water cause the heavier minerals to settle towards the bottom of the bed, while the lighter gangue rises to the top.
- Riffle Trapping: The heavier minerals are trapped behind the riffles.
- Washing: The flowing water washes away the lighter gangue material over the riffles.
- Discharge: The concentrated mineral product is periodically discharged from the table, typically by momentarily stopping the pulsation and tilting the table slightly. The tailings are continuously discharged from the lower end.
Mineral Products Separated in Tabling
Wilfley Tables are particularly effective in separating fine-grained minerals. Some common mineral products separated using tabling include:
- Sulphide Minerals: Lead, zinc, copper, and pyrite concentrates are frequently produced using Wilfley Tables.
- Precious Metals: Gold, silver, and platinum group minerals can be effectively concentrated.
- Heavy Minerals: Ilmenite, rutile, zircon, and monazite are separated from sand deposits.
- Barite: Used in drilling fluids, barite is often concentrated using tabling.
- Scheelite: A tungsten ore, scheelite is also amenable to separation by tabling.
The efficiency of the Wilfley Table depends on several factors, including particle size, specific gravity difference, feed rate, water flow rate, table inclination, and riffle design. Careful control of these parameters is essential for optimal performance.
Conclusion
The Wilfley Table remains a significant tool in mineral processing due to its ability to efficiently separate fine-grained minerals based on gravity. Its robust design and adaptability make it suitable for a wide range of applications, from precious metal recovery to industrial mineral concentration. While newer technologies have emerged, the Wilfley Table continues to be employed, often in conjunction with other separation methods, demonstrating its enduring value in the mining industry.
Answer Length
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