Jigging, Shaking Tables, and Spiral Concentrators
Introduction
Gravity separation is a fundamental mineral processing
technique that relies on the differences in density between various minerals to
separate them. This method has been employed for centuries and continues to be
an essential tool in the mining and mineral processing industry. Gravity
separation is cost-effective, environmentally friendly, and widely applicable,
making it an attractive option for separating valuable minerals from gangue
materials. In this article, we will explore three common gravity separation
techniques: jigging, shaking tables, and spiral concentrators.
Jigging
Jigging is one of the oldest and most widely used methods of
gravity separation in mineral processing. It is particularly effective for
separating minerals with significant differences in density. The principle
behind jigging relies on the pulsating water flow and the motion of a jig bed
to stratify and separate particles based on their density.
Principle of Operation:
The key components of a jigging system include the jig bed,
water supply, and pulsating mechanism. The jig bed is a rectangular or
trapezoidal compartment that can be filled with a bed of dense particles called
ragging. The ragging provides a stratification surface that helps in the
separation process.
The operation of a jig begins with the introduction of a
slurry of ore particles into the jig bed. Simultaneously, water is pulsed
through the bed in a rhythmic fashion. This pulsating motion causes the denser
particles to settle faster than the less dense ones. As a result, the
stratification of particles occurs, with the heavier minerals settling at the
bottom and the lighter gangue minerals rising to the top.
Applications:
Jigging is commonly used for the concentration of heavy
minerals, such as gold, tin, tungsten, and diamonds. It is especially effective
in recovering fine particles that may be difficult to recover using other
methods.
Shaking Tables
Shaking tables, also known as shaking concentrators or
gravity tables, are another widely employed gravity separation technique in
mineral processing. Shaking tables use a combination of lateral and
longitudinal motion to separate particles based on their density and size.
Principle of Operation:
A shaking table consists of a flat, rectangular deck with a
water wash system and a series of longitudinal riffles or grooves. The deck is
mounted on a reciprocating frame that imparts a back-and-forth shaking motion.
A slurry of ore particles is fed onto the deck near the top edge.
The shaking motion of the table causes the particles to
stratify based on their density. The heavier particles settle into the riffles,
while the lighter particles are carried away by the flowing water. The lateral
movement of the table helps in the separation of fine particles, while the
longitudinal movement aids in the concentration of heavier particles.
Applications:
Shaking tables are commonly used in the processing of
various ores, including gold, tungsten, tin, lead, and zinc. They are particularly
effective for recovering fine-grained minerals and are often used in
combination with other gravity separation techniques.
Spiral Concentrators
Spiral concentrators, also known as spiral separators or
spiral chutes, are gravity-based devices that are used to separate minerals by
density and shape. They are especially effective for concentrating and
recovering fine and ultrafine particles.
Principle of Operation:
A spiral concentrator consists of a helical trough with a
spiral groove running along its length. The slurry of ore particles is fed at
the top of the spiral concentrator and flows down the trough under the
influence of gravity. As the slurry moves down the spiral groove, centrifugal
forces cause the denser and larger particles to move towards the outer edge of
the spiral, while the lighter and smaller particles move towards the center.
The combination of gravity and centrifugal forces results in
the stratification of particles along the spiral groove. The concentrated heavy
minerals are collected at the outer edge of the spiral, while the lighter
gangue minerals are washed away towards the center.
Applications:
Spiral concentrators are commonly used in the processing of
heavy mineral sands, such as those containing ilmenite, rutile, and zircon.
They are also effective in the recovery of fine coal and can be used in various
industrial applications.
Advantages and Limitations of Gravity Separation
Gravity separation techniques offer several advantages in
mineral processing:
Low Operating Costs: Gravity separation does not require the
use of chemicals, which reduces operating costs and minimizes environmental
impact.
High Recovery Rates: When properly optimized, gravity
separation can achieve high recovery rates for valuable minerals.
Wide Applicability: Gravity separation can be used to
process a wide range of mineral types and sizes.
Reliability: Gravity separation equipment is relatively
simple and robust, making it reliable for continuous operation.
However, gravity separation also has some limitations:
Particle Size Limitations: Gravity separation becomes less
effective for very fine particles, which may not settle or stratify well.
Limited Selectivity: Gravity separation is based on
differences in density, so it may not be effective for minerals with similar
densities.
Equipment Complexity: Some gravity separation equipment,
such as spirals, can be complex and require careful maintenance.
Conclusion
Gravity separation is a valuable and widely used technique
in mineral processing, offering an environmentally friendly and cost-effective
means of separating valuable minerals from gangue materials. Jigging, shaking
tables, and spiral concentrators are three common methods employed in this
field, each with its own set of advantages and limitations. The choice of
gravity separation method depends on the specific characteristics of the ore
and the desired outcome. When properly applied and optimized, gravity separation
can play a crucial role in the successful extraction and concentration of
valuable minerals in the mining industry.