A Few Methods To Use Gravity Method to Process Gold Ore

1. Gravity Separation Methods

Gravity separation utilizes the density differential between minerals. In a moving medium (water, air, or heavy liquids), particles of different densities are subjected to hydrodynamic and mechanical forces, leading to stratification and effective separation.

• Placer Gold: Since gold exists as free natural particles with a density typically >16 t/m³, which is significantly higher than gangue, gravity separation is the preferred, high-efficiency, and economical method.

• Lode Gold: Gravity is rarely used alone; it is typically integrated into grinding and classification circuits (using jigs, spiral chutes, or shaking tables) to recover coarse free gold early, reducing the load on subsequent flotation or cyanidation stages.

1) Jigging (Jig Concentrators)

Jigging uses a diaphragm jig to create vertically alternating water flow driven by an eccentric mechanism.

• Rising Flow: The bed becomes loose and suspended; high-density coarse particles settle to the lower layer.

• Sinking Flow: A suction effect draws small-sized, high-density particles through the bed gaps into the lower hutch.

2) Shaking Table Separation

The shaking table consists of a deck and a transmission mechanism that performs longitudinal reciprocating motion.

• Mechanism: Particles are stratified vertically by gravity and separated horizontally by the differential motion of the deck and the cross-flow of water.

• Types: Classified into coarse sand, fine sand, and slime tables based on the feed particle size.

3) Chute/Sluice Separation

An ancient yet effective method using wooden or steel sluices (inclined at 3°–16°).

• Process: High-density particles settle at the bottom as concentrate, while lighter gangue is washed away as tailings.

• Operation: It is an intermittent process requiring manual "clean-ups" once the concentrate reaches a certain height.

4) Spiral Concentrators

This equipment leverages gravity, friction, centrifugal force, and water flow within a spiral-shaped trough.

• Stratification: Light coarse particles move to the outer rim, while heavy fine particles concentrate at the inner rim and exit through discharge ports.

• Advantages: Simple structure, no power required for the motion. Note: Less effective for particles >6mm or <0.05mm.

5) Cone Concentrators (Reichert Cones)

Evolved from fan-shaped sluices, these use a series of vertically stacked cones. The slurry is distributed from the center, and minerals are stratified by density as they flow outward/inward, achieving high-capacity multi-stage separation in a single unit.

2. Amalgamation Methods

Amalgamation uses mercury to capture gold. It is categorized into Internal and External processes.

1) Internal Amalgamation

Conducted inside grinding equipment (e.g., pan mills, stamp mills, or specialized amalgamation barrels).

• Process: Gold is liberated and immediately comes into contact with mercury to form amalgams.

• Drawback (Flouring): Intense grinding can break mercury into microscopic beads ("floured mercury") coated by oil or slime, leading to mercury loss and reduced gold recovery.

2) External Amalgamation

Conducted outside the grinding circuit using Amalgamation Plates (typically silver-plated copper plates).

• Application: Often installed at the discharge of ball mills to capture coarse "free gold" from the pulp.

• Operation: Mercury is coated onto the silvered surface. As pulp flows over (at 0.5–0.7 m/s), gold is trapped in the mercury layer, forming an amalgam paste that is periodically scraped off.

• Safety: Strict environmental controls are mandatory due to the high toxicity of mercury vapors and contact.