400TPH Alluvial Gold Washing Plant: Maximize Clay Recovery

1. Detailed Processing Flow

Step 1: Raw Ore Feeding Through the Feed Hopper

The raw alluvial gold ore is transported to the processing plant by dump truck or forklift and discharged into the feed hopper.

The feed hopper serves as a buffer storage unit, ensuring a relatively stable supply of raw material to the downstream equipment. The hopper capacity and dimensions can be designed according to the feeding equipment, site conditions, and required processing capacity.

Material is then automatically discharged from the hopper into the vibrating feeder.

Step 2: Preliminary Screening by the Vibrating Feeder

The vibrating feeder is equipped with 100 mm grizzly bars for preliminary separation of oversized materials.

During operation:

• Materials larger than 100 mm are separated and discharged to a designated stockpile area.
• Materials smaller than 100 mm pass through the grizzly bars and enter the trommel scrubber for further washing and screening.

This preliminary separation prevents excessively large rocks from entering the washing system, helping reduce unnecessary equipment wear and improve the efficiency of downstream processing.

The grizzly spacing can also be adjusted according to the characteristics of the raw alluvial ore.

Step 3: Clay Washing and Particle Classification by the Trommel Scrubber

The trommel scrubber is one of the most important pieces of equipment in this 400TPH alluvial gold washing plant.

Alluvial gold ore frequently contains clay, sticky soil, and compacted lumps. If these materials are not sufficiently disintegrated, fine gold particles may remain trapped inside the clay, reducing the efficiency of subsequent gravity separation.

The trommel scrubber uses mechanical agitation and water washing to break down clay lumps, clean the ore, and release gold particles from the surrounding materials.

After washing, the material is classified into three particle size fractions:

• 0–6 mm: Fine material, directed to centrifugal gold concentration.
• 6–20 mm: Medium-sized material, directed to sluice box recovery.
• 20–100 mm: Coarse material, transported to the stockpile area by belt conveyor.

The trommel scrubber's screening mesh sizes can be customized based on the particle size distribution of the raw ore and the occurrence characteristics of the gold.

Trommel scrubber or trommel screen: Which one should you choose?

The choice depends mainly on the clay content of the alluvial deposit.

• For alluvial gold ore containing sticky clay, a trommel scrubber is recommended because it provides both washing and screening functions.
• For alluvial gold ore with relatively low clay content, a trommel screen may be a more economical option because intensive clay scrubbing is unnecessary.

Selecting the appropriate washing equipment is essential for improving gold liberation and maintaining stable plant performance.

Step 4: Fine Gold Recovery Using a Centrifugal Gold Concentrator

The 0–6 mm material from the trommel scrubber is transported by a slurry pump to the gold centrifugal concentrator.

Fine alluvial gold can be difficult to recover using conventional sluice boxes alone, particularly when the gold particles are very small or have low settling velocities.

A gold centrifugal concentrator uses enhanced gravitational forces to separate gold particles from lighter gangue minerals.

During operation, the slurry enters the rotating concentration bowl. The centrifugal force helps concentrate high-density gold particles while lighter materials are discharged with the tailings.

The centrifugal concentrator is particularly useful for recovering fine gold that might otherwise escape through conventional gravity separation equipment.

To improve overall gold recovery, the tailings discharged from the gold centrifugal concentrator are directed to a sluice box for secondary gold recovery.

This combination of centrifugal concentration and sluice box recovery provides an additional opportunity to capture gold particles remaining in the fine material.

Step 5: Medium-Sized Gold Recovery Using Sluice Boxes

The 6–20 mm material separated by the trommel scrubber is sent directly to the sluice boxes for gold recovery.

A sluice box is a widely used gravity separation device in alluvial gold mining. It utilizes flowing water and differences in mineral density to separate gold from lighter sand, gravel, and other gangue materials.

As the material flows through the sluice box:

• Gold particles settle and become trapped in the sluice matting or riffles.
• Lighter sand and gravel are carried away by the water flow.
• Gold-bearing concentrate accumulates in the recovery section.

Sluice boxes offer a relatively simple structure, continuous operation, and low operating costs, making them suitable for large-scale alluvial gold processing.

The number and dimensions of sluice boxes should be determined according to the plant capacity, feed particle size distribution, gold particle size, and expected slurry flow rate.

Step 6: Coarse Material Transportation by Belt Conveyor

The 20–100 mm fraction from the trommel scrubber is discharged onto a belt conveyor and transported to the designated stockpile area.

This material is separated from the main gold recovery circuit according to the current process design.

However, its suitability for disposal or further processing should be evaluated through ore testing. If coarse gold particles or gold-bearing mineralized rocks are present in this fraction, additional crushing, washing, or recovery processes may be necessary.

This is an important consideration when designing an alluvial gold processing plant because gold distribution is not always uniform across different particle sizes.

Step 7: Final Gold Concentrate Upgrading by Shaking Tables

The gold-bearing concentrates collected from the centrifugal gold concentrators and sluice boxes are fed to shaking tables for final upgrading and purification.

A shaking table is a gravity separation machine that uses a combination of deck vibration, water flow, and differences in mineral density to separate valuable heavy minerals from lighter gangue materials.

During operation, gold-bearing concentrate is distributed across the inclined table surface. The reciprocating movement of the deck and flowing water separate materials according to their density and particle characteristics.

The resulting products generally include:

• Final gold-rich concentrate.
• Middlings, which may require further treatment or recirculation.
• Tailings containing relatively low concentrations of heavy minerals.

Shaking tables help improve concentrate grade by removing unwanted light minerals and reducing the amount of material requiring subsequent gold refining.

The number and specifications of shaking tables depend on the volume and characteristics of the concentrates generated by the upstream recovery equipment.