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In the field of placer gold mining, gravity separation has always been the core technology for processing placer gold due to its high efficiency, low investment, and environmental friendliness. The principle of gravity separation is to utilize the differences in density and particle size between mineral particles, with the assistance of fluid dynamics and mechanical forces, to separate gold from gangue. This article introduces the gravity separation process, the gold recovery method used on gold dredgers, and the latest advancements in gravity separation technology.
The gravity separation process aims to recover as much gold and associated valuable minerals from the raw ore as possible. It mainly includes three stages: pretreatment, desliming, and concentration.
For cemented clay lumps larger than 100 mm in placer gold ore, if not properly crushed, they will be discharged along with waste rock during screening, resulting in gold loss. Similarly, gold particles attached to gravel also need to be liberated through crushing.
Crushing and screening serve as pretreatment steps, capable of pre-removing 20%–40% of waste rock and laying the foundation for the success of subsequent processes. Commonly used equipment at this stage includes drum scrubbers, spiral washers, vibrating screens, and hydraulic washing screens. Among them, the drum scrubber can simultaneously complete crushing, screening, and classification operations, making it particularly suitable for moderately difficult placer ores.
Gold dredgers typically integrate crushing and screening functions into the trommel screen, supplemented by high-pressure water flushing. Land-based fixed concentrators often use trommel screens in combination with vibrating screens to carry out multi-stage wet screening. Screening efficiency and parameters (such as high-pressure water volume) must be customized based on the particle size characteristics of the ore to ensure complete dissociation and classification of the ore sand.
In placer gold ore, fine clay (<0.1 mm) usually contains little or no gold. Efficient removal of this fraction during processing helps reduce the load on downstream equipment and improves both throughput and concentrate grade.
The primary equipment used for desliming is the desliming bucket. In vein gold concentrators dealing with dense, high-grade materials, or in large-scale operations, desliming may be omitted before concentration to simplify the process and retain fine materials.
Gravity separation is the most economical and effective method for processing placer gold. In the roughing stage, a gold-bearing coarse concentrate with a grade of around 100 g/t can be obtained. The following treatment options can then be applied:
Traditional method: Manual gold panning using a pan, or discarding heavy minerals after recovering gold via amalgamation.
Large-scale recovery: After manual panning or amalgamation to obtain crude gold, the remaining heavy sand is transported to a concentration plant. There, magnetic separation, electrostatic separation, and other processes are used to comprehensively recover heavy minerals such as ilmenite, zircon, and monazite. This maximizes the resource value and minimizes waste.
A gold dredger is a floating device that integrates both mining and mineral processing. It is suitable for wide river valleys, gently sloping streams, and lakeside placer deposits located below the groundwater level. Gold dredgers feature large production capacity, low operational costs, excellent working conditions, and a high degree of mechanization.
·Single fixed chute process
·Chute–jig–shaking table process
·Three-stage jigging process
Enhanced Pretreatment: Improve ore crushing efficiency and optimize screening and classification (through multi-stage screening and grading systems).
Process Refinement: Add scavenging stages, reduce gold losses, and comprehensively improve recovery rates.
Equipment Upgrades: Widespread adoption of centrifugal concentrators with excellent performance in recovering fine and flake gold, significantly enhancing the overall processing level.
With increasing industrialization, gravity separation technologies and equipment are evolving rapidly toward high efficiency, automation, and fine particle recovery. Key innovations include:
Traditional fixed chutes are gradually being replaced by mobile chutes due to their lower recovery rates and higher labor intensity.
Continuous improvements in chute design have evolved from simple straight chutes to tapered chutes, spiral chutes, and multi-turn spiral chutes. Among these, multi-turn spiral chutes have shown excellent performance in placer gold beneficiation.
The widespread application of high-frequency circular jigs marks a significant breakthrough. Compared with traditional jigs, they increase recovery rates by 10%–15%, with a single unit capable of processing up to 20 m³/h. Large gold dredgers can be equipped with up to 18 units.
Efficient combination flowsheet: Jig concentrates are further purified by shaking tables, followed by selection with rotating spiral chutes, producing a final concentrate with a gold grade >95%, suitable for direct smelting.
Centrifugal concentrators are proving to be highly effective in placer gold recovery—especially on dredgers—and have become key equipment for capturing fine gold particles (<0.074 mm).
Conclusion
Xinhai Mining has been deeply engaged in the mineral processing industry for 30 years, with rich experience and advanced technical strength in gold ore beneficiation. We provide full-process mineral processing services, including:
·Equipment selection
·Equipment installation and commissioning
·On-site training and process optimization
We can tailor a gravity separation solution with high recovery and low operating costs, equipped with cutting-edge centrifugal separation technology to overcome the challenges of fine gold recovery.
In addition, our experienced team offers comprehensive services such as equipment installation, commissioning, process optimization, and operator training.
If you have any technical or equipment needs for placer gold beneficiation, please feel free to contact us!
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