Rock Gold Processing Plant Equipment List: Comprehensive Guide from Crushing to Smelting

Rock gold, also known as lode gold, exists embedded within quartz veins or sulfide rock formations. Unlike alluvial gold, which requires physical washing, rock gold necessitates a complex process of comminution and chemical or physical separation to liberate the precious metal from the host rock. Achieving high recovery rates depends entirely on the correct selection and configuration of mechanical equipment. This guide provides a detailed inventory of essential machinery for a hard rock gold processing plant, analyzing the function, selection criteria, and operational logic of each component in the beneficiation circuit.

Crushing System: Reducing Run-of-Mine Ore

The primary stage of any rock gold plant is size reduction. Run-of-Mine (ROM) ore typically ranges from 300mm to 1000mm. Chemical leaching and flotation require particle sizes often below 75 microns (200 mesh). Therefore, mechanical crushing is the first essential step to prepare the material for grinding.

Primary Crushing: Jaw Crusher

The Jaw Crusher serves as the primary breaking unit. It operates using compressive force applied between a fixed jaw plate and a moving jaw plate.

• Function: It accepts large rocks and reduces them to a size of approximately 100mm to 150mm.
• Mechanism: The toggle plate mechanism generates high crushing force, making it suitable for materials with compressive strengths up to 320 MPa.
• Operational Logic: The Jaw Crusher is selected for its simplicity and ability to handle variable feed sizes. It does not require fine discharge settings, as its sole purpose is to enable the material to be transported on conveyors to the secondary stage.

Secondary Crushing: Cone Crusher

Following the primary stage, the Cone Crusher reduces the ore further. This machine uses a mantle rotating within a concave bowl to crush rock via compression and inter-particle attrition.

• Function: Reducing 150mm stone down to 10mm-20mm.
• Efficiency: Crushing rock requires significantly less energy than grinding rock in a mill. Therefore, the operational objective is to minimize the output size of the crushing circuit.
• Types: Hydraulic cone crushers are preferred in modern plants over spring cone crushers due to their ability to clear tramp iron automatically and adjust settings under load. A finer crush at this stage directly translates to lower power consumption in the subsequent ball mill.

Tertiary Crushing: VSI Crusher (Optional)

In operations utilizing heap leaching or requiring an extremely fine feed for the ball mill (e.g., <6mm), a Sand Making Machine (Vertical Shaft Impact Crusher) is employed.

• Mechanism: This machine uses “rock-on-rock” impact energy.
• Benefit: It induces micro-fractures within the ore particles. These stress cracks improve the penetration rate of cyanide solutions in leaching operations and reduce the Bond Work Index for grinding operations.

Screening System: Particle Size Control

The Vibrating Screen functions as the quality control checkpoint of the crushing circuit. It is typically positioned in a “closed circuit” with the secondary or tertiary crusher.

The Closed Circuit Principle:

1. Crushed material is fed onto the screen deck.
2. Undersize material (passing through the mesh) proceeds to the fine ore bin or ball mill.
3. Oversize material (retained on the mesh) is recirculated back to the Cone Crusher for re-crushing.
   Without this feedback loop, oversized rocks would enter the grinding circuit. Large rocks in a ball mill cause erratic power draw, increased liner wear, and a significant reduction in throughput capacity. Multi-deck screens allow for the production of different aggregate sizes if the mine also sells construction materials.

Grinding and Classification: Liberation of Gold

Grinding is the process of reducing crushed ore to a powder, liberating the gold minerals from the gangue (waste rock). This stage accounts for the highest energy expenditure in the processing plant.

The Ball Mill

The Ball Mill is a rotating cylinder filled with steel grinding media. As the cylinder rotates, the balls tumble and cascade, impacting the ore.

• Media Selection: The size of the steel balls dictates the grinding efficiency. Using balls that are too large (e.g., >100mm) on fine feed can cause the “Smearing Effect.” Gold is malleable; excessive impact force can flatten gold particles into flakes rather than breaking the rock matrix. Flattened gold becomes difficult to recover via gravity or flotation as its surface area-to-mass ratio changes.
• Operational Parameters: The mill typically operates at 70-80% of critical speed. The pulp density (ratio of water to solids) must be strictly controlled (usually 65-75% solids) to ensure proper viscosity for grinding action.

Classification: Hydrocyclones

While older plants utilized Spiral Classifiers, modern facilities predominantly use Hydrocyclones.

• Function: The cyclone separates the ball mill discharge into two streams based on centrifugal force and particle mass.
  • Overflow: Fine material (e.g., 80% passing 75 microns) moves to the recovery stage.
  • Underflow: Coarse material returns to the ball mill inlet for regrinding.
• Advantage: Hydrocyclones have a small footprint and no moving parts. They provide a sharper cut point than mechanical classifiers, ensuring that gold is not over-ground (which leads to slime losses) nor under-ground (which leads to locked gold losses).

Beneficiation: Separation of Valuable Minerals

Once the ore is ground, the gold must be separated. The choice of equipment depends on the mineralogy of the ore.

1. Gravity Concentration (Free Gold Recovery)

Gravity separation relies on the specific gravity difference between gold (SG ~19.3) and quartz/gangue (SG ~2.6).

• Equipment: Centrifugal Concentrator and Shaking Table.
• Placement: The most effective location for a centrifugal concentrator is in the ball mill recirculating load (handling the cyclone underflow).
• Logic: Coarse free gold has a tendency to settle in the mill and circulate. Extracting this gold early prevents it from being over-ground into non-recoverable slime. The concentrate from the centrifugal unit is often upgraded further on a Shaking Table to produce a direct smeltable product.

2. Flotation (Sulfide-Associated Gold)

When gold is encapsulated within sulfide minerals (such as pyrite, arsenopyrite, or chalcopyrite), physical gravity separation is insufficient.

• Equipment: Flotation Machine.
• Process: Chemical collectors (such as Xanthates) and frothers are added to the slurry. These chemicals render the sulfide surfaces hydrophobic (water-repellent). Air is bubbled through the tank; the sulfides attach to the bubbles and rise to the surface as a froth, which is skimmed off.
• Result: This process produces a gold-bearing concentrate (e.g., 50-100g/t) rather than pure gold. This concentrate requires further treatment, such as roasting or intense cyanidation.

3. Cyanidation (CIL/CIP)

For oxidized ore or microscopic gold particles that cannot be recovered by gravity or flotation, chemical extraction is required.

• Equipment: Gold CIL Processing Plant (Carbon-in-Leach).
• Process: The slurry is pumped into a series of agitation tanks. Sodium cyanide is added to dissolve the gold. Activated carbon is added directly to the slurry to adsorb the dissolved gold complex.
• Equipment Features: The tanks utilize dual-impeller agitators to keep solids in suspension. Interstage screens prevent the carbon from moving downstream while allowing the slurry to flow.

Comparison of Processing Methods

Feature	Gravity Separation	Flotation	Cyanidation (CIL)
Target Gold	Coarse, Free Gold	Sulfide-bound Gold	Microscopic/Oxide Gold
Recovery Rate	40% – 70% (typical)	80% – 90%	90% – 98%
Operating Cost	Low	Medium	High
Environmental	Chemical-free	Chemical use	Cyanide management required

Tailings Management and Water Recovery

The waste material (tailings) must be disposed of safely, and process water should be recycled to minimize environmental impact and costs.

• Thickening: A High Efficiency Concentrator (Thickener) is used to settle solids. Flocculants are added to speed up sedimentation. The clear water overflow is returned to the grinding circuit (recycling up to 85% of process water).
• Filtration: A Filter Press can be used to dewater the underflow sludge, producing a dry cake that can be stacked. This method is increasingly preferred over wet tailings dams due to lower risk of dam failure.

2026 Industry Trends: Automation and Efficiency

The gold mining sector is moving towards automated process control.

• Smart Sensors: Installation of sensors on the belt conveyor to detect ore hardness allows the control system to automatically adjust the feed rate and water addition in the Ball Mill.
• Modular Design: Pre-fabricated steel structures for Mobile Stone Crusher units allow for rapid deployment in remote locations, reducing civil engineering requirements.

FAQs

Q1: What is the primary difference between CIL and CIP processes?
In CIL (Carbon-in-Leach), the leaching of gold by cyanide and the adsorption onto carbon occur simultaneously in the same tanks. In CIP (Carbon-in-Pulp), leaching occurs in the first few tanks, followed by adsorption in subsequent tanks. CIL is generally preferred for ores containing “preg-robbing” carbonaceous material, as the activated carbon competes with the natural carbon for the gold.
Q2: How is the size of the Ball Mill determined?
Ball mill sizing is calculated based on the required throughput (tons per hour), the work index of the ore (Bond Work Index), the feed size (F80), and the target product size (P80). An undersized mill creates a bottleneck, while an oversized mill results in unnecessary capital and energy expenditure.
Q3: Can oxide and sulfide ores be processed in the same circuit?
Processing both simultaneously is challenging due to different chemical requirements. Sulfides often require flotation or pre-oxidation, while oxides are treated directly with cyanide. The plant design must include bypass options or parallel circuits to handle mixed ore bodies effectively.
Q4: How does clay content affect the crushing circuit?
High clay content causes blockages in the crushing chamber and blinds the screens. If the moisture content exceeds 5-10% with clay, a Sand Washing Machine or rotary scrubber must be installed prior to the crushing stage to wash away the sticky fines.
Q5: What is the water consumption for a standard CIL plant?
A conventional CIL plant typically requires a water-to-solid ratio of 3:1 or 4:1 by weight during processing. However, with the integration of high-efficiency thickeners and tailings filtration systems, over 80% of this water is recycled. The net make-up water consumption can be reduced to approximately 0.5-0.8 tons of water per ton of ore.

Summary and Conclusion

Establishing a productive rock gold processing plant requires a strict adherence to metallurgical principles.

1. Comminution: Efficient reduction of rock size via Jaw and Cone crushers lowers the energy demand of the milling stage.
2. Classification: Hydrocyclones ensure the optimal particle size for downstream separation.
3. Recovery: The combination of gravity concentration for coarse gold and CIL or Flotation for fine gold typically yields the highest overall recovery rates.
4. Sustainability: Water recycling via thickeners is essential for long-term operational viability.

About ZONEDING

ZONEDING serves as a manufacturer of complete Beneficiation Equipment. The company specializes in the design and fabrication of machinery for Hard Rock Gold Mining, aggregate production, and mineral processing. With a focus on durability and factory-direct distribution, ZONEDING provides comprehensive solutions ranging from initial laboratory testing to equipment installation and commissioning.
Contact ZONEDING for technical consultation regarding flow sheet design and equipment specifications.