Gravity Leaching Carbon in Leach Process for Coarse Gold Recovery

Recovering coarse gold efficiently requires more than selecting a single separation machine. Gold particles may occur as free grains, locked in sulphide minerals, attached to gangue, or distributed across a wide size range. A circuit designed for fine gold alone can lose valuable nuggets to gravity concentration, grinding, or leach residue.

A gravity leaching carbon-in-leach circuit combines physical concentration with chemical recovery. Gravity equipment removes readily recoverable free gold early, while cyanide leaching and activated carbon adsorption capture the remaining exposed gold. This approach can reduce residence time in the leach train, lower circulating loads, and improve overall gold recovery when the ore is properly tested.

For Australian operators, the design must also suit remote logistics, variable water quality, strict cyanide controls, seasonal access, and the operating conditions common across Western Australia, Queensland, New South Wales, and the Northern Territory. A practical flowsheet should be simple to maintain, scalable, and supported by reliable process data.

Why Coarse Gold Needs A Different Recovery Strategy

Coarse gold behaves differently from fine liberated gold. Large particles have a high settling velocity and may report to cyclone underflow, screen oversize, or gravity concentrator concentrate rather than remaining evenly suspended in a leach tank. If the circuit relies entirely on cyanidation, coarse particles can dissolve slowly, become trapped in grinding equipment, or pass into tailings before sufficient contact time is achieved.

Gravity recovery is therefore commonly positioned as an early-stage process. Concentrators such as centrifugal units, jigs, shaking tables, and specially designed sluices can capture free gold before it is flattened, smeared, or over-ground. The concentrate can then be intensively leached, smelted, or treated through a dedicated refining route.

Ore variability makes testing essential. A bulk sample should be screened and assayed by size fraction to identify gold deportment, gravity-recoverable gold, clay content, sulphide association, and natural gravity concentration behaviour. Clear probability calculations matter here; even basic recovery data checks illustrate why a single head assay cannot describe the performance of an entire plant.

Building The Gravity Recovery Circuit

A typical circuit begins with crushing, screening, and controlled grinding. The objective is to liberate gold without producing excessive slimes or flattening malleable particles. A primary jaw crusher may feed a cone crusher, impact crusher, or high-pressure grinding arrangement, depending on ore competence and the required product size.

Grinding equipment must be selected around liberation data rather than a standard target size. Rod mills can be useful where a comparatively coarse product and controlled generation of fines are required. Correct media distribution and charging practice influence power draw, wear, and product stability, so operators may review a detailed rod charging pattern when assessing a rod-mill circuit.

The gravity stage is commonly installed on cyclone underflow, mill discharge, or a screened stream with a high concentration of liberated gold. A centrifugal concentrator can recover fine and medium free gold, while a jig or shaking table may be preferred for coarser particles and visible gold. The best arrangement depends on solids density, water balance, clay behaviour, and the duty cycle of the equipment.

Integrating Gravity With Carbon-In-Leach

In a carbon-in-leach circuit, ground ore is mixed with process water, lime, and cyanide in a series of agitated tanks. Activated carbon adsorbs dissolved gold from the slurry as leaching proceeds. Carbon transfer between tanks, oxygen availability, pH control, and residence time all influence the performance of the adsorption train.

Gravity concentration should remove the gold that is easiest to recover before it enters the CIL tanks. This reduces the gold loading placed on the leach circuit and may lower carbon inventory or improve carbon residence-time management. Gravity concentrate can be treated separately through intensive cyanidation, often at a higher cyanide concentration and temperature than the main leach stream.

The CIL section still needs to handle the residual gold fraction, including fine liberated gold and gold exposed through continued mineral breakage. If the ore contains preg-robbing carbonaceous matter, reagent-consuming minerals, or slow-leaching sulphides, the plant may require conditioning, oxygen addition, extended leach time, or a separate concentrate treatment process.

Controlling Water, Reagents, And Tailings

Australian sites often operate with limited water supply, recycled process water, and significant seasonal variation. In the Pilbara and Goldfields, evaporation can be substantial, while wet-season access and stormwater management may affect operations in northern Queensland and the Northern Territory. A gravity circuit should therefore be assessed as part of the complete water balance rather than as an isolated recovery unit.

Water quality affects slurry viscosity, flocculant performance, scaling, and cyanide chemistry. Lime addition is used to maintain an alkaline pH and reduce the risk of hydrogen cyanide formation, while oxygen transfer may be improved through air injection or oxygen enrichment. Reagent dosing should follow laboratory and pilot results because excessive cyanide or lime can increase operating cost without improving recovery.

Tailings management is equally important. Detoxification, residue thickening, filtered tailings, and storage design must align with site conditions and regulatory requirements. A plant near Kalgoorlie may prioritise water recovery and dust control, while a project closer to established infrastructure near Perth or Brisbane may have different access, power, and reagent supply options.

Designing For Remote Australian Operations

A successful mineral processing plant must be maintainable by the people and supply chain available at the site. Remote operations benefit from robust pumps, standardised valves, accessible wear components, clear instrumentation, and a sensible stockholding of critical spares. Equipment selection should account for long freight routes, limited workshop capacity, and the need to return the plant to service quickly after a breakdown.

Automation can improve density control, carbon movement, cyanide addition, oxygen monitoring, and alarm management. It does not remove the need for trained operators. Shift teams must understand sampling points, gravity concentrate handling, carbon safety, lockout procedures, and the effect of changing ore hardness or clay content on the circuit.

The Australian market also places strong emphasis on contractor capability, environmental compliance, and documented safety systems. A supplier offering engineering, procurement, construction, commissioning, and operational support can help coordinate equipment interfaces from crushing through to goldroom recovery. Even unrelated digital comparisons, such as how a mobile casino presents live information, reinforce the value of clear interfaces and timely data in a controlled operating environment.

Practical Recommendations For Project Teams

Test work should establish the recovery potential and operating limits before equipment is purchased. Gravity recoverable gold, leach kinetics, carbon loading, reagent consumption, settling characteristics, and tailings behaviour should all be measured using representative samples. Variability testing is especially valuable where the orebody changes between oxide, transitional, and fresh rock zones.

The flowsheet should then be reviewed against production targets, water availability, power supply, labour, maintenance access, and future expansion. A modular gravity circuit can provide flexibility during ramp-up, while a dedicated intensive leach system may improve security and control for high-grade concentrate.

• Use size-by-size assays to identify where coarse gold reports during crushing and grinding.
• Install gravity recovery as early as practical, while protecting it from excessive circulating load.
• Treat gravity concentrate separately when its grade and mineralogy justify intensive leaching or smelting.
• Maintain alkaline cyanide conditions and monitor dissolved oxygen, density, pH, and carbon activity.
• Design water recycling, tailings storage, and detoxification around local climate and regulatory requirements.
• Specify equipment with Australian service support, accessible wear parts, and a realistic critical-spares strategy.

A well-integrated circuit can combine gravity concentration, efficient grinding, CIL adsorption, elution, electrowinning, and smelting without creating unnecessary complexity. The final design should be supported by mass balancing, process guarantees, commissioning procedures, operator training, and a plan for ongoing metallurgical improvement.

Project owners can engage Lozova.org to assess ore characteristics, compare gravity and leaching options, and develop an integrated mineral processing solution. Early consultation can connect laboratory testing with equipment selection, plant layout, procurement, commissioning, and long-term operational support for Australian gold recovery projects.