This report describes the designed process route for the Balabag gold-silver project, a 2,000 t/d hybrid flotation, Merrill-Crowe, and carbon-in-leach plant.
Report context
The process design criteria for the Balabag gold and silver project were developed for a nominal plant capacity of 2,000 t/d, with a 95% availability factor applied to the mill plant and 67% to the crushing circuit. The plant is designed around a hybrid circuit incorporating bulk flotation, Merrill-Crowe precipitation, and carbon-in-leach processes.
Processing route
Crushing
Run-of-mine ore with a top size of 450 mm is dumped to a stationary grizzly. Crushing is completed in a two-stage jaw crusher circuit with a target product size of 50 mm. Oversize feed materials undergo manual breaking, while undersize material is contained in a 40 m³ capacity ore bin. A vibrating grizzly with a nominal 50 mm aperture feeds the primary jaw crusher operating at a 100 mm closed-side setting, with secondary crushing in a 254 mm x 1320 mm jaw crusher at a 50 mm closed-side setting.
Grinding
Grinding is completed in a closed-circuit SAG and ball mill system. Primary grinding uses a 3.8 m x 4.9 m grate discharge SAG mill operating at 75% solids and 35% by volume ball loading to produce a product with 220 µm P80. The SAG mill product is pumped to a cluster of 254 mm diameter cyclones, with the secondary cyclone underflow distributed to two secondary ball mills operating at 62% solids and 250% circulating load to produce a product with 80 µm P80.
Gravity Concentration Option
The gravity concentration circuit is being considered as an option but will not be installed initially, although space is allowed for future installation. It would consist of a vibrating screen with 600 µm aperture, a centrifugal gravity concentrator, and two shaking tables, with concentrates dried, fluxed, and smelted in the gold room.
Flotation
The secondary hydrocyclone overflow at 30% solids passes through a 2.6 m x 3.0 m conditioning tank for collector and frother addition, with lime added to adjust pulp alkalinity to pH 11. Bulk flotation is conducted in a series of six 16 m³ and three 8 m³ U-tank cells to produce a silver concentrate at 80% recovery. The tailings go to a 9 m diameter thickener as feed to the CIL circuit, while the concentrate is dewatered in a 5 m diameter thickener.
Flotation Concentrate Leaching
Thickened concentrate at 33% solids is transferred to a 6.1 m x 7.3 m aeration tank where lime is added to increase pH to 10.5-11.0, along with 0.03 m³/h raw cyanide solution. Leaching is conducted in six agitated tanks for a total of 56 h, with oxygen supplied by low pressure, high volume, oil-free air compressors. The leach solution is recovered from a 3.6 m diameter thickener, with the underflow at 60% solids pumped to a plate and frame filter press.
Merrill-Crowe Precipitation
Unclarified pregnant solution is treated in two clarifiers/filters operated in parallel, with one operating and one on standby. The clarified solution is deaerated to below 2 ppm O₂ in a vacuum tower and reacted with zinc dust using a screw feeder. A plate and frame filter press dewaters the precipitate, with the zinc precipitate smelted to doré bars.
Carbon-in-Leach
Bulk flotation tailings and repulped flotation concentrate leach residue are treated in CIL tanks. The underflow from the tails thickener at 45% solids is pumped to a 9.3 m x 11.6 m aeration tank with lime added to increase pH to 10.5-11.0. CIL is conducted in six agitated tanks for a total of 24 h, with cyanide dosed to maintain a strength of 0.07% CN. Carbon adsorption is done at 20 g/L, with a designed carbon loading of approximately 5,000 g/t.
Stripping and Electrowinning
A nominal 10 t/d loaded carbon is acid washed with 3% HCl, then stripped in a 1.5 m diameter by 12.0 m high stripping column using a 3.0% NaOH and 1.0% NaCN strip solution at 120 °C. Six electrowinning cells with 11 cathodes and 12 anodes each operate with a current of 3,352 A. The deposited gold and silver are harvested after a 15 h cycle time, dewatered, dried, and smelted to doré bars.
Detoxification
Barren pulp from the carbon adsorption stage is treated in two 7.3 m x 9.1 m detoxification tanks at approximately 42% solids with sodium metabisulfide and copper sulfate as reagents. Lime is used for pH adjustment, with a total retention time of 1.5 h. Discharge must meet DENR standards for effluents.
Key reported parameters
| Parameter | Value | Unit | Basis |
|---|---|---|---|
| Plant capacity | 2,000 | t/d | Design |
| Crushing product P80 | 50 | mm | Design |
| SAG mill product P80 | 220 | µm | Design |
| Ball mill product P80 | 80 | µm | Design |
| Bulk flotation time | 12 | min | Design |
| Concentrate leach time | 56 | h | Design |
| CIL leach time | 24 | h | Design |
| Gold recovery (Year 1) | 84.5 | % | Design |
| Silver recovery (Year 1) | 80.4 | % | Design |
| Gold recovery (Year 2) | 87.8 | % | Design |
| Silver recovery (Year 2) | 87.1 | % | Design |
Project website: https://tvird.com.ph/balabag/
Technical qualifications
The report does not include operating data from an existing plant, as the Balabag project was at the design stage. Recovery figures are based on metallurgical testwork and process design criteria. The gravity concentration circuit is optional and was not included in the initial plant design. The report notes that the company anticipated an exploration program during operations to extend mine life beyond four years.
Source: Technical report for the Balabag Gold-Silver Project, TVI Resource Development (Phils.) Inc., Recovery Methods section, page 98-105.
