This article outlines the process design basis, flowsheet, and key equipment for the proposed gold recovery plant at the Hosco Deposit, as detailed in the July 2012 feasibility study.
Report context
This article is based on the NI 43-101 Technical Report titled "Feasibility Study of the Hosco Deposit," dated July 2012. The study establishes a process design basis, mass and water balances, and equipment selection criteria for a mineral processing plant treating ore from the Joanna Hosco deposit.
Processing route
Process Design Basis
The plant design is based on an average daily ore throughput of 8,500 tonnes per day, or 3.1 million tonnes per year. The design daily feed rate is 9,500 tonnes per day. The plant operates 365 days per year with 14 days of scheduled maintenance shutdown, resulting in an overall plant utilization rate of approximately 85%, or 7,446 operating hours per year. The utilization rate was based on the availability of the autoclave, specified by the vendor responsible for testwork and design of the pressure oxidation area. The design gold head grade is 1.26 g/t, with a gold recovery of 87.5%, contributing to an annual gold production of 109,237 troy ounces.
The crusher utilization rate is approximately 65%. Major solid stream design parameters are summarized in Table 1.
Table 1: Major Process Solid Streams
| Stream | Annual (dry Mt/y) | Nominal (dry t/op. h) | Design (dry t/op. h) |
|---|---|---|---|
| Ore Processed | 3.10 | 416.7 | 465.7 |
| Flotation Concentrate | 0.155 | 20.8 | 23.3 |
| Flotation Tailings | 2.95 | 395.7 | 443.2 |
| Pressure Oxidation (POX) Tailings | 0.110 | 14.8 | 16.5 |
| Cyanidation Tailings | 0.153 | 20.5 | 22.9 |
Project website: https://miningdataonline.com/property/1909/Heva-Hosco-Joanna-Project.aspx
Process Description
Primary Crushing and Ore Handling: Run-of-mine ore with an F80 of 600 mm is dumped by 100-tonne haul trucks onto a static grizzly feeding a 270-tonne capacity hopper. The grizzly retains material larger than 850 mm, which is broken by a hydraulic rock breaker. An apron feeder controls the feed rate to the primary jaw crusher, which has a feed opening of 1,250 mm by 950 mm and installed power of 200 kW. The crusher product has a P80 of 110 mm. Crushed ore is conveyed to a silo with a live capacity of 2,360 tonnes, equivalent to approximately 5.5 hours of concentrator operation.
Grinding and Gravity Separation: The grinding circuit consists of a single pinion SAG mill operating in open circuit, feeding a ball mill in closed circuit with a hydrocyclone cluster. The SAG mill has a diameter of 9,144 mm, effective grinding length of 2,896 mm (30 ft diameter by 9.5 ft EGL), and installed power of 5,040 kW. The target grind size P80 is 90 μm.
A portion of the ball mill discharge is directed by gravity to two parallel Knelson gravity concentrators, which recover gravity-recoverable gold. The concentrate is upgraded on a shaking table, with tailings combined with the flotation concentrate. Gravity concentrate is sent to the gold room for smelting.
Flotation: The hydrocyclone overflow is directed to a conditioning tank with a residence time of 2 minutes. The slurry then flows through a rougher bank of eight mechanical tank cells (100 m³ each) with a total residence time of approximately 37 minutes. Flotation reagents include the gold collector Aero 208, frother MIBC, and sulphide collector PAX. The flotation circuit also includes a cleaner column (3.05 m diameter by 10 m high) and a cleaner scavenger column (2.44 m diameter by 8.5 m high), with a total estimated circuit gold recovery of 89.15%. Rougher tails are thickened in a high rate thickener and pumped to the flotation tailings pond.
Pressure Oxidation (POX): The flotation concentrate is thickened and pumped to the POX area, which includes a high pressure slurry feed system, a refractory-lined, multi-compartment horizontal autoclave, a conditioning tank, and vent gas handling. The autoclave operates at 220°C and 3,000 kPa (gauge) with a design retention time of 75 minutes. High purity (92.5%) oxygen for the oxidation reaction is supplied from an on-site vacuum pressure swing adsorption (VPSA) plant.
Neutralization and CCD: The oxidized slurry is washed in a counter current decantation (CCD) circuit consisting of two high rate thickeners to remove sulphuric acid and metal sulphates. The wash solution is sent to a neutralization circuit with six agitated tanks in series, where limestone and lime are used to precipitate dissolved metals. The circuit includes a high rate thickener, with the thickened solids combined with cyanidation tails for disposal. The CCD tailings are acidic and contain high arsenic levels, requiring a special impoundment design.
Cyanide Leaching and CIP: The washed POX residue is pumped to a conditioning tank with a residence time of approximately 30 minutes, where slaked lime is added to achieve a pH of about 10.5. The slurry then flows through a series of four agitated leaching tanks with a total residence time of approximately 48 hours. A NaCN solution is added to the first tank, and compressed air is sparged into each tank. The leached slurry is fed to a CIP circuit consisting of ten tanks in a carousel configuration, each containing one tonne of activated carbon. The design carbon concentration is 50 g/L.
Carbon Stripping and Regeneration: Loaded carbon is pumped to a carbon stripping vessel operating at 130°C and 65 psig. The strip solution is heated and circulated for 8 to 10 hours. After stripping, the carbon is cooled, rinsed, and dewatered on a screen before being stored. The carbon is regenerated in an electric kiln with a capacity of one tonne per day. Carbon fines are filtered and sold for their gold content.
Cyanide Destruction: Cyanide destruction uses the Inco SO2/Air process, with SO2, air, and CuSO4 added to an agitated tank. The target total cyanide content in the slurry discharge is less than 20 ppm. The discharge is combined with neutralization tails and pumped to the POX tailings pond.
Gold Room and Electrowinning: Gold is recovered from the pregnant solution using an electrowinning cell with a capacity of 1.4 m³. Loaded cathodes are cleaned in-situ, and the sludge is filtered, dried, and smelted in an induction furnace.
Reagents and Common Services:
- Flotation reagents (Aero 208, MIBC, PAX) and flocculants (Flomin 905MC, 4240SSH) are delivered in solid form and dissolved in batches.
- Caustic soda, HCl, and CuSO4 are delivered in totes.
- Quick lime is delivered by truck and stored in a silo, with a slaking circuit providing slurry.
- The POX area includes a limestone grinding circuit with a ball mill to produce a product with a P90 of 100 microns.
- A VPSA oxygen plant is operated by an industrial gas vendor.
- Process water is stored in a 15 m diameter by 5 m high tank, with a portion filtered for gland seal water and a demineralization package for autoclave seal water.
- A compressed air system, flotation blowers, and a steam boiler support plant operations.
Major Process Equipment
The major equipment list includes the primary jaw crusher (200 kW), crushed ore silo, SAG mill (5,040 kW), ball mill (5,040 kW), a hydrocyclone cluster with 500 mm cyclones (3 operating, 2 spares), gravity concentrators, flotation cells, a 11 m diameter concentrate dewatering thickener, a POX autoclave package with one autoclave and neutralization tanks, two 13 m diameter CCD thickeners, a 10 m diameter neutralization thickener, four leach tanks (8.1 m diameter), a CIP package with 10 tanks, and a carbon stripping and regeneration package.
Key reported parameters
| Item | Value | Basis |
|---|---|---|
| Nominal Daily Plant Feed | 8,500 t/d | Design |
| Design Daily Plant Feed | 9,500 t/d | Design |
| Annual Plant Utilization | 85% | Design (based on autoclave availability) |
| Annual Operating Hours | 7,446 h | Design |
| Nominal Gold Head Grade | 1.26 g/t | Design (from block model) |
| Gold Recovery | 87.5% | Design |
| Annual Gold Production | 109,237 troy oz/y | Calculated |
| Grind Size (P80) | 90 μm | Design |
| Primary Crusher Product (P80) | 110 mm | Design |
| SAG Mill Power | 5,040 kW | Design |
| Ball Mill Power | 5,040 kW | Design |
| SAG Mill Dimensions | 30 ft D x 9.5 ft EGL | Design |
| Ball Mill Dimensions | 18 ft D x 28 ft EGL | Design |
| Flotation Residence Time (Rougher) | ~37 minutes | Design |
| Flotation Circuit Gold Recovery | 89.15% | Estimated |
| POX Operating Conditions | 220°C, 3,000 kPa (gauge) | Design |
| POX Residence Time | 75 minutes | Design |
| CIP Tanks | 10 (one standby) | Design |
| CIP Tank Carbon Concentration | 50 g/L | Design |
| Leach Tank Residence Time | ~48 hours | Design |
| Cyanide Destruction Residence Time | 4 hours | Design |
| Cyanide Destruction Target (Total CN) | <20 ppm | Design |
| Carbon Strip Temperature/Pressure | 130°C / 65 psig | Design |
| Crushed Ore Silo Live Capacity | 2,360 t (~5.5 h) | Design |
Technical qualifications
The following limitations are specific to this report:
- Process design and equipment sizing were based on metallurgical testwork results, handbook references, reference projects, and vendor information.
- The plant utilization rate was based on autoclave availability as specified by the vendor responsible for the POX testwork and design.
- The average gold head grade was derived from the block model and optimized pit design.
- The design carbon concentration in the CIP tanks is 50 g/L.
- Reagent consumption and all flowsheets were based on the provided operational descriptions.
- The report does not provide detailed specifications for all ancillary equipment, such as pumps and conveyors beyond the major items listed.
Source: NI 43-101 Technical Report, "Feasibility Study of the Hosco Deposit," July 2012. Relevant sections include 17 Recovery Methods, Section 17.1 Process Design Basis, Section 17.2 General Flowsheet Mass and Water Balances, Section 17.3 Process Description, and associated tables and figures.
