This report summarizes the processing route and design parameters of the Salobo copper project, based on the technical report dated December 2019.
Report context
The Salobo Project technical report, dated December 2019, describes the processing facilities for a copper operation that has evolved through multiple feasibility and trade-off studies since the 1980s. The report details the design basis for the Salobo I and Salobo II plants, both of which are described as operational at the time of reporting, and notes a decision by Vale to proceed with a Salobo III expansion to increase total processing capacity.
Processing route
Flowsheet evolution
The process flowsheet was developed through several phases, incorporating metallurgical testwork and understanding of ore lithologies. Early CVRD and Anglo American testwork (1986–1987) supported a prefeasibility study by Bechtel in 1988, during which fluorine contamination of the concentrate was first recognized. A subsequent SMSA testwork program, including a pilot plant campaign at the CRC (1993–1998), contributed to a final feasibility study. Locked-cycle flotation tests, flotation variability, and grinding studies (2003–2004) supported a second feasibility study by Fluor Daniel that evaluated 12 Mtpa and 24 Mtpa production scenarios. A trade-off study (2005–2006) using high-pressure grinding rolls for tertiary crushing led to adoption of the HPGR approach over conventional semi-autogenous grinding.
HPGR was retained instead of SAG mills because of the high magnetite and copper content of critical-size pebbles, which would have required additional re-handling. The relatively high ore hardness and expected variability across ore lithologies were also cited as factors that would cause high-frequency throughput variability in a conventional SAG–ball mill–pebble crusher circuit.
Salobo I and II plant design
Salobo I was designed to process 12 Mtpa of ore, producing approximately 100 kt of copper-in-concentrate annually, with production commencing in June 2012. Salobo II doubled nominal throughput to 24 Mtpa with annualized copper-in-concentrate production of approximately 200 kt, commissioned in June 2014 as a mirror-image of Salobo I. Both plants were designed for 365-day per year operation, 24 hours per day, with a targeted 90% of actual operating time including availability and utilization.
The circuit is described as conventional with the exception of HPGR for tertiary crushing ahead of ball milling and extensive use of flotation columns in the cleaning circuit to reduce entrainment of fluorine-bearing non-sulphide gangue minerals such as fluorite and biotite.
Primary and secondary crushing
Run-of-mine ore at 2.5 m top size is hauled in 240 t trucks and fed to one of two primary gyratory crushers sized at 60 x 89 inches with 600 kW motors, each rated at 1,826 t/h. The crusher product has 80% passing 152 mm at an open-side setting of 140 mm. Primary crushed ore is conveyed to a common crushed ore stockpile with a live capacity of approximately 24,800 t and total capacity of 73,400 t.
Four reclaim feeders deliver ore to two operating double-deck vibrating screens with a 100 mm top deck aperture and 55 mm bottom deck aperture, producing an underflow with 80% passing 38 mm. Screen oversize is crushed in two MP-1000 cone crushers with 746 kW motors in a standard closed circuit. A third screen and crusher were added with the Salobo II plant, typically on standby.
Secondary-crushed product is conveyed via a 2 km pipe conveyor running at 2.5 m/s to a secondary crushed ore stockpile with a total capacity of approximately 171,000 t and live capacity of about 75,000 t.
High-pressure grinding rolls
Two parallel lines of four reclaim feeders each deliver crushed ore to the HPGR circuit. Ore is conveyed to four concrete silos providing approximately 20 minutes of surge at nominal capacity, then fed to four HPGR units. Each HPGR unit has a drum 2.0 m diameter by 1.5 m wide, with a maximum feed size of 55 mm. The HPGR product has 80% passing 17 mm while operating with a 40 mm gap and 150 bar hydraulic pressure on the floating roll.
HPGR product is screened at 8 mm on the bottom deck of banana screens, with the top deck aperture set at 15 mm. There are eight operating screens, with half dedicated to each plant line. Screen undersize at 80% passing 6 mm discharges to a ball mill discharge sump. Screen oversize is recirculated to the HPGR silos feed conveyor for further crushing, with a circulating load of typically 110%.
Grinding circuit
Slurry in the ball mill discharge sump is pumped to a battery of ten 660 mm hydrocyclones, of which seven are typically operating per line. Hydrocyclone underflow feeds by gravity to an overflow ball mill of 7.9 m diameter by 12.2 m long, equipped with a 17 MW gearless motor. Four ball mills operate in closed circuit, each with a dedicated hydrocyclone cluster. The design grinding circuit product is 80% passing 106 μm. Hydrocyclone overflow advances to the Rougher 1 flotation circuit at 45% solids by weight.
The ball mills were designed for a 30–35% ball charge using 76 mm diameter steel balls with a circulating load of approximately 300%. Operations adjusted conditions to a 30% ball charge with a circulating load of about 200%. Under these conditions, 15 MW are drawn from the mill motors. A higher ball charge would reportedly require addition of a retainer ring at the mill discharge.
Flotation circuit
The flotation circuit is of conventional design with extensive column flotation in cleaning stages. Lime is added at the front end of the circuit to raise the pH to about 10. Sodium hydrosulphide is added ahead of roughing to clean the surfaces of bornite and increase its recovery. PAX and a dithiophosphate are used as primary and secondary collectors, respectively. Propylene glycol and methyl isobutyl carbinol provide frothing.
Rougher 1 flotation is carried out in four parallel lines, one for each ball mill, with two cells per line. The mechanically agitated cells have a capacity of 200 m³ each, providing six minutes of design retention time. Rougher 1 concentrate advances to the cleaning circuit. Rougher 1 tailings advance to the Rougher 2 scavenger circuit, consisting of four lines with six mechanically-agitated 200 m³ cells per line, for a nominal retention time of 39 minutes. Staged Flotation Reactors are installed on rougher tailings, with their concentrate reporting to concentrate regrinding. SFR tailings gravitate to the tailings storage facility, while the concentrate advances to the regrinding circuit.
The cleaning circuit has three upgrading stages closed by a cleaner–scavenger bank of conventional agitated cells. Concentrate from each stage advances to the next, while tailings are moved back to the previous stage. Cleaner 1 tailings proceed to the cleaner–scavenger, and Cleaner 3 concentrate is the final concentrate.
Cleaner 1 circuit consists of 16 column cells, each 6 m diameter by 14 m height, arranged in four lines of four cells each, with a design residence time of 39 minutes. Cleaner 1 columns are fitted with a Microcel sparging system that introduces flotation air to recirculated slurry pumped through static mixers. Other columns use standard air spargers.
Cleaner 1 concentrate advances to Cleaner 2, consisting of eight cells in four lines of two columns each, 4.3 m diameter by 14 m height, for a design retention time of 34 minutes. Cleaner 2 concentrate advances to Cleaner 3, consisting of four cells in four lines of one cell each, each column 4.3 m diameter by 14 m height, for a design retention time of 39 minutes.
Cleaner 1 tailings are fed to the cleaner–scavenger section, made of four lines of four 200 m³ agitated cells each. Cleaner–scavenger tailings join Rougher 2 tailings to form the complete plant tailings stream, directed by gravity to the tailings storage facility. Cleaner–scavenger concentrate is combined with Rougher 2 concentrate and undergoes regrinding in one of four vertical mills fitted with 1.1 MW motors.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Nominal plant throughput (Salobo I) | 12 Mtpa | Design |
| Nominal plant throughput (Salobo II) | 24 Mtpa | Design |
| Targeted operating time | 90% | Design |
| Copper-in-concentrate production (Salobo I) | ~100 kt/a | Design |
| Copper-in-concentrate production (Salobo II) | ~200 kt/a | Design |
| Primary crusher rating | 1,826 t/h each | Design |
| Primary crusher product (P80) | 152 mm | Design |
| Screen underflow product (P80) | 38 mm | Design |
| HPGR product (P80) | 17 mm | Design |
| HPGR operating pressure | 150 bar | Operating |
| Grinding circuit product (P80) | 106 μm | Design |
| Ball mill motor power | 17 MW | Design |
| Ball charge | 30–35% design; 30% operating | Design/actual |
| Circulating load (grinding) | ~300% design; ~200% actual | Design/actual |
| Rougher 1 retention time | 6 min | Design |
| Rougher 2 retention time | 39 min | Design |
| Cleaner 1 retention time | 39 min | Design |
| Cleaner 2 retention time | 34 min | Design |
| Cleaner 3 retention time | 39 min | Design |
| HPGR screen aperture (top/bottom) | 15 mm / 8 mm | Design |
| Hydrocyclone diameter | 660 mm | Design |
| Ball mill dimensions | 7.9 m dia. x 12.2 m long | Design |
| Cleaner 1 column dimensions | 6 m dia. x 14 m height | Design |
| Cleaner 2 and 3 column dimensions | 4.3 m dia. x 14 m height | Design |
Project website: https://valebasemetals.com/our-operations/salobo/
Technical qualifications
The report does not include actual operating performance data for the Salobo I and II plants beyond the statement that both lines have proven capable of processing nominally 12 Mt of ore annually each. No metallurgical accounting for actual recovery, concentrate grade, or throughput beyond nominal figures is provided. The report describes the Salobo III expansion only as a decision by Vale to increase total ore processing capacity to 36 Mtpa; no design details, capital or operating cost estimates, or schedule for this expansion are provided. All process parameters are reported as design values or as operating adjustments noted in the report, such as the reduced ball charge and circulating load in the grinding circuit. The report does not state whether the noted operating adjustments are representative of long-term performance.
Source: Salobo Project Technical Report, December 2019, Sections 17.1 and 17.2.
