Copper World — 2023 Preliminary Feasibility Study

The 2023 PFS updates the 2022 PEA with additional testwork and process optimization for a 60,000 t/d sulfide concentrator and staged concentrate leach facility.

Report context

This preliminary feasibility study for the Copper World project, dated 2023, presents a process plant design updated from the 2022 Copper World Preliminary Economic Assessment. The update incorporates additional testwork conducted by various laboratories in 2022/23, along with process optimization based on both Hudbay's and equipment vendors' benchmark databases. The processing plant consists of a sulfide concentrator and a concentrate leach facility, with the concentrate leach facility to be built in stages starting in year four.

Processing route

Sulfide concentrator overview

The sulfide concentrator will have an installed capacity of 60,000 tons per day processed via a primary crushing circuit and a grinding circuit configured in semi-autogenous mill and ball mill configuration. Bulk flotation produces a copper and molybdenum concentrate, followed by separation of copper and molybdenum concentrate via reverse flotation. Bulk flotation tailings are thickened before sands/slime separation and discharged to the tailings storage facility. The process plant will operate two 12-hour shifts per day, 365 days a year, with an overall plant availability of 92%.

Crushing and stockpile

Run of mine feed is delivered by haul trucks to a primary gyratory crusher operating in open circuit. Nominal and design crusher feed rates are 3,333 tph and 3,833 tph respectively, based on a crusher runtime of 75%. Trucks discharge directly into the crusher, which is set in a dump pocket designed to allow two trucks to dump simultaneously. The crusher reduces feed from a design F80 of 9 inches and F100 of 25 inches to a P80 of 3.0 inches. Crusher discharge falls by gravity into a surge pocket, with an apron feeder withdrawing crushed feed onto a short sacrificial conveyor that transports material to the coarse feed stockpile feed conveyor.

The coarse feed stockpile has two reclaim chambers, a total capacity of 150,000 tons, and a live capacity of 60,000 tons. Reclaim uses two reclaim feeders at a nominal rate of 1,360 tph per feeder, discharging onto the SAG mill feed conveyor.

Grinding and classification

The grinding circuit consists of a SAG mill followed by a ball mill arranged in closed circuit with a cyclone cluster. Nominal feed throughput is 2,720 tph. The SAB circuit reduces reclaimed feed from an F80 of 3.0 inches to a P80 of 150 to 180 µm, feed source dependent. The circuit is configured to allow for future addition of a pebble crusher if required.

The SAG mill is a grate discharge with pebble ports, with SAG mill product discharging to a vibrating screen deck. Screen oversize is conveyed back to the SAG mill feed conveyor; screen undersize gravitates to the cyclone feed pump box. Steel media is added to the SAG mill as required to maintain mill throughput.

Ball mill discharge gravitates to the cyclone feed pump box, combining with SAG mill discharge before feeding the cyclone cluster. Process water is added to the SAG mill feed chute, ball mill feed chute and cyclone feed pump box as required. Cyclone underflow gravitates to the ball mill feed chute; cyclone overflow gravitates to the flotation feed conditioning tank. The circuit is configured to allow a portion of cyclone underflow to gravitate to the SAG mill feed chute as required for power balance. Ball mill design circulating load is 350%.

Bulk flotation

Cyclone overflow gravitates to bulk rougher conditioning tanks where mineral collectors, frother and sulfurization reagents are added. Conditioned slurry undergoes rougher flotation in Jameson cells for recovery of copper, molybdenum, silver and gold. Design data indicate 6 rougher Jameson cells with stage recovery of 95% for copper sulfide, 60% for acid-soluble copper, and 75% for molybdenum, producing a concentrate grade of 3.00% copper at 8% mass pull.

Bulk rougher concentrate is reground in a 4,023 HP regrind Isamill configured in open circuit with cyclones ahead of the mill. The regrind cyclone removes minus 35 µm particles; cyclone underflow discharges to the Isamill feed hopper. Water is added to maintain Isamill feed below 40% solids by volume. The regrind circuit produces a product P80 of 25 to 35 µm.

The regrind product is conditioned and discharged to cleaner flotation. Cleaner tails gravitate to a cleaner scavenger; cleaner scavenger concentrate is pumped back to the cleaner conditioning tank and tailings are pumped back to rougher conditioning tanks. Cleaner concentrate gravitates to a recleaner producing final bulk concentrate. Recleaner tailings are pumped back to the cleaner conditioning tank. All cleaning uses Jameson cells. Two cleaner stages are designed with stage recovery of 97% for copper sulfide, producing a nominal concentrate grade of 25.00% copper and a design concentrate grade of 18.00% copper.

Molybdenum flotation

Bulk concentrate thickener underflow is pumped to a molybdenum-copper separation flotation conditioning tank, where sodium hydrosulfide and carbon dioxide are added to suppress copper minerals. Conditioned slurry undergoes rougher flotation in Jameson cells for selective recovery of molybdenum.

Molybdenum rougher concentrate is further upgraded in three stages of cleaner flotation to produce final molybdenum concentrate that reports to the molybdenum thickener. Tailings from molybdenum roughers are pumped to the copper thickener. Design circuit recovery for molybdenum is 90%, with a design molybdenum concentrate grade of 50.00% molybdenum and a design copper content of 1.00%.

Concentrate dewatering

Copper concentrate is pumped to a high-rate thickener (unit area 2 ft²/ton/d, underflow density 60% solids). Thickener overflow is reused in bulk and molybdenum flotation circuits. Thickener underflow is pumped to an agitated concentrate stock tank ahead of pressure filtration. Design filtration rate is 98 lb/ft²/h with nominal filter cake moisture of 9%. Copper concentrate is discharged to a stockpile for loading to concentrate leach or third-party sale.

Molybdenum concentrate is pumped to a high-rate thickener (unit area 4.1 ft²/ton/d, underflow density 60% solids). Thickener overflow is reused in molybdenum flotation circuits. Thickener underflow is pumped to an agitated stock tank ahead of pressure filtration. Design filtration rate is 72 lb/ft²/h with nominal filter cake moisture below 15%, followed by drying in a Holoflite dryer to 5% moisture. Molybdenum concentrate is bagged into 2,200 lb bags for third-party sale.

Concentrate leach facility overview

The concentrate leach facility, based on the Glencore Technologies Albion Process, will operate two 12-hour shifts per day, 365 days a year with an overall plant availability of 95%. The leach facility will be built in stages with the final configuration capable of processing 735 tons per day of copper concentrate and plating 211 tons per day of copper cathode. The facility produces LME Grade A copper cathodes along with various byproducts.

Copper concentrate regrind and Albion leach

Copper concentrate from the storage area is loaded into a concentrate re-pulp feeder and slurried to target density in raffinate ahead of ultrafine grinding. Re-pulped concentrate is reground in a 2,562 HP regrind Isamill to a product P80 of 10 µm (P100 of 20 µm) with specific grinding energy of 22.5 kWh/ton.

Reground concentrate is oxidized in the Albion leach tanks utilizing 95% oxygen at atmospheric pressure and 203°F for 48 hours, achieving copper extraction to solution greater than 98% and sulfide oxidation greater than 75%. The oxidation process is autothermal, requiring no external heating. Design includes one parallel train with eight tanks per train; oxygen utilization is 90%.

Sulfur recovery and purification

Oxidized copper concentrate from the Albion leach tanks undergoes flotation in two Jameson cells for recovery of elemental sulfur created in the prior stage; unreacted sulfides are also recovered into the concentrate. Stage recovery for elemental sulfur is 96%, producing a sulfur concentrate grade of 95%. The sulfur concentrate is filtered to moisture below 30% and upgraded via sulfur melting purification.

Sulfur concentrate filter cake is purified by heating to 273–293°F, causing elemental sulfur to convert to liquid phase. Molten sulfur is filtered to separate clean molten sulfur from solid material. The molten sulfur is further processed onsite to create sulfuric acid or sold as molten sulfur. Sulfur extraction in purification is 88%, with product purity above 99%. Retained solids are returned to the Albion leach circuit. The sulfur burner acid plant uses a double-contact double-absorption process, producing 98% w/w H₂SO₄ acid.

Iron removal

Sulfur flotation tailings are pumped to the iron removal stage. Limestone is added and pH is controlled to precipitate iron, arsenic and other deleterious dissolved elements from the pregnant leach solution. Oxygen is injected to convert ferrous iron to ferric iron prior to precipitation as goethite. Feed solution iron grade is 20 mg/L; production solution iron grade is below 5 mg/L. Iron precipitation operates at feed acidity below pH 1.0 and product acidity of pH 2.0 to 2.5, with 6 hours residence time across three tanks in one train.

Slurry from iron removal tanks is pumped to a residue thickener (high rate, unit area 41 ft²/ton/d, underflow density 50% solids). Thickener overflow discharges to the pregnant leach solution pond. Residue thickener underflow is dewatered further via pressure filtration with 98.5% wash efficiency and filter cake moisture below 25%. To increase pregnant leach solution recovery, residue solids are washed during filtration; filtrate discharges to the residue thickener. Filter cake is repulped and pumped to the precious metal recovery plant.

Solvent extraction and electrowinning

Pregnant leach solution from the residue thickener overflow is pumped from the pregnant leach solution pond to the solvent extraction circuit. The circuit consists of a single train of mixer settlers configured as extraction 1, extraction 2, washing, stripping. Pregnant solution grades are 25 mg/L copper, below 5 mg/L iron, and below 5 mg/L H₂SO₄. Solvent extraction efficiency for copper is 95% across three extraction stages, one washing stage, and one stripping stage.

Loaded organic is pumped to the washing stage where iron is scrubbed away. Barren raffinate is pumped to the raffinate pond for reuse in the Albion leach stage to recycle regenerated acid. Washed loaded organic is stripped by return lean electrolyte from the electrowinning stage. Rich electrolyte grading 50 mg/L copper reports to electrowinning; lean electrolyte at 35 mg/L copper is recycled to solvent extraction stripping.

The electrowinning tank house plates copper onto permanent stainless-steel starter sheets with a cathode capacity of 77,000 tons per year. Current efficiency is 90% at 2.0 V operating voltage. Loaded starter sheets are harvested on a seven-day cycle; copper cathode is stripped automatically from stainless-steel starter sheets and produces LME Grade A quality.

Precious metals plant

Solid residue from the iron removal stage is pumped to the lime boil stage, where slurry is heated to 194°F and lime is added to unlock silver from the leach residue. Residence time is 4 hours at pH 10.5 across three units.

Lime-boiled residue discharges into cyanide leach tanks for 24 hours at pH 10.5 to extract silver and gold. Silver extraction is 97%. Leached residue undergoes solid-liquid separation and washing in a counter-current decantation circuit with four high-rate thickeners, 4.5:1 wash ratio using Merrill Crowe barren solution, and underflow density of 50% solids.

Pregnant leach solution is pumped to the Merrill Crowe circuit for precious metal recovery. Solution is clarified in leaf filters pre-coated with diatomaceous earth. Residual oxygen is removed by passing solution through a vacuum de-aeration column, with design dissolved oxygen below 1.0 ppm. Zinc dust is added at 600 lb/d to precipitate silver and gold. Precipitate is filtered, with filter cake fluxed and smelted to produce silver-gold doré. Barren solution is recycled to the first leach tank and used as wash solution on the final CCD stage.

Unreacted solid residue is subjected to SO₂/O₂ cyanide destruction with two stages and 60 minutes residence time per stage, then combined with flotation tailings and discharged to the tailings storage facility.

Tailings

Flotation tailings are directed to sands-slime separation cyclones for two stages of cyclone classification to generate a fines-deficient sands stream suitable for tailings storage facility embankment construction. Fines-deficient cyclone underflow is pumped via positive displacement pumps and dedicated pipelines to the tailings storage facility for embankment placement. Cyclone overflow discharges to the tailings thickener. The tailings thickener is sized to handle 100% of tailings volume; when fines-deficient sand is not required for embankment construction, all tailings report to the thickener. Residue from the concentrate leach process always discharges to the tailings thickener. Thickener underflow is pumped via a five-stage pumping system to the tailings storage facility.

Reagents and consumables

Reagents are prepared and stored in separate self-contained areas inside the process plant and delivered via dedicated metering pumps. Sodium isobutyl xanthate in pellet form is diluted to 20% solids w/w solution for bulk flotation. Diesel is transferred from mine bulk fuel storage to a holding tank for flotation circuits. MIBC frother is used at supplied solution strength. Sodium hydrosulfide is delivered as 40% solution. Flocculant powder is mixed on demand to 1% solids w/w. Quicklime is slaked on demand for flotation and precious metals plant. Limestone is slaked on demand for iron precipitation. Sodium cyanide, copper sulfate, and cobalt sulfate are dissolved and diluted to approximately 15–30% solids w/w. Solvent extraction reagents are held in storage tanks and metered to their respective circuits.

Water supply

Fresh water is sourced from wells located on the western side of the Santa Rita Mountains and pumped through booster tanks and pumps to a freshwater tank. From the storage tank, water is pumped around the plant for reagent mixing, slurry pump gland seals, and mill lubrication system cooling.

Process water is sourced from tailings and concentrate thickener overflows, tailings storage facility reclaim and seepage ponds, and from the freshwater tank as required. Process water is stored in a process water pond and transferred to a process water tank; excess overflows back to the pond. Tailings thickener overflow streams discharge directly to the process water tank.

Air supply

Three separate plant air compressors provide air service. Instrument air is dried using a refrigeration drier and stored in dedicated receivers. Plant air is fed directly to dedicated receivers. Each filtration stage has a dedicated high-pressure air supply and receiver. The acid plant has its own dedicated high-pressure and low-pressure air supply. All flotation cells in the process plant are self-aspirated; no low-pressure air is required for their duty.

Assay laboratory

The assay laboratory is provided by a third party onsite under contract for all required assay analytical services for both mine and process plant.

Key reported parameters

Technical qualifications

The process plant design is updated from the 2022 Copper World Preliminary Economic Assessment and shows additional testwork conducted by various laboratories in 2022/23. Process optimization is based on both Hudbay's and equipment vendors' benchmark databases. The concentrate leach facility design is based on the Glencore Technologies Albion Process (Glencore Technology, 2022). The study is at the preliminary feasibility level and the report explicitly states the design basis as design, not historical operating data or full feasibility testwork results. All availability figures, recovery values, and production capacities are design targets based on this study.

Source: 2023 Copper World – PFS, Form 43-101F1 Technical Report, Section 17 Recovery Methods.