Cobre Las Cruces Polymetallic Refinery Plans Flotation, Silver-Catalysed Ferric Leaching, Zinc SX-EW and Brine Leaching for Lead and Silver

First Quantum's 2024 technical report for Cobre Las Cruces near Seville describes a 2.2 Mtpa underground polymetallic sulphide operation. It reuses the existing copper leach, SX and EW plant and adds a new plant about 1 km away.

The Cobre Las Cruces: Polymetallic Primary Sulphide Project, Andalucía, Spain, NI 43-101 Technical Report, is dated February 2024 and was prepared by qualified persons of First Quantum Minerals (FQM) and Cameron Mining Consulting. The existing plant has treated 1.5 Mtpa of high-grade secondary chalcocite ore from the open pit, at a nominal design grade of 6.02% Cu, to make up to about 72,000 t a year of LME Grade A copper cathode. With the secondary sulphides depleted, the operation plans to mine the primary polymetallic sulphides (PMS) beneath the pit from underground. These carry zinc, copper, lead and silver, which the existing plant cannot recover effectively. The polymetallic refinery (PMR) project therefore expands and modifies the existing plant and adds a new processing facility.

Critical Data

Overview

Ore from underground arrives by Railveyor at a new crushing and SABC milling plant. Bulk rougher-scavenger flotation follows, and the concentrate is reground to 10 µm. The bulk concentrate is leached at atmospheric pressure in a silver-catalysed acidic ferric sulphate lixiviant (SICAL) that dissolves copper and zinc. Lead and silver precipitate as sulphates in the leach residue. Copper is recovered in the existing copper SX and EW circuits. Iron is then removed from the raffinate, and zinc is recovered in new primary and secondary zinc SX circuits, electrowon and cast to ingots. The primary leach residue is leached in brine, and silver and lead are cemented from that solution. Flotation tailings go to a new paste plant for underground backfill or to the tailings storage facility (TSF).

Key Process Stages

Crushing and milling. Railveyor ore tips into a run-of-mine bin, or onto an emergency stockpile. An apron feeder and vibrating grizzly feed a single-toggle jaw crusher to a P80 of about 160 mm. A domed stockpile holds about 6,700 t live, roughly 24 hours. The SAG mill runs in closed circuit with a screen because of the fine 35 µm target, and a pebble crusher re-used from the existing plant crushes the trommel oversize to P80 15 mm.

Flotation and regrind. Four 70 m³ rougher cells and four 70 m³ scavenger cells each give about 25 minutes. The combined concentrate is cycloned, and the underflow is reground in open circuit to P80 10 µm. Concentrate is pumped to the existing site, thickened in an existing 26 m thickener and filtered on three existing horizontal vacuum belt filters. Scavenger tails go to a 30 m high-rate thickener at the paste plant, at a target 70% solids.

Primary leach. Filtered concentrate is repulped with zinc raffinate and fed, with silver cement catalyst and sulphuric acid, to three 1,000 m³ pre-leach reactors with oxygen sparging. These give about ten hours at a controlled 80°C. Eight existing primary leach reactors then give about seven hours at about 90°C. The slurry is cooled, thickened in an existing 20 m thickener and filtered on three existing Larox tower filters. Gypsum is precipitated in cooling towers, and lime raises the PLS to about pH 1.5 ahead of copper SX.

Copper SX and EW. The existing copper SX and EW circuits, which have run at up to 72,000 t a year, are used essentially unchanged.

Iron removal. Copper raffinate passes four 400 m³ reactors, about six hours in total, with air sparging and lime to pH 4.0. A 40 m thickener and three 120 m² belt filters remove ferric hydroxide and gypsum. About a third of the iron residue goes to effluent treatment to fix arsenic as ferric arsenate, and the rest goes to the TSF.

Zinc SX, EW and casting. Zinc is extracted in three primary extraction mixer-settlers, washed in three stages and stripped in two. The primary raffinate (about 16 g/L Zn and 45 g/L acid) returns to the leach. A raffinate bleed is neutralized to pH 4.0 and passed through a secondary extraction circuit. Iron is stripped from an organic bleed with 6M hydrochloric acid, which is regenerated. Electrolyte at 90 g/L zinc is electrowon on permanent aluminium cathodes with silver-alloyed lead anodes, to a spent electrolyte of 45 g/L. The cathodes are melted in a 16 t/h induction furnace under ammonium chloride and cast on two lines of 108 moulds.

Secondary leach, silver and lead recovery. Primary leach residue is repulped in brine and leached in four reactors for two hours at about 80°C, which dissolves lead and silver as chloride complexes. Silver is cemented on lead plates in eight parallel reactors of 45 minutes each at about 80°C, filtered and purified into a saleable silver cement. The solution is adjusted to pH 2.2 to 2.4 and thickened. Lead is then cemented on rotating aluminium discs in twelve one-hour cementators and pressed into briquettes. A brine bleed goes through aluminium and sulphate removal with lime at pH 4.5 and about 70°C.

Paste backfill. The paste plant filters thickened flotation tailings on three vacuum disc filters. The cake is mixed with cement for underground backfill or sent to the final tailings conveyor.

Additional Interesting Data and Summary

The new plant sits on a cleared former waste stockpile south of the open pit. Residues from secondary leaching, iron removal and aluminium removal are loaded into trucks and hauled to impoundment facilities on the existing haul road. The design ore blend contains more of the harder stockwork ore than the resource model indicates, to add conservatism to crushing and milling.

In summary, the 2024 Las Cruces report converts a chalcocite leach operation into a polymetallic refinery. It floats a fine bulk concentrate, leaches it with a silver-catalysed ferric lixiviant for copper and zinc, and recovers lead and silver from the residue by brine leaching and cementation. Copper cathode, zinc ingots, silver cement and lead briquettes are produced on site.

Key Processes

• Jaw crushing and SABC milling to P80 35 µm
• Bulk rougher and scavenger flotation with regrind to P80 10 µm
• Silver-catalysed atmospheric ferric sulphate leaching
• Copper solvent extraction and electrowinning
• Iron removal by air oxidation and lime
• Zinc solvent extraction, electrowinning and ingot casting
• Acidic brine leaching of lead and silver
• Silver and lead cementation
• Aluminium and sulphate removal, and effluent treatment
• Paste backfill from filtered flotation tailings

Source: Cobre Las Cruces: Polymetallic Primary Sulphide Project, Andalucía, Spain, NI 43-101 Technical Report, First Quantum Minerals Ltd, February 2024.