Eagle Mine Humboldt Mill: Nickel and Copper Flotation Recovery

Source: Unnamed_Company_81 (2026)
Website: https://talonmetals.com/talon-metals-completes-previously-announced-acquisition-of-lundin-minings-eagle-mine-and-humboldt-mill-operations-creating-a-multi-asset-u-s-nickel-copper-company/

Critical Data

Overview

The Humboldt Mill, operated by Talon Metals Corp as part of the Eagle Mine project in Michigan, USA, is a former iron ore processing facility converted to recover nickel and copper from underground sulfide ores. Located near the Eagle Mine, the mill processes ore trucked from the mine via highway haul trucks to a Coarse Ore Storage Area (COSA) with 10,000 tonnes capacity. Since its conversion, the mill has employed a conventional three-stage crushing circuit followed by single-stage ball milling and a two-stage flotation process to produce separate high-grade nickel and copper concentrates. The facility boasts nameplate throughput of 2,000 tonnes per day (730,000 tonnes per year) and achieves metallurgical recoveries averaging 85% for nickel and 97% for copper, though recent monthly performance from January 2025 to February 2026 showed actual recoveries of 83.2% for nickel and 95.3% for copper. The significant copper recovery makes this operation a key North American supplier of critical battery metals. Tailings are deposited sub-aqueously in the former Humboldt iron ore open pit, now the Humboldt Tailings Disposal Facility (HTDF), minimizing environmental impact. The mill’s flowsheet remains virtually unchanged since commissioning, relying on proven technologies including bulk flotation, regrind, and separation flotation using lime to achieve final concentrate grades of 12–13% nickel and 28.6–30.5% copper.

Key Process Stages

• Stage 1: Three-stage Crushing – ROM ore (nominal minus 450 mm) undergoes primary jaw crushing to a P80 of 100 mm, followed by secondary and tertiary cone crushing to reduce the ore to a P80 of 8 mm. Tertiary crushed ore is stored in bins prior to grinding.
• Stage 2: Ball Mill Grinding – Crushed ore is fed to two parallel single-stage ball mill circuits operating in closed configuration with hydrocyclones, targeting a product P80 of 130 microns. Sodium carbonate is added for pH and water chemistry control.
• Stage 3: Bulk Rougher Flotation – The ground slurry undergoes bulk rougher flotation to produce a copper-nickel bulk concentrate, rejecting gangue minerals. Reagents include sodium isopropyl xanthate (SIPX), methyl isobutyl carbinol (MIBC), and carboxymethylcellulose (CMC).
• Stage 4: Regrinding and Cleaner Flotation – The bulk Cu-Ni concentrate is reground and subjected to multiple cleaning stages to further reject gangue minerals and upgrade the concentrate before separation.
• Stage 5: Separation Flotation and Dewatering – Lime is added to the bulk cleaner concentrate to selectively separate copper and nickel minerals. Final nickel concentrate (13% Ni, 2% Cu) and copper concentrate (31% Cu, 0.8% Ni) are dewatered to 8–10% moisture using thickeners and filter presses, then loaded into railcars for shipment to North American smelters.

Additional Interesting Data and Summary

The Humboldt Mill’s life-of-mine (LOM) processing plan for 2026–2030 outlines declining ore grades and throughput as the Eagle Mine approaches its end of life in 2030. Feed tonnage peaks at 787 kt in 2027–2029 before dropping to 497 kt in 2030, with nickel head grades decreasing from 1.46% to 0.95% and copper from 1.20% to 0.72%. Despite lower grades, overall recoveries are projected to remain robust, with nickel recovery ranging from 78.4% to 83.3% and copper recovery from 93.2% to 95.6%. Cobalt, gold, platinum, and palladium are also recovered as by-products, with cobalt recovery exceeding 79% and palladium recovery reaching 83.3%. The copper concentrate maintains a high quality of 30.5% Cu, while nickel concentrate targets 13% Ni, though recent actual nickel concentrate grade averaged 12.0% due to operational optimization for smelter conditions. The mill uses an on-stream analyzer for real-time monitoring of 12 streams and operates an onsite SGS laboratory for shift composites. Environmental management includes sub-aqueous tailings deposition in the former Humboldt iron ore pit (HTDF) and extensive water recycling from tailings and concentrate dewatering. Historically, a mine-related incident in 2024 temporarily depressed mill performance, but operations have since stabilized. Future challenges include the higher hardness of Keel ore, which may reduce throughput compared to historical averages. The facility’s strategic importance lies in supplying high-grade nickel and copper concentrates to North American smelters, supporting domestic battery metals supply chains. With a proven conventional flowsheet and strong metallurgical performance, the Eagle Mine and Humboldt Mill represent a model for sustainable sulfide ore processing in the Great Lakes region.

Key Processes: Flotation, Ball Mill, Crushing

Target Commodities: Copper, Nickel