Overview
The Humboldt Mill is a repurposed iron ore processing facility that now processes nickel-copper ore from the Eagle Mine in Michigan, USA. This conventional milling operation features a three-stage crushing circuit, ball mill grinding, and flotation separation to produce high-grade nickel and copper concentrates. With a nameplate capacity of 2,000 tonnes per day (730,000 tpa), the facility achieves impressive metallurgical recoveries of 85% for nickel and 97% for copper.
Key Process Stages
- Ore Transport & Storage: Haul trucks deliver ROM ore to the 10,000-tonne Coarse Ore Storage Area (COSA)
- Crushing Circuit: Three-stage reduction (primary jaw crusher to 100mm, secondary/tertiary cone crushers to 8mm)
- Grinding: Two parallel single-stage ball mills operating in closed circuit with hydrocyclones (target P₈₀ of 100 microns)
- Flotation: Bulk flotation followed by separation flotation with regrinding and cleaning stages
- Concentrate Handling: Dewatering to 8-10% moisture via thickeners and filter presses before rail shipment
- Tailings Management: Subaqueous deposition in historic Humboldt iron ore pit (HTDF)
- Water Recycling: Comprehensive water recovery from dewatering operations and tailings
Critical Data
| Parameter | Value |
|---|---|
| Throughput (2021-2022 avg) | 59,380 t/month |
| Nickel Concentrate Grade | 13.04% Ni, 2% Cu |
| Copper Concentrate Grade | 30.5% Cu, 0.8% Ni |
| Nickel Recovery | 84.9% |
| Copper Recovery | 97.4% |
| MgO in Concentrate | 3.44% (avg) |
| Key Reagents | SIPX, MIBC, Soda Ash, Lime, CMC |
Process Innovations
The facility features an on-stream analyzer monitoring 12 process streams with 12-hour composite sampling by SGS. The operation demonstrates flexibility in concentrate grade targeting, adjusting nickel concentrate grades based on market conditions while maintaining strict MgO control below 6%.
