Sorting the Earth — From Rocks to Ores
We asked the ground a question in Part 1; now we listen. Sorting is how the planet whispers, “this part is a wire, this part is a beam, this part is a window,” and we nod politely and put each piece on the correct conveyor.
Why sorting first (the art of saying “you are not ore”)
Every kilowatt you spend grinding barren rock is a kilowatt you don’t spend on building the world. So the first law: reject waste early. Dry physics — magnetism, density, optics — do most of the talking. Wet steps, when needed, come later and recirculate their water.
- Less mass downstream → smaller smelters, smaller power bills, smaller everything.
- Dry first → less water to manage; dust stays inside sealed equipment.
- Better product → smelters eat concentrate, not opinions.
Meet the line (modules like Lego)
1) Feeder & Primary Crusher
Big bites become medium bites. Jaw or gyratory crushers deliver 150–250 mm product.
Typical rating: 250–500 kW Duty: 60–90% availability2) Screens & Secondary/HPGR
Screens split material by size; secondary cones or HPGR (high‑pressure grinding rolls) make cubes out of chaos, preparing perfect feed for sorters.
Screens: 2–30 kW each HPGR: 2–6 MW (high throughput)3) Sensor‑Based Sorters
X‑ray, near‑IR, laser, or hyperspectral cameras see what eyes can’t. Air jets nudge the keepers. No drama, just a thousand gentle decisions per second.
Per lane: 50–250 kW Throughput: 50–400 t/h4) Magnetic & Eddy Separation
Magnetite leaps at magnets. Weakly magnetic minerals obey high‑intensity separators. Eddy currents push non‑ferrous bits like a polite bouncer.
Low/High‑intensity magnets Eddy current for aluminum/copper pieces5) Density (DMS) & Gravity
Dense media (or water spirals/jigs) separate heavy from light. When used, circuits are closed‑loop, water recirculated.
Water recirc > 90% Make-up water modest6) Conveyors Everywhere
Belts beat trucks for energy: ~0.02–0.05 kWh/ton‑km. Covered, sealed, quiet.
Low energy per ton Dust stays insideOre‑by‑ore playbook (pick your physics)
Magnetite Iron
Dominant physics: magnetism. Dry crushing & screening → low‑intensity magnetic separation.
- Energy: ~8–18 kWh/ton (dry route)
- Water: ~0.1–0.3 m³/ton (dust control)
- Yield (mass): ~40–55% → 65% Fe concentrate
Bauxite (Aluminum)
Dominant physics: size + density. Screen, wash, and de‑slime; avoid fine grinding.
- Energy: ~3–8 kWh/ton
- Water: ~0.2–0.5 m³/ton (recirculated)
- Yield (mass): ~60–75% → alumina‑grade feed
Copper Sulfide
Dominant physics: liberation + flotation. Dry crush → wet mill (fine) → froth flotation.
- Energy: ~20–40 kWh/ton (most in milling)
- Water: ~0.5–1.5 m³/ton (recycled)
- Yield (mass): ~2–4% → 25–35% Cu concentrate
Pre‑calculated flows
Plant capacity cheat sheet (assuming ~8,000 operating hours/year)
| Annual Feed | Throughput (t/h) | Typical Lines | Line Power (MW) | Notes |
|---|---|---|---|---|
| 5 Mt/yr | ~625 | 1–2 | Magnetite: ~5–10 Bauxite: ~2–5 Copper: ~12–25 |
Small campus; fits in ~5–8 ha |
| 10 Mt/yr | ~1,250 | 2–3 | Magnetite: ~10–20 Bauxite: ~5–10 Copper: ~25–40 |
Medium campus; ~8–15 ha |
| 20 Mt/yr | ~2,500 | 3–5 | Magnetite: ~20–35 Bauxite: ~10–18 Copper: ~40–70 |
Large campus; ~15–30 ha |
Power numbers reflect total line averages (crushing, screening, sorting, pumps) before smelting. We’ll power them with the solar seed factory next door.
Mass balance — Magnetite (example)
Feed 10 Mt/yr at 35% Fe; target 65% Fe concentrate.
| Stream | Mass (Mt/yr) | Comment |
|---|---|---|
| Feed | 10.0 | Crush → screen → magnets |
| Concentrate | ~4.5–5.5 | 40–55% mass yield |
| Rejects | ~4.5–5.5 | Back to engineered walls & bricks |
Line power: ~10–20 MW • Water: ~0.1–0.3 m³/ton (dust control)
Mass balance — Copper sulfide (example)
Feed 10 Mt/yr at 0.8% Cu; concentrate 30% Cu.
| Stream | Mass (Mt/yr) | Comment |
|---|---|---|
| Feed | 10.0 | Crush → mill → float |
| Cu concentrate | ~0.24–0.36 | 2.4–3.6% mass yield |
| Tailings (reclaimed) | ~9.64–9.76 | Thickened, stacked, reused |
Line power: ~25–40 MW • Water: ~0.5–1.5 m³/ton (recycled >85%)
Energy per ton — quick reference
| Unit Operation | Energy (kWh/ton) | Notes |
|---|---|---|
| Primary crushing | ~0.5–1.5 | Jaw/gyratory |
| Secondary / tertiary crushing | ~1–4 | Cones/HPGR prep |
| HPGR (coarse grind) | ~3–7 | Often replaces SAG |
| Ball/SAG milling (fine) | ~10–20 | Only if liberation demands |
| Sensor sorting (per ton feed) | ~0.2–1.0 | Cameras, air jets |
| Magnetic / eddy | ~0.1–0.5 | Low overhead |
| Conveying (per km) | ~0.02–0.05 | Ton‑km basis |
Rule: If a sorter can reject 20–50% of rock before fine grinding, downstream energy falls dramatically.
Energy & water budget (pre‑calculated)
10 Mt/yr Magnetite (dry‑first route)
| Component | Avg Power (MW) |
|---|---|
| Crushing & screens | ~6 |
| HPGR (if used) | ~6 |
| Magnets & sorters | ~2 |
| Conveyors & aux | ~2 |
| Total | ~16 MW |
Water: ~0.2 m³/ton (dust) → 2 Mm³/yr recirculated.
10 Mt/yr Copper (flotation route)
| Component | Avg Power (MW) |
|---|---|
| Crushing & screens | ~6 |
| Milling (fine) | ~20 |
| Flotation & pumps | ~6 |
| Conveyors & aux | ~4 |
| Total | ~36 MW |
Water: ~1.0 m³/ton feed → 10 Mm³/yr; recirc >85%, make‑up via lake.
Factory footprint & siting
Area & buildings (10 Mt/yr)
- Enclosed buildings: crushers, screens, sorters (noise & dust inside).
- Open air: conveyors with covers, magnets (as needed).
- Footprint: ~8–15 hectares including stockpiles & access.
- PV field next door: ~100–200 MWp to power sorting + growth.
Air, dust, sound
- Baghouses & misting keep PM levels boringly low.
- Acoustic panels & enclosures target <85 dBA at fence line.
- All conveyors covered; transfer points fully enclosed.
Q&A
“Are we using nasty chemicals?”
We prioritize dry physics. When a wet step is essential (e.g., flotation for copper), we use closed circuits with modern, low‑tox reagents and clean the water before release — usually we don’t release at all, we reuse.
“What happens to rejects?”
They become roads, blocks, and landscaped lake walls. Nothing gets abandoned; everything becomes place.
“Why all this effort before smelting?”
Because every percent of waste removed upstream multiplies into cheaper, smaller, faster downstream plants. It’s the difference between dragging a mountain into a furnace and inviting just the ore.
Up next: Solar as the Seed Factory — Panels that Build the Next Factory (Part 3). We’ll show how one sunny roof becomes a terawatt habit.