Presets
Playback
Flow
Film depth and secondary flow.
Feed and splitter
Changing grain sizes or counts restarts the run.
Layers
Model checks
The science
How a spiral concentrator separates minerals
A thin film of slurry flows down a helical trough. Grains settle through the film at a speed set by their size and density, so dense minerals reach the trough floor first. The curved path drives a secondary flow across the trough: water near the surface moves outward and water near the floor returns inward. Heavy grains on the floor are carried toward the inner edge while light grains stay in the fast surface layer and are swept outward. A splitter then divides the stream into concentrate, middlings and tailings.
Settling speed
The terminal velocity balances buoyant weight and drag. With the Schiller-Naumann drag law:
(π/6) d3 (ρp - ρw) g = ½ Cd ρw v2 (π/4) d2 Cd = (24/Re)(1 + 0.15 Re0.687)For small grains this reduces to Stokes' law, v = (ρp - ρw) g d2 / 18μ. Settling is hindered in real dense slurries; here grains are independent.
Performance measures
recovery = heavy grains in concentrate / all heavy grains grade = heavy grains / all grains in concentrateHonest simplifications
- A cross-section model with a prescribed secondary flow profile; the downstream helical motion is not simulated.
- No hindered settling, grain collisions or wash-water addition, which matter in real spirals.
- The bed roll-in speed is an adjustable stand-in for gravity and friction on the tilted floor.
- Random turbulent mixing is a single diffusion constant.
What to try
- Move the splitter inward to raise grade at the price of recovery; the third graph shows the trade-off.
- Same-size grains: with equal sizes density alone must separate them.
- Fine heavy minerals: small heavy grains settle as slowly as large light ones, so separation worsens.
- Deep film: settling takes longer than the grain spends in the trough, so recovery drops.