The oldest trick in the plant. You do not need to weigh anything — three assays and conservation of mass give the split and the recovery exactly. Feed equals concentrate plus tailing, in tonnes and in metal, and two equations in two unknowns close it.
The tailing assay is the one that matters and the one nobody trusts. It is the smallest number, so it carries the largest relative error, and the recovery is more sensitive to it than to either of the others. The calculation below shows how much.
You cannot have both. Push for a cleaner concentrate and you leave metal behind; push for recovery and the concentrate carries waste. The curve is a property of the ore and the grind, not of the operator — so it is measured, in a series of flotation tests, and never assumed. Put your tests in and the panel finds the point on your curve that the smelter's terms actually pay for.
Grinding is where the electricity goes — commonly more than half of a mine's power bill. Bond's law says the energy needed depends on the inverse square roots of the sizes, so every halving of the product size costs more than the halving before it.
| ore | Wi kWh/t |
|---|
A work index is measured, not looked up — but the table says whether a measured one is plausible. Anything above about 20 is a hard ore and the mill will be the constraint on the whole operation.
Before any equipment is bought, one number says whether a density difference can be separated in water at all. The concentration criterion compares how much denser the wanted mineral is than the fluid with how much denser the waste is — and it also says how fine you can go before it stops working.
Which property of the mineral is being exploited. Every separation needs a contrast in something — density, magnetism, conductivity, surface chemistry or colour — and if there is no contrast there is no process.
| method | exploits | works down to |
|---|
No separation can beat the grind. If a grain of ore mineral is still locked inside a grain of quartz, every process will treat the pair as one particle with the average density, the average surface and the average everything. The grind size that liberates is a property of the ore's texture, and it is read under a microscope — see Thin section — not guessed from a formula.