MINERAL PROCESSING KNOWLEDGE · COPPER ORE PROCESSING
Grinding a whole copper ore fine enough to liberate every copper grain is uneconomic; regrinding the rougher concentrate performs the same liberation work on a fraction of the mass.
Technical overview. Actual process selection depends on representative ore samples, mineralogy, testwork and site conditions.
The ideal grind size for a copper ore is the size at which the copper minerals are liberated, and for many primary ores that lies between 10 and 30 µm, far finer than a concentrator can afford to grind the whole ore. Regrinding the rougher concentrate is the standard response: it places the fine grinding where the value is, on a small stream, instead of on the entire tonnage.
Technical note: The sizes, mass splits and figures below are principles only. They are not engineering designs or performance guarantees. Grind sizes and circuit sizing must be established by testwork on representative ore samples and reviewed by qualified metallurgists.
1. Fine dissemination against coarse economics
Copper minerals in primary ore are often disseminated at very fine grain size, in the range of 10–30 µm. Grinding the whole ore to that size in the first grinding stage would consume an enormous amount of electrical energy. It would also slim the gangue, and slimes consume reagent, change pulp rheology and make both flotation and dewatering harder. A plant that grinds everything to the liberation size pays twice, once for the energy and once for the downstream consequences.
2. Step one: a deliberate coarse primary grind
The first step is to accept a grind coarser than the liberation size suggests. The ore is ground only to d₈₀ = 74–100 µm. At that size the copper minerals are partly liberated and partly present as coarse intergrowths with gangue, binary particles that still contain both copper and waste. This is an acceptable intermediate state, provided the circuit is designed to deal with the intergrowths later rather than attempting to float them clean in the roughers.
3. Step two: rougher and scavenger flotation to reject mass
Rougher and scavenger flotation then operate on the coarse feed. The duty of this stage is mass rejection rather than final grade. Between them the rougher and scavenger banks discard 70%–85% of the final tailings, and the copper rougher concentrate collected amounts to roughly 15%–30% of the original ore volume.
That ratio is the point: everything downstream of the roughers, regrind included, handles a small fraction of the tonnage, so a fine grind on that fraction is affordable in a way that a fine grind on the whole ore is not.
4. Step three: regrind the concentrate to expose the locked copper
The high-grade rougher concentrate is reground on its own, in a tower mill or a fine-grinding ball mill, to a target of 80%–90% passing 38 µm. At that size the coarse intergrowths that survived the rougher are opened and the fine copper minerals are exposed to the cleaning circuit. Several points follow from the purpose of the regrind:
- The target size should be set by the size at which the copper minerals are exposed, not taken as a default.
- The regrind mill is normally closed with a classifier, so that material already fine enough is not ground again.
- Collector is normally added after the regrind, where fresh surfaces are available to it.
- Overgrinding produces slimes that are difficult to float and difficult to dewater, and it can undo the benefit of the regrind.
5. Step four: cleaning in two or three stages
The reground concentrate passes to two or three stages of cleaning to produce the high-grade copper concentrate. Cleaning is where the liberation paid for in the regrind is converted into grade, because with the intergrowths opened the cleaners can reject gangue that previously travelled with the copper.
Taken together, the coarse primary grind, the rougher and scavenger mass rejection, the concentrate regrind and the multi-stage cleaning can reduce the grinding energy consumption of a concentrator by more than 30% compared with grinding the entire ore to the liberation size.
The regrind does not sit in isolation. Cleaner tailings return to the preceding cleaner or to the rougher, and scavenger froth returns to the rougher feed or the regrind, so the mill sees a circulating stream as well as fresh concentrate and should be sized for the load it carries.
| Stage | Size target | Key outcome |
|---|---|---|
| Primary grinding | d₈₀ = 74–100 µm | Partial liberation, with coarse intergrowths remaining |
| Rougher and scavenger flotation | Coarse feed, as ground | 70%–85% of the final tailings rejected |
| Rougher concentrate regrind | 80%–90% passing 38 µm | Intergrowths opened before cleaning |
| Cleaning, two to three stages | Regrind product | High-grade copper concentrate |
6. What to establish before a regrind circuit is built
A regrind circuit changes the circulating load, the reagent demand and the size distribution reaching every downstream cell. The following should be settled before it is designed:
- Liberation analysis, showing the size at which copper minerals are actually exposed and how the intergrowths are distributed.
- Rougher and scavenger testwork at the coarse grind, confirming that the proposed mass rejection is achievable on that ore.
- Regrind testwork on the concentrate itself, confirming the flotation response at 80%–90% passing 38 µm.
- Locked-cycle testing, confirming that the circulating load converges and that the design grade and recovery are stable values.
- Classifier performance, because the classifier closing the regrind circuit decides whether the fine product really is fine.
Without those answers a regrind mill is a piece of equipment looking for a purpose; with them, the mill, classifier and cleaning stages can be sized on evidence.
Conclusion
Regrinding rougher concentrate buys liberation where it matters. The ore is ground only to d₈₀ = 74–100 µm; rougher and scavenger flotation discard 70%–85% of the final tailings and leave a concentrate of roughly 15%–30% of the original ore volume; that concentrate is reground to 80%–90% passing 38 µm; and two to three cleaning stages convert the new liberation into grade. Together the sequence cuts grinding energy consumption by more than 30%.
How LiCheng Tech can help
LiCheng Tech supplies the equipment that surrounds this sequence: ball mills for primary and fine grinding, classifiers that close the regrind circuit, flotation machines for roughing, scavenging and cleaning, and the thickening and filtration train behind them. Share your liberation data, the size of your rougher concentrate and the grade you are targeting, and we can discuss how the regrind and cleaning stages would be arranged and prepare a proposal.
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