The Role of Ball Milling
Ball milling is the fine-grinding stage that follows crushing in most hard-rock gold plants. A rotating drum filled with steel balls grinds the ore down to the target size, liberating gold for recovery. It is the single most energy-intensive step in the plant, so getting the sizing right matters.
How a Ball Mill Works
A ball mill is a rotating cylindrical drum, partially filled with steel grinding balls. As the drum turns, the balls cascade onto the ore, crushing it by impact and attrition. The ground material leaves the mill and is classified, with oversize returned for another pass.
Sizing the Mill
Ball mill size is fixed from ore testwork, not guesswork:
- Bond work index — measures grinding hardness and sets the energy requirement.
- Target grind size (P80) — set by how fine the gold must be ground to liberate it.
- Throughput — the daily tonnage the mill must handle.
These inputs size the mill diameter, length and motor power. Xinhai builds ball mills up to 7 m in diameter, supplied from its own manufacturing bases.
Circuit Configurations
Ball mills run in closed circuit with hydrocyclones or classifiers, which return oversize for regrinding and send correctly sized material to recovery. The configuration — single-stage or two-stage, the classification arrangement — is chosen to match the ore and the throughput.