the process by which pellets are formed in drum, pan or conical granulators by the action of water on particles of ore or concentrate.

The surface tension of the thin film of water on the particles of ore produces the compressing effect, while the water that seeps by capillary action into the spaces between the particles binds the particles by negative capillary pressure. The strength of this binding effect depends primarily on the size and shape of the particles but also on the surface properties and wettability of the ore.

The consolidation of the particles into a pellet of the required size in the granulator is analogous to the formation of a snowball. The cohesive strength of the resulting pellets is proportional to the hydrophilicity and degree of dispersion of the particles. After pelletization, the pellets are hardened by roasting, during which ceramic bonds form between the particles or during which the particles are consolidated as a result of softening. Roasting is conducted in shaft furnaces, conveyer and ring roasting machines, and combined tube-grid furnaces. The annual output of roasting machines is from 0.5 to 5 million metric tons.

The pelletizing process was first proposed in the 1920’s. The first industrial pelletizers were constructed in the USA between 1945 and 1955. In 1973 the annual world capacity for the production of roasted pellets reached 150 million metric tons.