The bonding/strengthening mechanism of colemanite added organic binders in iron ore pelletization

The addition of boron compounds into pellet mix is proposed as a potential solution to overcome the insufficient compressive strengths of preheated and fired pellets produced with organic binders. Colemanite was tested as an alternative binder to bentonite either alone or in combination with some organic binders on magnetite pellets. The performances of the tested binders on pellet qualities: balling, wet pellet moisture content, drop number, compressive strengths and microstructure of pellets have been compared with the performances of reference bentonite binders. The results of the tests showed that the qualities of pellets are insufficient when organic binders and colemanite are used as binders alone. The former failed to provide sufficient preheated and fired pellet strengths, the latter failed in terms of wet and dry pellet quality. However, good quality wet, dry, preheated and fired pellets could be produced with the combination of these two binders. In addition, stronger pellets could be produced at lower firing temperatures like 1373 K thanks to addition of colemanite. The bonding mechanism of colemanite containing pellets was examined by scanning electron microscopy. It was found that the improved preheated and fired compressive strengths of colemanite-added pellets were due to the physical melting of colemanite at the contact point of magnetite grains during thermal treatment.

► Organic binders and colemanite were tested as alternative binder to bentonite.
► Colemanite was more effective than bentonite to get sufficient strength.
► Firing temperature can be lowered with addition of colemanite.
► Low firing temperatures will be beneficial to save energy in pelletization plants.
► Bonding mechanism was physical melting at the contact points of iron ore grains.