Replacement of bentonite in hematite ore pelletisation using a combination of sodium lignosulphonate and copper smelting slag

摘要

Bentonite is the most common binder used in iron ore pelletisation owing to its good bonding properties in green and dry pellets at both ambient and elevated temperatures. However, due to its high alumina and silica content, it increases the slag volume and energy consumption in downstream processes. Organic binders may be used to replace bentonite; however, they fail to provide strength at a high temperature (700-900 degrees C) due to poor thermal stability during pellet induration. In the present study, an organic binder Na lignosulphonate (NLS) has been used along with copper smelting slag (Cu-SS). FeO in Cu-SS provides diffusion bonding at high temperature and maintains the strength of pellets even after evaporation/burning of NLS. It also enhances recrystallisation bonding at relatively lower temperature to provide good strength. The study has been carried out with hematite ore and varying amounts of NLS and Cu-SS. Copper smelting slag (1.0%) addition with 0.5% NLS has been found to be optimum to provide very good green properties and similar to 300 kg/pellet cold crushing strength (CCS) at 1250 degrees C induration temperature. However, hematite pellets of similar basicity with 0.5% bentonite requires higher induration temperature (1300 degrees C) to achieve a similar CCS. The developed pellet also shows better reducibility (80%), similar reduction degradation index (18%) and swelling index (10%) to the usual bentonite pellet. Thus, the induration temperature of hematite pellet has been lowered by 50 degrees C using a combination of NLS and Cu-SS eliminating bentonite completely, which can provide a considerable energy and cost saving.