Sintering behaviour of pressed red mud wastes from zinc hydrometallurgy

The sinterability of two different ceramic wastes coming from the hydrometallurgy processing of zinc ores was investigated in view of their low-cost reuse as porous building materials for heat and sound insulation. Their chemical composition, the phase and mass changes during heat treatment were firstly investigated for setting up the thermal cycle for their densification. The materials demonstrated to sinter to high final density without any sintering aid at temperatures close to 1300 °C. Their sintering behaviour was strongly dependent on their composition and particularly on the amount and type of impurities, leading to the formation of a transitory liquid phases which assist the densification of the main crystalline phases, hematite and magnetite or zinc ferrite, as a function of the process used for iron separation. Many of the heavy metal oxides are part of low-soluble crystalline phases or of the glassy phase yielded at the higher temperatures: this behaviour could contribute to reduce the environmental impact of these materials dependent to the heavy metal leaching.