Thermal properties of mullite based porous ceramics derived from high silica tailings obtained after extracting alumina from high alumina coal ash

Abstract

In this study, to solve the problem of reducing the quantity and increasing the utilization of waste as resource for high silica tailings (HSTs) after extracting alumina from high alumina coal ash, lightweight thermal insulation materials for building were prepared by using the melt foaming method. The effects of the calcination temperature and holding time on the melting characteristics of ingredients with different melt indexes were investigated. The effects of the amount of foaming agent on the bulk density, total porosity, and thermal conductivity of porous ceramics were determined, and the thermal conductivity model structure was further elucidated by comparing the experimental data with the values predicted by a theoretical model. The results showed that porous ceramics with optimal performance were prepared by calcination at 1200 °C for 30–60 min with a melt index of 8 k, and the amount of added SiC foaming agent was 0.52 wt%. The bulk density, total porosity and thermal conductivity were determined for the prepared porous ceramics as 0.196 g cm−3, 93.8%, and 0.086 W m−1 K−1, respectively, where the added amount of HSTs reached 60 wt%. Comparison and verification of the thermal conductivity model confirmed that the prepared mullite based porous ceramics should be classified as materials with internal porosity, where the pores were dispersed in the mullite continuous phase to form isolated closed pores. The results obtained in this study are of economic significance for the reuse of HSTs at large dosages and with high added value.